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
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Performing a union on vector shapes


A union turns two overlapping shapes into one. This task can be easily accomplished with the Processing Toolbox. In this recipe, we'll merge the outline of a covered building to the footprint of the main building.

Getting ready

You can download the building files from the following URL and extract them to a directory named /qgis_data/union:

https://github.com/GeospatialPython/Learn/raw/master/union.zip

How to do it...

All we need to do is run the qgis:union algorithm:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. Import the processing module:

            import processing 
    
  4. Now, run the algorithm specifying the two input shapes and the single output file:

            processing.runandload("qgis:union",
                                  "/qgis_data/union/building.shp",
                                  "/qgis_data/union/walkway.shp",
                                  "/qgis_data/union/union.shp") 
    

How it works...

As you can tell from the structure...