QGIS User Guide

QGIS User Guide

QGIS User Guide

Release 1.8.0

QGIS Project

March 20, 2013

Contents

1 Preamble

2 Conventions

3 Foreword

5

3.1

Introduction To GIS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

4 Features

9

4.1

View data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

4.2

Explore data and compose maps

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

4.3

Create, edit, manage and export data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

4.4

Analyse data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

4.5

Publish maps on the Internet

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

4.6

Extend QGIS functionality through plugins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

4.7

What’s new in the version 1.8

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

1

3

5 Getting Started

15

5.1

Installation

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

5.2

Sample Data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

5.3

Sample Session

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16

5.4

Starting and Stopping QGIS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

5.5

Command Line Options

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

5.6

Projects

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19

5.7

Output

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19

6 QGIS GUI

21

6.1

Menu Bar

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

6.2

Toolbar

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27

6.3

Map Legend

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

27

6.4

Map View

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29

6.5

Status Bar

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

30

7 General Tools

33

7.1

Keyboard shortcuts

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33

7.2

Context help

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33

7.3

Rendering

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

34

7.4

Measuring

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35

7.5

Decorations

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

36

i

7.6

Annotation Tools

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

38

7.7

Spatial Bookmarks

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

39

7.8

Nesting Projects

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

40

8 QGIS Configuration

41

8.1

Panels and Toolbars

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

41

8.2

Project Properties

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

42

8.3

Options

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

42

8.4

Customization

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46

9 Working with Projections

49

9.1

Overview of Projection Support

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

9.2

Specifying a Projection

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

9.3

Define On The Fly (OTF) Reprojection

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

50

9.4

Custom Coordinate Reference System

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

52

10 QGIS Browser

53

11 Working with Vector Data

55

11.1 Supported Data Formats

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55

11.2 The Vector Properties Dialog

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

63

11.3 Editing

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

82

11.4 Query Builder

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

94

11.5 Field Calculator

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

95

12 Working with Raster Data

99

12.1 Working with Raster Data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

99

12.2 Raster Properties Dialog

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.3 Raster Calculator

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

13 Working with OGC Data

107

13.1 Working with OGC Data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

13.2 QGIS Server

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

14 Working with GPS Data

117

14.1 GPS Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

14.2 Live GPS tracking

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

15 GRASS GIS Integration

123

15.1 Starting the GRASS plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

15.2 Loading GRASS raster and vector layers

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

15.3 GRASS LOCATION and MAPSET

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

15.4 Importing data into a GRASS LOCATION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

15.5 The GRASS vector data model

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

15.6 Creating a new GRASS vector layer

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

15.7 Digitizing and editing a GRASS vector layer

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

15.8 The GRASS region tool

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

15.9 The GRASS toolbox

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

16 OpenStreetMap

141

16.1 The OpenStreetMap project

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

16.2 QGIS - OSM Connection

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

16.3 Installation

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

16.4 Basic user interface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

16.5 Loading OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

16.6 Viewing OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

16.7 Editing basic OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

16.8 Editing relations

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

16.9 Downloading OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

16.10 Uploading OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

ii

16.11 Saving OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

16.12 Import OSM data

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

17 Print Composer

153

17.1 Open a new Print Composer Template

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

17.2 Using Print Composer

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

17.3 Adding a current QGIS map canvas to the Print Composer

. . . . . . . . . . . . . . . . . . . . . 155

17.4 Adding other elements to the Print Composer

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

17.5 Navigation tools

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

17.6 Revert and Restore tools

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

17.7 Add Basic shape and Arrow

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

17.8 Add attribute table values

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

17.9 Raise, lower and align elements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.10 Creating Output

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.11 Saving and loading a print composer layout

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

18 Plugins

167

18.1 QGIS Plugins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

18.2 Using QGIS Core Plugins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

18.3 Coordinate Capture Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

18.4 DB Manager Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

18.5 Delimited Text Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

18.6 Diagram Overlay Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

18.7 Dxf2Shp Converter Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

18.8 eVis Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

18.9 fTools Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

18.10 GDAL Tools Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

18.11 Georeferencer Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.12 Interpolation Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

18.13 MapServer Export Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

18.14 Offline Editing Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

18.15 Oracle GeoRaster Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

18.16 Raster Terrain Analysis Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

18.17 Heatmap Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

18.18 Road Graph Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

18.19 Spatial Query Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

18.20 SPIT Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

18.21 SQL Anywhere Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

18.22 Zonal Statistics Plugin

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

19 Help and Support

213

19.1 Mailing lists

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

19.2 IRC

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

19.3 BugTracker

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

19.4 Blog

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

19.5 Plugins

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

19.6 Wiki

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

20 Appendix

217

20.1 GNU General Public License

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

20.2 GNU Free Documentation License

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

21 Literature and Web References

Index

227

229

iii

iv

CHAPTER

1

Preamble

This document is the original user guide of the described software Quantum GIS. The software and hardware described in this document are in most cases registered trademarks and are therefore subject to the legal requirements. Quantum GIS is subject to the GNU General Public License. Find more information on the Quantum GIS

Homepage http://www.qgis.org

.

The details, data, results etc. in this document have been written and verified to the best of knowledge and responsibility of the authors and editors. Nevertheless, mistakes concerning the content are possible.

Therefore, all data are not liable to any duties or guarantees. The authors, editors and publishers do not take any responsibility or liability for failures and their consequences. Your are always welcome to indicate possible mistakes.

This document has been typeset with reStructuredText. It is available as reST source code via github and online as HTML and PDF via http://documentation.qgis.org

. Translated versions of this document can be downloaded in several formats via the documentation area of the QGIS project as well. For more information about contributing to this document and about translating it, please visit: http://www.qgis.org/wiki/ .

Links in this Document

This document contains internal and external links. Clicking on an internal link moves within the document, while clicking on an external link opens an internet address. In PDF form, internal and external links are shown in blue and are handled by the system browser. In HTML form, the browser displays and handles both identically.

User, Installation and Coding Guide Authors and Editors:

Tara Athan

Peter Ersts

Radim Blazek

Anne Ghisla

Godofredo Contreras Otto Dassau

Stephan Holl N. Horning

Werner Macho Carson J.Q. Farmer Tyler Mitchell

Claudia A. Engel Brendan Morely David Willis

K. Koy

Jürgen E. Fischer

Larissa Junek

Tim Sutton

Diethard Jansen

Alex Bruy

Paolo Corti

Raymond Nijssen

Martin Dobias

Magnus Homann

Lars Luthman

Marco Hugentobler

Gavin Macaulay Gary E. Sherman

Richard Duivenvoorde Andreas Neumann

Sponsors

The update of this user manual was kindly sponsored by Kanton Solothurn , Switzerland.

Copyright (c) 2004 - 2013 QGIS Development Team

Internet: http://www.qgis.org

License of this document

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant

Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in Appendix

GNU

Free Documentation License

.

1

QGIS User Guide, Release 1.8.0

2 Chapter 1. Preamble

CHAPTER

2

Conventions

This section describes a collection of uniform styles throughout the manual. The conventions used in this manual are as follows:

GUI Conventions

The GUI convention styles are intended to mimic the appearance of the GUI. In general, the objective is to use the non-hover appearance, so a user can visually scan the GUI to find something that looks like the instruction in the manual.

• Menu Options: Layer → Add a Raster Layer or Settings → Toolbars → Digitizing

• Tool:

Add a Raster Layer

• Button : [Save as Default]

• Dialog Box Title: Layer Properties

• Tab: General

• Checkbox: Render

• Radio Button: Postgis SRID EPSG ID

• Select a Number:

• Select a String:

• Browse for a File:

• Select a Color:

• Slider:

• Input Text:

A shadow indicates a clickable GUI component.

Text or Keyboard Conventions

The manual also includes styles related to text, keyboard commands and coding to indicate different entities, such as classes, or methods. They don’t correspond to any actual appearance.

• Hyperlinks: http://qgis.org

• Keystroke Combinations: press Ctrl+B, meaning press and hold the Ctrl key and then press the B key.

• Name of a File: lakes.shp

• Name of a Class: NewLayer

3

QGIS User Guide, Release 1.8.0

• Method: classFactory

• Server: myhost.de

• User Text: qgis --help

Lines of code are indicated by a fixed-width font

PROJCS["NAD_1927_Albers",

GEOGCS["GCS_North_American_1927",

Platform-specific instructions

GUI sequences and small amounts of text can be formatted inline: Click

QGIS .

File QGIS

→ Quit to close

This indicates that on Linux, Unix and Windows platforms, click the File menu option first, then Quit from the dropdown menu, while on Macintosh OSX platforms, click the QGIS menu option first, then Quit from the dropdown menu. Larger amounts of text may be formatted as a list:

• do this;

• do that;

• do something else.

or as paragraphs.

Do this and this and this. Then do this and this and this and this and this and this and this and this and this.

Do that. Then do that and that and that and that and that and that and that and that and that and that and that and that and that and that and that.

Screenshots that appear throughout the user guide have been created on different platforms; the platform is indicated by the platform-specific icon at the end of the figure caption.

4 Chapter 2. Conventions

CHAPTER

3

Foreword

Welcome to the wonderful world of Geographical Information Systems (GIS)!

Quantum GIS (QGIS) is an Open Source Geographic Information System. The project was born in May of 2002 and was established as a project on SourceForge in June of the same year. We’ve worked hard to make GIS software (which is traditionally expensive proprietary software) a viable prospect for anyone with basic access to a Personal Computer. QGIS currently runs on most Unix platforms, Windows, and OS X. QGIS is developed using the Qt toolkit ( http://qt.digia.com

) and C++. This means that QGIS feels snappy to use and has a pleasing, easy-to-use graphical user interface (GUI).

QGIS aims to be an easy-to-use GIS, providing common functions and features. The initial goal was to provide a

GIS data viewer. QGIS has reached the point in its evolution where it is being used by many for their daily GIS data viewing needs. QGIS supports a number of raster and vector data formats, with new format support easily added using the plugin architecture.

QGIS is released under the GNU General Public License (GPL). Developing QGIS under this license means that you can inspect and modify the source code, and guarantees that you, our happy user, will always have access to a GIS program that is free of cost and can be freely modified. You should have received a full copy of the license with your copy of QGIS, and you also can find it in Appendix

GNU General Public License

.

Tip: Up-to-date Documentation

The latest version of this document can always be found in the documentation area of the QGIS website at http://documentation.qgis.org

3.1 Introduction To GIS

A Geographical Information System (GIS) (Mitchell 2005

Literature and Web References

) is a collection of soft-

ware 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

5

QGIS User Guide, Release 1.8.0

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.

3.1.1 Why is all this so new?

Well, it’s not. There are many new hardware devices that are enabling mobile geospatial services. Many open source geospatial applications are also available, but the existence of geospatially focused hardware and software is nothing new. Global positioning system (GPS) receivers are becoming commonplace, but have been used in various industries for more than a decade. Likewise, desktop mapping and analysis tools have also been a major commercial market, primarily focused on industries such as natural resource management.

What is new is how the latest hardware and software is being applied and who is applying it. Traditional users of mapping and analysis tools were highly trained GIS Analysts or digital mapping technicians trained to use

CAD-like tools. Now, the processing capabilities of home PCs and open source software (OSS) packages have enabled an army of hobbyists, professionals, web developers, etc. to interact with geospatial data. The learning curve has come down. The costs have come down. The amount of geospatial technology saturation has increased.

How is geospatial data stored? In a nutshell, there are two types of geospatial data in widespread use today. This is in addition to traditional tabular data that is also widely used by geospatial applications.

3.1.2 Raster Data

One type of geospatial data is called raster data or simply “a raster”. The most easily recognised form of raster data is digital satellite imagery or air photos. Elevation shading or digital elevation models are also typically represented as raster data. Any type of map feature can be represented as raster data, but there are limitations.

A raster is a regular grid made up of cells, or in the case of imagery, pixels. They have a fixed number of rows and columns. Each cell has a numeric value and has a certain geographic size (e.g. 30x30 meters in size).

Multiple overlapping rasters are used to represent images using more than one colour value (i.e. one raster for each set of red, green and blue values is combined to create a colour image). Satellite imagery also represents data in multiple “bands”. Each band is essentially a separate, spatially overlapping raster, where each band holds values of certain wavelengths of light. As you can imagine, a large raster takes up more file space.

A raster with smaller cells can provide more detail, but takes up more file space. The trick is finding the right balance between cell size for storage purposes and cell size for analytical or mapping purposes.

3.1.3 Vector Data

Vector data is also used in geospatial applications. If you stayed awake during trigonometry and coordinate geometry classes, you will already be familiar with some of the qualities of vector data. In its simplest sense, vectors are a way of describing a location by using a set of coordinates. Each coordinate refers to a geographic location using a system of x and y values.

6 Chapter 3. Foreword

QGIS User Guide, Release 1.8.0

This can be thought of in reference to a Cartesian plane - you know, the diagrams from school that showed an x and y-axis. You might have used them to chart declining retirement savings or increasing compound mortgage interest, but the concepts are essential to geospatial data analysis and mapping.

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 (x

1 a line from Point (x

1 y

1 y

1

, x

) to Point (x

2

2 y y

2

2

, x

3 y

3

, ... x n y n

) strung together in a certain order, like drawing

) 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.

3.1. Introduction To GIS 7

QGIS User Guide, Release 1.8.0

8 Chapter 3. Foreword

CHAPTER

4

Features

QGIS offers many common GIS functionalities provided by core features and plugins. As a short summary they are presented in six categories to gain a first insight.

4.1 View data

You can view and overlay vector and raster data in different formats and projections without conversion to an internal or common format. Supported formats include:

• Spatially-enabled tables and views using PostGIS, SpatiaLite and MSSQL Spatial, vector formats supported by the installed OGR library, including ESRI shapefiles, MapInfo, SDTS, GML and many more, see section

Working with Vector Data

.

• Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction Library) library, such as GeoTiff, Erdas Img., ArcInfo Ascii Grid, JPEG, PNG and many more, see section

Working with

Raster Data

.

• GRASS raster and vector data from GRASS databases (location/mapset), see section

GRASS GIS Integration

.

• Online spatial data served as OGC-compliant Web Map Service (WMS) or Web Feature Service (WFS), see section

Working with OGC Data

.

• OpenStreetMap data, see section

OpenStreetMap

.

4.2 Explore data and compose maps

You can compose maps and interactively explore spatial data with a friendly GUI. The many helpful tools available in the GUI include:

• QGIS browser

• On the fly projection

• Map composer

• Overview panel

• Spatial bookmarks

• Identify/select features

• Edit/view/search attributes

• Feature labeling

9

QGIS User Guide, Release 1.8.0

• Change vector and raster symbology

• Add a graticule layer - now via fTools plugin and as decoration

• Decorate your map with a north arrow scale bar and copyright label

• Save and restore projects

4.3 Create, edit, manage and export data

You can create, edit, manage and export vector maps in several formats. Raster data have to be imported into

GRASS to be able to edit and export them into other formats. QGIS offers the following:

• Digitizing tools for OGR supported formats and GRASS vector layer

• Create and edit shapefiles and GRASS vector layers

• Geocode images with the Georeferencer plugin

• GPS tools to import and export GPX format, and convert other GPS formats to GPX or down/upload directly to a GPS unit (on Linux, usb: has been addedto list of GPS devices)

• Visualize and edit OpenStreetMap data

• Create PostGIS layers from shapefiles with the SPIT plugin

• Improved handling of PostGIS tables

• Manage vector attribute tables with the new attribute table (see section

Working with the Attribute Table

) or

Table Manager plugin

• Save screenshots as georeferenced images

4.4 Analyse data

You can perform spatial data analysis on PostgreSQL/PostGIS and other OGR supported formats using the fTools

Python plugin. QGIS currently offers vector analysis, sampling, geoprocessing, geometry and database management tools. You can also use the integrated GRASS tools, which include the complete GRASS functionality of more than 400 modules (See Section

GRASS GIS Integration

). Or you work with SEXTANTE, which provides

powerful a geospatial analysis framework to call native and third party algorithms from QGIS, such as GDAL,

SAGA, GRASS, fTools and more (see section label_sextante).

4.5 Publish maps on the Internet

QGIS can be used to export data to a mapfile and to publish them on the Internet using a webserver with UMN

MapServer installed. QGIS can also be used as a WMS, WMS-C or WFS and WFS-T client, and as WMS or WFS server (see section

Working with OGC Data

).

4.6 Extend QGIS functionality through plugins

QGIS can be adapted to your special needs with the extensible plugin architecture. QGIS provides libraries that can be used to create plugins. You can even create new applications with C++ or Python!

10 Chapter 4. Features

QGIS User Guide, Release 1.8.0

4.6.1 Core Plugins

1. Add Delimited Text Layer (Loads and displays delimited text files containing x,y coordinates)

2. Coordinate Capture (Capture mouse coordinates in different CRS)

3. DB Manager (Exchange, edit and view layers and tables; execute SQL queries)

4. Diagram Overlay (Placing diagrams on vector layer)

5. Dxf2Shp Converter (Convert DXF to Shape)

6. GPS Tools (Loading and importing GPS data)

7. GRASS (GRASS GIS integration)

8. GDALTools (Integrate GDAL Tools into QGIS)

9. Georeferencer GDAL (Adding projection information to raster using GDAL)

10. Heatmap tool (Generating raster heatmaps from point data)

11. Interpolation plugin (interpolate based on vertices of a vector layer)

12. Mapserver Export (Export QGIS project file to a MapServer map file)

13. Offline Editing (Allow offline editing and synchronizing with database)

14. OpenStreetMap plugin (Viewer and editor for openstreetmap data)

15. Oracle Spatial GeoRaster support

16. Plugin Installer (Download and install QGIS python plugins)

17. Raster terrain analysis (Raster based terrain analysis)

18. Road graph plugin (Shortest Path network analysis)

19. SPIT (Import Shapefile to PostgreSQL/PostGIS)

20. SQL Anywhere Plugin (Store vector layers within a SQL Anywhere database)

21. Zonal statictics plugin (Calculate count, sum, mean of raster for each polygon of a vector layer)

22. Spatial Query plugin (Makes spatial queries on vector layers)

23. eVIS (Event Visualization Tool)

24. fTools (Tools for vector data analysis and management)

4.6.2 External Python Plugins

QGIS offers a growing number of external python plugins that are provided by the community. These plugins reside in the official plugins repository, and can be easily installed using the Python Plugin Installer (See Section

Loading an external QGIS Plugin

).

4.7 What’s new in the version 1.8

Please note that this is a release in our ‘cutting edge’ release series. As such it contains new features and extends the programmatic interface over QGIS 1.0.x and QGIS 1.7.0. We recommend that you use this version over previous releases.

This release includes hundreds of bug fixes and many new features and enhancements that will be described in this manual.

QGIS Browser

A stand alone app and a new panel in QGIS. The browser lets you easily navigate your file system and connection based (PostGIS, WFS etc.) datasets, preview them and drag and drop items into the canvas.

4.7. What’s new in the version 1.8

11

QGIS User Guide, Release 1.8.0

DB Manager

The DB manager is now officially part of QGIS core. You can drag layers from the QGIS Browser into DB

Manager and it will import your layer into your spatial database. Drag and drop tables between spatial databases and they will get imported. You can use the DB Manager to execute SQL queries against your spatial database and then view the spatial output for queries by adding the results to QGIS as a query layer. You can also create, edit, delete, and empty tables, and move them to another schema.

Terrain Analysis Plugin

A new core plugin was added for doing terrain analysis (slope, aspect, hillshade, relief and ruggedness index).

New symbol layer types

• Line Pattern Fill

• Point Pattern Fill

• Ellipse renderer (render ellipse and also rectangles, triangles, crosses)

New plugin repository

Note that the old repository is now no longer supported by default; plugin authors are kindly requested to move their plugins to the new repository. Get the QGIS Plugins list at http://plugins.qgis.org/plugins/ .

More new features

• Support for nesting projects within other projects to embed content from other project files

• Group Selected: Option to group layers to a group

• Message log: Lets you keep an eye on the messages QGIS generates during loading and operation

• GUI Customization: Allows setting up simplified QGIS interface by hiding various components of main window and widgets in dialogs

• Action Tool is now accessible from the map tools toolbar and allows you to click on a vector feature and execute an action

• New scale selector: select from a list of predefined scales

• Pan To Selected tool: Pans the map to selected feature(s); does not change the zoom level

• Copy and paste styles between layers

• Updated CRS selector dialog

• Define Legend-independent drawing order

• MSSQL Spatial Support - you can now connect to your Microsoft SQL Server spatial databases using QGIS

• Print Composers allows to have multiple lines on legend items using a specified character

• Expression based labeling

• Heatmap Plugin - a new core plugin has been added for generating raster heatmaps from point data

• The GPS live tracking user interface was overhauled and many fixes and improvements were added to it

• The menu was re-organised a little - we now have separate menus for Vector, Raster, Web and many plugins were updated to place their menus in the new Vector, Raster and Web top level menus

• Offset Curves - a new digitising tool for creating offset curves was added

• New tools in the Vector menu to Densify geometries and Build spatial index

• Export/add geometry column tool can export info using layer CRS, project CRS or ellipsoidal measurements

• Model/view based tree for rules in rule-based renderer

• Improvements in Spatial Bookmarks

• New Plugin metadata in metadata.txt

12 Chapter 4. Features

QGIS User Guide, Release 1.8.0

• Refactored postgres data provider: support for arbitrary key (including non-numeric and multi column), support for requesting a certain geometry type and/or srid in QgsDataSourceURI

• Added gdal_fillnodata to GDALTools plugin

• Support for PostGIS TopoGeometry datatype

• Python bindings for vector field symbol layer and general updates to the Python bindings

• Added a Benchmark program

• Added Row cache for attribute table

• UUID generation widget for attribute table

• Added support of editable views in SpatiaLite databases

• added expression based widget in field calculator

• Creation of event layers in analysis lib using linear referencing

• Load/save layer styles in the new symbology renderer from/to SLD document

• QGIS Server can act as WFS Server

• WFS Client support is now a core feature in QGIS

• Option to skip WKT geometry when copying from attribute table

• Support loading of zipped and gzipped layers

• The QGIS test suite now passes all tests on major platforms and nightly tests

• You can set tile size for WMS layers

4.7. What’s new in the version 1.8

13

QGIS User Guide, Release 1.8.0

14 Chapter 4. Features

CHAPTER

5

Getting Started

This chapter gives a quick overview of installing QGIS, some sample data from the QGIS web page and running a first and simple session visualizing raster and vector layers.

5.1 Installation

Installation of QGIS is very simple. Standard installer packages are available for MS Windows and Mac OS

X. For many flavors of GNU/Linux binary packages (rpm and deb) or software repositories to add to your installation manager are provided.

Get the latest information on binary packages at the QGIS website at http://download.qgis.org

.

5.1.1 Installation from source

If you need to build QGIS from source, please refer to the installation instructions. They are distributed with the

QGIS source code in a file called ‘INSTALL’. You can also find it online at https://github.com/qgis/Quantum-

GIS/blob/master/INSTALL

5.1.2 Installation on external media

QGIS allows to define a --configpath option that overrides the default path (e.g. ~/.qgis under Linux) for user configuration and forces QSettings to use this directory, too. This allows users to e.g. carry a QGIS installation on a flash drive together with all plugins and settings.

5.2 Sample Data

The user guide contains examples based on the QGIS sample dataset.

The Windows installer has an option to download the QGIS sample dataset. If checked, the data will be downloaded to your My Documents folder and placed in a folder called GIS Database. You may use Windows

Explorer to move this folder to any convenient location. If you did not select the checkbox to install the sample dataset during the initial QGIS installation, you can either

• use GIS data that you already have;

• download the sample data from the qgis website at http://download.qgis.org

; or

• uninstall QGIS and reinstall with the data download option checked, only if the above solutions are unsuccessful.

15

QGIS User Guide, Release 1.8.0

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" ,

DATUM[ "North_American_Datum_1927" ,

SPHEROID[ "Clarke 1866" , 6378206.4

, 294.978698213898

,

AUTHORITY[ "EPSG" , "7008" ]],

TOWGS84[ 3 , 142 , 183 , 0 , 0 , 0 , 0 ],

AUTHORITY[ "EPSG" , "6267" ]],

PRIMEM[ "Greenwich" , 0 ,

AUTHORITY[ "EPSG" , "8901" ]],

UNIT[ "degree" , 0.0174532925199433

,

AUTHORITY[ "EPSG" , "9108" ]],

AUTHORITY[ "EPSG" , "4267" ]],

PROJECTION[ "Albers_Conic_Equal_Area" ],

PARAMETER[ "standard_parallel_1" , 55 ],

PARAMETER[ "standard_parallel_2" , 65 ],

PARAMETER[ "latitude_of_center" , 50 ],

PARAMETER[ "longitude_of_center" , 154 ],

PARAMETER[ "false_easting" , 0 ],

PARAMETER[ "false_northing" , 0 ],

UNIT[ "us_survey_feet" , 0.3048006096012192

]]

If you intend to use QGIS as graphical frontend for GRASS, you can find a selection of sample locations (e.g.

Spearfish or South Dakota) at the official GRASS GIS website http://grass.osgeo.org/download/data.php

.

5.3 Sample Session

Now that you have QGIS installed and a sample dataset available, we would like to demonstrate a short and simple QGIS sample session.

We will visualize a raster and a vector layer.

We will use the landcover raster layer qgis_sample_data/raster/landcover.img and the lakes vector layer qgis_sample_data/gml/lakes.gml

.

5.3.1 Start QGIS

• Start QGIS by typing: “QGIS” at a command prompt, or if using precompiled binary, using the Applications menu.

• Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.

• Double click the icon in your Applications folder.

5.3.2 Load raster and vector layers from the sample dataset

1. Click on the

Load Raster icon.

2. Browse to the folder qgis_sample_data/raster/, select the ERDAS Img file landcover.img

and click [Open].

3. If the file is not listed, check if the Filetype combobox at the bottom of the dialog is set on the right type, in this case “Erdas Imagine Images (*.img, *.IMG)”.

16 Chapter 5. Getting Started

QGIS User Guide, Release 1.8.0

4. Now click on the

Load Vector icon.

5.

File should be selected as Source Type in the new Add Vector Layer dialog. Now click [Browse] to select the vector layer.

6. Browse to the folder qgis_sample_data/gml/, select “GML” from the filetype combobox, then select the GML file lakes.gml and click [Open], then in Add Vector dialog click [OK].

7. Zoom in a bit to your favorite area with some lakes.

8. Double click the lakes layer in the map legend to open the Properties dialog.

9. Click on the Style tab and select a blue as fill color.

10. Click on the Labels tab and check the as field containing label.

Display lables checkbox to enable labeling. Choose NAMES field

11. To improve readability of labels, you can add a white buffer around them, by clicking “Buffer” in the list on the left, checking Buffer labels?

and choosing 3 as buffer size.

12. Click [Apply], check if the result looks good and finally click [OK].

You can see how easy it is to visualize raster and vector layers in QGIS. Let’s move on to the sections that follow to learn more about the available functionality, features and settings and how to use them.

5.4 Starting and Stopping QGIS

In Section

Sample Session

you already learned how to start QGIS. We will repeat this here and you will see that

QGIS also provides further command line options.

• Assuming that QGIS is installed in the PATH, you can start QGIS by typing: qgis at a command prompt or by double clicking on the QGIS application link (or shortcut) on the desktop or in the application menu.

• Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.

• Double click the icon in your Applications folder. If you need to start QGIS in a shell, run /path-toinstallation-executable/Contents/MacOS/Qgis.

To stop QGIS, click the menu options File QGIS

→ Quit, or use the shortcut Ctrl+Q.

5.5 Command Line Options

QGIS supports a number of options when started from the command line. To get a list of the options, enter qgis --help on the command line. The usage statement for QGIS is: qgis --help

Quantum GIS - 1.8.0-Lisboa ’Lisboa’ (exported)

Quantum GIS (QGIS) is a viewer for spatial data sets, including raster and vector data.

Usage: qgis [options] [FILES] options:

[--snapshot filename]

[--width width]

[--height height]

[--lang language] emit snapshot of loaded datasets to given file width of snapshot to emit height of snapshot to emit use language for interface text

[--project projectfile] load the given QGIS project

[--extent xmin,ymin,xmax,ymax] set initial map extent

[--nologo]

[--noplugins]

[--nocustomization] hide splash screen don’t restore plugins on startup don’t apply GUI customization

5.4. Starting and Stopping QGIS 17

QGIS User Guide, Release 1.8.0

[--optionspath path]

[--configpath path]

[--help] use the given QSettings path use the given path for all user configuration 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

2. Vectors - Supported formats include ESRI Shapefiles and others supported by OGR and PostgreSQL layers using the PostGIS extension

Tip: Example Using command line arguments

You can start QGIS by specifying one or more data files on the command line. For example, assuming you are in the qgis_sample_data directory, you could start QGIS with a vector layer and a raster file set to load on startup using the following command: qgis ./raster/landcover.img ./gml/lakes.gml

Command line option --snapshot

This option allows you to create a snapshot in PNG format from the current view. This comes in handy when you have a lot of projects and want to generate snapshots from your data.

Currently it generates a PNG-file with 800x600 pixels. This can be adapted using the --width and --height command line arguments. A filename can be added after --snapshot.

Command line option --lang

Based on your locale QGIS, selects the correct localization.

If you would like to change your language, you can specify a language code. For example: --lang=it starts QGIS in italian localization. A list of currently supported languages with language code and status is provided at http://hub.qgis.org/wiki/quantumgis/GUI_Translation_Progress

Command line option --project

Starting QGIS with an existing project file is also possible. Just add the command line option --project followed by your project name and QGIS will open with all layers loaded described in the given file.

Command line option --extent

To start with a specific map extent use this option. You need to add the bounding box of your extent in the following order separated by a comma:

--extent xmin,ymin,xmax,ymax

Command line option --nologo

This command line argument hides the splash screen when you start QGIS.

Command line option --noplugins

If you have trouble at startup with plugins, you can avoid loading them at startup. They will still be available in

Plugins Manager after-wards.

Command line option --nocustomization

Using this command line argument existing GUI customization will not be applied at startup.

Command line option --optionspath

You can have multiple configurations and decide which one to use when starting QGIS using this option. See

Options

to check where does the operating system save the settings files. Presently there is no way to specify in which file where to write the settings, therefore you can create a copy of the original settings file and rename it.

Command line option --configpath

18 Chapter 5. Getting Started

QGIS User Guide, Release 1.8.0

This option is similar to the one above, but furthermore overrides the default path (~/.qgis) for user configuration and forces QSettings to use this directory, too. This allows users to e.g. carry QGIS installation on a flash drive together with all plugins and settings.

5.6 Projects

The state of your QGIS session is considered a Project. QGIS works on one project at a time. Settings are either considered as being per-project, or as a default for new projects (see Section

Options

). QGIS can save the state of

your workspace into a project file using the menu options File → Save Project or File → Save Project As .

Load saved projects into a QGIS session using File → Open Project or File → Open Recent Project.

If you wish to clear your session and start fresh, choose File → New Project . Either of these menu options will prompt you to save the existing project if changes have been made since it was opened or last saved.

The kinds of information saved in a project file include:

• Layers added

• Layer properties, including symbolization

• Projection for the map view

• Last viewed extent

The project file is saved in XML format, so it is possible to edit the file outside QGIS if you know what you are doing. The file format was updated several times compared to earlier QGIS versions. Project files from older

QGIS versions may not work properly anymore. To be made aware of this, in the General tab under Settings →

Options you can select:

Prompt to save project changes when required

Warn when opening a project file saved with an older version of QGIS

5.7 Output

There are several ways to generate output from your QGIS session. We have discussed one already in Section

Projects

saving as a project file. Here is a sampling of other ways to produce output files:

• Menu option File →

Save as Image opens a file dialog where you select the name, path and type of image

(PNG or JPG format). A world file with extension PNGW or JPGW saved in the same folder georeferences the image.

• Menu option File → New Print Composer opens a dialog where you can layout and print the current map canvas (see Section

Print Composer

).

5.6. Projects 19

QGIS User Guide, Release 1.8.0

20 Chapter 5. Getting Started

CHAPTER

6

QGIS GUI

When QGIS starts, you are presented with the GUI as shown below (the numbers 1 through 5 in yellow ovals refer to the six major areas of the interface as discussed below):

Figure 6.1: QGIS GUI with Alaska sample data

Note: Your window decorations (title bar, etc.) may appear different depending on your operating system and window manager.

The QGIS GUI is divided into five areas:

1. Menu Bar

2. Tool Bar

3. Map Legend

4. Map View

5. Status Bar

These five components of the QGIS interface are described in more detail in the following sections. Two more sections present keyboard shortcuts and context help.

21

QGIS User Guide, Release 1.8.0

6.1 Menu Bar

The menu bar provides access to various QGIS features using a standard hierarchical menu. The top-level menus and a summary of some of the menu options are listed below, together with the icons of the corresponding tools as they appear on the toolbar, as well as keyboard shortcuts. Keyboard shortcuts can also be configured manually

(shortcuts presented in this section are the defaults), using the [Configure Shortcuts] tool under Settings.

Although most menu options have a corresponding tool and vice-versa, the menus are not organized quite like the toolbars. The toolbar containing the tool is listed after each menu option as a checkbox entry. Some menu options only appear, if the corresponding plugin is loaded. For more information about tools and toolbars, see Section

Toolbar

.

6.1.1 File

Menu Option

New Project

Open Project

Open Recent Projects

Exit

Shortcut

Ctrl+N

Ctrl+O

Toolbar

File

File

Save Project

Save Project As

Save as Image

New Print Composer

Ctrl+P

Composer manager

Print Composers

Ctrl+S see

Projects

Ctrl+Shift+S see

Projects

File

File see

Output

see

Print Composer

File see

Print Composer

File see

Print Composer

Ctrl+Q

Reference see

Projects

see

Projects

see

Projects

22 Chapter 6. QGIS GUI

QGIS User Guide, Release 1.8.0

6.1.2 Edit

Menu Option

Undo

Redo

Cut Features

Copy Features

Paste Features

Add Feature

Move Feature(s)

Delete Selected

Simplify Feature

Add Ring

Add Part

Delete Ring

Delete Part

Reshape Features

Offset Curves

Split Features

Merge selected Features

Merge attr. of selected Features

Node Tool

Rotate Point Symbols

Shortcut

Ctrl+Z

Ctrl+Shift+Z

Ctrl+X

Reference see

Advanced digitizing

see

Advanced digitizing

Toolbar

Advanced Digitizing

Advanced Digitizing see

Digitizing an existing layer

Digitizing

Ctrl+C

Ctrl+V

Ctrl+.

see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing see

Advanced digitizing

see

Advanced digitizing

Advanced Digitizing

Advanced Digitizing see

Advanced digitizing

see

Advanced digitizing

Advanced Digitizing

Advanced Digitizing see

Advanced digitizing

see

Advanced digitizing

Advanced Digitizing

Advanced Digitizing see

Advanced digitizing

see

Advanced digitizing

see

Advanced digitizing

Advanced Digitizing

Advanced Digitizing

Advanced Digitizing see

Advanced digitizing

Advanced Digitizing see

Digitizing an existing layer

Digitizing see

Advanced digitizing

Advanced Digitizing

After activating

Toggle editing mode for a layer, you will find the Add Feature icon in the Edit menu depending on the layer type (point, line or polygon).

6.1.3 Edit (extra)

Menu Option

Add Feature

Add Feature

Add Feature

Shortcut Reference Toolbar see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing see

Digitizing an existing layer

Digitizing

6.1. Menu Bar 23

QGIS User Guide, Release 1.8.0

6.1.4 View

Menu Option

Pan Map

Pan Map to Selection

Zoom In

Zoom Out

Select

Identify Features

Measure

Zoom Full

Zoom To Layer

Zoom To Selection

Zoom Last

Zoom Next

Zoom Actual Size

Decorations

Map Tips

New Bookmark

Show Bookmarks

Refresh

Tile scale slider

Shortcut

Ctrl++

Ctrl+-

Ctrl+Shift+I

Ctrl+Shift+F

Ctrl+J

Ctrl+B

Reference Toolbar

Map Navigation

Map Navigation

Map Navigation

Map Navigation see

Select and deselect features

Attributes see

Measuring

Attributes

Attributes

Map Navigation

Map Navigation

Map Navigation

Map Navigation

Map Navigation

Map Navigation see

Decorations

Ctrl+Shift+B see

Spatial Bookmarks

Ctrl+R see

Spatial Bookmarks

see

Tilesets

Attributes

Attributes

Attributes

Map Navigation

Tile scale

6.1.5 Layer

Menu Option

New

Embed Layers and Groups ...

Add Vector Layer

Add Raster Layer

Add PostGIS Layer

Add SpatiaLite Layer

Add MSSQL Spatial Layer

Add WMS Layer

Add Delimited Text Layer

Create new GPX layer

Add Oracle GeoRaster layer

Add SQL Anywhere Layer

Add WFS Layer

Shortcut Reference see

Creating a new Vector layer

see

Nesting Projects

Ctrl+Shift+V see

Working with Vector Data

Ctrl+Shift+R see

Loading raster data in QGIS

Ctrl+Shift+D see

PostGIS Layers

Ctrl+Shift+L see

SpatiaLite Layers

Ctrl+Shift+M

Ctrl+Shift+W see see see

MSSQL Spatial Layers

WMS Client

Delimited Text Plugin

Toolbar

Manage Layers

Manage Layers

Manage Layers

Manage Layers

Manage Layers

Manage Layers

Manage Layers

Manage Layers see

GPS Plugin

see

Oracle GeoRaster Plugin

see

SQL Anywhere Plugin

Manage Layers

Manage Layers

Manage Layers

Manage Layers

Continued on next page

24 Chapter 6. QGIS GUI

QGIS User Guide, Release 1.8.0

Menu Option

Copy style

Paste style

Open Attribute Table

Save edits

Toggle editing

Save as...

Save selection as vector file...

Remove Layer

Set CRS of Layer(s)

Set project CRS from Layer

Properties

Query...

Labeling

Add to Overview

Add All To Overview

Remove All From Overview

Show All Layers

Hide All Layers

Table 6.1 – continued from previous page

Shortcut Reference see

Style Tab

see

Style Tab

Ctrl+D

Ctrl+Shift+C

Ctrl+Shift+O

Ctrl+Shift+U

Ctrl+Shift+H

See

Working with the Attribute Table

Toolbar

Attributes

Digitizing

Digitizing

Manage Layers

Manage Layers

Manage Layers

6.1.6 Settings

Menu Option

Panels

Toolbars

Shortcut

Toggle Full Screen Mode Ctrl-F

Reference see

Panels and Toolbars

see

Panels and Toolbars

Project Properties ...

Ctrl+Shift+P see

Projects

Custom CRS ...

Style Manager...

Configure shortcuts ...

Customization ...

Options ...

Snapping Options ...

see

Custom Coordinate Reference System

see

Style Manager

see see

Customization

Options

Toolbar

6.1.7 Plugins

Menu Option

Fetch Python Plugins

Manage Plugins

Python Console

GRASS

Shortcut Reference see

QGIS Plugins

see

Managing Plugins

see

GRASS GIS Integration

Toolbar

GRASS

6.1. Menu Bar 25

QGIS User Guide, Release 1.8.0

6.1.8 Vector

Menu Option

Analysis Tools

Coordinate Capture

Data Management Tools

Dxf2Shp

Geometry Tools

Geoprocessing Tools

GPS

Research Tools

Road Graph

Spatial Query

Shortcut Reference Toolbar see

fTools Plugin

see

Coordinate Capture Plugin

see

fTools Plugin

see

Dxf2Shp Converter Plugin

Vector see

fTools Plugin

see

fTools Plugin

see

GPS Plugin

see

fTools Plugin

see

Road Graph Plugin

see

Spatial Query Plugin

Vector

Vector

6.1.9 Raster

Menu Option

Raster calculator

Georeferencer

Heatmap

Interpolation

Terrain Analysis

Zonal Statistics

Projections

Conversion

Extraction

Analysis

Miscellaneous

GdalTools settings

Shortcut Reference see

Raster Calculator

see

Georeferencer Plugin

see

Heatmap Plugin

see

Interpolation Plugin

see

Raster Terrain Analysis Plugin

see

Zonal Statistics Plugin

see

GDAL Tools Plugin

see

GDAL Tools Plugin

see

GDAL Tools Plugin

see

GDAL Tools Plugin

see

GDAL Tools Plugin

see

GDAL Tools Plugin

Toolbar

Raster

Raster

Raster

Raster

6.1.10 Database

Menu Option

DB manager

→ eVis

Offline Editing

Spit

Shortcut Reference see

DB Manager Plugin

see

eVis Plugin

Toolbar

Database

Database see

Offline Editing Plugin

Database see

SPIT Plugin

Database

6.1.11 Web

Menu Option

MapServer Export ...

OpenStreetMap

Shortcut Reference Toolbar see

MapServer Export Plugin

Web see

OpenStreetMap

OpenStreetMap

26 Chapter 6. QGIS GUI

QGIS User Guide, Release 1.8.0

6.1.12 Help

Menu Option

Help Contents

What’s This?

API Documentation

QGIS Home Page

Check QGIS Version

About

QGIS Sponsors

Shortcut

F1

Shift+F1

Ctrl+H

Reference Toolbar

Help

Help

Please not that for Linux the Menu Bar items listed above are the default ones in KDE window manager. In

GNOME, Settings menu is missing and its items are to be found here:

Project Properties

Options

Configure Shortcuts

Style Manager

File

Edit

Edit

Edit

Custom CRS

Panels

Toolbars

Edit

View

View

Toggle Full Screen Mode View

Tile scale slider

Live GPS tracking

View

View

6.2 Toolbar

The toolbar provides access to most of the same functions as the menus, plus additional tools for interacting with the map. Each toolbar item has popup help available. Hold your mouse over the item and a short description of the tool’s purpose will be displayed.

Every menubar can be moved around according to your needs. Additionally every menubar can be switched off using your right mouse button context menu holding the mouse over the toolbars (read also

Panels and Toolbars

).

