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

[Markus Metz]

On Thu, Feb 20, 2014 at 8:25 PM, Stefan Lüdtke <sluedtke at gfz-potsdam.de> wrote:
> Hi,
> I experienced  a similar point, but, if I remember right, this was
> because I set the computational region to the extend of the catchment
> produced by r.water.outlet.

This is correct, r.watershed need a buffer of at least one cell around
the catchment, otherwise it can not find out where exactly the
catchment's borders are.

Markus M


So maybe the MASK has a similar effect and
> r.watershed needs kind of buffer. Should be easy to check ...
>
> HTH,
>
> Stefan
>
>
>
> On 02/20/2014 07:11 PM, Michel Wortmann wrote:
>> Here is what I think is strange though about your explanation, Markus:
>> If I first mask a watershed produced with r.water.outlet and then use
>> r.watershed to produce subbasins, it doesnt include the entire area of
>> the watershed but leaves small areas out, although these areas belong to
>> it. Is this a threshold problem?
>>
>> Tom, see image attached.
>>
>> Michel
>>
>> On 02/19/2014 04:42 PM, Thomas Adams wrote:
>>> I've been using GRASS 7 for this and have not seen a problem -- I hope
>>> I'm not overlooking the issue. Michel, can you provide an image that
>>> shows this?
>>>
>>> Thanks,
>>> Tom
>>>
>>> On Wednesday, February 19, 2014, Michel Wortmann
>>> <wortmann at pik-potsdam.de <mailto: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?
>>>     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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>>>
>>>
>>> --
>>> Thomas E Adams, III
>>> 718 McBurney Drive
>>> Lebanon, OH 45036
>>>
>>> 1 (513) 739-9512 (cell)
>>>
>>>
>>
>>
>>
>>
>>
>>
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>
> --
> Stefan Lüdtke
>
> Section 5.4-  Hydrology
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