[GRASS-user] v.net.path algorithm problem

[schorschli]

Hi,

I'm using v.net.path in a simple example:

http://n2.nabble.com/file/n4789540/Network.png 
http://n2.nabble.com/file/n4789540/Network.png Network.png 

In my example I calculate the shortest path from all green dots (101, 102,
103) to all grey squares (1, 2, 3,...).The nodes are piped in with a
textfile:

1 101 1
2 101 2
3 101 3
4 101 4
5 101 5
6 101 6
7 101 7
8 101 8
9 101 9
10 101 10
11 101 11
12 102 1
13 102 2
14 102 3
15 102 4
16 102 5
...

It seems to me, that the algorithm has some problems. It can not find a path
for all combinations. I get the following warning:


WARNING: Point with category [7] is not reachable from point with category
         [102]
WARNING: Point with category [8] is not reachable from point with category
         [102]
WARNING: Point with category [9] is not reachable from point with category
         [102]
WARNING: Point with category [10] is not reachable from point with category
         [102]
WARNING: Point with category [11] is not reachable from point with category
         [102]
WARNING: 5 destination(s) unreachable (including points out of threshold)


The strange thing is, that after inserting an additional node combination
(999 101 1) twice into the textfile around the prolematic points, the paths
can be generated without warnings or errors.  
So the unproblematic textfile looks like this:

...
15 102 4
16 102 5
17 102 6
999 101 1
18 102 7
19 102 8
999 101 1
20 102 9
21 102 10
22 102 11
23 103 1
24 103 2
...

Also calculating only a single problematic path (e.g 18 102 7) is working
fine.


Does anyone of you know, what could cause this strange behaviour? How does
the order of the nodes influence the algorithm?

Greetings Schorschli


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