Tip: Restoring toolbars

If you have accidentally hidden all your toolbars, you can get them back by choosing menu option Settings →

Toolbars

→. If a toolbar disappears under Windows, which seems to be a problem in QGIS from time to time, you have to remove \HKEY_CURRENT_USER\Software\QuantumGIS\qgis\UI\state in the registry.

When you restart QGIS, the key is written again with the default state, and all toolbars are visible again.

6.3 Map Legend

The map legend area lists all the layers in the project. The checkbox in each legend entry can be used to show or hide the layer.

A layer can be selected and dragged up or down in the legend to change the z-ordering. Z-ordering means that layers listed nearer the top of the legend are drawn over layers listed lower down in the legend.

Layers in the legend window can be organised into groups. There are two ways to do so:

6.2. Toolbar 27

QGIS User Guide, Release 1.8.0

1. Right click in the legend window and choose Add Group. Type in a name for the group and press Enter.

Now click on an existing layer and drag it onto the group.

2. Select some layers, right click in the legend window and choose Group Selected. The selected layers will automatically be placed in a new group.

To bring a layer out of a group you can drag it out, or right click on it and choose Make to toplevel item. Groups can be nested inside other groups.

The checkbox for a group will show or hide all the layers in the group with one click.

The content of the right mouse button context menu depends on whether the selected legend item is a raster or a vector layer. For GRASS vector layers

Toggle editing is not available. See section

Digitizing and editing a GRASS vector layer

for information on editing GRASS vector layers.

Right mouse button menu for raster layers

• Zoom to layer extent

• Zoom to best scale (100 %)

• Show in overview

• Remove

• Set Layer CRS

• Set Project CRS from Layer

• Properties

• Rename

• Copy Style

• Add New Group

• Expand all

• Collapse all

• Update Drawing Order

Additionally, according to layer position and selection

• Make to toplevel item

• Group Selected

Right mouse button menu for vector layers

• Zoom to layer extent

• Show in overview

• Remove

• Set Layer CRS

• Set Project CRS from Layer

• Open attribute table

• Toggle editing (not available for GRASS layers)

• Save as

• Save selection as

• Query

• Show Feature Count

• Properties

28 Chapter 6. QGIS GUI

QGIS User Guide, Release 1.8.0

• Rename

• Copy Style

• Add New Group

• Expand all

• Collapse all

• Update Drawing Order

Additionally, according to layer position and selection

• Make to toplevel item

• Group Selected

Right mouse button menu for layer groups

• Zoom to group

• Remove

• Set group CRS

• Rename

• Add New Group

• Expand all

• Collapse all

• Update Drawing Order

It is possible to select more than one layer or group at the same time by holding down the Ctrl key while selecting the layers with the left mouse button. You can then move all selected layers to a new group at the same time.

You are also able to delete more than one Layer or Group at once by selecting several Layers with the Ctrl key and pressing Ctrl+D afterwards. This way all selected Layers or groups will be removed from the layerlist.

6.3.1 Working with the Legend independent layer order

Since QGIS 1.8 there is a widget that allows to define a legend independent drawing order. You can activate it in the menu Settings → Panels. Determine the drawing order of the layers in the map view here. Doing so makes it possible to order your layers in order of importance, for example, but to still display them in the correct order (see

figure_layer_order

). Checking the

to default behavior.

control rendering order box underneath the list of layers will cause a revert

6.4 Map View

This is the “business end” of QGIS - maps are displayed in this area! The map displayed in this window will depend on the vector and raster layers you have chosen to load (see sections that follow for more information on how to load layers). The map view can be panned (shifting the focus of the map display to another region) and zoomed in and out. Various other operations can be performed on the map as described in the toolbar description above. The map view and the legend are tightly bound to each other - the maps in view reflect changes you make in the legend area.

Tip: Zooming the Map with the Mouse Wheel

You can use the mouse wheel to zoom in and out on the map. Place the mouse cursor inside the map area and roll the wheel forward (away from you) to zoom in and backwards (towards you) to zoom out. The mouse cursor position is the center where the zoom occurs. You can customize the behavior of the mouse wheel zoom using the

Map tools tab under the Settings → Options menu.

6.4. Map View 29

QGIS User Guide, Release 1.8.0

Figure 6.2: Define a legend independent layer order

Tip: Panning the Map with the Arrow Keys and Space Bar

You can use the arrow keys to pan in the map. Place the mouse cursor inside the map area and click on the right arrow key to pan East, left arrow key to pan West, up arrow key to pan North and down arrow key to pan South.

You can also pan the map using the space bar: just move the mouse while holding down space bar.

6.5 Status Bar

The status bar shows you your current position in map coordinates (e.g. meters or decimal degrees) as the mouse pointer is moved across the map view. To the left of the coordinate display in the status bar is a small button that will toggle between showing coordinate position or the view extents of the map view as you pan and zoom in and out.

Next to the coordinate display you find the scale display. It shows the scale of the map view. If you zoom in or out

QGIS shows you the current scale. Since QGIS 1.8 there is a scale selector which allows you to choose between predefined scales from 1:500 until 1:1000000.

A progress bar in the status bar shows progress of rendering as each layer is drawn to the map view. In some cases, such as the gathering of statistics in raster layers, the progress bar will be used to show the status of lengthy operations.

If a new plugin or a plugin update is available, you will see a message at the far right of the status bar. On the right side of the status bar is a small checkbox which can be used to temporarily prevent layers being rendered to the map view (see Section

Rendering

below). The icon immediately stops the current map rendering process.

To the right of the render functions you find the EPSG code of the current project CRS and a projector icon.

Clicking on this opens the projection properties for the current project.

Tip: Calculating the correct Scale of your Map Canvas

30 Chapter 6. QGIS GUI

QGIS User Guide, Release 1.8.0

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) clicking on the

CRS status 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’.

6.5. Status Bar 31

QGIS User Guide, Release 1.8.0

32 Chapter 6. QGIS GUI

CHAPTER

7

General Tools

7.1 Keyboard shortcuts

QGIS provides default keyboard shortcuts for many features. You find them in Section

Menu Bar

. Additionally

the menu option Settings → Configure Shortcuts allows to change the default keyboard shortcuts and to add new keyboard shortcuts to QGIS features.

Figure 7.1: Define shortcut options (KDE)

Configuration is very simple. Just select a feature from the list and click on [Change], [Set none] or [Set default].

Once you have found your configuration, you can save it as XML file and load it to another QGIS installation.

7.2 Context help

When you need help on a specific topic, you can access context help via the Help button available in most dialogs

- please note that third-party plugins can point to dedicated web pages.

33

QGIS User Guide, Release 1.8.0

7.3 Rendering

By default, QGIS renders all visible layers whenever the map canvas must be refreshed. The events that trigger a refresh of the map canvas include:

• Adding a layer

• Panning or zooming

• Resizing the QGIS window

• Changing the visibility of a layer or layers

QGIS allows you to control the rendering process in a number of ways.

7.3.1 Scale Dependent Rendering

Scale dependent rendering allows you to specify the minimum and maximum scales at which a layer will be visible. To set scale dependency rendering, open the Properties dialog by double-clicking on the layer in the legend. On the General tab, set the minimum and maximum scale values and then click on the

Use scale dependent rendering 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.

7.3.2 Controlling Map Rendering

Map rendering can be controlled in the following ways:

Suspending Rendering

To suspend rendering, click the Render checkbox in the lower right corner of the statusbar. When the

Render checkbox is not checked, QGIS does not redraw the canvas in response to any of the events described in

Section

Rendering

. Examples of when you might want to suspend rendering include:

• Add many layers and symbolize them prior to drawing

• Add one or more large layers and set scale dependency before drawing

• Add one or more large layers and zoom to a specific view before drawing

• Any combination of the above

Checking the Render checkbox enables rendering and causes an immediate refresh of the map canvas.

Setting Layer Add Option

You can set an option to always load new layers without drawing them. This means the layer will be added to the map, but its visibility checkbox in the legend will be unchecked by default. To set this option, choose menu option

Settings

→ Options → and click on the Rendering tab. Uncheck the

By default new layers added to the map should be displayed checkbox. Any layer added to the map will be off (invisible) by default.

Stopping Rendering

To stop the map drawing, press the ESC key. This will halt the refresh of the map canvas and leave the map partially drawn. It may take a bit of time between pressing ESC and the time the map drawing is halted.

34 Chapter 7. General Tools

QGIS User Guide, Release 1.8.0

Note: It is currently not possible to stop rendering - this was disabled in qt4 port because of User Interface (UI) problems and crashes.

Updating the Map Display During Rendering

You can set an option to update the map display as features are drawn. By default, QGIS does not display any features for a layer until the entire layer has been rendered. To update the display as features are read from the datastore, choose menu option Settings → Options click on the Rendering tab. Set the feature count to an appropriate value to update the display during rendering. Setting a value of 0 disables update during drawing (this is the default). Setting a value too low will result in poor performance as the map canvas is continually updated during the reading of the features. A suggested value to start with is 500.

Influence Rendering Quality

To influence the rendering quality of the map you have 2 options. Choose menu option Settings → Options click on the Rendering tab and select or deselect following checkboxes.

• Make lines appear less jagged at the expense of some drawing performance

• Fix problems with incorrectly filled polygons

7.4 Measuring

Measuring works within projected coordinate systems (e.g., UTM) and unprojected data. If the loaded map is defined with a geographic coordinate system (latitude/longitude), the results from line or area measurements will be incorrect. To fix this you need to set an appropriate map coordinate system (See Section

Working with

Projections

). All measuring modules also use the snapping settings from the digitizing module. This is useful, if

you want to measure along lines or areas in vector layers.

To select a measure tool click on and select the tool you want to use.

7.4.1 Measure length, areas and angles

QGIS is able to measure real distances between given points according to a defined ellipsoid. To configure this, choose menu option Settings → Options, click on the Map tools tab and choose the appropriate ellipsoid.

There you can also define a rubberband color and your preferred measurement units (meters or feet) and angle units (degrees, radians and gon). The tools then allows you to click points on the map. Each segment-length as well as the total shows up in the measure-window. To stop measuring click your right mouse button.

Figure 7.2: Measure Distance (KDE)

Areas can also be measured. In the measure window the accumulated area size appears. In addition, the measuring tool will snap to the currently selected layer, provided that layer has its snapping tolerance set. (See

Section

Setting the Snapping Tolerance and Search Radius

). So if you want to measure exactly along a line feature,

7.4. Measuring 35

QGIS User Guide, Release 1.8.0

or around a polygon feature, first set its snapping tolerance, then select the layer. Now, when using the measuring tools, each mouse click (within the tolerance setting) will snap to that layer.

Figure 7.3: Measure Area (KDE)

You can also measure angles, selecting Measure Angle tool. The cursor becomes cross-shaped. Click to draw the first segment of the angle you wish to measure, then move the the cursor to draw the desired angle. The measure is displayed in a popup dialog.

Figure 7.4: Measure Angle (KDE)

7.4.2 Select and deselect features

The QGIS toolbar provides several tools to select features in the map canvas. To select one or several features just click on and select your tool:

Select single feature

Select features by rectangle

Select features by polygon

Select features by freehand

Select features by radius

To deselect all selected features click on

Deselect features from all layers

.

7.5 Decorations

The Decorations of QGIS includes the Copyright Label, the North Arrow and the Scale Bar. They are used to

‘decorate’ the map by adding cartographic elements.

Note: Before QGIS 1.8 the same functionality was provided by the Decoration Plugin.

7.5.1 Copyright Label

Copyright label adds a Copyright label using the text you prefer to the map.

1. Select from menu View → Decorations → Copyright Label. The dialog starts (see

figure_decorations_1

).

2. Enter the text you want to place on the map. You can use HTML as shown in the example

36 Chapter 7. General Tools

QGIS User Guide, Release 1.8.0

Figure 7.5: The copyright Dialog

3. Choose the placement of the label from the Placement ‘Bottom Right’ drop-down box

4. Make sure the

5. Click [OK]

Enable Copyright Label checkbox is checked

In the example above (default) QGIS places a copyright symbol followed by the date in the lower right hand corner of the map canvas.

7.5.2 North Arrow

North Arrow places a simple north arrow on the map canvas. At present there is only one style available. You can adjust the angle of the arrow or let QGIS set the direction automatically. If you choose to let QGIS determine the direction, it makes its best guess as to how the arrow should be oriented. For placement of the arrow you have four options, corresponding to the four corners of the map canvas.

Figure 7.6: The North Arrow Dialog

7.5.3 Scale Bar

Scale Bar adds a simple scale bar to the map canvas. You control the style and placement, as well as the labeling of the bar.

QGIS only supports displaying the scale in the same units as your map frame. So if the units of your layers are in meters, you can’t create a scale bar in feet. Likewise if you are using decimal degrees, you can’t create a scale bar to display distance in meters.

To add a scale bar:

7.5. Decorations 37

QGIS User Guide, Release 1.8.0

Figure 7.7: The Scale Bar Dialog

1. Select from menu View → Decorations → Scale Bar The dialog starts (see

figure_decorations_3

)

2. Choose the placement from the Placement ‘Bottom Left’ drop-down list

3. Choose the style from the Scale bar style ‘Tick Down’ list

4. Select the color for the bar Color of bar ‘black’ or use the default black color

5. Set the size of the bar and its label Size of bar ‘30 degrees’

6. Make sure the Enable scale bar checkbox is checked

7. Optionally choose to automatically snap to a round number when the canvas is resized snap to round number on resize

8. Click [OK]

Automatically

Tip: Settings of Decorations

When you save a .qgs project, any changes you have made to NorthArrow, ScaleBar and Copyright will be saved in the project and restored the next time you load the project.

7.6 Annotation Tools

The Text Annotation tools in the attribute toolbar provides the possibility to place formatted text in a balloon on the QGIS map canvas. Use the Text Annotation tool and click into the map canvas.

38

Figure 7.8: Annotation text dialog

Chapter 7. General Tools

QGIS User Guide, Release 1.8.0

Double click on the item opens a dialog with various options. There is the text editor to enter the formatted text and other item settings. E.g. there is the choice of having the item placed on a map position (displayed by a marker symbol) or to have the item on a screen position (not related to the map). The item can be moved by map position

(drag the map marker) or by moving only the balloon. The icons are part of GIS theme, and are used by default in the other themes too.

The Move Annotation tool allows to move the annotation on the map canvas.

7.6.1 Form annotations

Additionally you can also create your own annotation forms. The Form Annotation tool is useful to display attributes of a vector layer in a customized qt designer form (see

figure_custom_annotation

). It is similar

to the designer forms for the Identify features tool, but displayed in an annotation item. Also see QGIS blog http://blog.qgis.org/node/143 for more information.

Figure 7.9: Customized qt designer annotation form

Note: If you press Ctrl+T while an Annotation tool is active (move annotation, text annotation, form annotation), the visibility states of the items are inverted.

7.7 Spatial Bookmarks

Spatial Bookmarks allow you to “bookmark” a geographic location and return to it later.

7.7.1 Creating a Bookmark

To create a bookmark:

1. Zoom or pan to the area of interest.

2. Select the menu option View → New Bookmark or press Ctrl-B.

3. Enter a descriptive name for the bookmark (up to 255 characters).

4. Press Enter to add the bookmark or [Delete] to remove the bookmark.

Note that you can have multiple bookmarks with the same name.

7.7. Spatial Bookmarks 39

QGIS User Guide, Release 1.8.0

7.7.2 Working with Bookmarks

To use or manage bookmarks, select the menu option View → Show Bookmarks. The Geospatial Bookmarks dialog allows you to zoom to or delete a bookmark. You can not edit the bookmark name or coordinates.

7.7.3 Zooming to a Bookmark

From the Geospatial Bookmarks dialog, select the desired bookmark by clicking on it, then click [Zoom To]. You can also zoom to a bookmark by double-clicking on it.

7.7.4 Deleting a Bookmark

To delete a bookmark from the Geospatial Bookmarks dialog, click on it then click [Delete]. Confirm your choice by clicking [Yes] or cancel the delete by clicking [No].

7.8 Nesting Projects

If you want to embed content from other project files into your project you can choose Layer → Embed Layers and Groups .

7.8.1 Embedding layers

The following dialog allows you to embed layers from other projects:

1. Press to look for another project from the Alaska dataset.

2. Select the project file grassland. You can see the content of the project (see

figure_embed_dialog

).

3. Press Ctrl and klick on the layers grassland and regions. The layers are embedded in the map legend and the map view now.

Figure 7.10: Select layers and groups to embed

While the embedded layers are editable you can’t change it’s properties like Style and Labeling.

Removing embedded layers

Right-click on the embedded layer and choose Remove .

40 Chapter 7. General Tools

CHAPTER

8

QGIS Configuration

QGIS is highly configurable through the Settings menu. Choose between Panels, Toolbars, Project properties,

Options and Customization.

8.1 Panels and Toolbars

In the Panels→ menu you can switch on and off QGIS widgets. The Toolbars→ menu provides the possibility to switch on and off icon groups in the QGIS toolbar (see

figure_panels_toolbars

).

Figure 8.1: The Panels and Toolbars menu

Tip: Activating the QGIS Overview

In QGIS you can use an overview panel that provides a full extent view of layers added to it. It can be selected under the menu Settings → Panels. Within the view is a rectangle showing the current map extent. This allows you to quickly determine which area of the map you are currently viewing. Note that labels are not rendered to the map overview even if the layers in the map overview have been set up for labeling. If you click and drag the red rectangle in the overview that shows your current extent, the main map view will update accordingly.

Tip: Show Log Messages

41

QGIS User Guide, Release 1.8.0

Since QGIS 1.8 it’s possible to track the QGIS messages. You can activate Log Messages in the menu Settings

→ Panels and follow the messages in the General and Plugin tab during loading and operation.

8.2 Project Properties

In the properties window for the project under Settings

→ Project Properties or

Settings

→ Project Properties you set project specific options. These include:

• In the General tab the project title, selection and background color, layer units, precision, and the option to save relative paths to layers can be defined. You can define the layer units (only used when CRS transformation is disabled) and the precision of decimal places to use.

• The CRS Coordinate Reference System tab enables you to choose the CRS for this project, and to enable on-the-fly re-projection of raster and vector layers when displaying layers from a different CRS.

• With the third Identifiable layers tab you set (or disable) which layers will respond to the identify tool. (See the Map tools paragraph from the

Options

section to enable identifying of multiple layers.)

• The tab OWS Server allows to define information about the QGIS mapserver Service Capabilities, the Extent and the CRS Restrictions as well as the WFS Capabilities. Activating the info response will allow to query the WMS layers.

Add WKT geometry to feature

8.3 Options

Some basic options for QGIS can be selected using the Options dialog. Select the menu option Settings →

Options . The tabs where you can optimize your options are:

8.3.1 General Tab

• Prompt to save project changes when required

Warn when opening a project file saved with an older version of QGIS

• Change Selection and Background color

• Change the QGIS Style

• Change the icon theme (choose between ‘default’, ‘classic’ and ‘gis’)

• Change icon size between 16, 24 and 32 pixel.

• Change the menu size

• Define double click action in legend (choose between ‘open layer properties’ and ‘open ‘) attribute table.

Capitalize layer names in legend

Display classification attribute names in legend

Create raster icons in legend

Hide splash screen at startup

Show tips at startup

Open identify results in a dock window (QGIS restart required)

Open snapping options in a dock window (QGIS restart required)

42 Chapter 8. QGIS Configuration

QGIS User Guide, Release 1.8.0

Open attribute table in a dock window

Add PostGIS layers with double click and select in extended mode

• Add new layers to selected or current group

• Copy geometry in WKT representation from attribute table

• Attribute table behavior (choose between ‘Show all features’ (default), ‘Show selected features’,’Show features in current canvas’)

• Attribute table row cache

• Define Representation for NULL values

• Prompt for raster sublayers . Some rasters support sublayers - they are called subdatasets in GDAL.

An example is netcdf files - if there are many netcdf variables, GDAL sees every variable as a subdataset.

The option is to control how to deal with sublayers when a file with sublayers is opened. You have the following choices:

– ‘Always’: always ask (if there are existing sublayers)

– ‘If needed’: ask if layer has no bands, but has sublayers

– ‘Never’: never prompt, will not load anything

– ‘Load all’: never prompt, but load all sublayers

• Scan for valid items in the browser dock . The ‘Check extension’ option was designed to speed up the loading of a directory, which can be time-consuming when ‘Check file contents’ is activated and there are many files (tens or hundreds).

• Scan for contents of compressed files (.zip) in browser dock up the loading of a directory. You have the following choices:

This option was also designed to speed

– ‘Basic Scan’: checks that the extension is supported by one of the drivers

– ‘Full Scan’: opens every file to check it is valid

– ‘Passthru’: don’t use this option it will be removed in the next QGIS version

8.3.2 GDAL tab

GDAL is a data exchange library for raster files. In this tab you can define which GDAL driver to be used for a raster format as in some cases more than one GDAL driver is available.

8.3.3 Plugins tab

• Add Path(s) to search for additional C++ plugin libraries.

8.3.4 Rendering Tab

• By default new layers added to the map should be displayed

• Define Number of features to draw before updating the display.

Use render caching where possible to speed up redraws

Make lines appear less jagged at the expense of some drawing performance

Fix problems with incorrectly filled polygons

8.3. Options 43

QGIS User Guide, Release 1.8.0

• Use new generation symbology for rendering

• Define the default Raster settings for visualisation: ‘RGB band selection’,

‘Contrast Enhancement’

Use standard deviation and

• Add/remove Path(s) to search for Scalable Vector Graphics (SVG) symbols

Additionally you can define whether to save the path for svg textures absolute or relative in the General tab of the

Settings

→ Project Properties menu.

8.3.5 Map tools Tab

• The Mode setting determines which layers will be shown by the Identify tool. By switching to ‘Top down’ or ‘Top down, stop at first’ instead of ‘Current layer’ attributes for all identifiable layers (see the Project properties section under:

Projects

to set which layers are identifiable) will be shown with the Identify tool.

• Open feature form, if a single feature is identified

• Define Search radius for identifying and displaying map tips as a percentage of the map width

• Define Ellipsoid for distance calculations

• Define Rubberband color for measure tools

• Define Decimal places

Keep base unit

Define preferred measurement units (‘meters’ or ‘feet’)

Define preferred angle units (‘Degrees’, ‘Radians’ or ‘Gon’)

• Define Mouse wheel action

• Define Zoom factor for wheel mouse

(‘Zoom’, ‘Zoom and recenter’, ‘Zoom to mouse cursor’, ‘Nothing’)

8.3.6 Overlays Tab

• Define Placement algorithm for labels, symboly and diagrams (choose between ‘Central point’

(standard), ‘Chain’, ‘Popmusic tabu chain’, ‘Popmusic tabu’ and ‘Popmusic chain’)

8.3.7 Digitizing Tab

• Define Rubberband Line color and Line width

• Define Default snap mode (‘To vertex’, ‘To segment’, ‘To vertex and segment’)

• Define Default snapping tolerance in map units or pixel

• Define search radius for vertex edits in ‘map units’ or ‘pixel’

• Show markers only for selected features

• Define vertex Marker style

Marker size .

(‘Cross’ (default), ‘Semi transparent circle’ or ‘None’) and vertex

Suppress attributes pop-up windows after each created feature

• Reuse last entered attribute values

44 Chapter 8. QGIS Configuration

QGIS User Guide, Release 1.8.0

• Validate geometries Editing complex lines/polygons with many nodes can end up with very slow rendering.

This is because the default validation procedures in QGIS can use a lot of time. To speed up rendering it is possible to select GEOS geometry validation (starting from GEOS 3.3) or to switch it off. GEOS geometry validation is much faster, but the disadvantage is that only the first geometry problem will be reported.

The next 3 options refer to the

Offset Curve tool in

Advanced digitizing

. Through the various settings, it is

possible to influence the shape of the line offset. These options are possible from GEOS 3.3 .

• Join style for curve offset

• Quadrantsegments for curve offset

• Miter limit for curve offset

8.3.8 CRS Tab

The CRS tab is divided in two areas. The first area allows to define the default CRS for new projects.

• Select a CRS and Always start new projects with this CRS.

• Enable on the fly re-projection by default

The second area allows to define the action, when a new layer is created, or when a layer without CRS is loaded.

• Prompt for Coordinate Reference System (CRS)

Use project Coordinate Reference System (CRS)

Use default Coordinate Reference System (CRS) displayed below

8.3.9 Locale Tab

• Overwrite system locale and Locale to use instead

• Information about active system locale

8.3.10 Network Tab

8.3. Options

Figure 8.2: Proxy-settings in QGIS

45

QGIS User Guide, Release 1.8.0

• Use proxy for web access and define ‘Host’, ‘Port’, ‘User’, and ‘Password’.

• Set the Proxy type according to your needs.

– Default Proxy: Proxy is determined based on the application proxy set using

– Socks5Proxy: Generic proxy for any kind of connection. Supports TCP, UDP, binding to a port (incoming connections) and authentication.

– HttpProxy: Implemented using the “CONNECT” command, supports only outgoing TCP connections; supports authentication.

– HttpCachingProxy: Implemented using normal HTTP commands, it is useful only in the context of

HTTP requests

– FtpCachingProxy: Implemented using an FTP proxy, it is useful only in the context of FTP requests

• Define Cache settings (path and size)

• Define WMS search address, default is http://geopole.org/wms/search?search=\%1\&type=rss

• Define Timeout for network requests (ms) - deeingebundenfault is 60000

Excluding some URLs can be added to the text box below the proxy-settings (see

Figure_Network_Tab

) by press-

ing the [Add] button. After that double-click into the just created URL-field and enter the URL you would like to exclude from using the proxy. Obviously the button [Remove] removes the selected entry.

If you need more detailed information about the different proxy-settings, please refer to the manual of the underlying QT-library-documentation at http://doc.trolltech.com/4.5/qnetworkproxy.html#ProxyType-enum .

Tip: Using Proxies

Using proxies can sometimes be tricky. It is useful to ‘trial and error’ the above proxy types and check if they succeed in your case.

You can modify the options according to your needs. Some of the changes may require a restart of QGIS before they will be effective.

• settings are saved in a texfile: $HOME/.config/QuantumGIS/qgis.conf

• you can find your settings in: $HOME/Library/Preferences/org.qgis.qgis.plist

• settings are stored in the registry under:

\HKEY\CURRENT_USER\Software\QuantumGIS\qgis

8.4 Customization

The customization tool is a new development in QGIS 1.8.. It lets you (de)activate almost every element in the

QGIS user interface. This can get very useful if you have a lot of plug-ins installed that you never use and that are filling your screen.

QGIS Customization is divided into five groups. In Docks you find the dock windows. Dock windows are applications that can be started and used as a floating, top-level window or embedded to the QGIS main window as a docked widget (see also

Panels and Toolbars

). In

Menus you can hide entries in the Menu bar. In the

Status Bar features like the coordinate information can be daectivated. In toolbar icons of QGIS and in

Widgets

Toolbars you can (de)activate the you can (de)activate dialogs as well as their buttons.

With Switch to catching widgets in main application you can click on elements in QGIS you want to be hidden and find the corresponding entry in Customization (see

figure_customization

). You can also save your

various different setups for different use cases as well. Before your changes are applied, you need to restart QGIS.

46 Chapter 8. QGIS Configuration

QGIS User Guide, Release 1.8.0

Figure 8.3: The Customization dialog

8.4. Customization 47

QGIS User Guide, Release 1.8.0

48 Chapter 8. QGIS Configuration

CHAPTER

9

Working with Projections

QGIS allows users to define a global and project-wide CRS (Coordinate Reference System) for layers without a pre-defined CRS. It also allows the user to define custom coordinate reference systems and supports on-the-fly

(OTF) projection of vector and raster layers. All these features allow the user to display layers with different CRS and have them overlay properly.

9.1 Overview of Projection Support

QGIS has support for approximately 2,700 known CRS. Definitions for each of these CRS are stored in a SQLite database that is installed with QGIS. Normally you do not need to manipulate the database directly. In fact, doing so may cause projection support to fail. Custom CRS are stored in a user database. See Section

Custom Coordinate

Reference System

for information on managing your custom coordinate reference systems.

The CRS available in QGIS are based on those defined by the European Petroleum Search Group (EPSG) and the

Institut Geographique National de France (IGNF) and are largely abstracted from the spatial reference tables used in GDAL. EPSG identifiers are present in the database and can be used to specify a CRS in QGIS.

In order to use OTF projection, your data must contain information about its coordinate reference system or you have to define a global, layer or project-wide CRS. For PostGIS layers QGIS uses the spatial reference identifier that was specified when the layer was created. For data supported by OGR, QGIS relies on the presence of a recognized means of specifying the CRS. In the case of shapefiles, this means a file containing the Well Known

Text (WKT) specification of the CRS. This projection file has the same base name as the shapefile and a prj extension. For example, a shapefile named alaska.shp would have a corresponding projection file named alaska.prj

.

Whenever you select a new CRS, the used layer units will automatically be changed in the General tab of the

Project Properties dialog under the Edit (Gnome, OSX) or Settings (KDE, Windows) menu.

9.2 Specifying a Projection

QGIS starts each new project using the global default projection.The global default CRS is EPSG:4326 - WGS

84 (proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs) and comes predefined in QGIS. This default can be changed using the [Select...] button in the first section, used to defining the Default Coordinate

Reference System to use when starting new projects, as shown in

figure_projection_1

. This choice will be saved

for use in subsequent QGIS sessions.

When you use layers that do not have a CRS, you need to define how QGIS responds to these layers. This can be done globally or project-wide in the CRS tab under Edit → Options (Gnome, OSX) or Settings → Options

(KDE, Windows).

The options shown in

figure_projection_1

are:

49

QGIS User Guide, Release 1.8.0

Figure 9.1: CRS tab in the QGIS Options Dialog

Prompt for CRS

Use project CRS

• Use default CRS displayed below

If you want to define the coordinate reference system for a certain layer without CRS information, you can also do that in the General tab of the raster (see

General Tab

) and vector (see

General Tab

) properties dialog. If your

layer already has a CRS defined, it will be displayed as shown in

Vector Layer Properties Dialog

.

Tip: CRS in the Map Legend

Right-clicking on a layer in the Map Legend (Section

Map Legend

) provides two CRS short cuts. Set layer CRS

takes you directly to the Coordinate Reference System Selector dialog (see

figure_projection_2

). Set project CRS

from Layer redefines the project CRS using the layer’s CRS

9.3 Define On The Fly (OTF) Reprojection

QGIS supports OTF reprojection for both raster and vector data. However, OTF is not activated by default. To use

OTF projection, you must activate the Enable on the fly CRS transformation checkbox in the CRS tab of the

Project Properties dialog.

There are three ways to achieve this end:

1. Select Project Properties from the Edit (Gnome, OSX) or Settings (KDE, Windows) menu.

2. Click on the

CRS status icon in the lower right-hand corner of the statusbar.

3. Turn OTF on by default, by selecting the CRS tab of the Options dialog and selecting Enable ‘on the fly’ reprojection by default .

If you have already loaded a layer, and want to enable OTF projection, the best practice is to open the Coordinate

Reference System tab of the Project Properties dialog, select a CRS, and activate the Enable on the fly CRS

50 Chapter 9. Working with Projections

QGIS User Guide, Release 1.8.0

transformation checkbox. The to the CRS shown next to the icon.

CRS status icon will no longer be greyed-out and all layers will be OTF projected

Figure 9.2: Projection Dialog

The Coordinate Reference System tab of the Project Properties dialog contains five important components as shown in

Figure_projection_2

and described below.

1. Enable on the fly CRS transformation - this checkbox is used to enable or disable OTF projection. When off, each layer is drawn using the coordinates as read from the data source and the components described below are inactive.When on, the coordinates in each layer are projected to the coordinate reference system defined for the map canvas.

2. Coordinate Reference System - this is a list of all CRS supported by QGIS, including Geographic, Projected and Custom coordinate reference systems. To define a CRS, select it from the list by expanding the appropriate node and selecting the CRS. The active CRS is preselected.

3. Proj4 text - this is the CRS string used by the Proj4 projection engine. This text is read-only and provided for informational purposes.

4. Filter - if you know the EPSG code, the identifier or the name for a Coordinate Reference System, you can use the search feature to find it. Enter the EPSG code, the identifier or the name.

5. Recently used CRS - if you have certain CRS that you frequently use in your everyday GIS work, these will be displayed in the table at the bottom of the Projection Dialog. Click on one of these buttons to select the associated CRS.

Tip: Project Properties Dialog

If you open the Project Properties dialog from the Edit (Gnome, OSX) or Settings (KDE, Windows) menu, you must click on the Coordinate Reference System tab to view the CRS settings.

Opening the dialog from the to the front.

CRS status icon will automatically bring the Coordinate Reference System tab

9.3. Define On The Fly (OTF) Reprojection 51

QGIS User Guide, Release 1.8.0

9.4 Custom Coordinate Reference System

If QGIS does not provide the coordinate reference system you need, you can define a custom CRS. To define a CRS, select

Custom CRS from the Edit (Gnome, OSX) or Settings (KDE, Windows) 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.

Figure 9.3: Custom CRS Dialog

Defining a custom CRS in QGIS requires a good understanding of the Proj.4 projection library. To begin, refer to the Cartographic Projection Procedures for the UNIX Environment - A User’s Manual by Gerald I. Evenden, U.S.

Geological Survey Open-File Report 90-284, 1990 (available at ftp://ftp.remotesensing.org/proj/OF90-284.pdf

).

This manual describes the use of the proj.4 and related command line utilities. The cartographic parameters used with proj.4 are described in the user manual and are the same as those used by QGIS.

The Custom Coordinate Reference System Definition dialog requires only two parameters to define a user CRS:

1. a descriptive name and

2. the cartographic parameters in PROJ.4 format.

To create a new CRS, click the

New button and enter a descriptive name and the CRS parameters. After that you can save your CRS by clicking the

Save button.

Note that the Parameters must begin with a +proj=-block, to represent the new coordinate reference system.

You can test your CRS parameters to see if they give sane results by clicking on the [Calculate] button inside the Test block and pasting your CRS parameters into the Parameters field. Then enter known WGS 84 latitude and longitude values in North and East fields respectively. Click on [Calculate] and compare the results with the known values in your coordinate reference system.

52 Chapter 9. Working with Projections

CHAPTER

10

QGIS Browser

The QGIS Browser is a new panel in QGIS that lets you easily navigate in your database. You can have access to common vector files (e.g. ESRI shapefile or MapInfo files), databases (e.g.PostGIS or MSSQL Spatial) and WMS/WFS connections. You can also view your GRASS data (to get the data into QGIS see

GRASS GIS

Integration

).

Figure 10.1: Qgis browser as a standalone application to view metadata, preview and attributes

Use QGIS Browser to preview your data. The drag and drop function makes it easy to get your data into the Map view and the Map legend.

1. Activate QGIS Browser: Right-click on the tool bar and click Browser .

2. Drag the panel into the legend window.

3. Klick on the Browser tab.

4. Browse in your database and choose the shapefile folder from qgis_sample_data.

5. Press the Shift key and klick on airports.shp and alaska.shp .

6. Press the left mouse button then drag and drop the files into the map canvas.

53

QGIS User Guide, Release 1.8.0

7. Right-click on a layer and choose Set project CRS from layer. For more information see

Working with

Projections

.

8. Click on Zoom Full to make the layers visible.

It’s also possible to run QGIS Browser as a standalone application.

Start qgis browser

• Type in “qbrowser” at a command prompt.

• Start QGIS browser using the Start menu or desktop shortcut, or double click on a QGIS project file.

• QGIS browser is not available yet from your your Applications folder.

However it can easily be made available.

In Finder use Go → Go to map...

and use it to find the folder

/Applications/QGIS.app/Contents/MacOS/bin

.

Use the key combination option command and drag qbrowser.app while holding down the left mouse button to the Applications folder.

This will create a link that you can use to start QGIS browser.

In

figure_browser_standalone_metadata

you can see the enhanced functionality of Qgis browser. The Param tab provides the details of your connection based datasets like PostGIS or MSSQL Spatial. The Metadata tab contains general information about the file (see

Metadata Tab

). With the Preview tab you can have a look at your

files without importing them into your QGIS project. It’s also possible to preview the attributes of your files in the

Attributes tab.

54 Chapter 10. QGIS Browser

CHAPTER

11

Working with Vector Data

11.1 Supported Data Formats

QGIS uses the OGR library to read and write vector data formats (GRASS vector and PostgreSQL support is supplied by native QGIS data provider plugins),including ESRI Shapefiles, MapInfo and Microstation file formats;

PostGIS, SpatiaLite, Oracle Spatial databases and many more. The vector data can also be loaded in read mode from zip and gzip archives into QGIS. At the date of this document, 69 vector formats are supported by the

OGR library (see OGR-SOFTWARE-SUITE

Literature and Web References

). The complete list is available at

http://www.gdal.org/ogr/ogr_formats.html

.

Note: Not all of the listed formats may work in QGIS for various reasons. For example, some require external commercial libraries or the GDAL/OGR installation of your OS was not build to support the format you want to use. Only those formats that have been well tested will appear in the list of file types when loading a vector into

QGIS. Other untested formats can be loaded by selecting *.*.

Working with GRASS vector data is described in Section

GRASS GIS Integration

.

This section describes how to work with several common formats: ESRI Shapefiles, PostGIS layers and SpatiaLite layers. Many of the features available in QGIS work the same, regardless of the vector data source. This is by design and includes the identify, select, labeling and attributes functions.

11.1.1 ESRI Shapefiles

The standard vector file format used in QGIS is the ESRI Shapefile. Support is provided by the OGR Simple

Feature Library ( http://www.gdal.org/ogr/ ).

A shapefile actually consists of several files. The following three are required:

1. .shp file containing the feature geometries.

2. .dbf file containing the attributes in dBase format.

3. .shx index file.

Shapefiles also can include a file with a .prj suffix, which contains the projection information. While it is very useful to have a projection file, it is not mandatory. A shapefile dataset can contain additional files. For further details see the ESRI technical specification at: http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf

.

Loading a Shapefile

To load a shapefile, start QGIS and click on the

Add Vector Layer toolbar button or simply type

55

QGIS User Guide, Release 1.8.0

Ctrl+Shift+V

. This will bring up a new window (see

figure_vector_1

).

Figure 11.1: Add Vector Layer Dialog

From the available options check File . Click on button [Browse]. That will bring up a standard open file dialog

(see

figure_vector_2

) which allows you to navigate the file system and load a shapefile or other supported data

source. The selection box Filter allows you to preselect some OGR supported file formats.

You can also select the Encoding type for the shapefile if desired.

Figure 11.2: Open an OGR Supported Vector Layer Dialog

Selecting a shapefile from the list and clicking [Open] loads it into QGIS.

Figure_vector_3

shows QGIS after loading the alaska.shp file.

Tip: Layer Colors

When you add a layer to the map, it is assigned a random color. When adding more than one layer at a time, different colors are assigned to each layer.

Once loaded, you can zoom around the shapefile using the map navigation tools. To change the style of a layer, open the Layer Properties dialog by double clicking on the layer name or by right-clicking on the name in the legend and choosing Properties from the popup menu. See Section

Style Tab

for more information on setting symbology of vector layers.

Tip: Load layer and project from mounted external drives on OS X

On OS X, portable drives that are mounted besides the primary hard drive do not show up under File → Open

Project as expected. We are working on a more OSX-native open/save dialog to fix this. As a workaround you can type ‘/Volumes’ in the File name box and press return. Then you can navigate to external drives and network mounts.

56 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Figure 11.3: QGIS with Shapefile of Alaska loaded

Improving Performance Shape

To improve the performance of drawing a shapefile, you can create a spatial index. A spatial index will improve the speed of both zooming and panning. Spatial indexes used by QGIS have a .qix extension.

Use these steps to create the index:

• Load a shapefile.

• Open the Layer Properties dialog by double-clicking on the shapefile name in the legend or by right-clicking and choosing Properties from the popup menu.

• In the tab General click the [Create Spatial Index] button.

Problem loading a shape .prj file

If you load a shapefile with .prj file and QGIS is not able to read the coordinate reference system from that file, you have to define the proper projection manually within the General tab of the Layer Properties dialog of the layer. This is due to the fact, that .prj files often do not provide the complete projection parameters, as used in

QGIS and listed in the CRS dialog.

For that reason, if you create a new shapefile with QGIS, two different projection files are created. A .prj

file with limited projection parameters, compatible with ESRI software, and a .qpj file, providing the complete parameters of the used CRS. Whenever QGIS finds a .qpj file, it will be used instead of the .prj.

11.1.2 Loading a MapInfo Layer

To load a MapInfo layer, click on the file type filter Filter

Add Vector Layer toolbar button or type Ctrl+Shift+V, change the

: to ‘Mapinfo File [OGR]’ and select the MapInfo layer you want to load.

11.1. Supported Data Formats 57

QGIS User Guide, Release 1.8.0

11.1.3 Loading an ArcInfo Binary Coverage

To load an ArcInfo binary coverage, click on the

Add Vector Layer toolbar button or press Ctrl+Shift+V to open the Add Vector Layer dialog. Select Directory . Change to Filter

Navigate to the directory that contains the coverage files and select it.

to ‘Arc/Info Binary Coverage’.

Similarly, you can load directory based vector files in the UK National Transfer Format as well as the raw TIGER

Format of the US Census Bureau.

11.1.4 PostGIS Layers

PostGIS layers are stored in a PostgreSQL database. The advantages of PostGIS are the spatial indexing, filtering and query capabilities it provides. Using PostGIS, vector functions such as select and identify work more accurately than with OGR layers in QGIS.

Creating a stored Connection

The first time you use a PostGIS data source, you must create a connection to the PostgreSQL database that contains the data. Begin by clicking on the

Add PostGIS Layer toolbar button, selecting the Add PostGIS

Layer...

option from the Layer menu or typing Ctrl+Shift+D. You can also open the Add Vector Layer dialog and select Database . The Add PostGIS Table(s) dialog will be displayed. To access the connection manager, click on the [New] button to display the Create a New PostGIS Connection dialog. The parameters required for a connection are:

• Name: A name for this connection. Can be the same as Database

• Service: Service parameter to be used alternatively to hostname/port (and potentially database). This can be defined in pg_service.conf

• Host: Name of the database host. This must be a resolvable host name the same as would be used to open a telnet connection or ping the host. If the database is on the same computer as QGIS, simply enter ‘localhost’ here.

