Markus, Thank you for replying and sorry for delay,
On Fri, Dec 28, 2012 at 4:37 PM, Markus Metz <[email protected]>wrote: > On Wed, Dec 19, 2012 at 3:25 PM, Margherita Di Leo <[email protected]> > wrote: > > Hi All, > > > > I have a friction map, a start polygon and an end polygon and would like > to > > find the least cost path, meaning not a corridor but a thin line. To now > > I've tried both r.cost and r.walk and r.drain eventually, but the result > of > > this latter > > > > r.drain input=friction@PERMANENT output=rdrain_out > > vector_points=start_line@PERMANENT > > > > is a path calculated *within* the start polygon (a closed line). > > I suppose this is because I don't provide a direction map to r.drain (I'm > > using GRASS 7). I read: > > > > If the input surface (a raster map layer) is a cumulative cost map > generated > > by the r.walk or r.cost modules, the -d flag and a movement direction > > surface "indir" must be specified. > > > > I assume it's a kind of flow direction or aspect, but what is the > physical > > meaning, and how can I calculate it? Could anyone please provide some > > further info. > > The physical meaning is movement direction in degrees CCW from East, > similar to e.g. flow direction output of r.watershed. The direction > map is an optional output of r.cost and r.walk, and should be used > with the indir option for r.drain. > > The workflow would thus be: > > 1) convert the first polygon to a raster map > 2) use all cells of the first polygon as start points for r.walk, > include the friction map > 3) convert the second polygon to a raster map > quite plain up to this point, but: > 4) use the second polygon as a MASK and get the coordinates of the > cell with the lowest cost > The cost map obtained by r.walk happens to be all 0 within the ending polygon. How should I choose my coordinates in this case? 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.
_______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
