[GRASS-dev] default for r.walk
michael.barton at asu.edu
Fri Oct 10 14:21:14 EDT 2008
I've been emailing with Helena to try to understand exactly how lambda
and a friction surface interacts with information about topography
(extracted from a DEM) in r.walk. It seems a good idea to put this
back on the list. Perhaps I'm the only one a little in the dark, but
maybe it can help others.
On Oct 10, 2008, at 10:40 AM, Helena Mitasova wrote:
>> To clarify for me, is it
>> total cost = (movement time cost + lambda) * friction costs
>> total cost = movement time cost + (lambda * friction costs)
> I did not look into the code but if there are no brackets in the
> code, this second interpretation applies.
For anyone familiar with the code, is this the case? If so, should I
be thinking in time units for creating a friction map? If I remember,
r.walk normally outputs in seconds to traverse the cell.
So, should the friction map be in additional seconds to traverse the
cell? Or is friction a weighting factor (i.e., multiplicative rather
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