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

Georeferencing a raster from control points

Sometimes, a raster that represents features on the earth is just an image with no georeferencing information. That is certainly the case with historical scanned maps. However, you can use a referenced data set of the same area to create tie points, or ground control points, and then use an algorithm to warp the image to fit the model of the earth. It is common for data collection systems to just store the ground control points (GCP) along with the raster to keep the image in as raw a format as possible. Each change to an image holds the possibility of losing data, so georeferencing an image on demand is often the best approach.

In this recipe, we'll georeference a historical survey map of the Louisiana and Mississippi Gulf Coast from 1853. The control points were manually created with the QGIS Georeferencer plugin and saved to a standardized control point file.

Getting ready

Download the following ZIP file, unzip the contents, and put the georef...