QGIS User Guide - OSGeo Server

QGIS User Guide - OSGeo Server
Quantum GIS
User Guide
Version 1.1.0 ’Pan’
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://qgis.osgeo.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 LATEX. It is available as LATEX source code via subversion and
online as PDF document via http://qgis.osgeo.org/documentation/manuals.html. Translated
versions of this document can be downloaded 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 links
are shown in blue, while external links are shown in red 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
Otto Dassau
Stephan Holl
Lars Luthman
Tyler Mitchell
Radim Blazek
Martin Dobias
Marco Hugentobler
Gavin Macaulay
Brendan Morely
Godofredo Contreras
Jürgen E. Fischer
Magnus Homann
Werner Macho
Gary E. Sherman
Claudia A. Engel
Anne Ghisla
Tim Sutton
Carson J.Q. Farmer
David Willis
With thanks to Tisham Dhar for preparing the initial msys (MS Windows) environment
documentation, to Tom Elwertowski and William Kyngesburye for help in the MAC OSX Installation
Section and to Carlos Dávila, Paolo Cavallini and Christian Gunning for revisions. If we have
neglected to mention any contributors, please accept our apologies for this oversight.
c 2004 - 2009 Quantum GIS Development Team
Copyright Internet: http://qgis.osgeo.org
Contents
Contents
Title
i
Preamble
ii
Table of Contents
iii
List of Figures
viii
List of Tables
x
List of QGIS Tips
xi
1 Foreword
1.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1
4
2 Introduction To GIS
2.1 Why is all this so new? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1 Raster Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.2 Vector Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3 Getting Started
3.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Sample Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Sample Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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4 Features at a Glance
4.1 Starting and Stopping QGIS . . . . .
4.1.1 Command Line Options . . .
4.2 QGIS GUI . . . . . . . . . . . . . . .
4.2.1 Menu Bar . . . . . . . . . . .
4.2.2 Toolbars . . . . . . . . . . . .
4.2.3 Map Legend . . . . . . . . .
4.2.4 Map View . . . . . . . . . . .
4.2.5 Map Overview . . . . . . . .
4.2.6 Status Bar . . . . . . . . . . .
4.3 Rendering . . . . . . . . . . . . . . .
4.3.1 Scale Dependent Rendering
4.3.2 Controlling Map Rendering .
4.4 Measuring . . . . . . . . . . . . . . .
4.4.1 Measure length and areas . .
4.5 Projects . . . . . . . . . . . . . . . .
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QGIS 1.1.0 User Guide
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iii
Contents
4.6 Output . . . . . . . . . . . . . . .
4.7 GUI Options . . . . . . . . . . . .
4.8 Spatial Bookmarks . . . . . . . .
4.8.1 Creating a Bookmark . .
4.8.2 Working with Bookmarks
4.8.3 Zooming to a Bookmark .
4.8.4 Deleting a Bookmark . . .
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6 Working with Raster Data
6.1 What is raster data? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 Loading raster data in QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3 Raster Properties Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5 Working with Vector Data
5.1 ESRI Shapefiles . . . . . . . . . . . . . . . . . . . . . . . .
5.1.1 Loading a Shapefile . . . . . . . . . . . . . . . . . .
5.1.2 Improving Performance . . . . . . . . . . . . . . . .
5.1.3 Loading a MapInfo Layer . . . . . . . . . . . . . . .
5.1.4 Loading an ArcInfo Binary Coverage . . . . . . . . .
5.2 PostGIS Layers . . . . . . . . . . . . . . . . . . . . . . . . .
5.2.1 Creating a stored Connection . . . . . . . . . . . . .
5.2.2 Loading a PostGIS Layer . . . . . . . . . . . . . . .
5.2.3 Some details about PostgreSQL layers . . . . . . .
5.2.4 Importing Data into PostgreSQL . . . . . . . . . . .
5.2.5 Improving Performance . . . . . . . . . . . . . . . .
5.3 SpatiaLite Layers . . . . . . . . . . . . . . . . . . . . . . . .
5.4 The Vector Properties Dialog . . . . . . . . . . . . . . . . .
5.4.1 General Tab . . . . . . . . . . . . . . . . . . . . . . .
5.4.2 Symbology Tab . . . . . . . . . . . . . . . . . . . . .
5.4.3 Metadata Tab . . . . . . . . . . . . . . . . . . . . . .
5.4.4 Labels Tab . . . . . . . . . . . . . . . . . . . . . . .
5.4.5 Actions Tab . . . . . . . . . . . . . . . . . . . . . . .
5.4.6 Attributes Tab . . . . . . . . . . . . . . . . . . . . . .
5.4.7 Diagram Tab . . . . . . . . . . . . . . . . . . . . . .
5.5 Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5.1 Setting the Snapping Tolerance and Search Radius
5.5.2 Topological editing . . . . . . . . . . . . . . . . . . .
5.5.3 Editing an Existing Layer . . . . . . . . . . . . . . .
5.5.4 Creating a New Layer . . . . . . . . . . . . . . . . .
5.5.5 Working with the Attribute Table . . . . . . . . . . .
5.6 Query Builder . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7 Select by query . . . . . . . . . . . . . . . . . . . . . . . . .
QGIS 1.1.0 User Guide
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iv
Contents
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
Symbology Tab . .
Transparency Tab
Colormap . . . . .
General Tab . . . .
Metadata Tab . . .
Pyramids Tab . . .
Histogram Tab . .
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7 Working with OGC Data
7.1 What is OGC Data . . . . . . . . .
7.2 WMS Client . . . . . . . . . . . . .
7.2.1 Overview of WMS Support
7.2.2 Selecting WMS Servers . .
7.2.3 Loading WMS Layers . . .
7.2.4 Server-Search . . . . . . .
7.2.5 Using the Identify Tool . . .
7.2.6 Viewing Properties . . . . .
7.2.7 WMS Client Limitations . .
7.3 WFS Client . . . . . . . . . . . . .
7.3.1 Loading a WFS Layer . . .
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8 Working with Projections
8.1 Overview of Projection Support . . . .
8.2 Specifying a Projection . . . . . . . . .
8.3 Define On The Fly (OTF) Projection .
8.4 Custom Coordinate Reference System
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9 GRASS GIS Integration
9.1 Starting the GRASS plugin . . . . . . . . . . . . . . .
9.2 Loading GRASS raster and vector layers . . . . . . . .
9.3 GRASS LOCATION and MAPSET . . . . . . . . . . .
9.3.1 Creating a new GRASS LOCATION . . . . . .
9.3.2 Adding a new MAPSET . . . . . . . . . . . . .
9.4 Importing data into a GRASS LOCATION . . . . . . .
9.5 The GRASS vector data model . . . . . . . . . . . . .
9.6 Creating a new GRASS vector layer . . . . . . . . . .
9.7 Digitizing and editing a GRASS vector layer . . . . . .
9.8 The GRASS region tool . . . . . . . . . . . . . . . . .
9.9 The GRASS toolbox . . . . . . . . . . . . . . . . . . .
9.9.1 Working with GRASS modules . . . . . . . . .
9.9.2 Working with the GRASS LOCATION browser
9.9.3 Customizing the GRASS Toolbox . . . . . . . .
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QGIS 1.1.0 User Guide
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v
Contents
10 Print Composer
10.1 Using Print Composer . . . . . . . . . . . . . . . . . . . . . . . . .
10.1.1 Adding a current QGIS map canvas to the Print Composer
10.1.2 Navigation tools . . . . . . . . . . . . . . . . . . . . . . . .
10.1.3 Adding other elements to the Print Composer . . . . . . . .
10.1.4 Raise, lower and align elements . . . . . . . . . . . . . . .
10.1.5 Creating Output . . . . . . . . . . . . . . . . . . . . . . . .
10.1.6 Saving and loading a print composer layout . . . . . . . . .
11 QGIS Plugins
11.1 Managing Plugins . . . . . . . . . . . . . . . .
11.1.1 Loading a QGIS Core Plugin . . . . . .
11.1.2 Loading an external QGIS Plugin . . . .
11.1.3 Using the QGIS Python Plugin Installer
11.2 Data Providers . . . . . . . . . . . . . . . . . .
12 Using QGIS Core Plugins
12.1 Delimited Text Plugin . . . . . . . . . . . . . .
12.2 Coordinate Capture Plugin . . . . . . . . . .
12.3 Decorations Plugins . . . . . . . . . . . . . .
12.3.1 Copyright Label Plugin . . . . . . . . .
12.3.2 North Arrow Plugin . . . . . . . . . . .
12.3.3 Scale Bar Plugin . . . . . . . . . . . .
12.4 Dxf2Shp Converter Plugin . . . . . . . . . . .
12.5 Georeferencer Plugin . . . . . . . . . . . . .
12.6 Quick Print Plugin . . . . . . . . . . . . . . .
12.7 GPS Plugin . . . . . . . . . . . . . . . . . . .
12.7.1 What is GPS? . . . . . . . . . . . . .
12.7.2 Loading GPS data from a file . . . . .
12.7.3 GPSBabel . . . . . . . . . . . . . . . .
12.7.4 Importing GPS data . . . . . . . . . .
12.7.5 Downloading GPS data from a device
12.7.6 Uploading GPS data to a device . . .
12.7.7 Defining new device types . . . . . . .
12.8 fTools Plugin . . . . . . . . . . . . . . . . . .
12.9 Interpolation Plugin . . . . . . . . . . . . . . .
12.10MapServer Export Plugin . . . . . . . . . . .
12.10.1Creating the Project File . . . . . . . .
12.10.2Creating the Map File . . . . . . . . .
12.10.3Testing the Map File . . . . . . . . . .
12.11OGR Converter Plugin . . . . . . . . . . . . .
12.12Oracle GeoRaster Plugin . . . . . . . . . . .
QGIS 1.1.0 User Guide
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vi
Contents
12.12.1Managing connections
12.12.2Selecting a GeoRaster
12.12.3Displaying GeoRaster
12.13Other core plugins . . . . . .
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142
142
143
145
13 Using external QGIS Python Plugins
146
14 Help and Support
14.1 Mailinglists .
14.2 IRC . . . . .
14.3 BugTracker .
14.4 Blog . . . . .
14.5 Wiki . . . . .
147
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149
149
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A Supported Data Formats
150
A.1 OGR Vector Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
A.2 GDAL Raster Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
B GRASS Toolbox modules
B.1 GRASS Toolbox data import and export modules . . . . . . .
B.2 GRASS Toolbox data type conversion modules . . . . . . . .
B.3 GRASS Toolbox region and projection configuration modules
B.4 GRASS Toolbox raster data modules . . . . . . . . . . . . . .
B.5 GRASS Toolbox vector data modules . . . . . . . . . . . . .
B.6 GRASS Toolbox imagery data modules . . . . . . . . . . . .
B.7 GRASS Toolbox database modules . . . . . . . . . . . . . . .
B.8 GRASS Toolbox 3D modules . . . . . . . . . . . . . . . . . .
B.9 GRASS Toolbox help modules . . . . . . . . . . . . . . . . .
C GNU General Public License
C.1 Quantum GIS Qt exception for GPL
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Cited literature
175
Index
176
QGIS 1.1.0 User Guide
vii
List of Figures
List of Figures
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
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35
36
37
38
39
40
A Simple QGIS Session
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
QGIS GUI with Alaska sample data
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Measure tools in action
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Proxy-settings in QGIS
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Add Vector Layer Dialog
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Open an OGR Supported Vector Layer Dialog
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QGIS with Shapefile of Alaska loaded
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Vector Layer Properties Dialog
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Symbolizing-options
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Select feature and choose action
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Vector properties dialog with diagram tab
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Diagram from temperature data overlayed on a map
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Edit snapping options on a layer basis . . . . . . . . . . . . . . . . . . . . . . . .
Enter Attribute Values Dialog after digitizing a new vector feature . . . . . . . . .
Creating a New Vector Dialog
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Attribute Table for Alaska layer
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Query Builder
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Raster Layers Properties Dialog
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Dialog for adding a WMS server, showing its available layers
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Dialog for searching WMS servers after some keywords . . . . . . . . . . . . . .
Adding a WFS layer
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CRS tab in the QGIS Options Dialog
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Projection Dialog
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Custom CRS Dialog
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GRASS data in the alaska LOCATION (adapted from Neteler & Mitasova 2008 [2])
Creating a new GRASS LOCATION or a new MAPSET in QGIS
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GRASS Digitizing Toolbar
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GRASS Digitizing Category Tab
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GRASS Digitizing Settings Tab
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GRASS Digitizing Symbolog Tab . . . . . . . . . . . . . . . . . . . . . . . . . . .
GRASS Digitizing Table Tab
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GRASS Toolbox and searchable Modules List
. . . . . . . . . . . . . . . . . . .
GRASS Toolbox Module Dialogs
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GRASS LOCATION browser
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Print Composer
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Print Composer map item tab content
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Customize print composer label and images
. . . . . . . . . . . . . . . . . . . .
Customize print composer legend and scalebar
. . . . . . . . . . . . . . . . . .
Print Composer with map view, legend, scalebar, and text added . . . . . . . . .
Plugin Manager
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
QGIS 1.1.0 User Guide
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Installing external python plugins . . . . . . . . . . . . . . . . . .
Delimited Text Dialog
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Coordinate Cature Plugin
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Copyright Label Plugin
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North Arrow Plugin
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Scale Bar Plugin
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Dxf2Shape Converter Plugin
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Georeferencer Plugin Dialog
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Add points to the raster image
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Quick Print Dialog
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Quick Print result as DIN A4 PDF using the alaska sample dataset
The GPS Tools dialog window
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The download tool
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Interpolation Plugin
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Interpolation of elevp data using IDW method
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Arrange raster and vector layers for QGIS project file
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Export to MapServer Dialog
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Test PNG created by shp2img with all MapServer Export layers
OGR Layer Converter Plugin
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Create Oracle connection dialog
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Select Oracle GeoRaster dialog
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QGIS 1.1.0 User Guide
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List of Tables
List of Tables
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PostGIS Connection Parameters . . . . . . . . . . . . . . . . . . . .
WMS Connection Parameters . . . . . . . . . . . . . . . . . . . . . .
GRASS Digitizing Tools . . . . . . . . . . . . . . . . . . . . . . . . .
Print Composer Tools . . . . . . . . . . . . . . . . . . . . . . . . . .
QGIS Core Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . .
fTools Analysis tools . . . . . . . . . . . . . . . . . . . . . . . . . . .
fTools Research tools . . . . . . . . . . . . . . . . . . . . . . . . . .
fTools Geoprocessing tools . . . . . . . . . . . . . . . . . . . . . . .
fTools Geometry tools . . . . . . . . . . . . . . . . . . . . . . . . . .
fTools Data management tools . . . . . . . . . . . . . . . . . . . . .
Other Core Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Current moderated external QGIS Plugins . . . . . . . . . . . . . . .
GRASS Toolbox: Raster and Image data import modules . . . . . .
GRASS Toolbox: Raster and Image data export modules . . . . . .
GRASS Toolbox: Vector data import modules . . . . . . . . . . . . .
GRASS Toolbox: Vector data export modules . . . . . . . . . . . . .
GRASS Toolbox: Data type conversion modules . . . . . . . . . . .
GRASS Toolbox: Region and projection configuration modules . . .
GRASS Toolbox: Develop raster map modules . . . . . . . . . . . .
GRASS Toolbox: Raster color management modules . . . . . . . . .
GRASS Toolbox: Spatial raster analysis modules . . . . . . . . . . .
GRASS Toolbox: Surface management modules . . . . . . . . . . .
GRASS Toolbox: Change raster category values and labels modules
GRASS Toolbox: Hydrologic modelling modules . . . . . . . . . . .
GRASS Toolbox: Reports and statistic analysis modules . . . . . . .
GRASS Toolbox: Develop vector map modules . . . . . . . . . . . .
GRASS Toolbox: Database connection modules . . . . . . . . . . .
GRASS Toolbox: Change vector field modules . . . . . . . . . . . .
GRASS Toolbox: Working with vector points modules . . . . . . . .
GRASS Toolbox: Spatial vector and network analysis modules . . .
GRASS Toolbox: Vector update by other maps modules . . . . . . .
GRASS Toolbox: Vector report and statistic modules . . . . . . . . .
GRASS Toolbox: Imagery analysis modules . . . . . . . . . . . . . .
GRASS Toolbox: Database modules . . . . . . . . . . . . . . . . . .
GRASS Toolbox: 3D Visualization . . . . . . . . . . . . . . . . . . .
GRASS Toolbox: Reference Manual . . . . . . . . . . . . . . . . . .
QGIS 1.1.0 User Guide
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QGIS Tips
QGIS Tips
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U P - TO - DATE D OCUMENTATION . . . . . . . . . . . . . . . . . . . . . . . .
E XAMPLE U SING COMMAND LINE ARGUMENTS . . . . . . . . . . . . . . .
R ESTORING TOOLBARS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Z OOMING THE M AP WITH THE M OUSE W HEEL . . . . . . . . . . . . . . .
PANNING THE M AP WITH THE A RROW K EYS AND S PACE B AR . . . . . . .
C ALCULATING THE CORRECT S CALE OF YOUR M AP C ANVAS . . . . . . .
U SING P ROXIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
L AYER C OLORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
QGIS U SER S ETTINGS AND S ECURITY . . . . . . . . . . . . . . . . . . .
