[GRASSLIST:6253] Network analysis with GRASS GIS

Bas Vanmeulebrouk bvanmeul at ebe.uct.ac.za
Fri Mar 25 06:17:23 EST 2005


Hi list,

I am new to GRASS GIS. I want to use it for some network analysis. I want to
calculate the minimum distance a public health worker has to travel to visit
all of his or her patients. I have found a very nice tutorial on this
subject (http://www.grass.itc.it/grass57/tutorial/network.html), and when I
follow the steps in this tutorial, I get the results I would expect. The
only problem is, I can't get all centers (the point which be visited by the
public health workers) to connect to the road network I am using. I use the
following steps, as in the tutorial:
- I have created a map with the links between the centers and the network
using v.distance
- I have combined the network, the links between the network and the centers
and the centers using v.patch
- I have built topology using v.clean

When I try v.net.salesman or v.net.steiner, I get an error "ERROR
Destination node <x> is unreachable from node <y>". If I leave out the
center at node y, the calculation is no problem. But I would like to include
node y as well of course. The v.net.alloc and v.net.iso comamnds provide
similar results: node y cannot be reached and won't be taken into account in
the analysis. 

Topology seems correct: there is a node where the links and the network
meet. I have been experimenting with the thresh parameter of v.clean,
without the desired result. Does anyone have a clue as to what I am doing
wrong? I am using GRASS GIS 6.0 on Debian. Any help will be greatly
appreciated.

Kind regards,

Bas Vanmeulebrouk. 




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