I'm happy to see these improvements to r.drain. In this context I want to mention that r.drain doesn't seem to work correctly in latlon locations.
Michael On 6/24/08 9:00 AM, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > Message: 4 > Date: Tue, 24 Jun 2008 07:27:37 -0700 > From: "Dylan Beaudette" <[EMAIL PROTECTED]> > Subject: Re: [GRASS-dev] Re: r.walk and r.drain improvements > To: [EMAIL PROTECTED] > Cc: [email protected] > Message-ID: > <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=ISO-8859-1 > > On Tue, Jun 24, 2008 at 6:06 AM, Hamish <[EMAIL PROTECTED]> wrote: >> Dylan: >>>> Interesting post Colin. Can you comment on the differences between >>>> r.drain and r.walk in this example [1], in light of your findings? >>>> 1. http://casoilresource.lawr.ucdavis.edu/drupal/node/544 >> >> teaching r.walk to follow ridgelines when possible would be cool for back >> country stuff. Perhaps r.mapcalc multiply the slope-cost input map with a >> r.param.scale feature map that likes ridges and saddles but doesn't like >> gullies and pits? treelines too. > > That is a good idea. I have done something similar in the past [1] , > with vegetated areas / lakes, to 'force' the cost surface in ways > beneficial to hiking. Vegetated areas were made easier to traverse > (closed canopy pine forests) and lakes were made impossible to > traverse. However, adding more of this kind of intuition via landform > element would be a great feature. > > 1. http://casoilresource.lawr.ucdavis.edu/drupal/node/244 > > >> >> Also set cost map to NULL if slope > x so it doesn't have you crossing >> cumulatively short but physically challenging 20m cliffs. >> > > Ah... that is what my example above is missing. I didn't know that > r.drain would go around NULL cells! > > Great tips. > > Dylan > > >> Colin: >>> Excellently documented example by the way. >>> >>> The path is probably quite similar but the point is that there is >>> currently no way to ensure that the r.drain path conforms to the >>> same path as the optimal path of cost accumulation (calculated >>> by r.walk or r.cost). >> >> AFAIR r.drain just blindly climbs to the next up/downhill D8 cell, in a loop, >> until it can climb/drop no more. thus it is not "least" cost at all, just one >> valid solution? (??) >> >> >> Hamish >> >> >> >> >> >> _______________________________________________ >> grass-dev mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-dev >> > __________________________________________ Michael Barton, Professor of Anthropology Director of Graduate Studies School of Human Evolution & Social Change Center for Social Dynamics & Complexity Arizona State University phone: 480-965-6213 fax: 480-965-7671 www: http://www.public.asu.edu/~cmbarton _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
