Re: [GRASS-user] Re: how to get raster region corresponding to vector polygon region?

Sun, 20 Jun 2010 11:49:22 -0700

Hi Hamish,
I like your r.reclass solution.  Just wondering, you say it is a "virtual" map, and easy to remove.  How is it virtual?  When I use it I get a new map in my raster list that doesn't seem to go away so it seems permanent to me.  Although I don't understand the underlying storage structure so maybe it is still virtual in that sense?

Thanks,
Ken


On 06/17/2010 07:52 PM, Hamish wrote: 
Marcello wrote:
  
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
    

another way (probably there are many),

v.to.rast
then a loop using r.reclass to make a temporary MASK map of each
category, then 
g.region rast=rasterized_vect
g.region zoom=rasterized_vect


r.reclass are tiny virtual maps (ie very quick to create+remove),
g.region zoom= starts at the current region and shrinks inward
until it hits a non-NULL cell. 



Hamish



      
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