[GRASS-user] Error while applying r.mapcalc to an output from GROW

[Markus Metz]

António Rocha:
>
> I applied this expression:
> if( grow02 at National ==null(),1,0)
>
> but from this output I obtain only NULLS.

NULL-values in any arithmetic or logical operation result in NULL [1].
The null() function represents the NULL value, thus a NULL value is
always present in the logical operation "grow02 at National == null()"
and the result will always be NULL.

try
if(isnull(grow02 at National),1,0)

Markus M

[1] http://grass.osgeo.org/grass64/manuals/html64_user/r.mapcalc.html