[GRASS-dev] Re: r.walk, r.cost & r.drain patches posted

[Michael Barton]

On Jan 6, 2009, at 4:03 PM, Colin Nielsen wrote:

>>
>> One fairly serious problem is that the backlinked paths are  
>> discontinuous,
>> with lots of gaps; the non-backlinked paths are continuous without  
>> gaps.
>
> I assume you used the "knight's move" option? I agree the
> discontinuous paths may cause some problems, especially when trying to
> vectorize the paths. However, the gaps are legitimate in the sense
> that they were created by the knight's move which makes small jumps
> for the sake of more accurate directionality (you can see this if you
> look closely at drain_backlinkvsnobacklink.png). Unlike the old
> r.drain function, the updated r.drain only draws the cells actually
> used in the cost algorithm.
>
> I'm not sure how we can overcome the vectorization problem though,
> especially since you need vectorization to determine the overall
> distance traveled.
>
>>
>> I've posted screenshots of the tests at:
>> http://www.public.asu.edu/~cmbarton/files/grass_cost/
>
> Thanks for the tests and the screenshots.
>
> -Colin

Hi Colin,

Thanks for the updates. I'll give them a try. While I understand the  
reason for the gaps in the paths now, I think that it is important to  
find some way to get rid of them. That is, there needs to be some  
algorithm that will 'connect the dots' of knights move jumps. These  
are supposed to be paths traversing a landscape. Even without  
vectorizing, the cell accumulation values will be inaccurate if cells  
are skipped in a path from point A to point B.

Michael