QGIS User Guide - QGIS Documentation

QGIS User Guide
Release 1.8
QGIS Project
May 14, 2014
Contents
1
Preamble
1
2
Conventions
3
3
Foreword
3.1 Introduction To GIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
5
4
Features
4.1 View data . . . . . . . . . . . . . . . . . .
4.2 Explore data and compose maps . . . . . .
4.3 Create, edit, manage and export data . . . .
4.4 Analyse data . . . . . . . . . . . . . . . .
4.5 Publish maps on the Internet . . . . . . . .
4.6 Extend QGIS functionality through plugins
4.7 What’s new in the version 1.8 . . . . . . .
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9
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11
Getting Started
5.1 Installation . . . . . . . . .
5.2 Sample Data . . . . . . . .
5.3 Sample Session . . . . . . .
5.4 Starting and Stopping QGIS
5.5 Command Line Options . .
5.6 Projects . . . . . . . . . . .
5.7 Output . . . . . . . . . . .
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15
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19
19
QGIS GUI
6.1 Menu Bar . .
6.2 Toolbar . . .
6.3 Map Legend
6.4 Map View .
6.5 Status Bar . .
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21
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27
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29
30
General Tools
7.1 Keyboard shortcuts
7.2 Context help . . .
7.3 Rendering . . . .
7.4 Measuring . . . .
7.5 Decorations . . . .
7.6 Annotation Tools .
7.7 Spatial Bookmarks
7.8 Nesting Projects .
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QGIS Configuration
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41
i
8.1
8.2
8.3
8.4
9
Panels and Toolbars
Project Properties . .
Options . . . . . . .
Customization . . .
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41
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42
46
Working with Projections
9.1 Overview of Projection Support . . . .
9.2 Specifying a Projection . . . . . . . . .
9.3 Define On The Fly (OTF) Reprojection
9.4 Custom Coordinate Reference System .
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49
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52
10 QGIS Browser
53
11 Working with Vector Data
11.1 Supported Data Formats . . .
11.2 The Vector Properties Dialog
11.3 Editing . . . . . . . . . . . .
11.4 Query Builder . . . . . . . .
11.5 Field Calculator . . . . . . .
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95
12 Working with Raster Data
99
12.1 Working with Raster Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
12.2 Raster Properties Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
12.3 Raster Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
13 Working with OGC Data
105
13.1 Working with OGC Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
13.2 QGIS Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
14 Working with GPS Data
115
14.1 GPS Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
14.2 Live GPS tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
15 GRASS GIS Integration
15.1 Starting the GRASS plugin . . . . . . . . .
15.2 Loading GRASS raster and vector layers . .
15.3 GRASS LOCATION and MAPSET . . . . .
15.4 Importing data into a GRASS LOCATION .
15.5 The GRASS vector data model . . . . . . .
15.6 Creating a new GRASS vector layer . . . . .
15.7 Digitizing and editing a GRASS vector layer
15.8 The GRASS region tool . . . . . . . . . . .
15.9 The GRASS toolbox . . . . . . . . . . . . .
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16 OpenStreetMap
16.1 The OpenStreetMap project
16.2 QGIS - OSM Connection .
16.3 Installation . . . . . . . . .
16.4 Basic user interface . . . . .
16.5 Loading OSM data . . . . .
16.6 Viewing OSM data . . . . .
16.7 Editing basic OSM data . .
16.8 Editing relations . . . . . .
16.9 Downloading OSM data . .
16.10 Uploading OSM data . . . .
16.11 Saving OSM data . . . . . .
16.12 Import OSM data . . . . . .
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17 SEXTANTE
151
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
ii
17.2
17.3
17.4
17.5
17.6
17.7
The SEXTANTE toolbox . . . . . . . . .
The SEXTANTE graphical modeler . . . .
The SEXTANTE batch processing interface
Using SEXTANTE from the console . . .
The SEXTANTE history manager . . . . .
Configuring external applications . . . . .
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153
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173
18 Print Composer
18.1 Open a new Print Composer Template . . . . . . . . . . .
18.2 Using Print Composer . . . . . . . . . . . . . . . . . . .
18.3 Adding a current QGIS map canvas to the Print Composer
18.4 Adding other elements to the Print Composer . . . . . . .
18.5 Navigation tools . . . . . . . . . . . . . . . . . . . . . .
18.6 Revert and Restore tools . . . . . . . . . . . . . . . . . .
18.7 Add Basic shape and Arrow . . . . . . . . . . . . . . . .
18.8 Add attribute table values . . . . . . . . . . . . . . . . .
18.9 Raise, lower and align elements . . . . . . . . . . . . . .
18.10 Creating Output . . . . . . . . . . . . . . . . . . . . . .
18.11 Saving and loading a print composer layout . . . . . . . .
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181
182
182
183
185
189
190
190
190
192
192
193
19 Plugins
19.1 QGIS Plugins . . . . . . . . .
19.2 Using QGIS Core Plugins . .
19.3 Coordinate Capture Plugin . .
19.4 DB Manager Plugin . . . . .
19.5 Delimited Text Plugin . . . .
19.6 Diagram Overlay Plugin . . .
19.7 Dxf2Shp Converter Plugin . .
19.8 eVis Plugin . . . . . . . . . .
19.9 fTools Plugin . . . . . . . . .
19.10 GDAL Tools Plugin . . . . .
19.11 Georeferencer Plugin . . . . .
19.12 Interpolation Plugin . . . . .
19.13 MapServer Export Plugin . .
19.14 Offline Editing Plugin . . . .
19.15 Oracle GeoRaster Plugin . . .
19.16 Raster Terrain Analysis Plugin
19.17 Heatmap Plugin . . . . . . .
19.18 Road Graph Plugin . . . . . .
19.19 Spatial Query Plugin . . . . .
19.20 SPIT Plugin . . . . . . . . .
19.21 SQL Anywhere Plugin . . . .
19.22 Zonal Statistics Plugin . . . .
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195
195
199
200
200
201
202
204
204
214
217
220
223
224
228
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231
232
236
237
237
239
239
20 Help and Support
20.1 Mailing lists
20.2 IRC . . . . .
20.3 BugTracker .
20.4 Blog . . . .
20.5 Plugins . . .
20.6 Wiki . . . .
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241
241
242
242
243
243
243
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21 Appendix
245
21.1 GNU General Public License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
21.2 GNU Free Documentation License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
22 Literature and Web References
255
Index
257
iii
iv
CHAPTER 1
Preamble
This document is the original user guide of the described software Quantum GIS. The software and hardware
described in this document are in most cases registered trademarks and are therefore subject to the legal requirements. Quantum GIS is subject to the GNU General Public License. Find more information on the Quantum GIS
Homepage http://www.qgis.org.
The details, data, results etc. in this document have been written and verified to the best of knowledge and
responsibility of the authors and editors. Nevertheless, mistakes concerning the content are possible.
Therefore, all data are not liable to any duties or guarantees. The authors, editors and publishers do not take
any responsibility or liability for failures and their consequences. Your are always welcome to indicate possible
mistakes.
This document has been typeset with reStructuredText. It is available as reST source code via github and online
as HTML and PDF via http://documentation.qgis.org. Translated versions of this document can be downloaded in
several formats via the documentation area of the QGIS project as well. For more information about contributing
to this document and about translating it, please visit: http://www.qgis.org/wiki/.
Links in this Document
This document contains internal and external links. Clicking on an internal link moves within the document, while
clicking on an external link opens an internet address. In PDF form, internal and external links are shown in blue
and are handled by the system browser. In HTML form, the browser displays and handles both identically.
User, Installation and Coding Guide Authors and Editors:
Tara Athan
Peter Ersts
Werner Macho
Claudia A. Engel
Larissa Junek
Tim Sutton
Radim Blazek
Anne Ghisla
Carson J.Q. Farmer
Brendan Morely
Diethard Jansen
Alex Bruy
Godofredo Contreras
Stephan Holl
Tyler Mitchell
David Willis
Paolo Corti
Raymond Nijssen
Otto Dassau
N. Horning
K. Koy
Jürgen E. Fischer
Gavin Macaulay
Richard Duivenvoorde
Martin Dobias
Magnus Homann
Lars Luthman
Marco Hugentobler
Gary E. Sherman
Andreas Neumann
Sponsors
The update of this user manual was kindly sponsored by Kanton Solothurn, Switzerland.
Copyright (c) 2004 - 2013 QGIS Development Team
Internet: http://www.qgis.org
License of this document
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in Appendix GNU
Free Documentation License.
1
QGIS User Guide, Release 1.8
2
Chapter 1. Preamble
CHAPTER 2
Conventions
This section describes a collection of uniform styles throughout the manual. The conventions used in this manual
are as follows:
GUI Conventions
The GUI convention styles are intended to mimic the appearance of the GUI. In general, the objective is to use the
non-hover appearance, so a user can visually scan the GUI to find something that looks like the instruction in the
manual.
• Menu Options: Layer → Add a Raster Layer or Settings → Toolbars → Digitizing
• Tool:
Add a Raster Layer
• Button : [Save as Default]
• Dialog Box Title: Layer Properties
• Tab: General
• Checkbox:
Render
• Radio Button:
Postgis SRID
EPSG ID
• Select a Number:
• Select a String:
• Browse for a File:
• Select a Color:
• Slider:
• Input Text:
A shadow indicates a clickable GUI component.
Text or Keyboard Conventions
The manual also includes styles related to text, keyboard commands and coding to indicate different entities, such
as classes, or methods. They don’t correspond to any actual appearance.
• Hyperlinks: http://qgis.org
• Keystroke Combinations: press Ctrl+B, meaning press and hold the Ctrl key and then press the B key.
• Name of a File: lakes.shp
• Name of a Class: NewLayer
• Method: classFactory
• Server: myhost.de
3
QGIS User Guide, Release 1.8
• User Text: qgis --help
Lines of code are indicated by a fixed-width font
PROJCS["NAD_1927_Albers",
GEOGCS["GCS_North_American_1927",
Platform-specific instructions
GUI sequences and small amounts of text can be formatted inline: Click
QGIS.
File
QGIS → Quit to close
This indicates that on Linux, Unix and Windows platforms, click the File menu option first, then Quit from
the dropdown menu, while on Macintosh OSX platforms, click the QGIS menu option first, then Quit from the
dropdown menu. Larger amounts of text may be formatted as a list:
•
do this;
•
do that;
•
do something else.
or as paragraphs.
Do this and this and this. Then do this and this and this and this and this and this and this and this and this.
Do that. Then do that and that and that and that and that and that and that and that and that and that and that
and that and that and that and that.
Screenshots that appear throughout the user guide have been created on different platforms; the platform is indicated by the platform-specific icon at the end of the figure caption.
4
Chapter 2. Conventions
CHAPTER 3
Foreword
Welcome to the wonderful world of Geographical Information Systems (GIS)!
Quantum GIS (QGIS) is an Open Source Geographic Information System. The project was born in May of 2002
and was established as a project on SourceForge in June of the same year. We’ve worked hard to make GIS
software (which is traditionally expensive proprietary software) a viable prospect for anyone with basic access
to a Personal Computer. QGIS currently runs on most Unix platforms, Windows, and OS X. QGIS is developed
using the Qt toolkit (http://qt.digia.com) and C++. This means that QGIS feels snappy to use and has a pleasing,
easy-to-use graphical user interface (GUI).
QGIS aims to be an easy-to-use GIS, providing common functions and features. The initial goal was to provide a
GIS data viewer. QGIS has reached the point in its evolution where it is being used by many for their daily GIS
data viewing needs. QGIS supports a number of raster and vector data formats, with new format support easily
added using the plugin architecture.
QGIS is released under the GNU General Public License (GPL). Developing QGIS under this license means that
you can inspect and modify the source code, and guarantees that you, our happy user, will always have access to
a GIS program that is free of cost and can be freely modified. You should have received a full copy of the license
with your copy of QGIS, and you also can find it in Appendix GNU General Public License.
Tip: Up-to-date Documentation
The latest version of this document can always be found in the documentation area of the QGIS website at
http://documentation.qgis.org
3.1 Introduction To GIS
A Geographical Information System (GIS) (Mitchell 2005 Literature and Web References) is a collection of software that allows you to create, visualize, query and analyze geospatial data. Geospatial data refers to information
about the geographic location of an entity. This often involves the use of a geographic coordinate, like a latitude
or longitude value. Spatial data is another commonly used term, as are: geographic data, GIS data, map data,
location data, coordinate data and spatial geometry data.
Applications using geospatial data perform a variety of functions. Map production is the most easily understood
function of geospatial applications. Mapping programs take geospatial data and render it in a form that is viewable,
usually on a computer screen or printed page. Applications can present static maps (a simple image) or dynamic
maps that are customised by the person viewing the map through a desktop program or a web page.
Many people mistakenly assume that geospatial applications just produce maps, but geospatial data analysis is
another primary function of geospatial applications. Some typical types of analysis include computing:
1. distances between geographic locations
2. the amount of area (e.g., square meters) within a certain geographic region
3. what geographic features overlap other features
5
QGIS User Guide, Release 1.8
4. the amount of overlap between features
5. the number of locations within a certain distance of another
6. and so on...
These may seem simplistic, but can be applied in all sorts of ways across many disciplines. The results of analysis
may be shown on a map, but are often tabulated into a report to support management decisions.
The recent phenomena of location-based services promises to introduce all sorts of other features, but many will
be based on a combination of maps and analysis. For example, you have a cell phone that tracks your geographic
location. If you have the right software, your phone can tell you what kind of restaurants are within walking
distance. While this is a novel application of geospatial technology, it is essentially doing geospatial data analysis
and listing the results for you.
3.1.1 Why is all this so new?
Well, it’s not. There are many new hardware devices that are enabling mobile geospatial services. Many open
source geospatial applications are also available, but the existence of geospatially focused hardware and software
is nothing new. Global positioning system (GPS) receivers are becoming commonplace, but have been used in
various industries for more than a decade. Likewise, desktop mapping and analysis tools have also been a major
commercial market, primarily focused on industries such as natural resource management.
What is new is how the latest hardware and software is being applied and who is applying it. Traditional users
of mapping and analysis tools were highly trained GIS Analysts or digital mapping technicians trained to use
CAD-like tools. Now, the processing capabilities of home PCs and open source software (OSS) packages have
enabled an army of hobbyists, professionals, web developers, etc. to interact with geospatial data. The learning
curve has come down. The costs have come down. The amount of geospatial technology saturation has increased.
How is geospatial data stored? In a nutshell, there are two types of geospatial data in widespread use today. This
is in addition to traditional tabular data that is also widely used by geospatial applications.
3.1.2 Raster Data
One type of geospatial data is called raster data or simply “a raster”. The most easily recognised form of raster
data is digital satellite imagery or air photos. Elevation shading or digital elevation models are also typically
represented as raster data. Any type of map feature can be represented as raster data, but there are limitations.
A raster is a regular grid made up of cells, or in the case of imagery, pixels. They have a fixed number of rows and
columns. Each cell has a numeric value and has a certain geographic size (e.g. 30x30 meters in size).
Multiple overlapping rasters are used to represent images using more than one colour value (i.e. one raster for
each set of red, green and blue values is combined to create a colour image). Satellite imagery also represents
data in multiple “bands”. Each band is essentially a separate, spatially overlapping raster, where each band holds
values of certain wavelengths of light. As you can imagine, a large raster takes up more file space.
A raster with smaller cells can provide more detail, but takes up more file space. The trick is finding the right
balance between cell size for storage purposes and cell size for analytical or mapping purposes.
3.1.3 Vector Data
Vector data is also used in geospatial applications. If you stayed awake during trigonometry and coordinate
geometry classes, you will already be familiar with some of the qualities of vector data. In its simplest sense,
vectors are a way of describing a location by using a set of coordinates. Each coordinate refers to a geographic
location using a system of x and y values.
This can be thought of in reference to a Cartesian plane - you know, the diagrams from school that showed an x
and y-axis. You might have used them to chart declining retirement savings or increasing compound mortgage
interest, but the concepts are essential to geospatial data analysis and mapping.
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There are various ways of representing these geographic coordinates depending on your purpose. This is a whole
area of study for another day - map projections.
Vector data takes on three forms, each progressively more complex and building on the former.
1. Points - A single coordinate (x y) represents a discrete geographic location
2. Lines - Multiple coordinates (x1 y1 , x2 y2 , x3 y3 , ... xn yn ) strung together in a certain order, like drawing
a line from Point (x1 y1 ) to Point (x2 y2 ) and so on. These parts between each point are considered line
segments. They have a length and the line can be said to have a direction based on the order of the points.
Technically, a line is a single pair of coordinates connected together, whereas a line string is multiple lines
connected together.
3. Polygons - When lines are strung together by more than two points, with the last point being at the same
location as the first, we call this a polygon. A triangle, circle, rectangle, etc. are all polygons. The key
feature of polygons is that there is a fixed area within them.
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Chapter 3. Foreword
CHAPTER 4
Features
QGIS offers many common GIS functionalities provided by core features and plugins. As a short summary they
are presented in six categories to gain a first insight.
4.1 View data
You can view and overlay vector and raster data in different formats and projections without conversion to an
internal or common format. Supported formats include:
• Spatially-enabled tables and views using PostGIS, SpatiaLite and MSSQL Spatial, vector formats supported
by the installed OGR library, including ESRI shapefiles, MapInfo, SDTS, GML and many more, see section
Working with Vector Data.
• Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction Library) library,
such as GeoTiff, Erdas Img., ArcInfo Ascii Grid, JPEG, PNG and many more, see section Working with
Raster Data.
• GRASS raster and vector data from GRASS databases (location/mapset), see section GRASS GIS Integration.
• Online spatial data served as OGC-compliant Web Map Service (WMS) or Web Feature Service (WFS), see
section Working with OGC Data.
• OpenStreetMap data, see section OpenStreetMap.
4.2 Explore data and compose maps
You can compose maps and interactively explore spatial data with a friendly GUI. The many helpful tools available
in the GUI include:
• QGIS browser
• On the fly projection
• Map composer
• Overview panel
• Spatial bookmarks
• Identify/select features
• Edit/view/search attributes
• Feature labeling
• Change vector and raster symbology
• Add a graticule layer - now via fTools plugin and as decoration
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• Decorate your map with a north arrow scale bar and copyright label
• Save and restore projects
4.3 Create, edit, manage and export data
You can create, edit, manage and export vector maps in several formats. Raster data have to be imported into
GRASS to be able to edit and export them into other formats. QGIS offers the following:
• Digitizing tools for OGR supported formats and GRASS vector layer
• Create and edit shapefiles and GRASS vector layers
• Geocode images with the Georeferencer plugin
• GPS tools to import and export GPX format, and convert other GPS formats to GPX or down/upload directly
to a GPS unit (on Linux, usb: has been addedto list of GPS devices)
• Visualize and edit OpenStreetMap data
• Create PostGIS layers from shapefiles with the SPIT plugin
• Improved handling of PostGIS tables
• Manage vector attribute tables with the new attribute table (see section Working with the Attribute Table) or
Table Manager plugin
• Save screenshots as georeferenced images
4.4 Analyse data
You can perform spatial data analysis on PostgreSQL/PostGIS and other OGR supported formats using the fTools
Python plugin. QGIS currently offers vector analysis, sampling, geoprocessing, geometry and database management tools. You can also use the integrated GRASS tools, which include the complete GRASS functionality of
more than 400 modules (See Section GRASS GIS Integration). Or you work with SEXTANTE, which provides
powerful a geospatial analysis framework to call native and third party algorithms from QGIS, such as GDAL,
SAGA, GRASS, fTools and more (see section SEXTANTE).
4.5 Publish maps on the Internet
QGIS can be used to export data to a mapfile and to publish them on the Internet using a webserver with UMN
MapServer installed. QGIS can also be used as a WMS, WMS-C or WFS and WFS-T client, and as WMS or WFS
server (see section Working with OGC Data).
4.6 Extend QGIS functionality through plugins
QGIS can be adapted to your special needs with the extensible plugin architecture. QGIS provides libraries that
can be used to create plugins. You can even create new applications with C++ or Python!
4.6.1 Core Plugins
1. Add Delimited Text Layer (Loads and displays delimited text files containing x,y coordinates)
2. Coordinate Capture (Capture mouse coordinates in different CRS)
3. DB Manager (Exchange, edit and view layers and tables; execute SQL queries)
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4. Diagram Overlay (Placing diagrams on vector layer)
5. Dxf2Shp Converter (Convert DXF to Shape)
6. GPS Tools (Loading and importing GPS data)
7. GRASS (GRASS GIS integration)
8. GDALTools (Integrate GDAL Tools into QGIS)
9. Georeferencer GDAL (Adding projection information to raster using GDAL)
10. Heatmap tool (Generating raster heatmaps from point data)
11. Interpolation plugin (interpolate based on vertices of a vector layer)
12. Mapserver Export (Export QGIS project file to a MapServer map file)
13. Offline Editing (Allow offline editing and synchronizing with database)
14. OpenStreetMap plugin (Viewer and editor for openstreetmap data)
15. Oracle Spatial GeoRaster support
16. Plugin Installer (Download and install QGIS python plugins)
17. Raster terrain analysis (Raster based terrain analysis)
18. Road graph plugin (Shortest Path network analysis)
19. SPIT (Import Shapefile to PostgreSQL/PostGIS)
20. SQL Anywhere Plugin (Store vector layers within a SQL Anywhere database)
21. Zonal statictics plugin (Calculate count, sum, mean of raster for each polygon of a vector layer)
22. Spatial Query plugin (Makes spatial queries on vector layers)
23. eVIS (Event Visualization Tool)
24. fTools (Tools for vector data analysis and management)
4.6.2 External Python Plugins
QGIS offers a growing number of external python plugins that are provided by the community. These plugins
reside in the official plugins repository, and can be easily installed using the Python Plugin Installer (See Section
Loading an external QGIS Plugin).
4.7 What’s new in the version 1.8
Please note that this is a release in our ‘cutting edge’ release series. As such it contains new features and extends
the programmatic interface over QGIS 1.0.x and QGIS 1.7.0. We recommend that you use this version over
previous releases.
This release includes hundreds of bug fixes and many new features and enhancements that will be described in
this manual.
QGIS Browser
A stand alone app and a new panel in QGIS. The browser lets you easily navigate your file system and connection
based (PostGIS, WFS etc.) datasets, preview them and drag and drop items into the canvas.
DB Manager
The DB manager is now officially part of QGIS core. You can drag layers from the QGIS Browser into DB
Manager and it will import your layer into your spatial database. Drag and drop tables between spatial databases
and they will get imported. You can use the DB Manager to execute SQL queries against your spatial database
4.7. What’s new in the version 1.8
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and then view the spatial output for queries by adding the results to QGIS as a query layer. You can also create,
edit, delete, and empty tables, and move them to another schema.
Terrain Analysis Plugin
A new core plugin was added for doing terrain analysis (slope, aspect, hillshade, relief and ruggedness index).
New symbol layer types
• Line Pattern Fill
• Point Pattern Fill
• Ellipse renderer (render ellipse and also rectangles, triangles, crosses)
New plugin repository
Note that the old repository is now no longer supported by default; plugin authors are kindly requested to move
their plugins to the new repository. Get the QGIS Plugins list at http://plugins.qgis.org/plugins/.
More new features
• Support for nesting projects within other projects to embed content from other project files
• Group Selected: Option to group layers to a group
• Message log: Lets you keep an eye on the messages QGIS generates during loading and operation
• GUI Customization: Allows setting up simplified QGIS interface by hiding various components of main
window and widgets in dialogs
• Action Tool is now accessible from the map tools toolbar and allows you to click on a vector feature and
execute an action
• New scale selector: select from a list of predefined scales
• Pan To Selected tool: Pans the map to selected feature(s); does not change the zoom level
• Copy and paste styles between layers
• Updated CRS selector dialog
• Define Legend-independent drawing order
• MSSQL Spatial Support - you can now connect to your Microsoft SQL Server spatial databases using QGIS
• Print Composers allows to have multiple lines on legend items using a specified character
• Expression based labeling
• Heatmap Plugin - a new core plugin has been added for generating raster heatmaps from point data
• The GPS live tracking user interface was overhauled and many fixes and improvements were added to it
• The menu was re-organised a little - we now have separate menus for Vector, Raster, Web and many plugins
were updated to place their menus in the new Vector, Raster and Web top level menus
• Offset Curves - a new digitising tool for creating offset curves was added
• New tools in the Vector menu to Densify geometries and Build spatial index
• Export/add geometry column tool can export info using layer CRS, project CRS or ellipsoidal measurements
• Model/view based tree for rules in rule-based renderer
• Improvements in Spatial Bookmarks
• New Plugin metadata in metadata.txt
• Refactored postgres data provider: support for arbitrary key (including non-numeric and multi column),
support for requesting a certain geometry type and/or srid in QgsDataSourceURI
• Added gdal_fillnodata to GDALTools plugin
• Support for PostGIS TopoGeometry datatype
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• Python bindings for vector field symbol layer and general updates to the Python bindings
• Added a Benchmark program
• Added Row cache for attribute table
• UUID generation widget for attribute table
• Added support of editable views in SpatiaLite databases
• added expression based widget in field calculator
• Creation of event layers in analysis lib using linear referencing
• Load/save layer styles in the new symbology renderer from/to SLD document
• QGIS Server can act as WFS Server
• WFS Client support is now a core feature in QGIS
• Option to skip WKT geometry when copying from attribute table
• Support loading of zipped and gzipped layers
• The QGIS test suite now passes all tests on major platforms and nightly tests
• You can set tile size for WMS layers
4.7. What’s new in the version 1.8
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Chapter 4. Features
CHAPTER 5
Getting Started
This chapter gives a quick overview of installing QGIS, some sample data from the QGIS web page and running
a first and simple session visualizing raster and vector layers.
5.1 Installation
Installation of QGIS is very simple. Standard installer packages are available for MS Windows and Mac OS
X. For many flavors of GNU/Linux binary packages (rpm and deb) or software repositories to add to your
installation manager are provided. Get the latest information on binary packages at the QGIS website at
http://download.qgis.org.
5.1.1 Installation from source
If you need to build QGIS from source, please refer to the installation instructions. They are distributed with the
QGIS source code in a file called ‘INSTALL’. You can also find it online at https://github.com/qgis/QuantumGIS/blob/master/INSTALL
5.1.2 Installation on external media
QGIS allows to define a --configpath option that overrides the default path (e.g. ~/.qgis under Linux) for user
configuration and forces QSettings to use this directory, too. This allows users to e.g. carry a QGIS installation on
a flash drive together with all plugins and settings.
5.2 Sample Data
The user guide contains examples based on the QGIS sample dataset.
The Windows installer has an option to download the QGIS sample dataset. If checked, the data will be downloaded to your My Documents folder and placed in a folder called GIS Database. You may use Windows
Explorer to move this folder to any convenient location. If you did not select the checkbox to install the sample
dataset during the initial QGIS installation, you can either
• use GIS data that you already have;
• download the sample data from the qgis website at http://download.qgis.org; or
• uninstall QGIS and reinstall with the data download option checked, only if the above solutions are unsuccessful.
For GNU/Linux and Mac OSX there are not yet dataset installation packages available as rpm, deb
or dmg. To use the sample dataset download the file qgis_sample_data as ZIP or TAR archive from
http://download.osgeo.org/qgis/data/ and unzip or untar the archive on your system. The Alaska dataset includes
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all GIS data that are used as examples and screenshots in the user guide, and also includes a small GRASS
database. The projection for the qgis sample dataset is Alaska Albers Equal Area with unit feet. The EPSG code
is 2964.
PROJCS["Albers Equal Area",
GEOGCS["NAD27",
DATUM["North_American_Datum_1927",
SPHEROID["Clarke 1866",6378206.4,294.978698213898,
AUTHORITY["EPSG","7008"]],
TOWGS84[-3,142,183,0,0,0,0],
AUTHORITY["EPSG","6267"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9108"]],
AUTHORITY["EPSG","4267"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["standard_parallel_1",55],
PARAMETER["standard_parallel_2",65],
PARAMETER["latitude_of_center",50],
PARAMETER["longitude_of_center",-154],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["us_survey_feet",0.3048006096012192]]
If you intend to use QGIS as graphical frontend for GRASS, you can find a selection of sample locations (e.g.
Spearfish or South Dakota) at the official GRASS GIS website http://grass.osgeo.org/download/data.php.
5.3 Sample Session
Now that you have QGIS installed and a sample dataset available, we would like to demonstrate a
short and simple QGIS sample session. We will visualize a raster and a vector layer. We will use
the landcover raster layer qgis_sample_data/raster/landcover.img and the lakes vector layer
qgis_sample_data/gml/lakes.gml.
5.3.1 Start QGIS
•
Start QGIS by typing: “QGIS” at a command prompt, or if using precompiled binary, using the Applications menu.
•
Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.
•
Double click the icon in your Applications folder.
5.3.2 Load raster and vector layers from the sample dataset
1. Click on the
Load Raster
icon.
2. Browse to the folder qgis_sample_data/raster/, select the ERDAS Img file landcover.img
and click [Open].
3. If the file is not listed, check if the Filetype combobox at the bottom of the dialog is set on the right type, in
this case “Erdas Imagine Images (*.img, *.IMG)”.
4. Now click on the
5.
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Load Vector
icon.
File should be selected as Source Type in the new Add Vector Layer dialog. Now click [Browse] to
select the vector layer.
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6. Browse to the folder qgis_sample_data/gml/, select “GML” from the filetype combobox, then select
the GML file lakes.gml and click [Open], then in Add Vector dialog click [OK].
7. Zoom in a bit to your favorite area with some lakes.
8. Double click the lakes layer in the map legend to open the Properties dialog.
9. Click on the Style tab and select a blue as fill color.
Display lables checkbox to enable labeling. Choose NAMES field
10. Click on the Labels tab and check the
as field containing label.
11. To improve readability of labels, you can add a white buffer around them, by clicking “Buffer” in the list on
the left, checking
Buffer labels? and choosing 3 as buffer size.
12. Click [Apply], check if the result looks good and finally click [OK].
You can see how easy it is to visualize raster and vector layers in QGIS. Let’s move on to the sections that follow
to learn more about the available functionality, features and settings and how to use them.
5.4 Starting and Stopping QGIS
In Section Sample Session you already learned how to start QGIS. We will repeat this here and you will see that
QGIS also provides further command line options.
•
•
•
Assuming that QGIS is installed in the PATH, you can start QGIS by typing: qgis at a command prompt
or by double clicking on the QGIS application link (or shortcut) on the desktop or in the application menu.
Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.
Double click the icon in your Applications folder. If you need to start QGIS in a shell, run /path-toinstallation-executable/Contents/MacOS/Qgis.
To stop QGIS, click the menu options
File
QGIS → Quit, or use the shortcut Ctrl+Q.
5.5 Command Line Options
QGIS supports a number of options when started from the command line. To get a list of the options, enter
qgis --help on the command line. The usage statement for QGIS is:
qgis --help
Quantum GIS - 1.8.0-Lisboa ’Lisboa’ (exported)
Quantum GIS (QGIS) is a viewer for spatial data sets, including
raster and vector data.
Usage: qgis [options] [FILES]
options:
[--snapshot filename]
emit snapshot of loaded datasets to given file
[--width width]
width of snapshot to emit
[--height height]
height of snapshot to emit
[--lang language]
use language for interface text
[--project projectfile]
load the given QGIS project
[--extent xmin,ymin,xmax,ymax] set initial map extent
[--nologo]
hide splash screen
[--noplugins]
don’t restore plugins on startup
[--nocustomization]
don’t apply GUI customization
[--optionspath path]
use the given QSettings path
[--configpath path]
use the given path for all user configuration
[--help]
this text
FILES:
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Files specified on the command line can include rasters,
vectors, and QGIS project files (.qgs):
1. Rasters - Supported formats include GeoTiff, DEM
and others supported by GDAL
2. Vectors - Supported formats include ESRI Shapefiles
and others supported by OGR and PostgreSQL layers using
the PostGIS extension
Tip: Example Using command line arguments
You can start QGIS by specifying one or more data files on the command line. For example, assuming you are
in the qgis_sample_data directory, you could start QGIS with a vector layer and a raster file set to load on startup
using the following command: qgis ./raster/landcover.img ./gml/lakes.gml
Command line option --snapshot
This option allows you to create a snapshot in PNG format from the current view. This comes in handy when you
have a lot of projects and want to generate snapshots from your data.
Currently it generates a PNG-file with 800x600 pixels. This can be adapted using the --width and --height
command line arguments. A filename can be added after --snapshot.
Command line option --lang
Based on your locale QGIS, selects the correct localization. If you would like to change your language,
you can specify a language code. For example: --lang=it starts QGIS in italian localization. A list of
currently supported languages with language code and status is provided at http://hub.qgis.org/wiki/quantumgis/GUI_Translation_Progress
Command line option --project
Starting QGIS with an existing project file is also possible. Just add the command line option --project
followed by your project name and QGIS will open with all layers loaded described in the given file.
Command line option --extent
To start with a specific map extent use this option. You need to add the bounding box of your extent in the
following order separated by a comma:
--extent xmin,ymin,xmax,ymax
Command line option --nologo
This command line argument hides the splash screen when you start QGIS.
Command line option --noplugins
If you have trouble at startup with plugins, you can avoid loading them at startup. They will still be available in
Plugins Manager after-wards.
Command line option --nocustomization
Using this command line argument existing GUI customization will not be applied at startup.
Command line option --optionspath
You can have multiple configurations and decide which one to use when starting QGIS using this option. See
Options to check where does the operating system save the settings files. Presently there is no way to specify in
which file where to write the settings, therefore you can create a copy of the original settings file and rename it.
Command line option --configpath
This option is similar to the one above, but furthermore overrides the default path (~/.qgis) for user configuration
and forces QSettings to use this directory, too. This allows users to e.g. carry QGIS installation on a flash drive
together with all plugins and settings.
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5.6 Projects
The state of your QGIS session is considered a Project. QGIS works on one project at a time. Settings are either
considered as being per-project, or as a default for new projects (see Section Options). QGIS can save the state of
your workspace into a project file using the menu options File →
Load saved projects into a QGIS session using File →
Save Project or File →
Save Project As.
Open Project or File → Open Recent Project.
If you wish to clear your session and start fresh, choose File →
New Project. Either of these menu options
will prompt you to save the existing project if changes have been made since it was opened or last saved.
The kinds of information saved in a project file include:
• Layers added
• Layer properties, including symbolization
• Projection for the map view
• Last viewed extent
The project file is saved in XML format, so it is possible to edit the file outside QGIS if you know what you are
doing. The file format was updated several times compared to earlier QGIS versions. Project files from older
QGIS versions may not work properly anymore. To be made aware of this, in the General tab under Settings →
Options you can select:
Prompt to save project changes when required
Warn when opening a project file saved with an older version of QGIS
5.7 Output
There are several ways to generate output from your QGIS session. We have discussed one already in Section
Projects saving as a project file. Here is a sampling of other ways to produce output files:
Save as Image
• Menu option File →
opens a file dialog where you select the name, path and type of image
(PNG or JPG format). A world file with extension PNGW or JPGW saved in the same folder georeferences
the image.
• Menu option File →
New Print Composer opens a dialog where you can layout and print the current
map canvas (see Section Print Composer).
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Chapter 5. Getting Started
CHAPTER 6
QGIS GUI
When QGIS starts, you are presented with the GUI as shown below (the numbers 1 through 5 in yellow ovals refer
to the six major areas of the interface as discussed below):
Figure 6.1: QGIS GUI with Alaska sample data
Note: Your window decorations (title bar, etc.) may appear different depending on your operating system and
window manager.
The QGIS GUI is divided into five areas:
1. Menu Bar
2. Tool Bar
3. Map Legend
4. Map View
5. Status Bar
These five components of the QGIS interface are described in more detail in the following sections. Two more
sections present keyboard shortcuts and context help.
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6.1 Menu Bar
The menu bar provides access to various QGIS features using a standard hierarchical menu. The top-level menus
and a summary of some of the menu options are listed below, together with the icons of the corresponding tools
as they appear on the toolbar, as well as keyboard shortcuts. Keyboard shortcuts can also be configured manually
(shortcuts presented in this section are the defaults), using the [Configure Shortcuts] tool under Settings.
Although most menu options have a corresponding tool and vice-versa, the menus are not organized quite like the
toolbars. The toolbar containing the tool is listed after each menu option as a checkbox entry. Some menu options
only appear, if the corresponding plugin is loaded. For more information about tools and toolbars, see Section
Toolbar.
6.1.1 File
Menu Option
Shortcut
Reference
Toolbar
Ctrl+N
see Projects
File
Ctrl+O
see Projects
see Projects
File
Save Project
Ctrl+S
see Projects
File
Save Project As
Ctrl+Shift+S
see Projects
File
New Project
Open Project
Open Recent Projects →
see Output
Save as Image
New Print Composer
Ctrl+P
Composer manager
Print Composers →
Exit
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see Print Composer
File
see Print Composer
see Print Composer
File
Ctrl+Q
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6.1.2 Edit
Menu Option
Shortcut
Reference
Toolbar
Undo
Ctrl+Z
see Advanced digitizing
Advanced Digitizing
Redo
Ctrl+Shift+Z
see Advanced digitizing
Advanced Digitizing
Cut Features
Ctrl+X
see Digitizing an existing layer
Digitizing
Copy Features
Ctrl+C
see Digitizing an existing layer
Digitizing
Paste Features
Ctrl+V
see Digitizing an existing layer
Digitizing
Add Feature
Ctrl+.
see Digitizing an existing layer
Digitizing
Move Feature(s)
see Digitizing an existing layer
Digitizing
Delete Selected
see Digitizing an existing layer
Digitizing
Simplify Feature
see Advanced digitizing
Advanced Digitizing
Add Ring
see Advanced digitizing
Advanced Digitizing
Add Part
see Advanced digitizing
Advanced Digitizing
Delete Ring
see Advanced digitizing
Advanced Digitizing
Delete Part
see Advanced digitizing
Advanced Digitizing
Reshape Features
see Advanced digitizing
Advanced Digitizing
Offset Curves
see Advanced digitizing
Advanced Digitizing
Split Features
see Advanced digitizing
Advanced Digitizing
Merge selected Features
see Advanced digitizing
Advanced Digitizing
Merge attr. of selected Features
see Advanced digitizing
Advanced Digitizing
Node Tool
see Digitizing an existing layer
Digitizing
Rotate Point Symbols
see Advanced digitizing
Advanced Digitizing
Toggle editing
mode for a layer, you will find the Add Feature icon in the Edit menu dependAfter activating
ing on the layer type (point, line or polygon).
6.1.3 Edit (extra)
Menu Option
Reference
Toolbar
Add Feature
see Digitizing an existing layer
Digitizing
Add Feature
see Digitizing an existing layer
Digitizing
Add Feature
see Digitizing an existing layer
Digitizing
6.1. Menu Bar
Shortcut
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6.1.4 View
Menu Option
Shortcut
Reference
Toolbar
Pan Map
Map Navigation
Pan Map to Selection
Map Navigation
Zoom In
Zoom Out
Select →
Ctrl+-
Identify Features
Measure →
Ctrl+Shift+I
Zoom Full
Map Navigation
Ctrl++
see Select and deselect features
Map Navigation
Attributes
see Measuring
Attributes
Attributes
Map Navigation
Ctrl+Shift+F
Zoom To Layer
Zoom To Selection
Map Navigation
Map Navigation
Ctrl+J
Zoom Last
Map Navigation
Zoom Next
Map Navigation
Zoom Actual Size
Decorations →
Map Navigation
see Decorations
Map Tips
Attributes
New Bookmark
Ctrl+B
see Spatial Bookmarks
Attributes
Show Bookmarks
Ctrl+Shift+B
see Spatial Bookmarks
Attributes
see Tilesets
Map Navigation
Tile scale
Refresh
Tile scale slider
Ctrl+R
6.1.5 Layer
Menu Option
New →
Embed Layers and Groups ...
Shortcut
Reference
see Creating a new Vector layer
see Nesting Projects
Toolbar
Manage Layers
Add Vector Layer
Ctrl+Shift+V
see Working with Vector Data
Manage Layers
Add Raster Layer
Ctrl+Shift+R
see Loading raster data in QGIS
Manage Layers
Add PostGIS Layer
Ctrl+Shift+D
see PostGIS Layers
Manage Layers
Add SpatiaLite Layer
Ctrl+Shift+L
see SpatiaLite Layers
Manage Layers
Add MSSQL Spatial Layer
Ctrl+Shift+M
see MSSQL Spatial Layers
Manage Layers
Add WMS Layer
Ctrl+Shift+W
see WMS Client
Manage Layers
Add Delimited Text Layer
see Delimited Text Plugin
Manage Layers
Create new GPX layer
see GPS Plugin
Manage Layers
Add Oracle GeoRaster layer
see Oracle GeoRaster Plugin
Manage Layers
Add SQL Anywhere Layer
see SQL Anywhere Plugin
Manage Layers
Add WFS Layer
Copy style
Manage Layers
see Style Tab
Continued on next page
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Table 6.1 – continued from previous page
Shortcut
Reference
Menu Option
Toolbar
see Style Tab
Paste style
Open Attribute Table
Attributes
Save edits
Digitizing
Toggle editing
Save as...
Save selection as vector file...
Remove Layer
Set CRS of Layer(s)
Set project CRS from Layer
Properties
Query...
Digitizing
See Working with the Attribute Table
Ctrl+D
Ctrl+Shift+C
Labeling
Add to Overview
Ctrl+Shift+O
Manage Layers
Show All Layers
Ctrl+Shift+U
Manage Layers
Hide All Layers
Ctrl+Shift+H
Manage Layers
Add All To Overview
Remove All From Overview
6.1.6 Settings
Menu Option
Panels →
Toolbars →
Toggle Full Screen Mode
Project Properties ...
Shortcut
Reference
see Panels and Toolbars
see Panels and Toolbars
Toolbar
Ctrl-F
Ctrl+Shift+P
see Projects
see Custom Coordinate Reference System
see Style Manager
Custom CRS ...
Style Manager...
Configure shortcuts ...
Customization ...
Options ...
Snapping Options ...
see Customization
see Options
6.1.7 Plugins
Menu Option
Fetch Python Plugins
Manage Plugins
Python Console
GRASS →
6.1. Menu Bar
Shortcut
Reference
Toolbar
see QGIS Plugins
see Managing Plugins
see GRASS GIS Integration
GRASS
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6.1.8 Vector
Menu Option
Analysis Tools →
Coordinate Capture →
Data Management Tools →
Dxf2Shp →
Geometry Tools →
Geoprocessing Tools →
GPS →
Research Tools →
Road Graph →
Spatial Query →
Shortcut
Reference
see fTools Plugin
see Coordinate Capture Plugin
see fTools Plugin
see Dxf2Shp Converter Plugin
see fTools Plugin
see fTools Plugin
see GPS Plugin
see fTools Plugin
see Road Graph Plugin
see Spatial Query Plugin
Toolbar
Vector
Vector
Vector
6.1.9 Raster
Menu Option
Raster calculator
Georeferencer →
Heatmap →
Interpolation →
Shortcut
Reference
see Raster Calculator
see Georeferencer Plugin
see Heatmap Plugin
see Interpolation Plugin
Toolbar
Raster
Raster
Raster
see Raster Terrain Analysis Plugin
see Zonal Statistics Plugin
see GDAL Tools Plugin
see GDAL Tools Plugin
see GDAL Tools Plugin
see GDAL Tools Plugin
see GDAL Tools Plugin
see GDAL Tools Plugin
Terrain Analysis
Zonal Statistics →
Projections →
Conversion →
Extraction →
Analysis →
Miscellaneous →
GdalTools settings
Raster
6.1.10 Database
Menu Option
DB manager →
eVis →
Offline Editing →
Spit →
Shortcut
Reference
see DB Manager Plugin
see eVis Plugin
see Offline Editing Plugin
see SPIT Plugin
Toolbar
Database
Database
Database
Database
6.1.11 Web
Menu Option
MapServer Export ... →
OpenStreetMap →
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Shortcut
Reference
see MapServer Export Plugin
see OpenStreetMap
Toolbar
Web
OpenStreetMap
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6.1.12 Help
Menu Option
Help Contents
What’s This?
API Documentation
QGIS Home Page
Shortcut
Reference
Toolbar
F1
Help
Shift+F1
Help
Ctrl+H
Check QGIS Version
About
QGIS Sponsors
Please not that for Linux
the Menu Bar items listed above are the default ones in KDE window manager. In
GNOME, Settings menu is missing and its items are to be found here:
Project Properties
Options
Configure Shortcuts
Style Manager
File
Edit
Edit
Edit
Custom CRS
Panels →
Toolbars →
Toggle Full Screen Mode
Tile scale slider
Live GPS tracking
Edit
View
View
View
View
View
6.2 Toolbar
The toolbar provides access to most of the same functions as the menus, plus additional tools for interacting with
the map. Each toolbar item has popup help available. Hold your mouse over the item and a short description of
the tool’s purpose will be displayed.
Every menubar can be moved around according to your needs. Additionally every menubar can be switched off
using your right mouse button context menu holding the mouse over the toolbars (read also Panels and Toolbars).
Tip: Restoring toolbars
If you have accidentally hidden all your toolbars, you can get them back by choosing menu option Settings →
Toolbars →. If a toolbar disappears under Windows, which seems to be a problem in QGIS from time to time,
you have to remove \HKEY_CURRENT_USER\Software\QuantumGIS\qgis\UI\state in the registry.
When you restart QGIS, the key is written again with the default state, and all toolbars are visible again.
6.3 Map Legend
The map legend area lists all the layers in the project. The checkbox in each legend entry can be used to show or
hide the layer.
A layer can be selected and dragged up or down in the legend to change the z-ordering. Z-ordering means that
layers listed nearer the top of the legend are drawn over layers listed lower down in the legend.
Layers in the legend window can be organised into groups. There are two ways to do so:
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1. Right click in the legend window and choose Add Group. Type in a name for the group and press Enter.
Now click on an existing layer and drag it onto the group.
2. Select some layers, right click in the legend window and choose Group Selected. The selected layers will
automatically be placed in a new group.
To bring a layer out of a group you can drag it out, or right click on it and choose Make to toplevel item. Groups
can be nested inside other groups.
The checkbox for a group will show or hide all the layers in the group with one click.
The content of the right mouse button context menu depends on whether the selected legend item is a raster or a
Toggle editing
is not available. See section Digitizing and editing a GRASS
vector layer. For GRASS vector layers
vector layer for information on editing GRASS vector layers.
Right mouse button menu for raster layers
• Zoom to layer extent
• Zoom to best scale (100 %)
• Show in overview
• Remove
• Set Layer CRS
• Set Project CRS from Layer
• Properties
• Rename
• Copy Style
• Add New Group
• Expand all
• Collapse all
• Update Drawing Order
Additionally, according to layer position and selection
• Make to toplevel item
• Group Selected
Right mouse button menu for vector layers
• Zoom to layer extent
• Show in overview
• Remove
• Set Layer CRS
• Set Project CRS from Layer
• Open attribute table
• Toggle editing (not available for GRASS layers)
• Save as
• Save selection as
• Query
• Show Feature Count
• Properties
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• Rename
• Copy Style
• Add New Group
• Expand all
• Collapse all
• Update Drawing Order
Additionally, according to layer position and selection
• Make to toplevel item
• Group Selected
Right mouse button menu for layer groups
• Zoom to group
• Remove
• Set group CRS
• Rename
• Add New Group
• Expand all
• Collapse all
• Update Drawing Order
It is possible to select more than one layer or group at the same time by holding down the Ctrl key while selecting
the layers with the left mouse button. You can then move all selected layers to a new group at the same time.
You are also able to delete more than one Layer or Group at once by selecting several Layers with the Ctrl key
and pressing Ctrl+D afterwards. This way all selected Layers or groups will be removed from the layerlist.
6.3.1 Working with the Legend independent layer order
Since QGIS 1.8 there is a widget that allows to define a legend independent drawing order. You can activate it in
the menu Settings → Panels. Determine the drawing order of the layers in the map view here. Doing so makes it
possible to order your layers in order of importance, for example, but to still display them in the correct order (see
figure_layer_order). Checking the
to default behavior.
control rendering order box underneath the list of layers will cause a revert
6.4 Map View
This is the “business end” of QGIS - maps are displayed in this area! The map displayed in this window will
depend on the vector and raster layers you have chosen to load (see sections that follow for more information on
how to load layers). The map view can be panned (shifting the focus of the map display to another region) and
zoomed in and out. Various other operations can be performed on the map as described in the toolbar description
above. The map view and the legend are tightly bound to each other - the maps in view reflect changes you make
in the legend area.
Tip: Zooming the Map with the Mouse Wheel
You can use the mouse wheel to zoom in and out on the map. Place the mouse cursor inside the map area and
roll the wheel forward (away from you) to zoom in and backwards (towards you) to zoom out. The mouse cursor
position is the center where the zoom occurs. You can customize the behavior of the mouse wheel zoom using the
Map tools tab under the Settings → Options menu.
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Figure 6.2: Define a legend independent layer order
Tip: Panning the Map with the Arrow Keys and Space Bar
You can use the arrow keys to pan in the map. Place the mouse cursor inside the map area and click on the right
arrow key to pan East, left arrow key to pan West, up arrow key to pan North and down arrow key to pan South.
You can also pan the map using the space bar: just move the mouse while holding down space bar.
6.5 Status Bar
The status bar shows you your current position in map coordinates (e.g. meters or decimal degrees) as the mouse
pointer is moved across the map view. To the left of the coordinate display in the status bar is a small button that
will toggle between showing coordinate position or the view extents of the map view as you pan and zoom in and
out.
Next to the coordinate display you find the scale display. It shows the scale of the map view. If you zoom in or out
QGIS shows you the current scale. Since QGIS 1.8 there is a scale selector which allows you to choose between
predefined scales from 1:500 until 1:1000000.
A progress bar in the status bar shows progress of rendering as each layer is drawn to the map view. In some
cases, such as the gathering of statistics in raster layers, the progress bar will be used to show the status of lengthy
operations.
If a new plugin or a plugin update is available, you will see a message at the far right of the status bar. On the right
side of the status bar is a small checkbox which can be used to temporarily prevent layers being rendered to the
map view (see Section Rendering below). The icon
immediately stops the current map rendering process.
To the right of the render functions you find the EPSG code of the current project CRS and a projector icon.
Clicking on this opens the projection properties for the current project.
Tip: Calculating the correct Scale of your Map Canvas
When you start QGIS, degrees is the default unit, and it tells QGIS that any coordinate in your layer is in degrees.