• Port: Port number the PostgreSQL database server listens on. The default port is 5432.

• Database: Name of the database.

• SSL mode: How the SSL connection will be negotiated with the server. Note that massive speedups in

PostGIS layer rendering can be achieved by disabling SSL in the connection editor. Following options are available:

– disable: only try an unencrypted SSL connection

– allow: try a non-SSL connection, if that fails, try an SSL connection

– prefer (the default): try an SSL connection, if that fails, try a non-SSL connection;

– require: only try an SSL connection.

• Username: User name used to login to the database.

• Password: Password used with Username to connect to the database.

Optional you can activate following checkboxes:

Save Username

Save Password

Only look in the geometry_columns table

Only look in the ‘public’ schema

58 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

• Also list tables with no geometry

• Use estimated table metadata

Once all parameters and options are set, you can test the connection by clicking on the [Test Connect] button.

Tip: QGIS User Settings and Security

Depending on your computing environment, storing passwords in your QGIS settings may be a security risk. Your customized settings for QGIS are stored based on the operating system:

• , the settings are stored in your home directory in .qgis/.

• , the settings are stored in the registry.

Loading a PostGIS Layer

Once you have one or more connections defined, you can load layers from the PostgreSQL database. Of course this requires having data in PostgreSQL. See Section

Importing Data into PostgreSQL

for a discussion on importing data into the database.

To load a layer from PostGIS, perform the following steps:

• If the Add PostGIS layers dialog is not already open, click on the

• Choose the connection from the drop-down list and click [Connect].

Add PostGIS Layer toolbar button.

• Select or unselect Also list tables with no geometry

• Optionally use some Search Options to define which features to load from the layer or use the [Build query] button to start the Query builder dialog.

• Find the layer(s) you wish to add in the list of available layers.

• Select it by clicking on it. You can select multiple layers by holding down the Shift key while clicking.

See Section

Query Builder

for information on using the PostgreSQL Query Builder to further define the layer.

• Click on the [Add] button to add the layer to the map.

Tip: PostGIS Layers

Normally a PostGIS layer is defined by an entry in the geometry_columns table. From version 0.9.0 on, QGIS can load layers that do not have an entry in the geometry_columns table. This includes both tables and views.

Defining a spatial view provides a powerful means to visualize your data. Refer to your PostgreSQL manual for information on creating views.

Some details about PostgreSQL layers

This section contains some details on how QGIS accesses PostgreSQL layers. Most of the time QGIS should simply provide you with a list of database tables that can be loaded, and load them on request. However, if you have trouble loading a PostgreSQL table into QGIS, the information below may help you understand any QGIS messages and give you direction on changing the PostgreSQL table or view definition to allow QGIS to load it.

QGIS requires that PostgreSQL layers contain a column that can be used as a unique key for the layer. For tables this usually means that the table needs a primary key, or a column with a unique constraint on it. In QGIS, this column needs to be of type int4 (an integer of size 4 bytes). Alternatively the ctid column can be used as primary key. If a table lacks these items, the oid column will be used instead. Performance will be improved if the column is indexed (note that primary keys are automatically indexed in PostgreSQL).

11.1. Supported Data Formats 59

QGIS User Guide, Release 1.8.0

If the PostgreSQL layer is a view, the same requirement exists, but views do not have primary keys or columns with unique constraints on them. In this case QGIS will try to find a column in the view that is derived from a suitable table column. It does this by parsing the view definition SQL. However there are several aspects of SQL that QGIS ignores these include the use of table aliases and columns that are generated by SQL functions.

If a suitable column cannot be found, QGIS will not load the layer. If this occurs, the solution is to alter the view so that it does include a suitable column (a type of int4 and either a primary key or with a unique constraint, preferably indexed).

11.1.5 Importing Data into PostgreSQL

Data can be imported into PostgreSQL/PostGIS using several tools, such as the SPIT plugin, or the command line tools shp2pgsql or ogr2ogr.

SPIT Plugin

QGIS comes with a core plugin named

SPIT

(Shapefile to PostGIS Import Tool). SPIT can be used to load multiple shapefiles at one time and includes support for schemas. See Section

SPIT Plugin

for more information.

shp2pgsql

PostGIS includes a utility called shp2pgsql that can be used to import shapefiles into a PostGIS enabled database.

For example, to import a shapefile named lakes.shp into a PostgreSQL database named gis_data, use the following command: shp2pgsql -s 2964 lakes.shp lakes_new | psql gis_data

This creates a new layer named lakes_new in the gis_data database. The new layer will have a spatial reference identifier (SRID) of 2964. See Section

Working with Projections

for more information on spatial reference systems and projections.

Tip: Exporting datasets from PostGIS

Like the import-tool shp2pgsql there is also a tool to export PostGIS-datasets as shapefiles: pgsql2shp. This is shipped within your PostGIS distribution.

ogr2ogr

Beside shp2pgsql and SPIT there is another tool for feeding geodata in PostGIS: ogr2ogr. This is part of your

GDAL installation.

To import a shapefile into PostGIS, do the following: ogr2ogr -f "PostgreSQL" PG:"dbname=postgis host=myhost.de user=postgres \ password=topsecret" alaska.shp

This will import the shapefile alaska.shp into the PostGIS-database postgis using the user postgres with the password topsecret on host server myhost.de.

Note that OGR must be built with PostgreSQL to support PostGIS. You can see this by typing ogrinfo --formats | grep -i post

If you like to use PostgreSQL’s COPY -command instead of the default INSERT INTO method you can export the following environment-variable (at least available on and ):

60 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

export PG_USE_COPY=YES ogr2ogr does not create spatial indexes like shp2pgsl does. You need to create them manually using the normal SQL-command CREATE INDEX afterwards as an extra step (as described in the next section

Improving

Performance

).

Improving Performance

Retrieving features from a PostgreSQL database can be time consuming, especially over a network. You can improve the drawing performance of PostgreSQL layers by ensuring that a PostGIS spatial index exists on each layer in the database. PostGIS supports creation of a GiST (Generalized Search Tree) index to speed up spatial searches of the data (GiST index information is taken from the PostGIS documentation available at http://postgis.refractions.net

).

The syntax for creating a GiST index is:

CREATE INDEX [indexname] ON [tablename]

USING GIST ( [geometryfield] GIST_GEOMETRY_OPS );

Note that for large tables, creating the index can take a long time. Once the index is created, you should perform a

VACUUM ANALYZE

. See the PostGIS documentation (POSTGIS-PROJECT

Literature and Web References

) for

more information.

The following is an example of creating a GiST index: [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;

VACUUM gis_data=# \q [email protected]:~/current$

11.1.6 Vector layers crossing 180° longitude

Many GIS packages don’t wrap vector maps, with a geographic reference system (lat/lon), crossing the 180 degrees longitude line ( http://postgis.refractions.net/documentation/manual-1.4/ST_Shift_Longitude.html

). As result, if we open such map in QGIS, we will see two far, distinct locations, that should show near each other. In

Figure_vector_4

the tiny point on the far left of the map canvas (Chatham Islands), should be within the grid, right of New Zealand main islands.

Figure 11.4: Map in lat/lon crossing the 180° longitude line

A workaround is to transform the longitude values using PostGIS and the ST_Shift_Longitude function This function reads every point/vertex in every component of every feature in a geometry, and if the longitude coordi-

11.1. Supported Data Formats 61

QGIS User Guide, Release 1.8.0

nate is < 0° adds 360° to it. The result would be a 0° - 360° version of the data to be plotted in a 180° centric map.

Figure 11.5: Crossing 180° longitude applying the ST_Shift_Longitude function

Usage

• Import data to PostGIS (

Importing Data into PostgreSQL

) using for example the PostGIS Manager plugin

or the SPIT plugin

• Use the PostGIS command line interface to issue the following command (this is an example where “TA-

BLE” is the actual name of your PostGIS table) gis_data=# update TABLE set the_geom=ST_Shift_Longitude(the_geom);

• If everything went right you should receive a confirmation about the number of features that were updated,

then you’ll be able to load the map and see the difference (

Figure_vector_5

)

11.1.7 SpatiaLite Layers

The first time you load data from a SpatiaLite database, begin by clicking on the

Add SpatiaLite Layer toolbar button or by selecting the Add SpatiaLite Layer...

option from the Layer menu or by typing Ctrl+Shift+L.

This will bring up a window, which will allow you to either connect to a SpatiaLite database already known to

QGIS, which you can choose from the dropdown menu or to define a new connection to a new database. To define a new connection, click on [New] and use the file browser to point to your SpatiaLite database, which is a file with a .sqlite extension.

If you want to save a vector layer to SpatiaLite format you can do this by right clicking the layer in the legend.

Then click on Save as.., define the name of the output file, select ‘SpatiaLite’ as format and the CRS. Also you can select ‘SQLite’ as format, and then add SPATIALITE=YES in the OGR data source creation option field. This tells OGR to create a SpatiaLite database. See also http://www.gdal.org/ogr/drv_sqlite.html

.

QGIS also supports editable views in SpatiaLite.

Creating a new SpatiaLite layer

If you want to create a new SpatiaLite layer, please refer to section

Creating a new SpatiaLite layer

.

62 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Tip: SpatiaLite data management Plugins

For SpatiaLite data management you can also use several Python plugins: QSpatiaLite, SpatiaLite Manager or DB

Manager (core plugin, recommended). They can be downloaded and installed with the Plugin Installer.

11.1.8 MSSQL Spatial Layers

QGIS also provides native MS SQL 2008 support. The

Add MSSQL Spatial Layer is part of the new toolbar button or available in the MS SQL node in the QBrowser tree, providing drag and drop import support.

11.2 The Vector Properties Dialog

The Layer Properties dialog for a vector layer provides information about the layer, symbology settings and labeling options. If your vector layer has been loaded from a PostgreSQL/PostGIS datastore, you can also alter the underlying SQL for the layer by invoking the Query Builder dialog on the General tab. To access the Layer

Properties dialog, double-click on a layer in the legend or right-click on the layer and select Properties from the popup menu.

Figure 11.6: Vector Layer Properties Dialog

11.2.1 Style Tab

Since QGIS 1.4.0 a new symbology was integrated in parallel to improve and finally replace the old symbology. QGIS 1.8 now uses the new symbology as default, which provides a variety of improvements and new features.

A description of the old symbology is available in section

Old Symbology

.

There are three types of symbols: marker symbols (for points), line symbols (for lines) and fill and outline symbols

(for polygons). Symbols can consist of one or more symbol layers. It is possible to define the color of a symbol and this color is then defined for all symbol layers. Some layers may have the color locked - for those the color

11.2. The Vector Properties Dialog 63

QGIS User Guide, Release 1.8.0

can not be altered. This is useful when you define the color of a multilayer symbol. Similarly, it is possible to define the width for line symbols, as well as size and rotation for marker symbols.

Available symbol layer types

• Point layers

– Font marker: Rendering with a font.

– Simple marker: Rendering with a hardcoded marker.

– SVG marker: Rendering with a SVG picture.

– Ellipse marker: Rendering with ellipse shapes derived from attributes.

– Vector field marker: Rendering with vector fields derived from attributes.

• Line layers

– Line decoration: Add a line decoration, e.g an arrow to indicate line direction.

– Marker line: A line rendered by repeating a marker symbol.

– Simple line: Usual rendering of a line (with specified width color and pen style).

• Polygon layers

– Centroid fill: Fill a polygon centroid with a hardcoded marker.

– SVG fill: Fill a polygon with a SVG symbol.

– Simple fill: Usual rendering of a polygon (with defined fill color, fill pattern and outline).

– Line pattern fill: Fill a polygon with a line pattern.

– Point pattern fill: Fill a polygon with a point pattern.

– Outline: Line decoration: Add a line decoration, e.g an arrow to indicate line direction.

– Outline: Marker line: Use a hardcoded marker as area outline.

– Outline: Simple line: Define width, color and pen style as area outline.

Color ramps

Color ramps are used to define a range of colors that can be used during the creation of renderers. The symbol’s color will be set from the color ramp.

There are three types of color ramps:

• Gradient: Linear gradient from one color to some other.

• Random: Randomly generated colors from a specified area of color space.

• ColorBrewer: Create color area from a color shema and a defined number of color classes.

Color ramps can be defined in the Color ramp tab of the Style Manager by clicking the [Add] button and then choosing a color ramp type (see section

vector_style_manager

).

Styles

A style groups a set of various symbols and color ramps. You can define your prefered or frequently used symbols, and can use it without having to recreate it everytime. Style items (symbols and color ramps) have always a name by which they can be queried from the style. There is at least one default style in QGIS (modifiable) and the user can add further styles. In the lower part of the Style tab there are four buttons for managing styles: Use [Restore

Default Style] to get back to your default settings, [Save As Default] to save your style as default, [Load Style...] to get to your own styles and [Save Style] to save your own styles. Layer styles can also be transferred from one layer to another layer. Activate a layer and choose Layer →

Copy style and switch to another layer. Then choose Layer →

Renderers

Paste style .

64 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

The renderer is responsible for drawing a feature together with the correct symbol. There are four types of renderers: single symbol, categorized (called unique color in the old symbology), graduated and rule-based. There is no continuous color renderer, because it is in fact only a special case of the graduated renderer. The categorized and graduated renderer can be created by specifying a symbol and a color ramp - they will set the colors for symbols appropriately. Working with the New Generation Symbology

In the Style tab you can choose one of the five renderers: single symbol, categorized, graduated, rule-based and point displacement. For each data type (points, lines and polygons) vector symbol layer types are available (see

vector_symbol_types

). Depending on the chosen renderer, the symbology Depending on the chosen renderer,

the Style tab provides different following sections. The new generation symbology dialog also provides a [Style

Manager] button which gives access to the Style Manager (see Section

Style Manager

). The Style Manager

allows you to edit and remove existing symbols and add new ones.

Tip: Select and change multiple symbols

The New Generation Symbology allows to select multiple symbols and right click to change color, transparency, size, or width of selected entries.

Single Symbol Renderer

The Single Symbol Renderer is used to render all features of the layer using a single user-defined symbol. The properties, that can be adjusted in the Style tab, depend partially on the type of the layer, but all types share the following structure. In the top left part of the tab, there is a preview of the current symbol to be rendered. In the bottom part of the tab, there is a list of symbols already defined for the current style, prepared to be used via selecting them from the list. The current symbol can be modified using the [Change] button below the preview, which opens a Symbol Properties dialog, or the [Change] button right of the preview, which opens an ordinary

Color dialog.

Figure 11.7: Single symbol line properties

In the Style tab you can apart from a general layer transparency also define to use millimeter or map units for the size scale. In the [Advanced] button next to the [Save as style] button you can use data-defined size scale and rotation. Here the Symbol levels → menu allows to enable and define the order in which the symbol layers are rendered (if the symbol consists of more than one layer).

After having done any needed changes, the symbol can be added to the list of current style symbols (using the

[Save as style] button) and then easily be used in the future. Furthermore you can use the [Save Style] button to save the symbol as a QGIS layer style file (.qml) or SLD file(.sld). Currently in version 1.8 SLDs can be exported from any type of renderer: single symbol, categorized, graduated or rule-based, but when importing an SLD, either a single symbol or rule-based renderer is created. That means that categorized or graduated styles are converted to rule-based. If you want to preserve those renderers, you have to stick to the QML format. On the other hand, it could be very handy sometimes to have this easy way of converting styles to rule-based.

Categorized Renderer

11.2. The Vector Properties Dialog 65

QGIS User Guide, Release 1.8.0

The Categorized Renderer is used to render all features from a layer, using a single user-defined symbol, which color reflects the value of a selected feature’s attribute. The Style tab allows you to select:

• The attribute (using the Column listbox)

• The symbol (using the Symbol dialog)

• The colors (using the Color Ramp listbox)

The [Advanced] button in the lower right corner of the dialog allows to set the fields containing rotation and size scale information. For convenience, the list in the bottom part of the tab lists the values of all currently selected attributes together, including the symbols that will be rendered.

The example in

figure_symbology_2

shows the category rendering dialog used for the rivers layer of the QGIS sample dataset.

Figure 11.8: Categorized Symbolizing options

You can create a custom color ramp choosing New color ramp... from the Color ramp dropdown menu. A dialog will prompt for the ramp type: Gradient, Random, ColorBrewer, then each one has options for number of steps and/or multiple stops in the color ramp. See

figure_symbology_3

for an example of custom color ramp.

Figure 11.9: Example of custom gradient color ramp with multiple stops

Graduated Renderer

The Graduated Renderer is used to render all the features from a layer, using a single user-defined symbol, whose color reflects the classification of a selected feature’s attribute to a class.

Like Categorized Renderer, it allows to define rotation and size scale from specified columns.

Analogue to the categorized rendered, the Style tab allows you to select:

66 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Figure 11.10: Graduated Symbolizing options

• The attribute (using the Column listbox)

• The symbol (using the Symbol Properties button)

• The colors (using the Color Ramp list)

Additionally, you can specify the number of classes and also the mode how to classify features inside the classes

(using the Mode list). The available modes are:

• Equal Interval

• Quantile

• Natural Breaks (Jenks)

• Standard Deviation

• Pretty Breaks

The listbox in the bottom part of the Style tab lists the classes together with their ranges, labels and symbols that will be rendered.

The example in

figure_symbology_4

shows the graduated rendering dialog for the rivers layer of the QGIS sample dataset.

Rule-based rendering

The rule-based renderer is used to render all the features from a layer, using rule based symbols, whose color reflects the classification of a selected feature’s attribute to a class. The rules are based on SQL statements. The dialog allows rule grouping by filter or scale and you can decide if you want to enable symbol levels or use only first matched rule.

The example in

figure_symbology_5

shows the rule-based rendering dialog for the rivers layer of the QGIS sample dataset.

To create a rule, activate an existing row by clicking on it or click on ‘+’ and click on the new rule. Then press the

[Edit] button. In the Rule properties dialog you can define a label for the rule. Press the button to open the

Expression builder. In the Function List, click on Fields and Values to view all attributes of the attribute table to be searched. To add an attribute to the Field calculator Expression field, double click its name in the Fields and

Values list. Generally you can use the various fields, values and functions to construct the calculation expression or you can just type it into the box (see

Field Calculator

).

Point displacement

11.2. The Vector Properties Dialog 67

QGIS User Guide, Release 1.8.0

Figure 11.11: Rule-based Symbolizing options

The point displacement renderer offers to visualize all features of a point layer, even if they have the same location.

To do this, the symbols of the points are placed on a displacement circle around a center symbol.

Figure 11.12: Point displacement dialog

Symbol Properties

The symbol properties dialog allows the user to specify different properties of the symbol to be rendered. In the bottom left part of the dialog, you find a preview of the current symbol as it will be displayed in the map canvas.

Above the preview is the list of symbol layers. To start the Symbol properties dialog, click the [ Change...] button in the Style tab of the Layer Properties dialog.

The buttons allow adding or removing layers, changing the position of layers, or locking layers for color changes.

In the right part of the dialog, there are shown the settings applicable to the single symbol layer selected in the symbol layer list. The most important is the Symbol Layer Type combobox, which allows you to choose the layer type. The available options depend on the layer type (Point, Line, Polygon). The symbol layer type options are described in section

vector_symbol_types

. You can also change the symbol layer properties in the

68 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

right part of the dialog. For example if you have chosen an SVG marker for a point layer it is now possible to change its color using Color button.

Figure 11.13: Line composed from three simple lines

11.2.2 Style Manager

The Style Manager is a small helper application, that lists symbols and color ramps available in a style. It also allows you to add and/or remove items. To launch the Style Manager, click on Settings → Style Manager in the main menu. Alternatively, you can access it via the Style tab.

Figure 11.14: Style Manager to manage symbols and color ramps

11.2.3 Old Symbology

Note: QGIS 1.8. still supports the usage of the old symbology, although it is recommended to switch to the new symbology, described in section

vector_new_symbology

, because the old symbology will be removed in one of

the next releases.

11.2. The Vector Properties Dialog 69

QGIS User Guide, Release 1.8.0

If you want or need to switch back to the old symbology you can click on the [Old symbology] button in the Style tab of the Layer Properties dialog.

You can also make the old symobolgy the default, deactivating in the Rendering tab under Settings → Options .

Use new generation symbology for rendering

The old QGIS symbology supports the following renderers:

• Single symbol - a single style is applied to every object in the layer.

• Graduated symbol - objects within the layer are displayed with different symbols classified by the values of a particular field.

• Continuous color - objects within the layer are displayed with a spread of colours classified by the numerical values within a specified field.

• Unique value - objects are classified by the unique values within a specified field with each value having a different symbol.

To change the symbology for a layer, simply double click on its legend entry and the vector Layer Properties dialog will be shown.

Style Options

Within this dialog you can style your vector layer. Depending on the selected rendering option you have the possibility to also classify your map features.

At least the following styling options apply for nearly all renderers:

• Fill style - Style for filling. Beside the given brushes you can select Fill style: ‘Texture’ and click the button for selecting your own texture file. Currently the fileformats *.jpeg, *.xpm, and *.png

are supported.

• Fill color - fill-color of your features.

• Outline options

– Outline style - Pen-style for your outline of your feature. You can also set this to ‘no Pen’.

– Outline color - color of the ouline of your feature.

– Outline width - width of your features.

Once you have styled your layer you also could save your layer-style to a separate file (ending with *.qml). To do this, use the button [Save Style...]. No need to say that [Load Style...] loads your saved layer-style-file.

If you wish to always use a particular style whenever the layer is loaded, use the [Save As Default] button to make your style the default. Also, if you make changes to the style that you are not happy with, use the [Restore

Default Style] button to revert to your default style.

Vector transparency

QGIS allows to set a transparency for every vector layer.

This can be done with the slider Transparency inside the Style tab. This is very useful for overlaying several vector layers.

11.2.4 Labels Tab

As for the symbology QGIS 1.8 currently provides an old and a new labeling engine in parallel. The Labels tab still contains the old labeling. The new labeling is implemented as a core application and will replace the features of the old labels tab in one of the next versions.

We recommend to switch to the new labeling, described in section

New Labeling

.

70 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

The old labeling in the Labels tab allows you to enable labeling features and control a number of options related to fonts, placement, style, alignment and buffering. We will illustrate this by labeling the lakes shapefile of the

QGIS sample dataset:

1. Load the Shapefile alaska.shp and GML file lakes.gml in QGIS

2. Zoom in a bit to your favorite area with some lake

3. Make the lakes layer active

4. Open the Layer Properties dialog

5. Click on the Labels tab

6. Check the Display labels checkbox to enable labeling

7. Choose the field to label with. We will use Field containing label

NAMES

8. Enter a default for lakes that have no name. The default label will be used each time QGIS encounters a lake with no value in the NAMES field.

9. If you have labels extending over several lines, check Multiline labels?

. QGIS will check for a true line return in your label field and insert the line breaks accordingly. A true line return is a single character \n,

(not two separate characters, like a backlash \ followed by the character n). To insert line returns in an attribute field configure the edit widget to be text edit (not line edit).

10. Click [Apply].

Now we have labels. How do they look? They are probably too big and poorly placed in relation to the marker symbol for the lakes.

Select the Font entry and use the [Font] and [Color] buttons to set the font and color. You can also change the angle and the placement of the text-label.

To change the position of the text relative to the feature:

1. Beneath the Basic label options change the placement by selecting one of the radio buttons in the Placement group. To fix our labels, choose the Right radio button.

2. the Font size units allows you to select between Points or Map units .

3. Click [Apply] to see your changes without closing the dialog.

Things are looking better, but the labels are still too close to the marker. To fix this we can use the options on the

Offset entry which is on the bottom of the menu. Here we can add offsets for the X and Y directions. Adding an

X offset of 5 will move our labels off the marker and make them more readable. Of course if your marker symbol or font is larger, more of an offset will be required.

The last adjustment we’ll make is to Buffer the labels. This just means putting a backdrop around them to make them stand out better. To buffer the lakes labels:

1. Click the

Buffer Labels checkbox to enable buffering.

2. Choose a size for the buffer using the spin box.

3. Choose a color by clicking on [Color] and choosing your favorite from the color selector. You can also set some transparency for the buffer if you prefer.

4. Click [Apply] to see if you like the changes.

If you aren’t happy with the results, tweak the settings and then test again by clicking [Apply].

A buffer of 1 points seems to give a good result. Notice you can also specify the buffer size in map units if that works out better for you.

The advanced entries inside the Label tab allow you control the appearance of the labels using attributes stored in the layer. The entries beginning with Data defined allow you to set all the parameters for the labels using fields in the layer.

Note that the Label tab provides a preview-box where your selected label is shown.

11.2. The Vector Properties Dialog 71

QGIS User Guide, Release 1.8.0

11.2.5 New Labeling

The new

Labeling core application provides smart labeling for vector point, line and polygon layers and only requires a few parameters. This new application will replace the current QGIS labeling, described in section

Labels Tab

and also supports on-the-fly transformated layers.

Using new labeling

1. Start QGIS and load a vector point, line or polygon layer.

2. Activate the layer in the legend and click on the

Labeling point layers

Labeling icon in the QGIS toolbar menu.

First step is to activate the Label this layer checkbox and select an attribute column to use for labeling. Click if you want to define labels based on expressions. After that you can define the text style and the scale-based visibility in the Label settings tab (see

Figure_labels_1

). Choose the Advanced tab for the label placement and the labeling priority. You can define if every part of a multipart feature is to be labeled here. With the wrap label on character function you can define a character for a line break in the labels. The Data defined settings tab provides you with the attribute-based definition of Font properties, Buffer properties and Position.

Figure 11.15: Smart labeling of vector point layers

Labeling line layers

First step is to activate the Label this layer checkbox in the Label settings tab and select an attribute column to use for labeling. Here you can also define labels based on expressions. After that you can define the text style and the scale-based visibility. Further labeling options are available through the Advanced tab. You can define the label placement and label distance, a line orientation dependend position and the labeling priority here. Furthermore you can define if every part of a multipart line is to be labeled, if lines shall be merged to avoid duplicate labels and if a direction symbol is added (see

Figure_labels_2

). It is also possible to supress labeling of features and wrap lables on characters. Use Data defined settings for attribute-based or database-connection-based settings.

Labeling polygon layers

First step is to activate the Label this layer checkbox and select an attribute column to use for labeling. Here you can also define labels based on expressions. In Label settings define the text style and the scale-based visibility

(see

Figure_labels_3

). Use the Advanced tab for label placement, label distance and labeling priority. Define if every part of a multipart feature is to be labeled, suppress labeling of features and wrap labels on characters here.

Use Data defined settings for attribute-based or database-connection-based settings.

Change engine settings

Additionally you can click the [Engine settings] button and select the search method, used to find the best label placement. Available is Chain, Popmusic Tabu, Popmusic Chain, Popmusic Tabu Chain and FALP.

Furthermore the number of candidates can be defined for point, line and polygon features, and you can define whether to show all labels (including colliding labels) and label candidates for debugging.

72 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Figure 11.16: Smart labeling of vector line layers

Figure 11.17: Smart labeling of vector polygon layers

Figure 11.18: Dialog to change label engine settings

11.2. The Vector Properties Dialog 73

QGIS User Guide, Release 1.8.0

Keywords to use in attribute columns for labeling

There is a list of supported key words, that can be used for the placement of labels in defined attribute columns.

• For horizontal alignment: left, center, right

• For vertical alignment: bottom, base, half, top

• Colors can be specified in svg notation, e.g. #ff0000

• for bold, underlined, strikeout and italic: 0 = false 1 = true

A combination of key words in one column also works, e.g.: base right or bottom left.

11.2.6 Fields Tab

and

Within the Fields tab the field attributes of the selected dataset can be manipulated. The buttons

Delete Column can be used, when the dataset is

Editing mode

.

New Column

At the moment only columns from PostGIS layers can be removed and added. The OGR library supports to add and remove columns, if you have a GDAL version >= 1.9 installed.

Edit Widget

Figure 11.19: Dialog to select an edit widget for an attribute column

Within the Fields tab you also find an edit widget column. This column can be used to define values or a range of values that are allowed to be added to the specific attribute table column. If you click on the [edit widget] button, a dialog opens, where you can define different widgets. These widgets are:

• Line edit: an edit field which allows to enter simple text (or restrict to numbers for numeric attributes).

• Classification: Displays a combo box with the values used for classification, if you have chosen ‘unique value’ as legend type in the Style tab of the properties dialog.

• Range: Allows to set numeric values from a specific range. The edit widget can be either a slider or a spin box.

• Unique values: The user can select one of the values already used in the attribute table. If editable is activated, a line edit is shown with autocompletion support, otherwise a combo box is used.

• File name: Simplifies the selection by adding a file chooser dialog.

74 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

• Value map: a combo box with predefined items. The value is stored in the attribute, the description is shown in the combo box. You can define values manually or load them from a layer or a CSV file.

• Enumeration: Opens a combo box with values that can be used within the columns type. This is currently only supported by the postgres provider.

• Immutable: The immutable attribute column is read-only. The user is not able to modify the content.

• Hidden: A hidden attribute column is invisible. The user is not able to see its content.

• Checkbox: Displays a checkbox and you can define what attribute is added to the column when the checkbox is activated or not.

• Text edit: This opens a text edit field that allows multiple lines to be used.

• Calendar: Opens a calendar widget to enter a date. Column type must be text.

• Value Relation: Offers values from a related table in a combobox. You can select layer, key column and value column.

• UUID Generator: Generates a read-only UUID (Universally Unique Identifiers) field, if empty.

11.2.7 General Tab

The General tab is essentially like that of the raster dialog. There are several options available:

• Change the display name of the layer

• Set a display field to be used for the Identify Results dialog

• Define a certain Edit User Interface for the vector layer written with the Qt Creator IDE and tools at http://qt.digia.com/Product/Developer-Tools/

• Create a Spatial Index (only for OGR supported formats)

• Add an Init function for the layer. They will overwrite existing QGIS widget initializations, if applied

• Update Extents information for a layer

• View or change the projection of the specific vector layer, clicking on Specify CRS

Furthermore you can activate and set Use scale dependent rendering , define provider specific options (e.g.

encoding) and with the [Query Builder] button you can create a subset of the features in the layer that will be visualized (also refer to section

Selection

).

11.2.8 Metadata Tab

The Metadata tab contains general information about the layer, including specifics about the type and location, number of features, feature type, and the editing capabilities. The Extents section, providing layer extent information, and the Layer Spatial Reference System section, providing information about the CRS of the layer.

This is a quick way to get information about the layer.

Additionally you can add/edit a title for the layer and some abtract information. These information will be saved in the QGIS project file for following sessions and will be used for QGIS server.

11.2.9 Actions Tab

QGIS provides the ability to perform an action based on the attributes of a feature. This can be used to perform any number of actions, for example, running a program with arguments built from the attributes of a feature or passing parameters to a web reporting tool.

11.2. The Vector Properties Dialog 75

QGIS User Guide, Release 1.8.0

Figure 11.20: General tab in vector layers properties dialog

76

Figure 11.21: Metadata tab in vector layers properties dialog

Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Figure 11.22: Overview action dialog with some sample actions

Actions are useful when you frequently want to run an external application or view a web page based on one or more values in your vector layer. They are devided into 6 types and can be used like this:

• Generic, Mac, Windows and Unix actions start an external process,

• Python actions execute a python expression,

• Generic and Python actions are visible everywhere,

• Mac, Windows and Unix actions are visible only on the respective platform (i.e. you can define three ‘Edit’ actions to open an editor and the users can only see and execute the one ‘Edit’ action for their platform to run the editor).

There are several examples included in the dialog. You can load them clicking on [Add default actions]. An example is performing a search based on an attribute value. This concept is used in the following discussion.

Defining Actions

Attribute actions are defined from the vector Layer Properties dialog. To define an action, open the vector Layer

Properties dialog and click on the Actions tab. Select ‘Generic’ as type and provide a descriptive name for the action. The action itself must contain the name of the application that will be executed when the action is invoked.

You can add one or more attribute field values as arguments to the application. When the action is invoked any set of characters that start with a % followed by the name of a field will be replaced by the value of that field.

The special characters %% will be replaced by the value of the field that was selected from the identify results or attribute table (see

using_actions

below). Double quote marks can be used to group text into a single argument to the program, script or command. Double quotes will be ignored if preceded by a backslash.

If you have field names that are substrings of other field names (e.g., col1 and col10) you should indicate so, by surrounding the field name (and the % character) with square brackets (e.g., [%col10]). This will prevent the

%col10 field name being mistaken for the %col1 field name with a 0 on the end. The brackets will be removed by QGIS when it substitutes in the value of the field. If you want the substituted field to be surrounded by square brackets, use a second set like this: [[%col10]].

Using the Identify Features tool you can open Identify Results dialog. It includes a (Derived) item that contains information relevant to the layer type. The values in this item can be accessed in a similar way to the other fields by using preceeding the derived field name by (Derived).. For example, a point layer has an X and Y field and the value of these can be used in the action with %(Derived).X and %(Derived).Y. The derived attributes are only available from the Identify Results dialog box, not the Attribute Table dialog box.

Two example actions are shown below:

11.2. The Vector Properties Dialog 77

QGIS User Guide, Release 1.8.0

• konqueror http://www.google.com/search?q=%nam

• konqueror http://www.google.com/search?q=%%

In the first example, the web browser konqueror is invoked and passed a URL to open. The URL performs a

Google search on the value of the nam field from our vector layer. Note that the application or script called by the action must be in the path or you must provide the full path. To be sure, we could rewrite the first example as: /opt/kde3/bin/konqueror http://www.google.com/search?q=%nam. This will ensure that the konqueror application will be executed when the action is invoked.

The second example uses the %% notation which does not rely on a particular field for its value. When the action is invoked, the %% will be replaced by the value of the selected field in the identify results or attribute table.

Using Actions

Actions can be invoked from either the Identify Results dialog, an Attribute Table dialog or from Run Feature Action (recall that these dialogs can be opened by clicking

Identify Features or

Open Attribute Table or

Run Feature Action

). 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 and the echo command (so it will only work or perhaps ). The layer in question has fields for a 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:

Acacia mearnsii -34.0800000000 150.0800000000

Acacia mearnsii -34.9000000000 150.1200000000

Acacia mearnsii -35.2200000000 149.9300000000

Acacia mearnsii -32.2700000000 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.

78 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

9. From the drop-down box The valid attribute names for this layer

Field].

10. Your action text now looks like this: select ‘NAMES’ and click [Insert firefox http://google.com/search?q=\%NAMES

11. To finalize the action click the [Insert action] button.

This completes the action and it is ready to use. The final text of the action should look like this: firefox http://google.com/search?q=\%NAMES

We can now use the action. Close the Layer Properties dialog and zoom in to an area of interest. Make sure the lakes layer is active and identify a lake. In the result box you’ll now see that our action is visible:

Figure 11.23: Select feature and choose action

When we click on the action, it brings up Firefox and navigates to the URL http://www.google.com/search?q=Tustumena .

It is also possible to add further attribute fields to the action. Therefore you can add a + to the end of the action text, select another field and click on [Insert Field]. In this example there is just no other field available that would make sense to search for.

You can define multiple actions for a layer and each will show up in the Identify Results dialog.

You can think of all kinds of uses for actions. For example, if you have a point layer containing locations of images or photos along with a file name, you could create an action to launch a viewer to display the image. You could also use actions to launch web-based reports for an attribute field or combination of fields, specifying them in the same way we did in our Google search example.

We can also make more complex examples, for instance on how to use Python actions.

Usually when we create an action to open a file with an external application we can use absolute paths, or eventually relative paths, in the second case the path is relative to the location of the external program executable file.

But what about we need to use relative paths, relative to the selected layer (a file based one, like a shapefile or spatialite)? The following code will do the trick: command = "firefox" ; imagerelpath = "images_test/test_image.jpg" ; layer = qgis .

utils .

iface .

activeLayer();

import os.path

; layerpath = layer .

source()

if

layer .

providerType() == ’ogr’

else

(qgis .

core .

QgsDataSourceURI(layer .

source()) .

database()

if

layer .

providerType() == ’spatialite’

else

None ); path = os .

path .

dirname( str (layerpath)); image = os .

path .

join(path,imagerelpath);

import subprocess

; subprocess .

Popen( [command, image ] ); we have to just remember that the action is one of type Python and to change the command and imagerelpath variables to fit our needs.

11.2. The Vector Properties Dialog 79

QGIS User Guide, Release 1.8.0

But what about if the relative path need to be relative to the (saved) project file? The code of the Python action would be: command = "firefox" ; imagerelpath = "images/test_image.jpg" ; projectpath = qgis .

core .

QgsProject .

instance() .

fileName();

import os.path

; path = os .

path .

dirname( str (projectpath))

if

projectpath != ’’

else

None ; image = os .

path .

join(path, imagerelpath);

import subprocess

; subprocess .

Popen( [command, image ] );

Another Python actions example if the one that allows us to add new layers to the project. For instance the following examples will add to the project respectively a vector and a raster. The name of files to be added to the project and the name to be given to the layer are data driven (filename and layname are column names of the table of attributes of the vector where the action was created): qgis .

utils .

iface .

addVectorLayer( ’/yourpath/[% "filename" %].shp’ , ’[% "layername" %]’ , ’ogr’ )

To add a raster (a tif image in this example) it becomes: qgis .

utils .

iface .

addRasterLayer( ’/yourpath/[% "filename" %].tif’ , ’[% "layername" %]’ )

11.2.10 Joins Tab

The Joins tab allows you to join a loaded attribute table to a loaded vector layer. As key columns you have to define a join layer, a join field and a target field. QGIS currently supports to join non spatial table formats supported by OGR, delimited text and the PostgreSQL provider (see

figure_joins_1

).

Figure 11.24: Join an attribute table to an existing vector layer

Additionally the add vector join dialog allows to:

Cache join layer in virtual memory •

Create attribute index on the join field

80 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

11.2.11 Diagrams Tab

The Diagrams tab allows you to add a graphic overlay to a vector layer (see

figure_diagrams_1

).

The current core implementation of diagrams provides support for piecharts and text diagrams. Text values of different data columns are displayed one below the other with a circle or a box and dividers. Diagram size is based on a fixed size or on linear scaling according to a classification attribute. The placement of the diagrams interacts with the new labeling, so position conflicts between diagrams and labels are detected and solved. In addition to chart positions can be fixed by the users hand.

Figure 11.25: Vector properties dialog with diagram tab

We will demonstrate an example and overlay the alaska boundary layer a text diagram showing some temperature data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section

Sample

Data

).

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 Diagrams tab, activate Display diagrams and from Diagram type

‘Text diagram’

4. As Background color we choose a light blue and set a fixed size to 18 mm.

5. Placement could be set to AroundPoint.

combobox select

6. In the diagram we want to display the values of the three columns T_F_JAN, T_F_JUL and T_F_MEAN.

First select T_F_JAN as Attributes and click the green [+] button, then T_F_JUL and finally T_F_MEAN.

7. Now click [Apply] to display the diagram in the QGIS main window.

8. You can now adapt the chart size, or change the attribute colors by double clicking on the color values in the attribute field.

Figure_diagrams_2

gives an impression.

9. Finally click [Ok].

Additionally in the Settings → Options dialog, there is a Overlay tab where it is possible to select the placement algorithm of the diagrams. The central point method is a generic one, the others use algorithms of the PAL library.

11.2. The Vector Properties Dialog 81

QGIS User Guide, Release 1.8.0

Figure 11.26: Diagram from temperature data overlayed on a map

They also consider diagram objects and labels in different layers. Also see section

Diagram Overlay Plugin

for additional diagram features.

11.3 Editing

QGIS supports various capabilities for editing OGR, PostGIS and SpatiaLite vector layers.

Note: The procedure for editing GRASS layers is different - see Section

Digitizing and editing a GRASS vector layer

for details.

Tip: Concurrent Edits

This version of QGIS does not track if somebody else is editing a feature at the same time as you. The last person to save their edits wins.

11.3.1 Setting the Snapping Tolerance and Search Radius

Before we can edit vertices, we must set the snapping tolerance and search radius to a value that allows us an optimal editing of the vector layer geometries.

Snapping tolerance

Snapping tolerance is the distance QGIS uses to search for the closest vertex and/or segment you are trying to connect when you set a new vertex or move an existing vertex. If you aren’t within the snapping tolerance,

QGIS will leave the vertex where you release the mouse button, instead of snapping it to an existing vertex and/or segment. The snapping tolerance setting affects all tools which work with tolerance.

1. A general, project wide snapping tolerance can be defined choosing Settings → Options . On Mac: go to QIS → Preferences...

, on Linux: Edit → Options . In the Digitizing tab you can select between to vertex, to segment or to vertex and segment as default snap mode. You can also define a default snapping tolerance and a search radius for vertex edits. The tolerance an be set either in map units or in pixels.

The advantage of choosing pixels, is that the snapping tolerance doesn’t have to be changed after zoom operations. In our small digitizing project (working with the Alaska dataset), we define the snapping units

82 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

in feet. Your results may vary, but something on the order of 300ft should be fine at a scale of 1:10 000 should be a reasonable setting.

2. A layer based snapping tolerance can be defined by choosing Settings → (or File →) Snapping options... to enable and adjust snapping mode and tolerance on a layer basis (see

figure_edit_1

).

Note that this layer based snapping overrides the global snapping option set in the Digitizing tab. So if you need to edit one layer, and snap its vertices to another layer, then enable snapping only on the snap to layer, then decrease the global snapping tolerance to a smaller value. Furthermore, snapping will never occur to a layer which is not checked in the snapping options dialog, regardless of the global snapping tolerance. So be sure to mark the checkbox for those layers that you need to snap to.

Figure 11.27: Edit snapping options on a layer basis

Search radius

Search radius is the distance QGIS uses to search for the closest vertex you are trying to move when you click on the map. If you aren’t within the search radius, QGIS won’t find and select any vertex for editing and it will pop up an annoying warning to that effect. Snap tolerance and search radius are set in map units or pixels, so you may find you need to experiment to get them set right. If you specify too big of a tolerance, QGIS may snap to the wrong vertex, especially if you are dealing with a large number of vertices in close proximity. Set search radius too small and it won’t find anything to move.

