Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By : Joel Lawhead
Book Image

QGIS Python Programming Cookbook, Second Edition - Second Edition

By: Joel Lawhead

Overview of this book

QGIS is a desktop geographic information system that facilitates data viewing, editing, and analysis. Paired with the most efficient scripting language—Python, we can write effective scripts that extend the core functionality of QGIS. Based on version QGIS 2.18, this book will teach you how to write Python code that works with spatial data to automate geoprocessing tasks in QGIS. It will cover topics such as querying and editing vector data and using raster data. You will also learn to create, edit, and optimize a vector layer for faster queries, reproject a vector layer, reduce the number of vertices in a vector layer without losing critical data, and convert a raster to a vector. Following this, you will work through recipes that will help you compose static maps, create heavily customized maps, and add specialized labels and annotations. As well as this, we’ll also share a few tips and tricks based on different aspects of QGIS.
Table of Contents (16 chapters)
QGIS Python Programming Cookbook - Second Edition
About the Author
About the Reviewer
Customer Feedback

Loading a map from a project

This recipe demonstrates how to load a project from a .qgs XML file. Loading a project will set up the map and project settings for a previously saved project within QGIS.

Getting ready

You will need to complete the previous recipe, Saving a map to a project, so that you have a project named myProject.qgs in your qgis_data directory.

How to do it...

For this recipe, you need to set up a file object, set a resource path, and then read the file object that references the project file. To do this, you need to perform the following steps:

  1. First, we import the core QtCore library for the file object:

            from PyQt4.QtCore import * 
  2. Next, we initiate the file object with the path to the project file:

            f = QFileInfo("/qgis_data/myProject.qgs") 
  3. Now, we access the project object:

            p = QgsProject.instance() 
  4. Then, we set the resource path for QGIS to find data and other files, in case the project was saved with relative paths instead of absolute...