[GRASSLIST:6280] Re: Network analysis with GRASS GIS

[Radim Blazek]

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.