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To get correct scale values, you can either change this to meter manually in the General tab under Settings →
CRS status
Project Properties or you can select a project Coordinate Reference System (CRS) clicking on the
icon in the lower right-hand corner of the statusbar. In the last case, the units are set to what the project projection
specifies, e.g. ‘+units=m’.
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CHAPTER 7
General Tools
7.1 Keyboard shortcuts
QGIS provides default keyboard shortcuts for many features. You find them in Section Menu Bar. Additionally
the menu option Settings → Configure Shortcuts allows to change the default keyboard shortcuts and to add new
keyboard shortcuts to QGIS features.
Figure 7.1: Define shortcut options
(KDE)
Configuration is very simple. Just select a feature from the list and click on [Change], [Set none] or [Set default].
Once you have found your configuration, you can save it as XML file and load it to another QGIS installation.
7.2 Context help
When you need help on a specific topic, you can access context help via the Help button available in most dialogs
- please note that third-party plugins can point to dedicated web pages.
7.3 Rendering
By default, QGIS renders all visible layers whenever the map canvas must be refreshed. The events that trigger a
refresh of the map canvas include:
• Adding a layer
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• Panning or zooming
• Resizing the QGIS window
• Changing the visibility of a layer or layers
QGIS allows you to control the rendering process in a number of ways.
7.3.1 Scale Dependent Rendering
Scale dependent rendering allows you to specify the minimum and maximum scales at which a layer will be
visible. To set scale dependency rendering, open the Properties dialog by double-clicking on the layer in the
legend. On the General tab, set the minimum and maximum scale values and then click on the
dependent rendering checkbox.
Use scale
You can determine the scale values by first zooming to the level you want to use and noting the scale value in the
QGIS status bar.
7.3.2 Controlling Map Rendering
Map rendering can be controlled in the following ways:
Suspending Rendering
To suspend rendering, click the
Render checkbox in the lower right corner of the statusbar. When the
Render checkbox is not checked, QGIS does not redraw the canvas in response to any of the events described in
Section Rendering. Examples of when you might want to suspend rendering include:
• Add many layers and symbolize them prior to drawing
• Add one or more large layers and set scale dependency before drawing
• Add one or more large layers and zoom to a specific view before drawing
• Any combination of the above
Checking the
Render checkbox enables rendering and causes an immediate refresh of the map canvas.
Setting Layer Add Option
You can set an option to always load new layers without drawing them. This means the layer will be added to the
map, but its visibility checkbox in the legend will be unchecked by default. To set this option, choose menu option
Settings → Options → and click on the Rendering tab. Uncheck the
By default new layers added to the map
should be displayed checkbox. Any layer added to the map will be off (invisible) by default.
Stopping Rendering
To stop the map drawing, press the ESC key. This will halt the refresh of the map canvas and leave the map
partially drawn. It may take a bit of time between pressing ESC and the time the map drawing is halted.
Note: It is currently not possible to stop rendering - this was disabled in qt4 port because of User Interface (UI)
problems and crashes.
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Updating the Map Display During Rendering
You can set an option to update the map display as features are drawn. By default, QGIS does not display any
features for a layer until the entire layer has been rendered. To update the display as features are read from
the datastore, choose menu option Settings → Options click on the Rendering tab. Set the feature count to an
appropriate value to update the display during rendering. Setting a value of 0 disables update during drawing (this
is the default). Setting a value too low will result in poor performance as the map canvas is continually updated
during the reading of the features. A suggested value to start with is 500.
Influence Rendering Quality
To influence the rendering quality of the map you have 2 options. Choose menu option Settings → Options click
on the Rendering tab and select or deselect following checkboxes.
•
Make lines appear less jagged at the expense of some drawing performance
•
Fix problems with incorrectly filled polygons
7.4 Measuring
Measuring works within projected coordinate systems (e.g., UTM) and unprojected data. If the loaded map
is defined with a geographic coordinate system (latitude/longitude), the results from line or area measurements
will be incorrect. To fix this you need to set an appropriate map coordinate system (See Section Working with
Projections). All measuring modules also use the snapping settings from the digitizing module. This is useful, if
you want to measure along lines or areas in vector layers.
To select a measure tool click on
and select the tool you want to use.
7.4.1 Measure length, areas and angles
QGIS is able to measure real distances between given points according to a defined ellipsoid. To configure
this, choose menu option Settings → Options, click on the Map tools tab and choose the appropriate ellipsoid.
There you can also define a rubberband color and your preferred measurement units (meters or feet) and angle
units (degrees, radians and gon). The tools then allows you to click points on the map. Each segment-length as
well as the total shows up in the measure-window. To stop measuring click your right mouse button.
Figure 7.2: Measure Distance
(KDE)
Areas can also be measured. In the measure window the accumulated area size appears. In addition, the
measuring tool will snap to the currently selected layer, provided that layer has its snapping tolerance set. (See
Section Setting the Snapping Tolerance and Search Radius). So if you want to measure exactly along a line feature,
or around a polygon feature, first set its snapping tolerance, then select the layer. Now, when using the measuring
tools, each mouse click (within the tolerance setting) will snap to that layer.
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Figure 7.3: Measure Area
(KDE)
You can also measure angles, selecting Measure Angle tool. The cursor becomes cross-shaped. Click to
draw the first segment of the angle you wish to measure, then move the the cursor to draw the desired angle. The
measure is displayed in a popup dialog.
Figure 7.4: Measure Angle
(KDE)
7.4.2 Select and deselect features
The QGIS toolbar provides several tools to select features in the map canvas. To select one or several features just
click on
and select your tool:
•
Select single feature
•
Select features by rectangle
•
Select features by polygon
•
Select features by freehand
•
Select features by radius
To deselect all selected features click on
Deselect features from all layers
.
7.5 Decorations
The Decorations of QGIS includes the Copyright Label, the North Arrow and the Scale Bar. They are used to
‘decorate’ the map by adding cartographic elements.
Note: Before QGIS 1.8 the same functionality was provided by the Decoration Plugin.
7.5.1 Copyright Label
Copyright label adds a Copyright label using the text you prefer to the map.
1. Select from menu View → Decorations → Copyright Label. The dialog starts (see figure_decorations_1).
2. Enter the text you want to place on the map. You can use HTML as shown in the example
3. Choose the placement of the label from the Placement ‘Bottom Right’ drop-down box
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Figure 7.5: The copyright Dialog
4. Make sure the
Enable Copyright Label checkbox is checked
5. Click [OK]
In the example above (default) QGIS places a copyright symbol followed by the date in the lower right hand corner
of the map canvas.
7.5.2 North Arrow
North Arrow places a simple north arrow on the map canvas. At present there is only one style available. You
can adjust the angle of the arrow or let QGIS set the direction automatically. If you choose to let QGIS determine
the direction, it makes its best guess as to how the arrow should be oriented. For placement of the arrow you have
four options, corresponding to the four corners of the map canvas.
Figure 7.6: The North Arrow Dialog
7.5.3 Scale Bar
Scale Bar adds a simple scale bar to the map canvas. You control the style and placement, as well as the
labeling of the bar.
QGIS only supports displaying the scale in the same units as your map frame. So if the units of your layers are in
meters, you can’t create a scale bar in feet. Likewise if you are using decimal degrees, you can’t create a scale bar
to display distance in meters.
To add a scale bar:
1. Select from menu View → Decorations → Scale Bar The dialog starts (see figure_decorations_3)
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Figure 7.7: The Scale Bar Dialog
2. Choose the placement from the Placement ‘Bottom Left’ drop-down list
3. Choose the style from the Scale bar style ‘Tick Down’ list
4. Select the color for the bar Color of bar ‘black’ or use the default black color
5. Set the size of the bar and its label Size of bar ‘30 degrees’
6. Make sure the
Enable scale bar checkbox is checked
7. Optionally choose to automatically snap to a round number when the canvas is resized
snap to round number on resize
Automatically
8. Click [OK]
Tip: Settings of Decorations
When you save a .qgs project, any changes you have made to NorthArrow, ScaleBar and Copyright will be saved
in the project and restored the next time you load the project.
7.6 Annotation Tools
Text Annotation tools in the attribute toolbar provides the possibility to place formatted text in a balloon
The
on the QGIS map canvas. Use the Text Annotation tool and click into the map canvas.
Figure 7.8: Annotation text dialog
Double click on the item opens a dialog with various options. There is the text editor to enter the formatted text
and other item settings. E.g. there is the choice of having the item placed on a map position (displayed by a marker
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symbol) or to have the item on a screen position (not related to the map). The item can be moved by map position
(drag the map marker) or by moving only the balloon. The icons are part of GIS theme, and are used by default in
the other themes too.
The
Move Annotation tool allows to move the annotation on the map canvas.
7.6.1 Form annotations
Additionally you can also create your own annotation forms. The
Form Annotation tool is useful to display attributes of a vector layer in a customized qt designer form (see figure_custom_annotation). It is similar
to the designer forms for the Identify features tool, but displayed in an annotation item. Also see QGIS blog
http://blog.qgis.org/node/143 for more information.
Figure 7.9: Customized qt designer annotation form
Note: If you press Ctrl+T while an Annotation tool is active (move annotation, text annotation, form annotation), the visibility states of the items are inverted.
7.7 Spatial Bookmarks
Spatial Bookmarks allow you to “bookmark” a geographic location and return to it later.
7.7.1 Creating a Bookmark
To create a bookmark:
1. Zoom or pan to the area of interest.
2. Select the menu option View → New Bookmark or press Ctrl-B.
3. Enter a descriptive name for the bookmark (up to 255 characters).
4. Press Enter to add the bookmark or [Delete] to remove the bookmark.
Note that you can have multiple bookmarks with the same name.
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7.7.2 Working with Bookmarks
To use or manage bookmarks, select the menu option View → Show Bookmarks. The Geospatial Bookmarks
dialog allows you to zoom to or delete a bookmark. You can not edit the bookmark name or coordinates.
7.7.3 Zooming to a Bookmark
From the Geospatial Bookmarks dialog, select the desired bookmark by clicking on it, then click [Zoom To]. You
can also zoom to a bookmark by double-clicking on it.
7.7.4 Deleting a Bookmark
To delete a bookmark from the Geospatial Bookmarks dialog, click on it then click [Delete]. Confirm your choice
by clicking [Yes] or cancel the delete by clicking [No].
7.8 Nesting Projects
If you want to embed content from other project files into your project you can choose Layer → Embed Layers
and Groups.
7.8.1 Embedding layers
The following dialog allows you to embed layers from other projects:
1. Press
to look for another project from the Alaska dataset.
2. Select the project file grassland. You can see the content of the project (see figure_embed_dialog).
3. Press Ctrl and klick on the layers grassland and regions. The layers are embedded in the map legend and
the map view now.
Figure 7.10: Select layers and groups to embed
While the embedded layers are editable you can’t change it’s properties like Style and Labeling.
Removing embedded layers
Right-click on the embedded layer and choose
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Chapter 7. General Tools
CHAPTER 8
QGIS Configuration
QGIS is highly configurable through the Settings menu. Choose between Panels, Toolbars, Project properties,
Options and Customization.
8.1 Panels and Toolbars
In the Panels→ menu you can switch on and off QGIS widgets. The Toolbars→ menu provides the possibility to
switch on and off icon groups in the QGIS toolbar (see figure_panels_toolbars).
Figure 8.1: The Panels and Toolbars menu
Tip: Activating the QGIS Overview
In QGIS you can use an overview panel that provides a full extent view of layers added to it. It can be selected
under the menu Settings → Panels. Within the view is a rectangle showing the current map extent. This allows
you to quickly determine which area of the map you are currently viewing. Note that labels are not rendered to
the map overview even if the layers in the map overview have been set up for labeling. If you click and drag the
red rectangle in the overview that shows your current extent, the main map view will update accordingly.
Tip: Show Log Messages
Since QGIS 1.8 it’s possible to track the QGIS messages. You can activate
Log Messages in the menu Settings
→ Panels and follow the messages in the General and Plugin tab during loading and operation.
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8.2 Project Properties
In the properties window for the project under Settings → Project Properties or
ties you set project specific options. These include:
Settings → Project Proper-
• In the General tab the project title, selection and background color, layer units, precision, and the option to
save relative paths to layers can be defined. You can define the layer units (only used when CRS transformation is disabled) and the precision of decimal places to use.
• The CRS Coordinate Reference System tab enables you to choose the CRS for this project, and to enable
on-the-fly re-projection of raster and vector layers when displaying layers from a different CRS.
• With the third Identifiable layers tab you set (or disable) which layers will respond to the identify tool. (See
the Map tools paragraph from the Options section to enable identifying of multiple layers.)
• The tab OWS Server allows to define information about the QGIS mapserver Service Capabilities, the Extent
and the CRS Restrictions as well as the WFS Capabilities. Activating the
info response will allow to query the WMS layers.
Add WKT geometry to feature
8.3 Options
Some basic options for QGIS can be selected using the Options dialog. Select the menu option Settings →
Options. The tabs where you can optimize your options are:
8.3.1 General Tab
•
Prompt to save project changes when required
•
Warn when opening a project file saved with an older version of QGIS
• Change Selection and Background color
• Change the QGIS Style
• Change the icon theme (choose between ‘default’, ‘classic’ and ‘gis’)
• Change icon size between 16, 24 and 32 pixel.
• Change the menu size
• Define double click action in legend (choose between ‘open layer properties’ and ‘open ‘) attribute table.
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•
Capitalize layer names in legend
•
Display classification attribute names in legend
•
Create raster icons in legend
•
Hide splash screen at startup
•
Show tips at startup
•
Open identify results in a dock window (QGIS restart required)
•
Open snapping options in a dock window (QGIS restart required)
•
Open attribute table in a dock window
•
Add PostGIS layers with double click and select in extended mode
•
Add new layers to selected or current group
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•
Copy geometry in WKT representation from attribute table
• Attribute table behavior (choose between ‘Show all features’ (default), ‘Show selected features’,’Show
features in current canvas’)
• Attribute table row cache
• Define Representation for NULL values
• Prompt for raster sublayers
. Some rasters support sublayers - they are called subdatasets in GDAL.
An example is netcdf files - if there are many netcdf variables, GDAL sees every variable as a subdataset.
The option is to control how to deal with sublayers when a file with sublayers is opened. You have the
following choices:
– ‘Always’: always ask (if there are existing sublayers)
– ‘If needed’: ask if layer has no bands, but has sublayers
– ‘Never’: never prompt, will not load anything
– ‘Load all’: never prompt, but load all sublayers
. The ‘Check extension’ option was designed to speed up
• Scan for valid items in the browser dock
the loading of a directory, which can be time-consuming when ‘Check file contents’ is activated and there
are many files (tens or hundreds).
• Scan for contents of compressed files (.zip) in browser dock
up the loading of a directory. You have the following choices:
This option was also designed to speed
– ‘Basic Scan’: checks that the extension is supported by one of the drivers
– ‘Full Scan’: opens every file to check it is valid
– ‘Passthru’: don’t use this option it will be removed in the next QGIS version
8.3.2 GDAL tab
GDAL is a data exchange library for raster files. In this tab you can define which GDAL driver to be used for a
raster format as in some cases more than one GDAL driver is available.
8.3.3 Plugins tab
• Add Path(s) to search for additional C++ plugin libraries.
8.3.4 Rendering Tab
•
By default new layers added to the map should be displayed
• Define Number of features to draw before updating the display.
•
Use render caching where possible to speed up redraws
•
Make lines appear less jagged at the expense of some drawing performance
•
Fix problems with incorrectly filled polygons
•
Use new generation symbology for rendering
• Define the default Raster settings for visualisation: ‘RGB band selection’,
‘Contrast Enhancement’
8.3. Options
Use standard deviation and
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• Add/remove Path(s) to search for Scalable Vector Graphics (SVG) symbols
Additionally you can define whether to save the path for svg textures absolute or relative in the General tab of the
Settings → Project Properties menu.
8.3.5 Map tools Tab
• The Mode setting determines which layers will be shown by the Identify tool. By switching to ‘Top down’
or ‘Top down, stop at first’ instead of ‘Current layer’ attributes for all identifiable layers (see the Project
properties section under: Projects to set which layers are identifiable) will be shown with the Identify tool.
•
Open feature form, if a single feature is identified
• Define Search radius for identifying and displaying map tips as a percentage of the map width
• Define Ellipsoid for distance calculations
• Define Rubberband color for measure tools
• Define Decimal places
•
Keep base unit
•
Define preferred measurement units (‘meters’ or ‘feet’)
•
Define preferred angle units (‘Degrees’, ‘Radians’ or ‘Gon’)
(‘Zoom’, ‘Zoom and recenter’, ‘Zoom to mouse cursor’, ‘Nothing’)
• Define Mouse wheel action
• Define Zoom factor for wheel mouse
8.3.6 Overlays Tab
• Define Placement algorithm
for labels, symboly and diagrams (choose between ‘Central point’
(standard), ‘Chain’, ‘Popmusic tabu chain’, ‘Popmusic tabu’ and ‘Popmusic chain’)
8.3.7 Digitizing Tab
• Define Rubberband Line color and Line width
• Define Default snap mode
(‘To vertex’, ‘To segment’, ‘To vertex and segment’)
• Define Default snapping tolerance in map units or pixel
• Define search radius for vertex edits in ‘map units’ or ‘pixel’
•
Show markers only for selected features
• Define vertex Marker style
Marker size.
(‘Cross’ (default), ‘Semi transparent circle’ or ‘None’) and vertex
•
Suppress attributes pop-up windows after each created feature
•
Reuse last entered attribute values
• Validate geometries Editing complex lines/polygons with many nodes can end up with very slow rendering.
This is because the default validation procedures in QGIS can use a lot of time. To speed up rendering it is
possible to select GEOS geometry validation (starting from GEOS 3.3) or to switch it off. GEOS geometry
validation is much faster, but the disadvantage is that only the first geometry problem will be reported.
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Offset Curve
The next 3 options refer to the
tool in Advanced digitizing. Through the various settings, it is
possible to influence the shape of the line offset. These options are possible from GEOS 3.3 .
• Join style for curve offset
• Quadrantsegments for curve offset
• Miter limit for curve offset
8.3.8 CRS Tab
The CRS tab is divided in two areas. The first area allows to define the default CRS for new projects.
• Select a CRS and Always start new projects with this CRS.
•
Enable on the fly re-projection by default
The second area allows to define the action, when a new layer is created, or when a layer without CRS is loaded.
•
Prompt for Coordinate Reference System (CRS)
•
Use project Coordinate Reference System (CRS)
•
Use default Coordinate Reference System (CRS) displayed below
8.3.9 Locale Tab
•
Overwrite system locale and Locale to use instead
• Information about active system locale
8.3.10 Network Tab
Figure 8.2: Proxy-settings in QGIS
•
Use proxy for web access and define ‘Host’, ‘Port’, ‘User’, and ‘Password’.
• Set the Proxy type
according to your needs.
– Default Proxy: Proxy is determined based on the application proxy set using
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– Socks5Proxy: Generic proxy for any kind of connection. Supports TCP, UDP, binding to a port (incoming connections) and authentication.
– HttpProxy: Implemented using the “CONNECT” command, supports only outgoing TCP connections;
supports authentication.
– HttpCachingProxy: Implemented using normal HTTP commands, it is useful only in the context of
HTTP requests
– FtpCachingProxy: Implemented using an FTP proxy, it is useful only in the context of FTP requests
• Define Cache settings (path and size)
• Define WMS search address, default is http://geopole.org/wms/search?search=\%1\&type=rss
• Define Timeout for network requests (ms) - deeingebundenfault is 60000
Excluding some URLs can be added to the text box below the proxy-settings (see Figure_Network_Tab) by pressing the [Add] button. After that double-click into the just created URL-field and enter the URL you would like to
exclude from using the proxy. Obviously the button [Remove] removes the selected entry.
If you need more detailed information about the different proxy-settings, please refer to the manual of the underlying QT-library-documentation at http://doc.trolltech.com/4.5/qnetworkproxy.html#ProxyType-enum.
Tip: Using Proxies
Using proxies can sometimes be tricky. It is useful to ‘trial and error’ the above proxy types and check if they
succeed in your case.
You can modify the options according to your needs. Some of the changes may require a restart of QGIS before
they will be effective.
•
settings are saved in a texfile: $HOME/.config/QuantumGIS/qgis.conf
•
you can find your settings in: $HOME/Library/Preferences/org.qgis.qgis.plist
•
settings are stored in the registry under:
\HKEY\CURRENT_USER\Software\QuantumGIS\qgis
8.4 Customization
The customization tool is a new development in QGIS 1.8.. It lets you (de)activate almost every element in the
QGIS user interface. This can get very useful if you have a lot of plug-ins installed that you never use and that are
filling your screen.
Figure 8.3: The Customization dialog
QGIS Customization is divided into five groups. In
Docks you find the dock windows. Dock windows are
applications that can be started and used as a floating, top-level window or embedded to the QGIS main window
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as a docked widget (see also Panels and Toolbars). In
Menus you can hide entries in the Menu bar. In the
Status Bar features like the coordinate information can be daectivated. In
toolbar icons of QGIS and in
Toolbars you can (de)activate the
Widgets you can (de)activate dialogs as well as their buttons.
With
Switch to catching widgets in main application you can click on elements in QGIS you want to be
hidden and find the corresponding entry in Customization (see figure_customization). You can also save your
various different setups for different use cases as well. Before your changes are applied, you need to restart QGIS.
8.4. Customization
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CHAPTER 9
Working with Projections
QGIS allows users to define a global and project-wide CRS (Coordinate Reference System) for layers without a
pre-defined CRS. It also allows the user to define custom coordinate reference systems and supports on-the-fly
(OTF) projection of vector and raster layers. All these features allow the user to display layers with different CRS
and have them overlay properly.
9.1 Overview of Projection Support
QGIS has support for approximately 2,700 known CRS. Definitions for each of these CRS are stored in a SQLite
database that is installed with QGIS. Normally you do not need to manipulate the database directly. In fact, doing
so may cause projection support to fail. Custom CRS are stored in a user database. See Section Custom Coordinate
Reference System for information on managing your custom coordinate reference systems.
The CRS available in QGIS are based on those defined by the European Petroleum Search Group (EPSG) and the
Institut Geographique National de France (IGNF) and are largely abstracted from the spatial reference tables used
in GDAL. EPSG identifiers are present in the database and can be used to specify a CRS in QGIS.
In order to use OTF projection, your data must contain information about its coordinate reference system or you
have to define a global, layer or project-wide CRS. For PostGIS layers QGIS uses the spatial reference identifier
that was specified when the layer was created. For data supported by OGR, QGIS relies on the presence of a
recognized means of specifying the CRS. In the case of shapefiles, this means a file containing the Well Known
Text (WKT) specification of the CRS. This projection file has the same base name as the shapefile and a prj
extension. For example, a shapefile named alaska.shp would have a corresponding projection file named
alaska.prj.
Whenever you select a new CRS, the used layer units will automatically be changed in the General tab of the
Project Properties dialog under the Edit (Gnome, OSX) or Settings (KDE, Windows) menu.
9.2 Specifying a Projection
QGIS starts each new project using the global default projection.The global default CRS is EPSG:4326 - WGS
84 (proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs) and comes predefined in QGIS. This
default can be changed using the [Select...] button in the first section, used to defining the Default Coordinate
Reference System to use when starting new projects, as shown in figure_projection_1. This choice will be saved
for use in subsequent QGIS sessions.
When you use layers that do not have a CRS, you need to define how QGIS responds to these layers. This can be
done globally or project-wide in the CRS tab under Edit →
Options (Gnome, OSX) or Settings →
Options
(KDE, Windows).
The options shown in figure_projection_1 are:
•
Prompt for CRS
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Figure 9.1: CRS tab in the QGIS Options Dialog
•
Use project CRS
•
Use default CRS displayed below
If you want to define the coordinate reference system for a certain layer without CRS information, you can also
do that in the General tab of the raster (see General Tab) and vector (see General Tab) properties dialog. If your
layer already has a CRS defined, it will be displayed as shown in Vector Layer Properties Dialog .
Tip: CRS in the Map Legend
Right-clicking on a layer in the Map Legend (Section Map Legend) provides two CRS short cuts. Set layer CRS
takes you directly to the Coordinate Reference System Selector dialog (see figure_projection_2). Set project CRS
from Layer redefines the project CRS using the layer’s CRS
9.3 Define On The Fly (OTF) Reprojection
QGIS supports OTF reprojection for both raster and vector data. However, OTF is not activated by default. To use
OTF projection, you must activate the
Enable on the fly CRS transformation checkbox in the CRS tab of the
Project Properties dialog.
There are three ways to achieve this end:
1. Select
Project Properties from the Edit (Gnome, OSX) or Settings (KDE, Windows) menu.
2. Click on the
CRS status
icon in the lower right-hand corner of the statusbar.
3. Turn OTF on by default, by selecting the CRS tab of the Options dialog and selecting
reprojection by default.
Enable ‘on the fly’
If you have already loaded a layer, and want to enable OTF projection, the best practice is to open the Coordinate
Reference System tab of the Project Properties dialog, select a CRS, and activate the
transformation checkbox. The
to the CRS shown next to the icon.
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CRS status
Enable on the fly CRS
icon will no longer be greyed-out and all layers will be OTF projected
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Figure 9.2: Projection Dialog
The Coordinate Reference System tab of the Project Properties dialog contains five important components as
shown in Figure_projection_2 and described below.
1. Enable on the fly CRS transformation - this checkbox is used to enable or disable OTF projection. When
off, each layer is drawn using the coordinates as read from the data source and the components described
below are inactive.When on, the coordinates in each layer are projected to the coordinate reference system
defined for the map canvas.
2. Coordinate Reference System - this is a list of all CRS supported by QGIS, including Geographic, Projected and Custom coordinate reference systems. To define a CRS, select it from the list by expanding the
appropriate node and selecting the CRS. The active CRS is preselected.
3. Proj4 text - this is the CRS string used by the Proj4 projection engine. This text is read-only and provided
for informational purposes.
4. Filter - if you know the EPSG code, the identifier or the name for a Coordinate Reference System, you can
use the search feature to find it. Enter the EPSG code, the identifier or the name.
5. Recently used CRS - if you have certain CRS that you frequently use in your everyday GIS work, these
will be displayed in the table at the bottom of the Projection Dialog. Click on one of these buttons to select
the associated CRS.
Tip: Project Properties Dialog
If you open the Project Properties dialog from the Edit (Gnome, OSX) or Settings (KDE, Windows) menu, you
must click on the Coordinate Reference System tab to view the CRS settings.
Opening the dialog from the
to the front.
CRS status icon will automatically bring the Coordinate Reference System tab
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9.4 Custom Coordinate Reference System
If QGIS does not provide the coordinate reference system you need, you can define a custom CRS. To define
Custom CRS from the Edit (Gnome, OSX) or Settings (KDE, Windows) menu. Custom CRS
a CRS, select
are stored in your QGIS user database. In addition to your custom CRS, this database also contains your spatial
bookmarks and other custom data.
Figure 9.3: Custom CRS Dialog
Defining a custom CRS in QGIS requires a good understanding of the Proj.4 projection library. To begin, refer to
the Cartographic Projection Procedures for the UNIX Environment - A User’s Manual by Gerald I. Evenden, U.S.
Geological Survey Open-File Report 90-284, 1990 (available at ftp://ftp.remotesensing.org/proj/OF90-284.pdf ).
This manual describes the use of the proj.4 and related command line utilities. The cartographic parameters
used with proj.4 are described in the user manual and are the same as those used by QGIS.
The Custom Coordinate Reference System Definition dialog requires only two parameters to define a user CRS:
1. a descriptive name and
2. the cartographic parameters in PROJ.4 format.
To create a new CRS, click the
New
you can save your CRS by clicking the
button and enter a descriptive name and the CRS parameters. After that
Save
button.
Note that the Parameters must begin with a +proj=-block, to represent the new coordinate reference system.
You can test your CRS parameters to see if they give sane results by clicking on the [Calculate] button inside
the Test block and pasting your CRS parameters into the Parameters field. Then enter known WGS 84 latitude
and longitude values in North and East fields respectively. Click on [Calculate] and compare the results with the
known values in your coordinate reference system.
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CHAPTER 10
QGIS Browser
The QGIS Browser is a new panel in QGIS that lets you easily navigate in your database. You can have access to common vector files (e.g. ESRI shapefile or MapInfo files), databases (e.g.PostGIS or MSSQL Spatial)
and WMS/WFS connections. You can also view your GRASS data (to get the data into QGIS see GRASS GIS
Integration).
Figure 10.1: Qgis browser as a standalone application to view metadata, preview and attributes
Use QGIS Browser to preview your data. The drag and drop function makes it easy to get your data into the Map
view and the Map legend.
1. Activate QGIS Browser: Right-click on the tool bar and click
Browser.
2. Drag the panel into the legend window.
3. Klick on the Browser tab.
4. Browse in your database and choose the shapefile folder from qgis_sample_data.
5. Press the Shift key and klick on airports.shp and alaska.shp .
6. Press the left mouse button then drag and drop the files into the map canvas.
7. Right-click on a layer and choose Set project CRS from layer. For more information see Working with
Projections.
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8. Click on
Zoom Full to make the layers visible.
It’s also possible to run QGIS Browser as a standalone application.
Start qgis browser
•
Type in “qbrowser” at a command prompt.
•
Start QGIS browser using the Start menu or desktop shortcut, or double click on a QGIS project file.
•
QGIS browser is not available yet from your your Applications folder. However it can easily be made available.
In Finder use Go → Go to map...
and use it to find the folder
/Applications/QGIS.app/Contents/MacOS/bin. Use the key combination option command and drag qbrowser.app while holding down the left mouse button to the Applications folder.
This will create a link that you can use to start QGIS browser.
In figure_browser_standalone_metadata you can see the enhanced functionality of Qgis browser. The Param
tab provides the details of your connection based datasets like PostGIS or MSSQL Spatial. The Metadata tab
contains general information about the file (see Metadata Tab). With the Preview tab you can have a look at your
files without importing them into your QGIS project. It’s also possible to preview the attributes of your files in the
Attributes tab.
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CHAPTER 11
Working with Vector Data
11.1 Supported Data Formats
QGIS uses the OGR library to read and write vector data formats (GRASS vector and PostgreSQL support is
supplied by native QGIS data provider plugins),including ESRI Shapefiles, MapInfo and Microstation file formats;
PostGIS, SpatiaLite, Oracle Spatial databases and many more. The vector data can also be loaded in read mode
from zip and gzip archives into QGIS. At the date of this document, 69 vector formats are supported by the
OGR library (see OGR-SOFTWARE-SUITE Literature and Web References). The complete list is available at
http://www.gdal.org/ogr/ogr_formats.html.
Note: Not all of the listed formats may work in QGIS for various reasons. For example, some require external
commercial libraries or the GDAL/OGR installation of your OS was not build to support the format you want to
use. Only those formats that have been well tested will appear in the list of file types when loading a vector into
QGIS. Other untested formats can be loaded by selecting *.*.
Working with GRASS vector data is described in Section GRASS GIS Integration.
This section describes how to work with several common formats: ESRI Shapefiles, PostGIS layers and SpatiaLite
layers. Many of the features available in QGIS work the same, regardless of the vector data source. This is by
design and includes the identify, select, labeling and attributes functions.
11.1.1 ESRI Shapefiles
The standard vector file format used in QGIS is the ESRI Shapefile. Support is provided by the OGR Simple
Feature Library ( http://www.gdal.org/ogr/ ).
A shapefile actually consists of several files. The following three are required:
1. .shp file containing the feature geometries.
2. .dbf file containing the attributes in dBase format.
3. .shx index file.
Shapefiles also can include a file with a .prj suffix, which contains the projection information. While it is very
useful to have a projection file, it is not mandatory. A shapefile dataset can contain additional files. For further
details see the ESRI technical specification at: http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf.
Loading a Shapefile
Add Vector Layer
To load a shapefile, start QGIS and click on the
toolbar button or simply type
Ctrl+Shift+V. This will bring up a new window (see figure_vector_1).
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Figure 11.1: Add Vector Layer Dialog
From the available options check
File. Click on button [Browse]. That will bring up a standard open file dialog
(see figure_vector_2) which allows you to navigate the file system and load a shapefile or other supported data
source. The selection box Filter
allows you to preselect some OGR supported file formats.
You can also select the Encoding type for the shapefile if desired.
Figure 11.2: Open an OGR Supported Vector Layer Dialog
Selecting a shapefile from the list and clicking [Open] loads it into QGIS. Figure_vector_3 shows QGIS after
loading the alaska.shp file.
Tip: Layer Colors
When you add a layer to the map, it is assigned a random color. When adding more than one layer at a time,
different colors are assigned to each layer.
Once loaded, you can zoom around the shapefile using the map navigation tools. To change the style of a layer,
open the Layer Properties dialog by double clicking on the layer name or by right-clicking on the name in the
legend and choosing Properties from the popup menu. See Section Style Tab for more information on setting
symbology of vector layers.
Tip: Load layer and project from mounted external drives on OS X
On OS X, portable drives that are mounted besides the primary hard drive do not show up under File → Open
Project as expected. We are working on a more OSX-native open/save dialog to fix this. As a workaround you can
type ‘/Volumes’ in the File name box and press return. Then you can navigate to external drives and network
mounts.
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Figure 11.3: QGIS with Shapefile of Alaska loaded
Improving Performance Shape
To improve the performance of drawing a shapefile, you can create a spatial index. A spatial index will improve
the speed of both zooming and panning. Spatial indexes used by QGIS have a .qix extension.
Use these steps to create the index:
• Load a shapefile.
• Open the Layer Properties dialog by double-clicking on the shapefile name in the legend or by right-clicking
and choosing Properties from the popup menu.
• In the tab General click the [Create Spatial Index] button.
Problem loading a shape .prj file
If you load a shapefile with .prj file and QGIS is not able to read the coordinate reference system from that file,
you have to define the proper projection manually within the General tab of the Layer Properties dialog of the
layer. This is due to the fact, that .prj files often do not provide the complete projection parameters, as used in
QGIS and listed in the CRS dialog.
For that reason, if you create a new shapefile with QGIS, two different projection files are created. A .prj
file with limited projection parameters, compatible with ESRI software, and a .qpj file, providing the complete
parameters of the used CRS. Whenever QGIS finds a .qpj file, it will be used instead of the .prj.
11.1.2 Loading a MapInfo Layer
To load a MapInfo layer, click on the
file type filter Filter
Add Vector Layer
toolbar button or type Ctrl+Shift+V, change the
: to ‘Mapinfo File [OGR]’ and select the MapInfo layer you want to load.
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11.1.3 Loading an ArcInfo Binary Coverage
To load an ArcInfo binary coverage, click on the
Add Vector Layer
toolbar button or press Ctrl+Shift+V to
open the Add Vector Layer dialog. Select
Directory. Change to Filter
Navigate to the directory that contains the coverage files and select it.
to ‘Arc/Info Binary Coverage’.
Similarly, you can load directory based vector files in the UK National Transfer Format as well as the raw TIGER
Format of the US Census Bureau.
11.1.4 PostGIS Layers
PostGIS layers are stored in a PostgreSQL database. The advantages of PostGIS are the spatial indexing, filtering and query capabilities it provides. Using PostGIS, vector functions such as select and identify work more
accurately than with OGR layers in QGIS.
Creating a stored Connection
The first time you use a PostGIS data source, you must create a connection to the PostgreSQL database that
Add PostGIS Layer
contains the data. Begin by clicking on the
toolbar button, selecting the
Add PostGIS
Layer... option from the Layer menu or typing Ctrl+Shift+D. You can also open the Add Vector Layer dialog
and select
Database. The Add PostGIS Table(s) dialog will be displayed. To access the connection manager,
click on the [New] button to display the Create a New PostGIS Connection dialog. The parameters required for a
connection are:
• Name: A name for this connection. Can be the same as Database
• Service: Service parameter to be used alternatively to hostname/port (and potentially database). This can
be defined in pg_service.conf
• Host: Name of the database host. This must be a resolvable host name the same as would be used to open a
telnet connection or ping the host. If the database is on the same computer as QGIS, simply enter ‘localhost’
here.
• Port: Port number the PostgreSQL database server listens on. The default port is 5432.
• Database: Name of the database.
• SSL mode: How the SSL connection will be negotiated with the server. Note that massive speedups in
PostGIS layer rendering can be achieved by disabling SSL in the connection editor. Following options are
available:
– disable: only try an unencrypted SSL connection
– allow: try a non-SSL connection, if that fails, try an SSL connection
– prefer (the default): try an SSL connection, if that fails, try a non-SSL connection;
– require: only try an SSL connection.
• Username: User name used to login to the database.
• Password: Password used with Username to connect to the database.
Optional you can activate following checkboxes:
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•
Save Username
•
Save Password
•
Only look in the geometry_columns table
•
Only look in the ‘public’ schema
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•
Also list tables with no geometry
•
Use estimated table metadata
Once all parameters and options are set, you can test the connection by clicking on the [Test Connect] button.
Tip: QGIS User Settings and Security
Depending on your computing environment, storing passwords in your QGIS settings may be a security risk. Your
customized settings for QGIS are stored based on the operating system:
•
, the settings are stored in your home directory in .qgis/.
•
, the settings are stored in the registry.
Loading a PostGIS Layer
Once you have one or more connections defined, you can load layers from the PostgreSQL database. Of
course this requires having data in PostgreSQL. See Section Importing Data into PostgreSQL for a discussion on
importing data into the database.
To load a layer from PostGIS, perform the following steps:
• If the Add PostGIS layers dialog is not already open, click on the
Add PostGIS Layer
toolbar button.
• Choose the connection from the drop-down list and click [Connect].
• Select or unselect
Also list tables with no geometry
• Optionally use some
Search Options to define which features to load from the layer or use the [Build
query] button to start the Query builder dialog.
• Find the layer(s) you wish to add in the list of available layers.
• Select it by clicking on it. You can select multiple layers by holding down the Shift key while clicking.
See Section Query Builder for information on using the PostgreSQL Query Builder to further define the
layer.
• Click on the [Add] button to add the layer to the map.
Tip: PostGIS Layers
Normally a PostGIS layer is defined by an entry in the geometry_columns table. From version 0.9.0 on, QGIS
can load layers that do not have an entry in the geometry_columns table. This includes both tables and views.
Defining a spatial view provides a powerful means to visualize your data. Refer to your PostgreSQL manual for
information on creating views.
Some details about PostgreSQL layers
This section contains some details on how QGIS accesses PostgreSQL layers. Most of the time QGIS should
simply provide you with a list of database tables that can be loaded, and load them on request. However, if you
have trouble loading a PostgreSQL table into QGIS, the information below may help you understand any QGIS
messages and give you direction on changing the PostgreSQL table or view definition to allow QGIS to load it.
QGIS requires that PostgreSQL layers contain a column that can be used as a unique key for the layer. For tables
this usually means that the table needs a primary key, or a column with a unique constraint on it. In QGIS, this
column needs to be of type int4 (an integer of size 4 bytes). Alternatively the ctid column can be used as primary
key. If a table lacks these items, the oid column will be used instead. Performance will be improved if the column
is indexed (note that primary keys are automatically indexed in PostgreSQL).
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If the PostgreSQL layer is a view, the same requirement exists, but views do not have primary keys or columns
with unique constraints on them. In this case QGIS will try to find a column in the view that is derived from a
suitable table column. It does this by parsing the view definition SQL. However there are several aspects of SQL
that QGIS ignores these include the use of table aliases and columns that are generated by SQL functions.
If a suitable column cannot be found, QGIS will not load the layer. If this occurs, the solution is to alter the
view so that it does include a suitable column (a type of int4 and either a primary key or with a unique constraint,
preferably indexed).
11.1.5 Importing Data into PostgreSQL
Data can be imported into PostgreSQL/PostGIS using several tools, such as the SPIT plugin, or the command line
tools shp2pgsql or ogr2ogr.
SPIT Plugin
SPIT
(Shapefile to PostGIS Import Tool). SPIT can be used to load
QGIS comes with a core plugin named
multiple shapefiles at one time and includes support for schemas. See Section SPIT Plugin for more information.
shp2pgsql
PostGIS includes a utility called shp2pgsql that can be used to import shapefiles into a PostGIS enabled database.
For example, to import a shapefile named lakes.shp into a PostgreSQL database named gis_data, use the
following command:
shp2pgsql -s 2964 lakes.shp lakes_new | psql gis_data
This creates a new layer named lakes_new in the gis_data database. The new layer will have a spatial reference identifier (SRID) of 2964. See Section Working with Projections for more information on spatial reference
systems and projections.
Tip: Exporting datasets from PostGIS
Like the import-tool shp2pgsql there is also a tool to export PostGIS-datasets as shapefiles: pgsql2shp. This is
shipped within your PostGIS distribution.
ogr2ogr
Beside shp2pgsql and SPIT there is another tool for feeding geodata in PostGIS: ogr2ogr. This is part of your
GDAL installation.
To import a shapefile into PostGIS, do the following:
ogr2ogr -f "PostgreSQL" PG:"dbname=postgis host=myhost.de user=postgres \
password=topsecret" alaska.shp
This will import the shapefile alaska.shp into the PostGIS-database postgis using the user postgres with the
password topsecret on host server myhost.de.
Note that OGR must be built with PostgreSQL to support PostGIS. You can see this by typing
ogrinfo --formats | grep -i post
If you like to use PostgreSQL’s COPY -command instead of the default INSERT INTO method you can export
the following environment-variable (at least available on
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export PG_USE_COPY=YES
ogr2ogr does not create spatial indexes like shp2pgsl does. You need to create them manually using the normal SQL-command CREATE INDEX afterwards as an extra step (as described in the next section Improving
Performance).
Improving Performance
Retrieving features from a PostgreSQL database can be time consuming, especially over a network. You can
improve the drawing performance of PostgreSQL layers by ensuring that a PostGIS spatial index exists on
each layer in the database. PostGIS supports creation of a GiST (Generalized Search Tree) index to speed
up spatial searches of the data (GiST index information is taken from the PostGIS documentation available at
http://postgis.refractions.net).
The syntax for creating a GiST index is:
CREATE INDEX [indexname] ON [tablename]
USING GIST ( [geometryfield] GIST_GEOMETRY_OPS );
Note that for large tables, creating the index can take a long time. Once the index is created, you should perform a
VACUUM ANALYZE. See the PostGIS documentation (POSTGIS-PROJECT Literature and Web References) for
more information.
The following is an example of creating a GiST index:
gsherman@madison:~/current$ psql gis_data
Welcome to psql 8.3.0, the PostgreSQL interactive terminal.
Type:
\copyright for distribution terms
\h for help with SQL commands
\? for help with psql commands
\g or terminate with semicolon to execute query
\q to quit
gis_data=# CREATE INDEX sidx_alaska_lakes ON alaska_lakes
gis_data-# USING GIST (the_geom GIST_GEOMETRY_OPS);
CREATE INDEX
gis_data=# VACUUM ANALYZE alaska_lakes;
VACUUM
gis_data=# \q
gsherman@madison:~/current$
11.1.6 Vector layers crossing 180° longitude
Many GIS packages don’t wrap vector maps, with a geographic reference system (lat/lon), crossing the 180 degrees longitude line (http://postgis.refractions.net/documentation/manual-1.4/ST_Shift_Longitude.html). As result, if we open such map in QGIS, we will see two far, distinct locations, that should show near each other. In
Figure_vector_4 the tiny point on the far left of the map canvas (Chatham Islands), should be within the grid, right
of New Zealand main islands.
Figure 11.4: Map in lat/lon crossing the 180° longitude line
A workaround is to transform the longitude values using PostGIS and the ST_Shift_Longitude function This
function reads every point/vertex in every component of every feature in a geometry, and if the longitude coordi11.1. Supported Data Formats
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nate is < 0° adds 360° to it. The result would be a 0° - 360° version of the data to be plotted in a 180° centric map.
Figure 11.5: Crossing 180° longitude applying the ST_Shift_Longitude function
Usage
• Import data to PostGIS (Importing Data into PostgreSQL) using for example the PostGIS Manager plugin
or the SPIT plugin
• Use the PostGIS command line interface to issue the following command (this is an example where “TABLE” is the actual name of your PostGIS table)
gis_data=# update TABLE set the_geom=ST_Shift_Longitude(the_geom);
• If everything went right you should receive a confirmation about the number of features that were updated,
then you’ll be able to load the map and see the difference (Figure_vector_5)
11.1.7 SpatiaLite Layers
The first time you load data from a SpatiaLite database, begin by clicking on the
Add SpatiaLite Layer
toolbar
button or by selecting the
Add SpatiaLite Layer... option from the Layer menu or by typing Ctrl+Shift+L.
This will bring up a window, which will allow you to either connect to a SpatiaLite database already known to
QGIS, which you can choose from the dropdown menu or to define a new connection to a new database. To define
a new connection, click on [New] and use the file browser to point to your SpatiaLite database, which is a file with
a .sqlite extension.
If you want to save a vector layer to SpatiaLite format you can do this by right clicking the layer in the legend.
Then click on Save as.., define the name of the output file, select ‘SpatiaLite’ as format and the CRS. Also you can
select ‘SQLite’ as format, and then add SPATIALITE=YES in the OGR data source creation option field. This
tells OGR to create a SpatiaLite database. See also http://www.gdal.org/ogr/drv_sqlite.html.
QGIS also supports editable views in SpatiaLite.
Creating a new SpatiaLite layer
If you want to create a new SpatiaLite layer, please refer to section Creating a new SpatiaLite layer.
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Tip: SpatiaLite data management Plugins
For SpatiaLite data management you can also use several Python plugins: QSpatiaLite, SpatiaLite Manager or DB
Manager (core plugin, recommended). They can be downloaded and installed with the Plugin Installer.
11.1.8 MSSQL Spatial Layers
Add MSSQL Spatial Layer
QGIS also provides native MS SQL 2008 support. The
is part of the new toolbar
button or available in the MS SQL node in the QBrowser tree, providing drag and drop import support.
11.2 The Vector Properties Dialog
The Layer Properties dialog for a vector layer provides information about the layer, symbology settings and
labeling options. If your vector layer has been loaded from a PostgreSQL/PostGIS datastore, you can also alter
the underlying SQL for the layer by invoking the Query Builder dialog on the General tab. To access the Layer
Properties dialog, double-click on a layer in the legend or right-click on the layer and select Properties from the
popup menu.
Figure 11.6: Vector Layer Properties Dialog
11.2.1 Style Tab
Since QGIS 1.4.0 a new symbology was integrated in parallel to improve and finally replace the old symbology. QGIS 1.8 now uses the new symbology as default, which provides a variety of improvements and new
features.
A description of the old symbology is available in section Old Symbology.
There are three types of symbols: marker symbols (for points), line symbols (for lines) and fill and outline symbols
(for polygons). Symbols can consist of one or more symbol layers. It is possible to define the color of a symbol
and this color is then defined for all symbol layers. Some layers may have the color locked - for those the color
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can not be altered. This is useful when you define the color of a multilayer symbol. Similarly, it is possible to
define the width for line symbols, as well as size and rotation for marker symbols.
Available symbol layer types
• Point layers
– Font marker: Rendering with a font.
– Simple marker: Rendering with a hardcoded marker.
– SVG marker: Rendering with a SVG picture.
– Ellipse marker: Rendering with ellipse shapes derived from attributes.
– Vector field marker: Rendering with vector fields derived from attributes.
• Line layers
– Line decoration: Add a line decoration, e.g an arrow to indicate line direction.
– Marker line: A line rendered by repeating a marker symbol.
– Simple line: Usual rendering of a line (with specified width color and pen style).
• Polygon layers
– Centroid fill: Fill a polygon centroid with a hardcoded marker.
– SVG fill: Fill a polygon with a SVG symbol.
– Simple fill: Usual rendering of a polygon (with defined fill color, fill pattern and outline).
– Line pattern fill: Fill a polygon with a line pattern.
– Point pattern fill: Fill a polygon with a point pattern.
– Outline: Line decoration: Add a line decoration, e.g an arrow to indicate line direction.
– Outline: Marker line: Use a hardcoded marker as area outline.
– Outline: Simple line: Define width, color and pen style as area outline.
Color ramps
Color ramps are used to define a range of colors that can be used during the creation of renderers. The symbol’s
color will be set from the color ramp.
There are three types of color ramps:
• Gradient: Linear gradient from one color to some other.
• Random: Randomly generated colors from a specified area of color space.
• ColorBrewer: Create color area from a color shema and a defined number of color classes.
Color ramps can be defined in the Color ramp tab of the Style Manager by clicking the [Add] button and then
choosing a color ramp type (see section vector_style_manager ).
Styles
A style groups a set of various symbols and color ramps. You can define your prefered or frequently used symbols,
and can use it without having to recreate it everytime. Style items (symbols and color ramps) have always a name
by which they can be queried from the style. There is at least one default style in QGIS (modifiable) and the user
can add further styles. In the lower part of the Style tab there are four buttons for managing styles: Use [Restore
Default Style] to get back to your default settings, [Save As Default] to save your style as default, [Load Style...]
to get to your own styles and [Save Style] to save your own styles. Layer styles can also be transferred from one
layer to another layer. Activate a layer and choose Layer →
choose Layer →
Copy style and switch to another layer. Then
Paste style.
Renderers
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The renderer is responsible for drawing a feature together with the correct symbol. There are four types of
renderers: single symbol, categorized (called unique color in the old symbology), graduated and rule-based. There
is no continuous color renderer, because it is in fact only a special case of the graduated renderer. The categorized
and graduated renderer can be created by specifying a symbol and a color ramp - they will set the colors for
symbols appropriately. Working with the New Generation Symbology
In the Style tab you can choose one of the five renderers: single symbol, categorized, graduated, rule-based and
point displacement. For each data type (points, lines and polygons) vector symbol layer types are available (see
vector_symbol_types). Depending on the chosen renderer, the symbology Depending on the chosen renderer,
the Style tab provides different following sections. The new generation symbology dialog also provides a [Style
Manager] button which gives access to the Style Manager (see Section Style Manager). The Style Manager
allows you to edit and remove existing symbols and add new ones.
Tip: Select and change multiple symbols
The New Generation Symbology allows to select multiple symbols and right click to change color, transparency,
size, or width of selected entries.
