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

Getting the output file names from processing algorithms

Sometimes, you need to know the variable name a QGIS processing algorithm uses to hold the location of temporary output files. Of course you can set the output file name for most algorithms, but if you are chaining several processes together, you can take advantage of the automatic cleanup for temporary files provided by QGIS when it exits if you use the temporary file. While the processing framework is mostly very consistent, the names of output variables vary. In this recipe, we'll use PyQGIS to programmatically get the output variable name.

Getting ready

Open the QGIS Python Console by going to the Plugins menu and selecting Python Console.

How to do it...

We'll import the processing module and create a function to access algorithm output names. Then, we'll test out a couple of algorithms to see if the function works as expected:

  1. First, we import the processing module:

            import processing 
  2. Next, we'll create a function that...