On 14/04/11 13:54, Martin Album Ytre-Eide wrote:
Hello.
I am trying to add some raster maps. I thought I could do this in
r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where
the maps overlap and ignoring areas where only on of the maps have
values.
This is due to the way r.mapcalc handles NULL values. See the man page,
section NULL support for an explanation.
I would like to do something similar to "v.overlay
operator=or".
Anyone who knows how to do this?
It depends on what you want the new map to contain as values. If you
want to add the value of old_1 to old_2 in places where they overlap,
one way would be to transform your null values to 0 using r.null null=
and then applying your formula.
If you just want a (any) value where one of the maps is non-null, then
you can use if. Something like this (untested):
new_map = if(!isnull(old_1) || !isnull(old_2), 1, null())
which should give you 1 where any of the two contains a value and a NULL
value elsewhere.
Moritz
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