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

[Christian Braun]

 Thanks for your answer, I missunderstood the meaning of r.thin.
But how can I get rather compact and smooth polygons representing watersheds
without any slivers or attached/appended fractals of the size of one raster
cell?
Is it possible to solve such a problem with v.clean or something like a
"raster smoothing" with r.neighbour?

Christian

> -----Original Message-----
> From: Maciej Sieczka [mailto:tutey at o2.pl] 
> Sent: Tuesday, August 21, 2007 9:21 PM
> To: Christian Braun
> Cc: 'Hamish'; grassuser at grass.itc.it
> Subject: Re: AW: [GRASS-user] Problems with r.terraflow and r.thin
> 
> 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.
> 
> Christian
> 
> 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 
> r.to.vect to extract watersheds as vector polygons (areas) 
> and rasterise their boundaries with v.to.rast type=line (if 
> this doesn't work, convert boundaries into lines first with 
> v.type, and run v.to.rast type=line on this).
> 
> Maciek
>