P OST GIS L AYERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E XPORTING DATASETS FROM P OST GIS . . . . . . . . . . . . . . . . . . .
I MPORTING S HAPEFILES C ONTAINING P OSTGRE SQL R ESERVED W ORDS
DATA I NTEGRITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M ANIPULATING ATTRIBUTE DATA . . . . . . . . . . . . . . . . . . . . . . .
S AVE R EGULARLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C ONCURRENT E DITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Z OOM IN B EFORE E DITING . . . . . . . . . . . . . . . . . . . . . . . . . .
V ERTEX M ARKERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ATTRIBUTE VALUE T YPES . . . . . . . . . . . . . . . . . . . . . . . . . . .
C ONGRUENCY OF PASTED F EATURES . . . . . . . . . . . . . . . . . . . .
F EATURE D ELETION S UPPORT . . . . . . . . . . . . . . . . . . . . . . . .
C HANGING THE L AYER D EFINITION . . . . . . . . . . . . . . . . . . . . . .
V IEWING A S INGLE B AND OF A M ULTIBAND R ASTER . . . . . . . . . . . .
G ATHERING R ASTER S TATISTICS . . . . . . . . . . . . . . . . . . . . . . .
O N WMS S ERVER URL S . . . . . . . . . . . . . . . . . . . . . . . . . . .
I MAGE E NCODING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
WMS L AYER O RDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . .
WMS L AYER T RANSPARENCY . . . . . . . . . . . . . . . . . . . . . . . . .
WMS P ROJECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACCESSING SECURED OGC- LAYERS . . . . . . . . . . . . . . . . . . . . .
F INDING WFS S ERVERS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACCESSING SECURE WFS S ERVERS . . . . . . . . . . . . . . . . . . . . .
P ROJECT P ROPERTIES D IALOG . . . . . . . . . . . . . . . . . . . . . . . .
GRASS DATA L OADING . . . . . . . . . . . . . . . . . . . . . . . . . . . .
L EARNING THE GRASS V ECTOR M ODEL . . . . . . . . . . . . . . . . . .
C REATING AN ATTRIBUTE TABLE FOR A NEW GRASS VECTOR LAYER . . .
D IGITIZING POLYGONES IN GRASS . . . . . . . . . . . . . . . . . . . . .
C REATING AN ADDITIONAL GRASS ’ LAYER ’ WITH QGIS . . . . . . . . . .
GRASS E DIT P ERMISSIONS . . . . . . . . . . . . . . . . . . . . . . . . .
D ISPLAY RESULTS IMMEDIATELY . . . . . . . . . . . . . . . . . . . . . . . .
QGIS 1.1.0 User Guide
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QGIS Tips
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C RASHING P LUGINS . . . . . . . . . . . .
U SING EXPERIMENTAL PLUGINS . . . . . .
P LUGINS S ETTINGS S AVED TO P ROJECT
C HOOSING THE RESAMPLING METHOD . .
A DD MORE REPOSITORIES . . . . . . . . .
QGIS 1.1.0 User Guide
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109
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xii
1 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://www.trolltech.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 (see Appendix A for a full
list of currently supported data formats).
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
C.
Tip 1 U P - TO - DATE D OCUMENTATION
The latest version of this document can always be found at http://download.osgeo.org/qgis/doc/manual/,
or in the documentation area of the QGIS website at http://qgis.osgeo.org/documentation/
1.1 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.
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 PostgreSQL tables using PostGIS, vector formats 1 supported by the installed
OGR library, including ESRI shapefiles, MapInfo, SDTS and GML.
• Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction
Library) library, such as GeoTiff, Erdas Img., ArcInfo Ascii Grid, JPEG, PNG.
1
OGR-supported database formats such as Oracle or mySQL are not yet supported in QGIS.
QGIS 1.1.0 User Guide
1
1 FOREWORD
• SpatiaLite databases (see Section 5.3)
• GRASS raster and vector data from GRASS databases (location/mapset),
• Online spatial data served as OGC-compliant Web Map Service (WMS) or Web Feature Service
(WFS).
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:
• 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
• decorate your map with a north arrow scale bar and copyright label
• save and restore projects
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 added to list of GPS devices)
• 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 5.5.5) or Table Manager
plugin
• save screenshots as georeferenced images
QGIS 1.1.0 User Guide
2
1.1 Features
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 300 modules (See Section 9).
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 or WFS client, and as WMS
server.
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!
• Core Plugins
Add WFS Layer
Add Delimited Text Layer
Coordinate Capture
Decorations (Copyright Label, North Arrow and Scale bar)
Diagram Overlay
Dxf2Shp Converter
Georeferencer
fTools
GPS Tools
GRASS integration
Interpolation Plugin
OGR Layer Converter
Quick Print
SPIT Shapefile to PostgreSQL/PostGIS Import Tool
Mapserver Export
Python Console
Python Plugin Installer
• Python Plugins
QGIS offers a growing number of external python plugins that are provided by the community. These plugins reside in the the official PyQGIS repository, and can be easily installed
using the python plugin installer (See Section 11).
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1 FOREWORD
1.2 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
• Toolbox Item:
nviz - Open 3D-View in NVIZ
• Checkbox: x Render
• Radio Button: ⊙ Postgis SRID EPSG ID
• Select a Number: Hue 60
N
H
• Select a String: Outline style —Solid Line H
• Browse for a File: . . .
• Select a Color: Outline color
• Slider: Transparency 0% ▽
• Input Text: Display Name lakes.shp
A shadow indicates a clickable GUI component.
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1.2 Conventions
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
• Single Keystroke: press p
• 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
• User Text: qgis --help
Code is indicated by a fixed-width font:
PROJCS["NAD_1927_Albers",
GEOGCS["GCS_North_American_1927",
Platform-specific instructions
File
QGIS} > Quit
GUI sequences and small amounts of text can be formatted inline: Click {
to close QGIS. 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 icons at the end of the figure caption.
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2 INTRODUCTION TO GIS
2 Introduction To GIS
A Geographical Information System (GIS)[1]2 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
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.
2.1 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 fo2
This chapter is by Tyler Mitchell (http://www.oreillynet.com/pub/wlg/7053) and used under the Creative Commons License. Tyler is the author of Web Mapping Illustrated, published by O’Reilly, 2005.
QGIS 1.1.0 User Guide
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2.1 Why is all this so new?
cused 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.
2.1.1 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.
2.1.2 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
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2 INTRODUCTION TO GIS
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.
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 y4, ... 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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3 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.
3.1 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://qgis.osgeo.org/download/.
Installation from source
If you need to build QGIS from source, please refer to the coding and compiling guide available at
http://qgis.osgeo.org/documentation/. The installation instructions are also distributed with the
QGIS source code.
3.2 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 http://qgis.osgeo.org/download; or
• uninstall QGIS and reinstall with the data download option checked.
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 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",
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3 GETTING STARTED
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.
3.3 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.
start QGIS
•
•
•
Start QGIS by typing: qgis at a command prompt.
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.
Load raster and vector layers from the sample dataset
1. Click on the
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Load Raster icon.
10
3.3 Sample Session
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
Load Vector icon.
5. In the new Add Vector Layer dialog click Browse .
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 Layer Properties dialog.
9. Click on the Symbology
tab and select a blue as fill color.
10. Click on the Labels tab and check the x Display labels checkbox to enable labeling.
Choose NAMES field as Field containing label.
11. Click Apply .
Figure 1: A Simple QGIS Session
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.
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4 FEATURES AT A GLANCE
4 Features at a Glance
After a first and simple sample session in Section 3 we now want to give you a more detailed overview
of the features of QGIS. Most features presented in the following chapters will be explained and
described in own sections later in the manual.
4.1 Starting and Stopping QGIS
In Section 3.3 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.
•
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.
To stop QGIS, click the menu options {
File
QGIS} > Quit, or use the shortcut Ctrl+Q .
4.1.1 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 - 1.1.0-Pan (Unstable) ’Pan (Unstable)’
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
[--lang language]
use language for interface text
[--project projectfile] load the given QGIS project
[--extent xmin,ymin,xmax,ymax] set initial map extent
[--help]
this text
FILES:
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
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4.2 QGIS GUI
2. Vectors - Supported formats include ESRI Shapefiles
and others supported by OGR and PostgreSQL layers using
the PostGIS extension
Tip 2 E XAMPLE U SING
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. 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 is provided at
http://wiki.qgis.org/qgiswiki/TranslatorsCorner
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
4.2 QGIS GUI
When QGIS starts, you are presented with the GUI as shown below (the numbers 1 through 6 in
yellow ovals refer to the six major areas of the interface as discussed below):
Note: Your window decorations (title bar, etc.) may appear different depending on your operating
system and window manager.
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4 FEATURES AT A GLANCE
Figure 2: QGIS GUI with Alaska sample data
The QGIS GUI is divided into six areas:
1. Menu Bar
2. Tool Bar
3. Map Legend
4. Map View
5. Map Overview
6. Status Bar
These six components of the QGIS interface are described in more detail in the following sections.
4.2.1 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. Although
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4.2 QGIS GUI
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. For
more information about tools and toolbars, see Section 4.2.2.
Menu Option
Shortcut
Reference
Toolbar
Ctrl+N see Section 4.5
⊠ File
see Section 4.5
⊠ File
• File
New Project
Open Project
Ctrl+O Open Recent Projects
Save Project
Save Project As
see Section 4.5
Ctrl+S
Ctrl+Shift+S
Save as Image
Print Composer
Exit
see Section 4.5
⊠ File
see Section 4.5
⊠ File
see Section 4.6
Ctrl+P
see Section 10
⊠ File
Ctrl+X
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
see Section 5.5.3
⊠ Digitizing
Ctrl+Q • Edit
Cut Features
Copy Features
Paste Features
Capture Point
Capture Line
Capture Polygon
Ctrl+C Ctrl+V
.
/ Ctrl+/ And Other Edit Menu Items
• View
⊠ Map Navigation
Pan Map
Zoom In
Zoom Out
Select Features
Identify Features
Measure Line
Measure Area
Zoom Full
QGIS 1.1.0 User Guide
Ctrl++
Ctrl+- I M
J F ⊠ Map Navigation
⊠ Map Navigation
⊠ Attributes
⊠ Attributes
⊠ Attributes
⊠ Attributes
⊠ Map Navigation
15
4 FEATURES AT A GLANCE
⊠ Map Navigation
Zoom To Layer
Zoom To Selection
Ctrl+J
⊠ Map Navigation
⊠ Map Navigation
Zoom Last
⊠ Map Navigation
Zoom Next
Zoom Actual Size
Map Tips
New Bookmark
Show Bookmarks
Refresh
Ctrl+B
B
Ctrl+R ⊠ Attributes
see Section 4.8
⊠ Attributes
see Section 4.8
⊠ Attributes
⊠ Map Navigation
see Section 5.5.4
⊠ Manage Layers
see Section 5
⊠ File
see Section 6
⊠ File
see Section 5.2
⊠ File
see Section 7.2
⊠ File
• Layer
New Vector Layer
Add a Vector Layer
Add a Raster Layer
Add a PostGIS Layer
Add a WMS Layer
N
V
R
D
W Open Attribute Table
⊠ Attributes
⊠ Digitizing
Toggle editing
Save As Shapefile
Save Selection As Shapefile
Remove Layer
Ctrl+D
⊠ Manage Layers
O
⊠ Manage Layers
Properties
Add to Overview
Add All To Overview
+ Remove All From Overview - Hide All Layers
H ⊠ Manage Layers
Show All Layers
⊠ Manage Layers
S • Settings
Panels
Toolbars
Toggle Fullscreen Mode
Project Properties
Custom CRS
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see Section 8.4
16
4.2 QGIS GUI
Options
see Section 4.7
• Plugins - (Futher menu items are added by plugins as they are loaded.)
Plugin Manager
see Section 11.1 ⊠ Plugins
• Help
Help Contents
QGIS Home Page
F1
⊠ Help
Ctrl+H
Check QGIS Version
About
4.2.2 Toolbars
The toolbars provide 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.
Tip 3 R ESTORING
TOOLBARS
If you have accidentally hidden all your toolbars, you can get them back by choosing menu option Settings >
Toolbars .
4.2.3 Map Legend
The map legend area is used to set the visibility and z-ordering of layers. Z-ordering means that
layers listed nearer the top of the legend are drawn over layers listed lower down in the legend. The
checkbox in each legend entry can be used to show or hide the layer.
Layers can be grouped in the legend window by adding a layer group and dragging layers into the
group. To do so, move the mouse pointer to the legend window, right click, choose Add group . A
new folder appears. Now drag the layers onto to the folder symbol. It is then possible to toggle the
visibility of all the layers in the group with one click. To bring layers out of a group, move the mouse
pointer to the layer symbol, right click, and choose Make to toplevel item . To give the folder a new
name, choose Rename in the right click menu of the group.
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4 FEATURES AT A GLANCE
The content of the right mouse button context menu depends on whether the loaded legend item you
hold your mouse over is a raster or a vector layer. For GRASS vector layers the toggle editing is
not available. See section 9.7 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
–
Properties
–
Rename
–
Add Group
–
Expand all
–
Collapse all
–
Show file groups
• Right mouse button menu for vector layers
–
Zoom to layer extent
–
Show in overview
–
Remove
–
Open attribute table
–
Toggle editing (not available for GRASS layers)
–
Save as shapefile
–
Save selection as shapefile
–
Properties
–
Make to toplevel item
–
Rename
–
Add Group
–
Expand all
–
Collapse all
–
Show file groups
• Right mouse button menu for layer groups
–
Remove
–
Rename
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4.2 QGIS GUI
–
Add Group
–
Expand all
–
Collapse all
–
Show file groups
If several vector data sources have the same vector type and the same attributes, their symbolisations
may be grouped. This means that if the symbolisation of one data source is changed, the others
automatically have the new symbolisation as well. To group symbologies, open the right click menu
in the legend window and choose Show file groups . The file groups of the layers appear. It is
now possible to drag a file from one file group into another one. If this is done, the symbologies are
grouped. Note that QGIS only permits the drag if the two layers are able to share symbology (same
vector geometry type and same attributes).
4.2.4 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 4 Z OOMING
THE
M AP
WITH THE
M OUSE W HEEL
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.
Tip 5 PANNING
THE
M AP
WITH THE
A RROW K EYS
AND
S PACE B AR
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.
4.2.5 Map Overview
The map overview area provides a full extent view of layers added to it. 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
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4 FEATURES AT A GLANCE
overview have been set up for labeling. You can add a single layer to the overview by right-clicking
on it in the legend and select x Show in overview . You can also add layers to, or remove all layers
from the overview using the Overview tools on the toolbar.
If you click and drag the red rectangle in the overview that shows your current extent, the main map
view will update accordingly.
4.2.6 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.
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 in 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 4.3 below). At the far right of the status bar is a projector icon.
Clicking on this opens the projection properties for the current project.
Tip 6 C ALCULATING
THE CORRECT
S CALE
OF YOUR
M AP C ANVAS
When you start QGIS, degrees is the default unit, and it tells QGIS that any coordinate in your layer is in
degrees. To get correct scale values, you can either change this to meter manually in the General tab
under Settings > Project Properties or you can select a project Coordinate Reference System (CRS)
projector 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’.
clicking on the
4.3 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
• Panning or zooming
• Resizing the QGIS window
• Changing the visibility of a layer or layers
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4.3 Rendering
QGIS allows you to control the rendering process in a number of ways.
4.3.1 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 x Scale dependent visibility checkbox.
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.
4.3.2 Controlling Map Rendering
Map rendering can be controlled in the following ways:
a) Suspending Rendering
To suspend rendering, click the
x Render checkbox in the lower right corner of the statusbar.
When the x Render box is not checked, QGIS does not redraw the canvas in response to any of
the events described in Section 4.3. 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
canvas.
x Render box enables rendering and causes and immediate refresh of the map
b) 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
x By default new layers added to the map should be displayed checkbox. Any layer added to the
map will be off (invisible) by default.
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4 FEATURES AT A GLANCE
c) 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.
d) Influence Rendering Quality
To influence the rendering quality of the map you have 3 options. Choose menu option Settings >
Options click on the Rendering
tab and select or deselect following checkboxes.
•
x Make lines appear less jagged at the expense of some drawing performance
•
x Fix problems with incorrectly filled polygons
•
x Continuously redraw the map when dragging the legend/map divider
4.4 Measuring
Measuring works within projected coordinate systems only (e.g., UTM). 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 8).
4.4.1 Measure length and areas
QGIS is also 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. The tool then allows you to click points on the map. Each
segment-length shows up in the measure-window and additionally the total length is printed. To stop
measuring click your right mouse button.
Areas can also be measured. The window shows the accumulated area-size in the measure
window
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4.5 Projects
Figure 3: Measure tools in action
(a) Measure lines
(b) Measure areas
4.5 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
4.7). QGIS can save the state of your workspace into a project file using the menu options File >
Save Project or File >
Save Project As .
Load saved projects into a QGIS session using
Open Recent Project .
>
Open Project
File
>
If you wish to clear your session and start fresh, choose File
>
File
or
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
x Warn when opening a project file saved with an older version of QGIS .
