Book Image

PostGIS Cookbook - Second Edition

By : Pedro Wightman, Bborie Park, Stephen Vincent Mather, Thomas Kraft, Mayra Zurbarán
Book Image

PostGIS Cookbook - Second Edition

By: Pedro Wightman, Bborie Park, Stephen Vincent Mather, Thomas Kraft, Mayra Zurbarán

Overview of this book

PostGIS is a spatial database that integrates the advanced storage and analysis of vector and raster data, and is remarkably flexible and powerful. PostGIS provides support for geographic objects to the PostgreSQL object-relational database and is currently the most popular open source spatial databases. If you want to explore the complete range of PostGIS techniques and expose related extensions, then this book is for you. This book is a comprehensive guide to PostGIS tools and concepts which are required to manage, manipulate, and analyze spatial data in PostGIS. It covers key spatial data manipulation tasks, explaining not only how each task is performed, but also why. It provides practical guidance allowing you to safely take advantage of the advanced technology in PostGIS in order to simplify your spatial database administration tasks. Furthermore, you will learn to take advantage of basic and advanced vector, raster, and routing approaches along with the concepts of data maintenance, optimization, and performance, and will help you to integrate these into a large ecosystem of desktop and web tools. By the end, you will be armed with all the tools and instructions you need to both manage the spatial database system and make better decisions as your project's requirements evolve.
Table of Contents (18 chapters)
Title Page
Packt Upsell
Contributors
Preface
Index

Performing advanced map-algebra operations


In a prior recipe, we used the expression-based map-algebra function ST_MapAlgebra() to convert the PRISM pixel values to their true values. The expression-based ST_MapAlgebra() method is easy to use, but limited to operating on at most two raster bands. This restricts the ST_MapAlgebra() function's usefulness for processes that require more than two input raster bands, such as the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI).

There is a variant of ST_MapAlgebra() designed to support an unlimited number of input raster bands. Instead of taking an expression, this ST_MapAlgebra() variant requires a callback function. This callback function is run for each set of input pixel values, and returns either a new pixel value, or NULL for the output pixel. Additionally, this variant of ST_MapAlgebra() permits operations on neighborhoods (sets of pixels around a center pixel).

PostGIS comes with a set of ready-to-use...