[GRASS-user] real distance analysis

[Michael Barton]

Dylan,

Looks very nice.

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

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


> From: Dylan Beaudette <dylan.beaudette at gmail.com>
> Reply-To: <dylan.beaudette at gmail.com>
> Date: Fri, 2 Jun 2006 12:09:26 -0700
> To: <grassuser at grass.itc.it>
> Cc: Michael Barton <michael.barton at asu.edu>
> Subject: Re: [GRASS-user] real distance analysis
> 
> On Friday 02 June 2006 10:30, Michael Barton wrote:
>> Hamish’s reply is the closest to what  you want I think. However, to
>> actually derive a buffer to define equal ground distance around a point, I
>> think  you might need a bit more explanation.
>> 
>> First create a slope map of your dem (r.slope.aspect). Then, as Hamish
>> says, run r.cost. This will calcuate a ‘cost’ based on the slope of the
>> map. He implies that the cost value in the cost map = the ground distance
>> to traverse each pixel (i.e., higher on steep slopes where the ground
>> distance is greater and less on flat terrain where the ground distance is
>> lower). I don’t know if this is how the algorithm works or not (or also
>> includes other factors), but the references he lists will clarify. If not,
>> you can use trig in the mapcalculator to figure ground distance using—as he
>> says—the resolution of the map (i.e., the horizontal distance to traverse
>> each cell) and the slope of the cell.
>> 
>> Assuming that r.cost on a slope map * resolution = ground distance. You can
>> use the resultant map to create a buffer around a point that represents
>> equal ground distance in all directions.
>> 
>> Michael
>> __________________________________________
>> Michael Barton, Professor of Anthropology
>> School of Human Evolution & Social Change
>> Center for Social Dynamics and Complexity
>> Arizona State University
>> 
>> phone: 480-965-6213
>> fax: 480-965-7671
>> www: http://www.public.asu.edu/~cmbarton
>> 
>> 
>> 
>> From: Bödőcs András <bodocs at ludens.elte.hu>
>> Reply-To: <bodocs at ludens.elte.hu>
>> Date: Thu, 1 Jun 2006 22:26:32 +0200
>> To: <grassuser at grass.itc.it>
>> Subject: [GRASS-user] real distance analysis
>> 
>> Dear All,
>> 
>> I am trying to solve the following problem, maybe does somebody an idea and
>> can help me…. (thanx in advance)
>> 
>> I would like to examine from an exact point that territory, which is inside
>> an determinated distance from the exact point. BUT I don’t want to use the
>> map projected distance (=Buffer zone), but the datas of a DEM.
>> I would like to measure the „really” surface, the climbing etc. For example
>>  I need the maximum distance „cirlce”  (30km or 30 mph doeas not matter)
>> around a point, but measured in the „filed”(=DEM) not on the map
>> (=projected area).
>> Does somebody have an idea, who can I start with it?
>> 
>> Many thanx
>> Regards
>> Andras
>> 
>> Bödőcs András
>> ELTE Institute of Archaeology
>> 1088 Budapest, Múzeum krt 4/B.
>> Hungary
>> T: +36-1-411-65-54,4855200/2916
>> F: +36-1-411-65-53
> 
> An example calculation (minus the multiplication by resolution) of distance
> from trail to points of interest, via a slope cost map here:
> 
> http://169.237.35.250/~dylan/temp/r.cost_example.png
> 
> This will be part of the GRASS talk at the Where 2.0 conference, I will be
> sure to post a link to the finished presentation.
> 
> Cheers,
> 
> -- 
> Dylan Beaudette
> Soils and Biogeochemistry Graduate Group
> University of California at Davis
> 530.754.7341
> 
>