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4 FEATURES AT A GLANCE
4.6 Output
There are several ways to generate output from your QGIS session. We have discussed one already
in Section 4.5: saving as a project file. Here is a sampling of other ways to produce output files:
Save as Image opens a file dialog where you select the name, path and type
• Menu option
of image (PNG or JPG format). From this release, a world file with extension PNGW or JPGW
saved in the same folder georeferences the image.
Print Composer opens a dialog where you can layout and print the current
• Menu option
map canvas (see Section 10).
4.7 GUI Options
Some basic options for QGIS can be selected using the
option Settings >
Options dialog. Select the menu
Options . The tabs where you can optmize your options are:
General Tab
•
x Ask to save project changes when required
•
x Warn when opening a project file saved with an older version of QGIS
•
x Change Selection and backgroud Color
• Change the icon theme (choose between default, classic, gis and nkids)
•
x Capitalise layer names in legend
•
x Display classification attribute names in legend
•
x Hide splash screen at startup
•
x Open attribute table in a dock window
• Define attribute table behavior (choose between show all features, show selected features and
show features in current canvas)
Rendering Tab
•
x By deafult new layers added to the map should be displayed
• Define number of features to draw before updating the display.
•
x Make lines appear less jagged at the expense of some drawing performance
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4.7 GUI Options
•
x Fix problems with incorrectly filled polygons
•
x Continously redraw when dragging the legend/map divider
Map tools Tab
• Define Search Radius as a percentage of the map width
• Define Ellipsoid for distance calculations
• Define Rubberband Color for Measure Tools
• Define Mouse wheel action (Zoom, Zoom and recenter, Zoom to mouse cursor, Nothing)
• Define Zoom factor for wheel mouse
Digitizing Tab
• Define Rubberband Color and line width for Digitizing
• Define default snap mode (to vertex, to segment, to vertex and segment)
• Define default snapping tolerance in layer units
• Define search radius for vertex edits in layer units
• Define vertex marker style (Cross or semi transparent circle)
CRS Tab
•
x Prompt for Coordinate Reference System (CRS)
•
x Project wide default Coordinate Reference System (CRS) will be used
•
x Global default Coordinate Reference System (CRS) displayed below will be used
• Select global default Coordinate Reference System (CRS)
Locale Tab
•
x Overwrite system locale and use defined locale instead
• Information about active system locale
Proxy Tab
•
x Use proxy for web access and define host, port, user, and password.
• Set the Proxy type according to your needs
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4 FEATURES AT A GLANCE
–
Default Proxy : Proxy is determined based on the application proxy set using
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
–
Excluding some URLs can be added to the textbox below the proxy-settings (see fig. 4) 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
unterlaying
QT-library-documentation
at
http://doc.trolltech.com/4.5/qnetworkproxy.html#ProxyType-enum.
Figure 4: Proxy-settings in QGIS
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
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4.8 Spatial Bookmarks
Tip 7 U SING P ROXIES
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 find your settings in: $HOME/Library/Preferences/org.qgis.qgis.plist
settings are stored in the registry under:
\\HKEY\CURRENT\USER\Software\QuantumGIS\qgis
4.8 Spatial Bookmarks
Spatial Bookmarks allow you to “bookmark” a geographic location and return to it later.
4.8.1 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. Click OK
to add the bookmark or Cancel
to exit without adding the bookmark.
Note that you can have multiple bookmarks with the same name.
4.8.2 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.
4.8.3 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.
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4 FEATURES AT A GLANCE
4.8.4 Deleting a Bookmark
To delete a bookmark from the
Geospatial Bookmarks dialog, click on it then click Delete .
Confirm your choice by clicking Yes
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5 Working with Vector Data
QGIS supports vector data in a number of formats, including those supported by the OGR library
data provider plugin, such as ESRI shapefiles, MapInfo MIF (interchange format) and MapInfo TAB
(native format). You find a list of OGR supported vector formats in Appendix A.1.
QGIS also supports PostGIS layers in a PostgreSQL database using the PostgreSQL data provider
plugin. Support for additional data types (eg. delimited text) is provided by additional data provider
plugins.
This section describes how to work with several common formats: ESRI shapefiles, PostGIS layers,
and SpatialLite 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.
Working with GRASS vector data is described in Section 9.
5.1 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:
• .shp file containing the feature geometries.
• .dbf file containing the attributes in dBase format.
• .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. .
5.1.1 Loading a Shapefile
To load a shapefile, start QGIS and click on the
Add a vector layer toolbar button or
simply type V . This will bring up a new window (see Figure5).
From the available options check ⊙ File. Click on Browse . That will bring up a standard open
file dialog (see Figure 6) which allows you to navigate the file system and load a shapefile or other
supported data source. The selection box Files of type . . . H
allows you to preselect some OGR
supported file formats.
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5 WORKING WITH VECTOR DATA
Figure 5: Add Vector Layer Dialog
You can also select the Encoding type for the shapefile if desired.
Selecting a shapefile from the list and clicking Open
loading the alaska.shp file.
loads it into QGIS. Figure 7 shows QGIS after
Tip 8 L AYER C OLORS
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
symbology 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 5.4.2 for more information on setting symbology of vector layers.
5.1.2 Improving Performance
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.
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5.1 ESRI Shapefiles
Figure 6: Open an OGR Supported Vector Layer Dialog
• In the tab General
click the Create Spatial Index
button.
5.1.3 Loading a MapInfo Layer
To load a MapInfo layer, click on the
, change
Add a vector layer toolbar bar button or type V the file type filter to Files of Type [OGR] MapInfo (*.mif *.tab *.MIF *.TAB) H
and select the layer
you want to load.
5.1.4 Loading an ArcInfo Binary Coverage
To load an ArcInfo binary coverage click on the
or type V to open the
Add Vector Layer
dialog.
Add a vector layer
Select ⊙ Directory.
toolbar button
Change to
Type Arc/Ingo Binary Coverage H . Navigate to the directory that contains the coverage files and
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5 WORKING WITH VECTOR DATA
Figure 7: QGIS with Shapefile of Alaska loaded
select it.
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.
5.2 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.
To use PostGIS layers you must:
• Create a stored connection in QGIS to the PostgreSQL database (if one is not already defined).
• Connect to the database.
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5.2 PostGIS Layers
• Select the layer to add to the map.
• Optionally provide a SQL where clause to define which features to load from the layer.
• Load the layer.
5.2.1 Creating a stored Connection
The first time you use a PostGIS data source, you must create a connection to the PostgreSQL
database that contains the data. Begin by clicking on the
Add a PostGIS Layer toolbar button,
Add a PostGIS Layer... option from the Layer menu or typing D . You can also
open the open the Add Vector Layer dialog and select ⊙ Database. The Add PostGIS Table(s)
selecting the
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 shown
in table 1.
Table 1: PostGIS Connection Parameters
Name
Host
Database
Port
Username
Password
SSL mode
A name for this connection. Can be the same as Database.
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.
Name of the database.
Port number the PostgreSQL database server listens on. The default port
is 5432.
User name used to login to the database.
Password used with Username to connect to the database.
How the SSL connection will be negotiated with the server. These are the
options:
• 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.
Note that massive speedups in PostGIS layer rendering can be achieved by
disabling SSL in the connection editor.
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5 WORKING WITH VECTOR DATA
Optional you can activate follwing checkboxes:
•
x Save Password
•
x Only look in the geometry_columns table
•
x Only look in the ’public’ schema
Once all parameters and options are set, you can test the connection by clicking on the
Test Connect button.
Tip 9 QGIS U SER S ETTINGS
AND
S ECURITY
Your customized settings for QGIS are stored based on the operating system.
, the settings are stored in
your home directory in .qt/qgisrc.
, the settings are stored in the registry. Depending on your
computing environment, storing passwords in your QGIS settings may be a security risk.
5.2.2 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 5.2.4 for a discussion on
importing data into the database.
To load a layer from PostGIS, perform the following steps:
• If the
Add PostGIS Table(s)
dialog is not already open,
click on the
Add a PostGIS Layer toolbar button.
• Choose the connection from the drop-down list and click Connect .
• Find the layer 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 5.6 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.
5.2.3 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
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5.2 PostGIS Layers
Tip 10 P OST GIS L AYERS
Normally a PostGIS layer is defined by an entry in the geometry_columns table. From version 1.0.0 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.
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).
If the PostgreSQL layer is a view, the same requirement exists, but views don’t 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).
When dealing with views, QGIS parses the view definition and
5.2.4 Importing Data into PostgreSQL
shp2pgsql
Data can be imported into PostgreSQL using a number of methods. 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 8 for more information on spatial reference
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5 WORKING WITH VECTOR DATA
systems and projections.
Tip 11 E XPORTING
DATASETS FROM
P OST GIS
Like the import-tool shp2pgsql there is also a tool to export PostGIS-datasets as shapefiles: pgsql2shp. This
is shipped within your PostGIS distribution.
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 x SPIT plugin and click OK . The
SPIT icon will be added to the plugin toolbar.
To import a shapefile,
click on the
SPIT tool in the toolbar to open the
SPIT - Shapefile to PostGIS Import Tool dialog. Select the PostGIS database you want to con-
nect to and click on Connect . 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 12 I MPORTING S HAPEFILES C ONTAINING P OSTGRE SQL R ESERVED W ORDS
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.
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 myhost.de.
Note that OGR must be built with PostgreSQL to support PostGIS. You can see this by typing
ogrinfo --formats | grep -i post
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5.2 PostGIS Layers
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
and
):
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 5.2.5).
5.2.5 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 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.
The syntax for creating a GiST3 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 [6] for more information.
The following is an example of creating a GiST index:
[email protected]:~/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;
3
GiST index information is taken from the PostGIS documentation available at http://postgis.refractions.net
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5 WORKING WITH VECTOR DATA
VACUUM
gis_data=# \q
[email protected]:~/current$
5.3 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 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.
5.4 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 - either by hand editing the SQL on
the General tab or 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.
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5.4 The Vector Properties Dialog
Figure 8: Vector Layer Properties Dialog
5.4.1 General Tab
The General tab is essentially like that of the raster dialog. It allows you to change the display
name, set scale dependent rendering options, create a spatial index of the vector file (only for OGR
supported formats and PostGIS) and view or change the projection of the specific vetor layer.
The Query Builder button allows you to create a subset of the features in the layer - but this button currently only is available when you open the attribute table and select the ... button next to
Advanced search.
5.4.2 Symbology Tab
QGIS supports a number of symbology renderers to control how vector features are displayed. Currently the following renderers are available:
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
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5 WORKING WITH VECTOR DATA
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.
Figure 9: Symbolizing-options
(a) Single symbol
(b) Graduated symbol
(c) Continous color
(d) Unique value
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 mapfeatures.
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5.4 The Vector Properties Dialog
At least the following styling options apply for nearly all renderers:
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
Fill color - fill-color of your features.
Fill style - Style for filling. Beside the given brushes you can select Fill style ? texture H
and click
the . . . button for selecting your own fill-style. Currently the fileformats *.jpeg, *.xpm, and
*.png are supported.
Once you have styled your layer you also could save your layer-style to a separate file (with *.qmlending). 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 Styel button to revert to your default style.
Vector transparency
QGIS 1.1.0 allows to set a transparency for every vector layer. This can be done with the slider
Transparency 0% ▽
inside the symbology tab (see fig. 8). This is very useful for
overlaying several vector layers.
5.4.3 Metadata Tab
The Metadata tab contains information about the layer, including specifics about the type and
location, number of features, feature type, and the editing capabilities. The Layer Spatial Reference
System section, providing projection information, and the Attribute field info section, listing fields and
their data types, are displayed on this tab. This is a quick way to get information about the layer.
5.4.4 Labels Tab
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 labelling the lakes shapefile of the qgis_example_dataset:
1. Load the Shapefile alaska.shp and GML file lakes.gml in QGIS.
2. Zoom in a bit to your favorite area with some lake.
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5 WORKING WITH VECTOR DATA
3. Make the lakes layer active.
4. Open the Layer Properties dialog.
tab.
5. Click on the Labels
6. Check the x Display labels checkbox to enable labeling.
7. Choose the field to label with. We’ll use Field containing label NAMES H .
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 have labels extending over several lines, check x 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).
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. Click on the Font
entry.
2. Change the placement by selecting one of the radio buttons in the Placement group. To fix our
labels, choose the ⊙ Right radio button.
3. the Font size units allows you to select between ⊙ Points or ⊙ Map units.
4. 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 Position entry. 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
tab.
2. Click the x Buffer Labels? checkbox to enable buffering.
3. Choose a size for the buffer using the spin box.
4. 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.
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5. 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 remaining 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
parameters for the labels using fields in the layer.
Not that the Label
allow you to set all the
tab provides a preview-box where your selected label is shown.
5.4.5 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.
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. 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. 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]].
The Identify Results dialog box 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
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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:
• 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 provided 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 or an
Attribute Table dialog.
(Recall that these dialogs can be opened by clicking
Identify Features or
Open Table .)
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.
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
or perhaps
). The layer in question has fields for a
and the echo command (so it will only work
species name 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:
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5.4 The Vector Properties Dialog
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.
9. From the drop-down box, select
NAMES H
and click Insert Field .
10. Your action text now looks like this:
firefox http://google.com/search?q=%NAMES
11. Fo 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:
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Figure 10: 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 also invoke actions from the attribute table by selecting a row and right-clicking, then choosing
the action from the popup menu.
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.
5.4.6 Attributes Tab
Within the Attributes
New Column
tab the attributes of the selected dataset can be manipulated. The buttons
and Delete Column
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5.4 The Vector Properties Dialog
moment only columns from PostGIS layers can be edited, because this feature is not yet supported
by the OGR library.
The Toggle editing mode
button toggles this mode.
edit widget
Within the Attributes tab you also find an edit widget and a value column. These two columns
can be used to define values or a range of values that are allowed to be added to the specific attribute
table columns. They are used to produce different edit widgets in the attribute dialog. These widgets
are:
• line edit: an edit field which allows to enter simple text (or restrict to numbers for numeric
attributes).
• unique value: a list of unique attribute values of all pre-existing features is produced and presented in a combo box for selection.
• unique value (editable): a combination of ‘line edit’ and ‘unique value’. The edit field completes
entered values to the unique value, but also allows to enter new values.
• value map: a combobox to select from a set of values specified in the value column the
Attributes tab. The possible values are delimited by a semicolon (e.g. high;medium;low).
It is also possible to prepend a label to each value, which is delimited with an equal sign (e.g.
high=1;medium=2;low=3). The label is shown in the combobox instead of the value.
• classification: if a unique value renderer is selected for the layer, the values used for the classes
are presented for selection in a combobox.
• range (editable): A edit field that allows to restrict numeric values to a given range. That range
is specified by entering minium and maximum value delimited by a semicolon (e.g. 0;360) in
the value column of the Attributes tab.
• range (slider): A slider widget is presented that allows selection of a value in a given range and
precision. The range is specifed by minimum, maximum value and a step width (e.g. 0;360;10)
in the value column of the Attributes tab.
• file name: the line edit widget is accompanied by a push button. When pressed it allows to
select a filename using the standard file dialog.
5.4.7 Diagram Tab
The Diagram tab allows you to add a grahic overlay to a vector layer. To activate this feature, open
the Plugin Manager and select the Diagram Overlay’ plugin. After this, there is a new tab in the vector
Layer Properties dialog where the settings for diagrams may be entered (see figure 11).
The current implementation of diagrams provides support for pie- and barcharts and for linear scaling
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Figure 11: Vector properties dialog with diagram tab
of the diagram size according to a classification attribute. We will demonstrate an example and
overlay the alaska boundary layer a barchart diagramm showing some temperature data from a
climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section 3.2.
1. First click on the
Load Vector 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 Diagram Overlay
and select Bar chart
as Diagram type.
4. In the diagram we want to display the values of the three columns T_F_JAN, T_F_JAN and T_F_MEAN. First select T_F_JAN as Attributes and click Add attribute , then T_F_JUL and finally
T_F_MEAN.
5. For linear scaling of the diagram size we define T_F_JUL as classification attribute.
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6. Now click on find maximum value , choose a size value and unit and click Apply
the diagram in the QGIS main window.
to display
7. You can now adapt the chart size, or change the attribute colors double clicking on the color
values in the attribute field. Figure 12 gives an impression.
8. Finally click Ok .
Figure 12: Diagram from temperature data overlayed on a map
5.5 Editing
QGIS supports basic capabilities for editing vector geometries. Before reading any further you should
note that at this stage editing support is still preliminary. Before performing any edits, always make a
backup of the dataset you are about to edit.
Note - the procedure for editing GRASS layers is different - see Section 9.7 for details.
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5.5.1 Setting the Snapping Tolerance and Search Radius
Before we can edit vertices, it is very important to 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
snap tolerance, QGIS will leave the vertex where you release the mouse button, instead of snapping
it to an existing vertex and/or segment.
1. A general, project wide snapping tolerance can be defined choosing Settings >
Options .
Options .) In the Digitizing tab
(On Mac: go to QGIS > Preferences, on Linux: Edit >
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. In our digitizing project (working with the
Alaska dataset), the units are 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
>
Project Properties. . . .
Snapping options. . .
In the General
(or File )
tab, section Digitize you can click on
to enable and adjust snapping mode and tolerance on a layer basis
(see Figure 13).
Figure 13: Edit snapping options on a layer basis
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5.5 Editing
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
Options . The same place where you define the general, project wide snapping tolerance.
