[GRASS-user] Re: vector operations based on rasters

[Daniel Victoria]

How about v.rast.stats

It will calculate raster univariate statistics for each vector polygon

http://grass.itc.it/grass62/manuals/html62_user/v.rast.stats

Daniel

On Thu, Sep 25, 2008 at 7:53 PM, Tim Michelsen
<timmichelsen at gmx-topmail.de> wrote:
> Hello,
> thanks for your help. but this is not all that I was looking for.
>>> Basically, I'd like to run v.extract/v.overlay not on a
>>> vector-to-vector basis but on a vector-to-raster basis.
>>
>> g.region rast=dem_name
>> v.in.region dem_box
>>
>> then v.overlay or v.select, depending on if you want to want to clip
>> touching vector areas at the bound or not.
> => With your tip I am just creating a boundary vector with the region
> extends.
>
> But my raster has been created by mapcalc:
>
>
> 1. I created the raster like this:
> (elev => SRTM DEM)
>
> r.mapcalc "myraster=if(elev < 1000,elev, null())
>
> => now I have a huge (by area) raster which contains cell values in floating
> points.
> => The raster now has areas with NULL values because the terrain elevation
> is above 1000 m.
>
> 2. now I have the vector
> landcover: Global Land Cover 2000
>
> Now I would like the polygons from the landcover, which are situated below
> 1000m.
> How can I achieve this?
>
> My idea:
> a) simplify the raster because the raster is too complex for data type
> conversion:
> r.mapcalc "myraster_simple=if(myraster,1, null())
>
> b) convert to vector:
> r.to.vect -s in=myraster_simple out=myraster_simple
>
> c) run v.overlay.
>
> Is there a simplier and more efficient approach?
>
> How do I also extract those areas of the raster which intersect with certain
> landuse types?
>
> Thanks and kind regards,
> Timmie
>
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