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PostGIS Cookbook

PostGIS Cookbook

By : Paolo Corti, Bborie Park
4.6 (12)
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PostGIS Cookbook

PostGIS Cookbook

4.6 (12)
By: Paolo Corti, Bborie Park

Overview of this book

An easy-to-use guide, full of hands-on recipes for manipulating spatial data in a PostGIS database. Each topic is explained and placed in context, and for the more inquisitive, there are more details of the concepts used. If you are a web developer or a software architect, especially in location-based companies, and want to expand the range of techniques you are using with PostGIS, then this book is for you. You should have some prior experience with PostgreSQL database and spatial concepts.
Table of Contents (13 chapters)
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12
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 Normalized Difference Vegetation Index (NDVI) and 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 ST_MapAlgebra...

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PostGIS Cookbook
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