5.5.2 Topological editing
Besides
layer
based
snapping
options
the
General
tab
in
menu
Settings
->
Project Properties. . . also provides some topological functionalities. In the Digitizing option group
you can x Enable topological editing and/or activate x Avoid intersections of new polygons .
Enable topological editing
The option x 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
The second topological option called x Avoid intersections of new polygons avoids 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.
5.5.3 Editing 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.
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Tip 13 DATA I NTEGRITY
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.
Tip 14 M ANIPULATING ATTRIBUTE
DATA
Currently only PostGIS layers are supported for adding or dropping attribute columns within this dialog. In
future versions of QGIS, other datasources will be supported, because this feature was recently implemented
in GDAL/OGR > 1.6.0
All editing sessions start by choosing the
Toggle editing option. This can be found in the con-
text menu after right clicking on the legend entry for that layer. Alternately, you can use the
Toggle editing button from the 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.
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 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 digitising session.
You can perform the following editing functions:
• Add Features:
•
Add Ring
•
Add Island
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Capture Line and
Capture Polygon
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5.5 Editing
Tip 15 S AVE R EGULARLY
Remember to toggle
Toggle editing off regularly. This allows you to save your recent changes, and
also confirms that your data source can accept all your changes.
Tip 16 C ONCURRENT E DITS
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.
•
Split Features
•
Move Features
•
Move Vertex
•
Add Vertex
•
Delete Vertex
•
Delete Selected
•
Cut Features
•
Copy Features
•
Paste Features
Adding Features
Before you start adding features, use the
pan and
zoom-in /
zoom-out tools to
first navigate to the area of interest.
Capture point ,
Capture line or
on the toolbar to put the QGIS cursor into digitizing mode.
Then you can use the
Capture polygon icons
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.
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Tip 17 Z OOM
IN
B EFORE E DITING
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.
Tip 18 V ERTEX M ARKERS
The current version of QGIS supports two kinds of vertex-markers - a semi-transparent circle or a cross. To
Options from the Settings menu and click on the Digitizing tab and
change the marker style, choose
select the appropriate entry.
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 14
shows setting attributes for a fictitious new river in Alaska.
Figure 14: Enter Attribute Values Dialog after digitizing a new vector feature
Move Feature
You can move features using the
Move Feature icon on the toolbar.
Split Feature
You can split features using the
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5.5 Editing
Tip 19 ATTRIBUTE VALUE T YPES
At least for shapefile editing the attribue 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 vica versa. If you need to do
so, you should edit the attributes in a second step within the Attribute table dialog.
Editing Vertices of a Feature
For both PostgreSQL/PostGIS and shapefile-based layers, the vertices of features can be edited.
Vertices can be directly edited, that is, you don’t have to choose which feature to edit before you
can change its geometry. In some cases, several features may share the same vertex and so the
following rules apply when the mouse is pressed down near map features:
• Lines - The nearest line to the mouse position is used as the target feature. Then (for moving
and deleting a vertex) the nearest vertex on that line is the editing target.
• Polygons - If the mouse is inside a polygon, then it is the target feature; otherwise the nearest
polygon is used. Then (for moving and deleting a vertex) the nearest vertex on that polygon is
the editing target.
You will need to set the property Settings >
Options > Digitizing > Search Radius 10
N
H
to a
number greater than zero. Otherwise QGIS will not be able to tell which feature is being edited.
Adding Vertices of a Feature
You can add new vertices to a feature by using the
Add Vertex icon on the toolbar.
Note, it doesn’t make sense to add more vertices to a Point feature!
In this version of QGIS, vertices can only be added to an existing line segment of a line feature. If
you want to extend a line beyond its end, you will need to move the terminating vertex first, then add
a new vertex where the terminus used to be.
Moving Vertices of a Feature
You can move vertices using the
Move Vertex icon on the toolbar.
Deleting Vertices of a Feature
You can delete vertices by using the
Delete Vertex icon on the toolbar.
Note, it doesn’t make sense to delete the vertex of a Point feature! Delete the whole feature instead.
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Similarly, a one-vertex line or a two-vertex polygon is also fairly useless and will lead to unpredictable
results elsewhere in QGIS, so don’t do that.
Warning: A vertex is identified for deletion as soon as you click the mouse near an eligible feature.
To undo, you will need to toggle Editing off and then discard your changes. (Of course this will mean
that other unsaved changes will be lost, too.)
Add Ring
Add Ring icon in the toolbar. This means inside an
existing area it is possible to digitize further polygons, that will occur as a ’whole’, so only the area in
between the boundaries of the outer and inner polygons remain as a ring polygon.
You can create ring polygons using the
Add Island
You can
add island polygons to a selected multipolygon. The new island polygon has to be
digitized outside the selected multipolygon.
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
5. Use the
Select tool to select the feature(s) on the source layer
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6. Click on the
Copy Features tool
7. Make the destination layer active by clicking on it in the legend
Paste Features tool
8. Click on the
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 20 C ONGRUENCY
OF
PASTED F EATURES
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 Features tool. You can select multiple features for deletion. Once you have the selection set, use the
Delete Selected tool to delete the features. There is no undo function, but
remember your layer isn’t really changed until you stop editing and choose to save your changes. So
if you make a mistake, you can always cancel the save.
The
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
paste 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.
delete. We could then use the
Tip 21 F EATURE D ELETION S UPPORT
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.
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Snap Mode
QGIS allows digitized vertices to be snapped to other vertices of the same layer. To set the snapping
tolerance, go to Settings > Options -> Digitizing . (On Mac: go to QGIS > Preferences, on
Linux: Edit >
Options .) Note that the snapping tolerance is in map units or pixels.
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. When you turn editing mode off (or quit
QGIS for that matter), you are then asked if you want to save your changes or 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.
5.5.4 Creating a New Layer
To create a new layer for editing, choose
New Vector Layer from the Layer menu. The
New Vector Layer dialog will be displayed as shown in Figure 15. Choose the type of layer (point,
line or polygon).
Note that QGIS does not yet support creation of 2.5D features (i.e. features with X,Y,Z coordinates) or
measure features. At this time, only shapefiles can be created. In a future version of QGIS, creation
of any OGR or PostgreSQL layer type will be supported.
Creation of GRASS-layers is supported within the GRASS-plugin. Please refer to section 9.6 for
more information on creating GRASS vector layers.
To complete the creation of the new layer, add the desired attributes by clicking on the Add
but-
ton and specifying a name and type for the attribute. Only Type real H , Type integer H , and
Type string H
attributes are supported. 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 5.5.3 above.
5.5.5 Working with the Attribute Table
To open the attribute table for a vector layer, make the layer active by clicking on it in the Map legend
Open Attribute Table from
area. Then use Layer Layer from the main menu and and choose
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5.5 Editing
Figure 15: Creating a New Vector Dialog
Open Attribute Table from the
the menu. It is also possible to rightlick on the layer and choose
dropdown menu. This will open a new window which displays the attributes for every feature in the
layer (figure 16).
Each column can be sorted by clicking on its 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 rown down). For a simple selection 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. For more complex searches use the Advanced
search ... , which will lauch the Search Query Builder described in Section 5.7.
To show selected records only, use the checkbox x Show selected records only . Using the buttons
at the bottom left of the window, selected fields can be removed, moved to the top of the table, or the
selection can
Selected features can also be copied to the clipboard, which can also be
be inverted.
. You can also zoom into the selected features on the map. Toggle editing allows to
done with Ctrl-C edit single values of attributes.
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5 WORKING WITH VECTOR DATA
Figure 16: Attribute Table for Alaska layer
5.6 Query Builder
The Query Builder allows you to define a subset of a table and display it as a layer in QGIS. It can
currently only be used with PostGIS layers. 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 17 shows an example of the query builder populated with data from a PostGIS layer
with attributes stored in PostgreSQL.
The query builder lists the layer’s database fields in the list box on the left. You can get a sample of
the data contained in the highlighted field by clicking on the Sample button. This retrieves the first
25 distinct values for the field from the database. To get a list of all possible values for a field, click
on the All button. To add a selected field or value to the query, double-click on it. You can use the
various buttons to construct the query or you can just type it into the SQL box.
To test a query, click on the Test
button. This will return a count of the number of records that will
be included in the layer. When satisfied with the query, click OK . The SQL for the where clause
will be shown in the SQL column of the layer list.
Tip 22 C HANGING
THE
L AYER D EFINITION
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
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5.7 Select by query
Figure 17: Query Builder
5.7 Select by query
With QGIS it is possible also to select features using a similar query builder interface to that used
in 5.6. In the above section the purpose of the query builder is to only show features meeting the
filter criteria as a ’virtual layer’ / subset. The purpose of the select by query function is to highlight all
features that meet a particular criteria. Select by query can be used with all vector data providers.
To do a ‘select by query’ on a loaded layer, click on the button
Open Table to open the attribute
table of the layer. Then click the Advanced... button at the bottom. This starts the Query Builder
that allows to define a subset of a table and display it as described in Section 5.6.
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6 WORKING WITH RASTER DATA
6 Working with Raster Data
This Section describes how to visualize and set raster layer properties. QGIS supports a number of
different raster formats. Currently tested formats include:
• Arc/Info Binary Grid
• Arc/Info ASCII Grid
• GRASS Raster
• GeoTIFF
• JPEG
• Spatial Data Transfer Standard Grids (with some limitations)
• USGS ASCII DEM
• Erdas Imagine
Because the raster implementation in QGIS is based on the GDAL library, other raster formats
implemented in GDAL are also likely to work - if in doubt try to open a sample and see if
it is supported. You find more details about GDAL supported formats in Appendix A.2 or at
http://www.gdal.org/formats_list.html. If you want to load GRASS raster data, please refer
to Section 9.2.
6.1 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.
6.2 Loading raster data in QGIS
Raster layers are loaded either by clicking on the
View >
Add Raster Layer menu option.
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Load Raster icon or by selecting the
More than one layer can be loaded at the same
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6.3 Raster Properties Dialog
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
•
Zoom to layer extent
•
Zoom to best scale (100%)
•
Show in overview
•
Remove
•
Properties
•
Rename
•
Add Group
•
Expand all
•
Collapse all
•
Show file groups
6.3 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: Figure 18 shows the
Raster Layer Properties dialog. There are several tabs on the dialog:
• Symbology
• Transparency
• Colormap
• General
• Metadata
• Pyramids
• Histogram
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Figure 18: Raster Layers Properties Dialog
6.3.1 Symbology Tab
QGIS can render raster layers in two different ways :
• Single band - one band of the image will be rendered as gray or in pseudocolors.
• 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 x Invert color map checkbox.
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6.3 Raster Properties Dialog
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 Grayscale H , where
grayscale is the default setting. Also available are
• Pseudocolor
• Freak Out
• Colormap
When selecting the entry color map Colormap H , the tab Colormap
becomes available. See
more on that at chapter 6.3.3.
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 images.
Three band color
This selection offers you a wide range of options to modify the appereance 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 23 V IEWING
A
S INGLE B AND
OF A
M ULTIBAND R ASTER
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.
6.3.2 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 reliefmap 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.
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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 in this tab.
As an example we want to set the water of our example rasterfile 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 rasterfile-name in the legend or by
right-clicking and choosing Properties from the popup meun.
3. select the Transparency
4. Click the
tab
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. Therefor
you can use the button
Export to file to save your transparency-list to a file. The button
Import from file loads your transparency-settings and applies them to the current rasterlayer.
6.3.3 Colormap
The Colormap
Symbology
tab is only available, when you have selected a single-band-rendering within the tab
(see chapt. 6.3.1).
Three ways of color interpolation are available:
• Discrete
• Linear
• Exact
The button Add Entry adds a color to the individual color-table. Double-Clicking on the valuecolumn lets you inserting 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.
Alternativly you can click on the button
Load colormap from Band , which tries to load the
table from the band (if it has any).
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The block Generate new color map allows you to create newly categorized colormaps. You only need
to select the number of classes 15
N
H
you need and press the button Classify . Currently only
one Classification mode Equal Interval H
is supported.
6.3.4 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 visability 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 spatial reference system is printed here as a PROJ.4-string. This can be modified by hitting
the Change button.
6.3.5 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. To update
the statistics you need to change to tab Histogram and press the button Refresh on the bottom
right, see ch. 6.3.7.
6.3.6 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 pyramides:
• Average
• Nearest Neighbour
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When checking the checkbox x 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.
6.3.7 Histogram Tab
The Histogram
tab allows you to view the distribution of the bands or colors in your raster. You must
first generate the raster statistics by clicking the Refresh button. You can choose which bands to
display by selecting them in the list box at the bottom left of the tab. Two different chart types are
allowed:
• Bar chart
• Line graph
You can define the number of chart columns to use and decide whether you want to
x Allow approximation or display x out of range values Once you view the histogram, you’ll
notice that the band statistics have been populated on the metadata
tab.
Tip 24 G ATHERING R ASTER S TATISTICS
To gather statistics for a layer, select pseudocolor rendering and click the Apply button. Gathering statistics
for a layer can be time consuming. Please be patient while QGIS examines your data!
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7 Working with OGC Data
QGIS supports WMS and WFS as data sources. The support is native; WFS is implemented as a
plugin.
7.1 What is OGC Data
The Open Geospatial Consortium (OGC), is an international organization with more than 300 commercial, governmental, nonprofit and research organisations 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
(though support of the PostgreSQL / PostGIS data provider, see Section 5.2), WFS and WMS as a
client.
7.2 WMS Client
7.2.1 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 and JPL OnEarth.
WMS servers act upon requests by the client (e.g. QGIS) for a raster map with a given extent, set of
layers, symbolisation 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.
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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 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.
7.2.2 Selecting WMS Servers
The first time you use the WMS feature, there are no servers defined. You can begin by clicking
the
menu.
Add WMS layer button inside the toolbar, or through the Layer >
The dialog
Add WMS Layer...
Add Layer(s) from a Server for adding layers from the WMS server pops up. Fortu-
nately you can add some servers to play with by clicking the Add default servers button. This will
add at least three WMS servers for you to use, including the NASA (JPL) WMS server. To define a
new WMS server in the Server Connections section, select New . Then enter the parameters to
connect to your desired WMS server, as listed in table 2:
Table 2: WMS Connection Parameters
Name
URL
Username
Password
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 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 to access a secured WMS-server. This parameter is optional
Password for a basic authentificated WMS-server. This parameter is optional.
If you need to set up a proxy-server to be able to receive WMS-services from the internet,
Options and
you can add your proxy-server in the options. Choose menu Settings >
click on the Proxy
the
tab.
There you can add your proxy-settings and enable them by setting
x Use proxy for web access .
Make sure that you select the correct proxy-type from the
Proxy type dropdown menu.
Once the new WMS Server connection has been created, it will be preserved for future QGIS ses-
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7.2 WMS Client
sions.
Tip 25 O N WMS S ERVER URL S
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.
7.2.3 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 Plugin dialog.
Your screen should now look a bit like Figure 19, which shows the response provided by the NASA
JPL OnEarth WMS server.
Figure 19: Dialog for adding a WMS server, showing its available layers
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.
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Tip 26 I MAGE E NCODING
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.
Layers
The Layers section lists the layers available from the selected WMS server. You may notice that
some layers are expandible, 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 27 WMS L AYER O RDERING
In this version of QGIS, 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 overlay layers in the opposite order, then you can select
Add WMS layer a second time, choose the same server again, and select the second group of layers that
you want to overlay the first group.
Transparency
In this version of QGIS, the transparency setting is hard-coded to be always on, where available.
Tip 28 WMS L AYER T RANSPARENCY
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.
You may notice that the x changes in the Coordinate Reference System (x available) header as you
select and deselect layers from the Layers section.
To choose a CRS, select Change... and a screen similar to Figure 23 in Section 8.3 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.
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Tip 29 WMS P ROJECTIONS
For best results, make the WMS layer the first layer you add to your project. This allows the project projection
to inherit the CRS you used to render the WMS layer. On-the-fly projection (see Section 8.2) can then be
used to fit any subsequent vector layers to the project projection. In this version of QGIS, if you add a WMS
layer later, and give it a different CRS to the current project projection, unpredictable results can occur.
7.2.4 Server-Search
Within QGIS 1.1.X you can search for WMS-servers. Figure 20 shows the newly created search tab with the Add Layer(s) from a Server -dialog.
Figure 20: Dialog for searching WMS servers after some keywords
As you can see it is possible to enter a search-string in the textfield an hit the Search
button.
After a short while the search result will be populated into the tab below the textfield.
Browse the result list and inspect your searchresults within the table. To visualize the results, select
an table entry, press the Add selected row to WMS-list button and change back to the server
tab.
QGIS automatically has updated your server list and the selected searchresult is already enabled in
the list of saved WMS-servers.
You only need to request the list of layers by clicking the Connect
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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.
7.2.5 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.
7.2.6 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 Metadata tab displays a wealth of information about the WMS server, generally collected from
the Capabilities statement returned from that server.
Many definitions can be gleaned by reading the WMS standards [7], [8], 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.
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– 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 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.
7.2.7 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
Once you’ve completed the
Add WMS layer procedure, there is no ability to change the set-
tings.
A workaround is 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 authentification. You can add the (optional) credentials when you add a
WMS-server. See section 7.2.2 for details.
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Tip 30 ACCESSING
SECURED
OGC- LAYERS
If you need to access secured layers with other secured methods than basic authentification, you could use
InteProxy as a transparent proxy, which does supports several authentification methods. More information
can be found at the InteProxy-manual found on the website http://inteproxy.wald.intevation.org.
