On Tue, Jan 8, 2013 at 6:20 PM, Margherita Di Leo <direg...@gmail.com>wrote:
> Markus, > > On Tue, Jan 8, 2013 at 5:44 PM, Markus Metz <markus.metz.gisw...@gmail.com > > wrote: > >> On Tue, Jan 8, 2013 at 3:41 PM, Margherita Di Leo <direg...@gmail.com> >> wrote: >> > Thanks for super quick answer, >> > >> > On Tue, Jan 8, 2013 at 3:25 PM, Markus Metz < >> markus.metz.gisw...@gmail.com> >> > 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. >> > > Sorry my mistake, I just checked the wrong map -_-" sorry. It just works > as you stated. > >> >> >> >> >> 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? >> > > Yes yes, > >> >> > >> >> >> >> 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 >> > > Thank you, I'm expanding the wiki with the example that you provided. > > Cheers, > 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 > margherita.di-...@jrc.ec.europa.eu > > 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 margherita.di-...@jrc.ec.europa.eu 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.
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