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

Pushing widgets to the message bar

Just like the status bar, the message bar can contain any type of widget, not just text. Although it is primarily intended for simple text messages, sometimes you may want to add items such as a progress bar to track processing. In this recipe, we'll display a progress bar in the message bar.

Getting ready

Open the QGIS Python console by selecting the Plugins menu and then clicking on Python Console.

How to do it...

First we'll build out our progress bar as we did earlier in this chapter. It will simply run on a timer. Then we'll add it to the message bar and we'll tell the message bar to stay visible for 10 seconds instead of the usual five seconds, so we can see the progress bar finish:

  1. First, we must import both the GUI and QGIS core libraries:

            from PyQt4.QtGui import * 
            from PyQt4.QtCore import * 
  2. Next, we create a custom class for our progress bar, including a method to increase the value of the progress bar:

            class Bar(QProgressBar...