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

Creating a layer-definition file

Layer styling is one of the most complex aspects of the QGIS Python API. Once you've developed the style for a layer, it is often useful to save the styling to the QGIS Markup Language (QML) XML format.

Getting ready

You will need to download the following zipped directory, named saveqml, and decompress it to your qgis_data/rasters directory:

How to do it...

We will create a color ramp for a digital elevation model (DEM) and then make it semi-transparent for overlay on a hillshaded tiff of the DEM. We'll save the style we create to a QML file:

  1. First, we'll need the Python Qt libraries:

            from PyQt4.QtCore import * 
            from PyQt4.QtGui import * 
  2. Next, we'll load up our two raster layers:

            hs = QgsRasterLayer("/qgis_data/saveqml/hillshade.tif",
            dem = QgsRasterLayer("/qgis_data/saveqml/dem.asc", "DEM") 
  3. Then...