[GRASS-user] r.watershed MFD strange basin

[Markus Metz]

On Mon, May 7, 2012 at 1:08 PM, ivan marchesini
<ivan.marchesini at gmail.com> wrote:
> Dear Grass users,
> I have noted a strange result from r.watershed using the MDF option
> (with all levels of convergence).
>
> This is a part of my DEM:
>
> http://imageshack.us/photo/my-images/690/demv.png/
>
>
> This is the result obtained using SDF:
>
> http://imageshack.us/photo/my-images/843/27420800.png/
>
>
> This is the result obtained using MDF:
>
> http://imageshack.us/photo/my-images/190/36629290.png/
>
>
>
> Please have a look to the last picture.
> In the central part of the image (near to the pointer) there is a little
> basin connected to the larger one that is on the other side of the
> valley.
>
> It seems an error.

Please report if the stream segments are as expected, because the
determination of half-basins and basins is based on the stream
segments.

If the stream segments seem out of place, something is wrong with the
identification of stream segments and you will need to look at flow
accumulation and check if that makes sense.

If the stream segments seem to be ok, something is wrong with
determining the left and right side of a stream.

Markus M