[GRASS-user] ridge extraction from DEM

[Michael Barton]

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