[GRASS-user] mountain ridges extraction from DEM

[Wolfgang]

Hello,
I would like to know if it is possible (and how) to generate the view to 
mountain ridges as shown in
http://www.viewfinderpanoramas.org/panoramas.html
There are also nowadys some apps for smartphones which does the same.
I already found r.horizon but this is, at least as I understand, only 
the view of the horizon and not all ridges.
I also found a paper on automatic ridge extraction, but it seems that 
this never was included to grass:
http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Frigeri_Alessandro_2.pdf
Many thanks
Wolfgang