Single Symbol Renderer
The Single Symbol Renderer is used to render all features of the layer using a single user-defined symbol. The
properties, that can be adjusted in the Style tab, depend partially on the type of the layer, but all types share
the following structure. In the top left part of the tab, there is a preview of the current symbol to be rendered. In
the bottom part of the tab, there is a list of symbols already defined for the current style, prepared to be used via
selecting them from the list. The current symbol can be modified using the [Change] button below the preview,
which opens a Symbol Properties dialog, or the [Change] button right of the preview, which opens an ordinary
Color dialog.
Figure 11.7: Single symbol line properties
In the Style tab you can apart from a general layer transparency also define to use millimeter or map units for the
size scale. In the [Advanced] button next to the [Save as style] button you can use data-defined size scale and
rotation. Here the Symbol levels → menu allows to enable and define the order in which the symbol layers are
rendered (if the symbol consists of more than one layer).
After having done any needed changes, the symbol can be added to the list of current style symbols (using the
[Save as style] button) and then easily be used in the future. Furthermore you can use the [Save Style] button to
save the symbol as a QGIS layer style file (.qml) or SLD file(.sld). Currently in version 1.8 SLDs can be exported
from any type of renderer: single symbol, categorized, graduated or rule-based, but when importing an SLD, either
a single symbol or rule-based renderer is created. That means that categorized or graduated styles are converted
to rule-based. If you want to preserve those renderers, you have to stick to the QML format. On the other hand, it
could be very handy sometimes to have this easy way of converting styles to rule-based.
Categorized Renderer
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The Categorized Renderer is used to render all features from a layer, using a single user-defined symbol, which
color reflects the value of a selected feature’s attribute. The Style tab allows you to select:
• The attribute (using the Column listbox)
• The symbol (using the Symbol dialog)
• The colors (using the Color Ramp listbox)
The [Advanced] button in the lower right corner of the dialog allows to set the fields containing rotation and size
scale information. For convenience, the list in the bottom part of the tab lists the values of all currently selected
attributes together, including the symbols that will be rendered.
The example in figure_symbology_2 shows the category rendering dialog used for the rivers layer of the QGIS
sample dataset.
Figure 11.8: Categorized Symbolizing options
You can create a custom color ramp choosing New color ramp... from the Color ramp dropdown menu. A dialog
will prompt for the ramp type: Gradient, Random, ColorBrewer, then each one has options for number of steps
and/or multiple stops in the color ramp. See figure_symbology_3 for an example of custom color ramp.
Figure 11.9: Example of custom gradient color ramp with multiple stops
Graduated Renderer
The Graduated Renderer is used to render all the features from a layer, using a single user-defined symbol, whose
color reflects the classification of a selected feature’s attribute to a class.
Like Categorized Renderer, it allows to define rotation and size scale from specified columns.
Analogue to the categorized rendered, the Style tab allows you to select:
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Figure 11.10: Graduated Symbolizing options
• The attribute (using the Column listbox)
• The symbol (using the Symbol Properties button)
• The colors (using the Color Ramp list)
Additionally, you can specify the number of classes and also the mode how to classify features inside the classes
(using the Mode list). The available modes are:
• Equal Interval
• Quantile
• Natural Breaks (Jenks)
• Standard Deviation
• Pretty Breaks
The listbox in the bottom part of the Style tab lists the classes together with their ranges, labels and symbols that
will be rendered.
The example in figure_symbology_4 shows the graduated rendering dialog for the rivers layer of the QGIS sample
dataset.
Rule-based rendering
The rule-based renderer is used to render all the features from a layer, using rule based symbols, whose color
reflects the classification of a selected feature’s attribute to a class. The rules are based on SQL statements. The
dialog allows rule grouping by filter or scale and you can decide if you want to enable symbol levels or use only
first matched rule.
The example in figure_symbology_5 shows the rule-based rendering dialog for the rivers layer of the QGIS sample
dataset.
To create a rule, activate an existing row by clicking on it or click on ‘+’ and click on the new rule. Then press the
[Edit] button. In the Rule properties dialog you can define a label for the rule. Press the
button to open the
Expression builder. In the Function List, click on Fields and Values to view all attributes of the attribute table to
be searched. To add an attribute to the Field calculator Expression field, double click its name in the Fields and
Values list. Generally you can use the various fields, values and functions to construct the calculation expression
or you can just type it into the box (see Field Calculator).
Point displacement
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Figure 11.11: Rule-based Symbolizing options
The point displacement renderer offers to visualize all features of a point layer, even if they have the same location.
To do this, the symbols of the points are placed on a displacement circle around a center symbol.
Figure 11.12: Point displacement dialog
Symbol Properties
The symbol properties dialog allows the user to specify different properties of the symbol to be rendered. In the
bottom left part of the dialog, you find a preview of the current symbol as it will be displayed in the map canvas.
Above the preview is the list of symbol layers. To start the Symbol properties dialog, click the [
Change...]
button in the Style tab of the Layer Properties dialog.
The buttons allow adding or removing layers, changing the position of layers, or locking layers for color changes.
In the right part of the dialog, there are shown the settings applicable to the single symbol layer selected in the
symbol layer list. The most important is the Symbol Layer Type
combobox, which allows you to choose
the layer type. The available options depend on the layer type (Point, Line, Polygon). The symbol layer type
options are described in section vector_symbol_types. You can also change the symbol layer properties in the
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right part of the dialog. For example if you have chosen an SVG marker for a point layer it is now possible to
change its color using Color button.
Figure 11.13: Line composed from three simple lines
11.2.2 Style Manager
The Style Manager is a small helper application, that lists symbols and color ramps available in a style. It also
allows you to add and/or remove items. To launch the Style Manager, click on Settings → Style Manager in the
main menu. Alternatively, you can access it via the Style tab.
Figure 11.14: Style Manager to manage symbols and color ramps
11.2.3 Old Symbology
Note: QGIS 1.8. still supports the usage of the old symbology, although it is recommended to switch to the new
symbology, described in section vector_new_symbology, because the old symbology will be removed in one of
the next releases.
If you want or need to switch back to the old symbology you can click on the [Old symbology] button in the Style
tab of the Layer Properties dialog.
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You can also make the old symobolgy the default, deactivating
in the Rendering tab under Settings →
Options.
Use new generation symbology for rendering
The old QGIS symbology supports the following renderers:
• Single symbol - a single style is applied to every object in the layer.
• Graduated symbol - objects within the layer are displayed with different symbols classified by the values
of a particular field.
• Continuous color - objects within the layer are displayed with a spread of colours classified by the numerical values within a specified field.
• Unique value - objects are classified by the unique values within a specified field with each value having a
different symbol.
To change the symbology for a layer, simply double click on its legend entry and the vector Layer Properties
dialog will be shown.
Style Options
Within this dialog you can style your vector layer. Depending on the selected rendering option you have the
possibility to also classify your map features.
At least the following styling options apply for nearly all renderers:
• Fill style - Style for filling. Beside the given brushes you can select Fill style:
‘Texture’ and click
the
button for selecting your own texture file. Currently the fileformats *.jpeg, *.xpm, and *.png
are supported.
• Fill color - fill-color of your features.
• Outline options
– Outline style - Pen-style for your outline of your feature. You can also set this to ‘no Pen’.
– Outline color - color of the ouline of your feature.
– Outline width - width of your features.
Once you have styled your layer you also could save your layer-style to a separate file (ending with *.qml). To
do this, use the button [Save Style...]. No need to say that [Load Style...] loads your saved layer-style-file.
If you wish to always use a particular style whenever the layer is loaded, use the [Save As Default] button to
make your style the default. Also, if you make changes to the style that you are not happy with, use the [Restore
Default Style] button to revert to your default style.
Vector transparency
QGIS allows to set a transparency for every vector layer. This can be done with the slider Transparency
inside the Style tab. This is very useful for overlaying several vector layers.
11.2.4 Labels Tab
As for the symbology QGIS 1.8 currently provides an old and a new labeling engine in parallel. The Labels
tab still contains the old labeling. The new labeling is implemented as a core application and will replace the
features of the old labels tab in one of the next versions.
We recommend to switch to the new labeling, described in section New Labeling.
The old labeling in the Labels tab allows you to enable labeling features and control a number of options related
to fonts, placement, style, alignment and buffering. We will illustrate this by labeling the lakes shapefile of the
QGIS sample dataset:
1. Load the Shapefile alaska.shp and GML file lakes.gml in QGIS
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2. Zoom in a bit to your favorite area with some lake
3. Make the lakes layer active
4. Open the Layer Properties dialog
5. Click on the Labels tab
6. Check the
Display labels checkbox to enable labeling
7. Choose the field to label with. We will use Field containing label
NAMES
8. Enter a default for lakes that have no name. The default label will be used each time QGIS encounters a
lake with no value in the NAMES field.
9. If you have labels extending over several lines, check
Multiline labels?. QGIS will check for a true line
return in your label field and insert the line breaks accordingly. A true line return is a single character \n,
(not two separate characters, like a backlash \ followed by the character n). To insert line returns in an
attribute field configure the edit widget to be text edit (not line edit).
10. Click [Apply].
Now we have labels. How do they look? They are probably too big and poorly placed in relation to the marker
symbol for the lakes.
Select the Font entry and use the [Font] and [Color] buttons to set the font and color. You can also change the
angle and the placement of the text-label.
To change the position of the text relative to the feature:
1. Beneath the Basic label options change the placement by selecting one of the radio buttons in the Placement
Right radio button.
group. To fix our labels, choose the
2. the Font size units allows you to select between
Points or
Map units.
3. Click [Apply] to see your changes without closing the dialog.
Things are looking better, but the labels are still too close to the marker. To fix this we can use the options on the
Offset entry which is on the bottom of the menu. Here we can add offsets for the X and Y directions. Adding an
X offset of 5 will move our labels off the marker and make them more readable. Of course if your marker symbol
or font is larger, more of an offset will be required.
The last adjustment we’ll make is to Buffer the labels. This just means putting a backdrop around them to make
them stand out better. To buffer the lakes labels:
1. Click the
Buffer Labels checkbox to enable buffering.
2. Choose a size for the buffer using the spin box.
3. Choose a color by clicking on [Color] and choosing your favorite from the color selector. You can also set
some transparency for the buffer if you prefer.
4. Click [Apply] to see if you like the changes.
If you aren’t happy with the results, tweak the settings and then test again by clicking [Apply].
A buffer of 1 points seems to give a good result. Notice you can also specify the buffer size in map units if that
works out better for you.
The advanced entries inside the Label tab allow you control the appearance of the labels using attributes stored
in the layer. The entries beginning with Data defined allow you to set all the parameters for the labels using
fields in the layer.
Note that the Label tab provides a preview-box where your selected label is shown.
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11.2.5 New Labeling
Labeling
core application provides smart labeling for vector point, line and polygon layers and only
The new
requires a few parameters. This new application will replace the current QGIS labeling, described in section
Labels Tab and also supports on-the-fly transformated layers.
Using new labeling
1. Start QGIS and load a vector point, line or polygon layer.
2. Activate the layer in the legend and click on the
Labeling
icon in the QGIS toolbar menu.
Labeling point layers
First step is to activate the
Label this layer checkbox and select an attribute column to use for labeling. Click
if you want to define labels based on expressions. After that you can define the text style and the scale-based
visibility in the Label settings tab (see Figure_labels_1 ). Choose the Advanced tab for the label placement and the
labeling priority. You can define if every part of a multipart feature is to be labeled here. With the wrap label on
character function you can define a character for a line break in the labels. The Data defined settings tab provides
you with the attribute-based definition of Font properties, Buffer properties and Position.
Figure 11.15: Smart labeling of vector point layers
Labeling line layers
First step is to activate the
Label this layer checkbox in the Label settings tab and select an attribute column to
use for labeling. Here you can also define labels based on expressions. After that you can define the text style and
the scale-based visibility. Further labeling options are available through the Advanced tab. You can define the label
placement and label distance, a line orientation dependend position and the labeling priority here. Furthermore
you can define if every part of a multipart line is to be labeled, if lines shall be merged to avoid duplicate labels
and if a direction symbol is added (see Figure_labels_2 ). It is also possible to supress labeling of features and
wrap lables on characters. Use Data defined settings for attribute-based or database-connection-based settings.
Labeling polygon layers
First step is to activate the
Label this layer checkbox and select an attribute column to use for labeling. Here
you can also define labels based on expressions. In Label settings define the text style and the scale-based visibility
(see Figure_labels_3 ). Use the Advanced tab for label placement, label distance and labeling priority. Define if
every part of a multipart feature is to be labeled, suppress labeling of features and wrap labels on characters here.
Use Data defined settings for attribute-based or database-connection-based settings.
Change engine settings
Additionally you can click the [Engine settings] button and select the search method, used to find the best label
placement. Available is Chain, Popmusic Tabu, Popmusic Chain, Popmusic Tabu Chain and FALP.
Furthermore the number of candidates can be defined for point, line and polygon features, and you can define
whether to show all labels (including colliding labels) and label candidates for debugging.
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Figure 11.16: Smart labeling of vector line layers
Figure 11.17: Smart labeling of vector polygon layers
Figure 11.18: Dialog to change label engine settings
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Keywords to use in attribute columns for labeling
There is a list of supported key words, that can be used for the placement of labels in defined attribute columns.
• For horizontal alignment: left, center, right
• For vertical alignment: bottom, base, half, top
• Colors can be specified in svg notation, e.g. #ff0000
• for bold, underlined, strikeout and italic: 0 = false 1 = true
A combination of key words in one column also works, e.g.: base right or bottom left.
11.2.6 Fields Tab
Within the Fields tab the field attributes of the selected dataset can be manipulated. The buttons
and
Delete Column
can be used, when the dataset is
Editing mode
New Column
.
At the moment only columns from PostGIS layers can be removed and added. The OGR library supports to add
and remove columns, if you have a GDAL version >= 1.9 installed.
Edit Widget
Figure 11.19: Dialog to select an edit widget for an attribute column
Within the Fields tab you also find an edit widget column. This column can be used to define values or a
range of values that are allowed to be added to the specific attribute table column. If you click on the [edit widget]
button, a dialog opens, where you can define different widgets. These widgets are:
• Line edit: an edit field which allows to enter simple text (or restrict to numbers for numeric attributes).
• Classification: Displays a combo box with the values used for classification, if you have chosen ‘unique
value’ as legend type in the Style tab of the properties dialog.
• Range: Allows to set numeric values from a specific range. The edit widget can be either a slider or a spin
box.
• Unique values: The user can select one of the values already used in the attribute table. If editable is
activated, a line edit is shown with autocompletion support, otherwise a combo box is used.
• File name: Simplifies the selection by adding a file chooser dialog.
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• Value map: a combo box with predefined items. The value is stored in the attribute, the description is
shown in the combo box. You can define values manually or load them from a layer or a CSV file.
• Enumeration: Opens a combo box with values that can be used within the columns type. This is currently
only supported by the postgres provider.
• Immutable: The immutable attribute column is read-only. The user is not able to modify the content.
• Hidden: A hidden attribute column is invisible. The user is not able to see its content.
• Checkbox: Displays a checkbox and you can define what attribute is added to the column when the checkbox is activated or not.
• Text edit: This opens a text edit field that allows multiple lines to be used.
• Calendar: Opens a calendar widget to enter a date. Column type must be text.
• Value Relation: Offers values from a related table in a combobox. You can select layer, key column and
value column.
• UUID Generator: Generates a read-only UUID (Universally Unique Identifiers) field, if empty.
11.2.7 General Tab
The General tab is essentially like that of the raster dialog. There are several options available:
• Change the display name of the layer
• Set a display field to be used for the Identify Results dialog
• Define a certain Edit User Interface for the vector layer written with the Qt Creator IDE and tools at
http://qt.digia.com/Product/Developer-Tools/
• Create a Spatial Index (only for OGR supported formats)
• Add an Init function for the layer. They will overwrite existing QGIS widget initializations, if applied
• Update Extents information for a layer
• View or change the projection of the specific vector layer, clicking on Specify CRS
Furthermore you can activate and set
Use scale dependent rendering, define provider specific options (e.g.
encoding) and with the [Query Builder] button you can create a subset of the features in the layer that will be
visualized (also refer to section Selection).
11.2.8 Metadata Tab
The Metadata tab contains general information about the layer, including specifics about the type and location, number of features, feature type, and the editing capabilities. The Extents section, providing layer extent
information, and the Layer Spatial Reference System section, providing information about the CRS of the layer.
This is a quick way to get information about the layer.
Additionally you can add/edit a title for the layer and some abtract information. These information will be saved
in the QGIS project file for following sessions and will be used for QGIS server.
11.2.9 Actions Tab
QGIS provides the ability to perform an action based on the attributes of a feature. This can be used to
perform any number of actions, for example, running a program with arguments built from the attributes of a
feature or passing parameters to a web reporting tool.
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Figure 11.20: General tab in vector layers properties dialog
Figure 11.21: Metadata tab in vector layers properties dialog
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Figure 11.22: Overview action dialog with some sample actions
Actions are useful when you frequently want to run an external application or view a web page based on one or
more values in your vector layer. They are devided into 6 types and can be used like this:
• Generic, Mac, Windows and Unix actions start an external process,
• Python actions execute a python expression,
• Generic and Python actions are visible everywhere,
• Mac, Windows and Unix actions are visible only on the respective platform (i.e. you can define three ‘Edit’
actions to open an editor and the users can only see and execute the one ‘Edit’ action for their platform to
run the editor).
There are several examples included in the dialog. You can load them clicking on [Add default actions]. An
example is performing a search based on an attribute value. This concept is used in the following discussion.
Defining Actions
Attribute actions are defined from the vector Layer Properties dialog. To define an action, open the vector Layer
Properties dialog and click on the Actions tab. Select ‘Generic’ as type and provide a descriptive name for the
action. The action itself must contain the name of the application that will be executed when the action is invoked.
You can add one or more attribute field values as arguments to the application. When the action is invoked any
set of characters that start with a % followed by the name of a field will be replaced by the value of that field.
The special characters %% will be replaced by the value of the field that was selected from the identify results or
attribute table (see using_actions below). Double quote marks can be used to group text into a single argument to
the program, script or command. Double quotes will be ignored if preceded by a backslash.
If you have field names that are substrings of other field names (e.g., col1 and col10) you should indicate so,
by surrounding the field name (and the % character) with square brackets (e.g., [%col10]). This will prevent the
%col10 field name being mistaken for the %col1 field name with a 0 on the end. The brackets will be removed
by QGIS when it substitutes in the value of the field. If you want the substituted field to be surrounded by square
brackets, use a second set like this: [[%col10]].
Using the Identify Features tool you can open Identify Results dialog. It includes a (Derived) item that contains
information relevant to the layer type. The values in this item can be accessed in a similar way to the other fields
by using preceeding the derived field name by (Derived).. For example, a point layer has an X and Y field and
the value of these can be used in the action with %(Derived).X and %(Derived).Y. The derived attributes
are only available from the Identify Results dialog box, not the Attribute Table dialog box.
Two example actions are shown below:
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• konqueror http://www.google.com/search?q=%nam
• konqueror http://www.google.com/search?q=%%
In the first example, the web browser konqueror is invoked and passed a URL to open. The URL performs a
Google search on the value of the nam field from our vector layer. Note that the application or script called by
the action must be in the path or you must provide the full path. To be sure, we could rewrite the first example as: /opt/kde3/bin/konqueror http://www.google.com/search?q=%nam. This will ensure
that the konqueror application will be executed when the action is invoked.
The second example uses the %% notation which does not rely on a particular field for its value. When the action
is invoked, the %% will be replaced by the value of the selected field in the identify results or attribute table.
Using Actions
Actions can be invoked from either the Identify Results dialog, an Attribute Table dialog or from Run FeaIdentify Features
Open Attribute Table
or
or
ture Action (recall that these dialogs can be opened by clicking
). To invoke an action, right click on the record and choose the action from the popup menu. Actions are listed in the popup menu by the name you assigned when defining the actions. Click on the action you
wish to invoke.
Run Feature Action
If you are invoking an action that uses the %% notation, right-click on the field value in the Identify Results dialog
or the Attribute Table dialog that you wish to pass to the application or script.
Here is another example that pulls data out of a vector layer and inserts them into a file using bash and the
or perhaps ). The layer in question has fields for a species name
echo command (so it will only work
taxon_name, latitude lat and longitude long. I would like to be able to make a spatial selection of a localities
and export these field values to a text file for the selected record (shown in yellow in the QGIS map area). Here is
the action to achieve this:
bash -c "echo \"%taxon_name %lat %long\" >> /tmp/species_localities.txt"
After selecting a few localities and running the action on each one, opening the output file will show something
like this:
Acacia
Acacia
Acacia
Acacia
mearnsii
mearnsii
mearnsii
mearnsii
-34.0800000000
-34.9000000000
-35.2200000000
-32.2700000000
150.0800000000
150.1200000000
149.9300000000
150.4100000000
As an exercise we create an action that does a Google search on the lakes layer. First we need to determine
the URL needed to perform a search on a keyword. This is easily done by just going to Google and doing a
simple search, then grabbing the URL from the address bar in your browser. From this little effort we see that the
format is: http://google.com/search?q=qgis, where QGIS is the search term. Armed with this information, we can
proceed:
1. Make sure the lakes layer is loaded.
2. Open the Layer Properties dialog by double-clicking on the layer in the legend or right-click and choose
Properties from the popup menu.
3. Click on the Actions tab.
4. Enter a name for the action, for example Google Search.
5. For the action, we need to provide the name of the external program to run. In this case, we can use Firefox.
If the program is not in your path, you need to provide the full path.
6. Following the name of the external application, add the URL used for doing a Google search, up to but not
included the search term: http://google.com/search?q=
7. The text in the Action field should now look like this: firefox http://google.com/search?q=
8. Click on the drop-down box containing the field names for the lakes layer. It’s located just to the left of
the [Insert Field] button.
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9. From the drop-down box The valid attribute names for this layer
Field].
select ‘NAMES’ and click [Insert
10. Your action text now looks like this: firefox http://google.com/search?q=%NAMES
11. To finalize the action click the [Insert action] button.
This completes the action and it is ready to use. The final text of the action should look like this:
firefox http://google.com/search?q=%NAMES
We can now use the action. Close the Layer Properties dialog and zoom in to an area of interest. Make sure the
lakes layer is active and identify a lake. In the result box you’ll now see that our action is visible:
Figure 11.23: Select feature and choose action
When we click on the action,
it brings up Firefox and navigates to the URL
http://www.google.com/search?q=Tustumena. It is also possible to add further attribute fields to the action. Therefore you can add a + to the end of the action text, select another field and click on [Insert Field]. In
this example there is just no other field available that would make sense to search for.
You can define multiple actions for a layer and each will show up in the Identify Results dialog.
You can think of all kinds of uses for actions. For example, if you have a point layer containing locations of
images or photos along with a file name, you could create an action to launch a viewer to display the image. You
could also use actions to launch web-based reports for an attribute field or combination of fields, specifying them
in the same way we did in our Google search example.
We can also make more complex examples, for instance on how to use Python actions.
Usually when we create an action to open a file with an external application we can use absolute paths, or eventually relative paths, in the second case the path is relative to the location of the external program executable file.
But what about we need to use relative paths, relative to the selected layer (a file based one, like a shapefile or
spatialite)? The following code will do the trick:
command = "firefox";
imagerelpath = "images_test/test_image.jpg";
layer = qgis.utils.iface.activeLayer();
import os.path;
layerpath = layer.source() if layer.providerType() == ’ogr’ else \
(qgis.core.QgsDataSourceURI(layer.source()).database() \
if layer.providerType() == ’spatialite’ else None);
path = os.path.dirname(str(layerpath));
image = os.path.join(path,imagerelpath);
import subprocess;
subprocess.Popen( [command, image ] );
we have to just remember that the action is one of type Python and to change the command and imagerelpath
variables to fit our needs.
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But what about if the relative path need to be relative to the (saved) project file? The code of the Python action
would be:
command="firefox";
imagerelpath="images/test_image.jpg";
projectpath=qgis.core.QgsProject.instance().fileName();
import os.path; path=os.path.dirname(str(projectpath)) \
if projectpath != ’’ else None;
image=os.path.join(path, imagerelpath);
import subprocess;
subprocess.Popen( [command, image ] );
Another Python actions example if the one that allows us to add new layers to the project. For instance the
following examples will add to the project respectively a vector and a raster. The name of files to be added to the
project and the name to be given to the layer are data driven (filename and layname are column names of the table
of attributes of the vector where the action was created):
qgis.utils.iface.addVectorLayer(’/yourpath/[% "filename" %].shp’,’[% "layername" %]’, ’ogr’)
To add a raster (a tif image in this example) it becomes:
qgis.utils.iface.addRasterLayer(’/yourpath/[% "filename" %].tif’,’[% "layername" %]’)
11.2.10 Joins Tab
The Joins tab allows you to join a loaded attribute table to a loaded vector layer. As key columns you have
to define a join layer, a join field and a target field. QGIS currently supports to join non spatial table formats
supported by OGR, delimited text and the PostgreSQL provider (see figure_joins_1).
Figure 11.24: Join an attribute table to an existing vector layer
Additionally the add vector join dialog allows to:
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•
Cache join layer in virtual memory
•
Create attribute index on the join field
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11.2.11 Diagrams Tab
The Diagrams tab allows you to add a graphic overlay to a vector layer (see figure_diagrams_1).
The current core implementation of diagrams provides support for piecharts and text diagrams. Text values of
different data columns are displayed one below the other with a circle or a box and dividers. Diagram size is based
on a fixed size or on linear scaling according to a classification attribute. The placement of the diagrams interacts
with the new labeling, so position conflicts between diagrams and labels are detected and solved. In addition to
chart positions can be fixed by the users hand.
Figure 11.25: Vector properties dialog with diagram tab
We will demonstrate an example and overlay the alaska boundary layer a text diagram showing some temperature
data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section Sample
Data).
Load Vector
1. First click on the
icon, browse to the QGIS sample dataset folder and load the two vector
shape layers alaska.shp and climate.shp.
2. Double click the climate layer in the map legend to open the Layer Properties dialog.
3. Click on the Diagrams tab, activate Display diagrams and from Diagram type
‘Text diagram’
combobox select
4. As Background color we choose a light blue and set a fixed size to 18 mm.
5. Placement could be set to AroundPoint.
6. In the diagram we want to display the values of the three columns T_F_JAN, T_F_JUL and T_F_MEAN.
First select T_F_JAN as Attributes and click the green [+] button, then T_F_JUL and finally T_F_MEAN.
7. Now click [Apply] to display the diagram in the QGIS main window.
8. You can now adapt the chart size, or change the attribute colors by double clicking on the color values in
the attribute field. Figure_diagrams_2 gives an impression.
9. Finally click [Ok].
Additionally in the Settings → Options dialog, there is a Overlay tab where it is possible to select the placement
algorithm of the diagrams. The central point method is a generic one, the others use algorithms of the PAL library.
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Figure 11.26: Diagram from temperature data overlayed on a map
They also consider diagram objects and labels in different layers. Also see section Diagram Overlay Plugin for
additional diagram features.
11.3 Editing
QGIS supports various capabilities for editing OGR, PostGIS and SpatiaLite vector layers.
Note: The procedure for editing GRASS layers is different - see Section Digitizing and editing a GRASS vector
layer for details.
Tip: Concurrent Edits
This version of QGIS does not track if somebody else is editing a feature at the same time as you. The last person
to save their edits wins.
11.3.1 Setting the Snapping Tolerance and Search Radius
Before we can edit vertices, we must set the snapping tolerance and search radius to a value that allows us an
optimal editing of the vector layer geometries.
Snapping tolerance
Snapping tolerance is the distance QGIS uses to search for the closest vertex and/or segment you are trying
to connect when you set a new vertex or move an existing vertex. If you aren’t within the snapping tolerance,
QGIS will leave the vertex where you release the mouse button, instead of snapping it to an existing vertex and/or
segment. The snapping tolerance setting affects all tools which work with tolerance.
1. A general, project wide snapping tolerance can be defined choosing Settings →
Options. On Mac: go
to QIS →
Preferences..., on Linux: Edit →
Options. In the Digitizing tab you can select between to
vertex, to segment or to vertex and segment as default snap mode. You can also define a default snapping
tolerance and a search radius for vertex edits. The tolerance an be set either in map units or in pixels.
The advantage of choosing pixels, is that the snapping tolerance doesn’t have to be changed after zoom
operations. In our small digitizing project (working with the Alaska dataset), we define the snapping units
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in feet. Your results may vary, but something on the order of 300ft should be fine at a scale of 1:10 000
should be a reasonable setting.
2. A layer based snapping tolerance can be defined by choosing Settings → (or File →) Snapping options... to
enable and adjust snapping mode and tolerance on a layer basis (see figure_edit_1 ).
Note that this layer based snapping overrides the global snapping option set in the Digitizing tab. So if you need
to edit one layer, and snap its vertices to another layer, then enable snapping only on the snap to layer, then
decrease the global snapping tolerance to a smaller value. Furthermore, snapping will never occur to a layer which
is not checked in the snapping options dialog, regardless of the global snapping tolerance. So be sure to mark the
checkbox for those layers that you need to snap to.
Figure 11.27: Edit snapping options on a layer basis
Search radius
Search radius is the distance QGIS uses to search for the closest vertex you are trying to move when you click
on the map. If you aren’t within the search radius, QGIS won’t find and select any vertex for editing and it will
pop up an annoying warning to that effect. Snap tolerance and search radius are set in map units or pixels, so you
may find you need to experiment to get them set right. If you specify too big of a tolerance, QGIS may snap to the
wrong vertex, especially if you are dealing with a large number of vertices in close proximity. Set search radius
too small and it won’t find anything to move.
The search radius for vertex edits in layer units can be defined in the Digitizing tab under Settings →
The same place where you define the general, project wide snapping tolerance.
Options.
11.3.2 Zooming and Panning
Before editing a layer, you should zoom in to your area of interest. This avoids waiting while all the vertex markers
are rendered across the entire layer.
pan
zoom-in
zoom-out
Apart from using the
and
/
icons on the toolbar with the mouse, navigating can also
be done with the mouse wheel, spacebar and the arrow keys.
Zooming and panning with the mouse wheel
While digitizing you can press the mouse wheel to pan inside of the main window and you can roll the mouse
wheel to zoom in and out on the map. For zooming place the mouse cursor inside the map area and roll it forward
(away from you) to zoom in and backwards (towards you) to zoom out. The mouse cursor position will be the
center of the zoomed area of interest. You can customize the behavior of the mouse wheel zoom using the Map
tools tab under the Settings → Options menu.
Panning with the arrow keys
Panning the map during digitizing is possible with the arrow keys. Place the mouse cursor inside the map area and
click on the right arrow key to pan east, left arrow key to pan west, up arrow key to pan north and down arrow key
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to pan south.
You can also use the spacebar to temporarily cause mouse movements to pan then map. The PgUp and PgDown
keys on your keyboard will cause the map display to zoom in or out without interrupting your digitizing session.
11.3.3 Topological editing
Besides layer based snapping options you can also define some topological functionalities in the Snapping options... dialog in the Settings (or File) menu. Here you can define
polygon layers you can activate the column
Enable topological editing and/or for
Avoid Int. which avoids intersection of new polygons.
Enable topological editing
The option
Enable topological editing is for editing and maintaining common boundaries in polygon mosaics.
QGIS ‘detects’ a shared boundary in a polygon mosaic and you only have to move the vertex once and QGIS will
take care about updating the other boundary.
Avoid intersections of new polygons
Avoid Int. column, called Avoid intersections of new polygons avoids
The second topological option in the
overlaps in polygon mosaics. It is for quicker digitizing of adjacent polygons. If you already have one polygon,
it is possible with this option to digitise the second one such that both intersect and QGIS then cuts the second
polygon to the common boundary. The advantage is that users don’t have to digitize all vertices of the common
boundary.
11.3.4 Digitizing an existing layer
By default, QGIS loads layers read-only: This is a safeguard to avoid accidentally editing a layer if there is a
slip of the mouse. However, you can choose to edit any layer as long as the data provider supports it, and the
underlying data source is writable (i.e. its files are not read-only). Layer editing is most versatile when used on
PostgreSQL/PostGIS data sources.
In general, editing vector layers is divided into a digitizing and an advanced digitizing toolbar, described in Section Advanced digitizing.
You can select and unselect both under Settings
→ Toolbars →.
Using the basic digitizing tools you can perform the following functions:
Icon
Purpose
Icon
Purpose
Toggle editing
Adding Features: Capture Point
Adding Features: Capture Line
Adding Features: Capture Polygon
Move Feature
Node Tool
Delete Selected
Cut Features
Copy Features
Paste Features
Save edits and continue
Table Editing: Vector layer basic editing toolbar
All editing sessions start by choosing the
clicking on the legend entry for that layer.
Toggle editing
option. This can be found in the context menu after right
Toggle editing
Alternately, you can use the Toggle Editing
button from the digitizing toolbar to start or stop the
editing mode. Once the layer is in edit mode, markers will appear at the vertices, and additional tool buttons on
the editing toolbar will become available.
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Tip: Save Regularly
Save Edits
Remember to
regularly. This will also check that your data source can accept all the changes.
Adding Features
You can use the
digitizing mode.
Add Feature
,
Add Feature
or
Add Feature
icons on the toolbar to put the QGIS cursor into
For each feature, you first digitize the geometry, then enter its attributes. To digitize the geometry, left-click on
the map area to create the first point of your new feature.
For lines and polygons, keep on left-clicking for each additional point you wish to capture. When you have
finished adding points, right-click anywhere on the map area to confirm you have finished entering the geometry
of that feature.
The attribute window will appear, allowing you to enter the information for the new feature. Figure_edit_2 shows
setting attributes for a fictitious new river in Alaska. In the Digitizing tab under the Settings → Options menu,
you can also activate
attribute values.
Suppress attributes pop-up windows after each created feature
Reuse last entered
Figure 11.28: Enter Attribute Values Dialog after digitizing a new vector feature
With the
Move Feature(s)
icon on the toolbar you can move existing features.
Tip: Attribute Value Types
For editing the attribute types are validated during the entry. Because of this, it is not possible to enter a number
into the text-column in the dialog Enter Attribute Values or vice versa. If you need to do so, you should edit the
attributes in a second step within the Attribute table dialog.
Node Tool
Node Tool
For both PostgreSQL/PostGIS and shapefile-based layers, the
provides manipulation capabilites of
feature vertices similar to CAD programs. It is possible to simply select multiple vertices at once and to move,
add or delete them alltogether. The node tool also works with ‘on the fly’ projection turned on and supports the
topological editing feature. This tool is, unlike other tools in Quantum GIS, persistent, so when some operation is
done, selection stays active for this feature and tool. If the node tool couldn’t find any features, a warning will be
displayed.
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Important is to set the property Settings →
Options → Digitizing → Search Radius:
greater than zero (i.e. 10). Otherwise QGIS will not be able to tell which vertex is being edited.
to a number
Tip: Vertex Markers
The current version of QGIS supports three kinds of vertex-markers: Semi transparent circle, Cross and None. To
change the marker style, choose
Options from the Settings menu and click on the Digitizing tab and select the
appropriate entry.
Basic operations
Start by activating the
of this feature.
Node Tool
and selecting a feature by clicking on it. Red boxes will appear at each vertex
• Selecting vertices: You can select vertices by clicking on them one at a time, by clicking on an edge to
select the vertices at both ends, or by clicking and dragging a rectangle around some vertices. When a
vertex is selected its color changes to blue. To add more vertices to the current selection, hold down the
Ctrl key while clicking. Hold down Ctrl or Shift when clicking to toggle the selection state of vertices
(vertices that are currently unselected will be selected as usual, but also vertices that are already selected
will become unselected).
• Adding vertices: To add a vertex simply double click near an edge and a new vertex will appear on the
edge near to the cursor. Note that the vertex will appear on the edge, not at the cursor position, therefore it
has to be moved if necessary.
• Deleting vertices: After selecting vertices for deletion, click the Delete key. Note that you cannot use the
Node Tool
to delete a complete feature; QGIS will ensure it retains the minimum number of vertices for
the feature type you are working on. To delete a complete feature use the
Delete Selected
tool.
• Moving vertices: Select all the vertices you want to move. Click on a selected vertex or edge and drag in
the direction you wish to move. All the selected vertices will move together. If snapping is enabled, the
whole selection can jump to the nearest vertex or line.
Each change made with the node tool is stored as a separate entry in the undo dialog. Remember that all operations
support topological editing when this is turned on. On the fly projection is also supported, and the node tool
provides tooltips to identify a vertex by hovering the pointer over it.
Cutting, Copying and Pasting Features
Selected features can be cut, copied and pasted between layers in the same QGIS project, as long as destination
layers are set to
Toggle editing
beforehand.
Features can also be pasted to external applications as text: That is, the features are represented in CSV format
with the geometry data appearing in the OGC Well-Known Text (WKT) format.
However in this version of QGIS, text features from outside QGIS cannot be pasted to a layer within QGIS. When
would the copy and paste function come in handy? Well, it turns out that you can edit more than one layer at a
time and copy/paste features between layers. Why would we want to do this? Say we need to do some work on a
new layer but only need one or two lakes, not the 5,000 on our big_lakes layer. We can create a new layer and
use copy/paste to plop the needed lakes into it.
As an example we are copying some lakes to a new layer:
1. Load the layer you want to copy from (source layer)
2. Load or create the layer you want to copy to (target layer)
3. Start editing for target layer
4. Make the source layer active by clicking on it in the legend
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Select Single Feature
5. Use the
Copy Features
6. Click on the
tool to select the feature(s) on the source layer
tool
7. Make the destination layer active by clicking on it in the legend
Paste Features
8. Click on the
tool
9. Stop editing and save the changes
What happens if the source and target layers have different schemas (field names and types are not the same)?
QGIS populates what matches and ignores the rest. If you don’t care about the attributes being copied to the target
layer, it doesn’t matter how you design the fields and data types. If you want to make sure everything - feature and
its attributes - gets copied, make sure the schemas match.
Tip: Congruency of Pasted Features
If your source and destination layers use the same projection, then the pasted features will have geometry identical
to the source layer. However if the destination layer is a different projection then QGIS cannot guarantee the geometry is identical. This is simply because there are small rounding-off errors involved when converting between
projections.
Deleting Selected Features
If we want to delete an entire polygon, we can do that by first selecting the polygon using the regular
Select Single Feature
tool. You can select multiple features for deletion. Once you have the selection set, use the
Delete Selected
The
tool to delete the features.
Cut Features
tool on the digitizing toolbar can also be used to delete features. This effectively deletes the
feature but also places it on a “spatial clipboard”. So we cut the feature to delete. We could then use the
Paste Features
tool to put it back, giving us a one-level undo capability. Cut, copy, and paste work on the currently
selected features, meaning we can operate on more than one at a time.
Tip: Feature Deletion Support
When editing ESRI shapefiles, the deletion of features only works if QGIS is linked to a GDAL version 1.3.2 or
greater. The OS X and Windows versions of QGIS available from the download site are built using GDAL 1.3.2
or higher.
Saving Edited Layers
When a layer is in editing mode, any changes remain in the memory of QGIS. Therefore they are not committed/saved immediately to the data source or disk. If you want to save edits to the current layer but want to continue
editing without leaving the editing mode, you can click the
Save Edits
button. When you turn editing mode off
Toggle editing
(or quit QGIS for that matter), you are also asked if you want to save your changes or
with the
discard them.
If the changes cannot be saved (e.g. disk full, or the attributes have values that are out of range), the QGIS
in-memory state is preserved. This allows you to adjust your edits and try again.
Tip: Data Integrity
It is always a good idea to back up your data source before you start editing. While the authors of QGIS have
made every effort to preserve the integrity of your data, we offer no warranty in this regard.
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11.3.5 Advanced digitizing
Icon
Purpose
Icon
Purpose
Undo
Redo
Simplify Feature
Add Ring
Add Part
Delete Ring
Delete Part
Reshape Features
Offset Curve
Split Features
Merge Selected Features
Rotate Point Symbols
Merge Attributes of Selected Features
Table Advanced Editing: Vector layer advanced editing toolbar
Undo and Redo
Undo
Redo
and
tools allow the user to undo or redo vector editing operations. There is also a dockable
The
widget, which shows all operations in the undo/redo history (see Figure_edit_3). This widget is not displayed by
default; it can be displayed by right clicking on the toolbar and activating the Undo/Redo check box. Undo/Redo
is however active, even if the widget is not displayed.
Figure 11.29: Redo and Undo digitizing steps
When Undo is hit, the state of all features and attributes are reverted to the state before the reverted operation
happened. Changes other than normal vector editing operations (for example changes done by a plugin), may or
may not be reverted, depending on how the changes were performed.
To use the undo/redo history widget simply click to select an operation in the history list; all features will be
reverted to the state they were in after the selected operation.
Simplify Feature
Simplify Feature
The
tool allows to reduce the number of vertices of a feature, as long as the geometry doesn’t
change. You need to select a feature, it will be highlighted by a red rubber band and a slider appears. Moving the
slider, the red rubber band is changing its shape to show how the feature is being simplified. Clicking [OK] the
new, simplified geometry will be stored. If a feature cannot be simplified (e.g. MultiPolygons), a message shows
up.
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Add Ring
Add Ring
icon in the toolbar. This means inside an existing area it is
You can create ring polygons using the
possible to digitize further polygons, that will occur as a ‘hole’, so only the area in between the boundaries of the
outer and inner polygons remain as a ring polygon.
Add Part
add part
polygons to a selected multipolygon. The new part polygon has to be digitized outside the
You can
selected multipolygon.
Delete Ring
Delete Ring
The
tool allows to delete ring polygons inside an existing area. This tool only works with polygon
layers. It doesn’t change anything when it is used on the outer ring of the polygon. This tool can be used on
polygon and multi-polygon features. Before you select the vertices of a ring, adjust the vertex edit tolerance.
Delete Part
Delete Part
tool allows to delete parts from multifeatures (e.g. to delete polygons from a multipolygon
The
feature). It won’t delete the last part of the feature, this last part will stay untouched. This tool works with all
multi-part geometries point, line and polygon. Before you select the vertices of a part, adjust the vertex edit
tolerance.
Reshape Features
Reshape Features
You can reshape line and polygon features using the
icon on the toolbar. It replaces the line or
polygon part from the first to the last intersection with the original line. With polygons this can sometimes lead to
unintended results. It is mainly useful to replace smaller parts of a polygon, not major overhauls and the reshape
line is not allowed to cross several polygon rings as this would generate an invalid polygon.
For example, you can edit the boundary of a polygon with this tool. First, click in the inner area of the polygon
next to the point where you want to add a new vertex. Then, cross the boundary and add the vertices outside the
polygon. To finish, right-click in the inner area of the polygon. The tool will automatically add a node where the
new line crosses the border. It is also possible to remove part of the area from the polygon, starting the new line
outside the polygon, adding vertices inside, and ending the line outside the polygon with a right click.
Note: The reshape tool may alter the starting position of a polygon ring or a closed line. So the point that is
represented ‘twice’ will not be the same any more. This may not be a problem for most applications, but it is
something to consider.
Offset Curves
Offset Curve
The
tool is a new editing tool. It creates parallel shifts of lines and polygon rings. The tool can
be applied to the edited layer (the geometries are modified) or also to background layers (creates copies of the
lines / rings and adds it to the the edited layer). It is thus ideally suited for the creation of distance line layers.The
displacement is shown at the bottom left of the taskbar.
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Split Features
You can split features using the
split.
Split Features
icon on the toolbar. Just draw a line across the feature you want to
Merge selected features
The
Merge Selected Features
tool allows to merge features that have common boundaries and the same attributes.
Merge attributes of selected features
Merge Attributes of Selected Features
The
tool allows to merge attributes of features with common boundaries and attributes without merging their boundaries.
Rotate Point Symbols
Rotate Point Symbols
tool is currently only supported by the old symbology engine. It allows to change the
The
rotation of point symbols in the map canvas, if you have defined a rotation column from the attribute table of the
point layer in the Style tab of the Layer Properties. Otherwise the tool is inactive.
Figure 11.30: Rotate Point Symbols
To change the rotation, select a point feature in the map canvas and rotate it holding the left mouse button pressed.
A red arrow with the rotation value will be visualized (see Figure_edit_4). When you release the left mouse button
again, the value will be updated in the attribute table.
Note: If you hold the Ctrl key pressed, the rotation will be done in 15 degree steps.
11.3.6 Creating a new Vector layer
QGIS allows to create new Shapefile layers and new SpatiaLite layers. Creation of a new GRASS layer is supported within the GRASS-plugin. Please refer to section Creating a new GRASS vector layer for more information
on creating GRASS vector layers.
Creating a new Shapefile layer
New Shapefile Layer... from the Layer menu. The
To create a new Shape layer for editing, choose New →
New Vector Layer dialog will be displayed as shown in Figure_edit_5. Choose the type of layer (point, line or
polygon) and the CRS (Coordinate Reference System).
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Figure 11.31: Creating a new Shapefile layer Dialog
Note that QGIS does not yet support creation of 2.5D features (i.e. features with X,Y,Z coordinates).
To complete the creation of the new Shapefile layer, add the desired attributes by clicking on the [Add] button
and specifying a name and type for the attribute. A first ‘id’ column is added as default but can be removed, if
not wanted. Only Type: real
, Type: integer
, and Type: string
attributes are supported.
Additionally and according to the attribute type you can also define the width and precision of the new attribute
column. Once you are happy with the attributes, click [OK] and provide a name for the shapefile. QGIS will
automatically add a .shp extension to the name you specify. Once the layer has been created, it will be added to
the map and you can edit it in the same way as described in Section Digitizing an existing layer above.
Creating a new SpatiaLite layer
To create a new SpatiaLite layer for editing, choose New →
New SpatiaLite Layer... from the Layer menu.
The New SpatiaLite Layer dialog will be displayed as shown in Figure_edit_6.
First step is to select an existing SpatiaLite database or to create a new SpatiaLite database. This can be done with
the browse button
to the right of the database field. Then add a name for the new layer and define the layer
type and the EPSG SRID. If desired you can select to
Create an autoincrementing primary key.
To define an attribute table for the new SpatiaLite layer, add the names of the attribute columns you want to create
with the according column type and click on the [Add to attribute list] button. Once you are happy with the
attributes, click [OK]. QGIS will automatically add the new layer to the legend and you can edit it in the same
way as described in Section Digitizing an existing layer above.
Further management of SpatiaLite-Layers can be done with the DB Manager see DB Manager Plugin.
11.3.7 Working with the Attribute Table
The attribute table displays features of a selected layer. Each row in the table represents one map feature and
each column contains a particular piece of information about the feature. Features in the table can be searched,
selected, moved or even edited.
To open the attribute table for a vector layer, make the layer active by clicking on it in the map legend area. Then
from the main menu Layer choose
11.3. Editing
Open Attribute Table. It is also possible to rightclick on the layer and
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Figure 11.32: Creating a New SpatiaLite layer Dialog
choose
Open Attribute Table from the dropdown menu.
This will open a new window which displays the feature attributes in the layer (figure_attributes_1). The number
of features and the number of selected features are shown in the attribute table title.
Selecting features in an attribute table
Each selected row in the attribute table displays the attributes of a selected feature in the layer. If the set of
features selected in the main window is changed, the selection is also updated in the attribute table. Likewise, if
the set of rows selected in the attribute table is changed, the set of features selected in the main window will be
updated.
Rows can be selected by clicking on the row number on the left side of the row. Multiple rows can be marked by
holding the Ctrl key. A continuous selection can be made by holding the Shift key and clicking on several
row headers on the left side of the rows. All rows between the current cursor position and the clicked row are
selected. Moving the cursor position in the attribute table, by clicking a cell in the table, does not change the row
selection. Changing the selection in the main canvas does not move the cursor position in the attribute table.
The table can be sorted by any column, by clicking on the column header. A small arrow indicates the sort order
(downward pointing means descending values from the top row down, upward pointing means ascending values
from the top row down).
For a simple search by attributes on only one column the Look for field can be used. Select the field (column)
from which the search should be performed from the dropdown menu and hit the [Search] button. The matching
rows will be selected and the total number of matching rows will appear in the title bar of the attribute table, and
in the status bar of the main window. For more complex searches use the Advanced search button
will launch the Search Query Builder described in Section Query Builder.
To show selected records only, use the checkbox
, which
Show selected only. To search selected records only, use the
checkbox
Search selected only. The
Case sensitive checkbox allows to select case sensitive. The other
buttons at the bottom left of the attribute table window provide following functionality:
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Figure 11.33: Attribute Table for Alaska layer
•
Unselect all
•
Move selected to top
•
Invert selection
•
Copy selected rows to clipboard
•
Zoom map to the selected rows
•
Pan map to the selected rows
•
Toggle editing mode
•
Delete selected features
•
New Column
•
Delete Column
•
Open field calculator
also with Ctrl+U
also with Ctrl+T
also with Ctrl+S
also with Ctrl+C
also with Ctrl+J
also with Ctrl+P
to edit single values and to enable functionalities described below also with Ctrl+E
also with Ctrl+D
for PostGIS layers and for OGR layers with GDAL version >= 1.6 also with Ctrl+W
for PostGIS layers and for OGR layers with GDAL version >= 1.9 also with Ctrl+L
also with Ctrl+I
Tip: Skip WKT geometry
If you want to use attribute data in external programs (such as Excel) use the
Copy selected rows to clipboard
button.
You can copy the information without vector geometries if you deactivate Settings → Options → General tab
Copy geometry in WKT representation from attribute table.
Save selected features as new layer
The selected features can be saved as any OGR supported vector format and also transformed into another Coordinate Reference System (CRS). Just open the right mouse menu of the layer and click on Save selection as →
to define the name of the output file, its format and CRS (see Section Map Legend). It is also possible to specify
OGR creation options within the dialog.
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Working with non spatial attribute tables
QGIS allows also to load non spatial tables. This includes currently tables supported by OGR, delimited text and
the PostgreSQL provider. The tables can be used for field lookups or just generally browsed and edited using
the table view. When you load the table you will see it in the legend field. It can be opened e.g. with the
Open Attribute Table
tool and is then editable like any other layer attribute table.
As an example you can use columns of the non spatial table to define attribute values or a range of values that are
allowed to be added to a specific vector layer during digitizing. Have a closer look at the edit widget in section
Fields Tab to find out more.
11.4 Query Builder
The Query Builder allows you to define a subset of a table using a SQL-like WHERE clause and display the result
in the main window. The query result then can be saved as a new vector layer.
