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 an error dialog

You can issue an error dialog box when you need to end a process due to a serious error. In this recipe, we'll create an example of an error dialog.

Getting ready

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

How to do it...

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

  1. First, we need to import the GUI library:

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

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

            msg.setText("This is an error!") 
  4. Subsequently, we set an icon number for the error icon:

  5. Finally, we execute the error dialog:


How it works...

An important feature of modal windows is that they always stay on top of the application, regardless of whether the user changes the window's focus. This feature ensures that the user...