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<font face="Helvetica, Arial, sans-serif">Hi Marcello,<br>
Thanks for this response! After my post I also figured out exactly
this method for doing it as well, although as you say would be great to
have a one-liner.<br>
I will probably just write a little script that performs all these
steps and takes in the relevant vector, cat, and raster values. <br>
<br>
thanks!<br>
ken<br>
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On 06/17/2010 04:17 PM, Marcello Gorini wrote:
<blockquote cite="mid:1276816672831-5193386.post@n2.nabble.com"
type="cite">
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Kwas wrote:
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<pre wrap="">
Hello,
I have a raster map (dem) and I want to select a region of the raster
corresponding to a polygon that is in a vector map.&nbsp; What is the best
way to do this?&nbsp; It looks like r.in.poly might be along the lines of
what I need but in that case I think I would need to generate the ascii
poly file first but I'm wondering if there is a better way?&nbsp; Seems
like
there should be a single command to do this.
My vector map has 45 polygons with cat values 1..45,&nbsp; so I would like
to get a section from my raster map corresponding to one of the
polygons specified by cat value.
appreciate any help!
thanks,
ken
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<pre wrap="">
Hello Ken,
I am also new to GRASS, but I have been doing what you want quite a lot
these days. There is probably a better way to do that (and I would like to
"hear" it very much, specially if there is a single command to do this), but
for now, I think the code below does the job:
g.region vect=your_vector
v.extract input=your_vector output=selected_polygon type=area
where="cat=desired_cat"
v.to.rast input=selected_polygon output=polygon_rasterized use=val type=area
r.mask input=polygon_rasterized
Now, any processing that you do will be applied only in the region
corresponding to the selected polygon.
If you want to create a raster corresponding to the selected polygon, just
do:
r.mapcalc "new_raster=any_old_raster"
To take out the mask, just type:
r.mask -r
Hope this helps,
Marcello.
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