11.4.1 Query
Open Attribute Table
from the menu bar. Click on the [Advanced Search] butOpen the attribute table choosing
ton to open the Query builder. For example, if you have a towns layer with a population field you could
select only larger towns by entering population > 100000 in the SQL box of the Query builder. Figure_attributes_2 shows an example of the Query builder populated with data from a PostGIS layer with attributes
stored in PostgreSQL. The Fields, Values and Operators sections help the user to construct the SQL-like query.
Figure 11.34: Query Builder
The Fields list contains all attribute columns of the attribute table to be searched. To add an attribute column to the
SQL where clause field, double click its name in the Fields list. Generally you can use the various fields, values
and operators to construct the query or you can just type it into the SQL box.
The Values list lists the values of an attribute table. To list all possible values of an attribute, select the attribute in
the Fields list and click the [all] button. To list the first 25 unique values of an attribute column, select the attribute
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column in the Fields list and click the [Sample] button. To add a value to the SQL where clause field, double click
its name in the Values list.
The Operators section contains all usable operators. To add an operator to the SQL where clause field, click the
appropriate button. Relational operators ( = , > , ...), string comparison operator (LIKE), logical operators (AND,
OR, ...) are available.
The [Test] button shows a message box with the number of features satisfying the current query, which is usable
in the process of query construction. The [Clear] button clears the text in the SQL where clause text field. The
[Save] and [Load] button allow to save and load SQL queries. The [OK] button closes the window and selects the
features satisfying the query. The [Cancel] button closes the window without changing the current selection.
Tip: Changing the Layer Definition
You can change the layer definition after it is loaded by altering the SQL query used to define the layer. To do this,
open the vector Layer Properties dialog by double-clicking on the layer in the legend and click on the [Query
Builder] button on the General tab. See Section The Vector Properties Dialog for more information.
11.4.2 Selection
With QGIS it is possible also to select features for visualisation using a similar query builder interface to that used
in Query Builder. In the above section the purpose of the query builder is to highlight all selected features meeting
the filter criteria in yellow. The rest of the features do not change their appearance.
Another possibility is to make a selection by right clicking on a layer in the legend and choosing Query .... If you
perform a SQL query here only the selected features are displayed in the map view. Features that don’t match the
SQL query are not visualised in the map view. The same function is available from the General tab in the vector
Layer Properties dialog. You can find a [Query builder] button right below. The selection described above can
be used with all vector data providers.
11.4.3 Save selected features as new layer
The selected features can be saved as any OGR supported vector format and also transformed into another Coordinate Reference System (CRS). Just open the right mouse menu of the layer and click on Save selection as →
to define the name of the output file, its format and CRS (see Section Map Legend). It is also possible to specify
OGR creation options within the dialog.
11.5 Field Calculator
Field Calculator
button in the attribute table allows to perform calculations on basis of existing attribute
The
values or defined functions, e.g to calculate length or area of geometry features. The results can be written to a
new attribute column or it can be used to update values in an already existing column.
You have to bring the vector layer in editing mode, before you can click on the field calculator icon to open the
dialog (see figure_attributes_3). In the dialog you first have to select whether you want to only update selected
features, create a new attribute field where the results of the calculation will be added or update an existing field.
If you choose to add a new field, you need to enter a field name, a field type (integer, real or string), the total field
width, and the field precision (see figure_attributes_3). For example, if you choose a field width of 10 and a field
precision of 3 it means you have 6 signs before the dot, then the dot and another 3 signs for the precision.
The Function List contains functions as well as fields and values. View the help function in the Selected Function
Help. In Expression you see the calculation expressions you create with the Function List. The most commonly
used operators, see Operators.
In the Function List, click on Fields and Values to view all attributes of the attribute table to be searched. To add
an attribute to the Field calculator Expression field, double click its name in the Fields and Values list. Generally
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Figure 11.35: Field Calculator
you can use the various fields, values and functions to construct the calculation expression or you can just type it
into the box. To display the values of a field, you just right click on the appropriate field. You can choose between
Load top 10 unique values and Load all unique values. On the right side opens the Field Values list with the
unique values. To add a value to the Field calculator Expression box, double click its name in the Field Values
list.
The Operators, Math, Conversions, String, Geometry and Record groups provides several functions. In Operators
you find mathematical operators. Find Math for mathematical functions. The Conversions group contains functions that convert one data type to another. The String group provides functions for data strings. In the Geometry
group you find functions for geometry objects. With Record group functions you can add a numeration to your
data set. To add a function to the Field calculator Expression box, click on the > and then doubleclick the function.
A short example illustrates how the field calculator works. We want to calculate the length of the railroads
layer from the QGIS sample dataset:
1. Load the Shapefile railroads.shp in QGIS and press
2. Click on
3. Select the
Toggle editing mode
and open the
Field Calculator
Open Attribute Table
.
dialog.
Create a new field checkbox to safe the calculations into a new field.
4. Add length as Output field name, real as Output field type and define Output field width 10 and a
Precision of 3.
5. Now click on function length in the Geometry group to add it as $length into the Field calculator
expression box and click [Ok].
6. You can now find a new column length in the attribute table.
The available functions are listed below.
column name "column name"
’string’
NULL
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a IS NULL
a IS NOT NULL
a IN (value[,value])
a NOT IN (value[,value])
a OR b
a AND b
NOT a
sqrt(a)
sin(a)
cos(a)
tan(a)
asin(a)
acos(a)
atan(a)
to int(a)
to real(a)
to string(a)
lower(a)
upper(a)
length(a)
atan2(y,x)
replace(*a*, replacethis, withthat)
regexp_replace(a,this,that)
substr(*a*,from,len)
a || b
$rownum
$area
$perimeter
$length
$id
$x
$y
xat(n)
yat(n)
a
a
a
a
a
a
a
a
a
a
a
a
a
a
+
-
= b
!= b and a <> b
>= b
<= b
> b
< b
~ b
LIKE b
ILIKE b
|wedge| b
* b
/ b
+ b
- b
a
a
a has no value
a has a value
a is below the values listed
a is not below the values listed
a or *b* is true
a and *b* is true
inverted truth value of a
square root of a
sinus of a
cosinus of b
tangens of a
arcussinus of a
arcuscosinus of a
arcustangens of a
convert string a to integer
convert string a to real
convert number a to string
convert string a to lower case
convert string a to upper case
length of string a
arcustangens of y/x using the signs of the two
arguments to determine the quadrant of the result
replace this with that in string a
replace the regular expression this with that
len characters of string *a* starting from from
(first character index is 1)
concatenate strings a and b
number current row
area of polygon
perimeter of polygon
length of line
feature id
x coordinate of point
y coordinate of point
X coordinate of the point of an n-th line (indeces
start at 0; negative values refer to the line end)
y coordinate of the point of an n-th line (indeces
start at 0; negative values refer to the line end)
a and b are equal
a and b are not equal
a is larger than or equal to b
a is less than or equal to b
a is larger than b
a is smaller than b
a matches the regular expression b
a equals b
a equals b (without regard to case-sensitive)
a raised to the power of b
a multiplied by b
a divided by b
a plus b
a minus b
positive sign
negative value of a
The field calculator Function list with the Selected Function Help , Operators and Expression menu are also
available through the rule-based rendering in the Style tab of the Layer properties and the expression based labeling
in the
Labeling
core application.
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CHAPTER 12
Working with Raster Data
12.1 Working with Raster Data
This Section describes how to visualize and set raster layer properties. QGIS uses the GDAL library to read and
write raster data formats, including Arc/Info Binary Grid, Arc/Info ASCII Grid, GeoTIFF, Erdas Imagine and
many more. GRASS raster support is supplied by a native QGIS data provider plugin. The raster data can also be
loaded in read mode from zip and gzip archives into QGIS.
At the date of this document, more than 100 raster formats are supported by the GDAL library
(see GDAL-SOFTWARE-SUITE Literature and Web References).
A complete list is available at
http://www.gdal.org/formats_list.html.
Note: Not all of the listed formats may work in QGIS for various reasons. For example, some require external
commercial libraries or the GDAL installation of your OS was not built to support the format you want to use.
Only those formats that have been well tested will appear in the list of file types when loading a raster into QGIS.
Other untested formats can be loaded by selecting the [GDAL] All files (*) filter.
Working with GRASS raster data is described in Section GRASS GIS Integration.
12.1.1 What is raster data?
Raster data in GIS are matrices of discrete cells that represent features on, above or below the earth’s surface. Each
cell in the raster grid is the same size, and cells are usually rectangular (in QGIS they will always be rectangular).
Typical raster datasets include remote sensing data such as aerial photography or satellite imagery and modelled
data such as an elevation matrix.
Unlike vector data, raster data typically do not have an associated database record for each cell. They are geocoded
by its pixel resolution and the x/y coordinate of a corner pixel of the raster layer. This allows QGIS to position the
data correctly in the map canvas.
QGIS makes use of georeference information inside the raster layer (e.g. GeoTiff) or in an appropriate world file
to properly display the data.
12.1.2 Loading raster data in QGIS
Load Raster
Raster layers are loaded either by clicking on the
icon or by selecting the Layer →
Add Raster
Layer menu option. More than one layer can be loaded at the same time by holding down the Control or Shift
key and clicking on multiple items in the dialog Open a GDAL Supported Raster Data Source.
Once a raster layer is loaded in the map legend you can click on the layer name with the right mouse button to
select and activate layer specific features or to open a dialog to set raster properties for the layer.
Right mouse button menu for raster layers
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• Zoom to layer extent
• Zoom to Best Scale (100%)
• Show in Overview
• Remove
• Set Layer CRS
• Set Project CRS from Layer
• Properties
• Rename
• Copy Style
• Add New Group
• Expand all
• Collapse all
• Update Drawing Order
12.2 Raster Properties Dialog
To view and set the properties for a raster layer, double click on the layer name in the map legend or right click on
the layer name and choose Properties from the context menu:
This will open the Raster Layer Properties dialog, (see figure_raster_1).
There are several tabs on the dialog:
• Style
• Transparency
• Colormap
• General
• Metadata
• Pyramids
• Histogram
12.2.1 Style Tab
QGIS can render raster layers in two different ways:
1. Single band - one band of the image will be rendered as gray or in pseudocolor or a freak out.
2. Three band color - three bands from the image will be rendered, each band representing the red, green or
blue component that will be used to create a color image.
Within both render types you can invert the color output using the
Invert color map checkbox.
Single Band Rendering
This selection offers you two possibilites to choose. At first you can select which band you like to use for rendering
(if the dataset has more than one band).
The second option offers a selection of available colortables for rendering.
The following settings are available through the dropdownbox Color map
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Figure 12.1: Raster Layers Properties Dialog
• Grayscale (default)
• Pseudocolor
• Freak Out
• Colormap
When selecting the entry ‘Colormap’ from Color map
For more information see Colormap.
combobox, the tab Colormap becomes available.
QGIS can restrict the data displayed to only show cells whose values are within a given number of standard
deviations of the mean for the layer.
This is useful when you have one or two cells with abnormally high values in a raster grid that are having a
negative impact on the rendering of the raster. This option is only available for pseudocolor and freak out images.
Three band color
This selection offers you a wide range of options to modify the appearance of your rasterlayer. For example you
could switch color-bands from the standard RGB-order to something else.
Also scaling of colors are available.
Tip: Viewing a Single Band of a Multiband Raster
If you want to view a single band (for example Red) of a multiband image, you might think you would set the
Green and Blue bands to “Not Set”. But this is not the correct way. To display the Red band, set the image type to
grayscale, then select Red as the band to use for Gray.
Contrast enhancement
Note: When adding GRASS rasters the option Contrast enhancement will be always set to automatically to
stretch to min max regardless if the Quantum GIS general options this is set to another value.
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12.2.2 Transparency Tab
QGIS has the ability to display each raster layer at varying transparency levels. Use the transparency slider to
indicate to what extent the underlying layers (if any) should be visible though the current raster layer. This is
very useful, if you like to overlay more than one rasterlayer, e.g. a shaded relief map overlayed by a classified
rastermap. This will make the look of the map more three dimensional.
Additionally you can enter a rastervalue, which should be treated as NODATA. This can be done manually or with
Add values from display
the
icon.
An even more flexible way to customize the transparency can be done in the Custom transparency options section.
The transparency of every pixel can be set here.
As an example we want to set the water of our example raster file landcover.tif to a transparency of 20 %.
The following steps are neccessary:
1. Load the rasterfile landcover.
2. Open the Properties dialog by double-clicking on the raster name in the legend or by right-clicking and
choosing Properties from the popup menu.
3. Select the Transparency tab
4. Click the
Add values manually
button. A new row will appear in the pixel-list.
5. Enter the raster-value (we use 0 here) and adjust the transparency to 20 %.
6. Press the [Apply] button and have a look at the map.
You can repeat the steps 4 and 5 to adjust more values with custom transparency.
As you can see this is quite easy to set custom transparency, but it can be quite a lot of work. Therefore you
Export to file
can use the button
to save your transparency list to a file. The button
transparency settings and applies them to the current raster layer.
Import from file
loads your
12.2.3 Colormap
The Colormap tab is only available, when you have selected a singleband rendering within the Style tab (see Style
Tab).
Three ways of color interpolation are available:
1. Discrete
2. Linear
3. Exact
The button [Add Entry] adds a color to the individual color table. Button [Delete Entry] deletes a color from the
individual color table and the [Sort] button sorts the color table according to the pixel values in the value column.
Double clicking on the value-column lets you insert a specific value. Double clicking on the color-column opens
the dialog Select color where you can select a color to apply on that value. Further you can also add labels for
each color but this value won’t be displayed when you use the identify feature tool.
You can also click on the button
Load color map from band
Load color map from file
And you can use the buttons
save the defined color table for other sessions.
or
, which tries to load the table from the band (if it has any).
Export color map to file
to load an existing color table or to
The block Generate new color map allows you to create newly categorized colormaps. You only need to select
the number of entries
supported - ‘Equal interval’
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12.2.4 General Tab
The General tab displays basic information about the selected raster, including the layer source and display name
in the legend (which can be modified). This tab also shows a thumbnail of the layer, its legend symbol, and the
palette.
Additionally scale-dependent visibility can be set in this tab. You need to check the checkbox and set an appropriate scale where your data will be displayed in the map canvas.
Also the coordinate reference system (CRS) is printed here as a PROJ.4-string. This can be modified by hitting
the [Specify] button.
12.2.5 Metadata Tab
The Metadata tab displays a wealth of information about the raster layer, including statistics about each band in
the current raster layer. Statistics are gathered on a ‘need to know’ basis, so it may well be that a given layers
statistics have not yet been collected.
This tab is mainly for information. You cannot change any values printed inside this tab.
12.2.6 Pyramids Tab
Large resolution raster layers can slow navigation in QGIS. By creating lower resolution copies of the data (pyramids), performance can be considerably improved as QGIS selects the most suitable resolution to use depending
on the level of zoom.
You must have write access in the directory where the original data is stored to build pyramids.
Several resampling methods can be used to calculate the pyramids:
• Average
• Nearest Neighbour
When checking the checkbox
Build pyramids internally if possible QGIS tries to build pyramids internally.
Please note that building pyramids may alter the original data file and once created they cannot be removed. If
you wish to preserve a ‘non-pyramided’ version of your raster, make a backup copy prior to building pyramids.
12.2.7 Histogram Tab
The Histogram tab allows you to view the distribution of the bands or colors in your raster. It is generated
automaticaly when you open Histogram tab. All existing bands will be displayed together. You can save the
histogram as an image with the
button.
12.3 Raster Calculator
The Raster Calculator in the Raster menu (see figure_raster_2) allows to perform calculations on basis of existing
raster pixel values. The results are written to a new raster layer with a GDAL supported format.
The Raster bands list contains all loaded raster layers that can be used. To add a raster to the raster calculator
expression field, double click its name in the Fields list. You can then use the operators to construct calculation
expressions or you can just type it into the box.
In the Result layer section you have to define an output layer. You can then define the extent of the calculation
area based on an input raster layer or based on X,Y coordinates and on Columns and Rows to set the resolution of
the output layer. If the input layer has a different resolution, the values will be resampled with nearest neighbor
algorithm.
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Figure 12.2: Raster Calculator
The Operators section contains all usable operators. To add an operator to the raster calculator expression box,
click the appropriate button. Mathematical calculations (+, -, *, ... ) and trigonometric functions (sin, cos,
tan, ... ) are available. Stay tuned for more operators to come!
With the
Add result to project checkbox the result layer will automatically added to the legend area and can
be visualized.
12.3.1 Examples
Convert elevation values from meter to feet
Creating an elevation raster feet from a raster in meter, you need to use the conversion factor for meters to feet:
3.28. The expression is:
elevation@1 * 3.28
Using a mask
If you want to mask out parts of a raster, because you are only interested in elevations above 0 meter, you can use
following expression to create a mask and apply the result to a raster in one step.
(elevation@1 >= 0) * elevation@1
For every cell greater than or equal to 0, set its value to 1, otherwise set it to 0. This creates the mask on the fly.
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CHAPTER 13
Working with OGC Data
13.1 Working with OGC Data
QGIS supports WMS and WFS as data sources.
13.1.1 What is OGC Data
The Open Geospatial Consortium (OGC), is an international organization with more than 300 commercial, governmental, nonprofit and research organizations worldwide. Its members develop and implement standards for
geospatial content and services, GIS data processing and exchange.
Describing a basic data model for geographic features an increasing number of specifications are developed to
serve specific needs for interoperable location and geospatial technology, including GIS. Further information can
be found under http://www.opengeospatial.org/.
Important OGC specifications are:
• WMS — Web Map Service
• WFS — Web Feature Service
• WCS — Web Coverage Service
• CAT — Web Catalog Service
• SFS — Simple Features for SQL
• GML — Geography Markup Language
OGC services are increasingly being used to exchange geospatial data between different GIS implementations
and data stores. QGIS can now deal with three of the above specifications, being SFS (through support of the
PostgreSQL / PostGIS data provider, see Section PostGIS Layers), WFS and WMS as a client.
13.1.2 WMS Client
Overview of WMS Support
QGIS currently can act as a WMS client that understands WMS 1.1, 1.1.1 and 1.3 servers. It has particularly been
tested against publicly accessible servers such as DEMIS.
WMS servers act upon requests by the client (e.g. QGIS) for a raster map with a given extent, set of layers,
symbolization style, and transparency. The WMS server then consults its local data sources, rasterizes the map,
and sends it back to the client in a raster format. For QGIS this would typically be JPEG or PNG.
WMS is generically a REST (Representational State Transfer) service rather than a fully-blown Web Service. As
such, you can actually take the URLs generated by QGIS and use them in a web browser to retrieve the same
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images that QGIS uses internally. This can be useful for troubleshooting, as there are several brands of WMS
servers in the market and they all have their own interpretation of the WMS standard.
WMS layers can be added quite simply, as long as you know the URL to access the WMS server, you have a
serviceable connection to that server, and the server understands HTTP as the data transport mechanism.
Selecting WMS Servers
The first time you use the WMS feature, there are no servers defined.
Add WMS layer
Begin by clicking the
button inside the toolbar, or through the Layer → Add WMS Layer... menu.
The dialog Add Layer(s) from a Server for adding layers from the WMS server appears. You can add some servers
to play with by clicking the [Add default servers] button. This will add two WMS demo servers for you to use, the
WMS servers of the DM Solutions Group and Lizardtech. To define a new WMS server in the tab Layers, select
the [New] button. Then enter the parameters to connect to your desired WMS server, as listed in table_OGC_1:
Name
A name for this connection. This name will be used in the Server Connections drop-down
box so that you can distinguish it from other WMS Servers.
URL
URL of the server providing the data. This must be a resolvable host name; the same
format as you would use to open a telnet connection or ping a host.
Username
Username to access a secured WMS-server. This parameter is optional.
Password
Password for a basic authenticated WMS-server. This parameter is optional.
Ignore GetMap
URI
Ignore GetMap URI reported in capabilities, use given URI from URL-field above.
Ignore
GetFeatureInfo
URI
Ignore GetFeatureInfo URI reported in capabilities , use given URI from URL-field
above
Table OGC 1: WMS Connection Parameters
If you need to set up a proxy-server to be able to receive WMS-services from the internet, you can add your
proxy-server in the options. Choose menu Settings → Options and click on the tab Network & Proxy. There you
can add your proxy-settings and enable them by setting the
select the correct proxy type from the Proxy type
Use proxy for web access. Make sure that you
dropdown menu.
Once the new WMS Server connection has been created, it will be preserved for future QGIS sessions.
Tip: On WMS Server URLs
Be sure, when entering in the WMS server URL, that you have the base URL. For example, you shouldn’t have
fragments such as request=GetCapabilities or version=1.0.0 in your URL.
Loading WMS Layers
Once you have successfully filled in your parameters you can select the [Connect] button to retrieve the capabilities of the selected server. This includes the Image encoding, Layers, Layer Styles and Projections. Since this is
a network operation, the speed of the response depends on the quality of your network connection to the WMS
server. While downloading data from the WMS server, the download progress is visualized in the left bottom of
the WMS dialog.
Your screen should now look a bit like figure_OGR_1, which shows the response provided by the DM Solutions
Group WMS server.
Image Encoding
The Image encoding section now lists the formats that are supported by both the client and server. Choose one
depending on your image accuracy requirements.
Tip: Image Encoding
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Figure 13.1: Dialog for adding a WMS server, showing its available layers
You will typically find that a WMS server offers you the choice of JPEG or PNG image encoding. JPEG is a lossy
compression format, whereas PNG faithfully reproduces the raw raster data.
Use JPEG if you expect the WMS data to be photographic in nature and/or you don’t mind some loss in picture
quality. This trade-off typically reduces by 5 times the data transfer requirement compared to PNG.
Use PNG if you want precise representations of the original data, and you don’t mind the increased data transfer
requirements.
Options
The Options field provides a text field where you can add a Layer name for the WMS-layer. This name will be
presented in the legend after loading the layer.
Below the layer name you can define Tile size, if you want to set tile sizes (eg. 256x256) to split up the WMS
request into multiple requests.
The Feature limit for GetFeatureInfo defines what features from the server to query.
If you select a WMS from the list a field with the default projection, provided by the mapserver, appears. If the
[Change...] button is active, you can click on it and change the default projection of the WMS to another CRS,
provided by the WMS server.
Layer Order
The tab Layer Order lists the selected layers available from the current connected WMS server. You may notice
that some layers are expandable, this means that the layer can be displayed in a choice of image styles.
You can select several layers at once, but only one image style per layer. When several layers are selected, they
will be combined at the WMS Server and transmitted to QGIS in one go.
Tip: WMS Layer Ordering
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WMS layers rendered by a server are overlaid in the order listed in the Layers section, from top to bottom of the
list. If you want to change the overlay order, you can use the tab Layer Order.
Transparency
In this version of QGIS, the Global transparency setting from the Layer Properties is hard-coded to be always on,
where available.
Tip: WMS Layer Transparency
The availability of WMS image transparency depends on the image encoding used: PNG and GIF support transparency, whilst JPEG leaves it unsupported.
Coordinate Reference System
A Coordinate Reference System (CRS) is the OGC terminology for a QGIS Projection.
Each WMS Layer can be presented in multiple CRSs, depending on the capability of the WMS server.
To choose a CRS, select [Change...] and a dialog similar to Figure Projection 3 in Working with Projections will
appear. The main difference with the WMS version of the screen is that only those CRSs supported by the WMS
Server will be shown.
Server-Search
Within QGIS you can search for WMS-servers. Figure_OGC_2 shows the tab Server Search with the Add Layer(s)
from a Server dialog.
Figure 13.2: Dialog for searching WMS servers after some keywords
As you can see it is possible to enter a search-string in the text field and hit the [Search] button. After a short while
the search result will be populated into the list below the text field. Browse the result list and inspect your search
results within the table. To visualize the results, select a table entry, press the [Add selected row to WMS-list]
button and change back to the tab Layers. QGIS automatically has updated your server list and the selected search
result is already enabled in the list of saved WMS-servers in the Layers tab. You only need to request the list of
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layers by clicking the [Connect] button. This option is quite handy when you want to search maps by specific
keywords.
Basically this option is a frontend to the API of http://geopole.org.
Tilesets
When using WMS-C (Cached WMS) Services like http://labs.metacarta.com/wms-c/Basic.py you are able to
browse through the tab Tilesets given by the server. Additional information like tile size, formats and supported
CRS are listed in this table. In combination with this feature you can use the tile scale slider from the View → Tile
scale slider, which gives you the available scales from the tileserver with nice slider docked in.
Using the Identify Tool
Once you have added a WMS server, and if any layer from a WMS server is queryable, you can then use the
Identify
tool to select a pixel on the map canvas. A query is made to the WMS server for each selection made. The
results of the query are returned in plain text. The formatting of this text is dependent on the particular WMS
server used. Viewing Properties
Once you have added a WMS server, you can view its properties by right-clicking on it in the legend, and selecting
Properties. Metadata Tab
The tab Metadata displays a wealth of information about the WMS server, generally collected from the Capabilities statement returned from that server. Many definitions can be cleaned by reading the WMS standards (see
OPEN-GEOSPATIAL-CONSORTIUM Literature and Web References), but here are a few handy definitions:
• Server Properties
– WMS Version — The WMS version supported by the server.
– Image Formats — The list of MIME-types the server can respond with when drawing the map.
QGIS supports whatever formats the underlying Qt libraries were built with, which is typically at least
image/png and image/jpeg.
– Identity Formats — The list of MIME-types the server can respond with when you use the Identify
tool. Currently QGIS supports the text-plain type.
• Layer Properties
– Selected — Whether or not this layer was selected when its server was added to this project.
– Visible — Whether or not this layer is selected as visible in the legend. (Not yet used in this version
of QGIS.)
– Can Identify — Whether or not this layer will return any results when the Identify tool is used on it.
– Can be Transparent — Whether or not this layer can be rendered with transparency. This version of
QGIS will always use transparency if this is Yes and the image encoding supports transparency
– Can Zoom In — Whether or not this layer can be zoomed in by the server. This version of QGIS
assumes all WMS layers have this set to Yes. Deficient layers may be rendered strangely.
– Cascade Count — WMS servers can act as a proxy to other WMS servers to get the raster data for a
layer. This entry shows how many times the request for this layer is forwarded to peer WMS servers
for a result.
– Fixed Width, Fixed Height — Whether or not this layer has fixed source pixel dimensions. This
version of QGIS assumes all WMS layers have this set to nothing. Deficient layers may be rendered
strangely.
– WGS 84 Bounding Box — The bounding box of the layer, in WGS 84 coordinates. Some WMS
servers do not set this correctly (e.g. UTM coordinates are used instead). If this is the case, then
the initial view of this layer may be rendered with a very ‘zoomed-out’ appearance by QGIS. The
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WMS webmaster should be informed of this error, which they may know as the WMS XML elements
LatLonBoundingBox, EX_GeographicBoundingBox or the CRS:84 BoundingBox.
– Available in CRS — The projections that this layer can be rendered in by the WMS server. These are
listed in the WMS-native format.
– Available in style — The image styles that this layer can be rendered in by the WMS server.
WMS Client Limitations
Not all possible WMS Client functionality had been included in this version of QGIS. Some of the more notable
exceptions follow.
Editing WMS Layer Settings
Add WMS layer
procedure, there is no ability to change the settings. A workaround is
Once you’ve completed the
to delete the layer completely and start again.
WMS Servers Requiring Authentication
Currently public accessible and secured WMS-services are supported. The secured WMS-servers can be accessed
by public authentication. You can add the (optional) credentials when you add a WMS-server. See section Selecting WMS Servers for details.
Tip: Accessing secured OGC-layers
If you need to access secured layers with other secured methods than basic authentication, you could use InteProxy
as a transparent proxy, which does support several authentication methods. More information can be found at the
InteProxy manual found on the website http://inteproxy.wald.intevation.org.
Tip: QGIS WMS Mapserver
From Version 1.7.0 QGIS has its own implementation of a WMS 1.3.0 Mapserver. Read more about this at chapter
QGIS Server.
13.1.3 WFS and WFS-T Client
In QGIS, a WFS layer behaves pretty much like any other vector layer. You can identify and select features and
view the attribute table. Since QGIS 1.6 editing (WFS-T) is also supported.
In general adding a WFS layer is very similar to the procedure used with WMS. The difference is there are no
default servers defined, so we have to add our own.
Loading a WFS Layer
As an example we use the DM Solutions WFS server and display a layer.
http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap
1. Click on the
Add WFS Layer
The URL is:
tool on the Layers toolbar, the dialog Add WFS Layer from a Server appears
2. Click on [New]
3. Enter ‘DM Solutions’ as name
4. Enter the URL (see above)
5. Click [OK]
6. Choose ‘DM Solutions’ from the Server Connections
combobox
7. Click [Connect]
8. Wait for the list of layers to be populated
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9. Select the Parks layer in the list
10. Click [Apply] to add the layer to the map
Note that proxy-settings you have set in your preferences are also recognized.
Figure 13.3: Adding a WFS layer
You’ll notice the download progress is visualized in the left bottom of the QGIS main window. Once the layer is
loaded, you can identify and select a province or two and view the attribute table.
Only WFS 1.0.0 is supported. At this point there have not been many tests against WFS versions implemented in
other WFS-servers. If you encounter problems with any other WFS-server, please do not hesitate to contact the
development team. Please refer to Section Mailing lists for further information about the mailinglists.
Tip: Finding WFS Servers
You can find additional WFS servers by using Google or your favorite search engine. There are a number of lists
with public URLs, some of them maintained and some not.
13.2 QGIS Server
QGIS Server is an open source WMS 1.3 and WFS 1.0.0 implementation which, in addition, implements advanced
cartographic features for thematic mapping. The QGIS Server is a FastCGI/CGI (Common Gateway Interface)
application written in C++ that works together with a webserver (e.g. Apache, Lighttpd). It is funded by the EU
projects Orchestra, Sany and the city of Uster in Switzerland.
It uses QGIS as backend for the GIS logic and for map rendering. Furthermore the Qt library is used for graphics
and for platform independent C++ programming. In contrast to other WMS software, the QGIS Server uses cartographic rules as a configuration language, both for the server configuration and for the user-defined cartographic
rules.
Moreover, the QGIS Server project provides the ‘Publish to Web’ plugin, a plugin for QGIS desktop which exports
the current layers and symbology as a web project for QGIS Server (containing cartographic visualization rules
expressed in SLD).
As QGIS desktop and QGIS Server use the same visualization libraries, the maps that are published on the web
look the same as in desktop GIS. The ‘Publish to Web’ plugin currently supports basic symbolization, with more
complex cartographic visualization rules introduced manually. As the configuration is performed with the SLD
standard and its documented extensions, there is only one standardised language to learn, which greatly simplifies
the complexity of creating maps for the Web.
In one of the following manuals we will provide a sample configuration to set up a QGIS Server. But for now we
recommend to read one of the following URLs to get more information:
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• http://karlinapp.ethz.ch/qgis_wms/
• http://hub.qgis.org/projects/quantum-gis/wiki/QGIS_Server_Tutorial
• http://linfiniti.com/2010/08/qgis-mapserver-a-wms-server-for-the-masses/
13.2.1 Sample installation on Debian Squeeze
At this point we will give a short and simple sample installation howto for Debian Squeeze. Many other OS
provide packages for QGIS Server, too. If you have to build it all from source, please refer to the URLs above.
Apart from qgis and qgis-mapserver you need a webserver, in our case apache2. You can install all packages with aptitude or apt-get install together with other necessary dependency packages. After installation you
should test, if the webserver and qgis server works as expected. Make sure the apache server is running with
/etc/init.d/apache2 start. Open a web browser and type URL: http://localhost. If apache is
up, you should see the message ‘It works!’.
Now we test the qgis server installation.
The qgis_mapserv.fcgi is available at
/usr/lib/cgi-bin/qgis_mapserv.fcgi and provides a standard wms that shows the state boundaries
of Alaska. Add the WMS with the URL http://localhost/cgi-bin/qgis_mapserv.fcgi as
described in Selecting WMS Servers.
Figure 13.4: Standard WMS with USA boundaries included in the qgis server (KDE)
13.2.2 Creating a WMS/WFS from a QGIS project
To provide a new qgis wms/wfs server we have to create a qgis project file with some data. Here we use the
‘alaska’ shapefile from the qgis_sample_dataset. Define the colors and styles of the layers in QGIS and define the
project CRS, if not already done.
Then open the OWS Server tab in the menu Settings → Project Properties and define the general fields under
‘Service Capabilities’. For WMS Capabilities define ‘Coordinate System Restrictions’ and ‘Advertised Extend’. Additionally you can enable the checkbox
Add WKT geometry to feature into response to make the layers queryable and add a ‘Maximum width’ and height that can be requested. For WFS Capabilities you only
need to select the layers that you want to provide as WFS. Now save the session in a project file alaska.qgs.
To provide the project as a WMS/WFS, we create a new folder /usr/lib/cgi-bin/project with admin
privileges and add the project file alaska.qgs and a copy of the qgis_mapserv.fcgi file - that’s all.
Now we test our project WMS and WFS, add the WMS and WFS as described in Loading WMS Layers and WFS
and WFS-T Client to QGIS and load the WMS. The URL is:
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Figure 13.5: Definitions for a qgis project WMS/WFS server (KDE)
http://localhost/cgi-bin/project/qgis_mapserv.fcgi
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CHAPTER 14
Working with GPS Data
14.1 GPS Plugin
14.1.1 What is GPS?
GPS, the Global Positioning System, is a satellite-based system that allows anyone with a GPS receiver to find
their exact position anywhere in the world. It is used as an aid in navigation, for example in airplanes, in boats and
by hikers. The GPS receiver uses the signals from the satellites to calculate its latitude, longitude and (sometimes)
elevation. Most receivers also have the capability to store locations (known as waypoints), sequences of locations
that make up a planned route and a tracklog or track of the receivers movement over time. Waypoints, routes and
tracks are the three basic feature types in GPS data. QGIS displays waypoints in point layers while routes and
tracks are displayed in linestring layers.
14.1.2 Loading GPS data from a file
There are dozens of different file formats for storing GPS data. The format that QGIS uses is called GPX (GPS
eXchange format), which is a standard interchange format that can contain any number of waypoints, routes and
tracks in the same file.
To load a GPX file you first need to load the plugin. Plugins →
Plugin Manager... opens the Plugin Manager
Dialog. Activate the
GPS Tools checkbox. When this plugin is loaded two buttons with a small handheld GPS
device will show up in the toolbar:
•
Create new GPX Layer
•
GPS Tools
For working with GPS data we provide an example GPX file available in the QGIS sample dataset:
qgis_sample_data/gps/national_monuments.gpx. See Section Sample Data for more information
about the sample data.
1. Click on the
GPS Tools
icon and open the Load GPX file tab (see figure_GPS_1).
2. Browse to the folder qgis_sample_data/gps/, select the GPX file national_monuments.gpx
and click [Open].
Use the [Browse...] button to select the GPX file, then use the checkboxes to select the feature types you want
to load from that GPX file. Each feature type will be loaded in a separate layer when you click [OK]. The file
national_monuments.gpx only includes waypoints.
Note: GPS units allow to store data in different coordinate systems. When downloading a GPX file (from
your GPS unit or a web site) and then loading it in Quantum GIS, be sure that the data stored in the GPX
file uses WGS84 (latitude/longitude). Quantum GIS expects this and it is the official GPX specification. See
http://www.topografix.com/GPX/1/1/
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Figure 14.1: The GPS Tools dialog window
14.1.3 GPSBabel
Since QGIS uses GPX files you need a way to convert other GPS file formats to GPX. This can be done for many
formats using the free program GPSBabel, which is available at http://www.gpsbabel.org. This program can also
transfer GPS data between your computer and a GPS device. QGIS uses GPSBabel to do these things, so it is
recommended that you install it. However, if you just want to load GPS data from GPX files you will not need it.
Version 1.2.3 of GPSBabel is known to work with QGIS, but you should be able to use later versions without any
problems.
14.1.4 Importing GPS data
To import GPS data from a file that is not a GPX file, you use the tool Import other file in the GPS Tools dialog.
Here you select the file that you want to import (and the file type), which feature type you want to import from it,
where you want to store the converted GPX file and what the name of the new layer should be. Note that not all
GPS data formats will support all three feature types, so for many formats you will only be able to choose between
one or two types.
14.1.5 Downloading GPS data from a device
QGIS can use GPSBabel to download data from a GPS device directly as new vector layers. For this we use the
Download from GPS tab of the GPS Tools dialog (see Figure_GPS_2). Here, we select the type of GPS device,
the port that it is connected to (or usb if your GPS supports this), the feature type that you want to download, the
GPX file where the data should be stored, and the name of the new layer.
Figure 14.2: The download tool
The device type you select in the GPS device menu determines how GPSBabel tries to communicate with your
GPS device. If none of the available types work with your GPS device you can create a new type (see section
Defining new device types).
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The port may be a file name or some other name that your operating system uses as a reference to the physical
port in your computer that the GPS device is connected to. It may also be simply usb, for usb enabled GPS units.
•
On Linux this is something like /dev/ttyS0 or /dev/ttyS1
•
On Windows it is COM1 or COM2.
When you click [OK] the data will be downloaded from the device and appear as a layer in QGIS.
14.1.6 Uploading GPS data to a device
You can also upload data directly from a vector layer in QGIS to a GPS device using the Upload to GPS tab of the
GPS Tools dialog. To do this you simply select the layer that you want to upload (which must be a GPX layer),
your GPS device type, and the port (or usb) that it is connected to. Just as with the download tool you can specify
new device types if your device isn’t in the list.
This tool is very useful in combination with the vector editing capabilities of QGIS. It allows you to load a map,
create waypoints and routes, and then upload them and use them on your GPS device.
14.1.7 Defining new device types
There are lots of different types of GPS devices. The QGIS developers can’t test all of them, so if you have one
that does not work with any of the device types listed in the Download from GPS and Upload to GPS tools you
can define your own device type for it. You do this by using the GPS device editor, which you start by clicking
the [Edit devices] button in the download or the upload tabs.
To define a new device you simply click the [New device] button, enter a name, a download command and an
upload command for your device, and click the [Update device] button. The name will be listed in the device
menus in the upload and download windows, and can be any string. The download command is the command that
is used to download data from the device to a GPX file. This will probably be a GPSBabel command, but you can
use any other command line program that can create a GPX file. QGIS will replace the keywords %type, %in,
and %out when it runs the command.
%type will be replaced by -w if you are downloading waypoints, -r if you are downloading routes and -t if
you are downloading tracks. These are command line options that tell GPSBabel which feature type to download.
%in will be replaced by the port name that you choose in the download window and %out will be replaced
by the name you choose for the GPX file that the downloaded data should be stored in. So if you create a device
type with the download command gpsbabel %type -i garmin -o gpx %in %out (this is actually the
download command for the predefined device type ‘Garmin serial’) and then use it to download waypoints from
port /dev/ttyS0 to the file output.gpx, QGIS will replace the keywords and run the command gpsbabel
-w -i garmin -o gpx /dev/ttyS0 output.gpx.
The upload command is the command that is used to upload data to the device. The same keywords are used, but
%in is now replaced by the name of the GPX file for the layer that is being uploaded, and %out is replaced by
the port name.
You can learn more about GPSBabel and it’s available command line options at http://www.gpsbabel.org.
Once you have created a new device type it will appear in the device lists for the download and upload tools.
14.2 Live GPS tracking
To activate Live GPS tracking in QGIS you need to select Settings →
docked window on the left side of the canvas.
GPS information. You will get a new
There are 4 possible screens in this GPS tracking window:
•
GPS position coordinates and for manually entering Vertices and Features.
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•
GPS signal strength of satellite connections.
•
GPS polar screen showing number and polar position of satellites.
•
GPS options screen (see figure_gps_options).
With a plugged in GPS receiver (has to be supported by your operating system) a simple click on [Connect] connects the GPS to QGIS. A second click (now on [Disconnect]) disconnects the GPS-receiver from your computer.
For GNU/Linux gpsd support is integrated to support connection to most GPS receivers. Therefore you first have
to configure gpsd properly to connect QGIS to it.
Warning: If you want to record your position to the canvas you have to create a new vector layer first and
switch it to editable status to be able to record your track.
14.2.1 Position and additional attributes
If the GPS is receiving signals from satellites you will see your position in latitude, longitude and altitude
together with additional attributes.
Figure 14.3: GPS tracking position and additional attributes
14.2.2 GPS signal strength
Here you can see the signal strenght of the satellites you are receiving signals from.
Figure 14.4: GPS tracking signal strength
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14.2.3 GPS polar window
If you want to know where in the sky all the connected satellites are, you have to switch to the polar screen.
You can also see the ID numbers of the satellites you are receiving signals from.
Figure 14.5: GPS tracking polar window
14.2.4 GPS options
In case of connection problems you can switch between:
•
Autodetect
•
Internal,
•
Serial device
•
gpsd (selecting Host, Port and Device your GPS is connected to).
A click on [Connect] again initiates the connection to the GPS receiver.
Figure 14.6: GPS tracking options window
You can activate
Automatically save added features when you are in editing mode. Or you can can activate
Automatically add points to the map canvas with a certain width and color.
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Activating
canvas.
Cursor you can use a slider
to shrink and grow the position cursor on the
Activating
Map centering allows to decide in which way the canvas will be updated. This includes ‘always’,
‘when leaving’ if your recorded coordinates start either to move out of canvas or ‘never’ to keep map extent.
Finally you can activate
logged.
Log file and define a path and a file where log messages about the gps tracking a
If you want to set a feature manually you have to go back to
point].
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Position
and click on [Add Point] or [Add track
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CHAPTER 15
GRASS GIS Integration
The GRASS plugin provides access to GRASS GIS (see GRASS-PROJECT Literature and Web References)
databases and functionalities. This includes visualization of GRASS raster and vector layers, digitizing vector
layers, editing vector attributes, creating new vector layers and analysing GRASS 2D and 3D data with more than
300 GRASS modules.
In this Section we’ll introduce the plugin functionalities and give some examples on managing and working with
GRASS data. Following main features are provided with the toolbar menu, when you start the GRASS plugin, as
described in section Starting the GRASS plugin :
•
Open mapset
•
New mapset
•
Close mapset
•
Add GRASS vector layer
•
Add GRASS raster layer
•
Create new GRASS vector
•
Edit GRASS vector layer
•
Open GRASS tools
•
Display current GRASS region
•
Edit current GRASS region
15.1 Starting the GRASS plugin
To use GRASS functionalities and/or visualize GRASS vector and raster layers in QGIS, you must select and load
the GRASS plugin with the Plugin Manager. Therefore click the menu Plugins →
GRASS and click [OK].
Manage Plugins, select
You can now start loading raster and vector layers from an existing GRASS LOCATION (see section Loading
GRASS raster and vector layers). Or you create a new GRASS LOCATION with QGIS (see section Creating
a new GRASS LOCATION) and import some raster and vector data (see Section Importing data into a GRASS
LOCATION) for further analysis with the GRASS Toolbox (see section The GRASS toolbox).
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15.2 Loading GRASS raster and vector layers
With the GRASS plugin, you can load vector or raster layers using the appropriate button on the toolbar menu.
As an example we use the QGIS alaska dataset (see Section Sample Data). It includes a small sample GRASS
LOCATION with 3 vector layers and 1 raster elevation map.
1. Create a new folder grassdata, download the QGIS alaska dataset qgis_sample_data.zip from
http://download.osgeo.org/qgis/data/ and unzip the file into grassdata.
2. Start QGIS.
3. If not already done in a previous QGIS session, load the GRASS plugin clicking on Plugins →
Plugins and activate
Manage
GRASS. The GRASS toolbar appears in the QGIS main window.
4. In the GRASS toolbar, click the
Open mapset
icon to bring up the MAPSET wizard.
5. For Gisdbase browse and select or enter the path to the newly created folder grassdata.
6. You should now be able to select the LOCATION
alaska and the MAPSET
demo.
7. Click [OK]. Notice that some previously disabled tools in the GRASS toolbar are now enabled.
Add GRASS raster layer
8. Click on
, choose the map name gtopo30 and click [OK]. The elevation layer will
be visualized.
Add GRASS vector layer
9. Click on
, choose the map name alaska and click OK. The alaska boundary vector
layer will be overlayed on top of the gtopo30 map. You can now adapt the layer properties as described
in chapter The Vector Properties Dialog, e.g. change opacity, fill and outline color.
10. Also load the other two vector layers rivers and airports and adapt their properties.
As you see, it is very simple to load GRASS raster and vector layers in QGIS. See following sections for editing
GRASS data and creating a new LOCATION. More sample GRASS LOCATIONs are available at the GRASS
website at http://grass.osgeo.org/download/data.php.
Tip: GRASS Data Loading
If you have problems loading data or QGIS terminates abnormally, check to make sure you have loaded the
GRASS plugin properly as described in section Starting the GRASS plugin.
15.3 GRASS LOCATION and MAPSET
GRASS data are stored in a directory referred to as GISDBASE. This directory often called grassdata, must
be created before you start working with the GRASS plugin in QGIS. Within this directory, the GRASS GIS
data are organized by projects stored in subdirectories called LOCATION. Each LOCATION is defined by its
coordinate system, map projection and geographical boundaries. Each LOCATION can have several MAPSETs
(subdirectories of the LOCATION) that are used to subdivide the project into different topics, subregions, or as
workspaces for individual team members (Neteler & Mitasova 2008 Literature and Web References). In order to
analyze vector and raster layers with GRASS modules, you must import them into a GRASS LOCATION (This
is not strictly true - with the GRASS modules r.external and v.external you can create read-only links
to external GDAL/OGR-supported data sets without importing them. But because this is not the usual way for
beginners to work with GRASS, this functionality will not be described here.).
15.3.1 Creating a new GRASS LOCATION
As an example here is how the sample GRASS LOCATION alaska, which is projected in Albers Equal Area
projection with unit feet was created for the QGIS sample dataset. This sample GRASS LOCATION alaska
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Figure 15.1: GRASS data in the alaska LOCATION
will be used for all examples and exercises in the following GRASS GIS related chapters. It is useful to download
and install the dataset on your computer Sample Data).
1. Start QGIS and make sure the GRASS plugin is loaded.
2. Visualize the alaska.shp Shapefile (see Section Loading a Shapefile) from the QGIS alaska dataset
Sample Data.
3. In the GRASS toolbar, click on the
New mapset
icon to bring up the MAPSET wizard.
4. Select an existing GRASS database (GISDBASE) folder grassdata or create one for the new LOCATION
using a file manager on your computer. Then click [Next].
5. We can use this wizard to create a new MAPSET within an existing LOCATION (see section Adding a new
MAPSET) or to create a new LOCATION altogether. Click on the radio button Create new location (see
figure_grass_location_2).
6. Enter a name for the LOCATION - we used alaska and click [Next].
7. Define the projection by clicking on the radio button
Projection to enable the projection list.
8. We are using Albers Equal Area Alaska (feet) projection. Since we happen to know that it is represented
by the EPSG ID 2964, we enter it in the search box. (Note: If you want to repeat this process for another
LOCATION and projection and haven’t memorized the EPSG ID, click on the
right-hand corner of the status bar (see Section Working with Projections)).
projector
icon in the lower
9. In Filter insert 2964 to select the projection.
10. Click [Next].
11. To define the default region, we have to enter the LOCATION bounds in north, south, east, and west direction. Here we simply click on the button Set current QGIS extent, to apply the extend of the loaded layer
alaska.shp as the GRASS default region extend.
12. Click [Next].
13. We also need to define a MAPSET within our new LOCATION. You can name it whatever you like - we
used demo (When creating a new LOCATION). GRASS automatically creates a special MAPSET called
PERMANENT designed to store the core data for the project, its default spatial extend and coordinate system
definitions (Neteler & Mitasova 2008 Literature and Web References)
14. Check out the summary to make sure it’s correct and click [Finish].
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15. The new LOCATION alaska and two MAPSETs demo and PERMANENT are created. The currently
opened working set is MAPSET demo, as you defined.
16. Notice that some of the tools in the GRASS toolbar that were disabled are now enabled.
Figure 15.2: Creating a new GRASS LOCATION or a new MAPSET in QGIS
If that seemed like a lot of steps, it’s really not all that bad and a very quick way to create a LOCATION. The
LOCATION alaska is now ready for data import (see section Importing data into a GRASS LOCATION). You
can also use the already existing vector and raster data in the sample GRASS LOCATION alaska included in
the QGIS alaska dataset Sample Data and move on to Section The GRASS vector data model.
15.3.2 Adding a new MAPSET
A user has only write access to a GRASS MAPSET he created. This means that besides access to his own MAPSET,
each user can read maps in other user’s MAPSETs, but he can modify or remove only the maps in his own MAPSET.
All MAPSETs include a WIND file that stores the current boundary coordinate values and the currently selected
raster resolution (Neteler & Mitasova 2008 Literature and Web References, see Section The GRASS region tool).
1. Start QGIS and make sure the GRASS plugin is loaded.
2. In the GRASS toolbar, click on the
New mapset
icon to bring up the MAPSET wizard.
3. Select the GRASS database (GISDBASE) folder grassdata with the LOCATION alaska, where we
want to add a further MAPSET, called test.
4. Click [Next].
5. We can use this wizard to create a new MAPSET within an existing LOCATION or to create a new
LOCATION altogether. Click on the radio button Select location (see figure_grass_location_2) and click
[Next].
6. Enter the name text for the new MAPSET. Below in the wizard you see a list of existing MAPSETs and
its owners.
7. Click [Next], check out the summary to make sure it’s all correct and click [Finish].
15.4 Importing data into a GRASS LOCATION
This Section gives an example how to import raster and vector data into the alaska GRASS LOCATION provided
by the QGIS alaska dataset. Therefore we use a landcover raster map landcover.img and a vector GML File
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lakes.gml from the QGIS alaska dataset Sample Data.
1. Start QGIS and make sure the GRASS plugin is loaded.
2. In the GRASS toolbar, click the
Open MAPSET
icon to bring up the MAPSET wizard.
3. Select as GRASS database the folder grassdata in the QGIS alaska dataset, as LOCATION alaska,
as MAPSET demo and click [OK].
4. Now click the
appears.
Open GRASS tools
icon. The GRASS Toolbox (see section The GRASS toolbox) dialog
5. To import the raster map landcover.img, click the module r.in.gdal in the Modules Tree tab. This
GRASS module allows to import GDAL supported raster files into a GRASS LOCATION. The module
dialog for r.in.gdal appears.
6. Browse to the folder raster in the QGIS alaska dataset and select the file landcover.img.
7. As raster output name define landcover_grass and click [Run]. In the Output tab you see
the currently running GRASS command r.in.gdal -o input=/path/to/landcover.img
output=landcover_grass.
