If you bring the patched data (nodes/terminals and arcs) into v.digit,
do you see dangling arcs (red) that might cause the network to be
disconnected? Particularly at the patched nodes?<br>
<br>
<br><br><div><span class="gmail_quote">On 8/3/07, <b class="gmail_sendername">Joseph Guillaume</b> <<a href="mailto:josephguillaume@gmail.com">josephguillaume@gmail.com</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi,
<br>
<br>I'm trying to run a travelling salesman analysis between point features
on a road map, but it tells me that two nodes are unreachable from one
another, which is a fatal error.
<br>
<br>I've successfully done this exact analysis using ARC/View, but I'm trying to find an
OSS alternative that works on Debian - and it seems GRASS is the only
software currently able to do network analyses.
<br>
<br>I patched together two ESRI shapefile datasets, following the Grass 6.0
v1.2 tutorial.
<br>I tried linking the attributes to the original datasets and tried
without linking.
<br>I tried putting the new points on both the same layer and a new layer.
<br>I tried running every single v.clean function on both the original and
patched datasets.
<br>I am certain that all the points are actually on the network.
<br>I've searched all mailing lists, reference materials, and bugtracker,
but didn't find anything explicitly related to unreachable nodes.
<br>
<br>Assuming the error message does mean that the map I am using has
segments disconnected from the rest of the network, the questions are:
<br>
<br>* How do I detect them and remove them?
<br>The node numbers given don't match the cat attribute, so I assumed they
referred to the id attribute. The two nodes referred to by id are
however connected to each other (directly) and to the main part of the
network. I suspect the node numbers therefore don't correspond to any
attribute as such, but are rather internal. In that case, how do I
identify the actual nodes/segments responsible?
<br>
<br>* Shouldn't the algorithm be tolerant of such errors anyway?
<br>I checked, and none of the relevant nodes are actually within segments I
can see are disconnected, so the analysis results should be the same if
the algorithm ignored the error... Is this perhaps because of the
heuristics used to solve this NP-hard problem? Does anyone know what
ArcView does differently?
<br>
<br>
<br>
<br>Any ideas?
<br>
<br>Cheers,
<br><span class="sg">
<br>Joseph Guillaume
<br>
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