[GRASS-user] [GRASS-dev] Bugs in r.stream.extract

[Huidae Cho]

Ming,

The discrepancy in flow accumulation between the two modules is explained
in the r.accumulate manual at
https://grass.osgeo.org/grass78/manuals/addons/r.accumulate.html. See
Examples => Flow accumulation. Most likely, this is because of
r.watershed's handling of border cells.

Thanks,
Huidae

On Wed, Nov 25, 2020 at 7:17 AM ming han <dustming at gmail.com> wrote:

> And another problem I got is that the flow accumulation I got from
> r.accumulate and r.watershed is different when r.accumulate using flow
> direction from r.watershed.  Again is there anyway r.watershed supports
> using flow direction, so we can get the consistent result.
>
> We need this when we need to adjust the flow direction from  r.watershed
> or r.stream.extract. and then we need to determine new flow accumulation
> with an adjusted flow direction dataset.  If the result is inconsistent,
> not sure what is the solution is.
>
> Cheers
> Ming
>
> ming han <dustming at gmail.com> 于2020年11月25日周三 上午6:38写道：
>
>> Hi Ken
>>
>>    Many thanks for your reply, I think I made a mistake, the flow
>> accumulation I provided to r.stream.extract did not match the DEM I
>> provided in r.stream.extract.  The streamline seems based on flow
>> accumulation derived from the provided DEM.
>>
>>    But, If I only want to use flow direction to drive streams, which
>> function I should use?
>>
>>    Is there any chance that  r.stream.extract can use flow direction as
>> inputs without DEM?
>>
>> Thanks
>> Ming
>>
>>
>> Ken Mankoff <mankoff at gmail.com> 于2020年11月24日周二 上午7:07写道：
>>
>>> Hi Ming,
>>>
>>> On 2020-11-23 at 09:05 -08, ming han <dustming at gmail.com> wrote...
>>> > Hope this email finds you well. I got a weird result when using
>>> > r.stream.extract, as shown in the following figure. The back grids is
>>> > the flow accumulation layer with a flow accumulation threshold larger
>>> > than 1000. while the blue line is the stream generated by
>>> > r.stream.extract. Why the stream from r.stream.extract did not follow
>>> > flow accumulation results? And how to fix this problem?
>>>
>>> Is there any chance you can share the raster that includes this region
>>> so I can examine it? And the exact command you ran?
>>>
>>>   -k.
>>>
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-- 
Huidae Cho, Ph.D., GISP
GRASS GIS Developer
https://idea.isnew.info
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