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

[Colin Nielsen]

Hamish,
That sounds about right. Which is why I'm trying to modify
r.walk/r.drain to be able to return the actual least-cost path. I've
finished the r.walk bit but I'm having trouble modifying the r.drain
function.

Re my original question, would it be better to make a separate module
or modify r.drain?

-Colin

On Tue, Jun 24, 2008 at 2:06 PM, Hamish <hamish_b at yahoo.com> 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.
>
> 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
>
>
>
>
>
>