8. When it says Succesfully finished click [View output]. The landcover_grass raster layer is now
imported into GRASS and will be visualized in the QGIS canvas.
9. To import the vector GML file lakes.gml, click the module v.in.ogr in the Modules Tree tab. This
GRASS module allows to import OGR supported vector files into a GRASS LOCATION. The module dialog
for v.in.ogr appears.
10. Browse to the folder gml in the QGIS alaska dataset and select the file lakes.gml as OGR file.
11. As vector output name define lakes_grass and click [Run]. You don’t have to care about the other
options in this example. In the Output tab you see the currently running GRASS command v.in.ogr -o
dsn=/path/to/lakes.gml output=lakes_grass.
12. When it says Succesfully finished click [View output]. The lakes_grass vector layer is now imported
into GRASS and will be visualized in the QGIS canvas.
15.5 The GRASS vector data model
It is important to understand the GRASS vector data model prior to digitizing.
In general, GRASS uses a topological vector model.
This means that areas are not represented as closed polygons, but by one or more boundaries. A boundary between
two adjacent areas is digitized only once, and it is shared by both areas. Boundaries must be connected and closed
without gaps. An area is identified (and labeled) by the centroid of the area.
Besides boundaries and centroids, a vector map can also contain points and lines. All these geometry elements
can be mixed in one vector and will be represented in different so called ‘layers’ inside one GRASS vector map.
So in GRASS a layer is not a vector or raster map but a level inside a vector layer. This is important to distinguish
carefully (Although it is possible to mix geometry elements, it is unusual and even in GRASS only used in special
cases such as vector network analysis. Normally you should prefere to store different geometry elements in
different layers.).
It is possible to store several ‘layers’ in one vector dataset. For example, fields, forests and lakes can be stored in
one vector. Adjacent forest and lake can share the same boundary, but they have separate attribute tables. It is also
possible to attach attributes to boundaries. For example, the boundary between lake and forest is a road, so it can
have a different attribute table.
The ‘layer’ of the feature is defined by ‘layer’ inside GRASS. ‘Layer’ is the number which defines if there are
more than one layer inside the dataset, e.g. if the geometry is forest or lake. For now, it can be only a number, in
the future GRASS will also support names as fields in the user interface.
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Attributes can be stored inside the GRASS LOCATION as DBase or SQLITE3 or in external database tables, for
example PostgreSQL, MySQL, Oracle, etc.
Attributes in database tables are linked to geometry elements using a ‘category’ value.
‘Category’ (key, ID) is an integer attached to geometry primitives, and it is used as the link to one key column in
the database table.
Tip: Learning the GRASS Vector Model
The best way to learn the GRASS vector model and its capabilities is to download one of the many GRASS
tutorials where the vector model is described more deeply. See http://grass.osgeo.org/gdp/manuals.php for more
information, books and tutorials in several languages.
15.6 Creating a new GRASS vector layer
Create new GRASS vector
To create a new GRASS vector layer with the GRASS plugin click the
toolbar icon. Enter
a name in the text box and you can start digitizing point, line or polygon geometries, following the procedure
described in Section Digitizing and editing a GRASS vector layer.
In GRASS it is possible to organize all sort of geometry types (point, line and area) in one layer, because GRASS
uses a topological vector model, so you don’t need to select the geometry type when creating a new GRASS vector.
This is different from Shapefile creation with QGIS, because Shapefiles use the Simple Feature vector model (see
Section Creating a new Vector layer).
Tip: Creating an attribute table for a new GRASS vector layer
If you want to assign attributes to your digitized geometry features, make sure to create an attribute table with
columns before you start digitizing (see figure_grass_digitizing_5).
15.7 Digitizing and editing a GRASS vector layer
Edit GRASS vector layer
The digitizing tools for GRASS vector layers are accessed using the
icon on the toolbar.
Make sure you have loaded a GRASS vector and it is the selected layer in the legend before clicking on the edit
tool. Figure figure_grass_digitizing_2 shows the GRASS edit dialog that is displayed when you click on the edit
tool. The tools and settings are discussed in the following sections.
Tip: Digitizing polygons in GRASS
If you want to create a polygon in GRASS, you first digitize the boundary of the polygon, setting the mode to ‘No
category’. Then you add a centroid (label point) into the closed boundary, setting the mode to ‘Next not used’.
The reason is, that a topological vector model links attribute information of a polygon always to the centroid and
not to the boundary.
Toolbar
In figure_grass_digitizing_1 you see the GRASS digitizing toolbar icons provided by
GRASS plugin.
Table table_grass_digitizing_1 explains the available functionalities.
the
Figure 15.3: GRASS Digitizing Toolbar
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Icon
Tool
Purpose
New Point
Digitize new point
New Line
Digitize new line
New
Boundary
Digitize new boundary (finish by selecting new tool)
New
Centroid
Digitize new centroid (label existing area)
Move vertex
Move one vertex of existing line or boundary and identify new position
Add vertex
Add a new vertex to existing line
Delete vertex
Delete vertex from existing line (confirm selected vertex by another click)
Move
element
Move selected boundary, line, point or centroid and click on new position
Split line
Split an existing line to 2 parts
Delete
element
Delete existing boundary, line, point or centroid (confirm selected element by another
click)
Edit
attributes
Edit attributes of selected element (note that one element can represent more features,
see above)
Close
Close session and save current status (rebuilds topology afterwards)
Table GRASS Digitizing 1: GRASS Digitizing Tools
Category Tab
The Category tab allows you to define the way in which the category values will be assigned to a new geometry
element.
Figure 15.4: GRASS Digitizing Category Tab
• Mode: what category value shall be applied to new geometry elements.
– Next not used - apply next not yet used category value to geometry element.
– Manual entry - manually define the category value for the geometry element in the ‘Category’-entry
field.
– No category - Do not apply a category value to the geometry element. This is e.g. used for area
boundaries, because the category values are connected via the centroid.
• Category - A number (ID) is attached to each digitized geometry element. It is used to connect each
geometry element with its attributes.
• Field (layer) - Each geometry element can be connected with several attribute tables using different GRASS
geometry layers. Default layer number is 1.
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Tip: Creating an additional GRASS ‘layer’ with QGIS
If you would like to add more layers to your dataset, just add a new number in the ‘Field (layer)’ entry box and
press return. In the Table tab you can create your new table connected to your new layer.
Settings Tab
The Settings tab allows you to set the snapping in screen pixels. The threshold defines at what distance new points
or line ends are snapped to existing nodes. This helps to prevent gaps or dangles between boundaries. The default
is set to 10 pixels.
Figure 15.5: GRASS Digitizing Settings Tab
Symbology Tab
The Symbology tab allows you to view and set symbology and color settings for various geometry types and their
topological status (e.g. closed / opened boundary).
Figure 15.6: GRASS Digitizing Symbolog Tab
Table Tab
The Table tab provides information about the database table for a given ‘layer’. Here you can add new columns to
an existing attribute table, or create a new database table for a new GRASS vector layer (see Section Creating a
new GRASS vector layer).
Tip: GRASS Edit Permissions
You must be the owner of the GRASS MAPSET you want to edit. It is impossible to edit data layers in a MAPSET
that is not yours, even if you have write permissions.
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Figure 15.7: GRASS Digitizing Table Tab
15.8 The GRASS region tool
The region definition (setting a spatial working window) in GRASS is important for working with raster layers.
Vector analysis is by default not limited to any defined region definitions. But all newly-created rasters will have
the spatial extension and resolution of the currently defined GRASS region, regardless of their original extension
and resolution. The current GRASS region is stored in the $LOCATION/$MAPSET/WIND file, and it defines
north, south, east and west bounds, number of columns and rows, horizontal and vertical spatial resolution.
It is possible to switch on/off the visualization of the GRASS region in the QGIS canvas using the
Display current GRASS region
button.
Edit current GRASS region
With the
icon you can open a dialog to change the current region and the symbology of
the GRASS region rectangle in the QGIS canvas. Type in the new region bounds and resolution and click [OK].
It also allows to select a new region interactively with your mouse on the QGIS canvas. Therefore click with the
left mouse button in the QGIS canvas, open a rectangle, close it using the left mouse button again and click [OK].
The GRASS module g.region provide a lot more parameters to define an appropriate region extend and resolution for your raster analysis. You can use these parameters with the GRASS Toolbox, described in Section The
GRASS toolbox.
15.9 The GRASS toolbox
Open GRASS Tools
The
box provides GRASS module functionalities to work with data inside a selected GRASS
LOCATION and MAPSET. To use the GRASS toolbox you need to open a LOCATION and MAPSET where you
have write-permission (usually granted, if you created the MAPSET). This is necessary, because new raster or
vector layers created during analysis need to be written to the currently selected LOCATION and MAPSET.
The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 330) GRASS modules
through a command line interface. To offer a more user friendly working environment, about 200 of the available
GRASS modules and functionalities are also provided by graphical dialogs within the GRASS plugin Toolbox.
15.9.1 Working with GRASS modules
The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 300) GRASS modules in
a command line interface. To offer a more user friendly working environment, about 200 of the available GRASS
modules and functionalities are also provided by graphical dialogs.
A complete list of GRASS modules available in the graphical Toolbox in QGIS version 1.8.0 is available in the
GRASS wiki ( http://grass.osgeo.org/wiki/GRASS-QGIS_relevant_module_list).
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Figure 15.8: GRASS Toolbox and Module Tree
It is also possible to customize the GRASS Toolbox content. This procedure is described in Section Customizing
the GRASS Toolbox.
As shown in figure_grass_toolbox_1 , you can look for the appropriate GRASS module using the thematically
grouped Modules Tree or the searchable Modules List tab.
Clicking on a graphical module icon a new tab will be added to the toolbox dialog providing three new sub-tabs
Options, Output and Manual.
Options
The Options tab provides a simplified module dialog where you can usually select a raster or vector layer visualized
in the QGIS canvas and enter further module specific parameters to run the module.
The provided module parameters are often not complete to keep the dialog clear. If you want to use further module
parameters and flags, you need to start the GRASS Shell and run the module in the command line.
A new feature in QGIS 1.8.0 is the support for a show advanced options button below the simplified module dialog
in the Options tab. At the moment it is only added to the module v.in.ascii as an example use, but will probably
be part of more / all modules in the GRASS toolbox in future versions of QGIS. This allows to use the complete
GRASS module options without the need to switch to the GRASS Shell.
Output
The Output tab provides information about the output status of the module. When you click the [Run] button, the
module switches to the Output tab and you see information about the analysis process. If all works well, you will
finally see a Successfully finished message.
Manual
The Manual tab shows the HTML help page of the GRASS module. You can use it to check further module
parameters and flags or to get a deeper knowledge about the purpose of the module. At the end of each module
manual page you see further links to the Main Help index, the Thematic index and the Full index.
These links provide the same information as if you use the module g.manual.
Tip: Display results immediately
If you want to display your calculation results immediately in your map canvas, you can use the ‘View Output’
button at the bottom of the module tab.
15.9.2 GRASS module examples
The following examples will demonstrate the power of some of the GRASS modules.
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Figure 15.9: GRASS Toolbox Module Options
Figure 15.10: GRASS Toolbox Module Output
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Figure 15.11: GRASS Toolbox Module Manual
Creating contour lines
The first example creates a vector contour map from an elevation raster (DEM). Assuming you have the Alaska
LOCATION set up as explained in Section Importing data into a GRASS LOCATION.
• First open the location by clicking the
Open mapset
button and choosing the Alaska location.
• Now load the gtopo30 elevation raster by clicking
raster from the demo location.
• Now open the Toolbox with the
Open GRASS tools
Add GRASS raster layer
and selecting the gtopo30
button.
• In the list of tool categories double click Raster → Surface Management → Generate vector contour lines.
• Now a single click on the tool r.contour will open the tool dialog as explained above Working with GRASS
modules. The gtopo30 raster should appear as the Name of input raster.
• Type into the Increment between Contour levels
intervals of 100 meters.)
the value 100. (This will create contour lines at
• Type into the Name for output vector map the name ctour_100.
• Click [Run] to start the process. Wait for several moments until the message Successfully finished
appears in the output window. Then click [View Output] and [close].
Since this is a large region, it will take a while to display. After it finishes rendering, you can open the layer
properties window to change the line color so that the contours appear clearly over the elevation raster, as in The
Vector Properties Dialog.
Next zoom in to a small mountainous area in the center of Alaska. Zooming in close you will notice that the
contours have sharp corners. GRASS offers the v.generalize tool to slightly alter vector maps while keeping their
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overall shape. The tool uses several different algorithms with different purposes. Some of the algorithms (i.e.
Douglas Peuker and Vertex reduction) simplify the line by removing some of the vertices. The resulting vector
will load faster. This process will be used when you have a highly detailed vector, but you are creating a very
small scale map, so the detail is unnecessary.
Tip: The simplify tool
Note that the QGIS fTools plugin has a Simplify geometries → tool that works just like the GRASS v.generalize
Douglas-Peuker algorithm.
However, the purpose of this example is different. The contour lines created by r.contour have sharp angles
that should be smoothed. Among the v.generalize algorithms there is Chaikens which does just that (also Hermite
splines). Be aware that these algorithms can add additional vertices to the vector, causing it to load even more
slowly.
• Open the GRASS toolbox and double click the categories Vector → Develop map → Generalization, then
click on the v.generalize module to open its options window.
• Check that the ‘ctour_100’ vector appears as the Name of input vector.
• From the list of algorithms choose Chaiken’s. Leave all other options at their default, and scroll down to the
last row to enter in the field Name for output vector map ‘ctour_100_smooth’, and click [Run].
• The process takes several moments. Once Successfully finished appears in the output windows,
click [View output] and then [close].
• You may change the color of the vector to display it clearly on the raster background and to contrast with
the original contour lines. You will notice that the new contour lines have smoother corners than the original
while staying faithful to the original overall shape.
Figure 15.12: GRASS module v.generalize to smooth a vector map
Tip: Other uses for r.contour
The procedure described above can be used in other equivalent situations. If you have a raster map of precipitation
data, for example, then the same method will be used to create a vector map of isohyetal (constant rainfall) lines.
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Creating a Hillshade 3D effect
Several methods are used to display elevation layers and give a 3D effect to maps. The use of contour lines as
shown above is one popular method often chosen to produce topographic maps. Another way to display a 3D
effect is by hillshading. The hillshade effect is created from a DEM (elevation) raster by first calculating the slope
and aspect of each cell, then simulating the sun’s position in the sky and giving a reflectance value to each cell.
Thus you get sun facing slopes lighted and the slopes facing away from the sun (in shadow) are darkened.
• Begin this example by loading the gtopo30 elevation raster. Start the GRASS toolbox and under the
Raster category double click to open Spatial analysis → Terrain analysis.
• Then click r.shaded.relief to open the module.
• Change the azimuth angle
270 to 315.
• Enter gtopo30_shade for the new hillshade raster, and click [Run].
• When the process completes, add the hillshade raster to the map. You should see it displayed in grayscale.
• To view both the hill shading and the colors of the gtopo30 together shift the hillshade map below the
gtopo30 map in the table of contents, then open the Properties window of gtopo30, switch to the
transparency tab and set its transparency level to about 25%.
You should now have the gtopo30 elevation with its colormap and transparency setting displayed above the
grayscale hillshade map. In order to see the visual effects of the hillshading, turn off the gtopo30_shade map,
then turn it back on.
Using the GRASS shell
The GRASS plugin in QGIS is designed for users who are new to GRASS, and not familiar with all the modules
and options. As such, some modules in the toolbox do not show all the options available, and some modules do
not appear at all. The GRASS shell (or console) gives the user access to those additional GRASS modules that
do not appear in the toolbox tree, and also to some additional options to the modules that are in the toolbox with
the simplest default parameters. This example demonstrates the use of an additional option in the r.shaded.relief
module that was shown above.
Figure 15.13: The GRASS shell, r.shaded.relief module
The module r.shaded.relief can take a parameter zmult which multiplies the elevation values relative to the X-Y
coordinate units so that the hillshade effect is even more pronounced.
• Load the gtopo30 elevation raster as above, then start the GRASS toolbox and click on the
GRASS shell.
In the shell window type the command r.shaded.relief map=gtopo30
shade=gtopo30_shade2 azimuth=315 zmult=3 and press [Enter].
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• After the process finishes shift to the Browse tab and double click on the new gtopo30_shade2 raster to
display in QGIS.
• As explained above, shift the shaded relief raster below the gtopo30 raster in the Table of Contents, then
check transparency of the colored gtopo30 layer. You should see that the 3D effect stands out more strongly
compared to the first shaded relief map.
Figure 15.14: Displaying shaded relief created with the GRASS module r.shaded.relief
Raster statistics in a vector map
The next example shows how a GRASS module can aggregate raster data and add columns of statistics for each
polygon in a vector map.
• Again using the Alaska data, refer to Importing data into a GRASS LOCATION to import the trees shapefile
from the shapefiles directory into GRASS.
• Now an intermediary step is required: centroids must be added to the imported trees map to make it a
complete GRASS area vector (including both boundaries and centroids).
• From the toolbox choose Vector → Manage features, and open the module v.centroids.
• Enter as the output vector map ‘forest_areas’ and run the module.
• Now load the forest_areas vector and display the types of forests - deciduous, evergreen, mixed in different colors: In the layer Properties window, Symbology tab, choose from Legend type
‘Unique value’ and set the Classification field to ‘VEGDESC’. (Refer to the explanation of the symbology
tab :ref:sec_symbology in the vector section).
• Next reopen the GRASS toolbox and open Vector → Vector update by other maps.
• Click on the v.rast.stats module. Enter gtopo30, and forest_areas.
• Only one additional parameter is needed: Enter column prefix elev, and click [run]. This is a computationally heavy operation which will run for a long time (probably up to two hours).
• Finally open the forest_areas attribute table, and verify that several new columns have been added
including elev_min, elev_max, elev_mean etc. for each forest polygon.
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15.9.3 Working with the GRASS LOCATION browser
Another useful feature inside the GRASS Toolbox is the GRASS LOCATION browser. In figure_grass_module_7
you can see the current working LOCATION with its MAPSETs.
In the left browser windows you can browse through all MAPSETs inside the current LOCATION. The right
browser window shows some meta information for selected raster or vector layers, e.g. resolution, bounding box,
data source, connected attribute table for vector data and a command history.
Figure 15.15: GRASS LOCATION browser
The toolbar inside the Browser tab offers following tools to manage the selected LOCATION:
•
Add selected map to canvas
•
Copy selected map
•
Rename selected map
•
Delete selected map
•
Set current region to selected map
•
Refresh browser window
The
Rename selected map and
Delete selected map only work with maps inside your currently selected
MAPSET. All other tools also work with raster and vector layers in another MAPSET.
15.9.4 Customizing the GRASS Toolbox
Nearly all GRASS modules can be added to the GRASS toolbox. A XML interface is provided to parse the pretty
simple XML files which configures the modules appearance and parameters inside the toolbox.
A sample XML file for generating the module v.buffer (v.buffer.qgm) looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE qgisgrassmodule SYSTEM "http://mrcc.com/qgisgrassmodule.dtd">
<qgisgrassmodule label="Vector buffer" module="v.buffer">
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<option key="input" typeoption="type" layeroption="layer" />
<option key="buffer"/>
<option key="output" />
</qgisgrassmodule>
The parser reads this definition and creates a new tab inside the toolbox when you select the module. A more
detailed description for adding new modules, changing the modules group, etc. can be found on the QGIS wiki at
http://hub.qgis.org/projects/quantum-gis/wiki/Adding_New_Tools_to_the_GRASS_Toolbox
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CHAPTER 16
OpenStreetMap
In recent years, the OpenStreetMap project has gained popularity because in many countries no free geodata such
as digital roadmaps are available. The objective of the OSM project is to create a free editable map of the world
from GPS data, aerial photography or from local knowledge. To support this objective, QGIS provides a plugin
that enables its users to work with OSM data.
The OpenStreetMap plugin, a core QGIS plugin, provides the basic functionalities for OSM data manipulation;
this includes data loading, importing, saving, downloading, editing and uploading data back to the OpenStreetMap
server. While implementing the OSM plugin an inspiration was taken from existing OSM data editors. The
purpose was to combine their functionalities to get the best possible result.
The following section gives a brief introduction to principles of the OSM project.
Parts of the following paragraphs are copied from the OpenStreetMap web site at http://www.openstreetmap.org.
16.1 The OpenStreetMap project
OpenStreetMap is a project to create a free editable map of the world. The maps are created using data from
portable GPS devices, aerial photography, other free sources or simply from local knowledge. The project was
started because most maps have legal or technical restrictions on their use, restricting people from using them in
creative, productive, or unexpected ways. Both rendered images and the vector dataset of OSM are available for
download under a Creative Commons Attribution ShareAlike 2.0 license.
OpenStreetMap was inspired by sites such as Wikipedia - the map display (see Figure_OpenStreetMap_1 ) features
a prominent Edit tab and a full revision history is maintained. Registered users can upload GPS track logs and edit
the vector data using the given editing tools.
OSM data primitive is an object class that can be stored via the API in the server. The three supported types of
data are: Node, Way and Relation.
• A node is a latitude/longitude pair of coordinates. It is used as building a block for other features and as a
feature itself (Points Of Interest), if they are tagged as required.
• A way is a list of at least two nodes that describe a linear feature such as a street, or similar. Nodes can be
members of multiple ways.
• A relation is a group of zero or more primitives with associated roles. It is used to specify relationships
between objects, and may also model an abstract object.
Several different logical features in a common map ‘Point Of Interest’, ‘Street’, ‘Tram Line’, ‘Bus Stop’ etc.) are
defined by these primitives. Map features are well-known in the OSM community and are stored as tags, based on
a key and a value. OSM is usually distributed in XML format. XML payload is used for the communication with
the OSM server as well.
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Figure 16.1: OpenStreetMap data in the web
16.2 QGIS - OSM Connection
The first part of this section describes how OSM data primitives are displayed in QGIS vector layers. As previously
mentioned, OSM data consists of Nodes, Ways and Relations. In QGIS, they are displayed in three different layer
types: Point layer, Line layer and Polygon layer. It is not possible to remove any of these layers and work with the
other ones.
• A Point layer displays all features of type Node that stands alone. That means that only Nodes that are not
included in any Way belongs to the Point layer.
• A Line layer displays those OSM features of type Way that are not closed. That means, none of these Ways
starts and ends with the same Node.
• A Polygon layer displays all Ways that are not included in Line layer.
OpenStreetMap has one more data primitive in addition to the three mentioned above. This is called Relation.
There is purposely no vector layer to display Relations. A Relation defines a connection between any number of
data primitives. After a Point, Line or Polygon is identified on a map, the plugin shows a list of all relations which
the identified feature is part of.
It was challenging to design the connection between OSM data and the standard QGIS editing tools. These tools
are made to edit a single vector layer at a time, no matter of what feature types it displays. This means that if OSM
data are loaded to QGIS through the plugin, you could (theoretically) edit the Point layer, Line layer or Polygon
layer with these standard tools separately.
A Line layer consists of two different types of OSM features, Ways and Nodes. In OSM format, a Way is composed
of Nodes. If you start editing a Line layer and change the shape of some line, your action affects not only the
OSM Way, but also the OSM Nodes that are part of it.
QGIS standard editing tools cannot tell the OSM provider, which members of which line has changed and how.
It can tell only what’s the new geometry of which line, and that’s not enough to propagate changes to the OSM
database correctly. The Line layer does also not know the identifiers of the line members. The same problem
occurs when you try to edit the Polygon layer.
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For this reason, the OSM plugin need its own tools for editing OSM data. While they are used, the OSM layers
can be changed correctly. The Plugin editing tools consists of tools for Point, Line, Polygon and Relation creation,
deletion and moving.
Note: To create a connection between the OSM plugin and standard editing tools, changes in QuantumGIS core
code would be necessary.
16.3 Installation
The OpenStreetMap plugin is a core plugin inside QGIS. The ‘OpenStreetMap’ plugin can be selected in the
Plugin Manager as described in section Loading a QGIS Core Plugin.
16.4 Basic user interface
The first time the OSM plugin is started (and after the first data are loaded), several new OSM plugin icons appear
in the QGIS toolbar menu together with new dock windows as shown in figure_OpenStreetMap_2.
Figure 16.2: OSM plugin user interface
16.4.1 OSM Features widget
The OSM Feature widget helps to identify OSM features. It shows basic information on the feature type and
identifier as well as information on who has changed a feature, and when. The OSM Feature widget also provides
all editing tools (in the top part of it). More information on those tools can be found in the sections below. The
widget is initially disabled. It activates itself after successful loading some OSM data.
16.4.2 OSM Undo/Redo widget
This Undo/Redo widget is used to undo and redo edit actions. It consists not only a classic Undo and Redo button,
but also shows a list with a brief description of the edit actions that were done. The OSM Undo/Redo widget is
initially closed. You can show it using a button on the OSM Feature widget.
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16.4.3 Toolbar menu icons
Load OSM from file
is used to load data from a special OpenStreetMap XML file.
Show/Hide OSM Feature Manager
is used to show or hide the OSM Feature widget. The OSM Feature widget is a panel
that helps with OSM feature identification and with OSM data editing.
Download OSM data
Upload OSM data
is used to download data from the OpenStreetMap server.
is used to upload changes (on current data).
Import data from a layer
is used to import data from a vector layer. At least one vector layer must be loaded and
current OSM data must be selected.
Save OSM to file
is used to save OSM data back to an XML file.
More detailed information on all the widgets, buttons and dialogs can be found in appropriate sections of this
plugin section according to their functionality (editing, identification, etc.).
16.5 Loading OSM data
The first action that should be done after starting the OSM Plugin is opening data from an OSM file. OSM data
can be import as shapefile or downloaded directly from the OpenStreetMap server. Here we are focusing on the
first mentioned method.
Load OSM from file
To load data from a file use the
icon. If there is no such button, maybe someone disabled
OpenStreetMap toolbar in your QGIS installation. You can enable it again selecting Settings → Toolbars →
OpenStreetMap.
Figure 16.3: Load OSM data dialog
The purpose of its elements is explained below.
OpenStreetMap file to load: Click on the
button to select the file:.osm file you want to load data from.
Add columns for tags: This option determines a connection between OSM and QGIS data. Each feature of OSM
data has some tags (pairs of key and value), that define the feature properties. Each feature of a QGIS vector layer
also has its attributes (key and value). With this option you can define which properties of OSM objects should be
visible when displaying detailed information about QGIS features.
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Replace current data: Checking this option means that new data should replace current data the user is working
with. Layers of current data will be removed and new ones will be loaded. When loading OSM data for the first
time, this option is not active, because there is nothing to replace.
Use custom renderer: This option determines how many details of the map will be used. There are three predefined OSM styles for map displaying. Use ‘Small scale’ if you want to view OSM data at low level, to see all
details and to edit something. If not you can use ‘Medium scale’ or ‘Large scale’. QGIS 1.8.0 doesn’t support
changing the renderer style dynamically.
Click [OK] to load your data. If this is the first time the OSM file is loaded, the plugin must first parse the database.
This may take few seconds or minutes - it depends on the amount of loaded data.
16.6 Viewing OSM data
Identify feature
After the OSM data are loaded, you can identify map features using the appropriate tool. Use the
button on the top-left of the OSM Feature widget. Using this tool you can easily explore all map objects. When
the mouse cursor is placed over an object, you can see all information on it directly in the OSM Feature widget.
There is also a dynamic rubberband displayed on the map so that the user is able to determine which feature is
currently identified.
The Properties tab of the widget contains of all feature tags. Clicking on the Relation tab shows you a list of all
relations connected with identified feature.
If you want to hold a feature for a while to be able to read its properties and relations, move the mouse cursor at the
same time, try left-clicking while you are over the feature. Identification process will stop until next left-clicking.
Sometimes there is more than one feature at a point where left-clicking was performed. This happens especially
when clicking on cross-roads or if you did not zoom enough into the map. In this situation only one of such
features is identified (and marked with the rubberband) but the plugin remembers all of them. Then (still in the
pause mode) you can cycle through the identified features by right-clicking.
16.7 Editing basic OSM data
‘Basic data’ in this context means non-relational OSM features - nodes and ways. If you prefer to examine how
to perform relational editing, skip this section and move on to the next one.
Basic data editing is a key part of the OSM Plugin. You can change the property, position or shape of any existing
basic feature. You can remove features or add new ones. All changes on nodes and ways are remembered by
Undo/Redo all changes can be easily uploaded to the OpenStreetMap server.
16.7.1 Changing feature tags
Changing the property/tag of an OSM feature can be done directly in the table of feature tags. The Tags table of
basic features can be found on the OSM Feature widget. Don’t forget to identify feature first.
If you want to change a tag value, just double-click in the appropriate row of column ‘Value’ and type, or select a
new value. If you want to remove a tag, click in the relevant row, then use the button
right bottom under the table.
Remove selected tags
on the
To add new tags just type the key and value into the last row of the table where ‘<next tag value>’ is written.
Notice that you cannot change the key of an existing tag pair. Conveniently, there are some combo boxes of all
existing tag keys and their typical values.
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Figure 16.4: Changing an OSM feature tag
16.7.2 Point creation
Create point
button on the OSM Feature widget. To create some points, just click on
For point creation there is a
the button and start clicking on the map. If your cursor is over some map feature, the feature is marked/identified
immediately. If you click on the map when a line or polygon is marked, a new point is created directly on such
line or polygon as its new member. If your cursor is over an existing point, a new point cannot be created. In such
case the OSM plugin will show following message:
Figure 16.5: OSM point creation message
The mechanism of helping a user to hit the line or polygon is called snapping and is enabled by default. If you
want to create a point very close to some line (but not on it) you must disable snapping by holding the Ctrl key
first.
16.7.3 Line creation
Create Line
For line creation, there is a
button on the OSM Feature widget. To create a line just click the button
and start left-clicking on the map. Each of your left-clicks is remembered as a vertex of the new line. Line creation
ends when the first right-click is performed. The new line will immediately appear on the map.
Note: A Line with less than two members cannot be created. In such case the operation is ignored.
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Snapping is performed to all map vertices - points from the Point vector layer and all Line and Polygon members.
Snapping can be disabled by holding the Ctrl key.
16.7.4 Polygon creation
Create polygon
button on the OSM Feature widget. To create a polygon just click
For polygon creation there is a
the button and start left-clicking on the map. Each of your left-clicks is remembered as a member vertex of the
new polygon. The Polygon creation ends when first right-click is performed. The new polygon will immediately
appear on the map. Polygon with less than three members cannot be created. In such case operation is ignored.
Snapping is performed to all map vertexes - points (from Point vector layer) and all Line and Polygon members.
Snapping can be disabled by holding the Ctrl key.
16.7.5 Map feature moving
Move feature
If you want to move a feature (no matter what type) please use the
button from the OSM Feature
widget menu. Then you can browse the map (features are identified dynamically when you go over them) and
click on the feature you want to move. If a wrong feature is selected after your click, don’t move it from the place.
Repeat right-clicking until the correct feature is identified. When selection is done and you move the cursor, you
are no more able to change your decision what to move. To confirm the move, click on the left mouse button. To
cancel a move, click another mouse button.
If you are moving a feature that is connected to another features, these connections won’t be damaged. Other
features will just adapt themselves to a new position of a moved feature.
Snapping is also supported in this operation, this means:
• When moving a standalone (not part of any line/polygon) point,snapping to all map segments and vertices
is performed.
• When moving a point that is a member of some lines/polygons,snapping to all map segments and vertices
is performed, except for vertices of point parents.
• When moving a line/polygon, snapping to all map vertices is performed. Note that the OSM Plugin tries
to snap only to the 3 closest-to-cursor vertices of a moved line/polygon, otherwise the operation would by
very slow. Snapping can be disabled by holding Ctrl key during the operation.
16.7.6 Map feature removing
If you want to remove a feature, you must identify it first. To remove an identified feature, use the
button on the OSM Feature widget. When removing a line/polygon, the line/polygon itself is
deleted, so are all its member points that doesn’t belong to any other line/polygon.
Remove this feature
When removing a point that is member of some lines/polygons, the point is deleted and the geometries of parent
lines/polygons are changed. The new parent geometry has less vertices than the old one.
If the parent feature was a polygon with three vertexes, its new geometry has only two vertexes. And because
there cannot exist polygon with only two vertices, as described above, the feature type is automatically changed
to Line.
If the parent feature was a line with two vertexes, its new geometry has only one vertex. And because there cannot
exist a line with only one vertex, the feature type is automatically changed to Point.
16.8 Editing relations
Thanks to existence of OSM relations we can join OSM features into groups and give them common properties in such way we can model any possible map object: borders of a region (as group of ways and points), routes of a
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bus, etc. Each member of a relation has its specific role. There is a pretty good support for OSM Relations in our
plugin. Let’s see how to examine, create, update or remove them.
16.8.1 Examining relation
If you want to see relation properties, first identify one of its members. After that open the Relations tab on the
OSM Feature widget. At the top of the tab you can see a list of all relations the identified feature is part of. Please
choose the one you want to examine and look at its information below. In the first table called ‘Relation tags’ you
find the properties of the selected relation. In the table called ‘Relation members’ you see brief information on the
relation members. If you click on a member, the plugin will make a rubberband on it in the map.
16.8.2 Relation creation
There are 2 ways to create a relation:
1. You can use the
Create relation
button on OSM Feature widget.
Add relation
2. You can create it from the Relation tab of OSM Feature widget using the
button.
In both cases a dialog will appear. For the second case, the feature that is currently identified is automatically
considered to be the first relation member, so the dialog is prefilled a little. When creating a relation, please select
its type first. You can select one of predefined relation types or write your own type. After that fill the relation
tags and choose its members.
Generate tags
If you have already selected a relation type, try using the
button. It will generate typical tags to
your relation type. Then you are expected to enter values to the keys. Choosing relation members can be done
either by writing member identifiers, types and roles or using the
Identify
tool and clicking on map.
Finally when type, tags and members are chosen, the dialog can be submitted. In such case the plugin creates a
new relation for you.
16.8.3 Changing relation
If you want to change an existing relation, identify it first (follow steps written above in Section Examining
Edit relation
relation). After that click on the
button. You will find it on the OSM Feature widget. A new dialog
appears, nearly the same as for the ‘create relation’ action. The dialog is pre-filled with information on given
relations. You can change relation tags, members or even its type. After submitting the dialog your changes will
be committed.
16.9 Downloading OSM data
Download OSM data
To download data from OpenStreetMap server click on the
button. If there is no such button,
the OSM toolbar may be disabled in your QGIS instalation. You can enable it again at Settings → Toolbars →
OpenStreetMap . After clicking the button a dialog occurs and provides following functionalities:
Extent: Specifies an area to download data from intervals of latitude and longitude degrees. Because there is some
restriction of OpenStreetMap server on how much data can be downloaded, the intervals must not be too wide.
More detailed info on extent specification can is shown after clicking the
Help
button on the right.
Download to: Here you are expected to write a path to the file where data will be stored. If you can’t remember
the structure of your disk, don’t panic. The browse button
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Figure 16.6: OSM download dialog
Open data automatically after download: Determines, if the download process should be followed by loading
the data process or not. If you prefer not to load data now, you can do it later by using the
button.
Load OSM from file
Open data automatically after download is checked.
Replace current data: This option is active only if
Checking this option means that downloaded data should replace current data we are working with now. Layers of
the current data will be removed and new ones will be loaded. When starting QGIS and downloading OSM data
for the first time, this option is initially inactive, because there is nothing to replace.
Use custom renderer: This option is active only if the
Open data automatically after download checkbox
is checked. It determines how many details will be in the map. There are three predefined OSM styles for map
displaying. Use ‘Small scale’ if you want to view OSM data at low level, to see all details and to edit something.
If not you can use ‘Medium scale’ or ‘Large scale’. QGIS 1.8.0 does not support changing the renderer style
dynamically.
Click the [Download] button to start the download process.
A progress dialog will continuously inform you about how much of data is already downloaded. When an error
occurs during the download process, a dialog tells you why. When action finishes successfully both the progress
dialog and download dialog will close themselves.
16.10 Uploading OSM data
Note that the upload is always done on current OSM data. Before opening the OSM Upload dialog, please be sure
that you really have the right active layer with OSM data.
Upload OSM data
To upload current data to the OSM server click on the
button. If there is no such button, OSM
toolbar in your QGIS installation is disabled. You can enable it again in Settings → Toolbars → OpenStreetMap .
After clicking the [Upload] button a new dialog will appear.
At the top of the dialog you can check, if you are uploading the correct data. There is a short name of a current
database. In the table you find information on how many changes will be uploaded. Statistics are displayed
separately for each feature type.
In the ‘Comment on your changes’ box you can write brief information on meaning of your upload operation.
Just write in brief what data changes you’ve done or let the box empty. Fill ‘OSM account’ arrays so that the
server could authenticate you. If you don’t have an account on the OSM server, it’s the best time to create one at
http://www.openstreetmap.org. Finally use [Upload] to start an upload operation.
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Figure 16.7: OSM upload dialog
16.11 Saving OSM data
Save OSM to file
To save data from a current map extent to an XML file click on the
button. If there is no such
button, the OSM toolbar in your QuantumGIS installation is probably disabled. You can enable it again in Settings
→ Toolbars → OpenStreetMap. After clicking on the button a new dialog appears.
Figure 16.8: OSM saving dialog
Select features you want to save into XML file and the file itself. Use the [OK] button to start the operation. The
process will create an XML file, in which OSM data from your current map extent are represented. The OSM
version of the output file is 0.6. Elements of OSM data (<node>, <way>, <relation>) do not contain information
on their changesets and uids. This information are not compulsory yet, see DTD for OSM XML version 0.6. In
the output file OSM elements are not ordered.
Notice that not only data from the current extent are saved. Into the output file the whole polygons and lines are
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saved even if only a small part of them is visible in the current extent. For each saved line/polygon all its member
nodes are saved too.
16.12 Import OSM data
To import OSM data from an opened non-OSM vector layer follow this instructions. Choose current OSM data
Import data from a layer
button. If there is no such button, someone
by clicking on one of their layers. Click on the
has probably disabled the OpenStreetMap toolbar in your QGIS installation. You can enable it again in Settings
→ Toolbars → OpenStreetMap.
After clicking on the button following message may show up:
Figure 16.9: OSM import message dialog
In such case there is no vector layer currently loaded. The import must be done from a loaded layer - please load a
vector layer from which you want to import data. After a layer is opened, your second try should give you a better
result (don’t forget to mark the current OSM layer again):
Figure 16.10: Import data to OSM dialog
Use the submit dialog to start the process of OSM data importing. Reject it if you are not sure you want to import
something.
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CHAPTER 17
SEXTANTE
17.1 Introduction
This chapter introduces SEXTANTE, the powerful geospatial analysis framework of QGIS. SEXTANTE is a
geoprocessing environment that can be used to call native and third party algorithms from QGIS, making your
spatial analysis tasks more productive and easy to accomplish.
In the following sections we will review how to use the graphical elements of SEXTANTE and take the most out
of each one of them
17.1.1 Basic elements of the SEXTANTE GUI
There are four basic elements in the SEXTANTE GUI, which are used to run SEXTANTE algorithms for different
purposes. Choosing one tool or another will depend on the kind of analysis that is to be performed and the
particular characteristics of each user and project. All of them (except for the batch processing interface, which is
called from the toolbox, as we will see) can be accessed from the SEXTANTE menu item (you will see more than
four entries. The remaining ones are not used to execute algorithms and will be explained later in this chapter).
• The SEXTANTE toolbox. The main element of the SEXTANTE GUI, it is used to execute a single algorithm
or run a batch process based on that algorithm.
Figure 17.1: SEXTANTE Toolbox
• The SEXTANTE graphical modeler. Several algorithms can be combined graphically using the modeler to
define a workflow, creating a single process that involves several sub-processes
• The SEXTANTE history manager. All actions performed using any of the aforementioned elements are
stored in a history file and can be later easily reproduced using the history manager
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Figure 17.2: SEXTANTE Models
Figure 17.3: SEXTANTE History
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• The SEXTANTE batch processing interface manager. This interface allows you to execute batch processes
and automate the execution of a single algorithm on multiple datasets.
Figure 17.4: SEXTANTE Batch Processing
Along the following sections we will review each one of this elements in detail.
17.2 The SEXTANTE toolbox
17.2.1 Introduction
The Toolbox is the main element of the SEXTANTE GUI, and the one that you are more likely to use in your daily
work. It shows the list of all available algorithms grouped in different blocks, and is the access point to run them
whether as a single process or as a batch process involving several executions of a same algorithm on different
sets of inputs.
Figure 17.5: SEXTANTE Toolbox
The toolbox contains all the algorithms available, divided into groups. Each group represents a so-called ‘algorithm provider’, which is a set of algorithms coming from the same source, for instance, from a third-party application with geoprocessing capabilities. Some of this groups represent algorithms from one of such third-party
applications (like SAGA, GRASS or R), while other contain algorithms directly coded along with SEXTANTE
elements, not relying on any additional software. Currently, these providers all reuse code from already existing QGIS plugins (more specifically, from the fTools vector library shiped along with QGIS and the contributed
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mmqgis plugin that you can install using the Plugin Manager), making them more useful, since they can be executed from elements such as the modeler or the batch processing interface, which we will soon describe.
Additionally, two more providers can be found, namely ‘Models’ and ‘Scripts’. This providers include usercreated algorithms, and allow you to define your own workflows and processing tasks. We will devote a full
section to them a bit later.
In the upper part of the toolbox you can find a text box. To reduce the number of algorithms shown in the toolbox
and make it easier to find the one you need, you can enter any word or phrase on the text box. Notice that, as you
type, the number of algorithms in the toolbox is reduced to just those which contain the text you have entered in
their names.
To execute an algorithm, just double-click on its name in the toolbox.
17.2.2 The algorithm dialog
Once you double-click on the name of the algorithm that you want to execute, a dialog similar to the next one is
shown (in this case, the dialog corresponds to the SAGA ‘Convergence index’ algorithm).
Figure 17.6: Parameters Dialog
This dialog is used to set the input values that the algorithm needs to be executed. It shows a table where input
values and configuration parameters are to be set. It, of course, has a different content depending on the requirements of the algorithm to be executed, and is created automatically based on those requirements. On the left side,
the name of the parameter is shown. On the right side the value of the parameter can be set.
Although the number and type of parameters depend on the characteristics of the algorithm, the structure is similar
for all of them. The parameters found on the table can be of one of the following types.
• A raster layer, to select from a list of all the ones available (currently opened) in QGIS. The selector contains
as well a button on its right-hand side, to let you select filenames that represent layers currently not loaded
in QGIS.
• A vector layer, to select from a list of all the ones available in the QGIS. Layers not loaded in QGIS can
be selected as well, as in the case of raster layers, but only if the algorithm does not require a table field
selected from the attributes table of the layer. In that case, only opened layers can be selected, since they
need to be open so as to retrieve the list of field names available.
You will see a button by each vector layer selector. If the algorithm contains several of them, you will be
able to toggle just one of them. If the button corresponding to a vector input is toggled, the algorithm will
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be executed iteratively on each one of its features. We will see more about this kind of execution at the end
of this section.
• A table, to select from a list of all the ones available in QGIS. Non-spatial tables are loaded into QGIS like
vector layers, and in fact they are treated as such by the program. Currently, the list of available tables that
you will see when executing a SEXTANTE algorithm that needs one of them is restricted to tables coming
from files in DBase (.dbf) or Comma-Separated Values (.csv) formats.
• An option, to choose from a selection list of possible options.
• A numerical value, to be introduced in a text box. You will find a button by its side. Clicking on it you
will see a dialog that allows you to enter a mathematical expression, so you can use it as a handy calculator.
Some useful variables related to data loaded into QGIS can be added to your expression, so you can select
a value derived from any of this variables such as the cellsize of a layer or the northern most coordinate of
another one.
Figure 17.7: Number Selector
• A range, with min and max values to be introduced in two text boxes.
• A text string, to be introduced in a text box.
• A field, to choose from the attributes table of a vector layer or a single table selected in another parameter.
• A Coordinate Reference System (CRS). You can type the EPSG code directly in the text box, or select it
from the CRS selection dialog that appear when you click on the button on the right-hand size
• A extent, to be entered by four number representing its xmin, xmax, ymin, ymax limits. Clicking on the
button on the right-hand side of the value selector, a pop-up menu will appear, giving you two option: to
select the value from a layer or the current canvas extent, or to define it by dragging directly onto the map
canvas.
Figure 17.8: SEXTANTE Extent
If you select the first option, you will see a window like the next one.
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Figure 17.9: SEXTANTE Extent List
If you select the second one, the parameters window will hide itself, so you can click and drag onto the
canvas. Once you have defined the selected rectangle, the dialog will reappear, containing the values in the
extent text box.
Figure 17.10: Extent Drag
• A list of elements (whether raster layers, vector ones or tables), to select from the list of the ones available
in QGIS. To make the selection, click on the small button on the left side of the corresponding row to see a
dialog like the following one.
• A small table to be edited by the user. These are used to define parameters like lookup tables or convolution
kernels, among others.
Click on the button on the right side to see the table and edit its values.
Depending on the algorithm, the number of rows can be modified or not, using the buttons on the right side
of the window.
You will find a [Help] button in the lower part of the parameters dialog. If a help file is available, it will be
shown, giving you more information about the algorithms and detailed descriptions of what each parameter does.
Unfortunately, most algorithms lack good documentation, but if you feel like contributing to the project, this would
be a good place to start.
A note on projections
SEXTANTE — and also most of the external applications whose algorithms are available from SEXTANTE —
does not perform any reprojection on input layers and assumes that all of them are already in a common coordinate
system and ready to be analized. Whenever you use more than one layer as input to an algorithm, whether vector
or raster, it is up to you to make sure that they are all in the same coordinate system.
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Figure 17.11: Multiple Selection
Figure 17.12: Fixed Table
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Note that, due to QGIS’s ‘on-the-fly’ reprojecting capabilities, although two layers might seem to overlap and
match, that might not be true if their original coordinates are used without reprojecting them onto a common coordinate system. That reprojection should be done manually and then use the resulting files as input to SEXTANTE.
Also note that the reprojection process can be performed with SEXTANTE, which incorporates tools to do so.
17.2.3 Data objects generated by SEXTANTE algorithms
Data objects generated by SEXTANTE can be of any of the following types:
• A raster layer
• A vector layer
• A table
• An HTML file (used for text and graphical outputs)
They are all saved to disk (there are no in-memory results), and the parameters table will contain a text box
corresponding to each one of these outputs, where you can type the output channel to use for saving it. An output
channel contains the information needed to save the resulting object somewhere. In the most usual case, you will
save it to a file, but the architecture of SEXTANTE allows for any other way of storing it. For instance, a vector
layer can be stored in a database or even uploaded to a remote server using a WFS-T service. Although solutions
like these are not yet implemented, SEXTANTE is prepared to handle them, and we expect to add new kinds of
output channels in a near feature.
To select an output channel, just click on the button on the right side of the text box. That will open a save-file
dialog, where you can select the desired filepath. Supported file extensions are shown in the file format selector of
the dialog, depending on the kind of output and the algorithm.
The format of the output is defined by the filename extension. The supported formats depend on the ones supported
by the algorithm itself. To select a format, just select the corresponding file extension (or add it if you are directly
typing the filepath instead). If the extension of the filepath you entered does not match any of the supported ones,
a default extension (usually .dbf for tables, .tif for raster layers and .shp for vector ones) will be appended
to the filepath and the file format corresponding to that extension will be used to save the layer or table.
If you do not enter any filename, the result will be saved as a temporary file and in the corresponding default file
format, and will be deleted once you exit QGIS (take care with that in case you save your project and it contains
temporary layers).
You can set a default folder for output data objects. Go to the configuration dialog (you can open it from the
SEXTANTE menu), and in the General group you will find a parameter named Output folder. This output folder
is used as the default path in case you type just a filename with no path (i.e. myfile.shp) when executing an
algorithm.
Apart from raster layers and tables, SEXTANTE also generates graphics and texts as HTML files. These results
are shown at the end of the algorithm execution in a new dialog. This dialog will keep the results produced
by SEXTANTE during the current session, and can be shown at any time by selecting in menu SEXTANTE →
SEXTANTE results viewer.
Some external applications might have files (with no particular extension restrictions) as output, but they do not
belong to any of the categories above. Those outut files will not be processed by QGIS (opened or included into the
current QGIS project), since most of the times correspond to file formats or elements not supported by QGIS. This
is, for instance, the case with LAS files used for LiDAR data. The files get created, but you won’t see anything
new in your QGIS working session.
For all the other types of outputs, you will find a check box that you can use to tell SEXTANTE not whether to
load the file once it is generated by the algorithm or not. By default, all files are opened.
SEXTANTE does not support optional outputs, so all outputs are created, but you can uncheck the corresponding
check box if you are not interested in a given output, which virtually makes it behave like an optional output
(although the layer is created anyway, but if you leave the text box empty, it will be saved to a temporary file and
deleted once you exit QGIS)
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17.2.4 Configuring SEXTANTE
As it has been mentioned, the configuration menu gives access to a new dialog where you can configure how
SEXTANTE works. Configuration parameters are structured in separate blocks that you can select on the lefthand side of the dialog.
Along with the aforementioned Output folder entry, the General block contains parameters for setting the default
rendering style for SEXTANTE layers (that is, layers generated by using algorithms from any of the SEXTANTE
components). Just create the style you want using QGIS, save it to a file, and then enter the path to that file in the
settings so SEXTANTE can use it. Whenever a layer is loaded by SEXTANTE and added to the QGIS canvas, it
will be rendered with that style.
Rendering stlyes can be configured individually for each algorithm and each one of its outputs. Just right-click on
the name of the algorithm in the toolbox and select Edit rendering styles. You will see a dialog like the one shown
next.
Figure 17.13: Rendering Styles
Select the style file (.qml) that you want for each output and press [OK].
Other configuration parameters in the General group are explained below:
• Use filename as layer name. The name of each resulting layer created by SEXTANTE is defined by the
algorithm generating it. In some cases, a fixed name might be used, that meaning that the same name will be
used, no matter which input layer is used. In other cases, the name might depend on the name of the input
layer or some of the parameters used to run the algorithm. If this checkbox is checked, the name will be
taken from the output filename instead. Notice, that, if the output is saved to a temporary file, the filename
of this temporary file is usually long and meaningless one intended to avoid collision with other already
existing filenames.
