How to do it...

To use ST_MapAlgebra() on more than two bands, we must use the callback function variant. This means we need to create a callback function. Callback functions can be written in any PostgreSQL PL language, such as PL/pgSQL or PL/R. Our callback functions are all written in PL/pgSQL, as this language is always included with a base PostgreSQL installation.

Our callback function uses the following equation to compute the three-band EVI:

The following code implements the MODIS EVI function in SQL:

CREATE OR REPLACE FUNCTION chp05.modis_evi(value double precision[][][], "position" int[][], VARIADIC userargs text[]) RETURNS double ...

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