[GRASS-dev] default for r.walk

[Helena Mitasova]

I opened the code and it has it right in header:

TOTAL COST = [(WALKING ENERGY ) + (LAMBDA*FRICTION)]

maybe this is how it should go into the man page

Helena




On Oct 10, 2008, at 2:21 PM, Michael Barton wrote:

> 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)?
>
> Thanks
> Michael
>