7.3 WFS 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. An exception is that editing is not supported at this time. To start
Plugin Manager... , activate the x WFS plugin
the WFS plugin you need to open Plugins >
checkbox and click OK .
Add WFS Layer icon appears next to the WMS icon. Click on it to open the dialog. 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.
A new
7.3.1 Loading a WFS Layer
As an example we use the DM Solutions WFS server and display a layer. The URL is:
http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap?VERSION=1.0.0&SERVICE=
wfs&REQUEST=GetCapabilities
1. Make sure the WFS plugin is loaded; if not, open the Plugin Manager and load it
2. Click on the
Add WFS Layer tool on the plugins toolbar
3. Click on New
4. Enter Name DM Solutions
as the name
5. Enter the URL (see previous page)
6. Click OK
7. Choose Server Connections DM Solutions H
from the drop-down box
8. Click Connect
9. Wait for the list of layers to be populated
10. Click on the Canadian Land
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7.3 WFS Client
11. Click Add
to add the layer to the map
12. Wait patiently for the features to appear
Note that the WFS-plugin also recognizes the proxy-settings you have set in your preferences.
Figure 21: 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.
Remember this plugin works best with UMN MapServer WFS servers. It still could be, that you might
experience random behavior and crashes. You can look forward to improvements in a future version
of the plugin.
This means that only WFS 1.0.0 is supported. At this point there have not been many test against
over WFS versions implemented in other WFS-servers. If you encounter problems with any other
WFS-server, please do not hesitate to contacting the development team. Please refer to Section 14
for further information about the mailinglists.
Tip 31 F INDING WFS S ERVERS
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.
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Tip 32 ACCESSING
SECURE
WFS S ERVERS
Within the dialog Create a new WFS-connection accidentily described QGIS does not support
authenficated WFS-connections yet. Within one of the next releases we expect to also support authenticated
WFS-servers. Meanwhile you could use InteProxy (http://inteproxy.wald.intevation.org) for accessing
authenticated WFS-servers.
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8 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 layers. All these features allow the user to display layers
with different CRS and have them overlay properly.
8.1 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 8.4 for information on managing your custom coordinate reference
systems.
The CRS available in QGIS are based on those defined by EPSG and are largely abstracted from the
spatial_references table in PostGIS version 1.x. The 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 format specific means of specifying the CRS. In the case
of shapefiles, this means a file containing the Well Known Text (WKT) specification of the CRS. The
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.
8.2 Specifying a Projection
QGIS no longer sets the map CRS to the coordinate reference system of the first layer loaded. When
you start a QGIS session with layers that do not have a CRS, you need to control and define the CRS
definition for these layers. This can be done globally or project-wide in the CRS tab under Edit >
Options (Gnome, OSX) or Settings >
Options (KDE, Windows). See Figure 22.
•
x Prompt for CRS
•
x Project wide default CRS will be used
•
x Global default CRS displayed below will be used
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The global default CRS proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs comes predefined
in QGIS but can of course be changed, and the new definition will be saved for subsequent QGIS
sessions.
Figure 22: CRS tab in the QGIS Options Dialog
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 (6.3.4) and vector (5.4.1) properties dialog. If your
layer already has a CRS defined, it will be displayed as shown in Figure 8.
8.3 Define On The Fly (OTF) Projection
QGIS does not have OTF projection enabled by default, and this function is currently only supported
Project Properties dialog, select a
for vector layers. To use OTF projection, you must open the
CRS and activate the x Enable on the fly projection checkbox. There are two ways to open the
dialog:
1. Select
Project Properties from the Edit (Gnome, OSX) or Settings (KDE, Windows)
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8.4 Custom Coordinate Reference System
menu.
projector icon in the lower right-hand corner of the statusbar.
2. Click on the
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 the CRS of the currently loaded layer, and activate the x Enable on the fly projection checkbox. The
projector
icon will show a green hook and all subsequently loaded vector layers will be OTF projected to the
defined CRS.
The Coordinate Reference System tab of the Project Properties dialog contains four important
components as shown in Figure 23 and described below.
1. Enable on the fly projection - 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. 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 use 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. Search - if you know the EPSG identifier or the name for a Coordinate Reference System, you
can use the search feature to find it. Enter the identifier and click on Find .
5. Recently used CRS - if you have certain CRS that you frequently use in your everyday GIS
work, these will be displayed as ’quick access’ buttons at the bottom of the Projection Dialog.
Click on one of these buttons to select the associated CRS.
Tip 33 P ROJECT P ROPERTIES D IALOG
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
dialog from the
tab to view the CRS settings. Opening the
projector icon will automatically bring the Coordinate Reference System
tab to the
front.
8.4 Custom Coordinate Reference System
If QGIS does not provide the coordinate reference system you need, you can define a custom CRS. To
define a CRS, select
Custom CRS from the Edit (Gnome, OSX) or Settings (KDE, Windows)
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Figure 23: Projection Dialog
menu. Custom CRS are stored in your QGIS user database. In addition to your custom CRS, this
database also contains your spatial bookmarks and other custom data.
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
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8.4 Custom Coordinate Reference System
Figure 24: Custom CRS Dialog
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.
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To create a new CRS, click the
New button and enter a descriptive name and the CRS
parameters. After that you can save your CRS by clicking the button
Save .
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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9 GRASS GIS Integration
The GRASS plugin provides access to GRASS GIS [4] 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 9.1:
•
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
9.1 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 >
Manage Plugins , select GRASS and click OK .
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You can now start loading raster and vector layers from an existing GRASS LOCATION (see Section
9.2). Or you create a new GRASS LOCATION with QGIS (see Section 9.3.1) and import some raster
and vector data (see Section 9.4) for further analysis with the GRASS Toolbox (see Section 9.9).
9.2 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 3.2). 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 >
Manage Plugins and selecting GRASS . The GRASS toolbar appears on the toolbar menu.
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 , choose the map name gtopo30 and click OK . The
elevation layer will be visualized.
8. Click on
9. Click on
Add GRASS vector layer , 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 5.4, 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 34 GRASS DATA L OADING
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 9.1.
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9.3 GRASS LOCATION and MAPSET
9.3 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 [2]). In order to analyze vector and raster layers with GRASS modules, you must
import them into a GRASS LOCATION. 4
Figure 25: GRASS data in the alaska LOCATION (adapted from Neteler & Mitasova 2008 [2])
9.3.1 Creating a new GRASS LOCATION
As an an example you find the instructions 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 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 3.2).
4
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
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Figure 26: Creating a new GRASS LOCATION or a new MAPSET in QGIS
1. Start QGIS and make sure the GRASS plugin is loaded
2. Visualize the alaska.shp Shapefile (see Section 5.1.1) from the QGIS alaska dataset 3.2.
3. In the GRASS toolbar, click on the
Open 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 9.3.2)
or to create a new LOCATION altogether. Click on the radio button ⊙ Create new location (see
Figure 26).
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
projector icon in the lower right-hand corner of the status bar (see Section 8.3)).
work with GRASS, this functionality will not be described here.
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9. Click Find
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. 5
14. Check out the summary to make sure it’s correct and click Finish
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.
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 9.4). You can also use the already
existing vector and raster data in the sample GRASS LOCATION alaska included in the QGIS alaska
dataset 3.2 and move on to Section 9.5.
9.3.2 Adding a new MAPSET
A user has only write access to a GRASS MAPSET he created. This means, besides access to his own
MAPSET, each user can also 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 [2], see Section 9.8).
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 26) 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.
5
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 [2]).
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7. Click Next , check out the summary to make sure it’s all correct and click Finish
9.4 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 lakes.gml from the QGIS alaska dataset 3.2.
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 9.9) 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.
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9.5 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 without gaps. An area is identified (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. 6
It is possible to store more ’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.
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 35 L EARNING
THE
GRASS V ECTOR M ODEL
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.
9.6 Creating a new GRASS vector layer
To
create
a
new
GRASS
vector
layer
with
the
GRASS
plugin
click
the
Create new GRASS vector toolbar icon. Enter a name in the text box and you can start digitizing point, line or polygone geometries, following the procedure described in Section 9.7.
6
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.
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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 5.5.4).
Tip 36 C REATING
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 31).
9.7 Digitizing and editing a GRASS vector layer
The digitizing tools for GRASS vector layers are accessed using the
Edit GRASS vector layer
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 28 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 37 D IGITIZING
POLYGONES IN
GRASS
If you want to create a polygone in GRASS, you first digitize the boundary of the polygone, 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 27 you see the GRASS digitizing toolbar icons provided by the GRASS plugin. Table 3
explains the available functionalities.
Figure 27: GRASS Digitizing Toolbar
Category Tab
The Category tab allows you to define the way in which the category values will be assigned to a
new geometry element.
• Mode: what category value shall be applied to new geometry elements.
– Next not used - apply next not yet used category value to geometry element.
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Table 3: GRASS Digitizing Tools
Icon
Tool
Purpose
New Point
Digitize new point
New Line
Digitize new line (finish by selecting new tool)
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)
– 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.
Tip 38 C REATING
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.
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Figure 28: GRASS Digitizing Category Tab
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 29: 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).
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9.7 Digitizing and editing a GRASS vector layer
Figure 30: 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 9.6).
Figure 31: GRASS Digitizing Table Tab
Tip 39 GRASS E DIT P ERMISSIONS
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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9.8 The GRASS region tool
The region definition (setting a spatial working window) in GRASS is important for working with
raster layers. Vector analysis is per default not limited to any defined region definitions. All newlycreated 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 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 9.9.
With the
9.9 The GRASS toolbox
The
Open GRASS Tools 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.
9.9.1 Working with GRASS modules
The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 300) GRASS
modules in command line modus. To offer a more user friendly working environment, about 200
of the available GRASS modules and functionalities are also provided by graphical dialogs. These
dialogs are grouped in thematic blocks, but are searchable as well. You find a complete list of GRASS
modules available in QGIS version 1.1.0 in appendix B. It is also possible to customize the GRASS
Toolbox content. It is described in Section 9.9.3.
As shown in Figure 32, you can look for the appropriate GRASS module using the thematically
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9.9 The GRASS toolbox
Figure 32: GRASS Toolbox and searchable Modules List
(a) Modules Tree
grouped Modules Tree
(b) Searchable Modules List
or the searchable Modules List
tab.
Clicking on a grapical module icon a new tab will be added to the toolbox dialog providing three
new sub-tabs Options , Output and Manual . In Figure 33 you see an example for the GRASS
module v.buffer.
Figure 33: GRASS Toolbox Module Dialogs
(a) Module Options
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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.
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 40 D ISPLAY
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.
9.9.2 Working with the GRASS LOCATION browser
Another useful feature inside the GRASS Toolbox is the GRASS LOCATION browser. In Figure 34 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.
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
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9.9 The GRASS toolbox
Figure 34: GRASS LOCATION browser
•
Delete selected map
•
Set current region to selected map
•
Refresh browser window
Rename selected map and
Delete selected map only work with maps inside your curThe
rently selected MAPSET. All other tools also work with raster and vector layers in another MAPSET.
9.9.3 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:
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9 GRASS GIS INTEGRATION
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE qgisgrassmodule SYSTEM "http://mrcc.com/qgisgrassmodule.dtd">
<qgisgrassmodule label="Vector buffer" module="v.buffer">
<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://wiki.qgis.org/qgiswiki/Adding_New_Tools_to_the_GRASS_Toolbox.
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10 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, 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
(also to Postscript and PDF), exported to image formats or to SVG 7 and you can save the layout as
template and load it again in another session. See a list of tools in table 4:
Table 4: Print Composer Tools
Icon
Purpose
Icon
Purpose
Load from template
Save as template
Export to an image format
Export print composition to SVG
Print or export as PDF or Postscript
Zoom to full extend
Zoom in
Zoom out
Refresh view
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
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
To access the print composer, click on the
Print button in the toolbar or choose File >
Print Composer .
7
Export to SVG supported, but it is not working properly with some recent QT4 versions. You should try and check
individual on your system
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10.1 Using Print Composer
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 convinience. After everything is
rendered and symbolized to your liking you click the
Print Composer icon.
Figure 35: 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 and text. Figure 35 shows the initial view of the print composer
with an activated x Snap to grid modus but before any elements are added. The print composer
provides two tabs:
• The General
tab allows you to set paper size, orientation, the print quality for the output file in
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dpi and to activate snapping to a grid of a defined resolution. Please note, the x Snap to grid
feature only works, if you define a grid resolution > 0. Furthermore you can also activate the
x Print as raster checkbox. This means all elements will be rastered before printing or saving
as Postscript of PDF.
• The Item
tab displays the properties for the selected map element.
Click the
Select/Move item icon to select an element (e.g. legend, scalebar or label) on the canvas.
Then click the Item tab and customize the settings for the selected element.
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.
10.1.1 Adding a current QGIS map canvas to the Print Composer
To add the QGIS map canvas, click on the
Add new map from QGIS map canvas button in
the print composer toolbar and drag a rectangle on the composer canvas with the left mouse button
to add the map. You will see an empty box with a "Map will be printed here" message. To display the
current map, you can choose between three different modes in the map Item tab:
• Preview Rectangle H
is the default setting. It only displays an empty box with a message
"Map will be printed here".
• Preview Cache H
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.
• Preview Render H
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.
You can resize the map later by clicking on the
Select/Move item 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 tab. Resize the map item specifying the
width and height or the scale. Define the map extend using Y and X min/max values or clicking the
set to map canvas extend button. Update the map preview and select, whether to see a preview
from cache or an empty rectangle with a "Map will be printed here" message. Define colors and
outline width for the element frame, set a background color and opacity for the map canvas. And you
can also select or unselect to display an element frame with the x frame checkbox (see Figure 36).
If you change the view on the QGIS map canvas by zooming or panning or changing vector or raster
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Figure 36: Print Composer map item tab content
(a) Width, height and extend dialog
(b) Properties dialog
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 tab (see Figure 36).
To move layers within the map element select the map element, click the
Move item content
icon and move the layers within the map element frame with the left mouse button.
10.1.2 Navigation tools
For map navigation the print composer provides 4 general tools:
•
Zoom in ,
•
Zoom out ,
•
Zoom to full extend and
•
Refresh the view , if you find the view in an inconsistent state.
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10.1.3 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.
Label and images
Add label or
Add image icon, place the element
with the left mouse button on the print composer canvas and position and customize their appearance
in the Item tab.
To add a label or an image, click the
Figure 37: Customize print composer label and images
(a) label item tab
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10 PRINT COMPOSER
Legend and scalebar
Add new legend or
Add new scalebar
icon, place the element with the left mouse button on the print composer canvas and position and
customize their appearance in the Item tab.
To add a map legend or a scalebar, click the
Figure 38: Customize print composer legend and scalebar
(a) legend item tab
(b) scalebar item tab
10.1.4 Raise, lower and align elements
Raise or lower functionalities for elements are inside the
Raise selected items pulldown
menu. Choose an element on the print composer canvas and select the matching functionality to
raise or lower the selected element compared to the other elements (see table 4).
There are several alignment functionalities available within the
Align selected items pulldown
menu (see table 4). 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
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box.
10.1.5 Creating Output
Figure 39 shows the print composer with an example print layout including each type of map element
described in the sections above.
Figure 39: Print Composer with map view, legend, scalebar, and text added
The print composer allows you to create several output formats and it is possible to define the resolution (print quality) and paper size:
• The
Print icon allows to print the layout to a connected printer or as PDF or Postscript
file depending on installed printer drivers.
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10 PRINT COMPOSER
• The
Export as image icon exports the composer canvas in several image formats such
as PNG, BPM, TIF, JPG, . . .
• The
Export as SVG icon saves the print composer canvas as a SVG (Scalable Vector
Graphic). 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.
10.1.6 Saving and loading a print composer layout
With the
Save as template and
Load from template icons you can save the current
state of a print composer session as a *.qpt template and load the template again in another session.
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11 QGIS Plugins
QGIS has been designed with a plugin architecture. This allows new features/functions to be easily
added to the application. Many of the features in QGIS are actually implemented as 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 12.
• 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 Plugin Installer.
More information about external plugins are provided in Section 13.
11.1 Managing Plugins
Managing plugins in general means loading or unloading them using the Plugin Manager. External
plugins first need to be installed using the Plugin Installer.
11.1.1 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 added using the Plugin Installer (see Section
13). Those plugins that are already loaded have a check mark to the left of their name. Figure 40
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 41 C RASHING P LUGINS
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 4.7 for location). Locate the plugins settings and change all the plugin
For example, to prevent the Delimited text plugin from
values to false to prevent them from loading.
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 40: Plugin Manager
11.1.2 Loading an external QGIS Plugin
There are two steps required to integrate external plugins into QGIS:
1. Download an external plugin from a repository using the Plugin Installer (Section 11.1.3).
The new external plugin will be added to the list of available plugins in the Plugin Manager.
2. Load the plugin using the Plugin Manager.
11.1.3 Using the QGIS Python Plugin Installer
In order to download and install an external Python plugin, click the menu
Plugins
>
Fetch Python Plugins... . The Plugin Installer window will appear (figure 41) with the tab
Plugins , containing a list of all locally installed Python plugins, as well as plugins available in
remote repositories. 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 Install plugin button.
