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

[JamesH]

Sorry to keep reviving this thread, espcially with a basic question.

I am using:
SELECT ST_MapAlgebraExpr(a.rast, 4, b.rast, 3, '([rast1] - [rast2])
/([rast1] + [rast2])::float') 
WHEN (rast1 + rast2 = 0) THEN = 999 ELSE ([rast1] - [rast2]) /([rast1] +
[rast2])::float END'
FROM ndvi a, ndvi b;

Where the WHEN statement is being used to prevent the error division by
zero.
However this returns: syntax error at or near "WHEN"

Can anyone advise on where I'm structuring this query wrongly.

Regards,
James

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GIS Undergraduate
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