The search radius for vertex edits in layer units can be defined in the Digitizing tab under Settings → Options .

The same place where you define the general, project wide snapping tolerance.

11.3.2 Zooming and Panning

Before editing a layer, you should zoom in to your area of interest. This avoids waiting while all the vertex markers are rendered across the entire layer.

Apart from using the pan and zoom-in

/ zoom-out icons on the toolbar with the mouse, navigating can also be done with the mouse wheel, spacebar and the arrow keys.

Zooming and panning with the mouse wheel

While digitizing you can press the mouse wheel to pan inside of the main window and you can roll the mouse wheel to zoom in and out on the map. For zooming place the mouse cursor inside the map area and roll it forward

(away from you) to zoom in and backwards (towards you) to zoom out. The mouse cursor position will be the center of the zoomed area of interest. You can customize the behavior of the mouse wheel zoom using the Map tools tab under the Settings → Options menu.

Panning with the arrow keys

Panning the map during digitizing is possible with the arrow keys. Place the mouse cursor inside the map area and click on the right arrow key to pan east, left arrow key to pan west, up arrow key to pan north and down arrow key

11.3. Editing 83

QGIS User Guide, Release 1.8.0

to pan south.

You can also use the spacebar to temporarily cause mouse movements to pan then map. The PgUp and PgDown keys on your keyboard will cause the map display to zoom in or out without interrupting your digitizing session.

11.3.3 Topological editing

Besides layer based snapping options you can also define some topological functionalities in the Snapping options...

dialog in the Settings (or File) menu. Here you can define polygon layers you can activate the column Avoid Int.

Enable topological editing which avoids intersection of new polygons.

and/or for

Enable topological editing

The option

Enable topological editing is for editing and maintaining common boundaries in polygon mosaics.

QGIS ‘detects’ a shared boundary in a polygon mosaic and you only have to move the vertex once and QGIS will take care about updating the other boundary.

Avoid intersections of new polygons

The second topological option in the Avoid Int.

column, called 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.

11.3.4 Digitizing an existing layer

By default, QGIS loads layers read-only: This is a safeguard to avoid accidentally editing a layer if there is a slip of the mouse. However, you can choose to edit any layer as long as the data provider supports it, and the underlying data source is writable (i.e. its files are not read-only). Layer editing is most versatile when used on

PostgreSQL/PostGIS data sources.

In general, editing vector layers is divided into a digitizing and an advanced digitizing toolbar, described in Section

Advanced digitizing

.

→ Toolbars →.

You can select and unselect both under Settings

Using the basic digitizing tools you can perform the following functions:

Icon Purpose Icon Purpose

Toggle editing

Adding Features: Capture Line

Adding Features: Capture Point

Adding Features: Capture Polygon

Move Feature

Delete Selected

Node Tool

Cut Features

Copy Features

Save edits and continue

Table Editing: Vector layer basic editing toolbar

Paste Features

All editing sessions start by choosing the clicking on the legend entry for that layer.

Toggle editing option. This can be found in the context menu after right

Alternately, you can use the Toggle Editing

Toggle editing button from the digitizing toolbar to start or stop the editing mode. Once the layer is in edit mode, markers will appear at the vertices, and additional tool buttons on the editing toolbar will become available.

84 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Tip: Save Regularly

Remember to

Save Edits regularly. This will also check that your data source can accept all the changes.

Adding Features

You can use the digitizing mode.

Add Feature

,

Add Feature or

Add Feature icons on the toolbar to put the QGIS cursor into

For each feature, you first digitize the geometry, then enter its attributes. To digitize the geometry, left-click on the map area to create the first point of your new feature.

For lines and polygons, keep on left-clicking for each additional point you wish to capture. When you have finished adding points, right-click anywhere on the map area to confirm you have finished entering the geometry of that feature.

The attribute window will appear, allowing you to enter the information for the new feature.

Figure_edit_2

shows setting attributes for a fictitious new river in Alaska. In the Digitizing tab under the Settings → Options menu, you can also activate attribute values .

Suppress attributes pop-up windows after each created feature Reuse last entered

Figure 11.28: Enter Attribute Values Dialog after digitizing a new vector feature

With the

Move Feature(s) icon on the toolbar you can move existing features.

Tip: Attribute Value Types

At least for shapefile editing the attribute types are validated during the entry. Because of this, it is not possible to enter a number into the text-column in the dialog Enter Attribute Values or vice versa. If you need to do so, you should edit the attributes in a second step within the Attribute table dialog.

Node Tool

For both PostgreSQL/PostGIS and shapefile-based layers, the

Node Tool provides manipulation capabilites of feature vertices similar to CAD programs. It is possible to simply select multiple vertices at once and to move, add or delete them alltogether. The node tool also works with ‘on the fly’ projection turned on and supports the topological editing feature. This tool is, unlike other tools in Quantum GIS, persistent, so when some operation is done, selection stays active for this feature and tool. If the node tool couldn’t find any features, a warning will be displayed.

11.3. Editing 85

QGIS User Guide, Release 1.8.0

Important is to set the property Settings →

Options

→ Digitizing → Search Radius: greater than zero (i.e. 10). Otherwise QGIS will not be able to tell which vertex is being edited.

to a number

Tip: Vertex Markers

The current version of QGIS supports three kinds of vertex-markers: Semi transparent circle, Cross and None. To change the marker style, choose

Options from the Settings menu and click on the Digitizing tab and select the appropriate entry.

Basic operations

Start by activating the of this feature.

Node Tool and selecting a feature by clicking on it. Red boxes will appear at each vertex

• Selecting vertices: You can select vertices by clicking on them one at a time, by clicking on an edge to select the vertices at both ends, or by clicking and dragging a rectangle around some vertices. When a vertex is selected its color changes to blue. To add more vertices to the current selection, hold down the

Ctrl key while clicking. Hold down Ctrl or Shift when clicking to toggle the selection state of vertices

(vertices that are currently unselected will be selected as usual, but also vertices that are already selected will become unselected).

• Adding vertices: To add a vertex simply double click near an edge and a new vertex will appear on the edge near to the cursor. Note that the vertex will appear on the edge, not at the cursor position, therefore it has to be moved if necessary.

• Deleting vertices: After selecting vertices for deletion, click the Delete key. Note that you cannot use the

Node Tool to delete a complete feature; QGIS will ensure it retains the minimum number of vertices for the feature type you are working on. To delete a complete feature use the

Delete Selected tool.

• Moving vertices: Select all the vertices you want to move. Click on a selected vertex or edge and drag in the direction you wish to move. All the selected vertices will move together. If snapping is enabled, the whole selection can jump to the nearest vertex or line.

Each change made with the node tool is stored as a separate entry in the undo dialog. Remember that all operations support topological editing when this is turned on. On the fly projection is also supported, and the node tool provides tooltips to identify a vertex by hovering the pointer over it.

Cutting, Copying and Pasting Features

Selected features can be cut, copied and pasted between layers in the same QGIS project, as long as destination layers are set to

Toggle editing beforehand.

Features can also be pasted to external applications as text: That is, the features are represented in CSV format with the geometry data appearing in the OGC Well-Known Text (WKT) format.

However in this version of QGIS, text features from outside QGIS cannot be pasted to a layer within QGIS. When would the copy and paste function come in handy? Well, it turns out that you can edit more than one layer at a time and copy/paste features between layers. Why would we want to do this? Say we need to do some work on a new layer but only need one or two lakes, not the 5,000 on our big_lakes layer. We can create a new layer and use copy/paste to plop the needed lakes into it.

As an example we are copying some lakes to a new layer:

1. Load the layer you want to copy from (source layer)

2. Load or create the layer you want to copy to (target layer)

3. Start editing for target layer

4. Make the source layer active by clicking on it in the legend

86 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

5. Use the

Select Single Feature tool to select the feature(s) on the source layer

6. Click on the

Copy Features tool

7. Make the destination layer active by clicking on it in the legend

8. Click on the

Paste Features tool

9. Stop editing and save the changes

What happens if the source and target layers have different schemas (field names and types are not the same)?

QGIS populates what matches and ignores the rest. If you don’t care about the attributes being copied to the target layer, it doesn’t matter how you design the fields and data types. If you want to make sure everything - feature and its attributes - gets copied, make sure the schemas match.

Tip: Congruency of Pasted Features

If your source and destination layers use the same projection, then the pasted features will have geometry identical to the source layer. However if the destination layer is a different projection then QGIS cannot guarantee the geometry is identical. This is simply because there are small rounding-off errors involved when converting between projections.

Deleting Selected Features

If we want to delete an entire polygon, we can do that by first selecting the polygon using the regular

Select Single Feature tool. You can select multiple features for deletion. Once you have the selection set, use the

Delete Selected tool to delete the features.

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 delete. We could then use the

Paste Features tool to put it back, giving us a one-level undo capability. Cut, copy, and paste work on the currently selected features, meaning we can operate on more than one at a time.

Tip: Feature Deletion Support

When editing ESRI shapefiles, the deletion of features only works if QGIS is linked to a GDAL version 1.3.2 or greater. The OS X and Windows versions of QGIS available from the download site are built using GDAL 1.3.2

or higher.

Saving Edited Layers

When a layer is in editing mode, any changes remain in the memory of QGIS. Therefore they are not committed/saved immediately to the data source or disk. If you want to save edits to the current layer but want to continue editing without leaving the editing mode, you can click the

Save Edits button. When you turn editing mode off with the discard them.

Toggle editing

(or quit QGIS for that matter), you are also asked if you want to save your changes or

If the changes cannot be saved (e.g. disk full, or the attributes have values that are out of range), the QGIS in-memory state is preserved. This allows you to adjust your edits and try again.

Tip: Data Integrity

It is always a good idea to back up your data source before you start editing. While the authors of QGIS have made every effort to preserve the integrity of your data, we offer no warranty in this regard.

11.3. Editing 87

QGIS User Guide, Release 1.8.0

11.3.5 Advanced digitizing

Icon Purpose

Undo

Simplify Feature

Add Part

Icon Purpose

Redo

Add Ring

Delete Ring

Delete Part

Offset Curve

Reshape Features

Split Features

Merge Selected Features

Merge Attributes of Selected Features

Rotate Point Symbols

Table Advanced Editing: Vector layer advanced editing toolbar

Undo and Redo

The

Undo and

Redo tools allow the user to undo or redo vector editing operations. There is also a dockable widget, which shows all operations in the undo/redo history (see

Figure_edit_3

). This widget is not displayed by

default; it can be displayed by right clicking on the toolbar and activating the Undo/Redo check box. Undo/Redo is however active, even if the widget is not displayed.

Figure 11.29: Redo and Undo digitizing steps

When Undo is hit, the state of all features and attributes are reverted to the state before the reverted operation happened. Changes other than normal vector editing operations (for example changes done by a plugin), may or may not be reverted, depending on how the changes were performed.

To use the undo/redo history widget simply click to select an operation in the history list; all features will be reverted to the state they were in after the selected operation.

Simplify Feature

The

Simplify Feature tool allows to reduce the number of vertices of a feature, as long as the geometry doesn’t change. You need to select a feature, it will be highlighted by a red rubber band and a slider appears. Moving the slider, the red rubber band is changing its shape to show how the feature is being simplified. Clicking [OK] the new, simplified geometry will be stored. If a feature cannot be simplified (e.g. MultiPolygons), a message shows up.

88 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Add Ring

You can create ring polygons using the

Add Ring icon in the toolbar. This means inside an existing area it is possible to digitize further polygons, that will occur as a ‘hole’, so only the area in between the boundaries of the outer and inner polygons remain as a ring polygon.

Add Part

You can add part polygons to a selected multipolygon. The new part polygon has to be digitized outside the selected multipolygon.

Delete Ring

The

Delete Ring tool allows to delete ring polygons inside an existing area. This tool only works with polygon layers. It doesn’t change anything when it is used on the outer ring of the polygon. This tool can be used on polygon and multi-polygon features. Before you select the vertices of a ring, adjust the vertex edit tolerance.

Delete Part

The

Delete Part tool allows to delete parts from multifeatures (e.g. to delete polygons from a multipolygon feature). It won’t delete the last part of the feature, this last part will stay untouched. This tool works with all multi-part geometries point, line and polygon. Before you select the vertices of a part, adjust the vertex edit tolerance.

Reshape Features

You can reshape line and polygon features using the

Reshape Features icon on the toolbar. It replaces the line or polygon part from the first to the last intersection with the original line. With polygons this can sometimes lead to unintended results. It is mainly useful to replace smaller parts of a polygon, not major overhauls and the reshape line is not allowed to cross several polygon rings as this would generate an invalid polygon.

For example, you can edit the boundary of a polygon with this tool. First, click in the inner area of the polygon next to the point where you want to add a new vertex. Then, cross the boundary and add the vertices outside the polygon. To finish, right-click in the inner area of the polygon. The tool will automatically add a node where the new line crosses the border. It is also possible to remove part of the area from the polygon, starting the new line outside the polygon, adding vertices inside, and ending the line outside the polygon with a right click.

Note: The reshape tool may alter the starting position of a polygon ring or a closed line. So the point that is represented ‘twice’ will not be the same any more. This may not be a problem for most applications, but it is something to consider.

Offset Curves

The

Offset Curve tool is a new editing tool. It creates parallel shifts of lines and polygon rings. The tool can be applied to the edited layer (the geometries are modified) or also to background layers (creates copies of the lines / rings and adds it to the the edited layer). It is thus ideally suited for the creation of distance line layers.The

displacement is shown at the bottom left of the taskbar.

11.3. Editing 89

QGIS User Guide, Release 1.8.0

Split Features

You can split features using the split.

Split Features icon on the toolbar. Just draw a line across the feature you want to

Merge selected features

The

Merge Selected Features tool allows to merge features that have common boundaries and the same attributes.

Merge attributes of selected features

The

Merge Attributes of Selected Features tool allows to merge attributes of features with common boundaries and attributes without merging their boundaries.

Rotate Point Symbols

The

Rotate Point Symbols tool is currently only supported by the old symbology engine. It allows to change the rotation of point symbols in the map canvas, if you have defined a rotation column from the attribute table of the point layer in the Style tab of the Layer Properties. Otherwise the tool is inactive.

Figure 11.30: Rotate Point Symbols

To change the rotation, select a point feature in the map canvas and rotate it holding the left mouse button pressed.

A red arrow with the rotation value will be visualized (see

Figure_edit_4

). When you release the left mouse button

again, the value will be updated in the attribute table.

Note: If you hold the Ctrl key pressed, the rotation will be done in 15 degree steps.

11.3.6 Creating a new Vector layer

QGIS allows to create new Shapefile layers and new SpatiaLite layers. Creation of a new GRASS layer is supported within the GRASS-plugin. Please refer to section

Creating a new GRASS vector layer

for more information on creating GRASS vector layers.

Creating a new Shapefile layer

To create a new Shape layer for editing, choose New → New Shapefile Layer...

from the Layer menu. The

New Vector Layer dialog will be displayed as shown in

Figure_edit_5

. Choose the type of layer (point, line or

polygon) and the CRS (Coordinate Reference System).

90 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Note that QGIS does not yet support creation of 2.5D features (i.e. features with X,Y,Z coordinates) or measure features.

Figure 11.31: Creating a new Shapefile layer Dialog

To complete the creation of the new Shapefile layer, add the desired attributes by clicking on the [Add] button and specifying a name and type for the attribute. A first ‘id’ column is added as default but can be removed, if not wanted. Only Type: real , Type: integer , and Type: string attributes are supported.

Additionally and according to the attribute type you can also define the width and precision of the new attribute column. Once you are happy with the attributes, click [OK] and provide a name for the shapefile. QGIS will automatically add a .shp extension to the name you specify. Once the layer has been created, it will be added to the map and you can edit it in the same way as described in Section

Digitizing an existing layer

above.

Creating a new SpatiaLite layer

To create a new SpatiaLite layer for editing, choose New → New SpatiaLite Layer...

from the Layer menu.

The New SpatiaLite Layer dialog will be displayed as shown in

Figure_edit_6

.

First step is to select an existing SpatiaLite database or to create a new SpatiaLite database. This can be done with the browse button to the right of the database field. Then add a name for the new layer and define the layer type and the EPSG SRID. If desired you can select to Create an autoincrementing primary key .

To define an attribute table for the new SpatiaLite layer, add the names of the attribute columns you want to create with the according column type and click on the [Add to attribute list] button. Once you are happy with the attributes, click [OK]. QGIS will automatically add the new layer to the legend and you can edit it in the same way as described in Section

Digitizing an existing layer

above.

The SpatiaLite creation dialog allows to create multiple layers without closing the dialog when you click [Apply].

11.3.7 Working with the Attribute Table

The attribute table displays features of a selected layer. Each row in the table represents one map feature and each column contains a particular piece of information about the feature. Features in the table can be searched, selected, moved or even edited.

11.3. Editing 91

QGIS User Guide, Release 1.8.0

Figure 11.32: Creating a New SpatiaLite layer Dialog

To open the attribute table for a vector layer, make the layer active by clicking on it in the map legend area. Then from the main menu Layer choose Open Attribute Table . It is also possible to rightclick on the layer and choose Open Attribute Table from the dropdown menu.

This will open a new window which displays the feature attributes in the layer (

figure_attributes_1

). The number

of features and the number of selected features are shown in the attribute table title.

92

Figure 11.33: Attribute Table for Alaska layer

Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

Selecting features in an attribute table

Each selected row in the attribute table displays the attributes of a selected feature in the layer. If the set of features selected in the main window is changed, the selection is also updated in the attribute table. Likewise, if the set of rows selected in the attribute table is changed, the set of features selected in the main window will be updated.

Rows can be selected by clicking on the row number on the left side of the row. Multiple rows can be marked by holding the Ctrl key. A continuous selection can be made by holding the Shift key and clicking on several row headers on the left side of the rows. All rows between the current cursor position and the clicked row are selected. Moving the cursor position in the attribute table, by clicking a cell in the table, does not change the row selection. Changing the selection in the main canvas does not move the cursor position in the attribute table.

The table can be sorted by any column, by clicking on the column header. A small arrow indicates the sort order

(downward pointing means descending values from the top row down, upward pointing means ascending values from the top row down).

For a simple search by attributes on only one column the Look for field can be used. Select the field (column) from which the search should be performed from the dropdown menu and hit the [Search] button. The matching rows will be selected and the total number of matching rows will appear in the title bar of the attribute table, and in the status bar of the main window. For more complex searches use the Advanced search button will launch the Search Query Builder described in Section

Query Builder

.

, which

To show selected records only, use the checkbox Show selected only . To search selected records only, use the checkbox Search selected only . The Case sensitive checkbox allows to select case sensitive. The other buttons at the bottom left of the attribute table window provide following functionality:

Unselect all also with Ctrl+U

Move selected to top also with Ctrl+T

Invert selection also with Ctrl+S

Copy selected rows to clipboard also with Ctrl+C

Zoom map to the selected rows also with Ctrl+J

Toggle editing mode to edit single values and to enable functionalities described below also with Ctrl+E

Delete selected features also with Ctrl+D

New Column for PostGIS layers and for OGR layers with GDAL version >= 1.6 also with Ctrl+W

Delete Column for PostGIS layers and for OGR layers with GDAL version >= 1.9 also with Ctrl+L

Open field calculator also with Ctrl+I

Tip: Skip WKT geometry

If you want to use attribute data in external programs (such as Excel) use the

Copy selected rows to clipboard button.

You can copy the information without vector geometries if you deactivate Settings → Options → General tab

Copy geometry in WKT representation from attribute table

.

Save selected features as new layer

The selected features can be saved as any OGR supported vector format and also transformed into another Coordinate Reference System (CRS). Just open the right mouse menu of the layer and click on Save selection as →

11.3. Editing 93

QGIS User Guide, Release 1.8.0

to define the name of the output file, its format and CRS (see Section

Map Legend

). It is also possible to specify

OGR creation options within the dialog.

Working with non spatial attribute tables

QGIS allows also to load non spatial tables. This includes currently tables supported by OGR, delimited text and the PostgreSQL provider. The tables can be used for field lookups or just generally browsed and edited using the table view. When you load the table you will see it in the legend field. It can be opened e.g. with the

Open Attribute Table tool and is then editable like any other layer attribute table.

As an example you can use columns of the non spatial table to define attribute values or a range of values that are allowed to be added to a specific vector layer during digitizing. Have a closer look at the edit widget in section

Fields Tab

to find out more.

11.4 Query Builder

The Query Builder allows you to define a subset of a table using a SQL-like WHERE clause and display the result in the main window. The query result then can be saved as a new vector layer.

11.4.1 Query

Open the attribute table choosing

Open Attribute Table from the menu bar. Click on the [Advanced Search] button to open the Query builder. For example, if you have a towns layer with a population field you could select only larger towns by entering population > 100000 in the SQL box of the Query builder.

Figure_attributes_2

shows an example of the Query builder populated with data from a PostGIS layer with attributes stored in PostgreSQL. The Fields, Values and Operators sections help the user to construct the SQL-like query.

Figure 11.34: Query Builder

The Fields list contains all attribute columns of the attribute table to be searched. To add an attribute column to the

SQL where clause field, double click its name in the Fields list. Generally you can use the various fields, values and operators to construct the query or you can just type it into the SQL box.

94 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

The Values list lists the values of an attribute table. To list all possible values of an attribute, select the attribute in the Fields list and click the [all] button. To list the first 25 unique values of an attribute column, select the attribute column in the Fields list and click the [Sample] button. To add a value to the SQL where clause field, double click its name in the Values list.

The Operators section contains all usable operators. To add an operator to the SQL where clause field, click the appropriate button. Relational operators ( = , > , ...), string comparison operator (LIKE), logical operators (AND,

OR

, ...) are available.

The [Test] button shows a message box with the number of features satisfying the current query, which is usable in the process of query construction. The [Clear] button clears the text in the SQL where clause text field. The

[Save] and [Load] button allow to save and load SQL queries. The [OK] button closes the window and selects the features satisfying the query. The [Cancel] button closes the window without changing the current selection.

Tip: Changing the Layer Definition

You can change the layer definition after it is loaded by altering the SQL query used to define the layer. To do this, open the vector Layer Properties dialog by double-clicking on the layer in the legend and click on the [Query

Builder] button on the General tab. See Section

The Vector Properties Dialog

for more information.

11.4.2 Selection

With QGIS it is possible also to select features for visualisation using a similar query builder interface to that used in

Query Builder

. In the above section the purpose of the query builder is to highlight all selected features meeting

the filter criteria in yellow. The rest of the features do not change their appearance.

Another possibility is to make a selection by right clicking on a layer in the legend and choosing Query .... If you perform a SQL query here only the selected features are displayed in the map view. Features that don’t match the

SQL query are not visualised in the map view. The same function is available from the General tab in the vector

Layer Properties dialog. You can find a [Query builder] button right below. The selection described above can be used with all vector data providers.

11.4.3 Save selected features as new layer

The selected features can be saved as any OGR supported vector format and also transformed into another Coordinate Reference System (CRS). Just open the right mouse menu of the layer and click on Save selection as → to define the name of the output file, its format and CRS (see Section

Map Legend

). It is also possible to specify

OGR creation options within the dialog.

11.5 Field Calculator

The

Field Calculator button in the attribute table allows to perform calculations on basis of existing attribute values or defined functions, e.g to calculate length or area of geometry features. The results can be written to a new attribute column or it can be used to update values in an already existing column.

You have to bring the vector layer in editing mode, before you can click on the field calculator icon to open the dialog (see

figure_attributes_3

). In the dialog you first have to select whether you want to only update selected

features, create a new attribute field where the results of the calculation will be added or update an existing field.

If you choose to add a new field, you need to enter a field name, a field type (integer, real or string), the total field width, and the field precision (see

figure_attributes_3

). For example, if you choose a field width of 10 and a field

precision of 3 it means you have 6 signs before the dot, then the dot and another 3 signs for the precision.

The Function List contains functions as well as fields and values. View the help function in the Selected Function

Help. In Expression you see the calculation expressions you create with the Function List. The most commonly used operators, see Operators.

11.5. Field Calculator 95

QGIS User Guide, Release 1.8.0

Figure 11.35: Field Calculator

In the Function List, click on Fields and Values to view all attributes of the attribute table to be searched. To add an attribute to the Field calculator Expression field, double click its name in the Fields and Values list. Generally you can use the various fields, values and functions to construct the calculation expression or you can just type it into the box. To display the values of a field, you just right click on the appropriate field. You can choose between

Load top 10 unique values and Load all unique values. On the right side opens the Field Values list with the unique values. To add a value to the Field calculator Expression box, double click its name in the Field Values list.

The Operators, Math, Conversions, String, Geometry and Record groups provides several functions. In Operators you find mathematical operators. Find Math for mathematical functions. The Conversions group contains functions that convert one data type to another. The String group provides functions for data strings. In the Geometry group you find functions for geometry objects. With Record group functions you can add a numeration to your data set. To add a function to the Field calculator Expression box, click on the > and then doubleclick the function.

A short example illustrates how the field calculator works. We want to calculate the length of the railroads layer from the QGIS sample dataset:

1. Load the Shapefile railroads.shp in QGIS and press

Open Attribute Table

.

2. Click on

Toggle editing mode and open the

Field Calculator dialog.

3. Select the Create a new field checkbox to safe the calculations into a new field.

4. Add length as Output field name, real as Output field type and define Output field width 10 and a

Precision of 3.

5. Now click on function length in the Geometry group to add it as $length into the Field calculator expression box and click [Ok].

6. You can now find a new column length in the attribute table.

The available functions are listed below.

96 Chapter 11. Working with Vector Data

QGIS User Guide, Release 1.8.0

column name "column name"

’string’

NULL a IS NULL a IS NOT NULL a IN (value[,value]) a NOT IN (value[,value]) a OR b a AND b

NOT a sqrt(a) sin(a) cos(a) tan(a) asin(a) acos(a) atan(a) to int(a) to real(a) tangens of a arcussinus of a arcuscosinus of a arcustangens of a to string(a) lower(a) upper(a) length(a) atan2(y,x) value of the field column name a string value null value a has no value a has a value a is below the values listed a is not below the values listed a or *b* is true a and *b* is true inverted truth value of a square root of a sinus of a cosinus of b convert string a to integer convert string a to real convert number a to string convert string a to lower case convert string a to upper case length of string a arcustangens of y/x using the signs of the two substr(*a*,from,len) arguments to determine the quadrant of the result replace(*a*, replacethis, withthat) replace this with that in string a regexp_replace(a,this,that) replace the regular expression this with that len characters of string *a* starting from from

(first character index is 1) a || b

$rownum concatenate strings a and b number current row

$area

$perimeter

$length

$id

$x

$y xat(n) area of polygon perimeter of polygon length of line feature id x coordinate of point y coordinate of point

X coordinate of the point of an n-th line (indeces yat(n) start at 0; negative values refer to the line end) y coordinate of the point of an n-th line (indeces start at 0; negative values refer to the line end) a and b are equal a and b are not equal a = b a != b a <> b a >= b a <= b a > b a < b a ~ b a LIKE b a ILIKE b a |wedge| b a * b a / b a is larger than or equal to b a is less than or equal to b a is larger than b a is smaller than b a matches the regular expression b a equals b a equals b (without regard to case-sensitive) a raised to the power of b a multiplied by b a divided by b a + b a - b

+ a

- a a plus b a minus b positive sign negative value of a

The field calculator Function list with the Selected Function Help , Operators and Expression menu are also available through the rule-based rendering in the Style tab of the Layer properties and the expression based labeling in the

Labeling core application.

11.5. Field Calculator 97

QGIS User Guide, Release 1.8.0

98 Chapter 11. Working with Vector Data

CHAPTER

12

Working with Raster Data

12.1 Working with Raster Data

This Section describes how to visualize and set raster layer properties. QGIS uses the GDAL library to read and write raster data formats, including Arc/Info Binary Grid, Arc/Info ASCII Grid, GeoTIFF, Erdas Imagine and many more. GRASS raster support is supplied by a native QGIS data provider plugin. The raster data can also be loaded in read mode from zip and gzip archives into QGIS.

At the date of this document, more than 100 raster formats are supported by the GDAL library

(see GDAL-SOFTWARE-SUITE

Literature and Web References

).

A complete list is available at http://www.gdal.org/formats_list.html

.

Note: Not all of the listed formats may work in QGIS for various reasons. For example, some require external commercial libraries or the GDAL installation of your OS was not built to support the format you want to use.

Only those formats that have been well tested will appear in the list of file types when loading a raster into QGIS.

Other untested formats can be loaded by selecting the [GDAL] All files (*) filter.

Working with GRASS raster data is described in Section

GRASS GIS Integration

.

12.1.1 What is raster data?

Raster data in GIS are matrices of discrete cells that represent features on, above or below the earth’s surface. Each cell in the raster grid is the same size, and cells are usually rectangular (in QGIS they will always be rectangular).

Typical raster datasets include remote sensing data such as aerial photography or satellite imagery and modelled data such as an elevation matrix.

Unlike vector data, raster data typically do not have an associated database record for each cell. They are geocoded by its pixel resolution and the x/y coordinate of a corner pixel of the raster layer. This allows QGIS to position the data correctly in the map canvas.

QGIS makes use of georeference information inside the raster layer (e.g. GeoTiff) or in an appropriate world file to properly display the data.

12.1.2 Loading raster data in QGIS

Raster layers are loaded either by clicking on the

Load Raster icon or by selecting the Layer →

Add Raster

Layer menu option. More than one layer can be loaded at the same time by holding down the Control or Shift key and clicking on multiple items in the dialog Open a GDAL Supported Raster Data Source.

99

QGIS User Guide, Release 1.8.0

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

• Set Layer CRS

• Set Project CRS from Layer

• Properties

• Rename

• Copy Style

• Add New Group

• Expand all

• Collapse all

• Update Drawing Order

12.2 Raster Properties Dialog

To view and set the properties for a raster layer, double click on the layer name in the map legend or right click on the layer name and choose Properties from the context menu:

This will open the Raster Layer Properties dialog, (see

figure_raster_1

).

There are several tabs on the dialog:

• Style

• Transparency

• Colormap

• General

• Metadata

• Pyramids

• Histogram

12.2.1 Style Tab

QGIS can render raster layers in two different ways:

1. Single band - one band of the image will be rendered as gray or in pseudocolor or a freak out.

2. Three band color - three bands from the image will be rendered, each band representing the red, green or blue component that will be used to create a color image.

Within both render types you can invert the color output using the

Single Band Rendering

Invert color map checkbox.

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).

100 Chapter 12. Working with Raster Data

QGIS User Guide, Release 1.8.0

Figure 12.1: Raster Layers Properties Dialog

The second option offers a selection of available colortables for rendering.

The following settings are available through the dropdownbox Color map

• Grayscale (default)

• Pseudocolor

• Freak Out

• Colormap

When selecting the entry ‘Colormap’ from Color map

For more information see

Colormap

.

combobox, the tab Colormap becomes available.

QGIS can restrict the data displayed to only show cells whose values are within a given number of standard deviations of the mean for the layer.

This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster. This option is only available for pseudocolor and freak out images.

Three band color

This selection offers you a wide range of options to modify the appearance of your rasterlayer. For example you could switch color-bands from the standard RGB-order to something else.

Also scaling of colors are available.

Tip: Viewing a Single Band of a Multiband Raster

If you want to view a single band (for example Red) of a multiband image, you might think you would set the

Green and Blue bands to “Not Set”. But this is not the correct way. To display the Red band, set the image type to grayscale, then select Red as the band to use for Gray.

12.2. Raster Properties Dialog 101

QGIS User Guide, Release 1.8.0

Contrast enhancement

Note: When adding GRASS rasters the option Contrast enhancement will be always set to automatically to stretch to min max regardless if the Quantum GIS general options this is set to another value.

12.2.2 Transparency Tab

QGIS has the ability to display each raster layer at varying transparency levels. Use the transparency slider to indicate to what extent the underlying layers (if any) should be visible though the current raster layer. This is very useful, if you like to overlay more than one rasterlayer, e.g. a shaded relief map overlayed by a classified rastermap. This will make the look of the map more three dimensional.

Additionally you can enter a rastervalue, which should be treated as NODATA. This can be done manually or with the

Add values from display icon.

An even more flexible way to customize the transparency can be done in the Custom transparency options section.

The transparency of every pixel can be set here.

As an example we want to set the water of our example raster file landcover.tif to a transparency of 20 %.

The following steps are neccessary:

1. Load the rasterfile landcover.

2. Open the Properties dialog by double-clicking on the raster name in the legend or by right-clicking and choosing Properties from the popup menu.

3. Select the Transparency tab

4. Click the

Add values manually button. A new row will appear in the pixel-list.

5. Enter the raster-value (we use 0 here) and adjust the transparency to 20 %.

6. Press the [Apply] button and have a look at the map.

You can repeat the steps 4 and 5 to adjust more values with custom transparency.

As you can see this is quite easy to set custom transparency, but it can be quite a lot of work. Therefore you can use the button

Export to file to save your transparency list to a file. The button transparency settings and applies them to the current raster layer.

Import from file loads your

12.2.3 Colormap

The Colormap tab is only available, when you have selected a singleband rendering within the Style tab (see

Style

Tab

).

Three ways of color interpolation are available:

1. Discrete

2. Linear

3. Exact

The button [Add Entry] adds a color to the individual color table. Button [Delete Entry] deletes a color from the individual color table and the [Sort] button sorts the color table according to the pixel values in the value column.

Double clicking on the value-column lets you insert a specific value. Double clicking on the color-column opens the dialog Select color where you can select a color to apply on that value. Further you can also add labels for each color but this value won’t be displayed when you use the identify feature tool.

102 Chapter 12. Working with Raster Data

QGIS User Guide, Release 1.8.0

You can also click on the button

And you can use the buttons

Load color map from band

, which tries to load the table from the band (if it has any).

Load color map from file save the defined color table for other sessions.

or

Export color map to file to load an existing color table or to

The block Generate new color map allows you to create newly categorized colormaps. You only need to select the number of entries supported - ‘Equal interval’ and press the button Classify. Currently only one Classification mode is

12.2.4 General Tab

The General tab displays basic information about the selected raster, including the layer source and display name in the legend (which can be modified). This tab also shows a thumbnail of the layer, its legend symbol, and the palette.

Additionally scale-dependent visibility can be set in this tab. You need to check the checkbox and set an appropriate scale where your data will be displayed in the map canvas.

Also the coordinate reference system (CRS) is printed here as a PROJ.4-string. This can be modified by hitting the [Specify] button.

12.2.5 Metadata Tab

The Metadata tab displays a wealth of information about the raster layer, including statistics about each band in the current raster layer. Statistics are gathered on a ‘need to know’ basis, so it may well be that a given layers statistics have not yet been collected.

This tab is mainly for information. You cannot change any values printed inside this tab. To update the statistics you need to change to tab Histogram and press the button [Refresh] on the bottom right, (see

Histogram Tab

).

12.2.6 Pyramids Tab

Large resolution raster layers can slow navigation in QGIS. By creating lower resolution copies of the data (pyramids), performance can be considerably improved as QGIS selects the most suitable resolution to use depending on the level of zoom.

You must have write access in the directory where the original data is stored to build pyramids.

Several resampling methods can be used to calculate the pyramids:

• Average

• Nearest Neighbour

When checking the checkbox Build pyramids internally if possible QGIS tries to build pyramids internally.

Please note that building pyramids may alter the original data file and once created they cannot be removed. If you wish to preserve a ‘non-pyramided’ version of your raster, make a backup copy prior to building pyramids.

12.2.7 Histogram Tab

The Histogram tab allows you to view the distribution of the bands or colors in your raster. It is generated automaticaly when you open Histogram tab. All existing bands will be displayed together. You can save the histogram as an image with the button.

Tip: Gathering Raster Statistics

12.2. Raster Properties Dialog 103

QGIS User Guide, Release 1.8.0

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!

12.3 Raster Calculator

The Raster Calculator in the Raster menu (see

figure_raster_2

) allows to perform calculations on basis of existing

raster pixel values. The results are written to a new raster layer with a GDAL supported format.

Figure 12.2: Raster Calculator

The Raster bands list contains all loaded raster layers that can be used. To add a raster to the raster calculator expression field, double click its name in the Fields list. You can then use the operators to construct calculation expressions or you can just type it into the box.

In the Result layer section you have to define an output layer. You can then define the extent of the calculation area based on an input raster layer or based on X,Y coordinates and on Columns and Rows to set the resolution of the output layer. If the input layer has a different resolution, the values will be resampled with nearest neighbor algorithm.

The Operators section contains all usable operators. To add an operator to the raster calculator expression box, click the appropriate button. Mathematical calculations (+, -, *, ... ) and trigonometric functions (sin, cos, tan

, ... ) are available. Stay tuned for more operators to come!

With the be visualized.

Add result to project checkbox the result layer will automatically added to the legend area and can

12.3.1 Examples

Convert elevation values from meter to feet

Creating an elevation raster feet from a raster in meter, you need to use the conversion factor for meters to feet:

3.28. The expression is:

104 Chapter 12. Working with Raster Data

QGIS User Guide, Release 1.8.0

[email protected] * 3.28

Using a mask

If you want to mask out parts of a raster, because you are only interested in elevations above 0 meter, you can use following expression to create a mask and apply the result to a raster in one step.

([email protected] >= 0) * [email protected]

For every cell greater than or equal to 0, set its value to 1, otherwise set it to 0. This creates the mask on the fly.

12.3. Raster Calculator 105

QGIS User Guide, Release 1.8.0

106 Chapter 12. Working with Raster Data

CHAPTER

13

Working with OGC Data

13.1 Working with OGC Data

QGIS supports WMS and WFS as data sources.

13.1.1 What is OGC Data

The Open Geospatial Consortium (OGC), is an international organization with more than 300 commercial, governmental, nonprofit and research organizations worldwide. Its members develop and implement standards for geospatial content and services, GIS data processing and exchange.

Describing a basic data model for geographic features an increasing number of specifications are developed to serve specific needs for interoperable location and geospatial technology, including GIS. Further information can be found under http://www.opengeospatial.org/ .

Important OGC specifications are:

• WMS — Web Map Service

• WFS — Web Feature Service

• WCS — Web Coverage Service

• CAT — Web Catalog Service

• SFS — Simple Features for SQL

• GML — Geography Markup Language

OGC services are increasingly being used to exchange geospatial data between different GIS implementations and data stores. QGIS can now deal with three of the above specifications, being SFS (through support of the

PostgreSQL / PostGIS data provider, see Section

PostGIS Layers

), WFS and WMS as a client.

13.1.2 WMS Client

Overview of WMS Support

QGIS currently can act as a WMS client that understands WMS 1.1, 1.1.1 and 1.3 servers. It has particularly been tested against publicly accessible servers such as DEMIS.

WMS servers act upon requests by the client (e.g. QGIS) for a raster map with a given extent, set of layers, symbolization style, and transparency. The WMS server then consults its local data sources, rasterizes the map, and sends it back to the client in a raster format. For QGIS this would typically be JPEG or PNG.

107

QGIS User Guide, Release 1.8.0

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.

Selecting WMS Servers

The first time you use the WMS feature, there are no servers defined.

Begin by clicking the

Add WMS layer button inside the toolbar, or through the Layer → Add WMS Layer... menu.

The dialog Add Layer(s) from a Server for adding layers from the WMS server appears. You can add some servers to play with by clicking the [Add default servers] button. This will add two WMS demo servers for you to use, the

WMS servers of the DM Solutions Group and Lizardtech. To define a new WMS server in the tab Layers, select the [New] button. Then enter the parameters to connect to your desired WMS server, as listed in

table_OGC_1

:

Name A name for this connection. This name will be used in the Server Connections drop-down box so that you can distinguish it from other WMS Servers.

URL

Username

Password

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 authenticated WMS-server. This parameter is optional.

Ignore GetMap URI reported in capabilities , use given URI from URL-field above.

Ignore GetMap

URI

Ignore

GetFeatureInfo

URI

Ignore GetFeatureInfo URI reported in capabilities above

, use given URI from URL-field

Table OGC 1: WMS Connection Parameters

If you need to set up a proxy-server to be able to receive WMS-services from the internet, you can add your proxy-server in the options. Choose menu Settings → Options and click on the tab Network & Proxy. There you can add your proxy-settings and enable them by setting the 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 sessions.

Tip: On WMS Server URLs

Be sure, when entering in the WMS server URL, that you have the base URL. For example, you shouldn’t have fragments such as request=GetCapabilities or version=1.0.0 in your URL.

Loading WMS Layers

Once you have successfully filled in your parameters you can select the [Connect] button to retrieve the capabilities of the selected server. This includes the Image encoding, Layers, Layer Styles and Projections. Since this is a network operation, the speed of the response depends on the quality of your network connection to the WMS server. While downloading data from the WMS server, the download progress is visualized in the left bottom of the WMS Plugin dialog.

Your screen should now look a bit like

figure_OGR_1

, which shows the response provided by the DM Solutions

Group WMS server.

Image Encoding

108 Chapter 13. Working with OGC Data

QGIS User Guide, Release 1.8.0

Figure 13.1: Dialog for adding a WMS server, showing its available layers

The Image encoding section now lists the formats that are supported by both the client and server. Choose one depending on your image accuracy requirements.

Tip: Image Encoding

You will typically find that a WMS server offers you the choice of JPEG or PNG image encoding. JPEG is a lossy compression format, whereas PNG faithfully reproduces the raw raster data.

Use JPEG if you expect the WMS data to be photographic in nature and/or you don’t mind some loss in picture quality. This trade-off typically reduces by 5 times the data transfer requirement compared to PNG.

Use PNG if you want precise representations of the original data, and you don’t mind the increased data transfer requirements.

Options

The Options field provides a text field where you can add a Layer name for the WMS-layer. This name will be presented in the legend after loading the layer.

Below the layer name you can define Tile size, if you want to set tile sizes (eg. 256x256) to split up the WMS request into multiple requests.

