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 cell size of a raster layer

The first key element of a geospatial raster is the width and height in pixels. The second key element is the ground distance of each pixel, also called the pixel size. Once you know the cell size and a coordinate somewhere on the image (usually the upper-left corner), you can begin using remote sensing tools on the image. In this recipe, we'll query the cell size of a raster.

Getting ready

Once again, we will use the SatImage raster available at

Place this raster in your /qgis_data/rasters directory.

How to do it...

We will load the raster as a layer and then use the QgsRasterLayer API to get the cell size for the x and y axis. To do this, we need to perform the following steps:

  1. Start QGIS.

  2. From the Plugins menu, select Python Console.

  3. Load the layer and validate it:

            rasterLyr = QgsRasterLayer("/qgis_data/rasters/satimage.tif",
                                       "Satellite Image") ...