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

Swapping raster bands

Computer displays render images in the visible spectrum of red, green, and blue light (RGB). However, raster images may contain bands outside the visible spectrum. Such rasters make poor visualizations, so you will often want to recombine the bands to change the RGB values.

Getting ready

For this recipe, we will use a false-color image, which you can download from

Unzip this .tif file and place it in your /qgis_data/rasters directory.

How to do it...

We will load this raster and swap the order of the first and second bands. Then, we will add it to the map. To do this, we need to perform the following steps:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. In the Python console, load the layer and ensure that it is valid:

            rasterLyr = QgsRasterLayer("/qgis_data/rasters/FalseColor.tif",
                                       "Band Swap") 
  4. Now, we must access the layer...