The Feature limit for GetFeatureInfo defines what features from the server to query.

If you select a WMS from the list a field with the default projection, provided by the mapserver, appears. If the

[Change...] button is active, you can click on it and change the default projection of the WMS to another CRS, provided by the WMS server.

Layer Order

The tab Layer Order lists the selected layers available from the current connected WMS server. You may notice that some layers are expandable, this means that the layer can be displayed in a choice of image styles.

13.1. Working with OGC Data 109

QGIS User Guide, Release 1.8.0

You can select several layers at once, but only one image style per layer. When several layers are selected, they will be combined at the WMS Server and transmitted to QGIS in one go.

Tip: WMS Layer Ordering

WMS layers rendered by a server are overlaid in the order listed in the Layers section, from top to bottom of the list. If you want to change the overlay order, you can use the tab Layer Order.

Transparency

In this version of QGIS, the Global transparency setting from the Layer Properties is hard-coded to be always on, where available.

Tip: WMS Layer Transparency

The availability of WMS image transparency depends on the image encoding used: PNG and GIF support transparency, whilst JPEG leaves it unsupported.

Coordinate Reference System

A Coordinate Reference System (CRS) is the OGC terminology for a QGIS Projection.

Each WMS Layer can be presented in multiple CRSs, depending on the capability of the WMS server. 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 tab.

To choose a CRS, select [Change...] and a dialog similar to Figure Projection 3 in

Working with Projections

will appear. The main difference with the WMS version of the screen is that only those CRSs supported by the WMS

Server will be shown.

Tip: WMS Projections

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

Working with Projections

) 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.

Server-Search

Within QGIS you can search for WMS-servers.

Figure_OGC_2

shows the tab Server Search with the Add Layer(s) from a Server dialog.

As you can see it is possible to enter a search-string in the text field and hit the [Search] button. After a short while the search result will be populated into the list below the text field. Browse the result list and inspect your search results within the table. To visualize the results, select a table entry, press the [Add selected row to WMS-list] button and change back to the tab Layers. QGIS automatically has updated your server list and the selected search result is already enabled in the list of saved WMS-servers in the Layers tab. You only need to request the list of layers by clicking the [Connect] button. This option is quite handy when you want to search maps by specific keywords.

Basically this option is a frontend to the API of http://geopole.org

.

Tilesets

When using WMS-C (Cached WMS) Services like http://labs.metacarta.com/wms-c/Basic.py

you are able to browse through the tab Tilesets given by the server. Additional information like tile size, formats and supported

CRS are listed in this table. In combination with this feature you can use the tile scale slider from the View → Tile scale slider , which gives you the available scales from the tileserver with nice slider docked in.

110 Chapter 13. Working with OGC Data

QGIS User Guide, Release 1.8.0

Figure 13.2: Dialog for searching WMS servers after some keywords

Using the Identify Tool

Once you have added a WMS server, and if any layer from a WMS server is queryable, you can then use the

Identify tool to select a pixel on the map canvas. A query is made to the WMS server for each selection made. The results of the query are returned in plain text. The formatting of this text is dependent on the particular WMS server used. Viewing Properties

Once you have added a WMS server, you can view its properties by right-clicking on it in the legend, and selecting

Properties . Metadata Tab

The tab Metadata displays a wealth of information about the WMS server, generally collected from the Capabilities statement returned from that server. Many definitions can be cleaned by reading the WMS standards (see

OPEN-GEOSPATIAL-CONSORTIUM

Literature and Web References

), but here are a few handy definitions:

• Server Properties

– WMS Version — The WMS version supported by the server.

– Image Formats — The list of MIME-types the server can respond with when drawing the map.

QGIS supports whatever formats the underlying Qt libraries were built with, which is typically at least image/png and image/jpeg.

– Identity Formats — The list of MIME-types the server can respond with when you use the Identify tool. Currently QGIS supports the text-plain type.

• Layer Properties

– Selected — Whether or not this layer was selected when its server was added to this project.

– Visible — Whether or not this layer is selected as visible in the legend. (Not yet used in this version of QGIS.)

– Can Identify — Whether or not this layer will return any results when the Identify tool is used on it.

– Can be Transparent — Whether or not this layer can be rendered with transparency. This version of

QGIS will always use transparency if this is Yes and the image encoding supports transparency

13.1. Working with OGC Data 111

QGIS User Guide, Release 1.8.0

– 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.

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 settings. 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 authentication. You can add the (optional) credentials when you add a WMS-server. See section

Selecting WMS Servers

for details.

Tip: Accessing secured OGC-layers

If you need to access secured layers with other secured methods than basic authentication, you could use InteProxy as a transparent proxy, which does support several authentication methods. More information can be found at the

InteProxy manual found on the website http://inteproxy.wald.intevation.org

.

Tip: QGIS WMS Mapserver

From Version 1.7.0 QGIS has its own implementation of a WMS 1.3.0 Mapserver. Read more about this at chapter

QGIS Server

.

13.1.3 WFS and WFS-T Client

In QGIS, a WFS layer behaves pretty much like any other vector layer. You can identify and select features and view the attribute table. Since QGIS 1.6 editing (WFS-T) is also supported.

In general adding a WFS layer is very similar to the procedure used with WMS. The difference is there are no default servers defined, so we have to add our own.

Loading a WFS Layer

As an example we use the DM Solutions WFS server and display a layer.

http://www2.dmsolutions.ca/cgi-bin/mswfs_gmap

The URL is:

112 Chapter 13. Working with OGC Data

QGIS User Guide, Release 1.8.0

1. Click on the

2. Click on [New]

Add WFS Layer tool on the Layers toolbar, the dialog Add WFS Layer from a Server appears

3. Enter ‘DM Solutions’ as name

4. Enter the URL (see above)

5. Click [OK]

6. Choose ‘DM Solutions’ from the Server Connections

7. Click [Connect]

8. Wait for the list of layers to be populated

9. Select the Parks layer in the list combobox

10. Click [Apply] to add the layer to the map

Note that proxy-settings you have set in your preferences are also recognized.

Figure 13.3: Adding a WFS layer

You’ll notice the download progress is visualized in the left bottom of the QGIS main window. Once the layer is loaded, you can identify and select a province or two and view the attribute table.

Only WFS 1.0.0 is supported. At this point there have not been many tests against WFS versions implemented in other WFS-servers. If you encounter problems with any other WFS-server, please do not hesitate to contact the development team. Please refer to Section

Mailing lists

for further information about the mailinglists.

Tip: Finding WFS Servers

You can find additional WFS servers by using Google or your favorite search engine. There are a number of lists with public URLs, some of them maintained and some not.

13.2 QGIS Server

QGIS Server is an open source WMS 1.3 and WFS 1.0.0 implementation which, in addition, implements advanced cartographic features for thematic mapping. The QGIS Server is a FastCGI/CGI (Common Gateway Interface) application written in C++ that works together with a webserver (e.g. Apache, Lighttpd). It is funded by the EU projects Orchestra, Sany and the city of Uster in Switzerland.

13.2. QGIS Server 113

QGIS User Guide, Release 1.8.0

It uses QGIS as backend for the GIS logic and for map rendering. Furthermore the Qt library is used for graphics and for platform independent C++ programming. In contrast to other WMS software, the QGIS Server uses cartographic rules as a configuration language, both for the server configuration and for the user-defined cartographic rules.

Moreover, the QGIS Server project provides the ‘Publish to Web’ plugin, a plugin for QGIS desktop which exports the current layers and symbology as a web project for QGIS Server (containing cartographic visualization rules expressed in SLD).

As QGIS desktop and QGIS Server use the same visualization libraries, the maps that are published on the web look the same as in desktop GIS. The ‘Publish to Web’ plugin currently supports basic symbolization, with more complex cartographic visualization rules introduced manually. As the configuration is performed with the SLD standard and its documented extensions, there is only one standardised language to learn, which greatly simplifies the complexity of creating maps for the Web.

In one of the following manuals we will provide a sample configuration to set up a QGIS Server. But for now we recommend to read one of the following URLs to get more information:

• http://karlinapp.ethz.ch/qgis_wms/

• http://www.qgis.org/wiki/QGIS_mapserver_tutorial

• http://linfiniti.com/2010/08/qgis-mapserver-a-wms-server-for-the-masses/

13.2.1 Sample installation on Debian Squeeze

At this point we will give a short and simple sample installation howto for Debian Squeeze. Many other OS provide packages for QGIS Server, too. If you have to build it all from source, please refer to the URLs above.

Apart from qgis and qgis-mapserver you need a webserver, in our case apache2. You can install all packages with aptitude or apt-get install together with other necessary dependency packages. After installation you should test, if the webserver and qgis server works as expected. Make sure the apache server is running with

/etc/init.d/apache2 start . Open a web browser and type URL: http://localhost. If apache is up, you should see the message ‘It works!’.

Now we test the qgis server installation.

The qgis_mapserv.fcgi

is available at

/usr/lib/cgi-bin/qgis_mapserv.fcgi

and provides a standard wms that shows the state boundaries of Alaska.

Add the WMS with the URL http://localhost/cgi-bin/qgis_mapserv.fcgi as described in

Selecting WMS Servers

.

114

Figure 13.4: Standard WMS with USA boundaries included in the qgis server (KDE)

Chapter 13. Working with OGC Data

QGIS User Guide, Release 1.8.0

13.2.2 Creating a WMS/WFS from a QGIS project

To provide a new qgis wms/wfs server we have to create a qgis project file with some data. Here we use the

‘alaska’ shapefile from the qgis_sample_dataset. Define the colors and styles of the layers in QGIS and define the project CRS, if not already done.

Figure 13.5: Definitions for a qgis project WMS/WFS server (KDE)

Then open the OWS Server tab in the menu Settings → Project Properties and define the general fields under

‘Service Capabilities’. For WMS Capabilities define ‘Coordinate System Restrictions’ and ‘Advertised Extend’. Additionally you can enable the checkbox Add WKT geometry to feature into response to make the layers queryable and add a ‘Maximum width’ and height that can be requested. For WFS Capabilities you only need to select the layers that you want to provide as WFS. Now save the session in a project file alaska.qgs.

To provide the project as a WMS/WFS, we create a new folder /usr/lib/cgi-bin/project with admin privileges and add the project file alaska.qgs and a copy of the qgis_mapserv.fcgi file - that’s all.

Now we test our project WMS and WFS, add the WMS and WFS as described in

Loading WMS Layers

and

WFS and WFS-T Client

to QGIS and load the WMS. The URL is: http://localhost/cgi-bin/project/qgis_mapserv.fcgi

13.2. QGIS Server 115

QGIS User Guide, Release 1.8.0

116 Chapter 13. Working with OGC Data

CHAPTER

14

Working with GPS Data

14.1 GPS Plugin

14.1.1 What is GPS?

GPS, the Global Positioning System, is a satellite-based system that allows anyone with a GPS receiver to find their exact position anywhere in the world. It is used as an aid in navigation, for example in airplanes, in boats and by hikers. The GPS receiver uses the signals from the satellites to calculate its latitude, longitude and (sometimes) elevation. Most receivers also have the capability to store locations (known as waypoints), sequences of locations that make up a planned route and a tracklog or track of the receivers movement over time. Waypoints, routes and tracks are the three basic feature types in GPS data. QGIS displays waypoints in point layers while routes and tracks are displayed in linestring layers.

14.1.2 Loading GPS data from a file

There are dozens of different file formats for storing GPS data. The format that QGIS uses is called GPX (GPS eXchange format), which is a standard interchange format that can contain any number of waypoints, routes and tracks in the same file.

To load a GPX file you first need to load the plugin. Plugins → Plugin Manager...

opens the Plugin Manager

Dialog. Activate the

GPS Tools checkbox. When this plugin is loaded two buttons with a small handheld GPS device will show up in the toolbar:

Create new GPX Layer

GPS Tools

For working with GPS data we provide an example GPX file available in the QGIS sample dataset: qgis_sample_data/gps/national_monuments.gpx

. See Section

Sample Data

for more information about the sample data.

1. Click on the

GPS Tools icon and open the Load GPX file tab (see

figure_GPS_1

).

2. Browse to the folder qgis_sample_data/gps/, select the GPX file national_monuments.gpx

and click [Open].

Use the [Browse...] button to select the GPX file, then use the checkboxes to select the feature types you want to load from that GPX file. Each feature type will be loaded in a separate layer when you click [OK]. The file national_monuments.gpx

only includes waypoints.

117

QGIS User Guide, Release 1.8.0

Figure 14.1: The GPS Tools dialog window

Note: GPS units allow to store data in different coordinate systems. When downloading a GPX file (from your GPS unit or a web site) and then loading it in Quantum GIS, be sure that the data stored in the GPX file uses WGS84 (latitude/longitude). Quantum GIS expects this and it is the official GPX specification. See http://www.topografix.com/GPX/1/1/

14.1.3 GPSBabel

Since QGIS uses GPX files you need a way to convert other GPS file formats to GPX. This can be done for many formats using the free program GPSBabel, which is available at http://www.gpsbabel.org

. This program can also transfer GPS data between your computer and a GPS device. QGIS uses GPSBabel to do these things, so it is recommended that you install it. However, if you just want to load GPS data from GPX files you will not need it.

Version 1.2.3 of GPSBabel is known to work with QGIS, but you should be able to use later versions without any problems.

14.1.4 Importing GPS data

To import GPS data from a file that is not a GPX file, you use the tool Import other file in the GPS Tools dialog.

Here you select the file that you want to import (and the file type), which feature type you want to import from it, where you want to store the converted GPX file and what the name of the new layer should be. Note that not all

GPS data formats will support all three feature types, so for many formats you will only be able to choose between one or two types.

14.1.5 Downloading GPS data from a device

QGIS can use GPSBabel to download data from a GPS device directly as new vector layers. For this we use the

Download from GPS tab of the GPS Tools dialog (see

Figure_GPS_2

). Here, we select the type of GPS device,

the port that it is connected to (or usb if your GPS supports this), the feature type that you want to download, the

GPX file where the data should be stored, and the name of the new layer.

118

Figure 14.2: The download tool

Chapter 14. Working with GPS Data

QGIS User Guide, Release 1.8.0

The device type you select in the GPS device menu determines how GPSBabel tries to communicate with your

GPS device. If none of the available types work with your GPS device you can create a new type (see section

Defining new device types

).

The port may be a file name or some other name that your operating system uses as a reference to the physical port in your computer that the GPS device is connected to. It may also be simply usb, for usb enabled GPS units.

• On Linux this is something like /dev/ttyS0 or /dev/ttyS1

• On Windows it is COM1 or COM2.

When you click [OK] the data will be downloaded from the device and appear as a layer in QGIS.

14.1.6 Uploading GPS data to a device

You can also upload data directly from a vector layer in QGIS to a GPS device using the Upload to GPS tab of the

GPS Tools dialog. To do this you simply select the layer that you want to upload (which must be a GPX layer), your GPS device type, and the port (or usb) that it is connected to. Just as with the download tool you can specify new device types if your device isn’t in the list.

This tool is very useful in combination with the vector editing capabilities of QGIS. It allows you to load a map, create waypoints and routes, and then upload them and use them on your GPS device.

14.1.7 Defining new device types

There are lots of different types of GPS devices. The QGIS developers can’t test all of them, so if you have one that does not work with any of the device types listed in the Download from GPS and Upload to GPS tools you can define your own device type for it. You do this by using the GPS device editor, which you start by clicking the [Edit devices] button in the download or the upload tabs.

To define a new device you simply click the [New device] button, enter a name, a download command and an upload command for your device, and click the [Update device] button. The name will be listed in the device menus in the upload and download windows, and can be any string. The download command is the command that is used to download data from the device to a GPX file. This will probably be a GPSBabel command, but you can use any other command line program that can create a GPX file. QGIS will replace the keywords %type, %in, and %out when it runs the command.

%type will be replaced by -w if you are downloading waypoints, -r if you are downloading routes and -t if you are downloading tracks. These are command line options that tell GPSBabel which feature type to download.

%in will be replaced by the port name that you choose in the download window and %out will be replaced by the name you choose for the GPX file that the downloaded data should be stored in. So if you create a device type with the download command gpsbabel %type -i garmin -o gpx %in %out (this is actually the download command for the predefined device type ‘Garmin serial’) and then use it to download waypoints from port /dev/ttyS0 to the file output.gpx, QGIS will replace the keywords and run the command gpsbabel

-w -i garmin -o gpx /dev/ttyS0 output.gpx

.

The upload command is the command that is used to upload data to the device. The same keywords are used, but

%in is now replaced by the name of the GPX file for the layer that is being uploaded, and %out is replaced by the port name.

You can learn more about GPSBabel and it’s available command line options at http://www.gpsbabel.org

.

Once you have created a new device type it will appear in the device lists for the download and upload tools.

14.2 Live GPS tracking

To activate Live GPS tracking in QGIS you need to select Settings → docked window on the left side of the canvas.

GPS information . You will get a new

14.2. Live GPS tracking 119

QGIS User Guide, Release 1.8.0

There are 4 possible screens in this GPS tracking window:

• GPS position coordinates and for manually entering Vertices and Features.

• GPS signal strength of satellite connections.

• GPS polar screen showing number and polar position of satellites.

• GPS options screen (see

figure_gps_options

).

With a plugged in GPS receiver (has to be supported by your operating system) a simple click on [Connect] connects the GPS to QGIS. A second click (now on [Disconnect]) disconnects the GPS-receiver from your computer.

For GNU/Linux gpsd support is integrated to support connection to most GPS receivers. Therefore you first have to configure gpsd properly to connect QGIS to it.

Warning: If you want to record your position to the canvas you have to create a new vector layer first and switch it to editable status to be able to record your track.

14.2.1 Position and additional attributes

If the GPS is receiving signals from satellites you will see your position in latitude, longitude and altitude together with additional attributes.

Figure 14.3: GPS tracking position and additional attributes

14.2.2 GPS signal strength

Here you can see the signal strenght of the satellites you are receiving signals from.

120

Figure 14.4: GPS tracking signal strength

Chapter 14. Working with GPS Data

QGIS User Guide, Release 1.8.0

14.2.3 GPS polar window

If you want to know where in the sky all the connected satellites are, you have to switch to the polar screen.

You can also see the ID numbers of the satellites you are receiving signals from.

Figure 14.5: GPS tracking polar window

14.2.4 GPS options

In case of connection problems you can switch between:

Autodetect

Internal ,

Serial device gpsd (selecting Host, Port and Device your GPS is connected to).

A click on [Connect] again initiates the connection to the GPS receiver.

Figure 14.6: GPS tracking options window

You can activate Automatically save added features when you are in editing mode. Or you can can activate

Automatically add points to the main windows with a certain width and color.

14.2. Live GPS tracking 121

QGIS User Guide, Release 1.8.0

Activating canvas.

Cursor you can use a slider to shrink and grow the position cursor on the

Activating Map centering allows to decide in which way the canvas will be updated. This includes ‘always’,

‘when leaving’ if your recorded coordinates start either to move out of canvas or ‘never’ to keep map extent.

Finally you can activate logged.

Log file and define a path and a file where log messages about the gps tracking a

If you want to set a feature manually you have to go back to point].

Position and click on [Add Point] or [Add track

122 Chapter 14. Working with GPS Data

CHAPTER

15

GRASS GIS Integration

The GRASS plugin provides access to GRASS GIS (see GRASS-PROJECT

Literature and Web References

)

databases and functionalities. This includes visualization of GRASS raster and vector layers, digitizing vector layers, editing vector attributes, creating new vector layers and analysing GRASS 2D and 3D data with more than

300 GRASS modules.

In this Section we’ll introduce the plugin functionalities and give some examples on managing and working with

GRASS data. Following main features are provided with the toolbar menu, when you start the GRASS plugin, as described in section

Starting the GRASS plugin

:

Open mapset

New mapset

Close mapset

Add GRASS vector layer

Add GRASS raster layer

Create new GRASS vector

Edit GRASS vector layer

Open GRASS tools

Display current GRASS region

Edit current GRASS region

15.1 Starting the GRASS plugin

To use GRASS functionalities and/or visualize GRASS vector and raster layers in QGIS, you must select and load the GRASS plugin with the Plugin Manager. Therefore click the menu Plugins →

GRASS and click [OK].

Manage Plugins , select

You can now start loading raster and vector layers from an existing GRASS LOCATION (see section

Loading

GRASS raster and vector layers

). Or you create a new GRASS LOCATION with QGIS (see section

Creating a new GRASS LOCATION

) and import some raster and vector data (see Section

Importing data into a GRASS

LOCATION

) for further analysis with the GRASS Toolbox (see section

The GRASS toolbox

).

123

QGIS User Guide, Release 1.8.0

15.2 Loading GRASS raster and vector layers

With the GRASS plugin, you can load vector or raster layers using the appropriate button on the toolbar menu.

As an example we use the QGIS alaska dataset (see Section

Sample Data

). It includes a small sample GRASS

LOCATION with 3 vector layers and 1 raster elevation map.

1. Create a new folder grassdata, download the QGIS alaska dataset qgis_sample_data.zip from http://download.osgeo.org/qgis/data/ and unzip the file into grassdata.

2. Start QGIS.

Manage 3. If not already done in a previous QGIS session, load the GRASS plugin clicking on Plugins →

Plugins and activate GRASS . The GRASS toolbar appears in the QGIS main window.

4. In the GRASS toolbar, click the

Open mapset icon to bring up the MAPSET wizard.

5. For Gisdbase browse and select or enter the path to the newly created folder grassdata.

6. You should now be able to select the LOCATION alaska and the MAPSET

7. Click [OK]. Notice that some previously disabled tools in the GRASS toolbar are now enabled.

demo

.

8. Click on be visualized.

Add GRASS raster layer

, choose the map name gtopo30 and click [OK]. The elevation layer will

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

The Vector Properties Dialog

, e.g. change opacity, fill and outline color.

10. Also load the other two vector layers rivers and airports and adapt their properties.

As you see, it is very simple to load GRASS raster and vector layers in QGIS. See following sections for editing

GRASS data and creating a new LOCATION. More sample GRASS LOCATIONs are available at the GRASS website at http://grass.osgeo.org/download/data.php

.

Tip: GRASS Data Loading

If you have problems loading data or QGIS terminates abnormally, check to make sure you have loaded the

GRASS plugin properly as described in section

Starting the GRASS plugin

.

15.3 GRASS LOCATION and MAPSET

GRASS data are stored in a directory referred to as GISDBASE. This directory often called grassdata, must be created before you start working with the GRASS plugin in QGIS. Within this directory, the GRASS GIS data are organized by projects stored in subdirectories called LOCATION. Each LOCATION is defined by its coordinate system, map projection and geographical boundaries. Each LOCATION can have several MAPSETs

(subdirectories of the LOCATION) that are used to subdivide the project into different topics, subregions, or as workspaces for individual team members (Neteler & Mitasova 2008

Literature and Web References

). In order to

analyze vector and raster layers with GRASS modules, you must import them into a GRASS LOCATION (This is not strictly true - with the GRASS modules r.external and v.external you can create read-only links to external GDAL/OGR-supported data sets without importing them. But because this is not the usual way for beginners to work with GRASS, this functionality will not be described here.).

15.3.1 Creating a new GRASS LOCATION

As an example here is how the sample GRASS LOCATION alaska, which is projected in Albers Equal Area projection with unit feet was created for the QGIS sample dataset. This sample GRASS LOCATION alaska

124 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

Figure 15.1: GRASS data in the alaska LOCATION will be used for all examples and exercises in the following GRASS GIS related chapters. It is useful to download and install the dataset on your computer

Sample Data

).

1. Start QGIS and make sure the GRASS plugin is loaded.

2. Visualize the alaska.shp Shapefile (see Section

Loading a Shapefile

) from the QGIS alaska dataset

Sample Data

.

3. In the GRASS toolbar, click on the

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

Adding a new

MAPSET

) or to create a new LOCATION altogether. Click on the radio button

Create new location (see

figure_grass_location_2

).

6. Enter a name for the LOCATION - we used alaska and click [Next].

7. Define the projection by clicking on the radio button Projection to enable the projection list.

8. We are using Albers Equal Area Alaska (feet) projection. Since we happen to know that it is represented by the EPSG ID 2964, we enter it in the search box. (Note: If you want to repeat this process for another

LOCATION and projection and haven’t memorized the EPSG ID, click on the right-hand corner of the status bar (see Section

Working with Projections

)).

projector icon in the lower

9. 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 (When creating a new LOCATION). GRASS automatically creates a special MAPSET called

PERMANENT designed to store the core data for the project, its default spatial extend and coordinate system definitions (Neteler & Mitasova 2008

Literature and Web References

)

14. Check out the summary to make sure it’s correct and click [Finish].

15.3. GRASS LOCATION and MAPSET 125

QGIS User Guide, Release 1.8.0

15. The new LOCATION alaska and two MAPSETs demo and PERMANENT are created. The currently opened working set is MAPSET demo, as you defined.

16. Notice that some of the tools in the GRASS toolbar that were disabled are now enabled.

Figure 15.2: Creating a new GRASS LOCATION or a new MAPSET in QGIS

If that seemed like a lot of steps, it’s really not all that bad and a very quick way to create a LOCATION. The

LOCATION alaska is now ready for data import (see section

Importing data into a GRASS LOCATION

). You

can also use the already existing vector and raster data in the sample GRASS LOCATION alaska included in the QGIS alaska dataset

Sample Data

and move on to Section

The GRASS vector data model

.

15.3.2 Adding a new MAPSET

A user has only write access to a GRASS MAPSET he created. This means that besides access to his own MAPSET, each user can read maps in other user’s MAPSETs, but he can modify or remove only the maps in his own MAPSET.

All MAPSETs include a WIND file that stores the current boundary coordinate values and the currently selected raster resolution (Neteler & Mitasova 2008

Literature and Web References

, see Section

The GRASS region tool

).

1. Start QGIS and make sure the GRASS plugin is loaded.

2. In the GRASS toolbar, click on the

New mapset icon to bring up the MAPSET wizard.

3. Select the GRASS database (GISDBASE) folder grassdata with the LOCATION alaska, where we want to add a further MAPSET, called test.

4. Click [Next].

5. We can use this wizard to create a new MAPSET within an existing LOCATION or to create a new

LOCATION altogether. Click on the radio button Select location (see

figure_grass_location_2

) and click

[Next].

6. Enter the name text for the new MAPSET. Below in the wizard you see a list of existing MAPSETs and its owners.

7. Click [Next], check out the summary to make sure it’s all correct and click [Finish].

15.4 Importing data into a GRASS LOCATION

This Section gives an example how to import raster and vector data into the alaska GRASS LOCATION provided by the QGIS alaska dataset. Therefore we use a landcover raster map landcover.img and a vector GML File

126 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

lakes.gml

from the QGIS alaska dataset

Sample Data

.

1. Start QGIS and make sure the GRASS plugin is loaded.

2. In the GRASS toolbar, click the

Open MAPSET icon to bring up the MAPSET wizard.

3. Select as GRASS database the folder grassdata in the QGIS alaska dataset, as LOCATION alaska, as MAPSET demo and click [OK].

4. Now click the appears.

Open GRASS tools icon. The GRASS Toolbox (see section

The GRASS toolbox

) dialog

5. To import the raster map landcover.img, click the module r.in.gdal in the Modules Tree tab. This

GRASS module allows to import GDAL supported raster files into a GRASS LOCATION. The module dialog for r.in.gdal appears.

6. Browse to the folder raster in the QGIS alaska dataset and select the file landcover.img.

7. As raster output name define landcover_grass and click [Run].

In the Output tab you see the currently running GRASS command r.in.gdal -o input=/path/to/landcover.img

output=landcover_grass

.

8. When it says Succesfully finished click [View output]. The landcover_grass raster layer is now imported into GRASS and will be visualized in the QGIS canvas.

9. To import the vector GML file lakes.gml, click the module v.in.ogr in the Modules Tree tab. This

GRASS module allows to import OGR supported vector files into a GRASS LOCATION. The module dialog for v.in.ogr appears.

10. Browse to the folder gml in the QGIS alaska dataset and select the file lakes.gml as OGR file.

11. As vector output name define lakes_grass and click [Run]. You don’t have to care about the other options in this example. In the Output tab you see the currently running GRASS command v.in.ogr -o dsn=/path/to/lakes.gml output=lakes_grass

.

12. When it says Succesfully finished click [View output]. The lakes_grass vector layer is now imported into GRASS and will be visualized in the QGIS canvas.

15.5 The GRASS vector data model

It is important to understand the GRASS vector data model prior to digitizing.

In general, GRASS uses a topological vector model.

This means that areas are not represented as closed polygons, but by one or more boundaries. A boundary between two adjacent areas is digitized only once, and it is shared by both areas. Boundaries must be connected and closed without gaps. An area is identified (and labeled) by the centroid of the area.

Besides boundaries and centroids, a vector map can also contain points and lines. All these geometry elements can be mixed in one vector and will be represented in different so called ‘layers’ inside one GRASS vector map.

So in GRASS a layer is not a vector or raster map but a level inside a vector layer. This is important to distinguish carefully (Although it is possible to mix geometry elements, it is unusual and even in GRASS only used in special cases such as vector network analysis. Normally you should prefere to store different geometry elements in different layers.).

It is possible to store several ‘layers’ in one vector dataset. For example, fields, forests and lakes can be stored in one vector. Adjacent forest and lake can share the same boundary, but they have separate attribute tables. It is also possible to attach attributes to boundaries. For example, the boundary between lake and forest is a road, so it can have a different attribute table.

The ‘layer’ of the feature is defined by ‘layer’ inside GRASS. ‘Layer’ is the number which defines if there are more than one layer inside the dataset, e.g. if the geometry is forest or lake. For now, it can be only a number, in the future GRASS will also support names as fields in the user interface.

15.5. The GRASS vector data model 127

QGIS User Guide, Release 1.8.0

Attributes can be stored inside the GRASS LOCATION as DBase or SQLITE3 or in external database tables, for example PostgreSQL, MySQL, Oracle, etc.

Attributes in database tables are linked to geometry elements using a ‘category’ value.

‘Category’ (key, ID) is an integer attached to geometry primitives, and it is used as the link to one key column in the database table.

Tip: Learning the GRASS Vector Model

The best way to learn the GRASS vector model and its capabilities is to download one of the many GRASS tutorials where the vector model is described more deeply. See http://grass.osgeo.org/gdp/manuals.php

for more information, books and tutorials in several languages.

15.6 Creating a new GRASS vector layer

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 polygon geometries, following the procedure described in Section

Digitizing and editing a GRASS vector layer

.

In GRASS it is possible to organize all sort of geometry types (point, line and area) in one layer, because GRASS uses a topological vector model, so you don’t need to select the geometry type when creating a new GRASS vector.

This is different from Shapefile creation with QGIS, because Shapefiles use the Simple Feature vector model (see

Section

Creating a new Vector layer

).

Tip: Creating an attribute table for a new GRASS vector layer

If you want to assign attributes to your digitized geometry features, make sure to create an attribute table with columns before you start digitizing (see

figure_grass_digitizing_5

).

15.7 Digitizing and editing a GRASS vector layer

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

figure_grass_digitizing_2

shows the GRASS edit dialog that is displayed when you click on the edit tool. The tools and settings are discussed in the following sections.

Tip: Digitizing polygons in GRASS

If you want to create a polygon in GRASS, you first digitize the boundary of the polygon, setting the mode to ‘No category’. Then you add a centroid (label point) into the closed boundary, setting the mode to ‘Next not used’.

The reason is, that a topological vector model links attribute information of a polygon always to the centroid and not to the boundary.

Toolbar

In

figure_grass_digitizing_1

you see the GRASS digitizing toolbar icons provided by the

GRASS plugin.

Table

table_grass_digitizing_1

explains the available functionalities.

128

Figure 15.3: GRASS Digitizing Toolbar

Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

Icon Tool

New Point

New Line

New

Boundary

Purpose

Digitize new point

Digitize new line

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

Delete element

Split an existing line to 2 parts

Delete existing boundary, line, point or centroid (confirm selected element by another click)

Edit attributes

Edit attributes of selected element (note that one element can represent more features, see above)

Close Close session and save current status (rebuilds topology afterwards)

Table GRASS Digitizing 1: GRASS Digitizing Tools

Category Tab

The Category tab allows you to define the way in which the category values will be assigned to a new geometry element.

Figure 15.4: GRASS Digitizing Category Tab

• Mode: what category value shall be applied to new geometry elements.

– Next not used - apply next not yet used category value to geometry element.

– Manual entry - manually define the category value for the geometry element in the ‘Category’-entry field.

– No category - Do not apply a category value to the geometry element. This is e.g. used for area boundaries, because the category values are connected via the centroid.

• Category - A number (ID) is attached to each digitized geometry element. It is used to connect each geometry element with its attributes.

15.7. Digitizing and editing a GRASS vector layer 129

QGIS User Guide, Release 1.8.0

• Field (layer) - Each geometry element can be connected with several attribute tables using different GRASS geometry layers. Default layer number is 1.

Tip: Creating an additional GRASS ‘layer’ with QGIS

If you would like to add more layers to your dataset, just add a new number in the ‘Field (layer)’ entry box and press return. In the Table tab you can create your new table connected to your new layer.

Settings Tab

The Settings tab allows you to set the snapping in screen pixels. The threshold defines at what distance new points or line ends are snapped to existing nodes. This helps to prevent gaps or dangles between boundaries. The default is set to 10 pixels.

Figure 15.5: GRASS Digitizing Settings Tab

Symbology Tab

The Symbology tab allows you to view and set symbology and color settings for various geometry types and their topological status (e.g. closed / opened boundary).

Figure 15.6: GRASS Digitizing Symbolog Tab

Table Tab

The Table tab provides information about the database table for a given ‘layer’. Here you can add new columns to an existing attribute table, or create a new database table for a new GRASS vector layer (see Section

Creating a new GRASS vector layer

).

Tip: GRASS Edit Permissions

You must be the owner of the GRASS MAPSET you want to edit. It is impossible to edit data layers in a MAPSET that is not yours, even if you have write permissions.

130 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

Figure 15.7: GRASS Digitizing Table Tab

15.8 The GRASS region tool

The region definition (setting a spatial working window) in GRASS is important for working with raster layers.

Vector analysis is by default not limited to any defined region definitions. But all newly-created rasters will have the spatial extension and resolution of the currently defined GRASS region, regardless of their original extension and resolution. The current GRASS region is stored in the $LOCATION/$MAPSET/WIND file, and it defines north, south, east and west bounds, number of columns and rows, horizontal and vertical spatial resolution.

It is possible to switch on/off the visualization of the GRASS region in the QGIS canvas using the

Display current GRASS region button.

With the

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

The

GRASS toolbox

.

15.9 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.

The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 330) GRASS modules through a command line interface. To offer a more user friendly working environment, about 200 of the available

GRASS modules and functionalities are also provided by graphical dialogs within the GRASS plugin Toolbox.

15.9.1 Working with GRASS modules

The GRASS Shell inside the GRASS Toolbox provides access to almost all (more than 300) GRASS modules in a command line interface. To offer a more user friendly working environment, about 200 of the available GRASS modules and functionalities are also provided by graphical dialogs.

15.8. The GRASS region tool 131

QGIS User Guide, Release 1.8.0

Figure 15.8: GRASS Toolbox and Module Tree

A complete list of GRASS modules available in the graphical Toolbox in QGIS version 1.8.0 is available in the

GRASS wiki ( http://grass.osgeo.org/wiki/GRASS-QGIS_relevant_module_list ).

It is also possible to customize the GRASS Toolbox content. This procedure is described in Section

Customizing the GRASS Toolbox

.

As shown in

figure_grass_toolbox_1

, you can look for the appropriate GRASS module using the thematically grouped Modules Tree or the searchable Modules List tab.

Clicking on a graphical module icon a new tab will be added to the toolbox dialog providing three new sub-tabs

Options , Output and Manual.

Options

The Options tab provides a simplified module dialog where you can usually select a raster or vector layer visualized in the QGIS canvas and enter further module specific parameters to run the module.

The provided module parameters are often not complete to keep the dialog clear. If you want to use further module parameters and flags, you need to start the GRASS Shell and run the module in the command line.

A new feature in QGIS 1.8.0 is the support for a show advanced options button below the simplified module dialog in the Options tab. At the moment it is only added to the module v.in.ascii as an example use, but will probably be part of more / all modules in the GRASS toolbox in future versions of QGIS. This allows to use the complete

GRASS module options without the need to switch to the GRASS Shell.

Output

The Output tab provides information about the output status of the module. When you click the [Run] button, the module switches to the Output tab and you see information about the analysis process. If all works well, you will finally see a Successfully finished message.

Manual

The Manual tab shows the HTML help page of the GRASS module. You can use it to check further module parameters and flags or to get a deeper knowledge about the purpose of the module. At the end of each module manual page you see further links to the Main Help index, the Thematic index and the Full index.

These links provide the same information as if you use the module g.manual.

Tip: Display results immediately

If you want to display your calculation results immediately in your map canvas, you can use the ‘View Output’ button at the bottom of the module tab.

132 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

Figure 15.9: GRASS Toolbox Module Options

15.9. The GRASS toolbox

Figure 15.10: GRASS Toolbox Module Output

133

QGIS User Guide, Release 1.8.0

Figure 15.11: GRASS Toolbox Module Manual

15.9.2 GRASS module examples

The following examples will demonstrate the power of some of the GRASS modules.

Creating contour lines

The first example creates a vector contour map from an elevation raster (DEM). Assuming you have the Alaska

LOCATION set up as explained in Section

Importing data into a GRASS LOCATION

.

• First open the location by clicking the

Open mapset button and choosing the Alaska location.

• Now load the gtopo30 elevation raster by clicking raster from the demo location.

Add GRASS raster layer and selecting the gtopo30

• Now open the Toolbox with the

Open GRASS tools button.

• In the list of tool categories double click Raster → Surface Management → Generate vector contour lines.

• Now a single click on the tool r.contour will open the tool dialog as explained above

Working with GRASS modules

. The gtopo30 raster should appear as the Name of input raster.

• Type into the Increment between Contour levels intervals of 100 meters.) the value 100. (This will create contour lines at

• Type into the Name for output vector map the name ctour_100.

• Click [Run] to start the process. Wait for several moments until the message Successfully finished appears in the output window. Then click [View Output] and [close].

134 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

Since this is a large region, it will take a while to display. After it finishes rendering, you can open the layer properties window to change the line color so that the contours appear clearly over the elevation raster, as in

The

Vector Properties Dialog

.

Next zoom in to a small mountainous area in the center of Alaska. Zooming in close you will notice that the contours have sharp corners. GRASS offers the v.generalize tool to slightly alter vector maps while keeping their overall shape. The tool uses several different algorithms with different purposes. Some of the algorithms (i.e.

Douglas Peuker and Vertex reduction) simplify the line by removing some of the vertices. The resulting vector will load faster. This process will be used when you have a highly detailed vector, but you are creating a very small scale map, so the detail is unnecessary.

Tip: The simplify tool

Note that the QGIS fTools plugin has a Simplify geometries → tool that works just like the GRASS v.generalize

Douglas-Peuker algorithm.

However, the purpose of this example is different. The contour lines created by r.contour have sharp angles that should be smoothed. Among the v.generalize algorithms there is Chaikens which does just that (also Hermite splines). Be aware that these algorithms can add additional vertices to the vector, causing it to load even more slowly.

• Open the GRASS toolbox and double click the categories Vector → Develop map → Generalization, then click on the v.generalize module to open its options window.

• Check that the ‘ctour_100’ vector appears as the Name of input vector.

• From the list of algorithms choose Chaiken’s. Leave all other options at their default, and scroll down to the last row to enter in the field Name for output vector map ‘ctour_100_smooth’, and click [Run].

• The process takes several moments. Once Successfully finished appears in the output windows, click [View output] and then [close].

• You may change the color of the vector to display it clearly on the raster background and to contrast with the original contour lines. You will notice that the new contour lines have smoother corners than the original while staying faithful to the original overall shape.

Figure 15.12: GRASS module v.generalize to smooth a vector map

Tip: Other uses for r.contour

15.9. The GRASS toolbox 135

QGIS User Guide, Release 1.8.0

The procedure described above can be used in other equivalent situations. If you have a raster map of precipitation data, for example, then the same method will be used to create a vector map of isohyetal (constant rainfall) lines.

Creating a Hillshade 3D effect

Several methods are used to display elevation layers and give a 3D effect to maps. The use of contour lines as shown above is one popular method often chosen to produce topographic maps. Another way to display a 3D effect is by hillshading. The hillshade effect is created from a DEM (elevation) raster by first calculating the slope and aspect of each cell, then simulating the sun’s position in the sky and giving a reflectance value to each cell.

Thus you get sun facing slopes lighted and the slopes facing away from the sun (in shadow) are darkened.

• Begin this example by loading the gtopo30 elevation raster. Start the GRASS toolbox and under the

Raster category double click to open Spatial analysis → Terrain analysis.

• Then click r.shaded.relief to open the module.

• Change the azimuth angle 270 to 315.

• Enter gtopo30_shade for the new hillshade raster, and click [Run].

• When the process completes, add the hillshade raster to the map. You should see it displayed in grayscale.

• To view both the hill shading and the colors of the gtopo30 together shift the hillshade map below the gtopo30 map in the table of contents, then open the Properties window of gtopo30, switch to the transparency tab and set its transparency level to about 25%.

You should now have the gtopo30 elevation with its colormap and transparency setting displayed above the grayscale hillshade map. In order to see the visual effects of the hillshading, turn off the gtopo30_shade map, then turn it back on.

Using the GRASS shell

The GRASS plugin in QGIS is designed for users who are new to GRASS, and not familiar with all the modules and options. As such, some modules in the toolbox do not show all the options available, and some modules do not appear at all. The GRASS shell (or console) gives the user access to those additional GRASS modules that do not appear in the toolbox tree, and also to some additional options to the modules that are in the toolbox with the simplest default parameters. This example demonstrates the use of an additional option in the r.shaded.relief

module that was shown above.

