> 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"
Then you must have some 0s in band 3? What is the result of SELECT ST_ValueCount(rast, 3, 0.0) FROM nclraster1 What do you want/expect as result when band 3 = 0? _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users