[postgis-users] NDVI Calculation from two bands within one Raster

[JamesH]

Attempted 
SELECT ST_MapAlgebraExpr(a.rast, 4, b.rast, 3, '(rast1 - rast2) /(rast1 +
rast2)::float') FROM nclraster1 a, nclraster1 b;

Returned "Neither raster provided has a NODATA value for the specified band
indices.  NODATA value set to minimum possible for 8BUI" 

Updated NoDataValues for bands 3 and 4 to 255 (were previously blank) and
when re-ran, returns:
"ERROR:  division by zero
CONTEXT:  SQL statement "SELECT (($1 - $2) /($1 + $2)::FLOAT)::double
precision"

Regards,
James

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