• Use only selected features. If this option is selected, whenever a vector layer is used as input for an
algorithm, only its selected features will be used. If the layer has no selected features, all of them will be
used.
Apart from the General block in the settings dialog, you will also find one for each algorithm provider. They
contain an Activate item that you can use to make algorithms appear or not in the toolbox. Also, some algorithm providers have their own configuration items, that we will explain later when covering particular algorithm
providers.
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17.3 The SEXTANTE graphical modeler
17.3.1 Introduction
The graphical modeler allows to create complex models using a simple and easy-to-use interface. When working
with a GIS, most analysis operations are not isolated, but part of a chain of operations instead. Using the graphical
modeler, that chain of processes can be wrapped into a single process, so it is easier and more convenient to
execute than a single process later on a different set on inputs. No matter how many steps and different algorithms
it involves, a model is executed as a single algorithm, thus saving time and effort, specially for larger models.
The modeler can be opened from the SEXTANTE menu, but also from the toolbox. In the Modeler branch of the
algorithms tree you will find a group named Tools, which contains an entry called Create new model.
The modeler has a working canvas where the structure of the model and the workflow it represents are shown. On
the left part of the window, a panel with two tabs can be used to add new elements to the model.
Figure 17.14: Modeler
Creating a model involves two steps:
1. Definition of necessary inputs*. These inputs will be added to the parameters window, so the user can set
their values when executing the model. The model itself is a SEXTANTE algorithm, so the parameters
window is generated automatically as it happens with all the algorithms included in SEXTANTE.
2. Definition of the workflow. Using the input data of the model, the workflow is defined adding algorithms
and selecting how they use those inputs or the outputs generated by other algorithms already in the model.
17.3.2 Definition of inputs
The first step to create a model is to define the inputs it needs. The following elements are found in the Inputs tabs
on the left side of the modeler window:
• Raster layer
• Vector layer
• String
• Table field
• Table
• Numerical value
• Boolean value
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Double-clicking on any of them, a dialog is shown to define its characteristics. Depending on the parameter itself,
the dialog will contain just one basic element (the description, which is what the user will see when executing the
model) or more of them. For instance, when adding a numerical value, as it can be seen in the next figure, apart
from the description of the parameter you have to set a default value and a range of valid values.
Figure 17.15: Model Parameters
For each added input, a new element is added to the modeler canvas.
Figure 17.16: Model Parameters
17.3.3 Definition of the workflow
Once the inputs have been defined, it is time to define the algorithms to apply on them. Algorithms can be found
in the Algorithms tab, grouped much in the same way as they are in the toolbox.
Figure 17.17: Model Parameters
To add an algorithm, double-click on its name. An execution dialog will appear, with a content similar to the
one found in the execution panel that SEXTANTE shows when executing the algorithm from the toolbox. the one
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shown next correspond to the SAGA ‘Convergence index’ algorithm, the same one we saw in the section dedicated
to the SEXTANTE toolbox.
Figure 17.18: Model Parameters
As you can see, some differences exist. Instead of the file output box that was used to set the filepath for output
layers and tables, a simple text box is. If the layer generated by the algorithm is just a temporary result that will
be used as the input of another algorithm and should not be kept as a final result, just do not edit that textbox.
Typing anything on it means that the result is a final one, and the text that you supply will be the description for
the output, which will be the one the user will see when executing the model.
Selecting the value of each parameter is also a bit different, since there are importante differences between the
context of the modeler and the toolbox one. Let’s see how to introduce the values for each type of parameter.
• Layers (raster and vector) and tables. They are selected from a list, but in this case the possible values are
not the layers or tables currently loaded in QGIS, but the list of model inputs of the corresponding type, or
other layers or tables generated by algorithms already added to the model.
• Numerical values. Literal values can be introduced directly on the textbox. But this textbox is also a list
that can be used to select any of the numerical value inputs of the model. In this case, the parameter will
take the value introduced by the user when executing the model.
• String. Like in the case of numerical values, literal strings can be typed, or an input string can be selected.
• Table field. The fields of the parent table or layer cannot be known at design-time, since they depend of the
selection of the user each time the model is executed. To set the value for this parameter, type the name of
a field directly in the textbox, or use the list to select a table field input already added to the model. The
validity of the selected field will be checked by SEXTANTE at run-time.
Once all the parameter have been assigned valid values, click on [OK] and the algorithm will be added to the
canvas. It will be linked to all the other elements in the canvas, whether algorithms or inputs, which provide
objects that are used as inputs for that algorithm.
Elements can be dragged to a different position within the canvas, to change the way the module structure is
displayed and make it more clear and intuitive. Links between elements are update automatically.
You can run your algorithm anytime clicking on the [Run] button. However, in order to use it from the toolbox, it
has to be saved and the modeler dialog closed, to allow the toolbox to refresh its contents.
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Figure 17.19: Model Parameters
17.3.4 Saving and loading models
Use the [Save] button to save the current model and the [Open] one to open any model previously saved. Model
are saved with the .model extension. If the model has been previously saved from the modeler window, you will
not be prompted for a filename, since there is already a file associated with that model, and it will be used.
Before saving a model, you have to enter a name and a group for it, using the text boxes in the upper part of the
window.
Models saved on the models folder (the default folder when you are prompted for a filename to save the model)
will appear in the toolbox in the corresponding branch. When the toolbox is invoked, SEXTANTE searches the
models folder for files with .model extension and loads the models they contain. Since a model is itself a
SEXTANTE algorithm, it can be added to the toolbox just like any other algorithm.
The models folder can be set from the SEXTANTE configuration dialog, under the Modeler group.
Models loaded from the models folder appear not only in the toolbox, but also in the algorithms tree in the
Algorithms tab of the modeler window. That means that you can incorporate a model as a part of a bigger model,
just as you add any other algorithm.
In some cases, SEXTANTE might not be able to load a model because it cannot find all the algorithms included
in its workflow. If you have used a given algorithm as part of your model, it should be available (that is, it
should appear on the toolbox) in order to load that model. Deactivating an algorithm provider in the SEXTANTE
configuration window renders all the algorithms in that provider unusable by the modeler, which might cause
problems when loading models. Keep that in mind when you have trouble loading or executing models.
17.3.5 Editing a model
You can edit the model you are currently creating, redefining the workflow and the relationships between the
algorithms and inputs that define the model itself.
If you right-click on an algorithm in the canvas representing the model, you will see a context menu like the one
shown next:
Selecting the Remove option will cause the selected algorithm to be removed. An algorithm can be removed only
if there are no other algorithms dependind on it. That is, if no output from the algorithm is used in a different one
as input. If you try to remove an algorithm that has others depending on it, SEXTANTE will show you a warning
message like the one you can see below:
Selecting the Edit option or simply double-clicking on the algorithm icon will show the parameters dialog of the
algorithm, so you can change the inputs and parameter values. Not all input elements available in the model will
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Figure 17.20: Modeler Right Click
Figure 17.21: Cannot Delete ALG
appear in this case as available inputs. Layers or values generated at a more advanced step in the workflow defined
by the model will not be available if they cause circular dependencies.
Select the new values and then click on the [OK] button as usual. The connections between the model elements
will change accordingly in the modeler canvas.
17.3.6 Activating and deactivating algorithms
Algorithms can be deactivated in the modeler, so they will not be executed once the model is run. This can be
used to test just a given part of the model, or when you do not need all the outputs it generates.
To deactivate an algorithm, right-click on its icon in the model canvas and select the Deactivate option. You will
see that the algorithm is represented now with a red label under its name indicating that is not active.
Figure 17.22: Deactivate
All algorithms depending (directly or undirectly) on that algorithm will also appear as inactive, since they cannot
be executed now.
To activate an algorithm, just right–click on its icon and select the Activate option.
17.3.7 Editing model help files and meta-information
You can document your models from SEXTANTE. Just click on the [Edit model help] button and a dialog like
the one shown next will appear.
On the right-hand side you will see a simple HTML page, created using the description of the input parameters
and outputs of the algorithm, along with some additional items like a general description of the model or its author.
The first time you open the help editor all those descriptions are empty, but you can edit them using the elements
on the left-hand side of the dialog. Select an element on the upper part and the write its description in the texbox
below.
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Figure 17.23: Help Edition
Model help is saved in a file in the same folder as the model itself. You do not have to worry about saving it, since
it is done automatically.
17.3.8 About available algorithms
You might notice that some algorithms that can be be executed from the toolbox do not appear in the list of
available ones when you are designing a model. To be included in a model, and algorithm must have a correct
semantic, so as to be properly linked to other in the workflow. If an algorithm does not have such well-defined
semantic (for instance, if the number of output layers cannot be know in advance), then it is not possible to use it
within a model, and thus does not appear in the list of them that you can find in the modeler dialog.
Additionaly, you will see some algorithms in the modeler that are not found in the toolbox. This algorithms are
meant to be used exclusively as part of a model, and they are of no interest in a different context. The ‘Calculator’
algorithm is an example of that. It is just a simple arithmetic calculator that you can use to modify numerical
values (entered by the user or generated by some other algorithm). This tools is really useful within a model, but
outside of that context, it doesn’t make too much sense.
17.3.9 SEXTANTE models as Python code
This feature is temporarily unavailable
Along with the tab that contains the graphical design of the model, you will find another one containing a Python
script which performs the same task as the model itself. Using that code, you can create a console script (we
will explain them later in this same manual) and modify it to incorporate actions and methods not available in the
graphical modeler, such as loops or conditional sentences.
This feature is also a very practical way of learning how to use SEXTANTE from the console and how to create
SEXTANTE algorithms using Python code, so you can use it as a learning tool when you start creating your own
SEXTANTE scripts.
You will find a button below the text field containing the Python code. Click on it to directly create a new script
from that code, without having to copy and paste it in the SEXTANTE script editor.
17.4 The SEXTANTE batch processing interface
17.4.1 Introduction
SEXTANTE algorithms (including models) can be executed as a batch process. That is, they can be executed
using not a single set of inputs, but several of them, executing the algorithm as many times as needed. This is
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useful when processing large amounts of data, since it is not necessary to launch the algorithm many times from
the toolbox.
To execute an algorithm as a batch process, right-click on its name in the toolbox and select the Execute as batch
process option in the pop-up menu that will appear.
Figure 17.24: Batch Processing Right Click
17.4.2 The parameters table
Executing a batch process is similar to performing a single execution of an algorithm. Parameter values have to
be defined, but in this case we need not just a single value for each parameter, but a set of them instead, one for
each time the algorithm has to be executed. Values are introduced using a table like the one shown next.
Figure 17.25: Batch Processing
Each line of this table represents a single execution of the algorithm, and each cell contains the value of one of the
parameters. It is similar to the parameters dialog that you see when executing an algorithm from the toolbox, but
with a different arrangement.
By default, the table contains just two rows. You can add or remove rows using the buttons on the lower part of
the window.
Once the size of the table has been set, it has to be filled with the desired values.
17.4.3 Filling the parameters table
For most parameters, setting its value is trivial. Just type the value or select it from the list of available options,
depending on the parameter type.
The main differences are found for parameters representing layers or tables, and for output filepaths. Regarding
input layers and tables, when an algorithm is executed as part of a batch process those input data objects are taken
directly from files, and not from the set of them already opened in QGIS. For this reason, any algorithm can be
executed as a batch process even if no data objects at all are opened and the algorithm cannot be run from the
toolbox.
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Filenames for input data objects are introduced directly typing or, more conveniently, clicking on the button on
the right hand of the cell, which shows a typical file chooser dialog. Multiple files can be selected at once. If the
input parameter represents a single data object and several files are selected, each one of them will be put in a
separate row, adding new ones if needed. If it represents a multiple input, all the selected files will be added to a
single cell, separated by semicolons (;).
Output data objects are always saved to a file and, unlike when executing an algorithm from the toolbox, saving to
a temporary one is not permitted. You can type the name directly or use the file chooser dialog that appears when
clicking on the accompanying button.
Once you select the file, a new dialog is shown to allow for autocompletion of other cells in the same column
(same parameter).
Figure 17.26: Batch Processing Save
If the default value (‘Do not autocomplete’) is selected, SEXTANTE will just put the selected filename in the
selected cell from the parameters table. If any of the other options is selected, all the cells below the selected one
will be automatically filled based on a defined criteria. This way, it is much easier to fill the table, and the batch
process can be defined with less effort.
Automatic filling can be done simply adding correlative numbers to the selected filepath, or appending the value
of another field at the same row. This is particularly useful for naming output data object according to input ones.
Figure 17.27: Batch Processing File Path
17.4.4 Executing the batch process
To execute the batch process once you have introduced all the necessary values, just click on [OK]. SEXTANTE
will show the progress of the global batch process in the progress bar in the lower part of the dialog.
17.5 Using SEXTANTE from the console
17.5.1 Introduction
The console allows advanced users to increase their productivity and perform complex operations that cannot be
performed using any of the other elements of the SEXTANTE GUI. Models involving several algorithms can be
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defined using the command-line interface, and additional operations such as loops and conditional sentences can
be added to create more flexible and powerful workflows.
There is not a SEXTANTE console in QGIS, but all SEXTANTE commands are available instead from QGIS
built-in Python console. That means that you can incorporate those command to your console work and connect
SEXTANTE algorithms to all the other features (including methods from the QGIS API) available from there.
The code that you can execute from the Python console, even if it does call any SEXTANTE method, can be
converted into a new SEXTANTE algorithm that you can later call from the toolbox, the graphical modeler or any
other SEXTANTE component, just like you do with any other SEXTANTE algorithm. In fact, some algorithms
that you can find in the toolbox, like all the ones in the mmqgis group, are simple scripts.
In this chapter we will see how to use SEXTANTE from the QGIS Python console, and also how to write your
own algorithms using Python.
17.5.2 Calling SEXTANTE from the Python console
The first thing you have to do is to import the SEXTANTE functions with the following line:
>>> import sextante
Now, there is basically just one (interesting) thing you can do with SEXTANTE from the console: to execute an
algorithm. That is done using the runalg() method, which takes the name of the algorithm to execute as its first
parameter, and then a variable number of additional parameter depending on the requirements of the algorithm.
So the first thing you need to know is the name of the algorithm to execute. That is not the name you see in the
toolbox, but rather a unique command–line name. To find the right name for your algorithm, you can use the
algslist() method. Type the following line in you console:
>>> sextante.alglist()
You will see something like this.
Accumulated Cost (Anisotropic)---------------->saga:accumulatedcost(anisotropic)
Accumulated Cost (Isotropic)------------------>saga:accumulatedcost(isotropic)
Add Coordinates to points--------------------->saga:addcoordinatestopoints
Add Grid Values to Points--------------------->saga:addgridvaluestopoints
Add Grid Values to Shapes--------------------->saga:addgridvaluestoshapes
Add Polygon Attributes to Points-------------->saga:addpolygonattributestopoints
Aggregate------------------------------------->saga:aggregate
Aggregate Point Observations------------------>saga:aggregatepointobservations
Aggregation Index----------------------------->saga:aggregationindex
Analytical Hierarchy Process------------------>saga:analyticalhierarchyprocess
Analytical Hillshading------------------------>saga:analyticalhillshading
Average With Mask 1--------------------------->saga:averagewithmask1
Average With Mask 2--------------------------->saga:averagewithmask2
Average With Thereshold 1--------------------->saga:averagewiththereshold1
Average With Thereshold 2--------------------->saga:averagewiththereshold2
Average With Thereshold 3--------------------->saga:averagewiththereshold3
B-Spline Approximation------------------------>saga:b-splineapproximation
...
That’s a list of all the available algorithms, alphabetically ordered, along with their corresponding command-line
names.
You can use a string as a parameter for this method. Instead of returning the full list of algorithm, it will only
display those that include that string. If, for instance, you are looking for an algorithm to calculate slope from a
DEM, type alglist("slope") to get the following result:
DTM Filter (slope-based)---------------------->saga:dtmfilter(slope-based)
Downslope Distance Gradient------------------->saga:downslopedistancegradient
Relative Heights and Slope Positions---------->saga:relativeheightsandslopepositions
Slope Length---------------------------------->saga:slopelength
Slope, Aspect, Curvature---------------------->saga:slopeaspectcurvature
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Upslope Area---------------------------------->saga:upslopearea
Vegetation Index[slope based]----------------->saga:vegetationindex[slopebased]
This result might change depending on the algorithms you have available.
It is easier now to find the algorithm you are looking for and its command-line name, in this case
saga:slopeaspectcurvature.
Once you know the command-line name of the algorithm, the next thing to do is to know the right syntax to
execute it. That means knowing which parameters are needed and the order in which they have to be passed when
calling the runalg() method. SEXTANTE has a method to describe an algorithm in detail, which can be used
to get a list of the parameters that an algorithms require and the outputs that it will generate. To do it, you can use
the alghelp(name_of_the_algorithm) method. Use the command-line name of the algorithm, not the
full descriptive name.
Calling the method with saga:slopeaspectcurvature as parameter, you get the following description.
>>> sextante.alghelp("saga:slopeaspectcurvature")
ALGORITHM: Slope, Aspect, Curvature
ELEVATION <ParameterRaster>
METHOD <ParameterSelection>
SLOPE <OutputRaster>
ASPECT <OutputRaster>
CURV <OutputRaster>
HCURV <OutputRaster>
VCURV <OutputRaster>
Now you have everything you need to run any algorithm. As we have already mentioned, there is only one single
command to execute algorithms: runalg(). Its syntax is as follows:
>>> sextante.runalg{name_of_the_algorithm, param1, param2, ..., paramN,
Output1, Output2, ..., OutputN)
The list of parameters and outputs to add depends on the algorithm you want to run, and is exactly the list that the
alghelp() method gives you, in the same order as shown.
Depending on the type of parameter, values are introduced differently. The next one is a quick review of how to
introduce values for each type of input parameter
• Raster Layer, Vector Layer or Table. Simply use a string with the name that identifies the data object to use
(the name it has in the QGIS Table of Contents) or a filename (if the corresponding layer is not opened, it
will be opened, but not added to the map canvas). If you have an instance of a QGIS object representing the
layer, you can also pass it as parameter. If the input is optional and you do not want to use any data object,
use None.
• Selection. If an algorithm has a selection parameter, the value of that parameter should be entered using an
integer value. To know the available options, you can use the algoptions command, as shown in the
following example:
>>> sextante.algoptions("saga:slopeaspectcurvature")
METHOD(Method)
0 - [0] Maximum Slope (Travis et al. 1975)
1 - [1] Maximum Triangle Slope (Tarboton 1997)
2 - [2] Least Squares Fitted Plane (Horn 1981, Costa-Cabral & Burgess 1996)
3 - [3] Fit 2.Degree Polynom (Bauer, Rohdenburg, Bork 1985)
4 - [4] Fit 2.Degree Polynom (Heerdegen & Beran 1982)
5 - [5] Fit 2.Degree Polynom (Zevenbergen & Thorne 1987)
6 - [6] Fit 3.Degree Polynom (Haralick 1983)
In this case, the algorithm has one of such such parameters, with 7 options. Notice that ordering is zerobased.
• Multiple input. The value is a string with input descriptors separated by semicolons. As in the case of single
layers or tables, each input descriptor can be the data object name, or its filepath.
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• Table Field from XXX. Use a string with the name of the field to use. This parameter is case-sensitive.
• Fixed Table. Type the list of all table values separated by commas and enclosed between quotes. Values
start on the upper row and go from left to right. You can also use a 2D array of value representing the table.
• CRS. Enter the EPSG code number of the desired CRS.
• Extent. You must use a string with xmin, xmax, ymin and ymax values separated by commas.
Boolean, file, string and numerical parameters do not need any additional explanations.
Input parameters such as strings booleans or numerical values have default values. To use them, use None in the
corresponding parameter entry.
For output data objects, type the filepath to be used to save it, just as it is done from the toolbox. If you want to
save the result to a temporary file, use None. The extension of the file determines the file format. If you enter a
file extension not included in the ones supported by the algorithm, the default file format for that output type will
be used, and its corresponding extension appended to the given filepath.
Unlike when an algorithm is executed from the toolbox, outputs are not added to the map canvas if you execute
that same algorithm from the Python console. If you want to add an output to it, you have to do it yourself after
running the algorithm. To do so, you can use QGIS API commands, or, even easier, use one of the handy methods
provided by SEXTANTE for such task.
The runalg() method returns a dictionary with the output names (the ones shown in the algorithm description)
as keys and the filepaths of those outputs as values. To add all the outputs generated by an algorithm, pass that
dictionary to the loadFromAlg() method. You can also load an individual layer passing its filepath to the
load() method.
17.5.3 Creating scripts and running them from the toolbox
You can create your own algorithms by writing the corresponding Python code and adding a few extra lines to
supply additional information needed by SEXTANTE. You can find a Create new script under the tools group in
the script algorithms block of the toolbox. Double click on it to open the script edition dialog. That’s where you
should type your code. Saving the script from there in the scripts folder (the default one when you open the
save file dialog), with .py extension, will automatically create the corresponding algorithm.
The name of the algorithm (the one you will see in the toolbox) is created from the filename, removing its extension
and replacing low hyphens with blank spaces.
Let’s have the following code, which calculates the Topographic Wetness Index (TWI) directly from a DEM
##dem=raster
##twi=output
ret_slope = sextante.runalg("saga:slopeaspectcurvature", dem, 0, None,
None, None, None, None)
ret_area = sextante.runalg("saga:catchmentarea(mass-fluxmethod)", dem,
0, False, False, False, False, None, None, None, None, None)
sextante.runalg("saga:topographicwetnessindex(twi), ret_slope[’SLOPE’],
ret_area[’AREA’], None, 1, 0, twi)
As you can see, it involves 3 algorithms, all of them coming from SAGA. The last one of them calculates de TWI,
but it needs a slope layer and a flow accumulation layer. We do not have these ones, but since we have the DEM,
we can calculate them calling the corresponding SAGA algorithms.
The part of the code where this processing takes place is not difficult to understand if you have read the previous
sections in this chapter. The first lines, however, need some additional explanation. They provide SEXTANTE
the information it needs to turn your code into an algorithm that can be run from any of its components, like the
toolbox or the graphical modeler.
These lines start with a double Python comment symbol and have the following structure:
[parameter_name]=[parameter_type] [optional_values]
Here is a list of all the parameter types that SEXTANTE supports in its scripts, their syntax and some examples.
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• raster. A raster layer
• vector. A vector layer
• table. A table
• number. A numerical value. A default value must be provided. For instance, depth=number 2.4
• string. A text string. As in the case of numerical values, a default value must be added. For instance,
name=string Victor
• boolean. A boolean value. Add True or False after it to set the default value. For example,
verbose=boolean True
• multiple raster. A set of input raster layers.
• multiple vector. A set of input vector layers.
• field. A field in the attributes table of a vector layer. The name of the layer has to be added after the
field tag. For instance, if you have declared a vector input with mylayer=vector, you could use
myfield=field mylayer to add a field from that layer as parameter.
• folder. A folder
• file. A filename
The parameter name is the name that will be shown to the user when executing the algorithm, and also the variable
name to use in the script code. The value entered by the user for that parameter will be assigned to a variable with
that name.
When showing the name of the parameter to the user, SEXTANTE will edit it to improve its appearance, replacing
low hyphens with blankspaces. So, for instance, if you want the user to see a parameter named A numerical
value, you can use the variable name A_numerical_value.
Layers and tables values are strings containing the filepath of the corresponding object. To turn them into a QGIS
object, you can use the sextante.getObjectFromUri() function. Multiple inputs also have a string value,
which contains the filepaths to all selected object, separated by semicolons.
Outputs are defined in a similar manner, using the following tags:
• output raster
• output vector
• output table
• output html
• output file
• output number
• output string
The value assigned to the output variables is always a string with a filepath. It will correspond to a temporary
filepath in case the use has not entered any output filename.
When you declare an output, SEXTANTE will try to add it to QGIS once the algorithm is finished. That is the
reason why, although the runalg() method does not load the layers it produces, the final TWI layer will be
loaded, since it is saved to the file entered by the user, which is the value of the corresponding output.
Do not use the load() method in your script algorithms, but just when working with the console line. If a layer
is created as output of an algorithm, it should be declared as such. Otherwise, you will not be able to properly
use the algorithm in the modeler, since its syntax (as defined by the tags explained above) will not match what the
algorithm really creates.
Hidden outputs (numbers and strings) do not have a value. Instead, it is you who has to assign a value to them. To
do so, just set the value of a variable with the name you used to declare that output. For instance, if you have used
this declaration,
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##average=output number
the following line will set the value of the output to 5:
average = 5
In addition to the tags for parameters and outputs, you can also define the group under which the algorithm will
be shown, using the group tag.
If you algorithm takes a long time to process, it is a good idea to inform the user. You have a global named
progress available, with two available methods: setText(text) and setPercentage(percent) to
modify the progress text and the progress bar.
Several examples are provided with SEXTANTE. Please, check them to see real examples of how to create algorithms using this feature of SEXTANTE. You can right-click on any script algorithm and select Edit script to edit
its code or just to see it.
17.5.4 Documenting your scripts
As in the case of models, you can create additional documentation for your script, to explain what they do and
how to use them. In the script editing dialog you will find a [Edit script help] button. Click on it and it will take
you to the help editing dialog. Check the chapter about the graphical modeler to know more about this dialog and
how to use it.
Help files are saved in the same folder as the script itself, adding the .help extension to the filename. Notice that
you can edit your script’s help before saving it for the first time. If you later close the script editing dialog without
saving the script (i.e. you discard it), the help content you wrote will be lost. If your script was already saved and
is associated to a filename, saving is done automatically.
17.6 The SEXTANTE history manager
17.6.1 The SEXTANTE history
Every time you execute a SEXTANTE algorithm, information about the process is stored in the SEXTANTE
history manager. Along with the parameters used, the date and time of the execution are also saved.
This way, it is easy to track the and control all the work that has been developed using SEXTANTE, and easily
reproduce it.
The SEXTANTE history manager is a set of registry entries grouped according to their date of execution, making
it easier to find information about an algorithm executed at any particular moment.
Figure 17.28: History
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Process information is kept as a command-line expression, even if the algorithm was launched from the toolbox.
This makes it also useful for those learning how to use the command-line interface, since they can call an algorithm
using the toolbox and then check the history manager to see how that same algorithm could be called from the
command line.
Apart from browsing the entries in the registry, processes can be re-executed, simply double-clicking on the
corresponding entry.
Along with algorithm executions, SEXTANTE communicates with the user using the other groups of the registry,
namely Errors, Warnings and Information. In case something is not working properly, having a look at the Errors
might help you to see what is happening. If you get in contact with a SEXTANTE developer to report a bug or
error, the information in that group will be very useful for him to find out what is going wrong.
When executing third party algorithms, this is usually done calling their command-line interfaces, which communicate with the user using the console. Although that console is not shown, a full dump of it is stored in the
Information group each time you run one of those algorithms. If, for instance, you are having problems executing
a SAGA algorithm, look for an entry name ‘SAGA execution console output’ to check all the messages generated
by SAGA and try to find out where the problem is.
Some algorithms, even if they can produce a result with the given input data, might add comments or additional
information to Warning in case they detect potential problems from that data, in order to warn you about them.
Make sure you check those messages in case you are having unexpected results.
17.7 Configuring external applications
17.7.1 Introduction
SEXTANTE can be extended using additional applications, calling them from within SEXTANTE. Currently,
SAGA, GRASS, OTB(Orfeo Toolbox) and R are supported, along with some other command-line applications
that provide spatial data analysis functionalities. Algorithms relying on an external application are managed by
their own algorithm provider.
This chapter will show you how to configure SEXTANTE to include these additional applications, and will explain
some particular features of the algorithm based on them. Once you have correctly configured the system, you will
be able to execute external algorithms from any SEXTANTE component like the toolbox or the graphical modeler,
just like you do with any other SEXTANTE geoalgorithm.
By default, all algorithms that rely on an external appplication not shipped with QGIS are not enabled. You can
enable them in the SEXTANTE configuration dialog. Make sure that the corresponding application is already
installed in your system. Enabling an algorithm provider without installing the application it needs will cause the
algorithms to appear in the toolbox, but an error will be thrown when you try to execute them.
This is because the algorithm descriptions (needed to create the parameters dialog and give SEXTANTE the
information it needs about the algorithm) are not included with each appllication, but with SEXTANTE instead.
That is,they are part of SEXTANTE, so you have them in your installation even if you have not installed any other
software. Running the algorithm, however, needs the application binaries to be installed in your system.
A note on file formats
When using an external software, opening a file in QGIS does not mean that it can be opened and processed as well
on that other software. In most cases, it can read what you have opened in QGIS, but in some cases, that might not
be the case. When using databases or uncommon file formats, whether for raster of vector layers, problems might
arise. If that happens, try to use well known file formats that you are sure that are understood by both programs,
and check to console output (in the history and log dialog) for knowing more about what is going wrong.
Using GRASS raster layers is, for instance, one case in which you might have trouble and not be able to complete
your work if you call an external algorithm using such a layer as input. For this reason, these layers will not
appear as available to SEXTANTE algorithms (we are currently working on solving this, and expect to have it
ready soon).
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You should, however, find no problems at all with vector layers, since SEXTANTE automatically converts from
the original file format to one accepted by the external application before passing the layer to it. This adds an extra
processing time, which might be significant if the layer has a large size, so do not be surprised if it takes more to
process a layer from a DB connection that one of a similar size stored in a shapefile.
Providers not using external applications can process any layer that you can open in QGIS, since they open it for
analysis trough QGIS.
Regarding output formats, raster layers can be saved as TIFF (.tif) files, while vector layers are saved as
shapefiles (.shp). These have been chosen as the ‘lingua franca’ between supported third party applications and
QGIS. If the output filename that you select is not one of the above, it will be modified, adding the corresponding
suffix, and the default file format will be used.
In the case of GDAL, the number of supported output formats is larger. When you open the file selection dialog,
you will see that you have more formats (and their corresponding extensions available). For more information
about which formats are supported, check the GDAL documentation.
A note on vector layer selections
By default, when an external algorithm takes a vector layer, it will use all its features, even if a selection exist
in QGIS. You can make an external algorithm aware of that selection by checking the Use selected features in
external applications item in the General settings group. When you do so, each time you execute an external
algorithm that uses a vector layer, the selected features of that layer will be exported to a new layer, and the
algorithm will work with that new layer instead.
Notice that if you select this option, a layer with no selection will behave like a layer with all its features selected,
not like an empty layer.
17.7.2 SAGA
SAGA algorithms can be run from SEXTANTE if you have SAGA installed in your system and you configure
SEXTANTE properly so it can find SAGA executables. In particular, the SAGA command-line executable is
needed to run SAGA algorithms. SAGA binaries are not included with SEXTANTE, so you have to download and
install the software yourself. Please check the SAGA website at for more information. SAGA 2.0.8 is needed.
Once SAGA is installed, and if you are running Windows, open the SEXTANTE configuration dialog. In the
SAGA block you will find a setting named SAGA Folder. Enter the path to the folder where SAGA is installed.
Close the configuration dialog and now you are ready to run SAGA algorithms from SEXTANTE.
In case you are using Linux, there is no need to configure that, and you will not see those folders. Instead, you
must make sure that SAGA is properly installed and its folder is added to the PATH environment variable. Just
open a console and type saga_cmd to check that the system can found where SAGA binaries are located.
About SAGA grid system limitations
Most of SAGA algorithms that require several input raster layers, require them to have the same grid system. That
is, to cover the same geographic area and have the same cellsize, so their corresponding grids match. When calling
SAGA algorithms from SEXTANTE, you can use any layer, regardless of its cellsize and extent. When multiple
raster layers are used as input for a SAGA algorithm, SEXTANTE resamples them to a common grid system and
then passes them to SAGA (unless the SAGA algorithm can operate with layers from different grid systems).
The definition of that common grid system is controlled by the user, and you will find several parameters in the
SAGA group of the setting window to do so. There are two ways of setting the target grid system:
• Setting it manually. You define the extent setting the values of the following parameters:
– Resampling min X
– Resampling max X
– Resampling min Y
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– Resampling max Y
– Resampling cellsize
Notice that SEXTANTE will resample input layers to that extent, even if they do not overlap with it.
• Setting it automatically from input layers. To select this option, just check the Use min covering grid system
for resampling option. All the other settings will be ignored and the minimum extent that covers all the
input layers will be used. The cellsize of the target layer is the maximum of all cellsizes of the input layers.
For algorithms that do not use multiple raster layers, or for those that do not need a unique input grid system, no
resampling is performed before calling SAGA, and those parameters are not used.
Limitations for multi-band layers
Unlike QGIS, SAGA has no support for multiband layers. If you want to use a multiband layer (such as
an RGB or multispectral image), you first have to split it into singlebanded images. To do so, you can use
the ‘SAGA/Grid - Tools/Split RGB image’ algorithm (which creates 3 images from an RGB image) or the
‘SAGA/Grid - Tools/Extract band’ algorithm (to extract a single band).
Limitations in cellsize
SAGA assumes that raster layers have the same cellsize in the X and Y axis. If you are working with a layer
with different values for its horizontal and vertical cellsizes, you might get unexcepted results. In this case, a
warning will be added to the SEXTANTE log, indicating that an input layer might not be suitable to be processed
by SAGA.
Logging
When SEXTANTE calls SAGA, it does it using its command-line interface, thus passing a set of commands to
perform all the required operation. SAGA show its progress by writing information to the console, which includes
the percentage of processing already done, along with additional content. This output is filtered by SEXTANTE
and used to update the progress bar while the algorithm is running.
Both the commands sent by SEXTANTE and the additional information printed by SAGA can be logged along
with other SEXTANTE log messages, and you might find them useful to track in detailed what is going on when
SEXTANTE runs a SAGA algorithm. You will find two settings, namely Log console output and Log execution
commands to activate that logging mechanism.
Most other providers that use an external application and call it through the command-line have similar options,
so you will find them as well in other places in the SEXTANTE settings list.
17.7.3 R and R scripts
R integration in SEXTANTE is different from that of SAGA in that there is not a predefined set of algorithms you
can run (except for a few examples). Instead, you should write your scripts and call R commands, much like you
would do from R, and in a very similar manner to what we saw in the chapter dedicated to SEXTANTE scripts.
This chapter shows you the syntax to use to call those R commands from SEXTANTE and how to use SEXTANTE
objects (layers, tables) in them.
The first thing you have to do, as we saw in the case of SAGA, is to tell SEXTANTE where you R binaries are
located. You can do so using the R folder entry in the SEXTANTE configuration dialog. Once you have set that
parameter, you can start creating your own R scripts and executing them.
Once again, this is different in Linux, and you just have to make sure that the R folder is included in the PATH
environment variable. If you can start R just typing R in a console, then you are ready to go.
To add a new algorithm that calls an R function (or a more complex R script that you have developed and you
would like to have available from SEXTANTE), you have to create a script file that tells SEXTANTE how to
perform that operation and the corresponding R commands to do so.
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Script files have the extension .rsx and creating them is pretty easy if you just have a basic knowledge of R
syntax and R scripting. They should be stored in the R scripts folder. You can set this folder in the R settings
group (available from the SEXTANTE settings dialog), just like you do with the folder for regular SEXTANTE
scripts.
Let’s have a look at a very simple file script file, which calls the R method spsample to create a random grid
within the boundary of the polygons in a given polygon layer. This method belong to the maptools package.
Since almost all the algorithms that you might like to incorporate into SEXTANTE will use or generate spatial
data, knowledge of spatial packages like maptools and, specially, sp, is mandatory.
##polyg=vector
##numpoints=number 10
##output=output vector
##sp=group
pts=spsample(polyg,numpoints,type="random")
output=SpatialPointsDataFrame(pts, as.data.frame(pts))
The first lines, which start with a double Python comment sign (##), tell SEXTANTE the inputs of the algorithm
described in the file and the outputs that it will generate. They work exactly with the same syntax as the SEXTANTE scripts that we have already seen, so they will not be described here again. Check the corresponding
section for more information.
When you declare an input parameter, SEXTANTE uses that information for two things: creating the user interface
to ask the user for the value of that parameter and creating a corresponding R variable that can be later used as
input for R commands.
In the above example, we are declaring an input of type vector named polyg. When executing the algorithm,
SEXTANTE will open in R the layer selected by the user and store it in a variable also named polyg. So the
name of a parameter is also the name of the variable that we can use in R for accesing the value of that parameter
(thus, you should avoid using reserved R words as parameter names).
Spatial elements such as vector and raster layers are read using the readOGR() and readGDAL() commands
(you do not have to worry about adding those commands to your description file, SEXTANTE will do it) and
stored as Spatial*DataFrame objects. Table fields are stored as strings containing the name of the selected
field.
Tables are opened using the read.csv() command. If a table entered by the user is not in CSV format, it will
be converted prior to importing it in R.
Knowing that, we can now understand the first line of our example script (the first line not starting with a Python
comment).
pts=spsample(polyg,numpoints,type="random")
The variable polygon already contains a SpatialPolygonsDataFrame object, so it can be used to call the
spsample method, just like the numpoints one, which indicates the number of points to add to the created
sample grid.
Since we have declared an output of type vector named out, we have to create a variable named out and store a
Spatial*DataFrame object in it (in this case, a SpatialPointsDataFrame). You can use any name for
your intermediate variables. Just make sure that the variable storing your final result has the same name that you
used to declare it, and contains a suitable value.
In this case, the result obtained from the spsample method has to be converted explicitly into a
SpatialPointsDataFrame object, since it is itself an object of class ppp, which is not a suitable class
to be retuned to SEXTANTE.
If you algorithm does not generate any layer, but a text result in the console instead, you have to tell SEXTANTE
that you want the console to be shown once the execution is finished. To do so, just start the command lines that
produce the results you want to print with the > (‘greater’) sign. The output of all other lines will not be shown.
For instance, here is the description file of an algorithms that performs a normality test on a given field (column)
of the attributes of a vector layer:
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##layer=vector
##field=field layer
##nortest=group
library(nortest)
>lillie.test(layer[[field]])
The output ot the last line is printed, but the output of the first is not (and neither are the outputs from other
command lines added automatically by SEXTANTE).
If your algorithm creates any kind of graphics (using the plot() method), add the following line:
##showplots
This will cause SEXTANTE to redirect all R graphical outputs to a temporary file, which will be later opened once
R execution has finished.
Both graphics and console results will be shown in the SEXTANTE results manager.
For more information, please check the script files provided with SEXTANTE. Most of them are rather simple and
will greatly help you understand how to create your own ones.
17.7.4 GRASS
Configuring GRASS is not much different from configuring SAGA. First, the path to the GRASS folder has to be
defined, but only if you are running Windows. Additionaly, a shell interpreter (usually msys.exe, which can be
found in most GRASS for Windows distributions) has to be defined and its path set up as well.
By default, SEXTANTE tries to configure its GRASS connector to use the GRASS distribution that ships along
with QGIS. This should work without problems in most systems, but if you experience problems, you might have
to do it manually. Also, if you want to use a different GRASS version, you can change that setting and point to
the folder where that other version is kept. GRASS 6.4 is needed for algorithms to work correctly.
If you are running Linux, you just have to make sure that GRASS is correctly installed, and that it can be run
without problem from a console.
GRASS algorithms use a region for calculations. This region can be defined manually using values similar to
the ones found in the SAGA configuration, or automatically, taking the minimum extent that covers all the input
layers used to execute the algorithm each time. If this is the behaviour you prefer, just check the Use min covering
region option in the GRASS configuration parameters.
GRASS includes help files describing each algorithm. If you set the GRASS help folder parameter, SEXTANTE
will open them when you use the [Show help] button from the parameters window of the algorithm.
The last parameter that has to be configured is related to the mapset. A mapset is needed to run GRASS, and
SEXTANTE creates a temporary one for each execution. You have to tell SEXTANTE if the data you are working
with uses geographical (lat/lon) coordinates or projected ones.
17.7.5 GDAL
No additional configuration is needed to run GDAL algorithms, since it is already incorporated to QGIS and
SEXTANTE can infere its configuration from it.
17.7.6 Orfeo ToolBox
Orfeo ToolBox (OTB) algorithms can be run from SEXTANTE if you have OTB installed in your system and
configured SEXTANTE properly so it can find all necessary files (command-line tools and libraries). Please note
that OTB binaries are not included in SEXTANTE, so you have to download and install the software yourself.
Please check the OTB website for more information.
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Once OTB is installed, start QGIS, open the SEXTANTE configuration dialog and configure OTB algorithm
provider. In the Orfeo Toolbox (image analysis) block you will find all settings related to OTB. First ensure that
algorithms are enabled.
Then configure path to the folder where OTB command-line tools and libraries are installed:
•
usually OTB applications folder point to /usr/lib/otb/applications and OTB command line
tools folder is /usr/bin
•
if you use OSGeo4W installer,
than install otb-bin package
C:\OSGeo4W\apps\orfeotoolbox\applications as OTB applications
C:\OSGeo4W\bin as OTB command line tools folder
and enter
folder and
17.7.7 TauDEM
To use this provider you need to install TauDEM command line tools.
Windows
Please visit TauDEM homepage for installation instructions and precompiled binaries for 32bit and 64bit systems.
IMPORTANT: you need TauDEM 5.0.6 executables, version 5.2 currently not supported.
Linux
There are no packages for most Linux distribution, so you should compile TauDEM by yourself. As TauDEM
uses MPICH2, first install it using your favorite package manager. Also TauDEM works fine with OpenMPI, so
you can use it instead of MPICH2.
Download TauDEM 5.0.6 source code and extract files in some folder.
Open linearpart.h file and add after line
#include "mpi.h"
add new line with
#include <stdint.h>
so you’ll get
#include "mpi.h"
#include <stdlib.h>
Save changes and close file. Now open tiffIO.h, find line #include "stdint.h" and replace quotes
("") with <>, so you’ll get
#include <stdint.h>
Save changes and close file. Create build directory and cd into it
mkdir build
cd build
Configure your build with command
CXX=mpicxx cmake -DCMAKE_INSTALL_PREFIX=/usr/local ..
and then compile
make
Finaly, to install TauDEM into /usr/local/bin, run
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sudo make install
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CHAPTER 18
Print Composer
The print composer provides growing layout and printing capabilities. It allows you to add elements such as the
QGIS map canvas, legend, scalebar, images, basic shapes, arrows and text labels. You can size, group, align and
position each element and adjust the properties to create your layout. The layout can be printed or exported to
image formats, Postscript, PDF or to SVG (export to SVG is not working properly with some recent Qt4 versions.
You should try and check individual on your system). You can save the layout as template and load it again in
another session. See a list of tools in table_composer_1:
Icon
Purpose
Icon
Purpose
Load from template
Save as template
Export to an image format
Export as PDF
Export print composition to SVG
Print or export as Postscript
Zoom to full extent
Zoom in
Zoom out
Refresh view
Revert last change
Restore last change
Add new map from QGIS map canvas
Add image to print composition
Add label to print composition
Add new legend to print composition
Add new scalebar to print composition
Add basic shape to print composition
Add arrow to print composition
Add attribute table to print composition
Select/Move item in print composition
Move content within an item
Group items of print composition
Ungroup items of print composition
Raise selected items
Lower selected items
Move selected items to top
Move selected items to bottom
Align selected items left
Align selected items right
Align selected items center
Align selected items center vertical
Align selected items top
Align selected items bottom
Table Composer 1: Print Composer Tools
All Print Composer tools are available in menus and as icons in a toolbar. The toolbar can be switched off and on
using the right mouse button holding the mouse over the toolbar.
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18.1 Open a new Print Composer Template
Before you start to work with the print composer, you need to load some raster and vector layers in the QGIS map
canvas and adapt their properties to suite your own convenience. After everything is rendered and symbolized to
your liking you click the
New Print Composer
icon in the toolbar or choose File → New Print Composer.
18.2 Using Print Composer
Opening the print composer provides you with a blank canvas to which you can add the current QGIS map canvas,
legend, scalebar, images, basic shapes, arrows and text. Figure_composer_1 shows the initial view of the print
composer with an activated
Snap to grid mode but before any elements are added.
Figure 18.1: Print Composer
The print composer provides three tabs:
• The Composition tab allows you to set paper size, orientation, the print quality for the output file in dpi and
to activate snapping to a grid of a defined resolution. Please note, the
Snap to grid feature only works,
if you define a grid resolution > 0. Furthermore you can also activate the
Print as raster checkbox. This
means all elements will be rastered before printing or saving as Postscript of PDF.
Select/Move item
• The Item Properties tab displays the properties for the selected map element. Click the
icon to select an element (e.g. legend, scalebar or label) on the canvas. Then click the Item Properties tab
and customize the settings for the selected element.
• The Command history tab displays a history of all changes applied to the print composer layout. With a
mouse click it is possible to undo and redo layout steps back and forth to a certain status.
You can add multiple elements to the composer. It is also possible to have more than one map view or legend or
scalebar in the print composer canvas. Each element has its own properties and in the case of the map, its own
extent. If you want to remove any elements from the composer canvas you can do that with the Delete or the
Backspace key.
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18.3 Adding a current QGIS map canvas to the Print Composer
Add new map
toolbar button in the print composer toolbar, to add the QGIS map canvas. Now drag a
Click on the
rectangle on the composer canvas with the left mouse button to add the map. To display the current map, you can
choose between three different modes in the map Item Properties tab:
• Rectangle is the default setting. It only displays an empty box with a message ‘Map will be printed here’.
• Cache renders the map in the current screen resolution. If case you zoom in or out the composer window,
the map is not rendered again but the image will be scaled.
• Render means, that if you zoom in or out the composer window, the map will be rendered again, but for
space reasons, only up to a maximum resolution.
Cache is default preview mode for newly added print composer maps.
Select/Move item
You can resize the map element by clicking on the
button, selecting the element, and dragging
one of the blue handles in the corner of the map. With the map selected, you can now adapt more properties in the
map Item Properties tab.
Move item content
icon and move the
To move layers within the map element select the map element, click the
layers within the map element frame with the left mouse button. After you found the right place for an element,
you can lock the element position within the print composer canvas. Select the map element and click on the right
Lock
mouse button to
activating the
the element position and again to unlock the element. You can lock the map element also
Lock layers for map item checkbox in the Map dialog of the Item Properties tab.
Note: QGIS is now able to show labels from the new labeling plugin also in the map composer, but it is not yet
scaled correctly. So it might be necessary to switch back to the standard labeling in some cases.
18.3.1 Map item properties tab — Map and Extents dialog
Map dialog
The Map dialog of the map Item Properies tab provides following functionalities (see figure_composer_2):
Figure 18.2: Map Dialog
• The Preview area allows to define the preview modes ‘Rectangle’, ‘Cache’ and ‘Render’, as described
above. Click on the [Update preview] button to apply changes to the map view.
• The Map area allows to resize the map element specifying the width and height or the scale. The field
Rotation
allows to rotate the map element content clockwise in degrees. Note, a coordinate frame
can only be added with the default value 0. Furthermore you can enable the checkboxes
map items and
Lock layers for
Draw map canvas items.
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If you change the view on the QGIS map canvas by zooming or panning or changing vector or raster properties,
you can update the print composer view selecting the map element in the print composer and clicking the [Update
preview] button.
Extents dialog
The Extents dialog of the map item tab provides following functionalities (see Figure figure_composer_3)):
Figure 18.3: Extents Dialog
• The Map extent area allow to specify the map extent using Y and X min/max values or clicking the [Set to
map canvas extent] button.
If you change the view on the QGIS map canvas by zooming or panning or changing vector or raster properties,
you can update the print composer view selecting the map element in the print composer and clicking the [Update
preview] button in the map Item Properties tab (see Figure figure_composer_2 a)).
18.3.2 Map item properties tab — Grid and General options dialog
Grid dialog
The Grid dialog of the map Item Properties tab provides following functionalities (see Figure_composer_4):
Figure 18.4: Grid Dialog
• The
Show grid checkbox allows to overlay a grid to the map element. As grid type you can specify to
use solid line or cross. Furthermore you can define an interval in X and Y direction, an X and Y offset, and
the width used for cross or line grid type.
• The
Draw annotation checkbox allows to add coordinates to the map frame. The annotation can be
drawn inside or outside the map frame. The annotation direction can be defined as horizontal, vertical,
horizontal and vertical, or boundary direction. And finally you can define the grid color, the annotation font,
the annotation distance from the map frame and the precision of the drawn coordinates.
General options dialog
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The General options dialog of the map Item Properties tab provides following functionalities (see Figure_composer_5):
Figure 18.5: General Options Dialog
• Here you can define color and outline width for the element frame, set a background color and opacity for
the map canvas. The [Position and size] button opens the Set item position dialog and allows to set the map
canvas position using reference points or coordinates. Furthermore you can select or unselect to display the
element frame with the
Show frame checkbox. With the Item ID you can create a relationship to the
other print composer items.
18.4 Adding other elements to the Print Composer
Besides adding a current QGIS map canvas to the Print Composer, it is also possible to add, position, move and
customize legend, scalebar, images and label elements.
18.4.1 Label item properties tab - Label and General options dialog
Add label
icon, place the element with the left mouse button on the print composer
To add a label, click the
canvas and position and customize their appearance in the label Item Properties tab.
Label dialog
The Label dialog of the label item tab provides following functionalities:
Figure 18.6: Label Options Dialog
• The Label dialog offers to add text labels to the composer canvas. You can define the horizontal and vertical
alignment, select font and font color for the text and it is possible to define a text margin in mm.
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General options dialog
The General options dialog of the label Item Properties tab provides following functionalities:
Figure 18.7: General Options Dialog
• Here you can define color and outline width for the element frame, set a background color and opacity for
the label. The Position button opens the Set items position dialog and allows to set the map canvas position
using reference points or coordinates. Furthermore you can select or unselect to display the element frame
with the
Show frame checkbox. Use the Item ID to create a relationship to other print composer items.
18.4.2 Image item properties tab - Picture options and General options dialog
Add image
icon, place the element with the left mouse button on the print composer
To add an image, click the
canvas and position and customize their appearance in the image Item Properties tab.
Picture options dialog
The Picture options dialog of the image Item Properties tab provides following functionalities (see figure_composer_5 a):
Figure 18.8: Picture Options Dialog Dialog
• The Preloaded Images field then shows all pictures stored in the selected directories.
• The Options area shows the current selected picture and allows to define width, height and clockwise
rotation of the picture. It is also possible to add a user specific SVG path. Activating the
Sync with map
checkbox synchronizes the rotation of a picture in the QGIS map canvas (i.e. a rotated north arrow) with
the appropriate print composer image.
