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

Calculating the bearing of a line

Sometimes, you need to know the compass bearing of a line to create specialized symbology or to use as input in a spatial calculation. Even though its name only mentions distance and area, the versatile QgsDistanceArea object includes this function as well. In this recipe, we'll calculate the bearing of the end points of a line. However, this recipe will work with any two points.

Getting ready

We'll use the line shapefile used in Measuring the distance between two points recipe. You can download the shapefile as a .zip file from

Unzip the shapefile into a directory named qgis_data/shapes within your root or home directory.

How to do it...

The steps to be performed are as simple as getting the two points we need and running them through the bearing function, converting from radians to degrees, and then converting to a positive compass bearing:

  1. First, import the Python math module:

            import math...