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 ...