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

[Michael Barton]

I'm happy to see these improvements to r.drain. In this context I want to
mention that r.drain doesn't seem to work correctly in latlon locations.

Michael


On 6/24/08 9:00 AM, "grass-dev-request at lists.osgeo.org"
<grass-dev-request at lists.osgeo.org> wrote:

> Message: 4
> Date: Tue, 24 Jun 2008 07:27:37 -0700
> From: "Dylan Beaudette" <dylan.beaudette at gmail.com>
> Subject: Re: [GRASS-dev] Re: r.walk and r.drain improvements
> To: hamish_b at yahoo.com
> Cc: grass-dev at lists.osgeo.org
> Message-ID:
> <3c5546140806240727j168f291eh2ddde34c874e5890 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> On Tue, Jun 24, 2008 at 6:06 AM, 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.
> 
> That is a good idea. I have done something similar in the past [1] ,
> with vegetated areas / lakes, to 'force' the cost surface in ways
> beneficial to hiking. Vegetated areas were made easier to traverse
> (closed canopy pine forests) and lakes were made impossible to
> traverse. However, adding more of this kind of intuition via landform
> element would be a great feature.
> 
> 1. http://casoilresource.lawr.ucdavis.edu/drupal/node/244
> 
> 
>> 
>> Also set cost map to NULL if slope > x so it doesn't have you crossing
>> cumulatively short but physically challenging 20m cliffs.
>> 
> 
> Ah... that is what my example above is missing. I didn't know that
> r.drain would go around NULL cells!
> 
> Great tips.
> 
> Dylan
> 
> 
>> 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
>> 
>> 
>> 
>> 
>> 
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>> 
> 

__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton