[GRASS-user] r.to.vect Produces Too Many Areas

[Micha Silver]

On 02/22/2010 10:12 PM, Rich Shepard wrote:
>   I've done something incorrectly but cannot find what that is.
>
>   Ran r.water.outlet and produced the output basin map. Then I applied
> r.null to that map setting nulls to zeros. Next I applied r.to.vect to 
> that
> map (with the '-s' option) setting feature to area.
>
>   When I look at the aspect map overlaid by the sub-basin map I see the 5
> extraneous cells that should not be there. You can see them on the 
> attached
> screen shot.
>
What I do in these cases is run v.clean with the rmarea option. I choose 
a threshold about 5X the cell resolution to get rid of any small areas 
like these. I think it comes from the way r.to.vect works (others with 
more knowledge might correct me). Any cell which touchs the contiguous 
area only at one corner is considered a separate polygon, so you end up 
with some square vector areas of size nsresXewres.

>   This did not happen the last time I used r.water.outlet, and the 
> drainage
> map does not suggest to me why these 5 cells are included.
>
>   Help would be appreciated in learning what happened and how to get this
> tail off the map.
>
> Thanks,
>
> Rich
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-- 
Micha Silver
http://www.surfaces.co.il/
Arava Development Co.  +972-52-3665918