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11.1 Managing Plugins
Figure 41: Installing external python plugins
• 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 button 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
its own directory.
•
button. The plugin is installed in
Linux and other unices:
./share/qgis/python/plugins
/home/$USERNAME/.qgis/python/plugins
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•
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
If the installation is successful, a confirmation message will appear telling you to go to Plugins >
Manage Plugins... to load the newly installed plugin.
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
Options
module home page. If you are using a proxy, you may need to configure it under Edit >
(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 usercontributed repositories, including the central QGIS Contributed Repository and other external repositories by clicking the Add 3rd party repositories 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
The Options
tab is where you can configure the settings of the Plugin Installer.
The
x Check for updates on 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
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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.
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 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,
• or Show all plugins, even those marked as experimental.
Tip 42 U SING
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.
11.2 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 (Appendix A.1). 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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12 Using QGIS Core Plugins
QGIS currently contains 19 core plugins that can be loaded using the Plugin Manager. Table 5 lists
each of the core plugins along with a description of their purpose and the toolbar-icon.
Table 5: QGIS Core Plugins
Icon
Plugin
Description
Add Delimited Text Layer
Loads and displays delimited text files containing x,y coordinates
Coordinate Capture
Capture mouse coordinate in different CRS
Copyright Label
Draws a copyright label with information
Diagram Overlay
Place charts (pie or bar) or proportional symbols over vector layers
DXF2Shape Converter
Converts from DXF to SHP file format
fTools
A suite of analysis, geometry, geoprocessing, and research tools
GPS Tools
Tools for loading and importing GPS data
GRASS
Activates the mighty GRASS Toolbox
Georeferencer
Adding projection info to Rasterfiles
Interpolation plugin
Interpolation on base of vertices of a vector layer
MapServer Export Plugin
Export a saved QGIS project file to a MapServer map file
North Arrow
Displays a north arrow overlayed onto the map
OGR Layer Converter
Translate vector layers between OGR suported formats
Oracle Georaster
Access Oracle Spatial GeoRasters
Plugin Installer
Downloads and installs QGIS python plugins
SPIT
Shapefile to PostgreSQL/PostGIS Import Tool
Qucik Print
Quickly print a map with minimal effort
Scalebar
Draws a scale bar
WFS
Load and display WFS layer
Tip 43 P LUGINS S ETTINGS S AVED
TO
P ROJECT
When you save a .qgs project, any changes you have made to NorthArrow, ScaleBar and Copyright plugins
will be saved in the project and restored next time you load the project.
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12.1 Delimited Text Plugin
12.1 Delimited Text Plugin
The Delimited Text plugin allows you to load a delimited text file as a layer in QGIS.
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 3.2):
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 ; 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.
Using the Plugin
To use the plugin you must first enable it as described in Section 11.1.
Click the new toolbar icon
Add Delimited Text Layer to open the Delimited Text dialog as
shown in Figure 42.
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 semi-colon (;). 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). After changing
the delimiter, click Parse .
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Figure 42: Delimited Text Dialog
Once you have parsed the file, choose the X and Y fields from the drop down lists and enter a Layer
name (e.g., elevp ) as shown in Figure 42. To add the layer to the map, click Add Layer . The
delimited text file now behaves as any other map layer in QGIS.
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12.2 Coordinate Capture Plugin
12.2 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 43: Coordinate Cature 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 you can also click on the
projector icon in the lower right-hand corner of the statusbar.
2. Click on the x Enable on the fly projection checkbox and select a projected coordinate system of your choice (see also Section 8).
3. Load the coordinate capture plugin in the Plugin Manager (see Section 11.1.1) and ensure that
the dialog is visible by going to View > Panels and ensuring that x Coordinate Capture
is enabled. The cordinate capture dialog appears as shown in Figure 43.
Click to the select the CRS to use for coordinate display icon and select a
different CRS from the one you selected above.
4. Click on the
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.
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12.3 Decorations Plugins
The Decorations Plugins includes the Copyright Label Plugin, the North Arrow Plugin and the Scale
Bar Plugin. They are used to “decorate” the map by adding cartographic elements.
12.3.1 Copyright Label Plugin
The title of this plugin is a bit misleading - you can add any random text to the map.
Figure 44: Copyright Label Plugin
1. Make sure the plugin is loaded
2. Click on Plugins > Decorations >
button from the Toolbar.
Copyright Label or use the
Copyright Label
3. Enter the text you want to place on the map. You can use HTML as shown in the example
4. Choose the placement of the label from the Placement Bottom Right H
drop-down box
5. Make sure the x Enable Copyright Label checkbox is checked
6. Click OK
In the example above (default) places a copyright symbol followed by the date in the lower right hand
corner of the map canvas.
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12.3 Decorations Plugins
12.3.2 North Arrow Plugin
The North Arrow plugin 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 45: North Arrow Plugin
12.3.3 Scale Bar Plugin
The Scale Bar plugin 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. Click on Plugins > Decorations >
the Toolbar.
Scale Bar or use the
2. Choose the placement from the Placement Bottom Left H
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12 USING QGIS CORE PLUGINS
3. Choose the style from the Scale bar style Tick Down H
list
4. Select the color for the bar Color of bar
5. Set the size of the bar and its label Size of bar 30 degrees
or use the default black color
N
H
6. Make sure the x Enable scale bar checkbox is checked
7. Optionally choose to automatically snap to a round number when the canvas is resized
x Automatically snap to round number on resize
8. Click OK
Figure 46: Scale Bar Plugin
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12.4 Dxf2Shp Converter Plugin
12.4 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:
• 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, polygone, 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.
Figure 47: Dxf2Shape Converter Plugin
Using the Plugin
1. Start QGIS, load the Dxf2Shape plugin in the Plugin Manager (see Section 11.1.1) and click
Dxf2Shape Converter icon which appears in the QGIS toolbar menu. The
Dxf2Shape plugin dialog appears as shown in Figure 47.
on the
2. Enter input DXF file, a name for the output Shapefile and the Shapefile type.
3. Enable the x Export text labels checkbox if you want to create an extra point layer with labels.
4. Click Ok .
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12.5 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 world file, or by transforming the
raster to a new coordinate system. The basic approach to georeferencing a raster is to locate points
on the raster for which you can accurately determine their coordinates. The source of the coordinates
can be:
1. The raster itself, sometimes coordinates are literally ‘written’ on the raster. In this case you can
enter the coordinates manually.
2. Other georeferenced data, this can be either vector or raster data that contain the same objects/features that you have on the raster that you want to georeference. 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 and load the Georeferencer Plugin (see Section 11.1.1) and click on
the
Georeferencer icon which appears in the QGIS toolbar menu. The Georeferencer Plugin
dialog appears as shown in Figure 48.
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)
1. To start georeferencing an unreferenced raster, we must load it using the . . . browse button.
The raster will show up in the main working area of the dialog. Once the raster is loaded, we
can start to enter reference points.
2. Using the
Add Point button, add points to the main working area and enter their coordinates (See Figure 49). For this procedure you have two options:
a) Click on a point in the raster map and enter the X and Y coordinates manually
b) Click on a point in the raster map and choose the button
from map canvas to add
the X and Y coordinates with the help of a georeferenced map already loaded in QGIS.
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
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Figure 48: Georeferencer Plugin Dialog
pan the working area in order to locate a relevant set of GCP points.
The points that are added to the map will be stored in a separate text file ([filename].points) which is
stored 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 also Load GCPs and Save GCPs to different
directories if you like.
Choosing the transformation
After you have added your GCPs to the raster image, you need to select the transformation type
for the georeferencing process. 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.
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Figure 49: Add points to the raster image
Currently, several algorithms are available:
1. Linear
2. Helmert
3. Polynomial 1
4. Polynomial 2
5. Polynomial 3
6. Thin plate spline (TPS)
• 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 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.
Running the transformation
1. When the GCPs have been collected, and the transformation has been chosen, press either
Create to create a new raster or Create and load layer to automatically add the new raster
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to the layer list.
2. A warning message will appear that will inform you that a new raster (in GeoTIFF format) will
be created.
3. After hitting OK, you will also be asked to choose a resampling method. There are three methods available:
a) Nearest neighbour
b) Linear
c) Cubic
Tip 44 C HOOSING
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.
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12.6 Quick Print Plugin
The
Quick Print Plugin makes it possible to export the current map canvas to PDF format
quickly and easily, with minimal effort. The only parameters that need to be specified are a Map Title,
a Map Name, and the Paper Size (See Figure 50). If you require additional control over the map
layout, please use the print composer plugin, described in Section 10.
Figure 50: Quick Print Dialog
Figure 51: Quick Print result as DIN A4 PDF using the alaska sample dataset
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12.7 GPS Plugin
12.7 GPS Plugin
12.7.1 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.
12.7.2 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...
>
x GPS Tools . When this plugin is loaded a button with a small handheld GPS device will show
up in the toolbar. An example GPX file is available in the QGIS sample dataset: /qgis_sample_data/gps/national_monuments.gpx. See Section 3.2 for more information about the sample data.
1. Click on the
2. Browse
GPS Tools icon and open the Load GPX file
tab (see figure ??).
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.
12.7.3 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
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Figure 52: The GPS Tools dialog window
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.
12.7.4 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.
12.7.5 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 53). 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.
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 12.7.7).
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,
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Figure 53: The download tool
for usb enabled GPS units.
On Linux this is something like /dev/ttyS0 or /dev/ttyS1 and on
Windows it’s COM1 or COM2.
When you click OK
the data will be downloaded from the device and appear as a layer in QGIS.
12.7.6 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.
12.7.7 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
tabs.
To define a new device you simply click the New device
button in the download or the upload
button, enter a name, a download com-
mand and an upload command for your device, and click the Update device
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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
GPS device: Garmin serial H )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
http://www.gpsbabel.org
GPSBabel
and
it’s
available
command
line
options
at
Once you have created a new device type it will appear in the device lists for the download and upload
tools.
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12.8 fTools Plugin
12.8 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 11.1). When enabled, the
fTools plugin adds a Tools menu to QGIS, providing functions ranging from Analysis and Research
Tools to Geometry and Geoprocessing Tools, as well as several useful Data Management Tools.
fTools functions
Tables 6 through 10 list the functions available via the fTools plugin, along with a brief description of each function. For further information on an individual fTools function, please click the
fTools Information menu item in the Tools menu.
Table 6: fTools Analysis tools
Icon
Analysis tools available via the fTools plugin
Purpose
Tool
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 neighbour statistics to assess the level of clustering
in a point vector layer.
Mean
nate(s)
coordi-
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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Table 7: fTools Research tools
Icon
Research tools available via the fTools plugin
Purpose
Tool
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 8: fTools Geoprocessing tools
Icon
Tool
Geoprocessing tools available via the fTools plugin
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.
Symetrical
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 indentical input values
are combined to form one single feature.
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Table 9: fTools Geometry tools
Icon
Geometry tools available via the fTools plugin
Purpose
Tool
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
Calculate and output (as polygons) the delaunay triangulation of an input
point vector layer.
Simplify geometry
Generalise lines or polygons with a modified Douglas-Peucker algorithm.
Multipart to singleparts
Convert multipart features to multiple singlepart features. Creates simple
polygons and lines.
Singleparts
multipart
Merge multiple features to a single multipart feature based on a unique
ID field.
to
Polygons to lines
Convert polygons to lines, multipart polygons to multiple singlepart lines.
Extract nodes
Extract nodes from line and polygon layers and output them as points.
Table 10: fTools Data management tools
Icon
Tool
Data management tools available via the fTools plugin
Purpose
Export to projection
Project features to new CRS and export as new shapefile.
Define projection
Specify the CRS for shapefiles whose CRS has not been defined.
Join attributes
Join additional attributes to vector layer attribute table and output results to a new shapefile. Additional attributes can be from a vector
layer or stand-alone dbf table.
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.
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12.9 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 intiuitive graphical user interface for creating interpolated
raster layers (See Figure 54). The plugin requires the following parameters to be specified before
running:
• Input vector layer: Specify the input point vector layer from a list of loaded point layers.
• Interpolation attribute: Select attribute column to be used for interpolation or enable the
x Use Z-Coordinate checkbox to use the layers stored Z values.
• Interpolation
Method:
Select
interpolation
Triangulated Irregular Network (TIN) . . . H
method.
This
can
be
either
or Inverse Distance Weighted (IDW) . . . H .
• 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 54: Interpolation Plugin
Using the plugin
1. Start QGIS and load an point vector layer (e.g., elevp.csv).
2. Load the Interpolation plugin in the Plugin Manager (see Section 11.1.1) and click on the
Interpolation icon which appears in the QGIS toolbar menu. The Interpolation plugin dialog
appears as shown in Figure 54.
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3. Select an input layer (e.g., elevp . . . H ) and column (e.g. ELEV) for interpolation.
4. Select an interpolation method (e.g. Triangular interpolation . . . H ), and specify the number
of rows and columns (e.g. 3663 cols and 1964 rows (this is equivalent to a 1000 meter pixel
resolution)) 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 . . . H
as Color Map in the Symbology
tab. Or
you can define a new color table as described in Section 6.3.
In Figure 55 you see the IDW interpolation result with a 366 cols x 196 rows (10 km) resolution for
the elevp.csv data visualized using the Pseudocolor color table. The processing only takes a few
minutes, and covers the northern part of Alaska.
Figure 55: Interpolation of elevp data using IDW method
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12.10 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.
12.10.1 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 56: 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
3.2.
1. Add the raster layer landcover.tif clicking on the
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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 ??)
4. Save a new project named mapserverproject.qgs using File >
Save Project .
12.10.2 Creating the Map File
The tool msexport to export a QGIS project file to a MapServer map file is installed in your QGIS
binary directory and can be used independently of QGIS. To use it from within QGIS, you need to
enable the MapServer Export Plugin first using the Plugin Manager (see Section 11.1.1).
Figure 57: Export to MapServer Dialog
Map file
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.
Qgis project file
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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.
Map Name
A name for the map. This name is prefixed to all images generated by the mapserver.
Map Width
Width of the output image in pixels.
Map Height
Height of the output image in pixels.
Map Units
Units of measure used for output
Image type
Format for the output image generated by MapServer
Web Template
Full path to the MapServer template file to be used with the map file
Web Header
Full path to the MapServer header file to be used with the map file
Web Footer
Full path to the MapServer footer file to be used with the map file
Only the Map file and QGIS project file inputs 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 57):
1. Start the MapServer dialog (see Figure 57) by clicking the
MapServer Export icon in
the toolbar menu.
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.
7. Choose “png” for the image type.
8. Click OK
efforts.
to generate the new map file qgisproject.map. QGIS displays the success of your
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.
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12.10.3 Testing the Map File
We can now test our work 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 58, all information
except the airport symbols are included.
Figure 58: Test PNG created by shp2img with all MapServer Export layers
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. 8
8
http://openlayers.org/presentations/mappingyourdata/
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12.11 OGR Converter Plugin
The OGR Layer Converter plugin adds the ability to convert vector data from one OGR-supported
vector format to another. The plugin is very simple to run, and only requires a few parameters to be
specified before running:
• Source Format/Datset/Layer: Enter OGR format and path to the vector file to be converted
• Target Format/Datset/Layer: Enter OGR format and path to the vector output file
Figure 59: OGR Layer Converter Plugin
Using the Plugin
1. Start QGIS, load the OGR converter plugin in the Plugin Manager (see Section 11.1.1) and
click on the
OGR Layer Converter icon which appears in the QGIS toolbar menu. The
OGR Layer Converter plugin dialog appears as shown in Figure ??.
2. Select the OGR-supported format (e.g., ESRI Shapefile . . . H ) and the path to the vector
input file (e.g., alaska.shp) in the Source area.
8
Supported formats may vary according to the installed GDAL/OGR package.
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3. Select the OGR-supported format (e.g., GML . . . H ) and define a path and the vector output
filename (e.g., alaska.gml) in the Target area.
4. Click Ok .
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12.12 Oracle GeoRaster Plugin
In Oracle databases, raster data can be stored in SDO_GEORASTER objects available with the
Oracle GeoRaster Plugin 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:
Oracle Spatial extension. In QGIS, the
$ gdal_translate -of georaster input_file.tif geor:scott/[email protected]
This will load the raster into the default GDAL_IMPORT table, as a column named RASTER.
12.12.1 Managing connections
Firstly, the Oracle GeoRaster Plugin must be enabled using the Plugin Manager (see Section 11.1.1).
The first time you load a GeoRaster in QGIS, you must create a connection to the Oracle database
that contains the data. To do this, begin by clicking on the
Select GeoRaster 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 60):
• Name: Enter a name for the database connection.
• 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.
Now, back on the main Oracle Spatial GeoRaster dialog window (See Figure 61), 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.
12.12.2 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
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Figure 60: Create Oracle connection dialog
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/[email protected],gdal_import,raster,geoid=”.
See
http://www.gdal.org/frmt_georaster.html for more information.
12.12.3 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 window 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:
gdaladdo georaster:scott/[email protected],georaster\_table,georaster,georid=6 -r
nearest 2 4 6 8 16 32
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Figure 61: Select Oracle GeoRaster dialog
This is an example using PL/SQL: cd ..
$ 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;
/
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12.13 Other core plugins
12.13 Other core plugins
The remaining core plugins are listed in Table 11, along with references to the chapters in this manual
which cover their usage.
