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 warning dialog

Sometimes, you need to notify a user when an issue is detected,which might lead to problems if the user continues. This situation calls for a warning dialog, which we will demonstrate in this recipe.

Getting ready

Open the QGIS Python console by going to the Plugins menu and selecting Python Console.

How to do it...

In this recipe, we will create a dialog, set the warning message and a warning icon, and display the dialog, as follows:

  1. First, we import the GUI library:

            from PyQt4.QtGui import * 
  2. Next, we initialize the warning dialog:

            msg = QMessageBox() 
  3. Then, we set the warning message:

            msg.setText("This is a warning...") 
  4. Now, add a warning icon to the dialog that has an enumeration index of 2:

  5. Finally, we call the show method to display the dialog:


How it works...

Message dialogs should be used sparingly because they interrupt the user experience and can easily...