[GRASS-user] Count points in a network between two locations

[Moritz Lennert]

On 01/02/13 19:55, Markus Metz wrote:
> On Fri, Feb 1, 2013 at 6:39 PM, Moritz Lennert
> <mlennert at club.worldonline.be>  wrote:
>> On 01/02/13 11:44, Johannes Radinger wrote:
>>>
>>> Thank you, that might work. I just realized that my permeabilities are
>>> given as probability and they are added up by a multiplication rule. Thus
>>> I don't need the sum but rather the product or at least a list of all
>>> barries
>>> between to sampling stations....
>>
>>
>> At this stage costs can only be summed AFAIK.
>>
>>
>>> thats what I tried now, v.distance to get from barriers to nearest
>>> vector lines from v.net.allpairs,
>>>    but the problem is that the v.net.allpairs lines are partly
>>> overlapping (sharing parts). So there
>>> are several barriers on partly overlapping lines, but I want to select
>>> all barriers per line category.
>>
>>
>>
>> IIUC v.net.allpairs actually creates several duplicate segments which seems
>> contrary to GRASS topology rules.
>
> GRASS topology supports overlapping lines.

Yes, but having several overlapping line segments that are actually the 
representation of the exact same path kind of seems against the idea of 
not duplicating information if not necessary.

>
>> Shouldn't these rather be represented by
>> single segments with multiple category values (like v.buffer in grass7) ?
>
> Yes, but only if the segment directions are also identical. For
> example, if backward direction costs are identical to forward
> direction costs, the path from node A to node B is a duplicate of the
> path from node B to node A, but in reverse direction.

Right, didn't think about direction here. I was more thinking about the 
situation where paths from A to B, C, D, E all have a common part before 
forking to the respective destination later on.

But I guess even for this situation overlapping lines are not so much of 
an evil to justify making this into an issue.

Moritz