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<TITLE>Re: [GRASS-user] real distance analysis</TITLE>
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<FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>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. <BR>
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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.<BR>
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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.<BR>
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Michael<BR>
__________________________________________<BR>
Michael Barton, Professor of Anthropology<BR>
School of Human Evolution & Social Change <BR>
Center for Social Dynamics and Complexity<BR>
Arizona State University<BR>
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phone: 480-965-6213<BR>
fax: 480-965-7671<BR>
www: <a href="http://www.public.asu.edu/~cmbarton">http://www.public.asu.edu/~cmbarton</a> <BR>
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<HR ALIGN=CENTER SIZE="3" WIDTH="95%"><B>From: </B>Bödőcs András <bodocs@ludens.elte.hu><BR>
<B>Reply-To: </B><bodocs@ludens.elte.hu><BR>
<B>Date: </B>Thu, 1 Jun 2006 22:26:32 +0200<BR>
<B>To: </B><grassuser@grass.itc.it><BR>
<B>Subject: </B>[GRASS-user] real distance analysis<BR>
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</SPAN></FONT><FONT SIZE="4"><FONT FACE="Arial"><SPAN STYLE='font-size:13.0px'>Dear All,<BR>
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I am trying to solve the following problem, maybe does somebody an idea and can help me…. (thanx in advance)<BR>
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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.<BR>
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).<BR>
Does somebody have an idea, who can I start with it?<BR>
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Many thanx<BR>
Regards<BR>
Andras<BR>
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</SPAN></FONT></FONT><FONT SIZE="5"><FONT FACE="Times New Roman"><SPAN STYLE='font-size:16.0px'>Bödőcs András<BR>
ELTE Institute of Archaeology<BR>
1088 Budapest, Múzeum krt 4/B.<BR>
Hungary<BR>
T: +36-1-411-65-54,4855200/2916<BR>
F: +36-1-411-65-53<BR>
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