Database Reference
In-Depth Information
Our callback function uses the following equation to compute the three-band EVI:
CREATE OR REPLACE FUNCTION
chap5.modis_evi(value double precision[][][],
position int[][], VARIADIC userargs text[])
RETURNS double precision
AS $$
DECLARE
L double precision;
C1 double precision;
C2 double precision;
G double precision;
_value double precision[3];
_n double precision;
_d double precision;
BEGIN
-- userargs provides coefficients
L := userargs[1]::double precision;
C1 := userargs[2]::double precision;
C2 := userargs[3]::double precision;
G := userargs[4]::double precision;
-- rescale values, optional
_value[1] := value[1][1][1] * 0.0001;
_value[2] := value[2][1][1] * 0.0001;
_value[3] := value[3][1][1] * 0.0001;
-- value can't be NULL
IF
_value[1] IS NULL OR
_value[2] IS NULL OR
_value[3] IS NULL
THEN
RETURN NULL;
END IF;
-- compute numerator and denominator
