On Tue, Jan 8, 2013 at 3:41 PM, Margherita Di Leo <[email protected]> wrote: > Thanks for super quick answer, > > On Tue, Jan 8, 2013 at 3:25 PM, Markus Metz <[email protected]> > wrote: >> >> >> Check if the friction map is not all zero or NULL for the second >> polygon, > > > the friction map within the ending polygon has everywhere value 1.
And what are the values of the friction map outside the ending polygon? Should also be 1 I guess. >> >> that the second >> polygon is actually reachable from the first polygon in the output of >> r.walk, > > > Not sure how to verify that, but i digitized a random point within the > ending polygon (i placed it somewhere in the center) and i used it as > starting point for r.drain, and obtained a nice least cost path line. Interesting. Are the costs anywhere larger than zero? > >> >> Also >> have a look at the direction output of r.walk. > > > Looks OK (it has values) but i'm still not sure what should i check in it. That the directions make sense. In GRASS 7 as of r54582 they are degrees CCW from East, zero is undefined, 360 is due East. A little example in the NC dataset: # walking from Macon county to Dare county g.region -p rast=elev_state_500m@PERMANENT v.to.rast in=boundary_county@PERMANENT use=val val=1 where="NAME = 'DARE'" out=dare v.to.rast in=boundary_county@PERMANENT use=val val=1 where="NAME = 'MACON'" out=macon r.mapcalc "friction = 0.0001" # use Knight's move r.walk elevation=elev_state_500m@PERMANENT friction=friction output=dare_cost outdir=dare_dir start_rast=dare -k r.mask raster=macon r.out.xyz in=dare_cost out=- | sort -t "|" -k 3 | head -n3 # gives # 234250|147750|490937.498669579 # 234250|147250|491132.5043559544 # 234250|146750|491258.3433474401 # Coordinates with lowest cost in Macon county are 234250,147750, and the lowest cost is > zero. r.mask -r # use directions input because the input is a cost surface # and vector output because of Knight's move in r.walk r.drain -d input=dare_cost indir=dare_dir output=macon2dare vector_output=macon2dare start_coordinates=234250,147750 Markus M > > Thanks, > madi >> >> >> HTH, >> >> Markus M >> >> > >> > Thanks in advance. >> > >> > Best, >> > madi >> > >> > -- >> > Margherita DI LEO >> > Postdoctoral Researcher >> > >> > European Commission - DG JRC >> > Institute for Environment and Sustainability (IES). Unit H03 – FRC >> > Via Fermi, 2749 >> > I-21027 Ispra (VA) - Italy - TP 261 >> > >> > Tel. +39 0332 78 3600 >> > [email protected] >> > >> > Disclaimer: The views expressed are purely those of the writer and may >> > not >> > in any circumstance be regarded as stating an official position of the >> > European Commission. > > > > > -- > Margherita DI LEO > Postdoctoral Researcher > > European Commission - DG JRC > Institute for Environment and Sustainability (IES). Unit H03 – FRC > Via Fermi, 2749 > I-21027 Ispra (VA) - Italy - TP 261 > > Tel. +39 0332 78 3600 > [email protected] > > Disclaimer: The views expressed are purely those of the writer and may not > in any circumstance be regarded as stating an official position of the > European Commission. _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
