<br><br><div class="gmail_quote">On Tue, Jan 8, 2013 at 6:20 PM, Margherita Di Leo <span dir="ltr"><<a href="mailto:diregola@gmail.com" target="_blank">diregola@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Markus,<div><br><div class="gmail_quote"><div class="im">On Tue, Jan 8, 2013 at 5:44 PM, Markus Metz <span dir="ltr"><<a href="mailto:markus.metz.giswork@gmail.com" target="_blank">markus.metz.giswork@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>On Tue, Jan 8, 2013 at 3:41 PM, Margherita Di Leo <<a href="mailto:diregola@gmail.com" target="_blank">diregola@gmail.com</a>> wrote:<br>
> Thanks for super quick answer,<br>
><br>
> On Tue, Jan 8, 2013 at 3:25 PM, Markus Metz <<a href="mailto:markus.metz.giswork@gmail.com" target="_blank">markus.metz.giswork@gmail.com</a>><br>
> wrote:<br>
>><br>
>><br>
>> Check if the friction map is not all zero or NULL for the second<br>
>> polygon,<br>
><br>
><br>
> the friction map within the ending polygon has everywhere value 1.<br>
<br>
</div>And what are the values of the friction map outside the ending<br>
polygon? Should also be 1 I guess.<br></blockquote><div><br></div></div><div>Sorry my mistake, I just checked the wrong map -_-" sorry. It just works as you stated. </div><div class="im"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><br>
>><br>
>> that the second<br>
>> polygon is actually reachable from the first polygon in the output of<br>
>> r.walk,<br>
><br>
><br>
> Not sure how to verify that, but i digitized a random point within the<br>
> ending polygon (i placed it somewhere in the center) and i used it as<br>
> starting point for r.drain, and obtained a nice least cost path line.<br>
<br>
</div>Interesting. Are the costs anywhere larger than zero?<br></blockquote><div><br></div></div><div>Yes yes, </div><div><div class="h5"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><br>
><br>
>><br>
>> Also<br>
>> have a look at the direction output of r.walk.<br>
><br>
><br>
> Looks OK (it has values) but i'm still not sure what should i check in it.<br>
<br>
</div>That the directions make sense. In GRASS 7 as of r54582 they are<br>
degrees CCW from East, zero is undefined, 360 is due East.<br>
<br>
<br>
A little example in the NC dataset:<br>
<br>
# walking from Macon county to Dare county<br>
<br>
g.region -p rast=elev_state_500m@PERMANENT<br>
<br>
v.to.rast in=boundary_county@PERMANENT use=val val=1 where="NAME =<br>
'DARE'" out=dare<br>
<br>
v.to.rast in=boundary_county@PERMANENT use=val val=1 where="NAME =<br>
'MACON'" out=macon<br>
<br>
r.mapcalc "friction = 0.0001"<br>
<br>
# use Knight's move<br>
r.walk elevation=elev_state_500m@PERMANENT friction=friction<br>
output=dare_cost outdir=dare_dir start_rast=dare -k<br>
<br>
r.mask raster=macon<br>
<br>
r.out.xyz in=dare_cost out=- | sort -t "|" -k 3 | head -n3<br>
<br>
# gives<br>
# 234250|147750|490937.498669579<br>
# 234250|147250|491132.5043559544<br>
# 234250|146750|491258.3433474401<br>
<br>
# Coordinates with lowest cost in Macon county are 234250,147750, and<br>
the lowest cost is > zero.<br>
<br>
r.mask -r<br>
<br>
# use directions input because the input is a cost surface<br>
# and vector output because of Knight's move in r.walk<br>
<br>
r.drain -d input=dare_cost indir=dare_dir output=macon2dare<br>
vector_output=macon2dare start_coordinates=234250,147750<br></blockquote><div><br></div></div></div><div>Thank you, I'm expanding the wiki with the example that you provided. </div><div><br></div><div>Cheers,</div><div>
madi </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br></blockquote></div><div class="im">-- <br><div><div><font color="#666666">Margherita DI LEO </font></div><div><font color="#666666">Postdoctoral Researcher</font></div><div><font color="#666666"><br></font></div><div>
<font color="#666666">European Commission - DG JRC </font></div>
<div><font color="#666666">Institute for Environment and Sustainability (IES). Unit H03 – FRC</font></div><div><font color="#666666">Via Fermi, 2749</font></div><div><font color="#666666">I-21027 Ispra (VA) - Italy - TP 261</font></div>
<div><font color="#666666"> </font></div><div><font color="#666666">Tel. <a href="tel:%2B39%200332%2078%203600" value="+390332783600" target="_blank">+39 0332 78 3600</a> </font></div><div><font color="#666666"><a href="mailto:margherita.di-leo@jrc.ec.europa.eu" target="_blank">margherita.di-leo@jrc.ec.europa.eu</a></font></div>
<div><font color="#666666"><br></font></div><div><font color="#666666">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.</font></div>
</div>
</div></div>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><div><div><font color="#666666">Margherita DI LEO </font></div><div><font color="#666666">Postdoctoral Researcher</font></div><div><font color="#666666"><br>
</font></div><div><font color="#666666">European Commission - DG JRC </font></div><div><font color="#666666">Institute for Environment and Sustainability (IES). Unit H03 – FRC</font></div><div><font color="#666666">Via Fermi, 2749</font></div>
<div><font color="#666666">I-21027 Ispra (VA) - Italy - TP 261</font></div><div><font color="#666666"> </font></div><div><font color="#666666">Tel. +39 0332 78 3600 </font></div><div><font color="#666666"><a href="mailto:margherita.di-leo@jrc.ec.europa.eu" target="_blank">margherita.di-leo@jrc.ec.europa.eu</a></font></div>
<div><font color="#666666"><br></font></div><div><font color="#666666">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.</font></div>
</div>