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• The Search directories area allows to add and remove directories with images in SVG format to the picture
database.
General options dialog
The General options dialog of the image Item Properties tab provides following functionalities:
Figure 18.9: General Options Dialog Dialog
• Here you can define color and outline width for the element frame, set a background color and opacity for
the picture. The [Position and size] button opens the Set item position dialog and allows to set the map
canvas position using reference points or coordinates. Furthermore you can select or unselect to display the
element frame with the
print composer items.
Show frame checkbox. With the Item ID you can create a relationship to other
18.4.3 Legend item properties tab - General, Legend items and Item option dialog
Add new legend
To add a map legend, click the
icon, place the element with the left mouse button on the print
composer canvas and position and customize their appearance in the legend Item Properties tab.
General dialog
The General dialog of the legend item tab provides following functionalities (see figure_composer_10):
Figure 18.10: General Dialog
• Here you can adapt the legend title. You can change the font of the legend title, layer and item name. You
can change width and height of the legend symbol and you can add layer, symbol, icon label and box space.
Since QGIS 1.8, you can wrap the text of the legend title to a given character.
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Legend items dialog
The Legend items dialog of the legend Item Properties tab provides following functionalities (see figure_composer_11):
Figure 18.11: Legend Items Dialog
• The legend items window lists all legend items and allows to change item order, edit layer names, remove
and restore items of the list. After changing the symbology in the QGIS main window you can click on
[Update] to adapt the changes in the legend element of the print composer. The item order can be changed
using the [Up] and [Down] buttons or with ‘drag and drop’ functionality.
General options dialog
The General options dialog of the legend Item Properties tab provides following functionalities (see figure_composer_12):
Figure 18.12: General Options Dialog
• Here you can define color and outline width for the element frame, set a background color and opacity for
the legend. The [Position and size] button opens the Set item position dialog and allows to set the map
canvas position using reference points or coordinates. Furthermore you can select or unselect to display the
element frame with the
composer items.
Show frame checkbox. Use the Item ID to create a relationship to other print
18.4.4 Scalebar item properties tab - Scalebar and General options dialog
Add new scalebar
To add a scalebar, click the
icon, place the element with the left mouse button on the print
composer canvas and position and customize their appearance in the scalebar Item Properties tab.
Scalebar dialog
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The Scalebar dialog of the scalebar Item Properties tab provides following functionalities (see figure_composer_13):
Figure 18.13: Scalebar Options Dialog
• The Scalebar dialog allows to define the segment size of the scalebar in map units, the map units used per
bar units, and how many left and right segments units from 0 should be used.
• You can define the scalebar style, available is single and double box, line ticks middle, up and down and a
numeric style.
• Furthermore you can define height, line width, label and box space of the scalebar. Add a unit label and
define the scalebar font and color.
General options dialog
The General options dialog of the scalebar Item Properties tab provides following features (see figure_composer_7
b)):
Figure 18.14: General Options Dialog
• Here you can define color and outline width for the element frame, set a background color and opacity for
the scalebar. The [Position and size] button opens the Set items position dialog and allows to set the map
canvas position using reference points or coordinates. Furthermore you can select or unselect to display the
element frame with the
Show frame checkbox. With the Item ID you can create a relationship to the
other print composer items.
18.5 Navigation tools
For map navigation the print composer provides 4 general tools:
•
Zoom in
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•
Zoom out
•
Zoom to full extend
•
Refresh the view
(if you find the view in an inconsistent state)
18.6 Revert and Restore tools
During the layout process it is possible to revert and restore changes. This can be done with the revert and restore
tools:
•
Revert last changes
•
Restore last changes
or by mouse click within the Command history tab (see figure_composer_9).
Figure 18.15: Command history in the Print Composer
18.7 Add Basic shape and Arrow
It is possible to add basic shapes (Ellipse, Rectangle, Triangle) and arrows to the print composer canvas.
The Shape dialog allows to draw an ellipse, rectangle, or triangle in the print composer canvas. You can define its
outline and fill color, the outline width and a clockwise rotation.
The Arrow dialog allows to draw an arrow in the print composer canvas. You can define color, outline and arrow
width and it is possible to use a default marker and no marker and a SVG marker. For the SVG marker you can
additionally add a SVG start and end marker from a directory on your computer.
18.8 Add attribute table values
It is possible to add parts of a vector attribute table to the print composer canvas.
Table dialog
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Figure 18.16: Shape Dialog
Figure 18.17: Arrow Dialog
The Table dialog of the attribute table item tab provides following functionalities (see figure_composer_20):
Figure 18.18: Table Dialog
• The Table dialog allows to select the vector layer and columns of the attribute table. Attribute columns can
be sorted and you can define to show its values ascending or descending.
• You can define the maximum number of rows to be displayed and if attributes are only shown for visible
features of the current composer canvas.
• Additionally you can define the grid characteristics of the table and the header and content font.
General options dialog
The General options dialog of the attribute table item tab provides following functionalities (see figure_composer_21):
• Here you can define color and outline width for the element frame, set a background color and opacity
for the table. The [Position and size] button opens the Set item position dialog and allows to set the map
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Figure 18.19: General Options Dialog
canvas position using reference points or coordinates. Furthermore you can select or unselect to display the
element frame with the
composeritems.
Show frame checkbox. Use the Item ID to create a relationship to the other print
18.9 Raise, lower and align elements
Raise selected items
pulldown menu. Choose an element
Raise or lower functionalities for elements are inside the
on the print composer canvas and select the matching functionality to raise or lower the selected element compared
to the other elements (see table_composer_1).
Align selected items
There are several alignment functionalities available within the
pulldown menu (see table_composer_1). To use an alignment functionality , you first select some elements and then click on the matching
alignment icon. All selected will then be aligned within to their common bounding box.
18.10 Creating Output
Figure_composer_22 shows the print composer with an example print layout including each type of map element
described in the sections above.
Figure 18.20: Print Composer with map view, legend, scalebar, coordinates and text added
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The print composer allows you to create several output formats and it is possible to define the resolution (print
quality) and paper size:
Print
icon allows to print the layout to a connected printer or a Postscript file depending on installed
• The
printer drivers.
• The
JPG,...
Export as image
• The
Export as PDF
saves the defined print composer canvas directly as a PDF.
• The
Export as SVG
icon saves the print composer canvas as a SVG (Scalable Vector Graphic).
icon exports the composer canvas in several image formats such as PNG, BPM, TIF,
Note: Currently the SVG output is very basic. This is not a QGIS problem, but a problem of the underlaying Qt
library. This will hopefully be sorted out in future versions.
18.11 Saving and loading a print composer layout
Save as template
Load from template
With the
and
icons you can save the current state of a print composer session
as a .qpt template and load the template again in another session.
Composer Manager
The
button in the QGIS toolbar and in File → Composer Manager allows to add a new composer template or to manage already existing templates.
Figure 18.21: The Print Composer Manager
18.11. Saving and loading a print composer layout
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CHAPTER 19
Plugins
19.1 QGIS Plugins
QGIS has been designed with a plugin architecture. This allows many new features/functions to be easily added
to the application. Many of the features in QGIS are actually implemented as either core or external plugins.
• Core Plugins are maintained by the QGIS Development Team and are automatically part of every QGIS
distribution. They are written in one of two languages: C++ or Python. More information about core plugins
are provided in Section Using QGIS Core Plugins
• External Plugins are currently all written in Python. They are stored in external repositories and maintained
by the individual authors. They can be added to QGIS using the Python Plugin Installer. More information
about external plugins is provided in Section Loading an external QGIS Plugin.
19.1.1 Managing Plugins
Managing plugins in general means loading or unloading them using the Plugin Manager. External plugins can
be installed and directly activated or uninstalled using the Python Plugin Installer. To deactivate and reactivate
external plugins, the Plugin Manager is used again.
Loading a QGIS Core Plugin
Loading a QGIS Core Plugin is done from the main menu Plugins → Manage Plugins
The Plugin Manager lists all the available plugins and their status (loaded or unloaded), including all core plugins
and all external plugins that have been installed and automatically activated using the Python Plugin Installer (see
Section Loading an external QGIS Plugin). Those plugins that are already loaded have a check mark to the left of
their name. Figure_plugins_1 shows the Plugin Manager dialog.
To enable a particular plugin, click on the checkbox to the left of the plugin name, and click [OK]. When you exit
the application, a list of loaded plugins is retained, and the next time you run QGIS these plugins are automatically
loaded.
Tip: Crashing Plugins
If you find that QGIS crashes on startup, a plugin may be at fault. You can stop all plugins from loading by editing
your stored settings file (see Options for location). Locate the plugins settings and change all the plugin values to
false to prevent them from loading.
For example, to prevent the ‘Delimited text’ plugin from loading, the entry in
$HOME/.config/QuantumGIS/qgis.conf on Linux should look like this: Add Delimited Text
Layer=false.
Do this for each plugin in the [Plugins] section. You can then start QGIS and add the plugins one at a time from
the Plugin Manager to determine which plugin is causing the problem.
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Figure 19.1: Plugin Manager
Loading an external QGIS Plugin
External QGIS plugins are written in Python. They are by default stored in either the ‘Official’ QGIS Repository,
or in various other external repositories maintained by individual authors. The ‘Official’ QGIS Repository is added
by default in Python Plugin installer.
Detailed documentation about the usage, minimum QGIS version, homepage, authors, and other important information are provided for the ‘Official’ QGIS Repository at http://plugins.qgis.org/plugins/. For other external
repositories, they might be available with the external plugins themselves. In general it is not included in this
manual.
Note: Updates of core python plugins may be available in this repository as external overlays.
Note: fTools, Mapserver Export, and the Plugin Installer are Python plugins, but they are also part of the QGIS
sources, and are automatically loaded and enabled inside the QGIS Plugin Manager (see Section Loading an
external QGIS Plugin).
Currently there are over 150 external plugins available from the ‘Official’ QGIS Repository. Some of these plugins
offer functionality that will be required by many users (for example: providing the user with the ability to view and
edit OpenStreetMap data, or to add GoogleMap layers) while others offer very specialized functions (for example:
Calculate economic pipe diameters for water supply networks).
It is, however, quite straightforward to search through all the available external plugins by providing keywords,
choosing a named repository and/or filtering on the status of plugins (currently installed or uninstalled in your
system). Searching and filtering is done from the QGIS Python Plugin Installer (see figure_plugins_2).
Tip: Add more repositories
To add external author repositories, open the Plugin Installer (Plugins → Fetch Python Plugins), go to the tab
Repositories, and click [Add]. If you do not want one or more of the added repositories, they can be disabled via
the [Edit...] button, or completely removed with the [Delete] button.
There is only one step required to integrate external plugins into QGIS:
• Download an external plugin from a repository using the Python Plugin Installer (see Using the QGIS
Python Plugin Installer). The new external plugin will be added to the list of available plugins in the Plugin
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Manager and is automatically loaded.
Using the QGIS Python Plugin Installer
Fetch Python Plugins. The Plugin
In order to download and install an external Python plugin, go to Plugins →
Installer window will appear (figure_plugins_2) with the tab Plugins, containing a list of all locally installed
Python plugins, as well as plugin available in remote repositories.
Figure 19.2: Installing external python plugins
Each plugin can be either:
• not installed - this means the plugin is available in the repository, but is not installed yet. In order to install
it, select the plugin from the list and click the button [Install plugin].
• new - this means that the plugin is newly available in the repository.
• installed - this indicates that the plugin is already installed. If it is also available in any repository the
[Reinstall plugin] button will be enabled. If the available version is older than the installed version, the
[Downgrade plugin] button will appear instead.
• upgradeable - this means that the plugin is installed, but there is an updated version available. In this case,
the [Upgrade plugin] and [Upgrade all] buttons will be enabled.
• invalid - this means that the plugin is installed, but is unavailable or broken. The reason will be explained
in the plugin description field.
Plugins tab
To install a plugin, select it from the list and click the [Install plugin] button. The plugin is then activated and
installed in its own directory.
•
Linux and other unices
– /share/qgis/python/plugins
– $HOME/.qgis/python/plugins
•
Mac OS X
– /Contents/MacOS/share/qgis/python/plugins
– /Users/$USERNAME/.qgis/python/plugins
•
Windows
– C:\Program Files\QGIS\python\plugins
– C:\Documents and Settings\$USERNAME\.qgis\python\plugins
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If the installation is successful, a confirmation message will appear.
If the installation fails, the reason for the failure will be displayed in a warning dialog. Most often, errors are the
result of connection problems and/or missing Python modules. In the former case you will likely need to wait
before trying the install again, in the latter case, you should install the missing modules relevant to your operating
system prior to using the plugin. For Linux, most required modules should be available via a package manager.
For install instructions in Windows visit the module home page.
If you are using a proxy, you may need to configure it under Edit → Options (Gnome, OSX) or Settings → Options
(KDE, Windows)‘ on the Proxy tab.
The [Uninstall plugin] button is enabled only if the selected plugin is installed and is not a core plugin. Note
that if you have installed an update to a core plugin, you can uninstall this update with the [Uninstall plugin] and
revert to the version shipped with Quantum GIS. This default version however, cannot be uninstalled.
Repositories tab
The second tab Repositories, contains a list of plugin repositories available for the Plugin Installer. By default,
only the QGIS Official Repository is enabled. You can add several user-contributed repositories, including the
central QGIS Contributed Repository and other external repositories by clicking the [Add ...] button. The added
repositories contain a large number of useful plugins which are not maintained by the QGIS Development Team.
As such, we cannot take any responsibility for them. You can also manage the repository list manually, that is
add, remove, and edit the entries. Temporarily disabling a particular repository is possible by clicking the [Edit
...] button.
Options tab
Check for updates on
The Options tab is where you can configure the settings of the Plugin Installer. The
startup checkbox tells QGIS to automatically look for plugin updates and news. By default, if this feature is
enabled all repositories listed and enabled in the Repositories tab are checked for updates each time the program
is started. The frequency of update checking can be adjusted using the dropdown menu, and may be adjusted
from once a day right up to once a month. If a new plugin or update is available for one of the installed plugins, a
notification will appear in the Status Bar. If the checkbox is disabled, looking for updates and news is performed
only when the Plugin Installer is manually launched from the menu.
Although the plugin installer update can handle ports different from 80, some internet connections will cause
problems when attempting to automatically check for updates. In these cases, a Looking for new plugins... indicator will remain visible in the Status Bar during your entire QGIS session, and may cause a program crash when
exiting. In this case please disable the checkbox.
In addition, you may specify the type of plugins that are displayed by the Python Plugin Installer. Under Allowed
plugins, you can specify whether you would like to:
•
Only show plugins from the official repository
•
Show all plugins except those marked as experimental
•
Show all plugins, even those marked as experimental
Tip: Using experimental plugins
Experimental plugins are generally unsuitable for production use. These plugins are in the early stages of development, and should be considered ‘incomplete’ or ‘proof of concept’ tools. The QGIS development team does not
recommend installing these plugins unless you intend to use them for testing purposes.
19.1.2 Data Providers
Data Providers are ‘special’ plugins that provides access to a data store. By default, QGIS supports PostGIS layers
and disk-based data stores supported by the GDAL/OGR library. A Data Provider plugin extends the ability of
QGIS to use other data sources.
Data Provider plugins are registered automatically by QGIS at startup. They are not managed by the Plugin
Manager but used behind the scenes when a data type is added as a layer in QGIS.
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19.2 Using QGIS Core Plugins
Icon
Plugin
Description
Manual Reference
Add Delimited Text
Layer
Loads text files containing x,y
coordinates
Delimited Text Plugin
Coordinate Capture
Capture mouse coordinate in different
CRS
Coordinate Capture Plugin
DB Manager
Diagram Overlay
Manage your databases within QGIS
Add Diagrams for vectors
DB Manager Plugin
Diagram Overlay Plugin
DXF2Shape
Converter
Converts from DXF to SHP file format
Dxf2Shp Converter Plugin
eVis
Event Visualization Tool
eVis Plugin
fTools
A suite of vector tools
fTools Plugin
GPS Tools
Tools for loading and importing GPS data
GPS Plugin
GRASS
GRASS functionality
GRASS GIS Integration
GDAL Tools
GDAL raster functionality
GDAL Tools Plugin
Georeferencer
GDAL
Georeference Raster with GDAL
Georeferencer Plugin
Heatmap
Create heatmap raster from input vector
points
Heatmap Plugin
Interpolation plugin
Interpolation on base of vertices of a
vector layer
Interpolation Plugin
MapServer Export
Plugin
Export a QGIS project file to a
MapServer map file
MapServer Export Plugin
Offline Editing
Offline editing and synchronizing with
database
Offline Editing Plugin
OpenStreetMap
Access OpenStreetMap
OpenStreetMap
Oracle Spatial
Georaster
Access Oracle Spatial GeoRasters
Oracle GeoRaster Plugin
Plugin Installer
Download and install python plugins
Using the QGIS Python Plugin
Installer
Raster Terrain
Analysis
Road graph Plugin
Compute geomorphological features
from DEMs
Shortest path analysis
Raster Terrain Analysis Plugin
SPIT
Shapefile to PostGIS Import Tool
Importing Data into PostgreSQL
SQL Anywhere
plugin
Access SQL anywhere DB
SQL Anywhere Plugin
Spatial Query
Spatial queries on vectors
Spatial Query Plugin
Zonal Statistics
Calculate raster statistics for vector
polygons
Zonal Statistics Plugin
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19.3 Coordinate Capture Plugin
The coordinate capture plugin is easy to use and provides the ability to display coordinates on the map canvas for
two selected Coordinate Reference Systems (CRS).
Figure 19.3: Coordinate Capture Plugin
1. Start QGIS, select
Project Properties from the Settings (KDE, Windows) or File (Gnome, OSX) menu
and click on the Projection tab. As an alternative you can also click on the
right-hand corner of the statusbar.
CRS status
icon in the lower
Enable on the fly projection checkbox and select a projected coordinate system of your
2. Click on the
choice (see also Working with Projections).
3. Load the coordinate capture plugin in the Plugin Manager (see Loading a QGIS Core Plugin) and ensure
that the dialog is visible by going to View → Panels and ensuring that
Coordinate Capture is enabled.
The coordinate capture dialog appears as shown in Figure figure_coordinate_capture_1.
4. Click on the
selected above.
Click to the select the CRS to use for coordinate display
icon and select a different CRS from the one you
5. To start capturing coordinates, click on [Start capture]. You can now click anywhere on the map canvas
and the plugin will show the coordinates for both of your selected CRS.
6. To enable mouse coordinate tracking click the
mouse tracking
icon.
7. You can also copy selected coordinates to the clipboard.
19.4 DB Manager Plugin
The DB Manager Plugin is officially part of QGIS core and intends to replace the SPIT Plugin and the PostGIS
Manager Plugin and additionally to integrate all other database formats supported by QGIS in one user interface.
DB Manager
Plugin provides several features. You can drag layers from the QGIS Browser into the DB
The
Manager and it will import your layer into your spatial database. You can drag and drop tables between spatial
databases and they will get imported. You can also use the DB Manager to execute SQL queries against your
spatial database and then view the spatial output for queries by adding the results to QGIS as a query layer.
The Database menu allows to connect to an existing database, to start the SQL-window and to exit the DB Manager
Plugin. The Schema menu includes tools to create and delete (empty) schemas and, if topology is available (e.g.
PostGIS 2) to start a TopoViewer. The menu Table allows to create and edit tables and to delete tables and views. It
is also possible to empty tables and to move tables from one to another schema. Finally you can also run Vacuum
Analyze and add Versioning Support to a table.
The Tree window lists all existing databases supported by QGIS. With a double-click you can connect to the
database. With the right-mouse button you can rename and delete existing schemas and tables. Tables can also be
added to the QGIS canvas with the context menu.
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Figure 19.4: DB Manager dialog (KDE)
If connected to a database, the main window of the DB Manager offers three tabs. The Info tab provides information about the table and its geometry as well as about existing Fields, Constraints and Indexes. It also allows to
run Vacuum Analyze and to create a spatial index on a selected table, if not already done. The Table tab shows all
attributes and the Preview tab renders the geometries as preview.
19.5 Delimited Text Plugin
The Delimited Text plugin allows you to load a delimited text file as a layer in QGIS.
19.5.1 Requirements
To view a delimited text file as layer, the text file must contain:
1. A delimited header row of field names. This must be the first line in the text file.
2. The header row must contain an X and Y field. These fields can have any name.
3. The x and y coordinates must be specified as a number. The coordinate system is not important.
As an example of a valid text file we import the elevation point data file elevp.csv coming with the QGIS
sample dataset (See Section Sample Data):
X;Y;ELEV
-300120;7689960;13
-654360;7562040;52
1640;7512840;3
[...]
Some items of note about the text file are:
1. The example text file uses ; (semicolon) as delimiter. Any character can be used to delimit the fields.
2. The first row is the header row. It contains the fields X, Y and ELEV.
3. No quotes (") are used to delimit text fields.
4. The x coordinates are contained in the X field.
5. The y coordinates are contained in the Y field.
19.5.2 Using the Plugin
To use the plugin you must first enable it as described in Section Managing Plugins.
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Click the new toolbar icon
ure_delimited_text_1.
Add Delimited Text Layer
to open the Delimited Text dialog as shown in fig-
Figure 19.5: Delimited Text Dialog
First select the file (e.g., qgis_sample_data/csv/elevp.csv) to import by clicking on the [Browse]
button. Once the file is selected, the plugin attempts to parse the file using the last used delimiter, in this case a
semicolon (;). To properly parse the file, it is important to select the correct delimiter. To change the delimiter to
tab use \t (this is a regular expression for the tab character).
Once the file is parsed, choose the X and Y fields from the dropdown lists and if available also the WKT field for
the CRS information. Finally enter a Layer name (e.g., elevp ) as shown in figure_delimited_text_1 . To add the
layer to the map, click [OK]. The delimited text file now behaves as any other map layer in QGIS.
19.6 Diagram Overlay Plugin
The Diagram Overlay Plugin allows you to add a graphic overlay to a vector layer (see figure_overlay_1). It
provides additional and not yet implemented features to the Diagrams tab, described in secion Diagrams Tab.
Before starting, the Diagram Overlay Plugin needs to be activated using the Plugin Manager (see Section Loading
a QGIS Core Plugin). It will then appear as Overlay tab in the Layer Properties dialog next to the Diagrams tab.
The Overlay tab provides support for Pie charts, Bar charts and proportional SVG symbols.
Similar to the Diagrams tab, we will demonstrate an example and overlay the alaska boundary layer a piechart
diagram showing some temperature data from a climate vector layer. Both vector layers are part of the QGIS
sample dataset (see Section Sample Data).
Load Vector
1. First click on the
icon, browse to the QGIS sample dataset folder and load the two vector
shape layers alaska.shp and climate.shp.
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Figure 19.6: Vector properties dialog with overlay tab
2. Double click the climate layer in the map legend to open the Layer Properties dialog.
3. Click on the Overlay tab, activate
combobox.
Display diagrams and select ‘Pie Chart’ from Diagram type
4. We want to display the values of the three columns T_F_JAN, T_F_JUL and T_F_MEAN. First select
T_F_JAN as Attributes and click the [Add] button, then T_F_JUL and finally T_F_MEAN.
5. Diagram size is based on linear scaling of a classification attribute. We choose T_F_JUL, click on [Find
maximum value] and set size to 20 and Size unit
to ‘Millimeter’.
6. Now click [Apply] to display the diagram in the QGIS main window.
7. You can now adapt the chart size, or change the attribute colors double clicking on the color values in the
attribute field. Figure_overlay_2 gives an impression.
8. Finally click [Ok].
Figure 19.7: Pie chart diagram from temperature data overlayed on a map
Additionally in the Settings → Options dialog, there is a Overlay tab where it is possible to select the placement
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algorithm of the diagrams. The ‘Central point’ method is a generic one, the others use algorithms of the PAL
library. They also consider diagram objects and labels in different layers.
19.7 Dxf2Shp Converter Plugin
The dxf2shape converter plugin can be used to convert vector data from DXF to Shapefile format. It requires the
following parameters to be specified before running:
Figure 19.8: Dxf2Shape Converter Plugin
• Input DXF file: Enter path to the DXF file to be converted
• Output Shp file: Enter desired name of the Shapefile to be created
• Output file type: Specify the geometry type of the output Shapefile. Currently supported types are polyline,
polygon, and point.
• Export text labels: When this checkbox is enabled, an additional Shapefile point layer will be created, and
the associated dbf table will contain information about the “TEXT” fields found in the dxf file, and the text
strings themselves.
19.7.1 Using the Plugin
1. Start QGIS, load the Dxf2Shape plugin in the Plugin Manager (see Section Loading a QGIS Core Plugin)
Dxf2Shape Converter
and click on the
icon which appears in the QGIS toolbar menu. The Dxf2Shape plugin
dialog appears as shown in Figure_dxf2shape_1.
2. Enter input DXF file, a name for the output Shapefile and the Shapefile type.
3. Enable the
Export text labels checkbox if you want to create an extra point layer with labels.
4. Click [OK].
19.8 eVis Plugin
The Biodiversity Informatics Facility at the American Museum of Natural History’s (AMNH) Center for Biodiversity and Conservation (CBC) (this section is derived from Horning, N., K. Koy, P. Ersts. 2009. eVis (v1.1.0)
User’s Guide. American Museum of Natural History, Center for Biodiversity and Conservation. Available from
http://biodiversityinformatics.amnh.org/, and released under the GNU FDL.) has developed the Event Visualization Tool (eVis), another software tool to add to the suite of conservation monitoring and decision support tools for
guiding protected area and landscape planning. This plugin enables users to easily link geocoded (i.e., referenced
with latitude and longitude or X and Y coordinates) photographs, and other supporting documents, to vector data
in QGIS.
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eVis is now automatically installed and enabled in new versions of QGIS, and as with all plugins, it can be disabled
and enabled using the Plugin Manager (See Managing Plugins).
The eVis plugin is made up of three modules: the ‘Database Connection tool’, ‘Event ID tool’, and the ‘Event
Browser’. These work together to allow viewing of geocoded photographs and other documents that are linked to
features stored in vector files, databases, or spreadsheets.
19.8.1 Event Browser
The Event Browser module provides the functionality to display geocoded photographs that are linked to vector
features displayed in the QGIS map window. Point data, for example, can be from a vector file that can be input
using QGIS or it can be from the result of a database query. The vector feature must have attribute information
associated with it to describe the location and name of the file containing the photograph and, optionally, the
compass direction the camera was pointed when the image was acquired. Your vector layer must be loaded into
QGIS before running the Event Browser.
Launch the Event Browser module
eVis Event Browser
icon or click on Database → eVis →
To launch the Event browser module either click on the
eVis Event Browser. This will open the Generic Event Browser window.
The Generic Event Browser window has three tabs displayed at the top of the window. The Display tab is used
to view the photograph and its associated attribute data. The Options tab provides a number of settings that can
be adjusted to control the behavior of the eVis plugin. Lastly, the Configure External Applications tab is used to
maintain a table of file extensions and their associated application to allow eVis to display documents other than
images.
Understanding the Display window
To see the Display window click on the Display tab in the Generic Event Browser window. The Display window
is used to view geocoded photographs and their associated attribute data.
1. Display window: A window where the photograph will appear.
2. Zoom in button: Zoom in to see more detail. If the entire image cannot be displayed in the display window,
scroll bars will appear on the left and bottom sides of the window to allow you to pan around the image.
3. Zoom out button: Zoom out to see more area.
4. Zoom to full extent button: Displays the full extent of the photograph.
5. Attribute information window: All of the attribute information for the point associated with the photograph being viewed is displayed here. If the file type being referenced in the displayed record is not an
image but is of a file type defined in the Configure External Applications tab then when you double-click
on the value of the field containing the path to the file the application to open the file will be launched to
view or hear the contents of the file. If the file extension is recognized the attribute data will be displayed in
green.
6. Navigation buttons: Use the Previous and Next buttons to load the previous or next feature when more
than one feature is selected.
7. Feature indicator: This heading indicates which feature is being displayed and how many features are
available for display.
Understanding the Options window
1. File path: A dropdown list to specify the attribute field that contains the directory path or URL for the
photographs or other documents being displayed. If the location is a relative path then the checkbox must
be clicked. The base path for a relative path can be entered in the Base Path text box below. Information
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Figure 19.9: The eVis display window
Figure 19.10: The eVis Options window
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about the different options for specifying the file location are noted in the section Specifying the location
and name of a photograph below.
2. Compass bearing display field: A dropdown list to specify the attribute field that contains the compass
bearing associated with the photograph being displayed. If compass bearing information is available it is
necessary to click the checkbox to the left of the dropdown menu title.
3. Compass offset setting: Compass offsets can be used to compensate for declination (adjust bearings colManual radiobutton to enter the offset
lected using magnetic bearings to true north bearings). Click the
in the text box or click the
From Attribute radiobutton to select the attribute field containing the offsets.
For both of these options east declinations should be entered using positive values and west declinations
should use negative values.
4. Directory base path: The base path onto which the relative path defined in Figure_eVis_2 (A) will be
appended.
5. Replace path: If this checkbox is checked, only the file name from the A will be appended to the Base Path.
6. Apply rule to all documents: If checked, the same path rules that are defined for photographs will be used
for non-image documents such as movies, text documents, and sound files. If not checked the path rules
will only apply to photographs and other documents will ignore the Base Path parameter.
7. Save settings: If the checkbox is checked the values for the associated parameters will be saved for the next
session when the window is closed or when the [Save] button below is pressed.
8. Reset values: Resets the values on this line to the default setting.
9. Restore faults: This will reset all of the fields to their default settings. It has the same effect as clicking all
of the [Reset] buttons.
10. Save: This will save the settings without closing the Options pane.
Understanding the Configure External Applications window
Figure 19.11: The eVis External Applications window
1. File reference table: A table containing file types that can be opened using eVis. Each file type needs a
file extension and the path to an application that can open that type of file. This provides the capability of
opening a broad range of files such as movies, sound recordings, and text documents instead of only images.
2. Add new file type: Add a new file type with a unique extension and the path for the application that can
open the file.
3. Delete current row: Delete the file type highlighted in the table and defined by a file extension and a path
to an associated application.
19.8.2 Specifying the location and name of a photograph
The location and name of the photograph can be stored using an absolute or relative path or a URL if the photograph is available on a web server. Examples of the different approaches are listed in Table evis_examples.
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X
780596
780596
780819
780596
Y
1784017
1784017
1784015
1784017
FILE
C:\Workshop\eVis_Data\groundphotos\DSC_0168.JPG
/groundphotos/DSC_0169.JPG
http://biodiversityinform.org/testdata/DSC_0170.JPG
pdf:http://www.test.com/attach.php?attachment_id-12
BEARING
275
80
10
76
19.8.3 Specifying the location and name of other supporting documents
Supporting documents such as text documents, videos, and sound clips can also be displayed or played by eVis.
To do this it is necessary to add an entry in the file reference table that can be accessed from the Configure External
Applications window in the Generic Event Browser that matches the file extension to an application that can be
used to open the file. It is also necessary to have the path or URL to the file in the attribute table for the vector
layer. One additional rule that can be used for URLs that don’t contain a file extension for the document you want
to open is to specify the file extension before the URL. The format is — file extension:URL. The URL
is preceded by the file extension and a colon, and is particularly useful for accessing documents from Wikis and
other web sites that use a database to manage the web pages (see Table evis_examples).
19.8.4 Using the Generic Event Browser
When the Event Browser window opens a photograph will appear in the display window if the document referenced in the vector file attribute table is an image and if the file location information in the Options window is
properly set. If a photograph is expected and it does not appear it will be necessary to adjust the parameters in the
Options window.
If a supporting document (or an image that does not have a file extension recognized by eVis) is referenced in the
attribute table the field containing the file path will be highlighted in green in the attribute information window if
that file extension is defined in the file reference table located in the Configure External Applications window. To
open the document double-click on the green-highlighted line in the attribute information window. If a supporting
document is referenced in the attribute information window and the file path is not highlighted in green then it
will be necessary to add an entry for the file’s filename extension in the Configure External Applications window.
If the file path is highlighted in green but does not open when double-clicked it will be necessary to adjust the
parameters in the Options window so the file can be located by eVis.
If no compass bearing is provided in the Options window a red asterisk will be displayed on top of the vector
feature that is associated with the photograph being displayed. If a compass bearing is provided then an arrow
will appear pointing in the direction indicated by the value in the compass bearing display field in the Generic
Event Browser window. The arrow will be centered over the point that is associated with the photograph or other
document.
To close the Generic Event Browser window click on the [Close] button from the Display window.
19.8.5 Event ID Tool
The ‘Event ID’ module allows you to display a photograph by clicking on a feature displayed in the QGIS map
window. The vector feature must have attribute information associated with it to describe the location and name
of the file containing the photograph and optionally the compass direction the camera was pointed when the image
was acquired. This layer must be loaded into QGIS before running the ‘Event ID’ tool.
Launch the Event ID module
Event ID
icon or click on Plugins → eVis → Event ID Tool.
To launch the ‘Event ID’ module either click on the
This will cause the cursor to change to an arrow with an ‘i’ on top of it signifying that the ID tool is active.
To view the photographs linked to vector features in the active vector layer displayed in the QGIS map window,
move the Event ID cursor over the feature and then click the mouse. After clicking on the feature, the Generic
Event Browser window is opened and the photographs on or near the clicked locality are available for display
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in the browser. If more than one photograph is available, you can cycle through the different features using the
[Previous] and [Next] buttons. The other controls are described in the ref:evis_browser section of this guide.
19.8.6 Database connection
The ‘Database Connection’ module provides tools to connect to and query a database or other ODBC resource,
such as a spreadsheet.
eVis can directly connect to four types of databases: Microsoft Access, PostgreSQL, MySQL, SQLite, and can
also read from ODBC connections. When reading from an ODBC database (such as an Excel spreadsheet) it is
necessary to configure your ODBC driver for the operating system you are using.
Launch the Database Connection module
eVis Database Connection
or click
To launch the ‘Database Connection’ module either click on the appropriate icon
on Plugins → eVis → Database Connection. This will launch the Database Connection window. The window
has three tabs: Predefined Queries, Database Connection, and SQL Query. The Output Console window at the
bottom of the window displays the status of actions initiated by the different sections of this module.
Connect to a database
Click on the Database Connection tab to open the database connection interface. Next, use the Database Type
combobox to select the type of database that you want to connect to. If a password or username is
required, that information can be entered in the Username and Password textboxes.
Enter the database host in the Database Host textbox. This option is not available if you selected “MS Access” as
the database type. If the database resides on your desktop you should enter “localhost”.
Enter the name of the database in the Database Name textbox. If you selected “ODBC” as the database type, you
need to enter the data source name.
When all of the parameters are filled in, click on the [Connect] button. If the connection is successful, a message
will be written in the Output Console window stating that the connection was established. If a connection was not
established you will need to check that the correct parameters were entered above.
1. Database Type: A dropdown list to specify the type of database that will be used.
2. Database Host: The name of the database host.
3. Port The port number if a MySQL or PostgreSQL database type is selected.
4. Database Name The name of the database.
5. Connect A button to connect to the database using the parameters defined above.
6. Output Console The console window where messages related to processing are displayed.
7. Username: Username for use when a database is password protected.
8. Password: Password for use when a database is password protected.
9. Predefined Queries: Tab to open the “Predefined Queries” window.
10. Database Connection: Tab to open the “Database Connection” window.
11. SQL Query: Tab to open the “SQL Query” window.
12. Help: Displays the on line help.
13. OK: Close the main “Database Connection” window.
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Figure 19.12: The eVis Database connection window
Running SQL queries
SQL queries are used to extract information from a database or ODBC resource. In eVis the output from these
queries is a vector layer added to the QGIS map window. Click on the SQL Query tab to display the SQL query
interface. SQL commands can be entered in this text window. A helpful tutorial on SQL commands is available at
http://www.w3schools.com/sql. For example, to extract all of the data from a worksheet in an Excel file, select
* from [sheet1$] where sheet1 is the name of the worksheet.
Click on the [Run Query] button to execute the command. If the query is successful a Database File Selection
window will be displayed. If the query is not successful an error message will appear in the Output Console
window.
In the Database File Selection window, enter the name of the layer that will be created from the results of the
query in the Name of New Layer textbox.
1. SQL Query Text Window: A screen to type SQL queries.
2. Run Query: Button to execute the query entered in the SQL Query Window.
3. Console Window: The console window where messages related to processing are displayed.
4. Help: Displays the on line help.
5. OK: Closes the main Database Connection window.
Use the X Coordinate
and Y Coordinate
comboboxes to select the field from the database that
store the X (or longitude) and Y (or latitude) coordinates. Clicking on the [OK] button causes the vector layer
created from the SQL query to be displayed in the QGIS map window.
To save this vector file for future use, you can use the QGIS ‘Save as...’ command that is accessed by right clicking
on the layer name in the QGIS map legend and then selecting ‘Save as...’
Tip: Creating a vector layer from a Microsoft Excel Worksheet
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Figure 19.13: The eVis SQL query tab
When creating a vector layer from a Microsoft Excel Worksheet you might see that unwanted zeros (“0”) have
been inserted in the attribute table rows beneath valid data.This can be caused by deleting the values for these cells
in Excel using the Backspace key. To correct this problem you need to open the Excel file (you’ll need to close
QGIS if there if you are connected to the file to allow you to edit the file) and then use Edit → Delete to remove
the blank rows from the file. To avoid this problem you can simply delete several rows in the Excel Worksheet
using Edit → Delete before saving the file.
Running predefined queries
With predefined queries you can select previously written queries stored in XML format in a file. This is particularly helpful if you are not familiar with SQL commands. Click on the Predefined Queries tab to display the
predefined query interface.
Open File
To load a set of predefined queries click on the
icon. This opens the Open File window which is used
to locate the file containing the SQL queries. When the queries are loaded their titles, as defined in the XML
file, will appear in the dropdown menu located just below the
displayed in the text window under the dropdown menu.
Open File
icon, the full description of the query is
Select the query you want to run from the dropdown menu and then click on the SQL Query tab to see that the
query has been loaded into the query window. If it is the first time you are running a predefined query or are
switching databases, you need to be sure to connect to the database.
Click on the [Run Query] button in the SQL Query tab to execute the command. If the query is successful a
Database File Selection window will be displayed. If the query is not successful an error message will appear in
the Output Console window.
1. Open Query File: Launches the “Open File” file browser to search for the XML file holding the predefined
queries.
2. Predefined Queries: A dropdown list with all of the queries defined by the predefined queries XML file.
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Figure 19.14: The eVis Predefined queries tab
3. Query description: A short description of the query. This description is from the predefined queries XML
file.
4. Console Window: The console window where messages related to processing are displayed.
5. Help: Displays the on line help.
6. OK: Closes the main “Database Connection” window.
XML format for eVis predefined queries
The XML tags read by eVis
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Tag
Description
query
Defines the beginning and end of a query statement.
shortdeA short description of the query that appears in the eVis dropdown menu.
scription
descripA more detailed description of the query displayed in the Predefined Query text window.
tion
databaseThe database type as defined in the Database Type dropdown menu in the Database Connection
type
tab.
databaseThe port as defined in the Port textbox in the Database Connection tab.
port
databaseThe database name as defined in the Database Name textbox in the Database Connection tab.
name
databaseuser-The database username as defined in the Username textbox in the Database Connection tab.
name
databasep- The database password as defined in the Password textbox in the Database Connection tab.
assword
sqlstateThe SQL command.
ment
autoconA flag (“true”” or “false”) to specify if the above tags should be used to automatically connect to
nect
database without running the database connection routine in the Database Connection tab.
A complete sample XML file with three queries is displayed below:
<?xml version="1.0"?>
<doc>
<query>
<shortdescription>Import all photograph points</shortdescription>
<description>This command will import all of the data in the SQLite database to QGIS
</description>
<databasetype>SQLITE</databasetype>
<databasehost />
<databaseport />
<databasename>C:\textbackslash Workshop/textbackslash
eVis\_Data\textbackslash PhotoPoints.db</databasename>
<databaseusername />
<databasepassword />
<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN
Points ON Points.rec_id=Attributes.point_ID</sqlstatement>
<autoconnect>false</autoconnect>
</query>
<query>
<shortdescription>Import photograph points "looking across Valley"</shortdescription>
<description>This command will import only points that have photographs "looking across
a valley" to QGIS</description>
<databasetype>SQLITE</databasetype>
<databasehost />
<databaseport />
<databasename>C:\Workshop\eVis_Data\PhotoPoints.db</databasename>
<databaseusername />
<databasepassword />
<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN
Points ON Points.rec_id=Attributes.point_ID where COMMENTS=’Looking across
valley’</sqlstatement>
<autoconnect>false</autoconnect>
</query>
<query>
<shortdescription>Import photograph points that mention "limestone"</shortdescription>
<description>This command will import only points that have photographs that mention
"limestone" to QGIS</description>
<databasetype>SQLITE</databasetype>
<databasehost />
<databaseport />
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<databasename>C:\Workshop\eVis_Data\PhotoPoints.db</databasename>
<databaseusername />
<databasepassword />
<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN
Points ON Points.rec_id=Attributes.point_ID where COMMENTS like ’%limestone%’
</sqlstatement>
<autoconnect>false</autoconnect>
</query>
</doc>
19.9 fTools Plugin
The goal of the fTools python plugin is to provide a one-stop resource for many common vector-based GIS tasks,
without the need for additional software, libraries, or complex workarounds. It provides a growing suite of spatial
data management and analysis functions that are both fast and functional.
fTools is now automatically installed and enabled in new versions of QGIS, and as with all plugins, it can be
disabled and enabled using the Plugin Manager (See Section Loading a QGIS Core Plugin). When enabled, the
fTools plugin adds a Vector menu to QGIS, providing functions ranging from Analysis and Research Tools to
Geometry and Geoprocessing Tools, as well as several useful Data Management Tools.
19.9.1 Analysis tools
Icon Tool
Purpose
Distance
Matrix
Measure distances between two point layers, and output results as a) Square distance
matrix, b) Linear distance matrix, or c) Summary of distances. Can limit distances to
the k nearest features.
Sum line
length
Calculate the total sum of line lengths for each polygon of a polygon vector layer.
Points in
polygon
Count the number of points that occur in each polygon of an input polygon vector layer.
List unique
values
List all unique values in an input vector layer field
Basic
statistic
Compute basic statistics (mean, std dev, N, sum, CV) on an input field.
Nearest
Neighbor
analysis
Compute nearest neighbor statistics assess the level of clustering in a point vector layer
Mean
coordinate(s)
Compute either the normal or weighted mean center of an entire vector layer, or
multiple features based on a unique ID field.
Line
intersections
Locate intersections between lines, and output results as a point shapefile. Useful for
locating road or stream intersections, ignores line intersections with length > 0.
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19.9.2 Research tools
Icon Tool
Purpose
Random selection
Randomly select n number of features, or n percentage of features
Random selection
within subsets
Randomly select features within subsets based on a unique ID field.
Random points
Generate pseudo-random points over a given input layer.
Regular points
Generate a regular grid of points over a specified region and export them as a
point shapefile.
Vector grid
Generate a line or polygon grid based on user specified grid spacing.
Select by location
Select features based on their location relative to another layer to form a new
selection, or add or subtract from the current selection.
Polygon from layer
extent
Create a single rectangular polygon layer from the extent of an input raster or
vector layer.
Table Ftools 2: fTools Research tools
19.9.3 Geoprocessing tools
Icon Tool
Purpose
Convex hull(s)
Create minimum convex hull(s) for an input layer, or based on an ID field.
Buffer(s)
Create buffer(s) around features based on distance, or distance field.
Intersect
Overlay layers such that output contains areas where both layers intersect.
Union
Overlay layers such that output contains intersecting and non-intersecting areas.
Symmetrical
difference
Overlay layers such that output contains those areas of the input and difference
layers that do not intersect.
Clip
Overlay layers such that output contains areas that intersect the clip layer.
Difference
Overlay layers such that output contains areas not intersecting the clip layer.
Dissolve
Merge features based on input field. All features with identical input values are
combined to form one single feature.
Table Ftools 3: fTools Geoprocessing tools
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19.9.4 Geometry tools
Icon Tool
Purpose
Check geometry
Check polygons for intersections, closed-holes, and fix node ordering.
Export/Add
geometry columns
Add vector layer geometry info to point (XCOORD, YCOORD), line
(LENGTH), or polygon (AREA, PERIMETER) layer.
Polygon centroids
Calculate the true centroids for each polygon in an input polygon layer.
Delaunay
triangulation
Voronoi Polygons
Calculate and output (as polygons) the delaunay triangulation of an input point
vector layer.
Calculate voronoi polygons of an input point vector layer.
Simplify geometry
Densify geometry
Generalize lines or polygons with a modified Douglas-Peucker algorithm.
Densify lines or polygons by adding vertices
Multipart to
singleparts
Convert multipart features to multiple singlepart features. Creates simple
polygons and lines.
Singleparts to
multipart
Merge multiple features to a single multipart feature based on a unique ID field.
Polygons to lines
Convert polygons to lines, multipart polygons to multiple singlepart lines.
Lines to polygons
Convert lines to polygons, multipart lines to multiple singlepart polygons.
Extract nodes
Extract nodes from line and polygon layers and output them as points.
Table Ftools 4: fTools Geometry tools
Note: The Simplify geometry tool can be used to remove duplicate nodes in line and polygon geometries, just set
the Simplify tolerance parameter to 0 and this will do the trick.
19.9.5 Data management tools
Icon Tool
Purpose
Define
projection
Specify the CRS for shapefiles whose CRS has not been defined.
Join
attributes by
location
Join additional attributes to vector layer based on spatial relationship. Attributes from
one vector layer are appended to the attribute table of another layer and exported as a
shapefile.
Split vector
layer
Split input layer into multiple separate layers based on input field.
Merge
shapefiles to
one
Create
spatial index
Merge several shapefiles within a folder into a new shapefile based on the layer type
(point, line, area).
Create a spatial index for OGR supported formats.
Table Ftools 5: fTools Data management tools
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19.10 GDAL Tools Plugin
19.10.1 What is GDALTools?
The GDAL Tools plugin offers a GUI to the collection of tools in the Geospatial Data Abstraction Library,
http://gdal.osgeo.org . These are raster management tools to query, re-project, warp and merge a wide variety
of raster formats. Also included are tools to create a contour (vector) layer, or a shaded relief from a raster DEM,
and to make a vrt (Virtual Raster Tile in XML format) from a collection of one or more raster files. These tools
are available when the plugin is installed and activated.
The GDAL Library
The GDAL library consists of a set of command line programs, each with a large list of options. Users comfortable
with running commands from a terminal may prefer the command line, with access to the full set of options. The
GDALTools plugin offers an easy interface to the tools, exposing only the most popular options.
19.10.2 List of GDAL tools
Figure 19.15: The GDALTools menu list
Projections
Warp
(Reproject)
This utility is an image mosaicing, reprojection and warping utility. The program can
reproject to any supported projection, and can also apply GCPs stored with the image if the
image is “raw” with control information. For more information you can read on the GDAL
website http://www.gdal.org/gdalwarp.html
Assign
projection
This tool allows to assign projection to rasters that already georeferenced but miss projection
information. Also with it help it is possible to alter existing projection definition. Both single
file and batch mode are supported. For more information please visit utility page at GDAL site
http://www.gdal.org/gdalwarp.html
Extract
projection
This utility helps you to extract projection information from an input file. If you want to
extract projection from a whole directory you can use the Batch mode. It creates both .prj
and .wld files.
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Conversion
Rasterize
Polygonize
Translate
This program burns vector geometries (points, lines and polygons) into the raster band(s) of a
raster image. Vectors are read from OGR supported vector formats. Note that the vector data
must in the same coordinate system as the raster data; on the fly reprojection is not provided. For
more information see http://www.gdal.org/gdal_rasterize.html
This utility creates vector polygons for all connected regions of pixels in the raster sharing a
common pixel value. Each polygon is created with an attribute indicating the pixel value of that
polygon. The utility will create the output vector datasource if it does not already exist,
defaulting to ESRI shapefile format. See also http://www.gdal.org/gdal_polygonize.html
This utility can be used to convert raster data between different formats, potentially performing
some operations like subsettings, resampling, and rescaling pixels in the process. For more
information you can read on http://www.gdal.org/gdal_translate.html
RGB
to PCT
This utility will compute an optimal pseudo-color table for a given RGB image using a median
cut algorithm on a downsampled RGB histogram. Then it converts the image into a
pseudo-colored image using the color table. This conversion utilizes Floyd-Steinberg dithering
(error diffusion) to maximize output image visual quality. The utility is also desribed at
http://www.gdal.org/rgb2pct.html
PCT
to RGB
This utility will convert a pseudocolor band on the input file into an output RGB file of the
desired format. For more information see http://www.gdal.org/pct2rgb.html
Extraction
Contour
Clipper
218
This program generates a vector contour file from the input raster elevation model (DEM). On
http://www.gdal.org/gdal_contour.html you can find more information.
This utility allows to clip (extract subset) raster using selected extent or based on mask layer
bounds. More information can be found at http://www.gdal.org/gdal_translate.html.
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Analysis
Sieve
This utility removes raster polygons smaller than a provided threshold size (in pixels) and
replaces them with the pixel value of the largest neighbor polygon. The result can be written
back to the existing raster band, or copied into a new file. For more information see
http://www.gdal.org/gdal_sieve.html .
Near
Black
This utility will scan an image and try to set all pixels that are nearly black (or nearly white)
around the edge to exactly black (or white). This is often used to “fix up” lossy compressed
aerial photos so that color pixels can be treated as transparent when mosaicing. See also
http://www.gdal.org/nearblack.html .
Fill
nodata
This utility fills selection raster regions (usually nodata areas) by interpolation from valid
pixels around the edges of the area. On http://www.gdal.org/gdal_fillnodata.html you can
find more information.
Proximity
This utility generates a raster proximity map indicating the distance from the center of each
pixel to the center of the nearest pixel identified as a target pixel. Target pixels are those in
the source raster for which the raster pixel value is in the set of target pixel values. For more
information see http://www.gdal.org/gdal_proximity.html .
Grid
This utility creates regular grid (raster) from the scattered data read from the OGR
datasource. Input data will be interpolated to fill grid nodes with values, you can choose from
various interpolation methods. The utility is also described on the GDAL website
http://www.gdal.org/gdal_grid.html .
