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

[JamesH]

When altering the query to be:
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?

Kind Regards,
James

-----
GIS Undergraduate
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