[GRASS5] r.mapcalc and NULL question

Markus Neteler neteler at geog.uni-hannover.de
Mon Jan 15 13:23:31 EST 2001


(cc to the list for some more explanations)

On Mon, Jan 15, 2001 at 09:35:13AM -0800, Rich Shepard wrote:
> On Mon, 15 Jan 2001, Markus Neteler wrote:
> > Assume you have a streams map (streams contain values, other cells=NULL).
> >
> > Now I want to add some values *everywhere* using r.mapcalc, but it is only
> > added in those cells not containing a NULL value.
> >
> > Any ideas how to overcome this problem?
> Markus,
>   Can you replace the NULL with a finite value such as -99 (for example)? If
> so, then you can set up a case to replace -99 with whatever value you want.
>   Alternatively, what I used to do in Idrisi is to build a new map with all
> cells containing zeros. Then I add my streams map to the zero map and now
> all non-stream cells have the value of zero. That removes the nulls and
> leaves the original maps intact.
> HTH,


thanks for your quick response. Of course I could do that, but I
am searching for a general solution as I am script programming (with
So the users don't want convert their maps qithin every loop... :-)
Generally r.null would do the job, but that's too time consuming for my

The NULLs I would like to keep for overlayed displaying (this wouldn't
work with ZEROs).

I am writing a script for my students to stepwise flood landscapes
with graphical output on the monitor for each step.

Hope there is a built-in r.mapcalc solution which I have overseen...


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