[GRASS-user] r.threshold: Where is the output?

[Margherita Di Leo]

Helmut,

On Thu, Jun 21, 2012 at 3:33 PM, Helmut Kudrnovsky <hellik at web.de> wrote:

> >>Do I run r.mapcalc on the accumulation map to replace negative values
> with
> > >   zeros? Or, is there a different preferred approachu?
> >
> >
> >you can use abs function of r.mapcalc
>
> would the -a flag of r.watershed be an option?
>
> http://grass.osgeo.org/grass64/manuals/html64_user/r.watershed.html
>
> -a
>    Use positive flow accumulation even for likely underestimates.[...]
>

sure, I didn't mention it because I assumed that flow accumulation was
already calculated..
The result is the same. Negative flow accumulation in the r.watershed
convention means that in those cells flow accumulation is likely
underestimated, i.e. part of the contributing area falls outside of the
computational region. It is not meant as "negative area" (nonsense), it's
only a convention.

Regards,
madi

>
>
-- 
Dr. Margherita Di Leo
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