Building Mapping Applications with QGIS

Erik Westra

• Publisher: Packt Publishing
• Year: 2014
• eBook ISBN: 9781783984664
• Edition: 1
• Topic: Computer Science
• Subtopic: Desktop Applications
• Index: Computer Science

QGIS is one of the premiere open source Geographical Information Systems. While developing Python geospatial applications can be challenging, QGIS simplifies the process by combining the necessary geoprocessing libraries with a sophisticated user interface, all of which can be directly controlled using Python code.

Starting with an introduction to QGIS and how to use the built-in QGIS Python Console, we will teach you how to write Python code that makes use of the geospatial capabilities of QGIS. Building on this, you will ultimately learn how to create your own sophisticated standalone mapping applications built on top of QGIS. You will learn how to use the Python Console as a window into the QGIS programming environment, and then use that environment to create your own Python scripts and plugins to customize QGIS. As your knowledge of the PyQGIS library grows, you will use it to perform a variety of real-world geospatial programming tasks, culminating in the creation of your own complex standalone applications to load, analyze, and display geospatial data.

Building Mapping Applications with QGIS

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Table of Contents

Building Mapping Applications with QGIS

Credits

About the Author

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers, and more

Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Errata

Piracy

Questions

1. Getting Started with QGIS

About QGIS

Installing and running QGIS

Understanding QGIS concepts

Linking QGIS and Python

Exploring the Python Console

Examining a Python plugin

Writing an external application

Summary

2. The QGIS Python Console

Using the console

Working with geospatial data in the console

Scripting the QGIS user interface

The status bar

The message bar

Progress indicators

QGIS logging

Custom dialogs and windows

Summary

3. Learning the QGIS Python API

About the QGIS Python APIs

Deciphering the C++ documentation

Organizing the QGIS Python libraries

The qgis.core package

Maps and map layers

Coordinate reference systems

Vector layers

Displaying vector data

Accessing vector data

Spatial indexes

Raster layers

How raster data is displayed

Accessing raster data

Other useful qgis.core classes

The qgis.gui package

The QgisInterface class

The QgsMapCanvas class

The QgsMapCanvasItem class

The QgsMapTool class

Other useful qgis.gui classes

Using the PyQGIS library

Analyzing raster data

Manipulating vector data and saving it to a shapefile

Using different symbols for different features within a map

Calculating the distance between two user-defined points

Summary

4. Creating QGIS Plugins

Getting ready

Understanding the QGIS plugin architecture

Creating a simple plugin

The plugin development process

Using the Plugin Builder

Automating the build process

Plugin help files

Unit testing

Distributing your plugin

Writing a useful plugin

Possibilities and limitations of plugins

Summary

5. Using QGIS in an External Application

Introducing Lex

Getting the data

Designing the application

Creating the application's framework

Adding the user interface

Connecting the actions

Creating the map canvas

Labeling the points

Filtering the landmarks

Implementing the zoom tool

Implementing the pan tool

Implementing the explore mode

Further improvements and enhancements

Summary

6. Mastering the QGIS Python API

Working with symbol layers

Combining symbol layers

Implementing symbol layers in Python

Implementing renderers in Python

Working with custom map layers

Creating custom map canvas items

Using memory-based layers

Summary

7. Selecting and Editing Features in a PyQGIS Application

Working with selections

Using the layer editing mode

Adding Points

Editing Points

Deleting Points and other features

Adding lines and polygons

Editing lines and polygons

Summary

8. Building a Complete Mapping Application using Python and QGIS

Introducing ForestTrails

Designing the ForestTrails application

Creating the application

Laying out the application

Defining the toolbar icons

The constants.py module

The forestTrails.py module

The mapTools.py module

The ui_mainWindow.py module

Running the application

Obtaining the basemap

Defining the map layers

Defining the map renderers

The Pan Tool

Implementing the track editing mode

Summary

9. Completing the ForestTrails Application

The Add Track map tool

Testing the application

Vertex snapping

The Edit Track map tool

The Delete Track map tool

The Get Info map tool

The Set Start Point and Set End Point actions

The Find Shortest Path action

Adjusting the toolbar actions

Suggested improvements

Summary

Index

Building Mapping Applications with QGIS

Copyright © 2014 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: December 2014

Production reference: 1231214

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham B3 2PB, UK.

ISBN 978-1-78398-466-4

www.packtpub.com

Credits

Author

Erik Westra

Reviewers

David McDermott

Pablo Pardo

Heegu Park

Christopher Wesson

Commissioning Editor

Pramila Balan

Acquisition Editor

Sonali Vernekar

Content Development Editor

Rikshith Shetty

Technical Editor

Shruti Rawool

Copy Editors

Alfida Paiva

Vikrant Phadkay

Project Coordinator

Kinjal Bari

Proofreaders

Cathy Cumberlidge

Ameesha Green

Sonia Sanghera

Indexer

Monica Ajmera Mehta

Production Coordinator

Conidon Miranda

Cover Work

Conidon Miranda

About the Author

Erik Westra has been a professional software developer for over 25 years, and has worked almost exclusively with Python for the past decade. Erik's early interest in graphical user interface design led to the development of one of the most advanced urgent courier dispatch systems used by messenger and courier companies worldwide. In recent years, he has been involved in the design and implementation of systems that match seekers and providers of goods and services across a range of geographical areas. This work has included the creation of real-time geocoders and map-based views of constantly changing data. He is based in New Zealand, and works for companies worldwide.

He is the author of Python Geospatial Development, Packt Publishing.

I would like to thank Ruth, the love of my life, for all her support and encouragement. I would also like to thank my two children, Anneke and Oscar, for reminding me what is important in life.

About the Reviewers

David McDermott (MPhys Geog PGCE (Cantab)) is a proud Yorkshireman who has a keen interest in science fiction and Rugby League, as well as in GIS.

He studied at the University of Hull, where he acquired a 2:1 master's degr...

Table of contents

• Building Mapping Applications with QGIS