Hi Nagy, On Sat, Dec 16, 2017 at 2:06 PM, Nagy Edmond <nagy.edmond....@gmail.com> wrote: > Hi Anna, > > Thank you for pointing that out. It always computes one way between two > points indeed, but there is something that I should bring to light. > > While I was initially computing least-cost paths with r.drain using r.walk > outputs as inputs I noticed a possible problem. I ran two parallel tests > with the same two points. In the first one, A was the starting position, > while B the stop position. In the second one, B was the start point and A > the stop point. In r.walk, the results were anisotropic indeed, both the > walking cost and the movement direction raster outputs turned out different, > as it would have been expected. But the r.drain module sadly did not > generate different least-cost paths, despite using different inputs. I have > also checked this more than once, just to be sure of it. > > At one point I have also come across an article (Gietl et al. 2008 - link > below) where the authors discuss and compare l.c.p. results obtained with > different GIS (including GRASS), and they had also experienced some problem > with the module (page 4), but I am not sure if it's the same I'm having. In > any case, if nothing can be done about it, then I will mention the > limitation in the documentation. >
you are right that r.drain seem to create the same path from A to B and back, there are some slight differences, but that can be just numerical cause. I am not sure why is that, if my expectation that the path for that DEM should be different is incorrect, or there is some problem in the algorithm. I don't think what the paper refers to is the same thing though. Anna > All the best, > Nagy Edmond > > article - > http://proceedings.caaconference.org/paper/106_gietl_et_al_caa2007/ > > > > -- > Sent from: http://osgeo-org.1560.x6.nabble.com/GRASS-PSC-f4051248.html > _______________________________________________ > grass-psc mailing list > grass-psc@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-psc _______________________________________________ grass-psc mailing list grass-psc@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-psc