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.bar...@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.bar...@asu.edu> > To: thomas...@starvision.com.hk > CC: grass-user grass-user <grass-user@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, <thomas...@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 > > > > > > > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- Dr. Margherita Di Leo
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