[postgis-users] ST_MapAlgebraExpr nodata value

[Pierre Racine]

> I understand that the nodataval in ST_MapAlgebraExpr burns the pixels which
> have nodata from the input raster with a new value but my question is:
> 
> The expected behaviour is that ST_MapAlgebraExpr keeps the nodataval from
> the input raster even though I change the nodataval parameter?

Right. It will change all the nodata values to another values but it will not set this nodata value as the nodata value of the raster. You have to explicitly do it by doing:

ST_SetBandNodataValue(ST_MapAlgebraExpr(..., 255), 255)

> Im using ST_SetNodataValue after ST_MapAlgebraExp but I dont know if this is
> the right procedure.

SetBandNodataValue. Yes it is the right procedure.

Pierre