Table 11: Other Core Plugins
Icon
Plugin
Manual Reference
Diagram Overlay
Chapter 5.4.7
GRASS
Chapter 9 and Appendix B
Plugin Installer
Chapter 11.1.3
SPIT
Chapter 5.2.4
WFS
Chapter 7.3
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13 USING EXTERNAL QGIS PYTHON PLUGINS
13 Using external QGIS Python Plugins
External QGIS plugins are written in Python. They are stored in either the ’Official’ or ’User contributed’ QGIS Repostories, or in various other external repositories maintained by individual authors. Table 12 shows a list of curently available ’Official’ plugins, with a short description. Detailed
documentation about the usage, minimum QGIS version, homepage, authors, and other important
information are provided with the external plugins themselves and is not included in this manual. 9 10
You will find an up-to-date list of ’Official’ plugins in the Official QGIS Repository at
http://qgis.osgeo.org/download/plugins.html. This list is also available automatically from the
Fetch Python Plugins... .
Plugins installer via
Table 12: Current moderated external QGIS Plugins
Icon
External plugin
Description
Zoom To Point
Zooms to a coordinate specified in the input dialog. You can specify the zoom level as well to control the view extent.
Plugin Installer
The most recent Python Plugin Installer.
A detailed description of the installation procedure for external python plugins can be found in Section
11.1.2.
Tip 45 A DD
MORE REPOSITORIES
To add the ’User contributed’ repository and/or several external author repositories, open the Plugin Installer
Fetch Python Plugins... ), go to the Repositories tab, and click
( Plugins >
Add 3rd party repositories . 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.
9
Updates of core plugins may be available in this repository as external overlays.
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 11.1.2).
10
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14 Help and Support
14.1 Mailinglists
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.
qgis-users
Your questions will reach a broader audience and answers will benefit others. You can subscribe to
the qgis-users mailing list by visiting the following URL:
http://lists.osgeo.org/mailman/listinfo/qgis-user
qgis-developer
If you are a developer facing problems of a more technical nature, you may want to join the qgisdeveloper mailing list here:
http://lists.osgeo.org/mailman/listinfo/qgis-developer
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
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
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/qgis-community-team
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
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14 HELP AND SUPPORT
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.
14.2 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/content/view/90/91 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.
14.3 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 https://trac.osgeo.org/qgis/. 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.
Feature requests can be submitted as well using the same ticket system as for bugs. Please make
sure to select the type enhancement.
If you have found a bug and fixed it yourself you can submit this patch also. Again, the lovely trac
ticketsystem at https://trac.osgeo.org/qgis/ has this type as well. Select patch from the typemenu. 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.
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14.4 Blog
14.4 Blog
The QGIS-community also runs a weblog (BLOG) at http://blog.qgis.org which has some interesting articles for users and developers as well. You are invited to contribute to the blog after
registering yourself!
14.5 Wiki
Lastly, we maintain a WIKI web site at http://www.qgis.org/wiki where you can find a variety of
useful information relating to QGIS development, release plans, links to download sites, message
translation-hints and so on. Check it out, there are some goodies inside!
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A
SUPPORTED DATA FORMATS
A Supported Data Formats
QGIS uses the GDAL/OGR library to read and write vector and raster data formats. Note that not all
of the format listed below may work in QGIS for various reasons. For example, some require external
commercial libraries or the GDAL 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 or raster into QGIS. Other untested formats can be loaded by selecting *.*.
A.1 OGR Vector Formats
At the date of this document, the following formats are supported by the OGR library [5]. A complete
is also available at http://www.gdal.org/ogr/ogr_formats.html.
• Arc/Info Binary Coverage
• Comma Separated Value (.csv)
• DODS/OPeNDAP
• ESRI Personal GeoDatabase
• ESRI ArcSDE
• ESRI Shapefile
• FMEObjects Gateway
• GeoJSON
• Geoconcept Export
• GeoRSS
• GML
• GMT
• GPX
• GRASS Vector 11
• Informix DataBlade
• INTERLIS
• IHO S-57 (ENC)
• Mapinfo File
• Microstation DGN
• OGDI Vectors
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GRASS support is supplied by the QGIS GRASS data provider plugin
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A.2 GDAL Raster Formats
• ODBC
• Oracle Spatial
• PostgreSQL12
• SDTS
• SQLite
• UK .NTF
• U.S. Census TIGER/Line
• VRT - Virtual Datasource
• X-Plane/Flighgear aeronautical data
A.2 GDAL Raster Formats
At the date of this document, the following formats are supported by the GDAL library [3]. A complete
is also available at http://www.gdal.org/formats_list.html.
• Arc/Info ASCII Grid
• ADRG/ARC Digitilized Raster Graphics
• Arc/Info Binary Grid (.adf)
• Magellan BLX Topo (.blx, .xlb)
• Microsoft Windows Device Independent Bitmap (.bmp)
• BSB Nautical Chart Format (.kap)
• VTP Binary Terrain Format (.bt)
• CEOS (Spot for instance)
• First Generation USGS DOQ (.doq)
• New Labelled USGS DOQ (.doq)
• Military Elevation Data (.dt0, .dt1)
• ERMapper Compressed Wavelets (.ecw)
• ESRI .hdr Labelled
• ENVI .hdr Labelled Raster
• Envisat Image Product (.n1)
• EOSAT FAST Format
• FITS (.fits)
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A
SUPPORTED DATA FORMATS
• Graphics Interchange Format (.gif)
• GMT compatible netCDF
• GRASS Rasters 13
• Golden Software Binary Grid
• TIFF / BigTIFF / GeoTIFF (.tif)
• Hierarchical Data Format Release 4 (HDF4)
• Hierarchical Data Format Release 5 (HDF5)
• ILWIS Raster Map (.mpr,.mpl)
• Intergraph Raster
• Erdas Imagine (.img)
• Atlantis MFF2e
• Japanese DEM (.mem)
• JPEG JFIF (.jpg)
• JPEG2000 (.jp2, .j2k)
• NOAA Polar Orbiter Level 1b Data Set (AVHRR)
• Erdas 7.x .LAN and .GIS
• In Memory Raster
• Vexcel MFF
• Vexcel MFF2
• Atlantis MFF
• Multi-resolution Seamless Image Database MrSID
• NITF
• NetCDF
• OGDI Bridge
• Oracle Spatial Georaster
• OGC Web Coverage Server
• OGC Web Map Server
• PCI .aux Labelled
• PCI Geomatics Database File
• Portable Network Graphics (.png)
• Netpbm (.ppm,.pgm)
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GRASS support is supplied by the QGIS GRASS data provider plugin
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A.2 GDAL Raster Formats
• USGS SDTS DEM (*CATD.DDF)
• SAR CEOS
• USGS ASCII DEM (.dem)
• X11 Pixmap (.xpm)
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B
GRASS TOOLBOX MODULES
B GRASS Toolbox modules
The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 300) GRASS
modules in command line modus. To offer a more user friendly working environment, about 200 of
the available GRASS modules and functionalities are also provided by graphical dialogs.
B.1 GRASS Toolbox data import and export modules
This Section lists all graphical dialogs in the GRASS Toolbox to import and export data into a currently
selected GRASS location and mapset.
Table 13: GRASS Toolbox: Raster and Image data import modules
Raster and Image data import modules in the GRASS Toolbox
Purpose
Convert an ESRI ARC/INFO ascii raster file (GRID) into a (binary) raster
map layer
r.in.ascii
Convert an ASCII raster text file into a (binary) raster map layer
r.in.aster
Georeferencing, rectification, and import of Terra-ASTER imagery and
relative DEM’s using gdalwarp
r.in.gdal
Import GDAL supported raster file into a GRASS binary raster map
layer
r.in.gdal.loc
Import GDAL supported raster file into a GRASS binary raster map
layer and create a fitted location
r.in.gdal.qgis
Import loaded raster into a GRASS binary raster map layer
r.in.gdal.qgis.loc
Import loaded raster file into a GRASS binary raster map layer and
create a fitted location
r.in.gridatb
Imports GRIDATB.FOR map file (TOPMODEL) into GRASS raster map
r.in.mat
Import a binary MAT-File(v4) to a GRASS raster
r.in.poly
Create raster maps from ascii polygon/line data files in the current directory
r.in.srtm
Import SRTM HGT files into GRASS
i.in.spotvgt
Import of SPOT VGT NDVI file into a raster map
Module name
r.in.arc
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B.1 GRASS Toolbox data import and export modules
Table 14: GRASS Toolbox: Raster and Image data export modules
Raster and Image data export modules in the GRASS Toolbox
Module name
Purpose
r.out.gdal.gtiff
Export raster layer to Geo TIFF
r.out.arc
Converts a raster map layer into an ESRI ARCGRID file
r.gridatb
Exports GRASS raster map to GRIDATB.FOR map file (TOPMODEL)
r.out.mat
Exports a GRASS raster to a binary MAT-File
r.out.bin
Exports a GRASS raster to a binary array
r.out.png
Export GRASS raster as non-georeferenced PNG image format
r.out.ppm
Converts a GRASS raster map to a PPM image file at the pixel resolution of the CURRENTLY DEFINED REGION
r.out.ppm3
Converts 3 GRASS raster layers (R,G,B) to a PPM image file at the
pixel resolution of the CURRENTLY DEFINED REGION
r.out.pov
Converts a raster map layer into a height-field file for POVRAY
r.out.tiff
Exports a GRASS raster map to a 8/24bit TIFF image file at the pixel
resolution of the currently defined region
r.out.vrml
Export a raster map to the Virtual Reality Modeling Language (VRML)
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B
GRASS TOOLBOX MODULES
Table 15: GRASS Toolbox: Vector data import modules
Module name
v.in.dxf
v.in.e00
v.in.garmin
v.in.gpsbabel
v.in.mapgen
v.in.ogr
v.in.ogr.qgis
v.in.ogr.loc
v.in.ogr.qgis.loc
v.in.ogr.all
v.in.ogr.all.loc
Vector data import modules in the GRASS Toolbox
Purpose
Import DXF vector layer
Import ESRI E00 file in a vector map
Import vector from gps using gpstrans
Import vector from gps using gpsbabel
Import MapGen or MatLab vectors in GRASS
Import OGR/PostGIS vector layers
Import loaded vector layers into GRASS binary vector map
Import OGR/PostGIS vector layers and create a fitted location
Import loaded vector layers into GRASS binary vector map and create
a fitted location
Import all the OGR/PostGIS vector layers in a given data source
Import all the OGR/PostGIS vector layers in a given data source and
create a fitted location
Table 16: GRASS Toolbox: Vector data export modules
Module name
v.out.ogr
v.out.ogr.gml
v.out.ogr.postgis
v.out.ogr.mapinfo
v.out.ascii
v.out.dxf
Vector data export modules in the GRASS Toolbox
Purpose
Export vector layer to various formats (OGR library)
Export vector layer to GML
Export vector layer to various formats (OGR library)
Mapinfo export of vector layer
Convert a GRASS binary vector map to a GRASS ASCII vector map
converts a GRASS vector map to DXF
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B.2 GRASS Toolbox data type conversion modules
B.2 GRASS Toolbox data type conversion modules
This Section lists all graphical dialogs in the GRASS Toolbox to convert raster to vector or vector to
raster data in a currently selected GRASS location and mapset.
Table 17: GRASS Toolbox: Data type conversion modules
Module name
r.to.vect.point
r.to.vect.line
r.to.vect.area
v.to.rast.constant
v.to.rast.attr
Data type conversion modules in the GRASS Toolbox
Purpose
Convert a raster to vector points
Convert a raster to vector lines
Convert a raster to vector areas
Convert a vector to raster using constant
Convert a vector to raster using attribute values
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B
GRASS TOOLBOX MODULES
B.3 GRASS Toolbox region and projection configuration modules
This Section lists all graphical dialogs in the GRASS Toolbox to manage and change the current
mapset region and to configure your projection.
Table 18: GRASS Toolbox: Region and projection configuration modules
Region and projection configuration modules in the GRASS Toolbox
Module name
Purpose
g.region.save
Save the current region as a named region
g.region.zoom
Shrink the current region until it meets non-NULL data from a given
raster map
g.region.multiple.raster Set the region to match multiple raster maps
g.region.multiple.vector Set the region to match multiple vector maps
g.proj.print
Print projection information of the current location
g.proj.geo
Print projection information from a georeferenced file (raster, vector or
image)
g.proj.ascii.new
Print projection information from a georeferenced ASCII file containing
a WKT projection description
g.proj.proj
Print projection information from a PROJ.4 projection description file
g.proj.ascii.new
Print projection information from a georeferenced ASCII file containing
a WKT projection description and create a new location based on it
g.proj.geo.new
Print projection information from a georeferenced file (raster, vector or
image) and create a new location based on it
g.proj.proj.new
Print projection information from a PROJ.4 projection description file
and create a new location based on it
m.cogo
A simple utility for converting bearing and distance measurements to
coordinates and vice versa. It assumes a cartesian coordinate system
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B.4 GRASS Toolbox raster data modules
B.4 GRASS Toolbox raster data modules
This Section lists all graphical dialogs in the GRASS Toolbox to work with and analyse raster data in
a currently selected GRASS location and mapset.
Table 19: GRASS Toolbox: Develop raster map modules
Module name
r.compress
r.region.region
r.region.raster
r.region.vector
r.region.edge
r.region.alignTo
r.null.val
r.null.to
r.quant
r.resamp.stats
r.resamp.interp
r.resample
r.resamp.rst
r.support
r.support.stats
r.proj
Develop raster map modules in the GRASS Toolbox
Purpose
Compresses and decompresses raster maps
Sets the boundary definitions to current or default region
Sets the boundary definitions from existent raster map
Sets the boundary definitions from existent vector map
Sets the boundary definitions by edge (n-s-e-w)
Sets region to align to a raster map
Transform cells with value in null cells
Transform null cells in value cells
This routine produces the quantization file for a floating-point map
Resamples raster map layers using aggregation
Resamples raster map layers using interpolation
GRASS raster map layer data resampling capability. Before you must
set new resolution
Reinterpolates and computes topographic analysis using regularized
spline with tension and smoothing
Allows creation and/or modification of raster map layer support files
Update raster map statistics
Re-project a raster map from one location to the current location
Table 20: GRASS Toolbox: Raster color management modules
Module name
r.colors.table
r.colors.rules
r.colors.rast
r.blend
r.composite
r.his
Raster color management modules in the GRASS Toolbox
Purpose
Set raster color table from setted tables
Set raster color table from setted rules
Set raster color table from existing raster
Blend color components for two raster maps by given ratio
Blend red, green, raster layers to obtain one color raster
Generates red, green and blue raster map layers combining hue, intensity, and saturation (his) values from user-specified input raster map
layers
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GRASS TOOLBOX MODULES
Table 21: GRASS Toolbox: Spatial raster analysis modules
Spatial raster analysis modules in the GRASS Toolbox
Module name
Purpose
r.buffer
Raster buffer
r.mask
Create a MASK for limiting raster operation
r.mapcalc
Raster map calculator
r.mapcalculator
Simple map algebra
r.neighbors
Raster neighbors analyses
v.neighbors
Count of neighbouring points
r.cross
Create a cross product of the category value from multiple raster map
layers
r.series
Makes each output cell a function of the values assigned to the corresponding cells in the output raster map layers
r.patch
Create a new raster map by combining other raster maps
r.statistics
Category or object oriented statistics
r.cost
Outputs a raster map layer showing the cumulative cost of moving between different geographic locations on an input raster map layer whose
cell category values represent cost
r.drain
Traces a flow through an elevation model on a raster map layer
r.shaded.relief
Create shaded map
r.slope.aspect.slope
Generate slope map from DEM (digital elevation model)
r.slope.aspect.aspect
Generate aspect map from DEM (digital elevation model)
r.param.scale
Extracts terrain parameters from a DEM
r.texture
Generate images with textural features from a raster map (first serie of
indices)
r.texture.bis
Generate images with textural features from a raster map (second serie
of indices)
r.los
Line-of-sigth raster analysis
r.clump
Recategorizes into unique categories contiguous cells
r.grow
Generates a raster map layer with contiguous areas grown by one cell
r.thin
Thin no-zero cells that denote line features
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B.4 GRASS Toolbox raster data modules
Table 22: GRASS Toolbox: Surface management modules
Module name
r.random
r.random.cells
v.kernel
r.contour
r.contour2
r.surf.fractal
r.surf.gauss
r.surf.random
r.bilinear
v.surf.bispline
r.surf.idw
r.surf.idw2
r.surf.contour
v.surf.idw
v.surf.rst
r.fillnulls
Surface management modules in the GRASS Toolbox
Purpose
Creates a random vector point map contained in a raster
Generates random cell values with spatial dependence
Gaussian kernel density
Produces a contours vector map with specified step from a raster map
Produces a contours vector map of specified contours from a raster
map
Creates a fractal surface of a given fractal dimension
GRASS module to produce a raster map layer of gaussian deviates
whose mean and standard deviation can be expressed by the user
Produces a raster map layer of uniform random deviates whose range
can be expressed by the user
Bilinear interpolation utility for raster map layers
Bicubic or bilinear spline interpolation with Tykhonov regularization
Surface interpolation utility for raster map layers
Surface generation program
Surface generation program from rasterized contours
Interpolate attribute values (IDW)
Interpolate attribute values (RST)
Fills no-data areas in raster maps using v.surf.rst splines interpolation
Table 23: GRASS Toolbox: Change raster category values and labels modules
Raster category and label modules in the GRASS Toolbox
Module name
Purpose
r.reclass.area.greater
Reclasses a raster map greater than user specified area size (in
hectares)
r.reclass.area.lesser
Reclasses a raster map less than user specified area size (in hectares)
r.reclass
Reclass a raster using a reclassification rules file
r.recode
Recode raster maps
r.rescale
Rescales the range of category values in a raster map layer
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GRASS TOOLBOX MODULES
Table 24: GRASS Toolbox: Hydrologic modelling modules
Module name
r.carve
r.fill.dir
r.lake.xy
r.lake.seed
r.topidx
r.basins.fill
r.water.outlet
Hydrologic modelling modules in the GRASS Toolbox
Purpose
Takes vector stream data, transforms it to raster, and subtracts depth
from the output DEM
Filters and generates a depressionless elevation map and a flow direction map from a given elevation layer
Fills lake from seed point at given level
Fills lake from seed at given level
Creates a 3D volume map based on 2D elevation and value raster maps
Generates a raster map layer showing watershed subbasins
Watershed basin creation program
Table 25: GRASS Toolbox: Reports and statistic analysis modules
Reports and statistic analysis modules in the GRASS Toolbox
Module name
Purpose
r.category
Prints category values and labels associated with user-specified raster
map layers
r.sum
Sums up the raster cell values
r.report
Reports statistics for raster map layers
r.average
Finds the average of values in a cover map within areas assigned the
same category value in a user-specified base map
r.median
Finds the median of values in a cover map within areas assigned the
same category value in a user-specified base map
r.mode
Finds the mode of values in a cover map within areas assigned the
same category value in a user-specified base map.reproject raster image
r.volume
Calculates the volume of data clumps, and produces a GRASS vector
points map containing the calculated centroids of these clumps
r.surf.area
Surface area estimation for rasters
r.univar
Calculates univariate statistics from the non-null cells of a raster map
r.covar
Outputs a covariance/correlation matrix for user-specified raster map
layer(s)
r.regression.line
Calculates linear regression from two raster maps: y = a + b * x
r.coin
Tabulates the mutual occurrence (coincidence) of categories for two
raster map layers
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B.5 GRASS Toolbox vector data modules
B.5 GRASS Toolbox vector data modules
This Section lists all graphical dialogs in the GRASS Toolbox to work with and analyse vector data in
a currently selected GRASS location and mapset.
