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

[Richard Chirgwin]

> ------------------------------
>
> Message: 2
> Date: Wed, 24 Mar 2010 15:34:28 +0100
> From: Markus Neteler <neteler at osgeo.org>
> Subject: Re: [GRASS-user] v.net.path algorithm problem
> To: schorschli <matthiasoswald at hotmail.com>
> Cc: GRASS user list <grass-user at lists.osgeo.org>
> Message-ID:
> 	<86782b611003240734q564f0210od118f99b05adb80f at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> On Wed, Mar 24, 2010 at 8:45 AM, schorschli <matthiasoswald at hotmail.com> wrote:
>   
>> Hi,
>>
>> I'm using v.net.path in a simple example:
>>
>> http://n2.nabble.com/file/n4789540/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)
>>     
>
> Perhaps some nodes are missing? I have success in the past by applying
> http://grass.osgeo.org/grass64/manuals/html64_user/v.net.html
>
> to the map.
>
> Markus
>
>
>   
Agreed, Markus. I get caught by this from time to time - it can drive me 
nuts on a bad day.

Matthias - if you zoom very closely to any of the categories in the 
error report, do you see a lack of connection between those points and 
the network lines?

Richard Chirgwin