Hi Johannes, thanks a lot for the info. I am doing effectively the same now by using R and rbinom but I am switching to rmultinom..
Cheers, Rainer Johannes Radinger <[email protected]> writes: > Hi Rainer, > > I don't know of any standard GRASS tool that performs such tasks. > > However I had a similar task, also an ecological topic and it was about > the redistribution of fish according to a dispersal kernel. So in my case > a number of fish (n_individuals) should be randomly distributed over a > raster map, but in my case with varying probabilities (used as weighting > factor) in the landscape. > > I solved that with the python/array interface of GRASS, in detail with a > random multinomial approach of numpy: > > # Import Python modules > import grass.script.array as garray > import numpy > > # Probability map, varying probability over the landscape, used as > weighting factor > probmap = garray.array() > probmap.read("probmap") > > # Output, redistributed individuals (n=500) > outputmap = garray.array() > n_individuals=500 > > outputmap[...] = numpy.random.multinomial(n_individuals, > (probmap/numpy.sum(probmap)).flat, size=1).reshape(probmap.shape) > outputmap.write("outputmap") > > > This approach is also implemented in the newest version of the GRASS-GIS > addon r.fidimo (GRASS70), which > is a fish dispersal model for river networks. > > So maybe that approach helps you! > > Best, > > Johannes > > > > > On Fri, Sep 6, 2013 at 1:17 PM, Rainer M Krug <[email protected]> wrote: > >> Hi >> >> I am writing a simulation of dispersal, and one possible dispersal >> approach is to distribute a certain number of seeds N randomly in the >> landscape. >> >> Therefore I would like to generate a random raster map with the sum of >> all cells equals to N. Is there a way of doing this easily in GRASS? >> >> At the moment, I am using an R function, which distributes the seeds, >> but due to computational time considerations, I would like to move it to >> GRASS. >> >> Thanks, >> >> Rainer >> >> >> -- >> Rainer M. Krug >> >> email: RMKrug<at>gmail<dot>com >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> <#secure method=pgpmime mode=sign> -- 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 Cell: +33 - (0)6 85 62 59 98 Fax : +33 - (0)9 58 10 27 44 Fax (D): +49 - (0)3 21 21 25 22 44 email: [email protected] Skype: RMkrug _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