DEM
terrain
models
Tools to analyze and visualize DEMs. It can create a shaded relief, a slope, an aspect, a color
relief, a Terrain Ruggedness Index, a Topographic Position Index and a roughness map from
any GDAL-supported elevation raster. For more information you can read on
http://www.gdal.org/gdaldem.html
Miscellaneous
Build
Virtual
Raster
Merge
Information
This program builds a VRT (Virtual Dataset) that is a mosaic of the list of input gdal datasets.
See also http://www.gdal.org/gdalbuildvrt.html .
This utility will automatically mosaic a set of images. All the images must be in the same
coordinate system and have a matching number of bands, but they may be overlapping, and at
different resolutions. In areas of overlap, the last image will be copied over earlier ones. The
utility is also described on http://www.gdal.org/gdal_merge.html .
This utility lists various information about a GDAL supported raster dataset. On
http://www.gdal.org/gdalinfo.html you can find more information.
Build
Overviews
The gdaladdo utility can be used to build or rebuild overview images for most supported file
formats with one of several downsampling algorithms. For more information see
http://www.gdal.org/gdaladdo.html .
Tile
Index
This utility builds a shapefile with a record for each input raster file, an attribute containing
the filename, and a polygon geometry outlining the raster. See also
http://www.gdal.org/gdaltindex.html .
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19.11 Georeferencer Plugin
The Georeferencer Plugin is a tool for generating world files for rasters. It allows you to reference rasters to
geographic or projected coordinate systems by creating a new GeoTiff or by adding a world file to the existing
image. The basic approach to georeferencing a raster is to locate points on the raster for which you can accurately
determine their coordinates.
Features
Icon
Purpose
Icon
Purpose
Open raster
Start georeferencing
Generate GDAL Script
Load GCP Points
Save GCP Points As
Transformation settings
Add Point
Delete Point
Move GCP Point
Pan
Zoom In
Zoom Out
Zoom To Layer
Zoom Last
Zoom Next
Link Georeferencer to QGIS
Link QGIS to Georeferencer
Table Georeferencer 1: Georeferencer Tools
19.11.1 Usual procedure
As X and Y coordinates (DMS (dd mm ss.ss), DD (dd.dd) or projected coordinates (mmmm.mm) which correspond with the selected point on the image, two alternative procedures can be used:
• The raster itself sometimes provides crosses with coordinates “written” on the image. In this case you can
enter the coordinates manually.
• Using already georeferenced layers, this can be either vector or raster data that contain the same objects/features that you have on the image that you want to georeference and the projection you want to
have your image. In this case you can enter the coordinates by clicking on the reference dataset loaded in
QGIS map canvas.
The usual procedure for georeferencing an image involves selecting multiple points on the raster, specifying their
coordinates, and choosing a relevant transformation type. Based on the input parameters and data, the plugin will
compute the world file parameters. The more coordinates you provide, the better the result will be.
The first step is to start QGIS, load the Georeferencer Plugin (see Section Loading a QGIS Core Plugin) and click
Georeferencer
on the
icon which appears in the QGIS toolbar menu. The Georeferencer Plugin dialog appears as
shown in figure_georeferencer_1.
For this example, we are using a topo sheet of South Dakota from SDGS. It can later be visualized together with the data from the GRASS spearfish60 location. You can download the topo sheet here:
http://grass.osgeo.org/sampledata/spearfish_toposheet.tar.gz.
Entering ground control points (GCPs)
button. The raster will show
1. To start georeferencing an unreferenced raster, we must load it using the
up in the main working area of the dialog. Once the raster is loaded, we can start to enter reference points.
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Figure 19.16: Georeferencer Plugin Dialog
Add Point
button, add points to the main working area and enter their coordinates (see Figure
2. Using the
figure_georeferencer_2). For this procedure you have three options:
• Click on a point in the raster image and enter the X and Y coordinates manually.
from map canvas
• Click on a point in the raster image and choose the button
to add the X and Y coordinates with the help of a georeferenced map already loaded in the QGIS map canvas.
• With the
button, you can move the GCPs in both windows, if they are at the wrong place.
3. Continue entering points. You should have at least 4 points, and the more coordinates you can provide, the
better the result will be. There are additional tools on the plugin dialog to zoom and pan the working area
in order to locate a relevant set of GCP points.
Figure 19.17: Add points to the raster image
The points that are added to the map will be stored in a separate text file ([filename].points) usually
together with the raster image. This allows us to reopen the Georeferencer plugin at a later date and add new
points or delete existing ones to optimize the result. The points file contains values of the form: mapX, mapY,
pixelX, pixelY. You can use the
Load GCP Points
and
Save GCP Points
buttons to manage the files.
Within the GCP table you can click on a column header and therewith enable e.g. numerical sorting. The GCP list
is automatically updated.
Defining the transformation settings
After you have added your GCPs to the raster image, you need to define the transformation settings for the
georeferencing process.
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Figure 19.18: Defining the georeferencer transformation settings
Available Transformation algorithms
Depending on how many ground control point you have captured, you may want to use different transformation
algorithms. Choice of transformation algorithm is also dependent on the type and quality of input data and the
amount of geometric distortion that you are willing to introduce to final result.
Currently, following algorithms are available:
• The Linear algorithm is used to create a world-file, and is different from the other algorithms, as it does
not actually transform the raster. This algorithm likely won’t be sufficient if you are dealing with scanned
material.
• The Helmert transformation performs simple scaling and rotation transformations.
• The Polynomial algorithms 1-3 are among the most widely used algorithms for georeferencing, and each
one differs by the degree of distortion introduced to match source and destination ground control points.
The most widely used polynomial algorithm is the second order polynomial transformation, which allows
some curvature. First order polynomial transformation (affine) preserves colliniarity and allows scaling,
translation and rotation only.
• The Thin plate spline (TPS) algorithm is a more modern georeferencing method, which is able to introduce local deformations in the data. This algorithm is useful when very low quality originals are being
georeferenced.
• The Projective transformation is a linear rotation and translation of coordinates.
Define the Resampling method
The type of resampling you choose will likely depending on your input data and the ultimate objective of the
exercise. If you don’t want to change statistics of the image, you might want to choose ‘Nearest neighbour’,
whereas a ‘Cubic resampling’ will likely provide a more smoothed result.
It is prossible to choose between five different resampling methods.
1. Nearest neighbour
2. Linear
3. Cubic
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4. Cubic Spline
5. Lanczos
Define the transformation settings
There are several options that need to be defined for the georeferenced output raster.
Create world file is only available, if you decide to use the linear transformation type,
• The checkbox
because this means that the raster image actually won’t be transformed. In this case, the field Output raster
is not activated, because only a new world-file will be created.
• For all other transformation type you have to define an Output raster. As default a new file ([filename]_modified) will be created in the same folder together with the original raster image.
• As a next step you have to define the Target SRS (Spatial Reference System) for the georeferenced raster
(see section Working with Projections).
• If you like, you can generate a pdf map and also a pdf report. The report includes information about the
used transformation parameters. An image of the residuals and a list with all GCPs and their RMS errors.
Set Target Resolution checkbox and define pixel resolution of the
• Furthermore you can activate the
output raster. Default horizontal and vertical resolution is 1,
• The
Use 0 for transparency when needed can be activated, if pixels with the value 0 shall be visualized
transparent. In our example toposheet all white areas would be transparent.
Load in QGIS when done loads the output raster automatically into the QGIS map canvas when
• Finally
the transformation is done.
Show and adapt raster properties
Clicking on the Raster properties dialog in the Settings menu opens the raster properties of the layer that you want
to georeference.
Configure the georeferencer
• You can define if you want to show GCP coordiniates and/or IDs.
• As residual units pixels and map units can be chosen.
• For the PDF report a left and right margin can be defined and you can also set the paper size for the PDF
map.
• Finally you can activate to
show georeferencer window docked.
Running the transformation
After all GCPs have been collected and all transformation settings are defined, just press the button
Start georeferencing
to create the new georeferenced raster.
19.12 Interpolation Plugin
The Interplation plugin can be used to generate a TIN or IDW interpolation of a point vector layer. It is very
simple to handle and provides an intuitive graphical user interface for creating interpolated raster layers (See
Figure_interpolation_1). The plugin requires the following parameters to be specified before running:
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• Input vector layer: Specify the input point vector layer(s) from a list of loaded point layers. If several
layers are specified, then data from all layers is used for interpolation. Note: It is possible to insert lines or
polygons as constraints for the triangulation, by specifying either “points”, “structure lines” or “break lines”
in the Type
combobox.
• Interpolation attribute: Select attribute column to be used for interpolation or enable the
Coordinate checkbox to use the layers stored Z values.
Use Z-
• Interpolation Method: Select interpolation method. This can be either ‘Triangulated Irregular Network
(TIN)’ or ‘Inverse Distance Weighted (IDW)’.
• Number of columns/rows: Specify the number row and colums for the output raster file.
• Output file: Specify a name for the output raster file.
Figure 19.19: Interpolation Plugin
19.12.1 Using the plugin
1. Start QGIS and load a point vector layer (e.g., elevp.csv).
2. Load the Interpolation plugin in the Plugin Manager (see Section Loading a QGIS Core Plugin) and click
Interpolation
icon which appears in the QGIS toolbar menu. The Interpolation plugin dialog appears
on the
as shown in Figure_interpolation_1.
3. Select an input layer (e.g., elevp
) and column (e.g., ELEV) for interpolation.
4. Select an interpolation method (e.g. ‘Triangulated Irregular Network (TIN)’), and specify a cellsize of 5000
as well as the raster output filename (e.g., elevation_tin).
5. Click [OK].
6. For the current example, double click elevation_tin in the layer list to open the raster Layer Properties
dialog and select ‘Pseudocolor’ as Color Map
in the Symbology tab. Or you can define a new color
table as described in section Working with Raster Data.
19.13 MapServer Export Plugin
You can use QGIS to ‘compose’ your map by adding and arranging layers, symbolizing them, customizing the
colors and then creating a map file for MapServer.
Note: Currently the plugin only works when you use ‘Old Symbology’ in QGIS. ‘New Symbology’ is not yet
supported.
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19.13.1 Creating the Project File
The MapServer Export Plugin operates on a saved QGIS project file and not on the current contents of the map
canvas and legend. This has been a source of confusion for a number of users. As described below, before you start
using the MapServer Export Plugin, you need to arrange the raster and vector layers you want to use in MapServer
and save this status in a QGIS project file.
Figure 19.20: Arrange raster and vector layers for QGIS project file
In this example, we demonstrate the four steps required to create a simple project file which can be used to create
the MapServer map file. We use raster and vector files from the QGIS sample dataset Sample Data.
1. Add the raster layer landcover.tif clicking on the
Add Raster Layer
icon.
2. Add the vector Shapefiles lakes.shp, majrivers.shp and airports.shp from the QGIS sample
dataset clicking on the
Add Vector Layer
icon.
3. Change the colors and symbolize the data as you like (for example see figure_mapserver_export_1)
4. Save a new project named mapserverproject.qgs using File →
Save Project.
19.13.2 Creating the Map File
To use the Mapserver Export plugin from within QGIS, you need to enable the MapServer Export Plugin first
using the Plugin Manager (see Loading a QGIS Core Plugin).
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Figure 19.21: Export to MapServer Dialog
Map file
Qgis
project
file
Map
Name
Map
Width
Map
Height
Map
Units
Image
type
Web
Template
Web
Header
Web
Footer
Enter the name for the map file to be created. You can use the button at the right to browse for
the directory where you want the map file created.
Enter the full path to the QGIS project file (.qgs) you want to export. You can use the button at
the right to browse for the QGIS project file.
A name for the map. This name is prefixed to all images generated by the mapserver.
Width of the output image in pixels.
Height of the output image in pixels.
Units of measure used for output.
Format for the output image generated by MapServer
Full path to the MapServer template file to be used with the map file
Full path to the MapServer header file to be used with the map file
Full path to the MapServer footer file to be used with the map file
Only the inputs Map file and QGIS project file are required to create a map file, however by omitting the other
parameters, you may end up creating a non-functional map file, depending on your intended use. Although QGIS
is good at creating a map file from your project file, it may require some tweaking to get the results you want. For
this example, we will create a map file using the project file mapserverproject.qgs we just created (see
Figure_mapserver_export_2):
MapServer Export
1. Click the
icon in the toolbar menu to start the MapServer dialog (see Figure_mapserver_export_2).
2. Enter the name (e.g., qgisproject.map) for your new map file.
3. Browse and find the QGIS project file (e.g., mapserverproject.qgs) you previously saved.
4. Enter a name (e.g., MyMap) for the map.
5. Enter the width and height (e.g., 600 for the width and 400 for the height) for your output image.
6. For this example, the layers are in meters, so we change the units to meters.
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7. Choose png for the image type.
8. Click [OK] to generate the new map file qgisproject.map. QGIS displays the success of your efforts.
Figure 19.22: Export to MapServer Succesfull Dialog
You can view the map file in any text editor or visualizer. If you take a look, you’ll notice that the export tool adds
the metadata needed to enable our map file for WMS.
19.13.3 Troubleshooting
If you get error messages from mapserver like:
loadSymbolSet(): Unable to access file. (./symbols/symbols.txt)
or:
msLoadFontset(): Unable to access file. Error opening fontset ./fonts/fonts.txt.
This means that that the map file is requesting for fonts or symbol definition files but that Mapserver cannot find
those.
Either comment the lines containing those names in the map file (this is possible if you do not have labels or use
styles from the symbols.txt). Or create those files (see below).
The most simple fonts.txt file (because arial is used in the QGIS generated map files) contains the following
line
# either relative to the map file or a full path:
arial /usr/share/fonts/truetype/msttcorefonts/arial.ttf
The most simple symbols.txt file contains the definition of a circle symbol (because a circle symbol is used
for point layers)
SYMBOLSET
SYMBOL
NAME "circle"
TYPE ellipse
FILLED true
POINTS
1 1
END
END
END
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19.13.4 Testing the Map File
We can now test our work.
If the map file is accessible for you mapserver cgi you can use the one of the url’s from the success dialog.
Another option is using the shp2img tool to create an image from the map file. The shp2img utility is part of
MapServer and FWTools. To create an image from our map:
• Open a terminal window
• If you didn’t save your map file in your home directory, change to the folder where you saved it.
• Run shp2img -m qgisproject.map -o mapserver\_test.png and display the image
This creates a PNG with all the layers included in the QGIS project file. In addition, the extent of the PNG will be
the same as when we saved the project. As you can see in figure_mapserver_export_4, all information except the
airport symbols are included.
Figure 19.23: Test PNG created by shp2img with all MapServer Export layers
19.13.5 Using Map File
If you plan to use the map file to serve WMS requests, you probably don’t have to tweak anything. If you plan to
use it with a mapping template or a custom interface, you may have a bit of manual work to do. To see how easy
it is to go from QGIS to serving maps on the web, take a look at Christopher Schmidt’s 5 minute flash video. He
used an older version of QGIS (version 0.8), but the demo applies equally well to newer versions.
19.14 Offline Editing Plugin
For data collection, it is a common situation to work with a laptop or a cell phone offline in the field. Upon
returning to the network, the changes need to be synchronized with the master data source, e.g. a PostGIS database.
If several persons are working simultaneously on the same datasets, it is difficult to merge the edits by hand, even
if people don’t change the same features.
Offline Editing
Plugin automates the synchronisation by copying the content of a datasource (usually PostGIS
The
or WFS-T) to a SpatiaLite database and storing the offline edits to dedicated tables. After being connected to the
network again, it is possible to apply the offline edits to the master dataset.
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19.14.1 Using the plugin
• Open some vector layers, e.g. from a PostGIS or WFS-T datasource
• Save it as a project
Convert to offline project
icon and select the layers to save. The content of the layers is saved to
• Press the
SpatiaLite tables.
• Edit the layers offline.
• After being connected again, upload the changes with the
Synchronize
button.
Figure 19.24: Create an offline project from PostGIS or WFS layers
19.15 Oracle GeoRaster Plugin
In Oracle databases, raster data can be stored in SDO_GEORASTER objects available with the Oracle Spatial
OracleGeoRasterPlugin
extension. In QGIS, the
is supported by GDAL, and depends on Oracle’s database product
being installed and working on your machine. While Oracle is proprietary software, they provide their software
free for development and testing purposes. Here is one simple example of how to load raster images to GeoRaster:
$ gdal_translate -of georaster input_file.tif geor:scott/tiger@orcl
This will load the raster into the default GDAL_IMPORT table, as a column named RASTER.
19.15.1 Managing connections
Firstly, the Oracle GeoRaster Plugin must be enabled using the Plugin Manager (see Section Loading a QGIS
Core Plugin). The first time you load a GeoRaster in QGIS, you must create a connection to the Oracle database
Select GeoRaster
that contains the data. To do this, begin by clicking on the
toolbar button, it will open the Select
Oracle Spatial GeoRaster dialog window. Click on [New] to open the dialog window, and specify the connection
parameters (See Figure_oracle_raster_1):
• Name: Enter a name for the database connection
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• Database instance: Enter the name of the database that you will connect to
• Username: Specify your own username that you will use to access the database
• Password: The password associated with your username that is required to access the database
Figure 19.25: Create Oracle connection dialog
Now, back on the main Oracle Spatial GeoRaster dialog window (see Figure_oracle_raster_2), use the drop-down
list to choose one connection, and use the [Connect] button to establish a connection. You may also [Edit] the
connection by opening the previous dialog and making changes to the connection information, or use the [Delete]
button to remove the connection from the drop-down list.
19.15.2 Selecting a GeoRaster
Once a connection has been established, the sub-datasets window will show the names of all the tables that contains
GeoRaster columns in that database in the format of a GDAL subdataset name.
Click on one of the listed subdatasets and then click on [Select] to choose the table name. Now another list of
subdatasets will show with the names of GeoRaster columns on that table. This is usually a short list, since most
users will not have more than one or two GeoRaster columns on the same table.
Click on one of the listed subdatasets and then click on [Select] to choose one of the the table/column combination.
The dialog will now show all the rows that contains GeoRaster objects. Note that the subdataset list will now show
the Raster Data Table and Raster Id’s pairs.
At anytime the Selection entry can be edited in order to go directly to a known GeoRaster or to go back to the
beginning and select another table name.
The Selection data entry can also be used to enter a Where clause at the end of the identification string, e.g.
geor:scott/tiger@orcl,gdal_import,raster,geoid=.
See
http://www.gdal.org/frmt_georaster.html for more information.
19.15.3 Displaying GeoRaster
Finally, by selecting a GeoRaster from the list of Raster Data Table and Raster Id’s, the raster image will be loaded
into QGIS.
The Select Oracle Spatial GeoRaster dialog can be closed now and next time it opens it will keep the same
connection, and will show the same previous list of subdataset making it very easy to open up another image from
the same context.
Note: GeoRasters that contains pyramids will display much faster but the pyramids need to be generated outside
of QGIS using Oracle PL/SQL or gdaladdo.
The following is example using gdaladdo:
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Figure 19.26: Select Oracle GeoRaster dialog
gdaladdo georaster:scott/tiger@orcl,georaster\_table,georaster,georid=6 \
-r nearest 2 4 6 8 16 32
This is an example using PL/SQL:
$ sqlplus scott/tiger
SQL> DECLARE
gr sdo_georaster;
BEGIN
SELECT image INTO gr FROM cities WHERE id = 1 FOR UPDATE;
sdo_geor.generatePyramid(gr, ’rLevel=5, resampling=NN’);
UPDATE cities SET image = gr WHERE id = 1;
COMMIT;
END;
19.16 Raster Terrain Analysis Plugin
The Raster Terrain Analysis Plugin can be used to calculate the slope, aspect, hillshade, ruggedness index
and relief for digital elevation models (DEM). It is very simple to handle and provides an intuitive graphical user
interface for creating new raster layers (See Figure_raster_terrain_1).
Description of the analysis:
• Slope: Calculates slope angle for each cell in degrees (based on first order derivative estimation).
• Aspect: Exposition (starting with 0 for north direction, in degrees counterclockwise).
• Hillshade: Create shaded map using light and shadow to provide a more three-dimensional appearance for
a shaded relief map.
• Ruggedness Index: A quantitative measurement of terrain heterogeneity as described by Riley et al. (1999).
It is calculated for every location, by summarizing the change in elevation within the 3x3 pixel grid.
• Relief: Creating a shaded relief map from digital elevation data. Implemented is a method to choose the
elevation colors analysing the frequency distribution.
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Figure 19.27: Raster Terrain Modelling Plugin (slope calculation)
19.16.1 Using the plugin
1. Start QGIS and load the gtopo30 raster layer from the GRASS sample location.
2. Load the Raster Terrain Analysis plugin in the Plugin Manager (see Section Loading a QGIS Core Plugin)
3. Select an analysis method from menu (e.g. Raster → Terrain Analysis → Slope). The Slope dialog appears
as shown in Figure_raster_terrain_1.
4. Specify an output file path, and an output file type.
5. Click [OK].
19.17 Heatmap Plugin
Heatmap
The
plugin allows to create a heatmap from a point vector map. A heatmap is a raster map showing
the density or magnitude of point related information. From the result “hotspots” can easily be identified.
19.17.1 Activate the Heatmap plugin
First this core plugin needs to be activated using the Plugin Manager (see Section Loading a QGIS Core Plugin).
After activation the heatmap icon
can be found in the Raster Toolbar.
Select from menu View → Toolbars → Raster to activate the Raster Toolbar when it is not yet activated.
19.17.2 Using the Heatmap plugin
Heatmap
The
toolbutton starts the dialog of the Heatmap plugin (see figure_heatmap_2).
The dialog has the following options:
• Input Point Vector dialog: Provides a selection of loaded point vector maps.
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• Output Raster: Using the
button you select the folder and the name of the output raster the Heatmap
plugin will generate. It is not necessary to give a file extension
• Output Format: Selection of the output format. Although all formats supported by GDAL can be choosen,
GeoTIFF is most in cases the best format to choose.
• Radius: can be used to give the radius in meters or mapunit. When the radius is choosen too small you will
not get a nice heatmap. In places where more circles around points overlap eachother the brighter hotspots
will occur!
• Decay Ratio: is used to show with which ratio the heat dies out from the center.
– When 0 is given (=minimum) the heat will be concentrated in the centre of given radius and be completely extinguished at the edge.
– When 10 is given (=maximum) the heat is concentrated at the edge and in the centre it is completely
extinguished. Higher given values are allowed but have no effect.
– When 1 is given the heat is spread evenly over the whole circle.
– When a negative Decay Ratio is given you will create a Coolmap instead of a Heatmap!
When the
Advanced checkbox is checked it will give acces to additional advanced options.
• Row and Column, can be used to change the pixelsize of the output raster. More rows and colums means
a smaller pixelsize and the size of the output file will become bigger and processing a bit slower. When
doubling the number of rows this will automatically double the size of Columns and the cell sizes will also
be halved. The area of the output raster will remain the same!
• Cell Size X and Cell Size Y influence the pixelsize of the output raster and will also change the rows and
columns.
The point vector layer may have attribute fields that can be used to create a heatmap:
• Use Radius from Field: the radius set from an attribute field.
• Use Weight from field: the weight factor set from an attribute field.
When the output raster is given, the [OK] button can be used to create a heatmap. The first result is a grey surface
that still needs to be given additional treatment to make it a heatmap.
Warning: Changing the raster size properties
When changing the raster size properties, this also changes the resulting output. The hotspot areas will become
bigger.
19.17.3 Creating a Heatmap
For the following example, we will use the airports vector point layer from the QGIS sample dataset (see Sample Data). Another exellent QGIS tutorial on making heatmaps can be found on http://qgis.spatialthoughts.com.
In Figure_Heatmap_1 the airports of Alaska are shown.
1. Select the
Heatmap
toolbutton. The heatmap dialog starts (see Figure_Heatmap_2).
2. In field Input Point Vector
select airpoirt from the list of point layers loaded in current project.
3. In field Output Raster give the name and location using the
button of the output raster. Give the
output raster file the name heatmap_airports to give an file extension is not necessary.
4. In field Output Format choose GeoTIFF.
5. In the field Radius give 1000000 meters.
6. The original Decay Ratio of 0.1 is fine.
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Figure 19.28: Airports of Alaska
7. Click on [OK] to create and load the new raster map (see Figure_Heatmap_3).
Figure 19.29: The Heatmap Dialog
The result after loading the heatmap is probably not the result which was expected. It is still a grey even surface
not showing any variation. First some additional configuration of this layer needs to be done to make the heatmap
present itself.
1. Open the properties dialog of layer heatmap_airports (select the layer heatmap_airports, open
context menu with right mouse button and select Properties).
2. Select the Symbology tab.
3. Change Color map
from ‘Grayscale’ to ‘Pseudocolor’.
4. Press the [Apply] button.
5. Switch to the Transparency tab and set Global transparency
to 40%.
6. Select [OK]
The final result is shown in Figure_Heatmap_4.
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Figure 19.30: The heatmap after loading looks like a grey surface
Figure 19.31: Final result of heatmap created of airports of Alaska
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19.18 Road Graph Plugin
The Road Graph Plugin is a C++ plugin for QGIS, that calculates the shortest path between two points on any
polyline layer and plots this path over the road network.
Figure 19.32: Road Graph Plugin
Main features:
• calculate path, it’s length and travel time
• optimize by length or by travel time
• export path to a vector layer
• highlight roads directions (this is slow and used mainly for debug purposes and for the settings testing)
As a roads layer you can use any polyline vector layer in any QGIS supported format. Two lines with a common
point are considered connected. Please note, it is required to use layer CRS as project CRS while editing roads
layer. This is due to the fact that recalculation of the coordinates between different CRS introduce some errors
that can result in discontinuities, even when ‘snapping’ is used.
In the layer attribute table the following fields can be used:
• speed on road section — numeric field;
• direction — any type, that can be casted to string. Forward and reverse directions are correspond to the
one-way road, both directions — two-way road
If some fields don’t have any value or do not exist — default values are used. You can change defaults and some
plugin settings in plugin settings dialog.
19.18.1 Using the plugin
After plugin activation you will see an additional panel on the left side of the main QGIS window. Now make
some definitions to the Road graph plugin settings dialog in the menu Vector → Road Graph.
Select a Start and a Stop point in the road network layer and click on [Calculate].
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19.19 Spatial Query Plugin
Spatial Query
plugin allows to make a spatial query (select features) in a target layer with reference to another
The
layer. The functionality is based on the GEOS library and depends on the selected source feature layer.
Possible operators are:
• Contains
• Equals
• Overlap
• Crosses
• Intersects
• Is disjoint
• Touches
• Within
19.19.1 Using the plugin
As an example we want to find regions in the Alaska dataset that contain airports. Following steps are necessary:
1. Start QGIS and load the vector layers regions.shp and airports.shp.
2. Load the Spatial Query plugin in the Plugin Manager (see Section Loading a QGIS Core Plugin) and click
on the
Spatial Query
icon which appears in the QGIS toolbar menu. The plugin dialog appears.
3. Select layer regions as source layer and airports as reference feature layer.
4. Select ‘Contains’ as operator and click [Apply].
Now you get a list of feature IDs from the query and you have several options as shown in figure_spatial_query_1.
• Click on the
Create layer with list of items
• Select an ID from the list and click on
Create layer with selected
• Select the ‘Remove from current selection’ in the field And use the result to
• Additionally you can
Zoom to item or display
.
Log messages.
19.20 SPIT Plugin
QGIS comes with a plugin named SPIT (Shapefile to PostGIS Import Tool). SPIT can be used to load multiple
shapefiles at one time and includes support for schemas. To use SPIT, open the Plugin Manager from the Plugins
menu, check the box next to the
toolbar.
SPIT plugin and click [OK]. The SPIT icon will be added to the plugin
SPIT
To import a shapefile, click on the
tool in the toolbar to open the SPIT - Shapefile to PostGIS Import
Tool dialog. Select the PostGIS database you want to connect to and click on [Connect]. If you want, you can
define or change some import options. Now you can add one or more files to the queue by clicking on the [Add]
button. To process the files, click on the [OK] button. The progress of the import as well as any errors/warnings
will be displayed as each shapefile is processed.
Tip: Importing Shapefiles Containing PostgreSQL Reserved Words
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Figure 19.33: Spatial Query analysis - regions contain airports
Figure 19.34: Using SPIT Plugin to import Shape files to PostGIS
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If a shapefile is added to the queue containing fields that are reserved words in the PostgreSQL database a dialog
will popup showing the status of each field. You can edit the field names prior to import and change any that are
reserved words (or change any other field names as desired). Attempting to import a shapefile with reserved words
as field names will likely fail.
19.21 SQL Anywhere Plugin
SQL Anywhere is a proprietary relational database management system (RDBMS) from Sybase. SQL Anywhere
includes spatial support including OGC, shape files etc. and built in functions to export to KML, GML and SVG
formats.
Figure 19.35: SQL Anywhere dialog (KDE)
SQL Anywhere
The
allows to connect to spatialy enabled SQL Anywhere databases. The Add SQL Anywhere
layer dialog is similar in functionality to the dialogs for PostGIS and SpatiaLite.
19.22 Zonal Statistics Plugin
Zonal Statistics Plugin
you can analyze the results of a thematic classification. It allows to calculate several
With the
values of the pixels of a raster layer with the help of a polygonal vector layer (see figure_zonal_statistics). You can
calculate the sum, the mean value and the total count of the pixels that are within a polygon. The plugin generates
output columns in the vector layer with a user-defined prefix.
Figure 19.36: Zonal statistics dialog (KDE)
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CHAPTER 20
Help and Support
20.1 Mailing lists
QGIS is under active development and as such it won’t always work like you expect it to. The preferred way to
get help is by joining the qgis-users mailing list. Your questions will reach a broader audience and answers will
benefit others.
20.1.1 qgis-users
This mailing list is used for discussion of QGIS in general, as well as specific questions regarding its
installation and use. You can subscribe to the qgis-users mailing list by visiting the following URL:
http://lists.osgeo.org/mailman/listinfo/qgis-user
20.1.2 fossgis-talk-liste
For the german speaking audience the german FOSSGIS e.V. provides the fossgis-talk-liste mailing list. This
mailing list is used for discussion of open source GIS in general including QGIS. You can subscribe to the fossgistalk-liste mailing list by visiting the following URL: https://lists.fossgis.de/mailman/listinfo/fossgis-talk-liste
20.1.3 qgis-developer
If you are a developer facing problems of a more technical nature, you may want to join the qgis-developer mailing
list here: http://lists.osgeo.org/mailman/listinfo/qgis-developer
20.1.4 qgis-commit
Each time a commit is made to the QGIS code repository an email is posted to this list. If you
want to be up to date with every change to the current code base, you can subscribe to this list at:
http://lists.osgeo.org/mailman/listinfo/qgis-commit
20.1.5 qgis-trac
This list provides email notification related to project management, including bug reports, tasks, and feature
requests. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-trac
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20.1.6 qgis-community-team
This list deals with topics like documentation, context help, user-guide, online experience including web sites,
blog, mailing lists, forums, and translation efforts. If you like to work on the user-guide as well, this list is a good
starting point to ask your questions. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgiscommunity-team
20.1.7 qgis-release-team
This list deals with topics like the release process, packaging binaries for various OS and announcing new releases
to the world at large. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-release-team
20.1.8 qgis-tr
This list deals with the translation efforts. If you like to work on the translation of the manuals or the graphical
user interface (GUI), this list is a good starting point to ask your questions. You can subscribe to this list at:
http://lists.osgeo.org/mailman/listinfo/qgis-tr
20.1.9 qgis-edu
This list deals with QGIS education efforts. If you like to work on QGIS education materials, this list is a good
starting point to ask your questions. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgisedu
20.1.10 qgis-psc
This list is used to discuss Steering Committee issues related to overall management and direction of Quantum
GIS. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-psc
You are welcome to subscribe to any of the lists. Please remember to contribute to the list by answering questions
and sharing your experiences. Note that the qgis-commit and qgis-trac are designed for notification only and not
meant for user postings.
20.2 IRC
We also maintain a presence on IRC - visit us by joining the #qgis channel on irc.freenode.net. Please wait
around for a response to your question as many folks on the channel are doing other things and it may take
a while for them to notice your question. Commercial support for QGIS is also available. Check the website
http://qgis.org/en/commercial-support.html for more information.
If you missed a discussion on IRC, not a problem! We log all discussion so you can easily catch up. Just go to
http://logs.qgis.org and read the IRC-logs.
20.3 BugTracker
While the qgis-users mailing list is useful for general ‘how do I do XYZ in QGIS’ type questions, you
may wish to notify us about bugs in QGIS. You can submit bug reports using the QGIS bug tracker at
http://hub.qgis.org/projects/quantum-gis/issues. When creating a new ticket for a bug, please provide an email
address where we can request additional information.
Please bear in mind that your bug may not always enjoy the priority you might hope for (depending on its severity).
Some bugs may require significant developer effort to remedy and the manpower is not always available for this.
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Feature requests can be submitted as well using the same ticket system as for bugs. Please make sure to select the
type Feature.
If you have found a bug and fixed it yourself you can submit this patch also. Again, the lovely redmine ticketsystem
at http://hub.qgis.org/projects/quantum-gis/issues has this type as well. Check Patch supplied checkbox and
attach your patch before submitting bug. Someone of the developers will review it and apply it to QGIS. Please
don’t be alarmed if your patch is not applied straight away — developers may be tied up with other committments.
20.4 Blog
The QGIS-community also runs a weblog at http://www.qgis.org/planet which has some interesting articles for
users and developers as well provided by other blogs in the community. You are invited to contribute your own
QGIS blog!
20.5 Plugins
The website http://plugins.qgis.org provides the official QGIS plugins web portal. Here you find a list of all stable
and experimental QGIS plugins available via the ‘Official QGIS Plugin Repository’.
20.6 Wiki
Lastly, we maintain a WIKI web site at http://hub.qgis.org/projects/quantum-gis/wiki where you can find a variety
of useful information relating to QGIS development, release plans, links to download sites, message translationhints and so on. Check it out, there are some goodies inside!
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CHAPTER 21
Appendix
21.1 GNU General Public License
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not
allowed.
Preamble
The licenses for most software are designed to take away your freedom to share and change it. By contrast,
the GNU General Public License is intended to guarantee your freedom to share and change free software–to
make sure the software is free for all its users. This General Public License applies to most of the Free Software
Foundation’s software and to any other program whose authors commit to using it. (Some other Free Software
Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your
programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed
to make sure that you have the freedom to distribute copies of free software (and charge for this service if you
wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of
it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to
surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the
software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients
all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must
show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you
legal permission to copy, distribute and/or modify the software.
Also, for each author’s protection and ours, we want to make certain that everyone understands that there is no
warranty for this free software. If the software is modified by someone else and passed on, we want its recipients
to know that what they have is not the original, so that any problems introduced by others will not reflect on the
original authors’ reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To
prevent this, we have made it clear that any patent must be licensed for everyone’s free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS
FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License applies to any program or other work which contains a notice placed by the copyright holder
saying it may be distributed under the terms of this General Public License. The “Program”, below, refers to
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any such program or work, and a “work based on the Program” means either the Program or any derivative
work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim
or with modifications and/or translated into another language. (Hereinafter, translation is included without
limitation in the term “modification”.) Each licensee is addressed as “you”.
Activities other than copying, distribution and modification are not covered by this License; they are outside
its scope. The act of running the Program is not restricted, and the output from the Program is covered only
if its contents constitute a work based on the Program (independent of having been made by running the
Program). Whether that is true depends on what the Program does.
1. You may copy and distribute verbatim copies of the Program’s source code as you receive it, in any medium,
provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice
and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any
warranty; and give any other recipients of the Program a copy of this License along with the Program.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty
protection in exchange for a fee.
2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the
Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided
that you also meet all of these conditions:
(a) You must cause the modified files to carry prominent notices stating that you changed the files and the
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(b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived
from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under
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(c) If the modified program normally reads commands interactively when run, you must cause it, when
started running for such interactive use in the most ordinary way, to print or display an announcement
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These requirements apply to the modified work as a whole. If identifiable sections of that work are not
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then this License, and its terms, do not apply to those sections when you distribute them as separate works.
But when you distribute the same sections as part of a whole which is a work based on the Program, the
distribution of the whole must be on the terms of this License, whose permissions for other licensees extend
to the entire whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you;
rather, the intent is to exercise the right to control the distribution of derivative or collective works based on
the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work
based on the Program) on a volume of a storage or distribution medium does not bring the other work under
the scope of this License.
3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:
(a) Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
(b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no
more than your cost of physically performing source distribution, a complete machine-readable copy
of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a
medium customarily used for software interchange; or,
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(c) Accompany it with the information you received as to the offer to distribute corresponding source
code. (This alternative is allowed only for noncommercial distribution and only if you received the
program in object code or executable form with such an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for making modifications to it. For an
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If distribution of executable or object code is made by offering access to copy from a designated place, then
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4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this
License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will
automatically terminate your rights under this License. However, parties who have received copies, or
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5. You are not required to accept this License, since you have not signed it. However, nothing else grants you
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If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other
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If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance
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free software distribution system, which is implemented by public license practices. Many people have
made generous contributions to the wide range of software distributed through that system in reliance on
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software through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this
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8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an
explicit geographical distribution limitation excluding those countries, so that distribution is permitted only
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9. The Free Software Foundation may publish revised and/or new versions of the General Public License from
time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.
21.1. GNU General Public License
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Each version is given a distinguishing version number. If the Program specifies a version number of this
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either of that version or of any later version published by the Free Software Foundation. If the Program
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10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are
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NO WARRANTY
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THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE
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ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
Quantum GIS Qt exception for GPL
In addition, as a special exception, the QGIS Development Team gives permission to link the code
of this program with the Qt library, including but not limited to the following versions (both free
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(or with modified versions of Qt that use the same license as Qt), and distribute linked combinations
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used other than Qt. If you modify this file, you may extend this exception to your version of the file,
but you are not obligated to do so. If you do not wish to do so, delete this exception statement from
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21.2 GNU Free Documentation License
Version 1.3, 3 November 2008
Copyright 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc
<http://fsf.org/>
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not
allowed.
Preamble
The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the
sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying
it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a
way to get credit for their work, while not being considered responsible for modifications made by others.
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This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free
in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free
software.
We have designed this License in order to use it for manuals for free software, because free software needs free
documentation: a free program should come with manuals providing the same freedoms that the software does.
But this License is not limited to software manuals; it can be used for any textual work, regardless of subject
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1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright
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A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied
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A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively
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The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant
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above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain
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The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in
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and a Back-Cover Text may be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic
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An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is
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The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold,
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title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding
the beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document to the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains
XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific
section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.)
21.2. GNU Free Documentation License
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To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled
XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the
Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as
regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided
that this License, the copyright notices, and the license notice saying this License applies to the Document are
reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not
use technical measures to obstruct or control the reading or further copying of the copies you make or distribute.
However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies
you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering
more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers
that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts
on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the title equally prominent and visible. You may add other
material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title
of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many
as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include
a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a
computer-network location from which the general network-using public has access to download using publicstandard network protocols a complete Transparent copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to
ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the
last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large
number of copies, to give them a chance to provide you with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above,
provided that you release the Modified Version under precisely this License, with the Modified Version filling the
role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses
a copy of it. In addition, you must do these things in the Modified Version:
1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed in the History section of the Document). You
may use the same title as a previous version if the original publisher of that version gives permission.
2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of
its principal authors, if it has fewer than five), unless they release you from this requirement.
3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
4. Preserve all the copyright notices of the Document.
5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
6. Include, immediately after the copyright notices, a license notice giving the public permission to use the
Modified Version under the terms of this License, in the form shown in the Addendum below.
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7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the
Document’s license notice.
8. Include an unaltered copy of this License.
9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year,
new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled
“History” in the Document, create one stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the
Document, and likewise the network locations given in the Document for previous versions it was based
on. These may be placed in the “History” section. You may omit a network location for a work that was
published at least four years before the Document itself, or if the original publisher of the version it refers
to gives permission.
11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section
numbers or the equivalent are not considered part of the section titles.
13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant
Section.
15. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and
contain no material copied from the Document, you may at your option designate some or all of these sections
as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice.
These titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified
Version by various parties—for example, statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover
Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one
of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you
are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from
the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for
publicity for or to assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms defined in
section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections
of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be
replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents,
make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author
or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming
one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections
Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.
6. COLLECTIONS OF DOCUMENTS
21.2. GNU Free Documentation License
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You may make a collection consisting of the Document and other documents released under this License, and
replace the individual copies of this License in the various documents with a single copy that is included in the
collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all
other respects.
You may extract a single document from such a collection, and distribute it individually under this License,
provided you insert a copy of this License into the extracted document, and follow this License in all other respects
regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents or works, in
or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the
compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not apply to the other works in the aggregate
which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document
is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket
the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document under the
terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright
holders, but you may include translations of some or all Invariant Sections in addition to the original versions of
these Invariant Sections. You may include a translation of this License, and all the license notices in the Document,
and any Warranty Disclaimers, provided that you also include the original English version of this License and the
original versions of those notices and disclaimers. In case of a disagreement between the translation and the
original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License.
Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your
rights under this License.
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated
(a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b)
permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies
you of the violation by some reasonable means, this is the first time you have received notice of violation of this
License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt
of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies
or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt
of a copy of some or all of the same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from
time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address
new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular
numbered version of this License “or any later version” applies to it, you have the option of following the terms
and conditions either of that specified version or of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version number of this License, you may choose
any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a
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proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance
of a version permanently authorizes you to choose that version for the Document.
11. RELICENSING
“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes
copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that
anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained
in the site means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons
Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as
future copyleft versions of that license published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published
under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the
MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at
any time before August 1, 2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document and put the
following copyright and license notices just after the title page:
Copyright © YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.3 or any later version
published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no
Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation
License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with ... Texts.” line with
this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and
with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two
alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in
parallel under your choice of free software license, such as the GNU General Public License, to permit their use
in free software.
21.2. GNU Free Documentation License
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254
Chapter 21. Appendix
CHAPTER 22
Literature and Web References
GDAL-SOFTWARE-SUITE. Geospatial data abstraction library. htt://www.gdal.org, 2012.
GRASS-PROJECT. Geographic ressource analysis support system. http://grass.osgeo.org , 2012.
MITCHELL, T. Web mapping illustrated, 2005.
NETELER, M., AND MITASOVA, H. Open source gis: A grass gis approach, 2008.
OGR-SOFTWARE-SUITE. Geospatial data abstraction library. http://www.gdal.org/ogr , 2012.
OPEN-GEOSPATIAL-CONSORTIUM.
http://portal.opengeospatial.org, 2002.
Web
map
service
(1.1.1)
implementation
specification.
OPEN-GEOSPATIAL-CONSORTIUM.
http://portal.opengeospatial.org, 2004.
Web
map
service
(1.3.0)
implementation
specification.
POSTGIS-PROJECT. Spatial support for postgresql. http://postgis.refractions.net/ , 2012.
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256
Chapter 22. Literature and Web References
Index
%%, 77
Actions, 77
Analysis tools, 214
annotation, 38
apache, 112
apache2, 112
Arc/Info_ASCII_Grid, 99
Arc/Info_Binary_Grid, 99
ArcInfo_Binary_Coverage, 57
attribute table, 91
Attribute_Actions, 77
Attribute_Table_Selection, 92
Avoid_Intersections_Of_Polygons, 84
bookmarks, 39
Browse_Maps, 52
Calculator_Field, 95
CAT, 105
Categorized_Renderer, 65
Centroid_fill, 64
CGI, 111
Chain, 72
change the symbology, 70
Colliding_Labels, 72
Color_interpolation, 102
Color_Ramp, 66
Color_ramps, 64
ColorBrewer, 66
Colormap, 102
command line options, 17
Common_Gateway_Interface, 111
Compose_Maps, 179
Composer_Manager, 193
Composer_Template, 181
Connection_Manager, 58
Context help, 33
Contrast_enhancement, 101
Coordinate_Reference_System, 49, 108
crashes, 195
Create_Maps, 179
Create_New_Layers, 90
crossing the 180 degrees longitude line, 61
CRS, 49, 108
CSV, 86
Custom_Color_Ramp, 66
Custom_CRS, 52
data providers, 198
DB_Manager, 62
Debian_Squeeze, 112
default_CRS, 49
define an action, 77
Derived_Fields, 95
Digitizing, 84
Discrete, 102
Displacement_plugin, 67
documentation, 5
editing, 82
EPSG, 49
Equal_Interval, 66
Erdas Imagine, 99
ESRI, 55
European_Petroleom_Search_Group, 49
example actions, 77
Export_as_image, 192
Export_as_PDF, 192
Export_as_SVG, 192
FALP, 72
FastCGI, 111
Field_Calculator, 95
Field_Calculator_Functions, 96
Fill_Color, 70
Fill_Style, 70
Font_Marker, 64
Freak_out, 100
FWTools, 227
GDAL, 99
Georeferencer tools, 220
GeoTIFF, 99
GeoTiff, 99
GiST (Generalized Search Tree) index, 61
GML, 105
Gradient_Color_Ramp, 66
Graduated_Renderer, 66
GRASS, 120, see Creating new vectors;editing;creating
a new layer
257
QGIS User Guide, Release 1.8
attribute linkage, 126
attribute storage, 126
category settings, 127
digitizing, 125
digitizing tools, 126
display results, 130, 133
loading data, 122
region, 129
region display, 129
region editing, 129
snapping tolerance, 128
Start Plugin, 121
symbology settings, 128
table editing, 128
toolbox, 133
topology, 125
vector data model, 125
GRASS toolbox, 129
Browser, 136
customize, 136
Grayscale, 100
Grid
Map_Grid, 184
Histogram, 103
IGNF, 49
Import_Maps, 52
Institut_Geographique_National_de_France, 49
InteProxy, 110
join a loaded attribute table to a loaded vector layer, 80
join layer, 80
Keyboard shortcuts, 33
Label_Engine_Settings, 72
Labeling_Engine, 70
Labeling_New, 70
Labeling_Old, 70
layer visibility, 27
layout toolbars, 27
Layout_Maps, 179
legend, 27
license
GPL, 245
Line_decoration, 64
load a shapefile, 55
loading_raster, 99
Manage_Color_Ramps, 70
Manage_Symbols, 70
Map overview, 41
Map_Legend, 187
Map_Navigation, 83
Map_Template, 181
MapInfo, 57
Mapserver_Export_Plugin, 224
Marker_line, 64
258
measure, 35
angles, 35
areas, 35
line length, 35
menus, 22
merge attributes of features, 90
Merge_Attributes_of_Selected_Features, 90
Merge_Selected_Features, 90
Metadata, 103
msexport, 225
Multi_Band_Raster, 100
multipolygon, 89
Natural_Breaks_(Jenks), 66
nesting projects, 40
New_Labeling, 71
New_Shapefile_Layer, 90
New_Spatialite_Layer, 91
New_Symbology, 63
Node_Tool, 85
Nodes, 86
Non_Spatial_Attribute_Tables, 93
OGC, 105
OGR, 55
OGR Simple Feature Library, 55
ogr2ogr, 60
Old_Symbology, 69
Old_Symbology_Renderers, 70
Open_Geospatial_Consortium, 105
Outline_Options, 70
output save as image, 19
Pan, 83
pan arrow keys, 30
pgsql2shp, 60
Picture_database, 186
plugins, 195
installing, 197
manager, 195
Python Plugin Installer, 197
types, 195
upgrading, 197
Point_Displacement_Renderer, 67
Popmusic_Chain, 72
Popmusic_Tabu, 72
Popmusic_Tabu_Chain, 72
PostGIS, 58
PostGIS spatial index, 61
PostgreSQL, 58
Pretty_Breaks, 66
print composer quick print, 19
print_composer
tools, 181
Printing
Export_Map, 192
Proj.4, 52
Proj4, 50
Proj4_text, 50
Index
QGIS User Guide, Release 1.8
Projections, 49
Proxy, 106
proxy-server, 106
Pseudocolor, 100
Publish_to_Web_plugin, 111
Pyramids, 103
QGIS_mapserver, 110
QGIS_Server, 111
QSpatiaLite, 62
Quantile, 66
Query_Builder, 94
Raster, 99
Raster_Calculator, 103
Renderer_Categorized, 65
Renderer_Graduated, 66
Renderer_Point_Displacement, 67
Renderer_Single_Symbol, 65
Renderers, 64
Renderers_Old_Symbology, 70
Rendering, 33
Rendering halting, 34
rendering quality, 35
Rendering scale dependent, 34
rendering update during drawing, 35
Rendering_Rule-based, 67
Research tools, 214
Revert_Layout_Actions, 190
ring polygons, 89
Rotate_Point_symbols, 90
Rotated_North_Arrow, 186
Rule-based_Rendering, 67
Scale, 34
scale calculate, 30
Scalebar
Map_Scalebar, 188
Search_Radius, 83
Secured_OGC_Authentication, 110
Select_using_Query, 95
SFS, 105
Shapefile, 55
Shapefile_to_Postgis_Import_Tool, 237
Shared_Polygon_Boundaries, 84
shp2img, 227
shp2pgsql, 60
Simple_fill, 64
Simple_line, 64
Simple_Marker, 64
Single_Band_Raster, 100
Single_Symbol_Renderer, 65
SLD, 111
SLD/SE, 111
Smart_Labeling, 71
Snapping, 82
Snapping_Tolerance, 82
spatial bookmarks
see bookmarks, 39
Index
Spatialite, 62
Spatialite_Manager, 62
SPIT, 237
Split_Features, 89
SQLite, 62
SRS, 108
ST_Shift_Longitude, 61
Style_Manager, 70
SVG_fill, 64
SVG_Marker, 64
Symbol_Properties, 68
Symbology, 100
Symbology_New, 63
Symbology_Old, 69
Three_Band_Color_Raster, 100
Tiger_Format, 57
Toggle Editing, 84
toolbar, 27
Topological_Editing, 84
Transparency, 101
Transparency_Vector, 70
UK_National_Transfer_Format, 57
US_Census_Bureau, 57
Vector_Transparency, 70
Vertex, 86
Vertices, 86
WCS, 105
WFS, 105, 110
WFS-T, 110
WFS_Transactional, 110
WKT, 49, 86
WMS, 105
WMS-C, 109
WMS_1.3.0, 110
WMS_client, 105
WMS_identify, 109
WMS_layer_transparency, 108
WMS_metadata, 109
WMS_properties, 109
WMS_tiles, 109
Work_with_Attribute_Table, 91
zoom mouse wheel, 29
Zoom_In Zoom_Out, 83
259