[GRASS-dev] Re: r.walk and r.drain improvements

[Hamish]

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.

Also set cost map to NULL if slope > x so it doesn't have you crossing cumulatively short but physically challenging 20m cliffs.


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