Hi Micha, On Fri, Jun 8, 2012 at 4:48 PM, Micha Silver <mi...@arava.co.il> wrote:
> > Hi Madi: > > Regarding the threshold value in your auxilliary parsing.py script, do you > think it might be better to calcuclate a suggested value from the size of > the original DEM, rather than just put in some random 10,000 or so. > > Obviously the user has to understand, and change the threshold to suit his > needs, but if the script is going to contain some value, maybe it should be > something "reasonable". I thought, for example to choose a suggested thresh > size of num_cells/100. i.e.: > > N=`r.univar -g | grep "^n=" | cut -d "=" -f 2` > > THRESH=$(( $N / 100)) > > Does that sound reasonable? Since the python auxilliary script runs > independently of GRASS, I'm not sure how how this would all merge together. > But it's worth thinking about. > I've added comments in the wiki page in the python script section, about the threshold and the name of the DEM, both parameters should be changed manually. For what concerns a "reasonable" value of the threshold, well, it actually depends on too many factors, by the way, I've provided already some ways to start from a "reasonable" value (all exposed in the wiki page): 1) r.basin has a flag -a which uses a default value of threshold, corresponding to 1 km^2 (this value comes from literature and it's suitable for _italian_ territory, this means that it could be completely wrong for other territories) 2) r.threshold has a different reasoning. It starts from a relationship between the slope and the upslope area. 3) r.stream.preview: it simply allow user to have a preview of the threshold in order to quickly set a "reasonable" value. (this is a piece of wx.stream, which I'm not satisfied of and am re-writing from scratch). Anyway, if you think that the wiki page looks confusing, I really appreciate your help in editing :-) Thanks, madi -- Dr. Margherita Di Leo
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