[GRASS-user] create a mask to exclude plate area

[Vincent Bain]

Bonsoir Étienne,
Je crois comprendre que ton problème se rapporte à l'identification de
zones sur des critères géomorphologiques. Peut-être pourrais-tu partir
sur un traitement avec r.mapcalc ou des outils comme r.reclass pour
"lisser" ta topo ou du moins discrétiser ta carte des pentes, afin
d'identifier des zones homogènes. Puis transformer ces zones en
polygones (r.to.vect) et faire des ratios entre périmètre et
superficie...

I guess your problem is related to a geomorphological identification
process. I suggest you to try and make a kind of slopes reclassification
in order to discretize and aggregate homogenous slope areas, then turn
these areas into a polygon vector map. After that you can compute ratios
between perimeters, areas, X/Y extension, and so on...

Amuse-toi bien

Enjoy it !

Vincent.

Le lundi 19 juillet 2010 à 21:39 +0200, Etienne DELAY (deust 2010) a
écrit :
> 
> > How? Which command(s) exactly? Using r.mapcalc? There is also r.mask [1]
> > Also, tres-important, did you define the "region" of your interest using 
> > "g.region"[2]?
> > 
> >> Now I have to exclude the plate areas (eg trays Spanish) but I can not
> >> see any use for this test.
> >> I thought r.mapcalc place an order with a request to both  area and on
> >> slope.
> > 
> > That is right. r.mapcalc (or most of the raster modules) will ignore the 
> > MASKed-out cells by the raster map named MASK.
> > 
> > Radom example grepped from the grass-user list:
> > 
> > --%<--- Re: How To use a raster MASK correctly? --17/10/2009 20:09 --%<---
> > Figured it out.  Used the following r.mapcalc expression:
> > r.mapcalc "new_hillshade=if(europe_dem < 100, 180, europe_hillshade)"
> > -->%---
> > 
> > Cordialement, Nikos
> > 
> > ---
> > [1] <http://grass.osgeo.org/grass65/manuals/html65_user/r.mask.html>
> > [2] <http://grass.osgeo.org/grass65/manuals/html65_user/g.region.html>
> > 
> 
> Hello Nikos
> sorry for the French, I need to think in my language :-)
> So I have no problem using r.mapcalc for 1st and 2nd criteria, and to
> assemble the two masks. The region is also parameterize, but now, it has
> become a 3rd test, I must arrive in isolating the flat portions of the
> mountain in Spain, if not that is reflected in part authorize my mask,
> but not know  structural problems in they vineyards ...
> 
> I want to use something like:
> 
> r.mapcalc "Maskplate= if((Area>100000ha && slope<=10%), 1, null())
> 
> mais l'utilisation de aire ne me satisfait pas vraiment.... parce quelle
> peut changer en longueur et largeur...
> 
> but the use of area does not really satisfy me .... because what can
> change in length and width ...
> 
> Is there a solution would be to make visual grade, to define the
> geomorphological unite?
> 
> thank you very much ;-)
>