On 23/11/18 14:28, Markus Metz wrote:
On Tue, Nov 20, 2018 at 9:16 AM Stefan Blumentrath
<[email protected] <mailto:[email protected]>> wrote:
>
> Dear all,
>
>
>
> In an r.mapcalc expression, I would like to trace values along a
direction map for 1 to n steps (e.g. looking 4 steps ahead along a path
or stream or along a given direction (degrees or 45degrees).
>
>
>
> I tried using the neighborhood modifier within an eval function in
r.mapcalc. Unfortunately, using this command:
>
> r.mapcalc --o << EOF
>
> eval(elev_200 = elevation[1,1] - 200, elev_5 = 5 * elev_200[1,1],
elev_p = pow(elev_5, 2))
>
> gradient_1 = (0.5 * elev_200) + 0.8 * elev_p
>
> EOF
elev_200 is an internal variable of the elev function with a single
value, and not a (temporary) map. Therefore elev_200[1,1] can't work.
You would need several calls to r.mapcalc, with the first one creating
the map elev_200, e.g.
r.mapcalc "elev_200 = elevation[1,1] - 200"
r.mapcalc "elev_p = pow(5 * elev_200[1,1], 2)"
r.mapcalc "gradient_1 = (0.5 * elev_200) + 0.8 * elev_p"
Cf the man page (Notes section):
"Any maps generated by a r.mapcalc command only exist after the entire
command has completed. All maps are generated concurrently, row-by-row
(i.e. there is an implicit "for row in rows {...}" around the entire
expression). Thus the #, @, and [ ] operators cannot be used on a map
generated within same r.mapcalc command run. "
Moritz
_______________________________________________
grass-user mailing list
[email protected]
https://lists.osgeo.org/mailman/listinfo/grass-user
