[GRASS-dev] r.watershed2 with MFD

[Markus Metz]

Dylan Beaudette wrote:
> On Fri, Dec 5, 2008 at 1:55 AM, Markus Metz <markus_metz at gmx.de> wrote:
>   
>> I took the request for MFD support in r.watershed by Helena and Dylan to
>> heart and implemented it, but still need a few more days to clean up the
>> code, then I want to submit it as r.watershed2.mfd to grass-addons.
>>
>>     
> Is there any way to
> cleanly merge this with the existing r.watershed code in SVN so that
> we can test it?
>   
Also considering Michael's remarks, I suggets that I then not submit to
grass-addons, but to grass 7. Not to grass-6.4.x, because this code is
now more experimental and documentation still needs to be written.
The MFD algorithm seems to be robust and produces the expected results
with nice differences according to the convergence factor, but the other
outputs are different and I don't know yet if this is ok and desired or not.
The basins and half-basins are different, less so for coarser
resolution, rather disastrous with MFD for the 1m LIDAR DEM in the North
Carolina dataset. It seems that such a DEM should be processed with
coarser resolution to obtain basins and half-basins that make sense,
apparently both for SFD and MFD, but these a just first impressions.
Slope length (LS for USLE) and slope steepness (S for USLE) are about
99.9% identical between SFD and MFD with the DEM <elevation> in the
North Carolina dataset. Streams are again different, i.e. MFD streams
need to be thinned then they are very similar to SFD, but MFD streams
make sense.
Once I have added MFD to segmented mode too and updated the
documentation, the module is ready to be submitted and scrutinised by
others.

This is no easy feat to modify r.watershed, I want to make sure the old
behaviour is preserved when adding new functionality and I need some
more time before submitting. I don't like to submit code with bugs...

Markus Metz