On Tue, Jun 12, 2012 at 11:28 AM, Margherita Di Leo <[email protected]> wrote: > Hi, > > there is also r.convergence add-on: > http://grass.osgeo.org/wiki/GRASS_AddOns#r.convergence
BTW, the topographic convergence index is also available in r.watershed in GRASS 7. Markus M > > Regards, > madi > > On Tue, Jun 12, 2012 at 4:24 AM, Michael Barton <[email protected]> > 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 <[email protected]> >> To: [email protected] >> CC: grass-user grass-user <[email protected]> >> >> >> 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, <[email protected]> >> 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 >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> > > > > -- > Dr. Margherita Di Leo > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
