[GRASS-user] 回覆： Re: ridge extraction from DEM

[Margherita Di Leo]

Hi,

there is also r.convergence add-on:
http://grass.osgeo.org/wiki/GRASS_AddOns#r.convergence

Regards,
madi

On Tue, Jun 12, 2012 at 4:24 AM, Michael Barton <michael.barton at asu.edu>wrote:

> Invert the DEM by multiplying all values by -1 and adding the maximum
> original height value. This makes the maximum height 0 and everything less
> than that increasingly greater than 0
>
> Run r.watershed on the inverted DEM choosing stream segments as output.
>
> The stream segments from the inverted DEM are your ridgelines. You can
> keep them in raster or thin them (r.thin) and convert them to vector
> (r.to.vect).
>
> I've copied the GRASS user list again because this is a general question
> that others might be interested in.
>
> Michael
>
>
>
> On Jun 11, 2012, at 7:29 PM, Thomaswplee wrote:
>
> How to make ridge vector line with reversed accumlated flow as in
> watershed?
>
> Still reverse DEM plus vectorization of ridge raster?
>
> Thomas
>
>
>
> -------- Original message --------
> Subject: Re: ridge extraction from DEM
> From: Michael Barton <michael.barton at asu.edu>
> To: thomaslee at starvision.com.hk
> CC: grass-user grass-user <grass-user at lists.osgeo.org>
>
>
> Thomas,
>
> I don't remember posting anything about r.ppa. I did a quick search and
> found a post by Māris Nartišs (
> http://lists.osgeo.org/pipermail/grass-user/2005-October/030883.html).
>
> r.param.scale will extract ridges. You will need to adjust the optional
> parameters (especially processing window size) to get the ridges you want.
>
> An alternative method is to invert the DEM and run r.watershed on it,
> extracting the 'streams'. The 'streams' of the inverted DEM will follow
> ridges.
>
> Michael
>
>
>
> On Jun 11, 2012, at 9:26 AM, <thomaslee at starvision.com.hk>
> wrote:
>
> > Dear Michael,
> >
> > I am interested in ridge extraction but not able to find the r.ppa
> mentioned by
> >
> >
> > Chang, Y.C., Frigeri, A., 2002. Implementing the automatic
> > extraction of ridge and valley axes using the PPA algorithm in
> > Grass GIS. In: Open Source Free Software GIS GRASS
> > Users Conference, 2002.
> >
> >
> > Implementing the automatic extraction of ridge and
> > valley axes using the PPA algorithm in Grass GIS
> >
> >
> > Do you have any solution since your message in 2007 about ridge
> extraction.
>
> _____________________
> C. Michael Barton
> Visiting Scientist, Integrated Science Program
> National Center for Atmospheric Research &
> University Corporation for Atmospheric Research
> 303-497-2889 (voice)
>
> Director, Center for Social Dynamics & Complexity
> Professor of Anthropology, School of Human Evolution & Social Change
> Arizona State University
> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>
>
> _____________________
> C. Michael Barton
> Visiting Scientist, Integrated Science Program
> National Center for Atmospheric Research &
> University Consortium for Atmospheric Research
> 303-497-2889 (voice)
>
> Director, Center for Social Dynamics & Complexity
> Professor of Anthropology, School of Human Evolution & Social Change
> Arizona State University
> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>
>
>
>
>
>
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>
>


-- 
Dr. Margherita Di Leo
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