Figure 15.13: The GRASS shell, r.shaded.relief module

The module r.shaded.relief can take a parameter zmult which multiplies the elevation values relative to the X-Y coordinate units so that the hillshade effect is even more pronounced.

136 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

• Load the gtopo30 elevation raster as above, then start the GRASS toolbox and click on the

GRASS shell.

In the shell window type the command r.shaded.relief map=gtopo30 shade=gtopo30_shade2 azimuth=315 zmult=3 and press [Enter].

• After the process finishes shift to the Browse tab and double click on the new gtopo30_shade2 raster to display in QGIS.

• As explained above, shift the shaded relief raster below the gtopo30 raster in the Table of Contents, then check transparency of the colored gtopo30 layer. You should see that the 3D effect stands out more strongly compared to the first shaded relief map.

Figure 15.14: Displaying shaded relief created with the GRASS module r.shaded.relief

Raster statistics in a vector map

The next example shows how a GRASS module can aggregate raster data and add columns of statistics for each polygon in a vector map.

• Again using the Alaska data, refer to

Importing data into a GRASS LOCATION

to import the trees shapefile from the shapefiles directory into GRASS.

• Now an intermediary step is required: centroids must be added to the imported trees map to make it a complete GRASS area vector (including both boundaries and centroids).

• From the toolbox choose Vector → Manage features, and open the module v.centroids.

• Enter as the output vector map ‘forest_areas’ and run the module.

• Now load the forest_areas vector and display the types of forests - deciduous, evergreen, mixed in different colors: In the layer Properties window, Symbology tab, choose from Legend type

‘Unique value’ and set the Classification field to ‘VEGDESC’. (Refer to the explanation of the symbology tab :ref:sec_symbology in the vector section).

• Next reopen the GRASS toolbox and open Vector → Vector update by other maps.

• Click on the v.rast.stats module. Enter gtopo30, and forest_areas.

• Only one additional parameter is needed: Enter column prefix elev, and click [run]. This is a computationally heavy operation which will run for a long time (probably up to two hours).

15.9. The GRASS toolbox 137

QGIS User Guide, Release 1.8.0

• Finally open the forest_areas attribute table, and verify that several new columns have been added including elev_min, elev_max, elev_mean etc. for each forest polygon.

15.9.3 Working with the GRASS LOCATION browser

Another useful feature inside the GRASS Toolbox is the GRASS LOCATION browser. In

figure_grass_module_7

you can see the current working LOCATION with its MAPSETs.

In the left browser windows you can browse through all MAPSETs inside the current LOCATION. The right browser window shows some meta information for selected raster or vector layers, e.g. resolution, bounding box, data source, connected attribute table for vector data and a command history.

Figure 15.15: GRASS LOCATION browser

The toolbar inside the Browser tab offers following tools to manage the selected LOCATION:

Add selected map to canvas

Copy selected map

Rename selected map

Delete selected map

Set current region to selected map

Refresh browser window

The Rename selected map and Delete selected map only work with maps inside your currently selected

MAPSET

. All other tools also work with raster and vector layers in another MAPSET.

15.9.4 Customizing the GRASS Toolbox

Nearly all GRASS modules can be added to the GRASS toolbox. A XML interface is provided to parse the pretty simple XML files which configures the modules appearance and parameters inside the toolbox.

A sample XML file for generating the module v.buffer (v.buffer.qgm) looks like this:

138 Chapter 15. GRASS GIS Integration

QGIS User Guide, Release 1.8.0

<?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://hub.qgis.org/projects/quantum-gis/wiki/Adding_New_Tools_to_the_GRASS_Toolbox

15.9. The GRASS toolbox 139

QGIS User Guide, Release 1.8.0

140 Chapter 15. GRASS GIS Integration

CHAPTER

16

OpenStreetMap

In recent years, the OpenStreetMap project has gained popularity because in many countries no free geodata such as digital roadmaps are available. The objective of the OSM project is to create a free editable map of the world from GPS data, aerial photography or from local knowledge. To support this objective, QGIS provides a plugin that enables its users to work with OSM data.

The OpenStreetMap plugin, a core QGIS plugin, provides the basic functionalities for OSM data manipulation; this includes data loading, importing, saving, downloading, editing and uploading data back to the OpenStreetMap server. While implementing the OSM plugin an inspiration was taken from existing OSM data editors. The purpose was to combine their functionalities to get the best possible result.

The following section gives a brief introduction to principles of the OSM project.

Parts of the following paragraphs are copied from the OpenStreetMap web site at http://www.openstreetmap.org

.

16.1 The OpenStreetMap project

OpenStreetMap is a project to create a free editable map of the world. The maps are created using data from portable GPS devices, aerial photography, other free sources or simply from local knowledge. The project was started because most maps have legal or technical restrictions on their use, restricting people from using them in creative, productive, or unexpected ways. Both rendered images and the vector dataset of OSM are available for download under a Creative Commons Attribution ShareAlike 2.0 license.

OpenStreetMap was inspired by sites such as Wikipedia - the map display (see

Figure_OpenStreetMap_1

) features a prominent Edit tab and a full revision history is maintained. Registered users can upload GPS track logs and edit the vector data using the given editing tools.

OSM data primitive is an object class that can be stored via the API in the server. The three supported types of data are: Node, Way and Relation.

• A node is a latitude/longitude pair of coordinates. It is used as building a block for other features and as a feature itself (Points Of Interest), if they are tagged as required.

• A way is a list of at least two nodes that describe a linear feature such as a street, or similar. Nodes can be members of multiple ways.

• A relation is a group of zero or more primitives with associated roles. It is used to specify relationships between objects, and may also model an abstract object.

Several different logical features in a common map ‘Point Of Interest’, ‘Street’, ‘Tram Line’, ‘Bus Stop’ etc.) are defined by these primitives. Map features are well-known in the OSM community and are stored as tags, based on a key and a value. OSM is usually distributed in XML format. XML payload is used for the communication with the OSM server as well.

141

QGIS User Guide, Release 1.8.0

Figure 16.1: OpenStreetMap data in the web

16.2 QGIS - OSM Connection

The first part of this section describes how OSM data primitives are displayed in QGIS vector layers. As previously mentioned, OSM data consists of Nodes, Ways and Relations. In QGIS, they are displayed in three different layer types: Point layer, Line layer and Polygon layer. It is not possible to remove any of these layers and work with the other ones.

• A Point layer displays all features of type Node that stands alone. That means that only Nodes that are not included in any Way belongs to the Point layer.

• A Line layer displays those OSM features of type Way that are not closed. That means, none of these Ways starts and ends with the same Node.

• A Polygon layer displays all Ways that are not included in Line layer.

OpenStreetMap has one more data primitive in addition to the three mentioned above. This is called Relation.

There is purposely no vector layer to display Relations. A Relation defines a connection between any number of data primitives. After a Point, Line or Polygon is identified on a map, the plugin shows a list of all relations which the identified feature is part of.

It was challenging to design the connection between OSM data and the standard QGIS editing tools. These tools are made to edit a single vector layer at a time, no matter of what feature types it displays. This means that if OSM data are loaded to QGIS through the plugin, you could (theoretically) edit the Point layer, Line layer or Polygon layer with these standard tools separately.

A Line layer consists of two different types of OSM features, Ways and Nodes. In OSM format, a Way is composed of Nodes. If you start editing a Line layer and change the shape of some line, your action affects not only the

OSM Way, but also the OSM Nodes that are part of it.

QGIS standard editing tools cannot tell the OSM provider, which members of which line has changed and how.

It can tell only what’s the new geometry of which line, and that’s not enough to propagate changes to the OSM database correctly. The Line layer does also not know the identifiers of the line members. The same problem occurs when you try to edit the Polygon layer.

142 Chapter 16. OpenStreetMap

QGIS User Guide, Release 1.8.0

For this reason, the OSM plugin need its own tools for editing OSM data. While they are used, the OSM layers can be changed correctly. The Plugin editing tools consists of tools for Point, Line, Polygon and Relation creation, deletion and moving.

Note: To create a connection between the OSM plugin and standard editing tools, changes in QuantumGIS core code would be necessary.

16.3 Installation

The OpenStreetMap plugin is a core plugin inside QGIS. The ‘OpenStreetMap’ plugin can be selected in the

Plugin Manager as described in section

Loading a QGIS Core Plugin

.

16.4 Basic user interface

The first time the OSM plugin is started (and after the first data are loaded), several new OSM plugin icons appear in the QGIS toolbar menu together with new dock windows as shown in

figure_OpenStreetMap_2

.

Figure 16.2: OSM plugin user interface

16.4.1 OSM Features widget

The OSM Feature widget helps to identify OSM features. It shows basic information on the feature type and identifier as well as information on who has changed a feature, and when. The OSM Feature widget also provides all editing tools (in the top part of it). More information on those tools can be found in the sections below. The widget is initially disabled. It activates itself after successful loading some OSM data.

16.4.2 OSM Undo/Redo widget

This Undo/Redo widget is used to undo and redo edit actions. It consists not only a classic Undo and Redo button, but also shows a list with a brief description of the edit actions that were done. The OSM Undo/Redo widget is initially closed. You can show it using a button on the OSM Feature widget.

16.3. Installation 143

QGIS User Guide, Release 1.8.0

16.4.3 Toolbar menu icons

Load OSM from file is used to load data from a special OpenStreetMap XML file.

Show/Hide OSM Feature Manager is used to show or hide the OSM Feature widget. The OSM Feature widget is a panel that helps with OSM feature identification and with OSM data editing.

Download OSM data is used to download data from the OpenStreetMap server.

Upload OSM data is used to upload changes (on current data).

Import data from a layer is used to import data from a vector layer. At least one vector layer must be loaded and current OSM data must be selected.

Save OSM to file is used to save OSM data back to an XML file.

More detailed information on all the widgets, buttons and dialogs can be found in appropriate sections of this plugin section according to their functionality (editing, identification, etc.).

16.5 Loading OSM data

The first action that should be done after starting the OSM Plugin is opening data from an OSM file. OSM data can be import as shapefile or downloaded directly from the OpenStreetMap server. Here we are focusing on the first mentioned method.

To load data from a file use the

Load OSM from file icon. If there is no such button, maybe someone disabled

OpenStreetMap toolbar in your QGIS installation. You can enable it again selecting Settings → Toolbars →

OpenStreetMap

.

Figure 16.3: Load OSM data dialog

The purpose of its elements is explained below.

OpenStreetMap file to load: Click on the button to select the file:.osm file you want to load data from.

Add columns for tags: This option determines a connection between OSM and QGIS data. Each feature of OSM data has some tags (pairs of key and value), that define the feature properties. Each feature of a QGIS vector layer also has its attributes (key and value). With this option you can define which properties of OSM objects should be visible when displaying detailed information about QGIS features.

144 Chapter 16. OpenStreetMap

QGIS User Guide, Release 1.8.0

Replace current data: Checking this option means that new data should replace current data the user is working with. Layers of current data will be removed and new ones will be loaded. When loading OSM data for the first time, this option is not active, because there is nothing to replace.

Use custom renderer: This option determines how many details of the map will be used. There are three predefined OSM styles for map displaying. Use ‘Small scale’ if you want to view OSM data at low level, to see all details and to edit something. If not you can use ‘Medium scale’ or ‘Large scale’. QGIS 1.8.0 doesn’t support changing the renderer style dynamically.

Click [OK] to load your data. If this is the first time the OSM file is loaded, the plugin must first parse the database.

This may take few seconds or minutes - it depends on the amount of loaded data.

16.6 Viewing OSM data

After the OSM data are loaded, you can identify map features using the appropriate tool. Use the

Identify feature button on the top-left of the OSM Feature widget. Using this tool you can easily explore all map objects. When the mouse cursor is placed over an object, you can see all information on it directly in the OSM Feature widget.

There is also a dynamic rubberband displayed on the map so that the user is able to determine which feature is currently identified.

The Properties tab of the widget contains of all feature tags. Clicking on the Relation tab shows you a list of all relations connected with identified feature.

If you want to hold a feature for a while to be able to read its properties and relations, move the mouse cursor at the same time, try left-clicking while you are over the feature. Identification process will stop until next left-clicking.

Sometimes there is more than one feature at a point where left-clicking was performed. This happens especially when clicking on cross-roads or if you did not zoom enough into the map. In this situation only one of such features is identified (and marked with the rubberband) but the plugin remembers all of them. Then (still in the pause mode) you can cycle through the identified features by right-clicking.

16.7 Editing basic OSM data

‘Basic data’ in this context means non-relational OSM features - nodes and ways. If you prefer to examine how to perform relational editing, skip this section and move on to the next one.

Basic data editing is a key part of the OSM Plugin. You can change the property, position or shape of any existing basic feature. You can remove features or add new ones. All changes on nodes and ways are remembered by

Undo/Redo all changes can be easily uploaded to the OpenStreetMap server.

16.7.1 Changing feature tags

Changing the property/tag of an OSM feature can be done directly in the table of feature tags. The Tags table of basic features can be found on the OSM Feature widget. Don’t forget to identify feature first.

If you want to change a tag value, just double-click in the appropriate row of column ‘Value’ and type, or select a new value. If you want to remove a tag, click in the relevant row, then use the button right bottom under the table.

Remove selected tags on the

To add new tags just type the key and value into the last row of the table where ‘<next tag value>’ is written.

Notice that you cannot change the key of an existing tag pair. Conveniently, there are some combo boxes of all existing tag keys and their typical values.

16.6. Viewing OSM data 145

QGIS User Guide, Release 1.8.0

Figure 16.4: Changing an OSM feature tag

16.7.2 Point creation

For point creation there is a

Create point button on the OSM Feature widget. To create some points, just click on the button and start clicking on the map. If your cursor is over some map feature, the feature is marked/identified immediately. If you click on the map when a line or polygon is marked, a new point is created directly on such line or polygon as its new member. If your cursor is over an existing point, a new point cannot be created. In such case the OSM plugin will show following message:

Figure 16.5: OSM point creation message

The mechanism of helping a user to hit the line or polygon is called snapping and is enabled by default. If you want to create a point very close to some line (but not on it) you must disable snapping by holding the Ctrl key first.

16.7.3 Line creation

For line creation, there is a

Create Line button on the OSM Feature widget. To create a line just click the button and start left-clicking on the map. Each of your left-clicks is remembered as a vertex of the new line. Line creation ends when the first right-click is performed. The new line will immediately appear on the map.

Note: A Line with less than two members cannot be created. In such case the operation is ignored.

146 Chapter 16. OpenStreetMap

QGIS User Guide, Release 1.8.0

Snapping is performed to all map vertices - points from the Point vector layer and all Line and Polygon members.

Snapping can be disabled by holding the Ctrl key.

16.7.4 Polygon creation

For polygon creation there is a

Create polygon button on the OSM Feature widget. To create a polygon just click the button and start left-clicking on the map. Each of your left-clicks is remembered as a member vertex of the new polygon. The Polygon creation ends when first right-click is performed. The new polygon will immediately appear on the map. Polygon with less than three members cannot be created. In such case operation is ignored.

Snapping is performed to all map vertexes - points (from Point vector layer) and all Line and Polygon members.

Snapping can be disabled by holding the Ctrl key.

16.7.5 Map feature moving

If you want to move a feature (no matter what type) please use the

Move feature button from the OSM Feature widget menu. Then you can browse the map (features are identified dynamically when you go over them) and click on the feature you want to move. If a wrong feature is selected after your click, don’t move it from the place.

Repeat right-clicking until the correct feature is identified. When selection is done and you move the cursor, you are no more able to change your decision what to move. To confirm the move, click on the left mouse button. To cancel a move, click another mouse button.

If you are moving a feature that is connected to another features, these connections won’t be damaged. Other features will just adapt themselves to a new position of a moved feature.

Snapping is also supported in this operation, this means:

• When moving a standalone (not part of any line/polygon) point,snapping to all map segments and vertices is performed.

• When moving a point that is a member of some lines/polygons,snapping to all map segments and vertices is performed, except for vertices of point parents.

• When moving a line/polygon, snapping to all map vertices is performed. Note that the OSM Plugin tries to snap only to the 3 closest-to-cursor vertices of a moved line/polygon, otherwise the operation would by very slow. Snapping can be disabled by holding Ctrl key during the operation.

16.7.6 Map feature removing

If you want to remove a feature, you must identify it first.

To remove an identified feature, use the

Remove this feature button on the OSM Feature widget. When removing a line/polygon, the line/polygon itself is deleted, so are all its member points that doesn’t belong to any other line/polygon.

When removing a point that is member of some lines/polygons, the point is deleted and the geometries of parent lines/polygons are changed. The new parent geometry has less vertices than the old one.

If the parent feature was a polygon with three vertexes, its new geometry has only two vertexes. And because there cannot exist polygon with only two vertices, as described above, the feature type is automatically changed to Line.

If the parent feature was a line with two vertexes, its new geometry has only one vertex. And because there cannot exist a line with only one vertex, the feature type is automatically changed to Point.

16.8 Editing relations

Thanks to existence of OSM relations we can join OSM features into groups and give them common properties in such way we can model any possible map object: borders of a region (as group of ways and points), routes of a

16.8. Editing relations 147

QGIS User Guide, Release 1.8.0

bus, etc. Each member of a relation has its specific role. There is a pretty good support for OSM Relations in our plugin. Let’s see how to examine, create, update or remove them.

16.8.1 Examining relation

If you want to see relation properties, first identify one of its members. After that open the Relations tab on the

OSM Feature widget. At the top of the tab you can see a list of all relations the identified feature is part of. Please choose the one you want to examine and look at its information below. In the first table called ‘Relation tags’ you find the properties of the selected relation. In the table called ‘Relation members’ you see brief information on the relation members. If you click on a member, the plugin will make a rubberband on it in the map.

16.8.2 Relation creation

There are 2 ways to create a relation:

1. You can use the

Create relation button on OSM Feature widget.

2. You can create it from the Relation tab of OSM Feature widget using the

Add relation button.

In both cases a dialog will appear. For the second case, the feature that is currently identified is automatically considered to be the first relation member, so the dialog is prefilled a little. When creating a relation, please select its type first. You can select one of predefined relation types or write your own type. After that fill the relation tags and choose its members.

If you have already selected a relation type, try using the

Generate tags button. It will generate typical tags to your relation type. Then you are expected to enter values to the keys. Choosing relation members can be done either by writing member identifiers, types and roles or using the

Identify tool and clicking on map.

Finally when type, tags and members are chosen, the dialog can be submitted. In such case the plugin creates a new relation for you.

16.8.3 Changing relation

If you want to change an existing relation, identify it first (follow steps written above in Section

Examining relation

). After that click on the

appears, nearly the same as for the ‘create relation’ action. The dialog is pre-filled with information on given relations. You can change relation tags, members or even its type. After submitting the dialog your changes will be committed.

Edit relation button. You will find it on the OSM Feature widget. A new dialog

16.9 Downloading OSM data

To download data from OpenStreetMap server click on the

Download OSM data button. If there is no such button, the OSM toolbar may be disabled in your QGIS instalation. You can enable it again at Settings → Toolbars →

OpenStreetMap

. After clicking the button a dialog occurs and provides following functionalities:

Extent: Specifies an area to download data from intervals of latitude and longitude degrees. Because there is some restriction of OpenStreetMap server on how much data can be downloaded, the intervals must not be too wide.

More detailed info on extent specification can is shown after clicking the

Help button on the right.

Download to: Here you are expected to write a path to the file where data will be stored. If you can’t remember the structure of your disk, don’t panic. The browse button will help you.

148 Chapter 16. OpenStreetMap

QGIS User Guide, Release 1.8.0

Figure 16.6: OSM download dialog

Open data automatically after download: Determines, if the download process should be followed by loading

Load OSM from file the data process or not. If you prefer not to load data now, you can do it later by using the button.

Replace current data: This option is active only if Open data automatically after download is checked.

Checking this option means that downloaded data should replace current data we are working with now. Layers of the current data will be removed and new ones will be loaded. When starting QGIS and downloading OSM data for the first time, this option is initially inactive, because there is nothing to replace.

Use custom renderer: This option is active only if the Open data automatically after download checkbox is checked. It determines how many details will be in the map. There are three predefined OSM styles for map displaying. Use ‘Small scale’ if you want to view OSM data at low level, to see all details and to edit something.

If not you can use ‘Medium scale’ or ‘Large scale’. QGIS 1.8.0 does not support changing the renderer style dynamically.

Click the [Download] button to start the download process.

A progress dialog will continuously inform you about how much of data is already downloaded. When an error occurs during the download process, a dialog tells you why. When action finishes successfully both the progress dialog and download dialog will close themselves.

16.10 Uploading OSM data

Note that the upload is always done on current OSM data. Before opening the OSM Upload dialog, please be sure that you really have the right active layer with OSM data.

To upload current data to the OSM server click on the

Upload OSM data button. If there is no such button, OSM toolbar in your QGIS installation is disabled. You can enable it again in Settings → Toolbars → OpenStreetMap .

After clicking the [Upload] button a new dialog will appear.

At the top of the dialog you can check, if you are uploading the correct data. There is a short name of a current database. In the table you find information on how many changes will be uploaded. Statistics are displayed separately for each feature type.

In the ‘Comment on your changes’ box you can write brief information on meaning of your upload operation.

Just write in brief what data changes you’ve done or let the box empty. Fill ‘OSM account’ arrays so that the server could authenticate you. If you don’t have an account on the OSM server, it’s the best time to create one at http://www.openstreetmap.org

. Finally use [Upload] to start an upload operation.

16.10. Uploading OSM data 149

QGIS User Guide, Release 1.8.0

16.11 Saving OSM data

Figure 16.7: OSM upload dialog

To save data from a current map extent to an XML file click on the

Save OSM to file button. If there is no such button, the OSM toolbar in your QuantumGIS installation is probably disabled. You can enable it again in Settings

→ Toolbars → OpenStreetMap. After clicking on the button a new dialog appears.

Figure 16.8: OSM saving dialog

Select features you want to save into XML file and the file itself. Use the [OK] button to start the operation. The process will create an XML file, in which OSM data from your current map extent are represented. The OSM version of the output file is 0.6. Elements of OSM data (<node>, <way>, <relation>) do not contain information on their changesets and uids. This information are not compulsory yet, see DTD for OSM XML version 0.6. In the output file OSM elements are not ordered.

Notice that not only data from the current extent are saved. Into the output file the whole polygons and lines are

150 Chapter 16. OpenStreetMap

QGIS User Guide, Release 1.8.0

saved even if only a small part of them is visible in the current extent. For each saved line/polygon all its member nodes are saved too.

16.12 Import OSM data

To import OSM data from an opened non-OSM vector layer follow this instructions. Choose current OSM data by clicking on one of their layers. Click on the

Import data from a layer button. If there is no such button, someone has probably disabled the OpenStreetMap toolbar in your QGIS installation. You can enable it again in Settings

→ Toolbars → OpenStreetMap.

After clicking on the button following message may show up:

Figure 16.9: OSM import message dialog

In such case there is no vector layer currently loaded. The import must be done from a loaded layer - please load a vector layer from which you want to import data. After a layer is opened, your second try should give you a better result (don’t forget to mark the current OSM layer again):

Figure 16.10: Import data to OSM dialog

Use the submit dialog to start the process of OSM data importing. Reject it if you are not sure you want to import something.

16.12. Import OSM data 151

QGIS User Guide, Release 1.8.0

152 Chapter 16. OpenStreetMap

CHAPTER

17

Print Composer

The print composer provides growing layout and printing capabilities. It allows you to add elements such as the

QGIS map canvas, legend, scalebar, images, basic shapes, arrows and text labels. You can size, group, align and position each element and adjust the properties to create your layout. The layout can be printed or exported to image formats, Postscript, PDF or to SVG (export to SVG is not working properly with some recent Qt4 versions.

You should try and check individual on your system). You can save the layout as template and load it again in another session. See a list of tools in

table_composer_1

:

Icon Purpose Icon Purpose

Load from template

Export to an image format

Export print composition to SVG

Zoom to full extent

Zoom out

Revert last change

Add new map from QGIS map canvas

Add label to print composition

Add new scalebar to print composition

Add arrow to print composition

Select/Move item in print composition

Group items of print composition

Raise selected items

Move selected items to top

Save as template

Export as PDF

Print or export as Postscript

Zoom in

Refresh view

Restore last change

Add image to print composition

Add new legend to print composition

Add basic shape to print composition

Add attribute table to print composition

Move content within an item

Ungroup items of print composition

Lower selected items

Move selected items to bottom

Align selected items left

Align selected items center

Align selected items right

Align selected items center vertical

Align selected items top

Table Composer 1: Print Composer Tools

Align selected items bottom

All Print Composer tools are available in menus and as icons in a toolbar. The toolbar can be switched off and on using the right mouse button holding the mouse over the toolbar.

153

QGIS User Guide, Release 1.8.0

17.1 Open a new Print Composer Template

Before you start to work with the print composer, you need to load some raster and vector layers in the QGIS map canvas and adapt their properties to suite your own convenience. After everything is rendered and symbolized to your liking you click the

New Print Composer icon in the toolbar or choose File → New Print Composer.

17.2 Using Print Composer

Opening the print composer provides you with a blank canvas to which you can add the current QGIS map canvas, legend, scalebar, images, basic shapes, arrows and text.

Figure_composer_1

shows the initial view of the print composer with an activated Snap to grid mode but before any elements are added.

Figure 17.1: Print Composer

The print composer provides three tabs:

• The Composition tab allows you to set paper size, orientation, the print quality for the output file in dpi and to activate snapping to a grid of a defined resolution. Please note, the Snap to grid feature only works, if you define a grid resolution > 0. Furthermore you can also activate the Print as raster checkbox. This means all elements will be rastered before printing or saving as Postscript of PDF.

• The Item Properties 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 Properties tab and customize the settings for the selected element.

• The Command history tab displays a history of all changes applied to the print composer layout. With a mouse click it is possible to undo and redo layout steps back and forth to a certain status.

You can add multiple elements to the composer. It is also possible to have more than one map view or legend or scalebar in the print composer canvas. Each element has its own properties and in the case of the map, its own extent. If you want to remove any elements from the composer canvas you can do that with the Delete or the

Backspace key.

154 Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

17.3 Adding a current QGIS map canvas to the Print Composer

Click on the

Add new map toolbar button in the print composer toolbar, to add the QGIS map canvas. Now drag a rectangle on the composer canvas with the left mouse button to add the map. To display the current map, you can choose between three different modes in the map Item Properties tab:

• Rectangle is the default setting. It only displays an empty box with a message ‘Map will be printed here’.

• Cache renders the map in the current screen resolution. If case you zoom in or out the composer window, the map is not rendered again but the image will be scaled.

• Render means, that if you zoom in or out the composer window, the map will be rendered again, but for space reasons, only up to a maximum resolution.

Cache is default preview mode for newly added print composer maps.

You can resize the map element 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 Properties tab.

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. After you found the right place for an element, you can lock the element position within the print composer canvas. Select the map element and click on the right mouse button to activating the

Lock the element position and again to unlock the element. You can lock the map element also

Lock layers for map item checkbox in the Map dialog of the Item Properties tab.

Note: QGIS is now able to show labels from the new labeling plugin also in the map composer, but it is not yet scaled correctly. So it might be necessary to switch back to the standard labeling in some cases.

17.3.1 Map item properties tab — Map and Extents dialog

Map dialog

The Map dialog of the map Item Properies tab provides following functionalities (see

figure_composer_2

):

Figure 17.2: Map Dialog

• The Preview area allows to define the preview modes ‘Rectangle’, ‘Cache’ and ‘Render’, as described above. Click on the [Update preview] button to apply changes to the map view.

• The Map area allows to resize the map element specifying the width and height or the scale. The field

Rotation allows to rotate the map element content clockwise in degrees. Note, a coordinate frame

17.3. Adding a current QGIS map canvas to the Print Composer 155

QGIS User Guide, Release 1.8.0

can only be added with the default value 0. Furthermore you can enable the checkboxes map items and

Draw map canvas items

.

Lock layers for

If you change the view on the QGIS map canvas by zooming or panning or changing vector or raster properties, you can update the print composer view selecting the map element in the print composer and clicking the [Update preview] button.

Extents dialog

The Extents dialog of the map item tab provides following functionalities (see Figure

figure_composer_3

)):

Figure 17.3: Extents Dialog

• The Map extent area allow to specify the map extent using Y and X min/max values or clicking the [Set to map canvas extent] button.

If you change the view on the QGIS map canvas by zooming or panning or changing vector or raster properties, you can update the print composer view selecting the map element in the print composer and clicking the [Update preview] button in the map Item Properties tab (see Figure

figure_composer_2

a)).

17.3.2 Map item properties tab — Grid and General options dialog

Grid dialog

The Grid dialog of the map Item Properties tab provides following functionalities (see

Figure_composer_4

):

156

Figure 17.4: Grid Dialog

• The Show grid checkbox allows to overlay a grid to the map element. As grid type you can specify to use solid line or cross. Furthermore you can define an interval in X and Y direction, an X and Y offset, and the width used for cross or line grid type.

• The Draw annotation checkbox allows to add coordinates to the map frame. The annotation can be drawn inside or outside the map frame. The annotation direction can be defined as horizontal, vertical,

Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

horizontal and vertical, or boundary direction. And finally you can define the grid color, the annotation font, the annotation distance from the map frame and the precision of the drawn coordinates.

General options dialog

The General options dialog of the map Item Properties tab provides following functionalities (see

Figure_composer_5

):

Figure 17.5: General Options Dialog

• Here you can define color and outline width for the element frame, set a background color and opacity for the map canvas. The [Position and size] button opens the Set item position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the other print composer items.

Show frame checkbox. With the Item ID you can create a relationship to the

17.4 Adding other elements to the Print Composer

Besides adding a current QGIS map canvas to the Print Composer, it is also possible to add, position, move and customize legend, scalebar, images and label elements.

17.4.1 Label item properties tab - Label and General options dialog

To add a label, click the

Add label icon, place the element with the left mouse button on the print composer canvas and position and customize their appearance in the label Item Properties tab.

Label dialog

The Label dialog of the label item tab provides following functionalities:

• The Label dialog offers to add text labels to the composer canvas. You can define the horizontal and vertical alignment, select font and font color for the text and it is possible to define a text margin in mm.

General options dialog

The General options dialog of the label Item Properties tab provides following functionalities:

• Here you can define color and outline width for the element frame, set a background color and opacity for the label. The Position button opens the Set items position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the Show frame checkbox. Use the Item ID to create a relationship to other print composer items.

17.4.2 Image item properties tab - Picture options and General options dialog

To add an image, click the

Add image icon, place the element with the left mouse button on the print composer canvas and position and customize their appearance in the image Item Properties tab.

Picture options dialog

17.4. Adding other elements to the Print Composer 157

QGIS User Guide, Release 1.8.0

Figure 17.6: Label Options Dialog

Figure 17.7: General Options Dialog

The Picture options dialog of the image Item Properties tab provides following functionalities (see

figure_composer_5

a):

• The Preloaded Images field then shows all pictures stored in the selected directories.

• The Options area shows the current selected picture and allows to define width, height and clockwise rotation of the picture. It is also possible to add a user specific SVG path. Activating the

Sync with map checkbox synchronizes the rotation of a picture in the QGIS map canvas (i.e. a rotated north arrow) with the appropriate print composer image.

• The Search directories area allows to add and remove directories with images in SVG format to the picture database.

General options dialog

The General options dialog of the image Item Properties tab provides following functionalities:

• Here you can define color and outline width for the element frame, set a background color and opacity for the picture. The [Position and size] button opens the Set item position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the print composer items.

Show frame checkbox. With the Item ID you can create a relationship to other

17.4.3 Legend item properties tab - General, Legend items and Item option dialog

To add a map legend, click the

Add new legend icon, place the element with the left mouse button on the print composer canvas and position and customize their appearance in the legend Item Properties tab.

158 Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

Figure 17.8: Picture Options Dialog Dialog

Figure 17.9: General Options Dialog Dialog

17.4. Adding other elements to the Print Composer 159

QGIS User Guide, Release 1.8.0

General dialog

The General dialog of the legend item tab provides following functionalities (see

figure_composer_10

):

Figure 17.10: General Dialog

• Here you can adapt the legend title. You can change the font of the legend title, layer and item name. You can change width and height of the legend symbol and you can add layer, symbol, icon label and box space.

Since QGIS 1.8, you can wrap the text of the legend title to a given character.

Legend items dialog

The Legend items dialog of the legend Item Properties tab provides following functionalities (see

figure_composer_11

):

Figure 17.11: Legend Items Dialog

• The legend items window lists all legend items and allows to change item order, edit layer names, remove and restore items of the list. After changing the symbology in the QGIS main window you can click on

[Update] to adapt the changes in the legend element of the print composer. The item order can be changed using the [Up] and [Down] buttons or with ‘drag and drop’ functionality.

General options dialog

The General options dialog of the legend Item Properties tab provides following functionalities (see

figure_composer_12

):

160 Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

Figure 17.12: General Options Dialog

• Here you can define color and outline width for the element frame, set a background color and opacity for the legend. The [Position and size] button opens the Set item position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the composer items.

Show frame checkbox. Use the Item ID to create a relationship to other print

17.4.4 Scalebar item properties tab - Scalebar and General options dialog

To add a scalebar, click the

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 scalebar Item Properties tab.

Scalebar dialog

The Scalebar dialog of the scalebar Item Properties tab provides following functionalities (see

figure_composer_13

):

Figure 17.13: Scalebar Options Dialog

• The Scalebar dialog allows to define the segment size of the scalebar in map units, the map units used per bar units, and how many left and right segments units from 0 should be used.

• You can define the scalebar style, available is single and double box, line ticks middle, up and down and a numeric style.

• Furthermore you can define height, line width, label and box space of the scalebar. Add a unit label and define the scalebar font and color.

General options dialog

17.4. Adding other elements to the Print Composer 161

QGIS User Guide, Release 1.8.0

The General options dialog of the scalebar Item Properties tab provides following features (see

figure_composer_7

b)):

Figure 17.14: General Options Dialog

• Here you can define color and outline width for the element frame, set a background color and opacity for the scalebar. The [Position and size] button opens the Set items position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the other print composer items.

Show frame checkbox. With the Item ID you can create a relationship to the

17.5 Navigation tools

For map navigation the print composer provides 4 general tools:

Zoom in

Zoom out

Zoom to full extend

Refresh the view

(if you find the view in an inconsistent state)

17.6 Revert and Restore tools

During the layout process it is possible to revert and restore changes. This can be done with the revert and restore tools:

Revert last changes

Restore last changes or by mouse click within the Command history tab (see

figure_composer_9

).

17.7 Add Basic shape and Arrow

It is possible to add basic shapes (Ellipse, Rectangle, Triangle) and arrows to the print composer canvas.

The Shape dialog allows to draw an ellipse, rectangle, or triangle in the print composer canvas. You can define its outline and fill color, the outline width and a clockwise rotation.

The Arrow dialog allows to draw an arrow in the print composer canvas. You can define color, outline and arrow width and it is possible to use a default marker and no marker and a SVG marker. For the SVG marker you can additionally add a SVG start and end marker from a directory on your computer.

162 Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

Figure 17.15: Command history in the Print Composer

Figure 17.16: Shape Dialog

17.7. Add Basic shape and Arrow

Figure 17.17: Arrow Dialog

163

QGIS User Guide, Release 1.8.0

17.8 Add attribute table values

It is possible to add parts of a vector attribute table to the print composer canvas.

Table dialog

The Table dialog of the attribute table item tab provides following functionalities (see

figure_composer_20

):

Figure 17.18: Table Dialog

• The Table dialog allows to select the vector layer and columns of the attribute table. Attribute columns can be sorted and you can define to show its values ascending or descending.

• You can define the maximum number of rows to be displayed and if attributes are only shown for visible features of the current composer canvas.

• Additionally you can define the grid characteristics of the table and the header and content font.

General options dialog

The General options dialog of the attribute table item tab provides following functionalities (see

figure_composer_21

):

164

Figure 17.19: General Options Dialog

• Here you can define color and outline width for the element frame, set a background color and opacity for the table. The [Position and size] button opens the Set item position dialog and allows to set the map canvas position using reference points or coordinates. Furthermore you can select or unselect to display the element frame with the composeritems.

Show frame checkbox. Use the Item ID to create a relationship to the other print

Chapter 17. Print Composer

QGIS User Guide, Release 1.8.0

17.9 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_composer_1

).

There are several alignment functionalities available within the

Align selected items pulldown menu (see

table_composer_1

). To use an alignment functionality , you first select some elements and then click on the matching

alignment icon. All selected will then be aligned within to their common bounding box.

17.10 Creating Output

Figure_composer_22

shows the print composer with an example print layout including each type of map element described in the sections above.

Figure 17.20: Print Composer with map view, legend, scalebar, coordinates 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 a Postscript file depending on installed printer drivers.

• The

JPG,...

Export as image icon exports the composer canvas in several image formats such as PNG, BPM, TIF,

• The

Export as PDF saves the defined print composer canvas directly as a PDF.

• The

Export as SVG icon saves the print composer canvas as a SVG (Scalable Vector Graphic).

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.

17.9. Raise, lower and align elements 165

QGIS User Guide, Release 1.8.0

17.11 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.

The

Composer Manager button in the QGIS toolbar and in File → Composer Manager allows to add a new composer template or to manage already existing templates.

Figure 17.21: The Print Composer Manager

166 Chapter 17. Print Composer

CHAPTER

18

Plugins

18.1 QGIS Plugins

QGIS has been designed with a plugin architecture. This allows many new features/functions to be easily added to the application. Many of the features in QGIS are actually implemented as either core or external plugins.

• Core Plugins are maintained by the QGIS Development Team and are automatically part of every QGIS distribution. They are written in one of two languages: C++ or Python. More information about core plugins are provided in Section

Using QGIS Core Plugins

• External Plugins are currently all written in Python. They are stored in external repositories and maintained by the individual authors. They can be added to QGIS using the Python Plugin Installer. More information about external plugins is provided in Section

Loading an external QGIS Plugin

.

18.1.1 Managing Plugins

Managing plugins in general means loading or unloading them using the Plugin Manager. External plugins can be installed and directly activated or uninstalled using the Python Plugin Installer. To deactivate and reactivate external plugins, the Plugin Manager is used again.

Loading a QGIS Core Plugin

Loading a QGIS Core Plugin is done from the main menu Plugins → Manage Plugins

The Plugin Manager lists all the available plugins and their status (loaded or unloaded), including all core plugins and all external plugins that have been installed and automatically activated using the Python Plugin Installer (see

Section

Loading an external QGIS Plugin

). Those plugins that are already loaded have a check mark to the left of

their name.

Figure_plugins_1

shows the Plugin Manager dialog.

To enable a particular plugin, click on the checkbox to the left of the plugin name, and click [OK]. When you exit the application, a list of loaded plugins is retained, and the next time you run QGIS these plugins are automatically loaded.

Tip: Crashing Plugins

If you find that QGIS crashes on startup, a plugin may be at fault. You can stop all plugins from loading by editing your stored settings file (see

Options

for location). Locate the plugins settings and change all the plugin values to false to prevent them from loading.

For example, to prevent the ‘Delimited text’ plugin from loading, the entry in

$HOME/.config/QuantumGIS/qgis.conf

on Linux should look like this: Add Delimited Text

Layer=false .

167

QGIS User Guide, Release 1.8.0

Figure 18.1: Plugin Manager

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.

Loading an external QGIS Plugin

External QGIS plugins are written in Python. They are by default stored in either the ‘Official’ QGIS Repository, or in various other external repositories maintained by individual authors. The ‘Official’ QGIS Repository is added by default in Python Plugin installer.

Detailed documentation about the usage, minimum QGIS version, homepage, authors, and other important information are provided for the ‘Official’ QGIS Repository at http://plugins.qgis.org/plugins/ . For other external repositories, they might be available with the external plugins themselves. In general it is not included in this manual.

Note: Updates of core python plugins may be available in this repository as external overlays.

Note: fTools, Mapserver Export, and the Plugin Installer are Python plugins, but they are also part of the QGIS sources, and are automatically loaded and enabled inside the QGIS Plugin Manager (see Section

Loading an external QGIS Plugin

).

Currently there are over 150 external plugins available from the ‘Official’ QGIS Repository. Some of these plugins offer functionality that will be required by many users (for example: providing the user with the ability to view and edit OpenStreetMap data, or to add GoogleMap layers) while others offer very specialized functions (for example:

Calculate economic pipe diameters for water supply networks).

It is, however, quite straightforward to search through all the available external plugins by providing keywords, choosing a named repository and/or filtering on the status of plugins (currently installed or uninstalled in your system). Searching and filtering is done from the QGIS Python Plugin Installer (see

figure_plugins_2

).

Tip: Add more repositories

To add external author repositories, open the Plugin Installer (Plugins → Fetch Python Plugins), go to the tab

168 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Repositories , and click [Add]. If you do not want one or more of the added repositories, they can be disabled via the [Edit...] button, or completely removed with the [Delete] button.

There is only one step required to integrate external plugins into QGIS:

• Download an external plugin from a repository using the Python Plugin Installer (see

Using the QGIS

Python Plugin Installer

). The new external plugin will be added to the list of available plugins in the Plugin

Manager and is automatically loaded.

Using the QGIS Python Plugin Installer

In order to download and install an external Python plugin, go to Plugins → Fetch Python Plugins . The Plugin

Installer

window will appear (

figure_plugins_2

) with the tab Plugins, containing a list of all locally installed

Python plugins, as well as plugin available in remote repositories.

Figure 18.2: Installing external python plugins

Each plugin can be either:

• not installed - this means the plugin is available in the repository, but is not installed yet. In order to install it, select the plugin from the list and click the button [Install plugin].

• new - this means that the plugin is newly available in the repository.

• installed - this indicates that the plugin is already installed. If it is also available in any repository the

[Reinstall plugin] button will be enabled. If the available version is older than the installed version, the

[Downgrade plugin] button will appear instead.

• upgradeable - this means that the plugin is installed, but there is an updated version available. In this case, the [Upgrade plugin] and [Upgrade all] buttons will be enabled.

• invalid - this means that the plugin is installed, but is unavailable or broken. The reason will be explained in the plugin description field.