Table 26: GRASS Toolbox: Develop vector map modules
Develop vector map modules in the GRASS Toolbox
Module name
Purpose
v.build.all
Rebuild topology of all vectors in the mapset
v.clean.break
Break lines at each intersection of vector map
v.clean.snap
Cleaning topology: snap lines to vertex in threshold
v.clean.rmdangles
Cleaning topology: remove dangles
v.clean.chdangles
Cleaning topology: change the type of boundary dangle to line
v.clean.rmbridge
Remove bridges connecting area and island or 2 islands
v.clean.chbridge
Change the type of bridges connecting area and island or 2 islands
v.clean.rmdupl
Remove duplicate lines (pay attention to categories!)
v.clean.rmdac
Remove duplicate area centroids
v.clean.bpol
Break polygons. Boundaries are broken on each point shared between
2 and more polygons where angles of segments are different
v.clean.prune
Remove vertices in threshold from lines and boundaries
v.clean.rmarea
Remove small areas (removes longest boundary with adjacent area)
v.clean.rmline
Remove all lines or boundaries of zero length
v.clean.rmsa
Remove small angles between lines at nodes
v.type.lb
Convert lines to boundaries
v.type.bl
Convert boundaries to lines
v.type.pc
Convert points to centroids
v.type.cp
Convert centroids to points
v.centroids
Add missing centroids to closed boundaries
v.build.polylines
Build polylines from lines
v.segment
Creates points/segments from input vector lines and positions
v.to.points
Create points along input lines
v.parallel
Create parallel line to input lines
v.dissolve
Dissolves boundaries between adjacent areas
v.drape
Convert 2D vector to 3D vector by sampling of elevation raster
v.transform
Performs an affine transformation on a vector map
v.proj
Allows projection conversion of vector files
v.support
Updates vector map metadata
generalize
Vector based generalization
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GRASS TOOLBOX MODULES
Table 27: GRASS Toolbox: Database connection modules
Database connection modules in the GRASS Toolbox
Module name
Purpose
v.db.connect
Connect a vector to database
v.db.sconnect
Disconnect a vector from database
v.db.what.connect
Set/Show database connection for a vector
Table 28: GRASS Toolbox: Change vector field modules
Module name
v.category.add
v.category.del
v.category.sum
v.reclass.file
v.reclass.attr
Change vector field modules in the GRASS Toolbox
Purpose
Add elements to layer (ALL elements of the selected layer type!)
Delete category values
Add a value to the current category values
Reclass category values using a rules file
Reclass category values using a column attribute (integer positive)
Table 29: GRASS Toolbox: Working with vector points modules
Module name
v.in.region
v.mkgrid.region
v.in.db
v.random
v.kcv
v.outlier
v.hull
v.delaunay.line
v.delaunay.area
v.voronoi.line
v.voronoi.area
Working with vector points modules in the GRASS Toolbox
Purpose
Create new vector area map with current region extent
Create grid in current region
Import vector points from a database table containing coordinates
Randomly generate a 2D/3D GRASS vector point map
Randomly partition points into test/train sets
Romove outliers from vector point data
Create a convex hull
Delaunay triangulation (lines)
Delaunay triangulation (areas)
Voronoi diagram (lines)
Voronoi diagram (areas)
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B.5 GRASS Toolbox vector data modules
Table 30: GRASS Toolbox: Spatial vector and network analysis modules
Spatial vector and network analysis modules in the GRASS Toolbox
Module name
Purpose
v.extract.where
Select features by attributes
v.extract.list
Extract selected features
v.select.overlap
Select features overlapped by features in another map
v.buffer
Vector buffer
v.distance
Find the nearest element in vector ’to’ for elements in vector ’from’.
v.net.nodes
Create nodes on network
v.net.alloc
Allocate network
v.net.iso
Cut network by cost isolines
v.net.salesman
Connect nodes by shortest route (traveling salesman)
v.net.steiner
Connect selected nodes by shortest tree (Steiner tree)
v.patch
Create a new vector map by combining other vector maps
v.overlay.or
Vector union
v.overlay.and
Vector intersection
v.overlay.not
Vector subtraction
v.overlay.xor
Vector non-intersection
Table 31: GRASS Toolbox: Vector update by other maps modules
Vector update by other maps modules in the GRASS Toolbox
Module name
Purpose
v.rast.stats
Calculates univariate statistics from a GRASS raster map based on
vector objects
v.what.vect
Uploads map for which to edit attribute table
v.what.rast
Uploads raster values at positions of vector points to the table
v.sample
Sample a raster file at site locations
Table 32: GRASS Toolbox: Vector report and statistic modules
Module name
v.to.db
v.report
v.univar
v.normal
Vector report and statistic modules in the GRASS Toolbox
Purpose
Put geometry variables in database
Reports geometry statistics for vectors
Calculates univariate statistics on selected table column for a GRASS
vector map
Tests for normality for points
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B
GRASS TOOLBOX MODULES
B.6 GRASS Toolbox imagery data modules
This Section lists all graphical dialogs in the GRASS Toolbox to work with and analyse imagery data
in a currently selected GRASS location and mapset.
Table 33: GRASS Toolbox: Imagery analysis modules
Module name
i.image.mosaik
i.rgb.his
i.his.rgb
i.landsat.rgb
i.fusion.brovey
i.zc
i.mfilter
i.tasscap4
i.tasscap5
i.tasscap7
i.fft
i.ifft
r.describe
r.bitpattern
r.kappa
i.oif
QGIS 1.1.0 User Guide
Imagery analysis modules in the GRASS Toolbox
Purpose
Mosaic up to 4 images
Red Green Blue (RGB) to Hue Intensity Saturation (HIS) raster map
color transformation function
Hue Intensity Saturation (HIS) to Red Green Blue (RGB) raster map
color transform function
Auto-balancing of colors for LANDSAT images
Brovey transform to merge multispectral and high-res pancromatic
channels
Zero-crossing edge detection raster function for image processing
Tasseled Cap (Kauth Thomas) transformation for LANDSAT-TM 4 data
Tasseled Cap (Kauth Thomas) transformation for LANDSAT-TM 5 data
Tasseled Cap (Kauth Thomas) transformation for LANDSAT-TM 7 data
Fast fourier transform (FFT) for image processing
Inverse fast fourier transform for image processing
Prints terse list of category values found in a raster map layer
Compares bit patterns with a raster map
Calculate error matrix and kappa parameter for accuracy assessment
of classification result
Calculates optimal index factor table for landsat tm bands
166
B.7 GRASS Toolbox database modules
B.7 GRASS Toolbox database modules
This Section lists all graphical dialogs in the GRASS Toolbox to manage, connect and work with
internal and external databases. Working with spatial external databases is enabled via OGR and
not covered by these modules.
Table 34: GRASS Toolbox: Database modules
Database management and analysis modules in the GRASS Toolbox
Module name
Purpose
db.connect
Sets general DB connection mapset
db.connect.schema
Sets general DB connection mapset with a schema
v.db.reconnect.all
Reconnect vector to a new database
db.login
Set user/password for driver/database
db.in.ogr
Imports attribute tables in various formats
v.db.addtable
Create and add a new table to a vector
v.db.addcol
Adds one or more columns to the attribute table connected to a given
vector map
v.db.dropcol
Drops a column from the attribute table connected to a given vector
map
v.db.renamecol
Renames a column in a attribute table connected to a given vector map
v.db.update_const
Allows to assign a new constant value to a column
v.db.update_query
Allows to assign a new constant value to a column only if the result of
a query is TRUE
v.db.update_op
Allows to assign a new value, result of operation on column(s), to a
column in the attribute table connected to a given map
v.db.update_op_query
Allows to assign a new value to a column, result of operation on column(s), only if the result of a query is TRUE
db.execute
Execute any SQL statement
db.select
Prints results of selection from database based on SQL
v.db.select
Prints vector map attributes
v.db.select.where
Prints vector map attributes with SQL
v.db.join
Allows to join a table to a vector map table
v.db.univar
Calculates univariate statistics on selected table column for a GRASS
vector map
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B
GRASS TOOLBOX MODULES
B.8 GRASS Toolbox 3D modules
This Section lists all graphical dialogs in the GRASS Toolbox to work with 3D data. GRASS provides
more modules, but they are currently only available using the GRASS Shell.
Table 35: GRASS Toolbox: 3D Visualization
3D visualization and analysis modules in the GRASS Toolbox
Module name
Purpose
nviz
Open 3D-View in nviz
B.9 GRASS Toolbox help modules
The GRASS GIS Reference Manual offers a complete overview of the available GRASS modules, not
limited to the modules and their often reduced functionalities implemented in the GRASS Toolbox.
Table 36: GRASS Toolbox: Reference Manual
Module name
g.manual
Reference Manual modules in the GRASS Toolbox
Purpose
Display the HTML manual pages of GRASS
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Literature
[1] T. Mitchell. Web mapping illustrated, published by o’reilly, 2005.
[2] M. Neteler and H. Mitasova. Open source gis: A grass gis approach. 3. edition, springer, new
york, 2008.
Web-References
[3] GDAL-Software-Suite. http://www.gdal.org, 2009.
[4] GRASS GIS. http://grass.osgeo.org, 2009.
[5] OGR-Software-Suite. http://www.gdal.org/ogr/, 2009.
[6] PostGIS. http://postgis.refractions.net/, 2009.
[7] Web Map Service (1.1.1) Implementation Specification. http://portal.opengeospatial.org,
2002.
[8] Web Map Service (1.3.0) Implementation Specification. http://portal.opengeospatial.org,
2004.
Index
%%, 43
Geoprocessing tools, 132
GRASS, 85
attribute linkage, 91
attribute storage, 91
category settings, 92
digitizing, 91
digitizing tools, 92, 93
display results, 98
edit permissions, 95
loading data, 86
region, 96
display, 96
editing, 96
snapping tolerance, 94
starting QGIS, 85
symbology settings, 94
table editing, 95
toolbox, 96
Browser, 98
customize, 99
modules, 154
topology, 91
vector data model, 91
actions, 43
defining, 43
examples, 44
using, 44
Allow Editing, 52
Analysis tools, 131
attributes, 46
bookmarks, 27
command line options, 12
coordinate reference system, 72
crashes, 109
CRS, 72
data
sample, 9
Data management tools, 133
data providers, 113
delimited text, 29
documentation, 1
editing, 49
an existing layer, 51
copying features, 56
creating a new layer, 58
cutting features, 56
icons, 52
pasting features, 56
saving changes, 58
snap, 58
working with the attribute table, 58
EPSG, 79
ESRI
shapefiles, 29
identify
WMS, 74
installation, 9
layer
visibility, 17
layers
initial visibility, 21
layout
toolbars, 17
legend, 17
license
exception, 174
GPL, 169
GDAL
supported formats, 151
Geometry tools, 133
main window, 13
176
Index
map
overview, 19
view, 19
MapInfo
MIF files, 29
TAB files, 29
measure, 22
measure:areas, 22
measure:line length, 22
menus, 14
MIF files, 29
OGC
Authentication, 76
coordinate reference system, 72
CRS, 72
introduction, 69
search, 73
WMS
client, 69
OGR, 29
supported formats, 150
pan
arrow keys, 19
plugin
georeferencer, 114
grass toolbox, 114, 145
plugins, 109, 146
coordinate capture, 114
copyright, 114
core, 114
delimited text, 114
diagram, 114, 145
DXF2Shape, 114
ftools, 114
georaster, 114
gps, 114
installing, 110
Interpolation, 114
manager, 109
managing, 109
QGIS 1.1.0 User Guide
MapServer Export, 114
north arrow, 114
OGR converter, 114
Plugin Installer, 114, 145, 146
Python Plugin Installer, 110
quick print, 114
scalebar, 114
spit, 114, 145
types, 109
upgrading, 110
Zoom To Point, 146
plugins settings, 114
PostGIS, 29, 79
Exporting, 36
layers, 32
query builder, 61
spatial index, 37
GiST, 37
SPIT, 36
editing field names, 36
importing data, 35
loading, 36
reserved words, 36
PostgreSQL
connection, 32, 33
testing, 34
connection manager, 33
connection parameters, 33
database, 33
host, 33
layer details, 34
loading layers, 32, 34
password, 33
port, 33
PostGIS, 29
query builder, 61
sslmode, 33
username, 33
Print composer
tools, 101
Projections
coordinate reference system, 72
177
Index
CRS, 72
custom, 81
enabling, 81
specifying, 79
SRS, 72
WMS, 72
working with, 79
projects, 23
WMS, 69
rendering, 20
options, 21
quality, 22
scale dependent, 21
suspending, 21
update during drawing, 22
Research tools, 132
Query Builder, 60
adding fields, 60
changing layer definitions, 60
generating sample list, 60
getting all values, 60
testing queries, 60
query builder
PostGIS, 61
PostgreSQL, 61
scale, 21
calculate, 20
security, 34
settings, 34
shapefile
format, 29
loading, 29
specification, 29
shapefiles, 29
SHP files, 29
spatial bookmarks,
seebookmarks27
spatial index
shapefiles, 30
SpatiaLite
layers, 38
SpatiaLite layers
properties dialog, 38
SRS, 72
symbology
changing, 40
raster layer
classify, 67
raster layers, 62
context menu, 63
data formats, 62
definition, 62
GDAL implementation, 62
georeferenced, 62
histogram, 68
loading, 63
metadata, 67
metadata), 68
properties, 67
pyramids, 67
resolution pyramids, 67
standard deviation, 65
statistics, 68
supported channels, 64
supported formats, 151
transparency, 65
rasters
metadata, 74
properties, 74
QGIS 1.1.0 User Guide
TAB files, 29
Toggle Editing, 52
toolbars, 17
vector layers, 29–61
add
island, 56
ring, 56
adding
feature, 53
vertex, 55
ArcInfo Binary Coverage, 31
178
Index
copy
feature, 56
cut
feature, 56
deleting
feature, 57
vertex, 55
diagram, 47
editing, 51
vertex, 55
ESRI shapefiles, 29
MapInfo, 31
move
feature, 54
moving
vertex, 55
paste
feature, 56
PostGIS, see PostGIS
properties dialog, 38
renderers
continuous color, 40
graduated symbol, 40
single symbol, 39
unique value, 40
SpatlaLIte, see SpatiaLite
split
feature, 54
styles, 40
symbology, 39
transparency, 41
connection parameters, 70
layers, 71
limits, 75
coordinate reference system, 72
CRS, 72
GetFeatureInfo, 74
identify, 74
image encoding, 72
layer settings
editing, 75
layer transparency, 72
metadata, 74
properties, 74
remote server
authentication, 75
basic authentification, 75
layer ordering, 72
selection, 70
URL, 71
search, 73
secured layers, 76
serversearch, 73
URL, 70
zoom
mouse wheel, 19
WFS
authenticate remote server, 78
remote server, 77
secured WFS server, 78
WKT, 79
WMS
authentification, 70
capabilites, 74
client, 69
about, 69
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