[GRASS-dev] r.watershed question

[Michael Barton]

Thanks for the information. I did look through the docs but didn't see  
this. I guess I missed it.

So...

r.mapcalc positive_accum=if(accum_map<0,accum_map*-1,accum_map)

...would produce a normal flow accumulation map, but one that  
underestimates flow in some areas?


Michael
____________________
C. Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

Phone: 480-965-6262
Fax: 480-965-7671
www: <www.public.asu.edu/~cmbarton>



On Dec 20, 2008, at 1:59 AM, Markus Metz wrote:

>
>
> Michael Barton wrote:
>> Should r.watershed be giving negative accumulation values?
> Yes. Negative accumulation values indicate that these cells receive  
> offmap inflow or inflow from a MASKed area from somewhere upstream.  
> This has always been the case for flow accumulation output. Negative  
> flow accumulation can be interpreted as "at least so many cells  
> drain into this cell, but probably more cells that were not included  
> in the region/unMASKed area". State that more clearly in the manpage?
>
> Regards,
>
> Markus M