Plugins tab

To install a plugin, select it from the list and click the [Install plugin] button. The plugin is then activated and installed in its own directory.

• Linux and other unices

– /share/qgis/python/plugins

– $HOME/.qgis/python/plugins

• Mac OS X

– /Contents/MacOS/share/qgis/python/plugins

18.1. QGIS Plugins 169

QGIS User Guide, Release 1.8.0

– /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.

If the installation fails, the reason for the failure will be displayed in a warning dialog. Most often, errors are the result of connection problems and/or missing Python modules. In the former case you will likely need to wait before trying the install again, in the latter case, you should install the missing modules relevant to your operating system prior to using the plugin. For Linux, most required modules should be available via a package manager.

For install instructions in Windows visit the module home page.

If you are using a proxy, you may need to configure it under Edit → Options (Gnome, OSX) or Settings → Options

(KDE, Windows)‘ on the Proxy tab.

The [Uninstall plugin] button is enabled only if the selected plugin is installed and is not a core plugin. Note that if you have installed an update to a core plugin, you can uninstall this update with the [Uninstall plugin] and revert to the version shipped with Quantum GIS. This default version however, cannot be uninstalled.

Repositories tab

The second tab Repositories, contains a list of plugin repositories available for the Plugin Installer. By default, only the QGIS Official Repository is enabled. You can add several user-contributed repositories, including the central QGIS Contributed Repository and other external repositories by clicking the [Add ...] button. The added repositories contain a large number of useful plugins which are not maintained by the QGIS Development Team.

As such, we cannot take any responsibility for them. You can also manage the repository list manually, that is add, remove, and edit the entries. Temporarily disabling a particular repository is possible by clicking the [Edit

...] button.

Options tab

The Options tab is where you can configure the settings of the Plugin Installer. The 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 can be adjusted using the dropdown menu, and may be adjusted from once a day right up to once a month. If a new plugin or update is available for one of the installed plugins, a notification will appear in the Status Bar. If the checkbox is disabled, looking for updates and news is performed only when the Plugin Installer is manually launched from the menu.

Although the plugin installer update can handle ports different from 80, some internet connections will cause problems when attempting to automatically check for updates. In these cases, a Looking for new plugins... indicator will remain visible in the Status Bar during your entire QGIS session, and may cause a program crash when exiting. In this case please disable the checkbox.

In addition, you may specify the type of plugins that are displayed by the Python Plugin Installer. Under Allowed plugins

, you can specify whether you would like to:

• Only show plugins from the official repository

Show all plugins except those marked as experimental

Show all plugins, even those marked as experimental

Tip: Using experimental plugins

Experimental plugins are generally unsuitable for production use. These plugins are in the early stages of development, and should be considered ‘incomplete’ or ‘proof of concept’ tools. The QGIS development team does not recommend installing these plugins unless you intend to use them for testing purposes.

170 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.1.2 Data Providers

Data Providers are ‘special’ plugins that provides access to a data store. By default, QGIS supports PostGIS layers and disk-based data stores supported by the GDAL/OGR library. A Data Provider plugin extends the ability of

QGIS to use other data sources.

Data Provider plugins are registered automatically by QGIS at startup. They are not managed by the Plugin

Manager but used behind the scenes when a data type is added as a layer in QGIS.

18.1. QGIS Plugins 171

QGIS User Guide, Release 1.8.0

18.2 Using QGIS Core Plugins

Icon Plugin

Add Delimited Text

Layer

Coordinate Capture

DB Manager

Diagram Overlay

DXF2Shape

Converter eVis fTools

GPS Tools

GRASS

GDAL Tools

Georeferencer

GDAL

Heatmap

Description

Loads text files containing x,y coordinates

Capture mouse coordinate in different

CRS

Manage your databases within QGIS

Add Diagrams for vectors

Converts from DXF to SHP file format

Event Visualization Tool

A suite of vector tools

Tools for loading and importing GPS data

GRASS functionality

GDAL raster functionality

Georeference Raster with GDAL

Manual Reference

Delimited Text Plugin

Coordinate Capture Plugin

DB Manager Plugin

Diagram Overlay Plugin

Dxf2Shp Converter Plugin eVis Plugin

fTools Plugin

GPS Plugin

GRASS GIS Integration

GDAL Tools Plugin

Georeferencer Plugin

Heatmap Plugin

Interpolation plugin

MapServer Export

Plugin

Offline Editing

OpenStreetMap

Oracle Spatial

Georaster

Plugin Installer

Create heatmap raster from input vector points

Interpolation on base of vertices of a vector layer

Export a QGIS project file to a

MapServer map file

Offline editing and synchronizing with database

Access OpenStreetMap

Access Oracle Spatial GeoRasters

Download and install python plugins

Interpolation Plugin

MapServer Export Plugin

Offline Editing Plugin

OpenStreetMap

Oracle GeoRaster Plugin

Raster Terrain

Analysis

Road graph Plugin

SPIT

Compute geomorphological features from DEMs

Shortest path analysis

Shapefile to PostGIS Import Tool

Using the QGIS Python Plugin

Installer

Raster Terrain Analysis Plugin

Road Graph Plugin

Importing Data into PostgreSQL

SQL Anywhere plugin

Spatial Query

Zonal Statistics

Access SQL anywhere DB

Spatial queries on vectors

Calculate raster statistics for vector polygons

SQL Anywhere Plugin

Spatial Query Plugin

Zonal Statistics Plugin

172 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.3 Coordinate Capture Plugin

The coordinate capture plugin is easy to use and provides the ability to display coordinates on the map canvas for two selected Coordinate Reference Systems (CRS).

Figure 18.3: Coordinate Capture Plugin

1. Start QGIS, select Project Properties from the Settings (KDE, Windows) or File (Gnome, OSX) menu and click on the Projection tab. As an alternative you can also click on the right-hand corner of the statusbar.

CRS status icon in the lower

2. Click on the Enable on the fly projection checkbox and select a projected coordinate system of your choice (see also

Working with Projections

).

3. Load the coordinate capture plugin in the Plugin Manager (see

Loading a QGIS Core Plugin

) and ensure

that the dialog is visible by going to View → Panels and ensuring that Coordinate Capture is enabled.

The coordinate capture dialog appears as shown in Figure

figure_coordinate_capture_1

.

4. Click on the selected above.

Click to the select the CRS to use for coordinate display icon and select a different CRS from the one you

5. To start capturing coordinates, click on [Start capture]. You can now click anywhere on the map canvas and the plugin will show the coordinates for both of your selected CRS.

6. To enable mouse coordinate tracking click the mouse tracking

7. You can also copy selected coordinates to the clipboard.

icon.

18.4 DB Manager Plugin

The DB Manager Plugin is officially part of QGIS core and intends to replace the SPIT Plugin and the PostGIS

Manager Plugin and additionally to integrate all other database formats supported by QGIS in one user interface.

The

DB Manager

Plugin provides several features. You can drag layers from the QGIS Browser into the DB

Manager and it will import your layer into your spatial database. You can drag and drop tables between spatial databases and they will get imported. You can also use the DB Manager to execute SQL queries against your spatial database and then view the spatial output for queries by adding the results to QGIS as a query layer.

The Database menu allows to connect to an existing database, to start the SQL-window and to exit the DB Manager

Plugin. The Schema menu includes tools to create and delete (empty) schemas and, if topology is available (e.g.

PostGIS 2) to start a TopoViewer. The menu Table allows to create and edit tables and to delete tables and views. It is also possible to empty tables and to move tables from one to another schema. Finally you can also run Vacuum

Analyze and add Versioning Support to a table.

The Tree window lists all existing databases supported by QGIS. With a double-click you can connect to the database. With the right-mouse button you can rename and delete existing schemas and tables. Tables can also be added to the QGIS canvas with the context menu.

18.3. Coordinate Capture Plugin 173

QGIS User Guide, Release 1.8.0

Figure 18.4: DB Manager dialog (KDE)

If connected to a database, the main window of the DB Manager offers three tabs. The Info tab provides information about the table and its geometry as well as about existing Fields, Constraints and Indexes. It also allows to run Vacuum Analyze and to create a spatial index on a selected table, if not already done. The Table tab shows all attributes and the Preview tab renders the geometries as preview.

18.5 Delimited Text Plugin

The Delimited Text plugin allows you to load a delimited text file as a layer in QGIS.

18.5.1 Requirements

To view a delimited text file as layer, the text file must contain:

1. A delimited header row of field names. This must be the first line in the text file.

2. The header row must contain an X and Y field. These fields can have any name.

3. The x and y coordinates must be specified as a number. The coordinate system is not important.

As an example of a valid text file we import the elevation point data file elevp.csv coming with the QGIS sample dataset (See Section

Sample Data

):

X;Y;ELEV

300120 ; 7689960 ; 13

654360 ; 7562040 ; 52

1640 ; 7512840 ; 3

[ ...

]

Some items of note about the text file are:

1. The example text file uses ; (semicolon) as delimiter. Any character can be used to delimit the fields.

2. The first row is the header row. It contains the fields X, Y and ELEV.

3. No quotes (") are used to delimit text fields.

4. The x coordinates are contained in the X field.

5. The y coordinates are contained in the Y field.

18.5.2 Using the Plugin

To use the plugin you must first enable it as described in Section

Managing Plugins

.

174 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Click the new toolbar icon

ure_delimited_text_1

.

Add Delimited Text Layer to open the Delimited Text dialog as shown in

fig-

Figure 18.5: Delimited Text Dialog

First select the file (e.g., qgis_sample_data/csv/elevp.csv) to import by clicking on the [Browse] button. Once the file is selected, the plugin attempts to parse the file using the last used delimiter, in this case a semicolon (;). To properly parse the file, it is important to select the correct delimiter. To change the delimiter to tab use \t (this is a regular expression for the tab character).

Once the file is parsed, choose the X and Y fields from the dropdown lists and if available also the WKT field for the CRS information. Finally enter a Layer name (e.g., elevp ) as shown in

figure_delimited_text_1

. To add the layer to the map, click [OK]. The delimited text file now behaves as any other map layer in QGIS.

18.6 Diagram Overlay Plugin

The Diagram Overlay Plugin allows you to add a graphic overlay to a vector layer (see

figure_overlay_1

). It

provides additional and not yet implemented features to the Diagrams tab, described in secion

Diagrams Tab

.

Before starting, the Diagram Overlay Plugin needs to be activated using the Plugin Manager (see Section

Loading a QGIS Core Plugin

). It will then appear as Overlay tab in the Layer Properties dialog next to the Diagrams tab.

The Overlay tab provides support for Pie charts, Bar charts and proportional SVG symbols.

Similar to the Diagrams tab, we will demonstrate an example and overlay the alaska boundary layer a piechart diagram showing some temperature data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section

Sample Data

).

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.

18.6. Diagram Overlay Plugin 175

QGIS User Guide, Release 1.8.0

Figure 18.6: Vector properties dialog with overlay tab

2. Double click the climate layer in the map legend to open the Layer Properties dialog.

3. Click on the Overlay tab, activate combobox.

Display diagrams and select ‘Pie Chart’ from Diagram type

4. We want to display the values of the three columns T_F_JAN, T_F_JUL and T_F_MEAN. First select

T_F_JAN as Attributes and click the [Add] button, then T_F_JUL and finally T_F_MEAN.

5. Diagram size is based on linear scaling of a classification attribute. We choose T_F_JUL, click on [Find maximum value] and set size to 20 and Size unit to ‘Millimeter’.

6. Now click [Apply] to display the diagram in the QGIS main window.

7. You can now adapt the chart size, or change the attribute colors double clicking on the color values in the attribute field.

Figure_overlay_2

gives an impression.

8. Finally click [Ok].

Figure 18.7: Pie chart diagram from temperature data overlayed on a map

Additionally in the Settings → Options dialog, there is a Overlay tab where it is possible to select the placement

176 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

algorithm of the diagrams. The ‘Central point’ method is a generic one, the others use algorithms of the PAL library. They also consider diagram objects and labels in different layers.

18.7 Dxf2Shp Converter Plugin

The dxf2shape converter plugin can be used to convert vector data from DXF to Shapefile format. It requires the following parameters to be specified before running:

Figure 18.8: Dxf2Shape Converter Plugin

• Input DXF file: Enter path to the DXF file to be converted

• Output Shp file: Enter desired name of the Shapefile to be created

• Output file type: Specify the geometry type of the output Shapefile. Currently supported types are polyline, polygon, and point.

• Export text labels: When this checkbox is enabled, an additional Shapefile point layer will be created, and the associated dbf table will contain information about the “TEXT” fields found in the dxf file, and the text strings themselves.

18.7.1 Using the Plugin

1. Start QGIS, load the Dxf2Shape plugin in the Plugin Manager (see Section

Loading a QGIS Core Plugin

)

and click on the

Dxf2Shape Converter icon which appears in the QGIS toolbar menu. The Dxf2Shape plugin dialog appears as shown in

Figure_dxf2shape_1

.

2. Enter input DXF file, a name for the output Shapefile and the Shapefile type.

3. Enable the

4. Click [OK].

Export text labels checkbox if you want to create an extra point layer with labels.

18.8 eVis Plugin

The Biodiversity Informatics Facility at the American Museum of Natural History’s (AMNH) Center for Biodiversity and Conservation (CBC) (this section is derived from Horning, N., K. Koy, P. Ersts. 2009. eVis (v1.1.0)

User’s Guide. American Museum of Natural History, Center for Biodiversity and Conservation. Available from http://biodiversityinformatics.amnh.org/ , and released under the GNU FDL.) has developed the Event Visualization Tool (eVis), another software tool to add to the suite of conservation monitoring and decision support tools for guiding protected area and landscape planning. This plugin enables users to easily link geocoded (i.e., referenced with latitude and longitude or X and Y coordinates) photographs, and other supporting documents, to vector data in QGIS.

18.7. Dxf2Shp Converter Plugin 177

QGIS User Guide, Release 1.8.0

eVis is now automatically installed and enabled in new versions of QGIS, and as with all plugins, it can be disabled and enabled using the Plugin Manager (See

Managing Plugins

).

The eVis plugin is made up of three modules: the ‘Database Connection tool’, ‘Event ID tool’, and the ‘Event

Browser’. These work together to allow viewing of geocoded photographs and other documents that are linked to features stored in vector files, databases, or spreadsheets.

18.8.1 Event Browser

The Event Browser module provides the functionality to display geocoded photographs that are linked to vector features displayed in the QGIS map window. Point data, for example, can be from a vector file that can be input using QGIS or it can be from the result of a database query. The vector feature must have attribute information associated with it to describe the location and name of the file containing the photograph and, optionally, the compass direction the camera was pointed when the image was acquired. Your vector layer must be loaded into

QGIS before running the Event Browser.

Launch the Event Browser module

To launch the Event browser module either click on the eVis Event Browser eVis Event Browser . This will open the Generic Event Browser window.

icon or click on Database → eVis →

The Generic Event Browser window has three tabs displayed at the top of the window. The Display tab is used to view the photograph and its associated attribute data. The Options tab provides a number of settings that can be adjusted to control the behavior of the eVis plugin. Lastly, the Configure External Applications tab is used to maintain a table of file extensions and their associated application to allow eVis to display documents other than images.

Understanding the Display window

To see the Display window click on the Display tab in the Generic Event Browser window. The Display window is used to view geocoded photographs and their associated attribute data.

1. Display window: A window where the photograph will appear.

2. Zoom in button: Zoom in to see more detail. If the entire image cannot be displayed in the display window, scroll bars will appear on the left and bottom sides of the window to allow you to pan around the image.

3. Zoom out button: Zoom out to see more area.

4. Zoom to full extent button: Displays the full extent of the photograph.

5. Attribute information window: All of the attribute information for the point associated with the photograph being viewed is displayed here. If the file type being referenced in the displayed record is not an image but is of a file type defined in the Configure External Applications tab then when you double-click on the value of the field containing the path to the file the application to open the file will be launched to view or hear the contents of the file. If the file extension is recognized the attribute data will be displayed in green.

6. Navigation buttons: Use the Previous and Next buttons to load the previous or next feature when more than one feature is selected.

7. Feature indicator: This heading indicates which feature is being displayed and how many features are available for display.

Understanding the Options window

1. File path: A dropdown list to specify the attribute field that contains the directory path or URL for the photographs or other documents being displayed. If the location is a relative path then the checkbox must be clicked. The base path for a relative path can be entered in the Base Path text box below. Information

178 Chapter 18. Plugins

Figure 18.9: The eVis display window

QGIS User Guide, Release 1.8.0

18.8. eVis Plugin

Figure 18.10: The eVis Options window

179

QGIS User Guide, Release 1.8.0

about the different options for specifying the file location are noted in the section

Specifying the location and name of a photograph

below.

2. Compass bearing display field: A dropdown list to specify the attribute field that contains the compass bearing associated with the photograph being displayed. If compass bearing information is available it is necessary to click the checkbox to the left of the dropdown menu title.

3. Compass offset setting: Compass offsets can be used to compensate for declination (adjust bearings collected using magnetic bearings to true north bearings). Click the Manual radiobutton to enter the offset in the text box or click the From Attribute radiobutton to select the attribute field containing the offsets.

For both of these options east declinations should be entered using positive values and west declinations should use negative values.

4. Directory base path: The base path onto which the relative path defined in

Figure_eVis_2

(A) will be appended.

5. Replace path: If this checkbox is checked, only the file name from the A will be appended to the Base Path.

6. Apply rule to all documents: If checked, the same path rules that are defined for photographs will be used for non-image documents such as movies, text documents, and sound files. If not checked the path rules will only apply to photographs and other documents will ignore the Base Path parameter.

7. Save settings: If the checkbox is checked the values for the associated parameters will be saved for the next session when the window is closed or when the [Save] button below is pressed.

8. Reset values: Resets the values on this line to the default setting.

9. Restore faults: This will reset all of the fields to their default settings. It has the same effect as clicking all of the [Reset] buttons.

10. Save: This will save the settings without closing the Options pane.

Understanding the Configure External Applications window

Figure 18.11: The eVis External Applications window

1. File reference table: A table containing file types that can be opened using eVis. Each file type needs a file extension and the path to an application that can open that type of file. This provides the capability of opening a broad range of files such as movies, sound recordings, and text documents instead of only images.

2. Add new file type: Add a new file type with a unique extension and the path for the application that can open the file.

3. Delete current row: Delete the file type highlighted in the table and defined by a file extension and a path to an associated application.

18.8.2 Specifying the location and name of a photograph

The location and name of the photograph can be stored using an absolute or relative path or a URL if the photograph is available on a web server. Examples of the different approaches are listed in Table

evis_examples

.

180 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

X

780596

780596

780819

780596

Y FILE

1784017 C:\Workshop\eVis_Data\groundphotos\DSC_0168.JPG

1784017 /groundphotos/DSC_0169.JPG

1784015 http://biodiversityinformatics.amnh.org/evis_testdata/DSC_0170.JPG

1784017 pdf:http://www.testsite.com/attachments.php?attachment_id-12

BEARING

275

80

10

76

18.8.3 Specifying the location and name of other supporting documents

Supporting documents such as text documents, videos, and sound clips can also be displayed or played by eVis.

To do this it is necessary to add an entry in the file reference table that can be accessed from the Configure External

Applications window in the Generic Event Browser that matches the file extension to an application that can be used to open the file. It is also necessary to have the path or URL to the file in the attribute table for the vector layer. One additional rule that can be used for URLs that don’t contain a file extension for the document you want to open is to specify the file extension before the URL. The format is — file extension:URL. The URL is preceded by the file extension and a colon, and is particularly useful for accessing documents from Wikis and other web sites that use a database to manage the web pages (see Table

evis_examples

).

18.8.4 Using the Generic Event Browser

When the Event Browser window opens a photograph will appear in the display window if the document referenced in the vector file attribute table is an image and if the file location information in the Options window is properly set. If a photograph is expected and it does not appear it will be necessary to adjust the parameters in the

Options window.

If a supporting document (or an image that does not have a file extension recognized by eVis) is referenced in the attribute table the field containing the file path will be highlighted in green in the attribute information window if that file extension is defined in the file reference table located in the Configure External Applications window. To open the document double-click on the green-highlighted line in the attribute information window. If a supporting document is referenced in the attribute information window and the file path is not highlighted in green then it will be necessary to add an entry for the file’s filename extension in the Configure External Applications window.

If the file path is highlighted in green but does not open when double-clicked it will be necessary to adjust the parameters in the Options window so the file can be located by eVis.

If no compass bearing is provided in the Options window a red asterisk will be displayed on top of the vector feature that is associated with the photograph being displayed. If a compass bearing is provided then an arrow will appear pointing in the direction indicated by the value in the compass bearing display field in the Generic

Event Browser window. The arrow will be centered over the point that is associated with the photograph or other document.

To close the Generic Event Browser window click on the [Close] button from the Display window.

18.8.5 Event ID Tool

The ‘Event ID’ module allows you to display a photograph by clicking on a feature displayed in the QGIS map window. The vector feature must have attribute information associated with it to describe the location and name of the file containing the photograph and optionally the compass direction the camera was pointed when the image was acquired. This layer must be loaded into QGIS before running the ‘Event ID’ tool.

Launch the Event ID module

To launch the ‘Event ID’ module either click on the

Event ID icon or click on Plugins → eVis → Event ID Tool.

This will cause the cursor to change to an arrow with an ‘i’ on top of it signifying that the ID tool is active.

To view the photographs linked to vector features in the active vector layer displayed in the QGIS map window, move the Event ID cursor over the feature and then click the mouse. After clicking on the feature, the Generic

Event Browser window is opened and the photographs on or near the clicked locality are available for display

18.8. eVis Plugin 181

QGIS User Guide, Release 1.8.0

in the browser. If more than one photograph is available, you can cycle through the different features using the

[Previous] and [Next] buttons. The other controls are described in the ref:evis_browser section of this guide.

18.8.6 Database connection

The ‘Database Connection’ module provides tools to connect to and query a database or other ODBC resource, such as a spreadsheet.

eVis can directly connect to four types of databases: Microsoft Access, PostgreSQL, MySQL, SQLite, and can also read from ODBC connections. When reading from an ODBC database (such as an Excel spreadsheet) it is necessary to configure your ODBC driver for the operating system you are using.

Launch the Database Connection module

To launch the ‘Database Connection’ module either click on the appropriate icon eVis Database Connection or click on Plugins → eVis → Database Connection. This will launch the Database Connection window. The window has three tabs: Predefined Queries, Database Connection, and SQL Query. The Output Console window at the bottom of the window displays the status of actions initiated by the different sections of this module.

Connect to a database

Click on the Database Connection tab to open the database connection interface. Next, use the Database Type combobox to select the type of database that you want to connect to. If a password or username is required, that information can be entered in the Username and Password textboxes.

Enter the database host in the Database Host textbox. This option is not available if you selected “MS Access” as the database type. If the database resides on your desktop you should enter “localhost”.

Enter the name of the database in the Database Name textbox. If you selected “ODBC” as the database type, you need to enter the data source name.

When all of the parameters are filled in, click on the [Connect] button. If the connection is successful, a message will be written in the Output Console window stating that the connection was established. If a connection was not established you will need to check that the correct parameters were entered above.

1. Database Type: A dropdown list to specify the type of database that will be used.

2. Database Host: The name of the database host.

3. Port The port number if a MySQL or PostgreSQL database type is selected.

4. Database Name The name of the database.

5. Connect A button to connect to the database using the parameters defined above.

6. Output Console The console window where messages related to processing are displayed.

7. Username: Username for use when a database is password protected.

8. Password: Password for use when a database is password protected.

9. Predefined Queries: Tab to open the “Predefined Queries” window.

10. Database Connection: Tab to open the “Database Connection” window.

11. SQL Query: Tab to open the “SQL Query” window.

12. Help: Displays the on line help.

13. OK: Close the main “Database Connection” window.

182 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.12: The eVis Database connection window

Running SQL queries

SQL queries are used to extract information from a database or ODBC resource. In eVis the output from these queries is a vector layer added to the QGIS map window. Click on the SQL Query tab to display the SQL query interface. SQL commands can be entered in this text window. A helpful tutorial on SQL commands is available at http://www.w3schools.com/sql . For example, to extract all of the data from a worksheet in an Excel file, select

* from [sheet1$] where sheet1 is the name of the worksheet.

Click on the [Run Query] button to execute the command. If the query is successful a Database File Selection window will be displayed. If the query is not successful an error message will appear in the Output Console window.

In the Database File Selection window, enter the name of the layer that will be created from the results of the query in the Name of New Layer textbox.

1. SQL Query Text Window: A screen to type SQL queries.

2. Run Query: Button to execute the query entered in the SQL Query Window.

3. Console Window: The console window where messages related to processing are displayed.

4. Help: Displays the on line help.

5. OK: Closes the main Database Connection window.

Use the X Coordinate and Y Coordinate comboboxes to select the field from the database that store the X (or longitude) and Y (or latitude) coordinates. Clicking on the [OK] button causes the vector layer created from the SQL query to be displayed in the QGIS map window.

To save this vector file for future use, you can use the QGIS ‘Save as...’ command that is accessed by right clicking on the layer name in the QGIS map legend and then selecting ‘Save as...’

Tip: Creating a vector layer from a Microsoft Excel Worksheet

18.8. eVis Plugin 183

QGIS User Guide, Release 1.8.0

Figure 18.13: The eVis SQL query tab

When creating a vector layer from a Microsoft Excel Worksheet you might see that unwanted zeros (“0”) have been inserted in the attribute table rows beneath valid data.This can be caused by deleting the values for these cells in Excel using the Backspace key. To correct this problem you need to open the Excel file (you’ll need to close

QGIS if there if you are connected to the file to allow you to edit the file) and then use Edit → Delete to remove the blank rows from the file. To avoid this problem you can simply delete several rows in the Excel Worksheet using Edit → Delete before saving the file.

Running predefined queries

With predefined queries you can select previously written queries stored in XML format in a file. This is particularly helpful if you are not familiar with SQL commands. Click on the Predefined Queries tab to display the predefined query interface.

To load a set of predefined queries click on the

Open File icon. This opens the Open File window which is used to locate the file containing the SQL queries. When the queries are loaded their titles, as defined in the XML file, will appear in the dropdown menu located just below the displayed in the text window under the dropdown menu.

Open File icon, the full description of the query is

Select the query you want to run from the dropdown menu and then click on the SQL Query tab to see that the query has been loaded into the query window. If it is the first time you are running a predefined query or are switching databases, you need to be sure to connect to the database.

Click on the [Run Query] button in the SQL Query tab to execute the command. If the query is successful a

Database File Selection window will be displayed. If the query is not successful an error message will appear in the Output Console window.

1. Open Query File: Launches the “Open File” file browser to search for the XML file holding the predefined queries.

2. Predefined Queries: A dropdown list with all of the queries defined by the predefined queries XML file.

184 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.14: The eVis Predefined queries tab

3. Query description: A short description of the query. This description is from the predefined queries XML file.

4. Console Window: The console window where messages related to processing are displayed.

5. Help: Displays the on line help.

6. OK: Closes the main “Database Connection” window.

XML format for eVis predefined queries

The XML tags read by eVis

18.8. eVis Plugin 185

QGIS User Guide, Release 1.8.0

Tag query shortdescription description

Description

Defines the beginning and end of a query statement.

A short description of the query that appears in the eVis dropdown menu.

A more detailed description of the query displayed in the Predefined Query text window.

databasetype databaseport

The database type as defined in the Database Type dropdown menu in the Database Connection tab.

The port as defined in the Port textbox in the Database Connection tab.

databasename

The database name as defined in the Database Name textbox in the Database Connection tab.

databaseuserThe database username as defined in the Username textbox in the Database Connection tab.

name

The database password as defined in the Password textbox in the Database Connection tab.

databasepassword sqlstatement autoconnect

The SQL command.

A flag (“true”” or “false”) to specify if the above tags should be used to automatically connect to database without running the database connection routine in the Database Connection tab.

A complete sample XML file with three queries is displayed below:

<?xml version="1.0"?>

<doc>

<query>

<shortdescription>Import all photograph points</shortdescription>

<description>This command will import all of the data in the SQLite database to QGIS

</description>

<databasetype>SQLITE</databasetype>

<databasehost />

<databaseport />

<databasename>C:\textbackslash Workshop/textbackslash eVis\_Data\textbackslash PhotoPoints.db</databasename>

<databaseusername />

<databasepassword />

<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN

Points ON Points.rec_id=Attributes.point_ID</sqlstatement>

<autoconnect>false</autoconnect>

</query>

<query>

<shortdescription>Import photograph points "looking across Valley"</shortdescription>

<description>This command will import only points that have photographs "looking across a valley" to QGIS</description>

<databasetype>SQLITE</databasetype>

<databasehost />

<databaseport />

<databasename>C:\Workshop\eVis_Data\PhotoPoints.db</databasename>

<databaseusername />

<databasepassword />

<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN

Points ON Points.rec_id=Attributes.point_ID where COMMENTS=’Looking across valley’</sqlstatement>

<autoconnect>false</autoconnect>

</query>

<query>

<shortdescription>Import photograph points that mention "limestone"</shortdescription>

<description>This command will import only points that have photographs that mention

"limestone" to QGIS</description>

<databasetype>SQLITE</databasetype>

<databasehost />

<databaseport />

186 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

<databasename>C:\Workshop\eVis_Data\PhotoPoints.db</databasename>

<databaseusername />

<databasepassword />

<sqlstatement>SELECT Attributes.*, Points.x, Points.y FROM Attributes LEFT JOIN

Points ON Points.rec_id=Attributes.point_ID where COMMENTS like ’%limestone%’

</sqlstatement>

<autoconnect>false</autoconnect>

</query>

</doc>

18.9 fTools Plugin

The goal of the fTools python plugin is to provide a one-stop resource for many common vector-based GIS tasks, without the need for additional software, libraries, or complex workarounds. It provides a growing suite of spatial data management and analysis functions that are both fast and functional.

fTools is now automatically installed and enabled in new versions of QGIS, and as with all plugins, it can be disabled and enabled using the Plugin Manager (See Section

Loading a QGIS Core Plugin

). When enabled, the

fTools plugin adds a Vector menu to QGIS, providing functions ranging from Analysis and Research Tools to

Geometry and Geoprocessing Tools, as well as several useful Data Management Tools.

18.9.1 Analysis tools

Icon Tool

Distance

Matrix

Purpose

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.

Calculate the total sum of line lengths for each polygon of a polygon vector layer.

Sum line length

Points in polygon

List unique values

Count the number of points that occur in each polygon of an input polygon vector layer.

List all unique values in an input vector layer field

Basic statistic

Nearest

Neighbor analysis

Compute basic statistics (mean, std dev, N, sum, CV) on an input field.

Compute nearest neighbor statistics assess the level of clustering in a point vector layer

Mean coordinate(s)

Compute either the normal or weighted mean center of an entire vector layer, or multiple features based on a unique ID field.

Line intersections

Locate intersections between lines, and output results as a point shapefile. Useful for locating road or stream intersections, ignores line intersections with length > 0.

Table Ftools 1: fTools Analysis tools

18.9. fTools Plugin 187

QGIS User Guide, Release 1.8.0

18.9.2 Research tools

Icon Tool

Random selection

Random selection within subsets

Random points

Purpose

Randomly select n number of features, or n percentage of features

Randomly select features within subsets based on a unique ID field.

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.

Generate a line or polygon grid based on user specified grid spacing.

Vector grid

Select by location Select features based on their location relative to another layer to form a new selection, or add or subtract from the current selection.

Polygon from layer extent

Create a single rectangular polygon layer from the extent of an input raster or vector layer.

Table Ftools 2: fTools Research tools

18.9.3 Geoprocessing tools

Icon Tool

Convex hull(s)

Buffer(s)

Intersect

Union

Symmetrical difference

Clip

Purpose

Create minimum convex hull(s) for an input layer, or based on an ID field.

Create buffer(s) around features based on distance, or distance field.

Overlay layers such that output contains areas where both layers intersect.

Overlay layers such that output contains intersecting and non-intersecting areas.

Overlay layers such that output contains those areas of the input and difference layers that do not intersect.

Overlay layers such that output contains areas that intersect the clip layer.

Difference

Dissolve

Overlay layers such that output contains areas not intersecting the clip layer.

Merge features based on input field. All features with identical input values are combined to form one single feature.

Table Ftools 3: fTools Geoprocessing tools

188 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.9.4 Geometry tools

Icon Tool

Check geometry

Export/Add geometry columns

Polygon centroids

Purpose

Check polygons for intersections, closed-holes, and fix node ordering.

Add vector layer geometry info to point (XCOORD, YCOORD), line

(LENGTH), or polygon (AREA, PERIMETER) layer.

Calculate the true centroids for each polygon in an input polygon layer.

Delaunay triangulation

Voronoi Polygons

Calculate and output (as polygons) the delaunay triangulation of an input point vector layer.

Calculate voronoi polygons of an input point vector layer.

Simplify geometry Generalize lines or polygons with a modified Douglas-Peucker algorithm.

Densify geometry Densify lines or polygons by adding vertices

Multipart to singleparts

Convert multipart features to multiple singlepart features. Creates simple polygons and lines.

Singleparts to multipart

Polygons to lines

Merge multiple features to a single multipart feature based on a unique ID field.

Lines to polygons

Convert polygons to lines, multipart polygons to multiple singlepart lines.

Convert lines to polygons, multipart lines to multiple singlepart polygons.

Extract nodes Extract nodes from line and polygon layers and output them as points.

Table Ftools 4: fTools Geometry tools

Note: The Simplify geometry tool can be used to remove duplicate nodes in line and polygon geometries, just set the Simplify tolerance parameter to 0 and this will do the trick.

18.9.5 Data management tools

Icon Tool Purpose

Define projection

Join attributes by location

Split vector layer

Specify the CRS for shapefiles whose CRS has not been defined.

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 input layer into multiple separate layers based on input field.

Merge shapefiles to one

Create spatial index

Merge several shapefiles within a folder into a new shapefile based on the layer type

(point, line, area).

Create a spatial index for OGR supported formats.

Table Ftools 5: fTools Data management tools

18.9. fTools Plugin 189

QGIS User Guide, Release 1.8.0

18.10 GDAL Tools Plugin

18.10.1 What is GDALTools?

The GDAL Tools plugin offers a GUI to the collection of tools in the Geospatial Data Abstraction Library, http://gdal.osgeo.org

. These are raster management tools to query, re-project, warp and merge a wide variety of raster formats. Also included are tools to create a contour (vector) layer, or a shaded relief from a raster DEM, and to make a vrt (Virtual Raster Tile in XML format) from a collection of one or more raster files. These tools are available when the plugin is installed and activated.

The GDAL Library

The GDAL library consists of a set of command line programs, each with a large list of options. Users comfortable with running commands from a terminal may prefer the command line, with access to the full set of options. The

GDALTools plugin offers an easy interface to the tools, exposing only the most popular options.

18.10.2 List of GDAL tools

Figure 18.15: The GDALTools menu list

Projections

Warp

(Reproject)

Assign projection

Extract projection

This utility is an image mosaicing, reprojection and warping utility. The program can reproject to any supported projection, and can also apply GCPs stored with the image if the image is “raw” with control information. For more information you can read on the GDAL website http://www.gdal.org/gdalwarp.html

This tool allows to assign projection to rasters that already georeferenced but miss projection information. Also with it help it is possible to alter existing projection definition. Both single file and batch mode are supported. For more information please visit utility page at GDAL site http://www.gdal.org/gdalwarp.html

This utility helps you to extract projection information from an input file. If you want to extract projection from a whole directory you can use the Batch mode. It creates both .prj

and .wld files.

190 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Conversion

Rasterize

Polygonize

Translate

RGB to PCT

PCT to RGB

This program burns vector geometries (points, lines and polygons) into the raster band(s) of a raster image. Vectors are read from OGR supported vector formats. Note that the vector data must in the same coordinate system as the raster data; on the fly reprojection is not provided. For more information see http://www.gdal.org/gdal-rasterize.html

This utility creates vector polygons for all connected regions of pixels in the raster sharing a common pixel value. Each polygon is created with an attribute indicating the pixel value of that polygon. The utility will create the output vector datasource if it does not already exist, defaulting to ESRI shapefile format. See also http://www.gdal.org/gdal_polygonize.html

This utility can be used to convert raster data between different formats, potentially performing some operations like subsettings, resampling, and rescaling pixels in the process. For more information you can read on http://www.gdal.org/gdal_translate.html

This utility will compute an optimal pseudo-color table for a given RGB image using a median cut algorithm on a downsampled RGB histogram. Then it converts the image into a pseudo-colored image using the color table. This conversion utilizes Floyd-Steinberg dithering

(error diffusion) to maximize output image visual quality. The utility is also desribed at http://www.gdal.org/rgb2pct.html

This utility will convert a pseudocolor band on the input file into an output RGB file of the desired format. For more information see http://www.gdal.org/pct2rgb.html

Extraction

Contour

This program generates a vector contour file from the input raster elevation model (DEM). On http://www.gdal.org/gdal_contour.html

you can find more information.

Clipper

This utility allows to clip (extract subset) raster using selected extent or based on mask layer bounds. More information can be found at http://www.gdal.org/gdal_translate.html

.

18.10. GDAL Tools Plugin 191

QGIS User Guide, Release 1.8.0

Analysis

Sieve

Near

Black

Fill nodata

This utility removes raster polygons smaller than a provided threshold size (in pixels) and replaces them with the pixel value of the largest neighbor polygon. The result can be written back to the existing raster band, or copied into a new file. For more information see http://www.gdal.org/gdal_sieve.html

.

This utility will scan an image and try to set all pixels that are nearly black (or nearly white) around the edge to exactly black (or white). This is often used to “fix up” lossy compressed aerial photos so that color pixels can be treated as transparent when mosaicing. See also http://www.gdal.org/nearblack.html

.

This utility fills selection raster regions (usually nodata areas) by interpolation from valid pixels around the edges of the area. On http://www.gdal.org/gdal_fillnodata.html

you can find more information.

Proximity This utility generates a raster proximity map indicating the distance from the center of each pixel to the center of the nearest pixel identified as a target pixel. Target pixels are those in the source raster for which the raster pixel value is in the set of target pixel values. For more information see http://www.gdal.org/gdal_proximity.html

.

Grid This utility creates regular grid (raster) from the scattered data read from the OGR datasource. Input data will be interpolated to fill grid nodes with values, you can choose from various interpolation methods. The utility is also described on the GDAL website http://www.gdal.org/gdal_grid.html

.

DEM terrain models

Tools to analyze and visualize DEMs. It can create a shaded relief, a slope, an aspect, a color relief, a Terrain Ruggedness Index, a Topographic Position Index and a roughness map from any GDAL-supported elevation raster. For more information you can read on http://www.gdal.org/gdaldem.html

Miscellaneous

Build

Virtual

Raster

Merge

This program builds a VRT (Virtual Dataset) that is a mosaic of the list of input gdal datasets.

See also http://www.gdal.org/gdalbuildvrt.html

.

Information

Build

Overviews

Tile

Index

This utility will automatically mosaic a set of images. All the images must be in the same coordinate system and have a matching number of bands, but they may be overlapping, and at different resolutions. In areas of overlap, the last image will be copied over earlier ones. The utility is also described on http://www.gdal.org/gdal_merge.html

.

This utility lists various information about a GDAL supported raster dataset. On http://www.gdal.org/gdalinfo.html

you can find more information.

The gdaladdo utility can be used to build or rebuild overview images for most supported file formats with one of several downsampling algorithms. For more information see http://www.gdal.org/gdaladdo.html

.

This utility builds a shapefile with a record for each input raster file, an attribute containing the filename, and a polygon geometry outlining the raster. See also http://www.gdal.org/gdaltindex.html

.

192 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.11 Georeferencer Plugin

The Georeferencer Plugin is a tool for generating world files for rasters. It allows you to reference rasters to geographic or projected coordinate systems by creating a new GeoTiff or by adding a world file to the existing image. The basic approach to georeferencing a raster is to locate points on the raster for which you can accurately determine their coordinates.

Features

Icon Purpose Icon Purpose

Open raster

Generate GDAL Script

Save GCP Points As

Add Point

Move GCP Point

Zoom In

Zoom To Layer

Zoom Next

Link QGIS to Georeferencer

Table Georeferencer 1: Georeferencer Tools

Start georeferencing

Load GCP Points

Transformation settings

Delete Point

Pan

Zoom Out

Zoom Last

Link Georeferencer to QGIS

18.11.1 Usual procedure

As X and Y coordinates (DMS (dd mm ss.ss), DD (dd.dd) or projected coordinates (mmmm.mm) which correspond with the selected point on the image, two alternative procedures can be used:

• The raster itself sometimes provides crosses with coordinates “written” on the image. In this case you can enter the coordinates manually.

• Using already georeferenced layers, this can be either vector or raster data that contain the same objects/features that you have on the image that you want to georeference and the projection you want to have your image. In this case you can enter the coordinates by clicking on the reference dataset loaded in

QGIS map canvas.

The usual procedure for georeferencing an image involves selecting multiple points on the raster, specifying their coordinates, and choosing a relevant transformation type. Based on the input parameters and data, the plugin will compute the world file parameters. The more coordinates you provide, the better the result will be.

The first step is to start QGIS, load the Georeferencer Plugin (see Section

Loading a QGIS Core Plugin

) and click

on the

Georeferencer icon which appears in the QGIS toolbar menu. The Georeferencer Plugin dialog appears as shown in

figure_georeferencer_1

.

For this example, we are using a topo sheet of South Dakota from SDGS. It can later be visualized together with the data from the GRASS spearfish60 location.

You can download the topo sheet here: http://grass.osgeo.org/sampledata/spearfish_toposheet.tar.gz

.

Entering ground control points (GCPs)

1. To start georeferencing an unreferenced raster, we must load it using the 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.

18.11. Georeferencer Plugin 193

QGIS User Guide, Release 1.8.0

Figure 18.16: Georeferencer Plugin Dialog

2. Using the

Add Point button, add points to the main working area and enter their coordinates (see Figure

figure_georeferencer_2

). For this procedure you have three options:

• Click on a point in the raster image and enter the X and Y coordinates manually.

