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.
Hi Bas,
maybe this is helpful:
http://mpa.itc.it/corso_dit2004/grass04_4_vector_network_neteler.pdf
(800kb)
to see how to connect points to the network. Probably there
are still nodes missing?
Markus
On Fri, Mar 25, 2005 at 01:17:23PM +0200, Bas Vanmeulebrouk wrote:
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.
--
Markus Neteler <neteler itc it> http://mpa.itc.it
ITC-irst - Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18 - 38050 Povo (Trento), Italy
Bas Vanmeulebrouk wrote:
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
Which tools? Should be tool=snap,break threshold=x.
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.
There is probably still some gap in the network, try to find it using d.path, then decide appropriate clean tool.
Radim
Kind regards,
Bas Vanmeulebrouk.