[GRASS-user] Raster processing

[Markus Metz]

On Mon, Jan 28, 2013 at 7:33 PM, Surendran Neelakantan
<surendrankn at gmail.com> wrote:
> Hi
>
> I am a new user of GRASS
>
> I have been working on a python Geo-processing  tool in ESRI ARCGIS desktop.
> This is basically a DEM data processing which involves "Extract by Mask"
> "Flow Direction", "Flow Accumulation","Slope" ,"Watershed" ,"Zonal
> statistics "
>
> I would like to   rewrite the tool to make it work with GRASS  so that
> later everyone can use this.  I have gone through the documentation  but I
> really not able to figure out the equivalent commands in Grass.

First of all, set the region to the DEM with

g.region -p rast=DEM

Create a MASK with r.mask or r.mapcalc or r.to.vect

Zoom to the masked area

g.region -p zoom=DEM

Note that there is no need to clip or extract a subregion of the DEM
if the region is set properly

Flow direction, flow accumulation, watershed can be calculated with r.watershed

Slope can be calculated with r.slope.aspect

Zonal statistics can be calculated with r.univar or r.statistics or
r.statistics2 or r.statistics3, depending on the desired output.

HTH,

Markus M