[Fwd: [GRASS-user] r.cost vs. costallocation (arcgis)]

António M . Rodrigues amrodrigues at fcsh.unl.pt
Mon Mar 15 12:05:09 EDT 2010

On Mon, 15 Mar 2010 15:21:23 +0100, Paolo Cavallini wrote
> António M. Rodrigues ha scritto:
> > Allocation surface / grid: a raster whose value of each cell is the code of the nearest target. 
> > If the possible targets are hospital 1 and 2, each cell in the allocation surface will contain values 
1 or 
> > 2, depending on which is the nearest hospital.
> > I was surprised r.cost didn't provide this information (allocation surface), since this is quite 
> > output when using this methodology with arcinfo (using a function called costdistance); but yes, 
> > quite sure there must be a way of doing this in GRASS.
> If I understand correctly, you just need to calculate several cost 
> maps (you can do that in a loop), and use mapcalculator for this 
> (function MIN). Would this do? All the best.
> -- 
> Paolo Cavallini: http://www.faunalia.it/pc

Actually no. Each of those cost maps (or accessibility maps) would contain the cost (time) of traveling 
to a specific target (end point). 

a similar question was addressed here (http://www.mail-archive.com/grass- 
user at lists.osgeo.org/msg01811.html), but the solution is not the best, since it produces least-cost 
paths between specific locations. 

I enclose one image from a previous study (results produced with arcinfo). It represents an 
"allocation surface" (this last one is what I need but r.cost doesn't produce). It is like a buffer, but the 
values are not produced based on some isotropic surface, but rather on friction costs.

I've been reading about scripting and programming in GRASS, since I believe the solution probably 
involves writing some code based on r.cost. 

But of course, any help is welcomed.
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