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 file input dialog

The best way to get a filename from the user is to have them browse to the file using a dialog. You can have the user type in a filename using the text input dialog, but this method is prone to errors. In this recipe, we'll create a file dialog and print the chosen filename to the console.

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 and configure the dialog, browse to a file, and print the chosen filename, as follows:

  1. First, we import the GUI library:

            from PyQt4.QtGui import * 
  2. Next, we initialize the file dialog and specify its window title:

            qfd = QFileDialog() 
            title = 'Open File' 
  3. Now, we specify a path to the directory we want the file dialog to start in:

            path = "/Users/joellawhead/qgis_data" 
  4. Then, we configure the file dialog with the preceding parameters and assign the output to a variable: