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 ...