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

Displaying a progress bar

A progress bar is a dynamic dialog that displays the percentage of completion bar for a running process that the user must wait for before continuing. A progress bar is more advanced than a simple dialog, because it needs to be updated continuously. In this recipe, we'll create a simple progress dialog based on a timer.

Getting ready

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

How to do it...

The steps for this recipe include creating a custom class based on the QProgressBar, initializing the dialog and setting its size and title, creating a timer, connecting the progress bar to the timer, starting the time, and displaying the progress. To do this, we need to perform the following steps:

  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...