> SELECT > ST_MapAlgebraExpr(a.rast, 4, b.rast, 3, '(a.rast - b.rast) /(a.rast + > b.rast)::float') > FROM > nclraster1 a, nclraster1 b; > > instead of rast1 - rast2 etc. > > Returns an error of > ERROR: missing FROM-clause entry for table "a" > LINE 1: SELECT ((a.rast - b.rast) /(a.rast + b.rast)::float)::double... > > Can anyone explain this?
In the expression, you don't refer to the pixels of a.rast with "a.rast" but with "rast1". so your query should be: SELECT ST_MapAlgebraExpr(a.rast, 4, b.rast, 3, '(rast1 - rast2) /(rast1 + rast2)::float') FROM nclraster1 a, nclraster1 b; Pierre _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
