[GRASS-user] Interpreting r.watershed accumulation map

[Helmut Kudrnovsky]

Rich Shepard wrote
> On Sun, 16 Oct 2016, Sören Gebbert wrote:
> 
>> I don't know why this happens.
> 
>    I sent Laurant the DEM and the Itzi simulation run worked for him using
> grass-7.0.5, but it fails here with grass-7.0.6, 7.2.svn, and 7.3.svn.
> There
> must be something different here on this particular host; I've no idea
> where
> to start looking for differences.
> 
>    Also, there are differences in the elevation maps produced by different
> grass versions when the same source DEM is re-projected. The same command
> was used in each version:
> 
> r.proj --o loc=Oregon-Dayton-feet map=topography in=be_cropped
> out=be_cropped
> meth=bilinear
> 
>    The output from 7.0.x is smaller, and shows greater elevation
> differencs,
> that those of 7.2.svn and 7.3.svn (the latter two appear the same); copies
> attached.
> 
>    If anyone has suggestions on identifying what's different on this host
> that prevents Itzi from running, please share your expertise with me.
> 
> Rich
> 
> 
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> 
> be_cropped70.png (135K)
> <http://osgeo-org.1560.x6.nabble.com/attachment/5291143/0/be_cropped70.png>
> be_cropped73.png (146K)
> <http://osgeo-org.1560.x6.nabble.com/attachment/5291143/1/be_cropped73.png>

If a GRASS command gives really different results by different GRASS
versions and the different behaviour isn't documented in the manual or in
the news of the new release, the best way that this will be checked:

- open a ticket at trac (1)
- provide data and used commands to reproduce the issue 

otherwise there is a good chance that 

- the issue will get lost in the mailing list while the subject of the
threats points to another issue 
- devs can't test the issue 

(1) https://trac.osgeo.org/grass



-----
best regards
Helmut
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