• Click on a point in the raster image and choose the button from map canvas to add the X and Y coordinates with the help of a georeferenced map already loaded in the QGIS map canvas.

• With the button, you can move the GCPs in both windows, if they are at the wrong place.

3. Continue entering points. You should have at least 4 points, and the more coordinates you can provide, the better the result will be. There are additional tools on the plugin dialog to zoom and pan the working area in order to locate a relevant set of GCP points.

Figure 18.17: Add points to the raster image

The points that are added to the map will be stored in a separate text file ([filename].points) usually together with the raster image. This allows us to reopen the Georeferencer plugin at a later date and add new points or delete existing ones to optimize the result. The points file contains values of the form: mapX, mapY, pixelX, pixelY

. You can use the

Load GCP Points and

Save GCP Points buttons to manage the files.

Within the GCP table you can click on a column header and therewith enable e.g. numerical sorting. The GCP list is automatically updated.

Defining the transformation settings

After you have added your GCPs to the raster image, you need to define the transformation settings for the georeferencing process.

194 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.18: Defining the georeferencer transformation settings

Available Transformation algorithms

Depending on how many ground control point you have captured, you may want to use different transformation algorithms. Choice of transformation algorithm is also dependent on the type and quality of input data and the amount of geometric distortion that you are willing to introduce to final result.

Currently, following algorithms are available:

• The Linear algorithm is used to create a world-file, and is different from the other algorithms, as it does not actually transform the raster. This algorithm likely won’t be sufficient if you are dealing with scanned material.

• The Helmert transformation performs simple scaling and rotation transformations.

• The Polynomial algorithms 1-3 are among the most widely used algorithms for georeferencing, and each one differs by the degree of distortion introduced to match source and destination ground control points.

The most widely used polynomial algorithm is the second order polynomial transformation, which allows some curvature. First order polynomial transformation (affine) preserves colliniarity and allows scaling, translation and rotation only.

• The Thin plate spline (TPS) algorithm is a more modern georeferencing method, which is able to introduce local deformations in the data. This algorithm is useful when very low quality originals are being georeferenced.

• The Projective transformation is a linear rotation and translation of coordinates.

Define the Resampling method

The type of resampling you choose will likely depending on your input data and the ultimate objective of the exercise. If you don’t want to change statistics of the image, you might want to choose ‘Nearest neighbour’, whereas a ‘Cubic resampling’ will likely provide a more smoothed result.

It is prossible to choose between five different resampling methods.

1. Nearest neighbour

2. Linear

3. Cubic

18.11. Georeferencer Plugin 195

QGIS User Guide, Release 1.8.0

4. Cubic Spline

5. Lanczos

Define the transformation settings

There are several options that need to be defined for the georeferenced output raster.

• The checkbox Create world file is only available, if you decide to use the linear transformation type, because this means that the raster image actually won’t be transformed. In this case, the field Output raster is not activated, because only a new world-file will be created.

• For all other transformation type you have to define an Output raster.

As default a new file ([filename]_modified) will be created in the same folder together with the original raster image.

• As a next step you have to define the Target SRS (Spatial Reference System) for the georeferenced raster

(see section

Working with Projections

).

• If you like, you can generate a pdf map and also a pdf report. The report includes information about the used transformation parameters. An image of the residuals and a list with all GCPs and their RMS errors.

• Furthermore you can activate the Set Target Resolution checkbox and define pixel resolution of the output raster. Default horizontal and vertical resolution is 1,

• The Use 0 for transparency when needed can be activated, if pixels with the value 0 shall be visualized transparent. In our example toposheet all white areas would be transparent.

• Finally Load in QGIS when done loads the output raster automatically into the QGIS map canvas when the transformation is done.

Show and adapt raster properties

Clicking on the Raster properties dialog in the Settings menu opens the raster properties of the layer that you want to georeference.

Configure the georeferencer

• You can define if you want to show GCP coordiniates and/or IDs.

• As residual units pixels and map units can be chosen.

• For the PDF report a left and right margin can be defined and you can also set the paper size for the PDF map.

• Finally you can activate to show georeferencer window docked .

Running the transformation

After all GCPs have been collected and all transformation settings are defined, just press the button

Start georeferencing to create the new georeferenced raster.

18.12 Interpolation Plugin

The Interplation plugin can be used to generate a TIN or IDW interpolation of a point vector layer. It is very simple to handle and provides an intuitive graphical user interface for creating interpolated raster layers (See

Figure_interpolation_1

). The plugin requires the following parameters to be specified before running:

196 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

• Input vector layer: Specify the input point vector layer(s) from a list of loaded point layers. If several layers are specified, then data from all layers is used for interpolation. Note: It is possible to insert lines or polygons as constraints for the triangulation, by specifying either “points”, “structure lines” or “break lines” in the Type combobox.

• Interpolation attribute: Select attribute column to be used for interpolation or enable the

Coordinate checkbox to use the layers stored Z values.

Use Z-

• Interpolation Method: Select interpolation method. This can be either ‘Triangulated Irregular Network

(TIN)’ or ‘Inverse Distance Weighted (IDW)’.

• Number of columns/rows: Specify the number row and colums for the output raster file.

• Output file: Specify a name for the output raster file.

Figure 18.19: Interpolation Plugin

18.12.1 Using the plugin

1. Start QGIS and load a point vector layer (e.g., elevp.csv).

2. Load the Interpolation plugin in the Plugin Manager (see Section

Loading a QGIS Core Plugin

) and click

on the

Interpolation icon which appears in the QGIS toolbar menu. The Interpolation plugin dialog appears as shown in

Figure_interpolation_1

.

3. Select an input layer (e.g., elevp ) and column (e.g., ELEV) for interpolation.

4. Select an interpolation method (e.g. ‘Triangulated Irregular Network (TIN)’), and specify a cellsize of 5000 as well as the raster output filename (e.g., elevation_tin).

5. Click [OK].

6. For the current example, double click elevation_tin in the layer list to open the raster Layer Properties dialog and select ‘Pseudocolor’ as Color Map table as described in section

Working with Raster Data

.

in the Symbology tab. Or you can define a new color

18.13 MapServer Export Plugin

You can use QGIS to ‘compose’ your map by adding and arranging layers, symbolizing them, customizing the colors and then creating a map file for MapServer.

Note: Currently the plugin only works when you use ‘Old Symbology’ in QGIS. ‘New Symbology’ is not yet supported.

18.13. MapServer Export Plugin 197

QGIS User Guide, Release 1.8.0

18.13.1 Creating the Project File

The MapServer Export Plugin operates on a saved QGIS project file and not on the current contents of the map canvas and legend. This has been a source of confusion for a number of users. As described below, before you start using the MapServer Export Plugin, you need to arrange the raster and vector layers you want to use in MapServer and save this status in a QGIS project file.

Figure 18.20: Arrange raster and vector layers for QGIS project file

In this example, we demonstrate the four steps required to create a simple project file which can be used to create the MapServer map file. We use raster and vector files from the QGIS sample dataset

Sample Data

.

1. Add the raster layer landcover.tif clicking on the

Add Raster Layer icon.

2. Add the vector Shapefiles lakes.shp, majrivers.shp and airports.shp from the QGIS sample dataset clicking on the

Add Vector Layer icon.

3. Change the colors and symbolize the data as you like (for example see

figure_mapserver_export_1

)

4. Save a new project named mapserverproject.qgs using File → Save Project .

18.13.2 Creating the Map File

To use the Mapserver Export plugin from within QGIS, you need to enable the MapServer Export Plugin first using the Plugin Manager (see

Loading a QGIS Core Plugin

).

198 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.21: Export to MapServer Dialog

Map file

Qgis project file

Map

Name

Map

Width

Map

Height

Map

Units

Image type

Web

Template

Web

Header

Web

Footer

Enter the name for the map file to be created. You can use the button at the right to browse for the directory where you want the map file created.

Enter the full path to the QGIS project file (.qgs) you want to export. You can use the button at the right to browse for the QGIS project file.

A name for the map. This name is prefixed to all images generated by the mapserver.

Width of the output image in pixels.

Height of the output image in pixels.

Units of measure used for output.

Format for the output image generated by MapServer

Full path to the MapServer template file to be used with the map file

Full path to the MapServer header file to be used with the map file

Full path to the MapServer footer file to be used with the map file

Only the inputs Map file and QGIS project file are required to create a map file, however by omitting the other parameters, you may end up creating a non-functional map file, depending on your intended use. Although QGIS is good at creating a map file from your project file, it may require some tweaking to get the results you want. For this example, we will create a map file using the project file mapserverproject.qgs we just created (see

Figure_mapserver_export_2

):

1. Click the

MapServer Export

ure_mapserver_export_2

).

icon in the toolbar menu to start the MapServer dialog (see

Fig-

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.

18.13. MapServer Export Plugin 199

QGIS User Guide, Release 1.8.0

7. Choose png for the image type.

8. Click [OK] to generate the new map file qgisproject.map. QGIS displays the success of your efforts.

Figure 18.22: Export to MapServer Succesfull Dialog

You can view the map file in any text editor or visualizer. If you take a look, you’ll notice that the export tool adds the metadata needed to enable our map file for WMS.

18.13.3 Troubleshooting

If you get error messages from mapserver like: loadSymbolSet(): Unable to access file. (./symbols/symbols.txt) or: msLoadFontset(): Unable to access file. Error opening fontset ./fonts/fonts.txt.

This means that that the map file is requesting for fonts or symbol definition files but that Mapserver cannot find those.

Either comment the lines containing those names in the map file (this is possible if you do not have labels or use styles from the symbols.txt). Or create those files (see below).

The most simple fonts.txt file (because arial is used in the QGIS generated map files) contains the following line

# either relative to the map file or a full path: arial / usr / share / fonts / truetype / msttcorefonts / arial .

ttf

The most simple symbols.txt file contains the definition of a circle symbol (because a circle symbol is used for point layers)

SYMBOLSET

SYMBOL

NAME "circle"

TYPE ellipse

FILLED true

POINTS

1 1

END

END

END

200 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.13.4 Testing the Map File

We can now test our work.

If the map file is accessible for you mapserver cgi you can use the one of the url’s from the success dialog.

Another option is using the shp2img tool to create an image from the map file. The shp2img utility is part of

MapServer and FWTools. To create an image from our map:

• Open a terminal window

• If you didn’t save your map file in your home directory, change to the folder where you saved it.

• Run shp2img -m qgisproject.map -o mapserver\_test.png and display the image

This creates a PNG with all the layers included in the QGIS project file. In addition, the extent of the PNG will be the same as when we saved the project. As you can see in

figure_mapserver_export_4

, all information except the

airport symbols are included.

Figure 18.23: Test PNG created by shp2img with all MapServer Export layers

18.13.5 Using Map File

If you plan to use the map file to serve WMS requests, you probably don’t have to tweak anything. If you plan to use it with a mapping template or a custom interface, you may have a bit of manual work to do. To see how easy it is to go from QGIS to serving maps on the web, take a look at Christopher Schmidt’s 5 minute flash video . He used an older version of QGIS (version 0.8), but the demo applies equally well to newer versions.

18.14 Offline Editing Plugin

For data collection, it is a common situation to work with a laptop or a cell phone offline in the field. Upon returning to the network, the changes need to be synchronized with the master data source, e.g. a PostGIS database.

If several persons are working simultaneously on the same datasets, it is difficult to merge the edits by hand, even if people don’t change the same features.

The

Offline Editing

Plugin automates the synchronisation by copying the content of a datasource (usually PostGIS or WFS-T) to a SpatiaLite database and storing the offline edits to dedicated tables. After being connected to the network again, it is possible to apply the offline edits to the master dataset.

18.14. Offline Editing Plugin 201

QGIS User Guide, Release 1.8.0

18.14.1 Using the plugin

• Open some vector layers, e.g. from a PostGIS or WFS-T datasource

• Save it as a project

• Press the

Convert to offline project

SpatiaLite tables.

icon and select the layers to save. The content of the layers is saved to

• Edit the layers offline.

• After being connected again, upload the changes with the

Synchronize button.

Figure 18.24: Create an offline project from PostGIS or WFS layers

18.15 Oracle GeoRaster Plugin

In Oracle databases, raster data can be stored in SDO_GEORASTER objects available with the Oracle Spatial extension. In QGIS, the

OracleGeoRasterPlugin is supported by GDAL, and depends on Oracle’s database product being installed and working on your machine. While Oracle is proprietary software, they provide their software free for development and testing purposes. Here is one simple example of how to load raster images to GeoRaster:

$ gdal_translate -of georaster input_file.tif geor:scott/[email protected]

This will load the raster into the default GDAL_IMPORT table, as a column named RASTER.

18.15.1 Managing connections

Firstly, the Oracle GeoRaster Plugin must be enabled using the Plugin Manager (see Section

Loading a QGIS

Core Plugin

). The first time you load a GeoRaster in QGIS, you must create a connection to the Oracle database

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_oracle_raster_1

):

• Name: Enter a name for the database connection

202 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

• Database instance: Enter the name of the database that you will connect to

• Username: Specify your own username that you will use to access the database

• Password: The password associated with your username that is required to access the database

Figure 18.25: Create Oracle connection dialog

Now, back on the main Oracle Spatial GeoRaster dialog window (see

Figure_oracle_raster_2

), use the drop-down

list to choose one connection, and use the [Connect] button to establish a connection. You may also [Edit] the connection by opening the previous dialog and making changes to the connection information, or use the [Delete] button to remove the connection from the drop-down list.

18.15.2 Selecting a GeoRaster

Once a connection has been established, the sub-datasets window will show the names of all the tables that contains

GeoRaster columns in that database in the format of a GDAL subdataset name.

Click on one of the listed subdatasets and then click on [Select] to choose the table name. Now another list of subdatasets will show with the names of GeoRaster columns on that table. This is usually a short list, since most users will not have more than one or two GeoRaster columns on the same table.

Click on one of the listed subdatasets and then click on [Select] to choose one of the the table/column combination.

The dialog will now show all the rows that contains GeoRaster objects. Note that the subdataset list will now show the Raster Data Table and Raster Id’s pairs.

At anytime the Selection entry can be edited in order to go directly to a known GeoRaster or to go back to the beginning and select another table name.

The Selection data entry can also be used to enter a Where clause at the end of the identification string, e.g.

geor:scott/[email protected],gdal_import,raster,geoid=

.

See http://www.gdal.org/frmt_georaster.html

for more information.

18.15.3 Displaying GeoRaster

Finally, by selecting a GeoRaster from the list of Raster Data Table and Raster Id’s, the raster image will be loaded into QGIS.

The Select Oracle Spatial GeoRaster dialog can be closed now and next time it opens it will keep the same connection, and will show the same previous list of subdataset making it very easy to open up another image from the same context.

Note: GeoRasters that contains pyramids will display much faster but the pyramids need to be generated outside of QGIS using Oracle PL/SQL or gdaladdo.

The following is example using gdaladdo:

18.15. Oracle GeoRaster Plugin 203

QGIS User Guide, Release 1.8.0

Figure 18.26: Select Oracle GeoRaster dialog gdaladdo georaster:scott/[email protected],georaster\_table,georaster,georid=6 -r nearest 2 4 6 8 16 32

This is an example using PL/SQL:

$ sqlplus scott/tiger

SQL> DECLARE gr sdo_georaster;

BEGIN

SELECT image INTO gr FROM cities WHERE id = 1 FOR UPDATE; sdo_geor.generatePyramid(gr, ’rLevel=5, resampling=NN’);

UPDATE cities SET image = gr WHERE id = 1;

END;

COMMIT;

18.16 Raster Terrain Analysis Plugin

The Raster Terrain Analysis Plugin can be used to calculate the slope, aspect, hillshade, ruggedness index and relief for digital elevation models (DEM). It is very simple to handle and provides an intuitive graphical user interface for creating new raster layers (See

Figure_raster_terrain_1

).

Description of the analysis:

• Slope: Calculates slope angle for each cell in degrees (based on first order derivative estimation).

• Aspect: Exposition (starting with 0 for north direction, in degrees counterclockwise).

• Hillshade: Create shaded map using light and shadow to provide a more three-dimensional appearance for a shaded relief map.

• Ruggedness Index: A quantitative measurement of terrain heterogeneity as described by Riley et al. (1999).

It is calculated for every location, by summarizing the change in elevation within the 3x3 pixel grid.

• Relief: Creating a shaded relief map from digital elevation data. Implemented is a method to choose the elevation colors analysing the frequency distribution.

18.16.1 Using the plugin

1. Start QGIS and load the gtopo30 raster layer from the GRASS sample location.

204 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.27: Raster Terrain Modelling Plugin (slope calculation)

2. Load the Raster Terrain Analysis plugin in the Plugin Manager (see Section

Loading a QGIS Core Plugin

)

3. Select an analysis method from menu (e.g. Raster → Terrain Analysis → Slope). The Slope dialog appears as shown in

Figure_raster_terrain_1

.

4. Specify an output file path, and an output file type.

5. Click [OK].

18.17 Heatmap Plugin

The

Heatmap plugin allows to create a heatmap from a point vector map. A heatmap is a raster map showing the density or magnitude of point related information. From the result “hotspots” can easily be identified.

18.17.1 Activate the Heatmap plugin

First this core plugin needs to be activated using the Plugin Manager (see Section

Loading a QGIS Core Plugin

).

After activation the heatmap icon can be found in the Raster Toolbar.

Select from menu View → Toolbars → Raster to activate the Raster Toolbar when it is not yet activated.

18.17.2 Using the Heatmap plugin

The

Heatmap toolbutton starts the dialog of the Heatmap plugin (see

figure_heatmap_2

).

The dialog has the following options:

• Input Point Vector dialog: Provides a selection of loaded point vector maps.

• Output Raster: Using the button you select the folder and the name of the output raster the Heatmap plugin will generate. It is not necessary to give a file extension

18.17. Heatmap Plugin 205

QGIS User Guide, Release 1.8.0

• Output Format: Selection of the output format. Although all formats supported by GDAL can be choosen,

GeoTIFF is most in cases the best format to choose.

• Radius: can be used to give the radius in meters or mapunit. When the radius is choosen too small you will not get a nice heatmap. In places where more circles around points overlap eachother the brighter hotspots will occur!

• Decay Ratio: is used to show with which ratio the heat dies out from the center.

– When 0 is given (=minimum) the heat will be concentrated in the centre of given radius and be completely extinguished at the edge.

– When 10 is given (=maximum) the heat is concentrated at the edge and in the centre it is completely extinguished. Higher given values are allowed but have no effect.

– When 1 is given the heat is spread evenly over the whole circle.

– When a negative Decay Ratio is given you will create a Coolmap instead of a Heatmap!

When the

Advanced checkbox is checked it will give acces to additional advanced options.

• Row and Column, can be used to change the pixelsize of the output raster. More rows and colums means a smaller pixelsize and the size of the output file will become bigger and processing a bit slower. When doubling the number of rows this will automatically double the size of Columns and the cell sizes will also be halved. The area of the output raster will remain the same!

• Cell Size X and Cell Size Y influence the pixelsize of the output raster and will also change the rows and columns.

The point vector layer may have attribute fields that can be used to create a heatmap:

• Use Radius from Field: the radius set from an attribute field.

• Use Weight from field: the weight factor set from an attribute field.

When the output raster is given, the [OK] button can be used to create a heatmap. The first result is a grey surface that still needs to be given additional treatment to make it a heatmap.

Warning: Changing the raster size properties

When changing the raster size properties, this also changes the resulting output. The hotspot areas will become bigger.

18.17.3 Creating a Heatmap

For the following example, we will use the airports vector point layer from the QGIS sample dataset (see

Sample Data

). Another exellent QGIS tutorial on making heatmaps can be found on

http://qgis.spatialthoughts.com

.

In

Figure_Heatmap_1

the airports of Alaska are shown.

1. Select the

Heatmap toolbutton. The heatmap dialog starts (see

Figure_Heatmap_2

).

2. In field Input Point Vector select airpoirt from the list of point layers loaded in current project.

3. In field Output Raster give the name and location using the button of the output raster. Give the output raster file the name heatmap_airports to give an file extension is not necessary.

4. In field Output Format choose GeoTIFF.

5. In the field Radius give 1000000 meters.

6. The original Decay Ratio of 0.1 is fine.

7. Click on [OK] to create and load the new raster map (see

Figure_Heatmap_3

).

206 Chapter 18. Plugins

Figure 18.28: Airports of Alaska

QGIS User Guide, Release 1.8.0

18.17. Heatmap Plugin

Figure 18.29: The Heatmap Dialog

207

QGIS User Guide, Release 1.8.0

The result after loading the heatmap is probably not the result which was expected. It is still a grey even surface not showing any variation. First some additional configuration of this layer needs to be done to make the heatmap present itself.

Figure 18.30: The heatmap after loading looks like a grey surface

1. Open the properties dialog of layer heatmap_airports (select the layer heatmap_airports, open context menu with right mouse button and select Properties).

2. Select the Symbology tab.

3. Change Color map

4. Press the [Apply] button.

from ‘Grayscale’ to ‘Pseudocolor’.

5. Switch to the Transparency tab and set Global transparency

6. Select [OK]

The final result is shown in

Figure_Heatmap_4

.

to 40%.

208

Figure 18.31: Final result of heatmap created of airports of Alaska

Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

18.18 Road Graph Plugin

The Road Graph Plugin is a C++ plugin for QGIS, that calculates the shortest path between two points on any polyline layer and plots this path over the road network.

Figure 18.32: Road Graph Plugin

Main features:

• calculate path, it’s length and travel time

• optimize by length or by travel time

• export path to a vector layer

• highlight roads directions (this is slow and used mainly for debug purposes and for the settings testing)

As a roads layer you can use any polyline vector layer in any QGIS supported format. Two lines with a common point are considered connected. Please note, it is required to use layer CRS as project CRS while editing roads layer. This is due to the fact that recalculation of the coordinates between different CRS introduce some errors that can result in discontinuities, even when ‘snapping’ is used.

In the layer attribute table the following fields can be used:

• speed on road section — numeric field;

• direction — any type, that can be casted to string. Forward and reverse directions are correspond to the one-way road, both directions — two-way road

If some fields don’t have any value or do not exist — default values are used. You can change defaults and some plugin settings in plugin settings dialog.

18.18.1 Using the plugin

After plugin activation you will see an additional panel on the left side of the main QGIS window. Now make some definitions to the Road graph plugin settings dialog in the menu Vector → Road Graph.

Select a Start and a Stop point in the road network layer and click on [Calculate].

18.18. Road Graph Plugin 209

QGIS User Guide, Release 1.8.0

18.19 Spatial Query Plugin

The

Spatial Query plugin allows to make a spatial query (select features) in a target layer with reference to another layer. The functionality is based on the GEOS library and depends on the selected source feature layer.

Possible operators are:

• Contains

• Equals

• Overlap

• Crosses

• Intersects

• Is disjoint

• Touches

• Within

18.19.1 Using the plugin

As an example we want to find regions in the Alaska dataset that contain airports. Following steps are necessary:

1. Start QGIS and load the vector layers regions.shp and airports.shp.

2. Load the Spatial Query plugin in the Plugin Manager (see Section

Loading a QGIS Core Plugin

) and click

on the

Spatial Query icon which appears in the QGIS toolbar menu. The plugin dialog appears.

3. Select layer regions as source layer and airports as reference feature layer.

4. Select ‘Contains’ as operator and click [Apply].

Now you get a list of feature IDs from the query and you have several options as shown in

figure_spatial_query_1

.

• Click on the

Create layer with list of items

• Select an ID from the list and click on

Create layer with selected

• Select the ‘Remove from current selection’ in the field And use the result to

• Additionally you can

Zoom to item or display

Log messages

.

.

18.20 SPIT Plugin

QGIS comes with a plugin named SPIT (Shapefile to PostGIS Import Tool). SPIT can be used to load multiple shapefiles at one time and includes support for schemas. To use SPIT, open the Plugin Manager from the Plugins menu, check the box next to the toolbar.

SPIT plugin and click [OK]. The SPIT icon will be added to the plugin

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 connect to and click on [Connect]. If you want, you can define or change some import options. Now you can add one or more files to the queue by clicking on the [Add] button. To process the files, click on the [OK] button. The progress of the import as well as any errors/warnings will be displayed as each shapefile is processed.

Tip: Importing Shapefiles Containing PostgreSQL Reserved Words

210 Chapter 18. Plugins

QGIS User Guide, Release 1.8.0

Figure 18.33: Spatial Query analysis - regions contain airports

18.20. SPIT Plugin

Figure 18.34: Using SPIT Plugin to import Shape files to PostGIS

211

QGIS User Guide, Release 1.8.0

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.

18.21 SQL Anywhere Plugin

SQL Anywhere is a proprietary relational database management system (RDBMS) from Sybase. SQL Anywhere includes spatial support including OGC, shape files etc. and built in functions to export to KML, GML and SVG formats.

Figure 18.35: SQL Anywhere dialog (KDE)

The

SQL Anywhere allows to connect to spatialy enabled SQL Anywhere databases. The Add SQL Anywhere layer dialog is similar in functionality to the dialogs for PostGIS and SpatiaLite.

18.22 Zonal Statistics Plugin

With the

Zonal Statistics Plugin you can analyze the results of a thematic classification. It allows to calculate several values of the pixels of a raster layer with the help of a polygonal vector layer (see

figure_zonal_statistics

). You can

calculate the sum, the mean value and the total count of the pixels that are within a polygon. The plugin generates output columns in the vector layer with a user-defined prefix.

212

Figure 18.36: Zonal statistics dialog (KDE)

Chapter 18. Plugins

CHAPTER

19

Help and Support

19.1 Mailing lists

QGIS is under active development and as such it won’t always work like you expect it to. The preferred way to get help is by joining the qgis-users mailing list. Your questions will reach a broader audience and answers will benefit others.

19.1.1 qgis-users

This mailing list is used for discussion of QGIS in general, as well as specific questions regarding its installation and use.

You can subscribe to the qgis-users mailing list by visiting the following URL: http://lists.osgeo.org/mailman/listinfo/qgis-user

19.1.2 fossgis-talk-liste

For the german speaking audience the german FOSSGIS e.V. provides the fossgis-talk-liste mailing list. This mailing list is used for discussion of open source GIS in general including QGIS. You can subscribe to the fossgistalk-liste mailing list by visiting the following URL: https://lists.fossgis.de/mailman/listinfo/fossgis-talk-liste

19.1.3 qgis-developer

If you are a developer facing problems of a more technical nature, you may want to join the qgis-developer mailing list here: http://lists.osgeo.org/mailman/listinfo/qgis-developer

19.1.4 qgis-commit

Each time a commit is made to the QGIS code repository an email is posted to this list.

If you want to be up to date with every change to the current code base, you can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-commit

19.1.5 qgis-trac

This list provides email notification related to project management, including bug reports, tasks, and feature requests. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-trac

213

QGIS User Guide, Release 1.8.0

19.1.6 qgis-community-team

This list deals with topics like documentation, context help, user-guide, online experience including web sites, blog, mailing lists, forums, and translation efforts. If you like to work on the user-guide as well, this list is a good starting point to ask your questions. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgiscommunity-team

19.1.7 qgis-release-team

This list deals with topics like the release process, packaging binaries for various OS and announcing new releases to the world at large. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-release-team

19.1.8 qgis-tr

This list deals with the translation efforts. If you like to work on the translation of the manuals or the graphical user interface (GUI), this list is a good starting point to ask your questions. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-tr

19.1.9 qgis-edu

This list deals with QGIS education efforts. If you like to work on QGIS education materials, this list is a good starting point to ask your questions. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgisedu

19.1.10 qgis-psc

This list is used to discuss Steering Committee issues related to overall management and direction of Quantum

GIS. You can subscribe to this list at: http://lists.osgeo.org/mailman/listinfo/qgis-psc

You are welcome to subscribe to any of the lists. Please remember to contribute to the list by answering questions and sharing your experiences. Note that the qgis-commit and qgis-trac are designed for notification only and not meant for user postings.

19.2 IRC

We also maintain a presence on IRC - visit us by joining the #qgis channel on irc.freenode.net. Please wait around for a response to your question as many folks on the channel are doing other things and it may take a while for them to notice your question. Commercial support for QGIS is also available. Check the website http://qgis.org/en/commercial-support.html

for more information.

If you missed a discussion on IRC, not a problem! We log all discussion so you can easily catch up. Just go to http://logs.qgis.org

and read the IRC-logs.

19.3 BugTracker

While the qgis-users mailing list is useful for general ‘how do I do XYZ in QGIS’ type questions, you may wish to notify us about bugs in QGIS. You can submit bug reports using the QGIS bug tracker at http://hub.qgis.org/projects/quantum-gis/issues . When creating a new ticket for a bug, please provide an email address where we can request additional information.

Please bear in mind that your bug may not always enjoy the priority you might hope for (depending on its severity).

Some bugs may require significant developer effort to remedy and the manpower is not always available for this.

214 Chapter 19. Help and Support

QGIS User Guide, Release 1.8.0

Feature requests can be submitted as well using the same ticket system as for bugs. Please make sure to select the type Feature.

If you have found a bug and fixed it yourself you can submit this patch also. Again, the lovely redmine ticketsystem at http://hub.qgis.org/projects/quantum-gis/issues has this type as well. Check Patch supplied checkbox and attach your patch before submitting bug. Someone of the developers will review it and apply it to QGIS. Please don’t be alarmed if your patch is not applied straight away — developers may be tied up with other committments.

19.4 Blog

The QGIS-community also runs a weblog at http://www.qgis.org/planet which has some interesting articles for users and developers as well provided by other blogs in the community. You are invited to contribute your own

QGIS blog!

19.5 Plugins

The website http://plugins.qgis.org

provides the official QGIS plugins web portal. Here you find a list of all stable and experimental QGIS plugins available via the ‘Official QGIS Plugin Repository’.

19.6 Wiki

Lastly, we maintain a WIKI web site at http://hub.qgis.org/projects/quantum-gis/wiki where you can find a variety of useful information relating to QGIS development, release plans, links to download sites, message translationhints and so on. Check it out, there are some goodies inside!

19.4. Blog 215

QGIS User Guide, Release 1.8.0

216 Chapter 19. Help and Support

CHAPTER

20

Appendix

20.1 GNU General Public License

Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307,

USA

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software–to make sure the software is free for all its users. This General Public License applies to most of the Free Software

Foundation’s software and to any other program whose authors commit to using it. (Some other Free Software

Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author’s protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors’ reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone’s free use or not licensed at all.

217

QGIS User Guide, Release 1.8.0

The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS

FOR COPYING, DISTRIBUTION AND MODIFICATION

0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The “Program”, below, refers to any such program or work, and a “work based on the Program” means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term “modification”.) Each licensee is addressed as “you”.

Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the

Program). Whether that is true depends on what the Program does.

1. You may copy and distribute verbatim copies of the Program’s source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the

Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

(a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

(b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

(c) If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works.

But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

(a) Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

218 Chapter 20. Appendix

QGIS User Guide, Release 1.8.0

(b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

(c) Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this

License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients’ exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License.

If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this

License.

8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only

20.1. GNU General Public License 219

QGIS User Guide, Release 1.8.0

in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies a version number of this

License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free

Software Foundation.

10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software

Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

NO WARRANTY

11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR

THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTH-

ERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE

THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IM-

PLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABIL-

ITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND

PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFEC-

TIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL

ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDIS-

TRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, IN-

CLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING

OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO

LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU

OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PRO-

GRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBIL-

ITY OF SUCH DAMAGES.

Quantum GIS Qt exception for GPL

In addition, as a special exception, the QGIS Development Team gives permission to link the code of this program with the Qt library, including but not limited to the following versions (both free and commercial): Qt/Non-commerical Windows, Qt/Windows, Qt/X11, Qt/Mac, and Qt/Embedded

(or with modified versions of Qt that use the same license as Qt), and distribute linked combinations including the two. You must obey the GNU General Public License in all respects for all of the code used other than Qt. If you modify this file, you may extend this exception to your version of the file, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

20.2 GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc

< http://fsf.org/ >

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

220 Chapter 20. Appendix

QGIS User Guide, Release 1.8.0

Preamble

The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does.

But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The Document, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant

Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent.

An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called Opaque.

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format,

LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML,

PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machinegenerated HTML, PostScript or PDF produced by some word processors for output purposes only.

The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

20.2. GNU Free Documentation License 221

QGIS User Guide, Release 1.8.0

The “publisher” means any person or entity that distributes copies of the Document to the public.

A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains

XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.)

To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled

XYZ” according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the

Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute.

However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using publicstandard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

4. Preserve all the copyright notices of the Document.

222 Chapter 20. Appendix

QGIS User Guide, Release 1.8.0

5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

6. Include, immediately after the copyright notices, a license notice giving the public permission to use the

Modified Version under the terms of this License, in the form shown in the Addendum below.

7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the

Document’s license notice.

8. Include an unaltered copy of this License.

9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled

“History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the

Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.

14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant

Section.

15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice.

These titles must be distinct from any other section titles.

You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified

Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover

Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

20.2. GNU Free Documentation License 223

QGIS User Guide, Release 1.8.0

In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections

Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit.

When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form.

Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License.

Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated

(a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this

License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/ .

224 Chapter 20. Appendix

QGIS User Guide, Release 1.8.0

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the

Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons

Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the

MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

Copyright © YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no

Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation

License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with ... Texts.” line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

20.2. GNU Free Documentation License 225

QGIS User Guide, Release 1.8.0

226 Chapter 20. Appendix

CHAPTER

21

Literature and Web References

GDAL-SOFTWARE-SUITE. Geospatial data abstraction library. htt://www.gdal.org, 2012.

GRASS-PROJECT. Geographic ressource analysis support system.

http://grass.osgeo.org

, 2012.

MITCHELL, T. Web mapping illustrated, 2005.

NETELER, M., AND MITASOVA, H. Open source gis: A grass gis approach, 2008.

OGR-SOFTWARE-SUITE. Geospatial data abstraction library.

http://www.gdal.org/ogr , 2012.

OPEN-GEOSPATIAL-CONSORTIUM.

Web map service (1.1.1) implementation specification.

http://portal.opengeospatial.org

, 2002.

OPEN-GEOSPATIAL-CONSORTIUM.

Web map service (1.3.0) implementation specification.

http://portal.opengeospatial.org

, 2004.

POSTGIS-PROJECT. Spatial support for postgresql.

http://postgis.refractions.net/ , 2012.

227

QGIS User Guide, Release 1.8.0

228 Chapter 21. Literature and Web References

Index

%%,

77

Actions,

77

Analysis tools,

187

annotation,

38

apache,

114

apache2,

114

Arc/Info_ASCII_Grid,

99

Arc/Info_Binary_Grid,

99

ArcInfo_Binary_Coverage,

57

attribute table,

91

Attribute_Actions,

77

Attribute_Table_Selection,

92

Avoid_Intersections_Of_Polygons,

84

bookmarks,

39

Browse_Maps,

52

Calculator_Field,

95

CAT,

107

Categorized_Renderer,

65

Centroid_fill,

64

CGI,

113

Chain,

72

change the symbology,

70

Colliding_Labels,

72

Color_interpolation,

102

Color_Ramp,

66

Color_ramps,

64

ColorBrewer,

66

Colormap,

102

command line options,

17

Common_Gateway_Interface,

113

Compose_Maps,

151

Composer_Manager,

165

Composer_Template,

153

Connection_Manager,

58

Context help,

33

Contrast_enhancement,

102

Coordinate_Reference_System,

49

,

110

crashes,

167

Create_Maps,

151

Create_New_Layers,

90

crossing the 180 degrees longitude line,

61

CRS,

49

,

110

CSV,

86

Custom_Color_Ramp,

66

Custom_CRS,

52

data providers,

170

DB_Manager,

62

Debian_Squeeze,

114

default_CRS,

49

define an action,

77

Derived_Fields,

95

Digitizing,

84

Discrete,

102

Displacement_plugin,

67

documentation,

5

editing,

82

EPSG,

49

Equal_Interval,

66

Erdas Imagine,

99

ESRI,

55

European_Petroleom_Search_Group,

49

example actions,

77

Export_as_image,

165

Export_as_PDF,

165

Export_as_SVG,

165

FALP,

72

FastCGI,

113

Field_Calculator,

95

Field_Calculator_Functions,

96

Fill_Color,

70

Fill_Style,

70

Font_Marker,

64

Freak_out,

101

FWTools,

200

GDAL,

99

Georeferencer tools,

193

GeoTIFF,

99

GeoTiff,

99

GiST (Generalized Search Tree) index,

61

229

QGIS User Guide, Release 1.8.0

GML,

107

Gradient_Color_Ramp,

66

Graduated_Renderer,

66

GRASS,

122

, see Creating new vectors;editing;creating

a new layer attribute linkage,

128

attribute storage,

128

category settings,

129

digitizing,

127

digitizing tools,

128

display results,

132

,

135

loading data,

124

region,

131

region display,

131

region editing,

131

snapping tolerance,

130

Start Plugin,

123

symbology settings,

130

table editing,

130

toolbox,

135

topology,

127

vector data model,

127

GRASS toolbox,

131

Browser,

138

customize,

138

Grayscale,

101

Grid

Map_Grid,

156

Histogram,

IGNF,

49

103

Import_Maps,

InteProxy,

112

52

Institut_Geographique_National_de_France,

49

join a loaded attribute table to a loaded vector layer, join layer,

80

80

Map_Navigation,

83

Map_Template,

153

MapInfo,

57

Mapserver_Export_Plugin,

197

Marker_line,

64

measure,

35

angles,

35

areas,

35

line length,

35

menus,

22

merge attributes of features,

90

Merge_Attributes_of_Selected_Features,

90

Merge_Selected_Features,

90

Metadata,

103

msexport,

198

Multi_Band_Raster,

100

multipolygon,

89

Natural_Breaks_(Jenks),

66

nesting projects,

40

New_Labeling,

71

New_Shapefile_Layer,

90

New_Spatialite_Layer,

91

New_Symbology,

63

Node_Tool,

85

Nodes,

86

Non_Spatial_Attribute_Tables,

94

OGC,

107

OGR,

55

OGR Simple Feature Library,

55

ogr2ogr,

60

Old_Symbology,

69

Old_Symbology_Renderers,

70

Open_Geospatial_Consortium,

107

Outline_Options,

70

output save as image,

19

Keyboard shortcuts,

Manage_Symbols,

Map overview,

Map_Legend,

41

158

33

Label_Engine_Settings,

Labeling_Engine,

Labeling_New,

Labeling_Old, layer visibility, layout toolbars,

Layout_Maps, legend, license

27

GPL,

217

70

70

27

27

151

70

Line_decoration,

64

load a shapefile, loading_raster,

55

99

Manage_Color_Ramps,

70

72

70

Pan,

83

pan arrow keys,

30

pgsql2shp,

60

Picture_database,

157

plugins,

167

installing,

169

manager,

167

Python Plugin Installer,

169

types,

167

upgrading,

169

Point_Displacement_Renderer,

67

Popmusic_Chain,

72

Popmusic_Tabu,

72

Popmusic_Tabu_Chain,

72

PostGIS,

58

PostGIS spatial index,

61

PostgreSQL,

58

Pretty_Breaks,

66

print composer quick print,

19

print_composer tools,

153

230 Index

Printing

Export_Map,

165

Proj.4,

52

Proj4,

51

Proj4_text,

51

Projections,

49

Proxy,

108

proxy-server,

108

Pseudocolor,

101

Publish_to_Web_plugin,

114

Pyramids,

103

QGIS_mapserver,

112

QGIS_Server,

113

QSpatiaLite,

62

Quantile,

66

Query_Builder,

94

Raster,

99

Raster_Calculator,

104

Raster_statistics,

103

Renderer_Categorized,

65

Renderer_Graduated,

66

Renderer_Point_Displacement,

67

Renderer_Single_Symbol,

65

Renderers,

64

Renderers_Old_Symbology,

70

Rendering,

34

Rendering halting,

34

rendering quality,

35

Rendering scale dependent,

34

rendering update during drawing,

35

Rendering_Rule-based,

67

Research tools,

187

Revert_Layout_Actions,

162

ring polygons,

89

Rotate_Point_symbols,

90

Rotated_North_Arrow,

157

Rule-based_Rendering,

67

Scale,

34

scale calculate,

30

Scalebar

Map_Scalebar,

161

Search_Radius,

83

Secured_OGC_Authentication,

112

Select_using_Query,

95

SFS,

107

Shapefile,

55

Shapefile_to_Postgis_Import_Tool,

210

Shared_Polygon_Boundaries,

84

shp2img,

200

shp2pgsql,

60

Simple_fill,

64

Simple_line,

64

Simple_Marker,

64

Single_Band_Raster,

100

Single_Symbol_Renderer,

65

SLD,

113

Index

QGIS User Guide, Release 1.8.0

SLD/SE,

113

Smart_Labeling,

71

Snapping,

82

Snapping_Tolerance,

82

spatial bookmarks see bookmarks,

39

Spatialite,

62

Spatialite_Manager,

62

SPIT,

210

Split_Features,

89

SQLite,

62

SRS,

110

ST_Shift_Longitude,

61

Style_Manager,

70

SVG_fill,

64

SVG_Marker,

64

Symbol_Properties,

68

Symbology,

100

Symbology_New,

63

Symbology_Old,

69

Three_Band_Color_Raster,

100

Tiger_Format,

57

Toggle Editing,

84

toolbar,

27

Topological_Editing,

84

Transparency,

102

Transparency_Vector,

70

UK_National_Transfer_Format,

57

US_Census_Bureau,

57

Vector_Transparency,

70

Vertex,

86

Vertices,

86

WCS,

107

WFS,

107

,

112

WFS-T,

112

WFS_Transactional,

112

WKT,

49

,

86

WMS,

107

WMS-C,

110

WMS_1.3.0,

112

WMS_client,

107

WMS_identify,

111

WMS_layer_transparency,

110

WMS_metadata,

111

WMS_properties,

111

WMS_tiles,

110

Work_with_Attribute_Table,

91

zoom mouse wheel,

29

Zoom_In Zoom_Out,

83

231

Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement

Table of contents