PostGIS Cookbook - Second Edition

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 ...