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@lists.osgeo.org"
<grass-dev-request@lists.osgeo.org> wrote:
Message: 4
Date: Tue, 24 Jun 2008 07:27:37 -0700
From: "Dylan Beaudette" <dylan.beaudette@gmail.com>
Subject: Re: [GRASS-dev] Re: r.walk and r.drain improvements
To: hamish_b@yahoo.com
Cc: grass-dev@lists.osgeo.org
Message-ID:
<3c5546140806240727j168f291eh2ddde34c874e5890@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Tue, Jun 24, 2008 at 6:06 AM, Hamish <hamish_b@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
_______________________________________________
grass-dev mailing list
grass-dev@lists.osgeo.org
grass-dev Info Page
__________________________________________
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
I have been working on the grass-6.3.0 release version which I
compiled from source myself.
Several problems:
1) I tried to run the unaltered r.drain on a cost surface made with an
unaltered r.walk and there were pits in it causing the r.drain to fail
to find the start point. Should that even be possible? How could there
be pits in a cost surface?
2) I just tried to do a simple comparison with r.cost and found that
it isn't functioning properly at all. It gets to "Finding cost path"
and starts counting percents. It works fine until 99% and then it
lists 100% many times, 101% many times and so on. It was around 250%
when I stopped it. Perhaps this is something in my current
compile....? I have no idea.
On Tue, Jun 24, 2008 at 5:04 PM, Michael Barton <michael.barton@asu.edu> wrote:
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
I'll try to look into latlong but that may be beyond my current ability.
-Colin
On 6/24/08 9:00 AM, "grass-dev-request@lists.osgeo.org"
<grass-dev-request@lists.osgeo.org> wrote:
Message: 4
Date: Tue, 24 Jun 2008 07:27:37 -0700
From: "Dylan Beaudette" <dylan.beaudette@gmail.com>
Subject: Re: [GRASS-dev] Re: r.walk and r.drain improvements
To: hamish_b@yahoo.com
Cc: grass-dev@lists.osgeo.org
Message-ID:
<3c5546140806240727j168f291eh2ddde34c874e5890@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Tue, Jun 24, 2008 at 6:06 AM, Hamish <hamish_b@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
_______________________________________________
grass-dev mailing list
grass-dev@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev
__________________________________________
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
_______________________________________________
grass-dev mailing list
grass-dev@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev