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

[Dylan Beaudette]

On Mon, Jun 23, 2008 at 4:02 AM, Colin Nielsen <colin.nielsen at gmail.com> wrote:
> I realized that the r.drain function does not adequately create a
> least-cost path on a cumulative cost surface. This is because there is
> no check within the r.drain function to ensure that the "steepest"
> downhill change in cost value is actually the same as the direction of
> cost accumulation during the cost calculation. This means that there
> is a disconnect between the movement direction in r.walk and the path
> created by r.drain.
>
> To fix this I have added the creation of a movement direction output
> raster to the r.walk code. This way the original movement directions
> will be preserved and the true least-cost path may be found using
> another module which traces the directional surface backwards.
>
> My question is, should the direction tracing module be:
> a) incorporated into r.drain with a flag specifying a cost surface
> rather than dem input, and an additional direction input
> b) write a new, separate module called r.costpath
>
> More modules or more complex modules?
>
> Thanks for the advice,
> -Colin

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


Cheers,

Dylan