[R-sig-Geo] Shapefile - GRID operations

[Rainer M Krug]

On Mon, Sep 8, 2008 at 12:30 PM, Jean-Paul Kibambe Lubamba
<jean-paul.kibambe at uclouvain.be> wrote:
> Hello everybody,
>
> I have one GRID with my weights values over my study area. I have also an
> Administrative boundaries shapefile of my study area with an unique value
> of my variable of interest for each administrative unit.
>
> I want to distribute my unique value by administrative unit for each pixel
> of my GRID taking into account the weights of each pixel.
>
> So I want to do the following steps :
>
> 1. select an Administrative unit (value of interest = Vi)
> 2. clip the GRID at the boundaries of that admin unit
> 3. calculate the sum of the weights for that clipped grid (= Wi)
> 4. clipped grid * Vi / Wi
> ... the same for all my administrative units.
>
> 5. at the end, have a new GRID of my study area with the value of my
> variable of interest distributed over all my administrative units.

Look into the function overlay() in the package sp. This will do what you need.

Rainer


>
>
> So for sure (I mean), there is a more efficient way to do it with R...
> Anyone could help me ?
>
> Thanks in advance !
>
>
> JP
>
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-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

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