[GRASS-user] SRTM r.watershed at multiple scales

[Markus Metz]

On Wed, Feb 19, 2014 at 2:56 PM, Michel Wortmann
<wortmann at pik-potsdam.de> wrote:
> Markus,
> last year you asked me whether the r.watershed output is not aligned to the
> r.water.outlet output in GRASS7 (s.b.). Ie. it leaves small areas out. Back
> then, I wasnt using GRASS7, but I can confirm now that it still does it and
> it is still rather annoying. Have you ever heard of the reasons or attempted
> to fix this?

The reason is that r.watershed determines basins from streams, the ID
of basins is set from the streams. If a basin on a shore does not have
a stream outlet with at least <threshold> surface flow accumulation,
it will not be delineated, and there will be no streams in that area.

With r.water.outlet, you define an outlet and the upstream catchment
area will be traced from that outlet.

Markus M

> Thanks,
> Michel
>
> On 08/26/2013 03:25 PM, Markus Neteler wrote:
>>
>> On 08/22/2013 08:52 AM, Markus Neteler wrote:
>>>
>>> >>
>>> >>Hi Michel,
>>> >>
>>> >>On Wed, Aug 21, 2013 at 1:18 PM, Michel Wortmann
>>> >><wortmann at pik-potsdam.de>  wrote:
>>> >>...
>>>
>>>> >>>
>>>> >>>As the r.watershed algorithm often leaves small areas at the edges
>>>> >>>uncovered, you'll have to fill those before or after patching,
>>>> >>> otherwise
>>>> >>>you'll have holes in your subbasin map.
>>>
>>> >>
>>> >>... just curious: does this happen still in the latest GRASS 7 version?
>>> >>
>>> >>Markus
>
>
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