[R-sig-Geo] Selecting n cells more then minDist apart

[Rainer M Krug]

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On 26/01/12 12:44, Brian wrote:
> Hi Rainer,
> 
> how about aggregating to a lower resolution, where the cell center
> - cell center distances correspond to your minDist? Then sample as
> one would normally and then take the cell center coordinates from
> your sample back to your original raster.

Wouldn't work in my case, as the underlying raster on which I want to
sample, has sometimes single isolated cells, and it is important to
have a chance of sampling these as well in a later step. And if under
the aggregated resolution two of these isolated cells are in one
celll, there is a problem.

> A bit of geometry will tell you what the resolution needs to be
> and please tell me you are not sampling a longlat projection!

No - its a UTM grid.

I looked again at my application, and I realized as I can also set the
minimum distance, and then distribute the points. So I decided to use
the r.random.cells function and specify the distance.

My application is a sensitivity analysis, and it does not matter if I
change the distance which results in different number of cells
selected, or change the number of cells and then distribute them.

Thanks a lot for your help,

Rainer


> 
> Either the r.region GRASS function or the aggregate 'raster'
> function should do.
> 
> there's my cents/sense...
> 
> HTH,
> 
> Brian


- -- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
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email:      Rainer at krugs.de

Skype:      RMkrug
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