[GRASS-dev] default for r.walk

Michael Barton 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
>> OR
>> 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  
than additive)?


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