AW: [GRASS-user] Problems with r.terraflow and r.thin

Maciej Sieczka tutey at
Tue Aug 21 15:21:09 EDT 2007

Christian Braun wrote:
> Hi,
> ok I had to learn that you can't compare the results of r.terraflow and
> r.watershed regarding the watershed generation. I think r.watershed gives me
> the better results, so I will try to use this module.
> But I still have the problem with r.thin to get rid of the linear features
> describing watersheds. The pics I had attached are, of course, the results
> of thining my watersheds of r.terraflow. First pic result watersheds of
> r.terraflow, second pic the thining result.


Forgive me if I got you wrong, but are you by any chance running r.thin
on a raster map made of adjacent watershed polygons? Please note that
r.thin is supposed to be used for thinning raster *line* features. The
manual reads: "Thins non-zero cells that denote linear features in a
raster map layer".

If you need watershed borders as raster lines, you can use to
extract watersheds as vector polygons (areas) and rasterise their
boundaries with type=line (if this doesn't work, convert
boundaries into lines first with v.type, and run type=line on


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