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

Obtaining the width and height of a raster

All raster layers have a width and height in pixels. Because remote sensing data can be considered an image as well as an array or matrix, you will often see different terms used, including columns and rows or pixels and lines. These different terms surface many times within the QGIS API.

Getting ready

We will use the SatImage raster again, which is available at

Place this raster in your /qgis_data/rasters directory.

How to do it...

  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/satimage.tif",
                                       "Satellite Image") 
  4. Check the name of the SatImage after unzipping.

  5. Obtain the layer's width, which should be 2592:

  6. Now, get the raster's height, which will return 2693: