[GRASS-user] Building topologically correct stream network

ivan marchesini marchesini at unipg.it
Thu Jul 23 09:41:02 EDT 2009


If I well remember, the problems of 0 values in the category data were
related to braiding or similar artifacts deriving from rasterization

r.strahler used with threshold not too small should clean network and
solve the task...

here [1] (in italian.. sorry...) you can find some pictures about this

sorry but it was more than one year ago and I don't remember well all
these problems..


Il giorno mer, 22/07/2009 alle 19.35 -0700, Hamish ha scritto:
> stephen wrote:
> >> Well, I am not sure what I am going to do.  I would look at the
> >> code, but I am not adept at C.
> none the less, it doesn't hurt to look, depending on how it is written
> it might be understandable / tweakable.
> MMetz:
> > > What exactly is wrong with topology? The existence of these dangles?
> note the v.strahler help page makes special mention that if you used
> r.watershed you should check the topology. Maybe it makes a bitter deal
> out of that than is really the case?
> S:
> > Maybe there is nothing wrong.  On further reflection the area that
> > I am trying to use this procedure on is very flat and there are
> > intermittent streams and wetlands (site visit) all over the
> > study area.  These non-connected lines maybe showing
> > intermittentancy?
> do you see a "ladder effect" in the r.to.vect river network?
> (like a braided river with all joins at right angles)
> maybe that is the problematic topology the module is concerned about?
> Hamish
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