[GRASS-user] How to assign costs to nodes using v.net.distance

[Markus Metz]

On Thu, Mar 28, 2013 at 2:52 PM, דור פרידמן <dof1985 at gmail.com> wrote:
> Hello all,
>
> After I've got my v.net.distance up and running I have to adjust my analysis
> method to the software's capabilities. Basically, I have a 3 layered
> network: myroads_net2 which contain layers as follow:
>
> Layer 1: Arch (roads)
> Layer 2: Points (Landfills - destinations)
> Layer 3: Points (Settlements - source)
>
> As one might understood I'm trying to calculate the lowest cost route
> between each settlement (layer 3) to each landfill (layer 2).

I think v.net.distance is the wrong module for this task because it
finds for each 'from' feature the nearest 'to' feature and not the
shortest path from each 'from' feature to each 'to' feature. Actually,
I don't think any of the v.net.* modules does exactly that. You could
file a ticket for enhancement to request such a module.

> Roads' costs
> are constant, which now set to 1 (currency per distance unit - I guess that
> it is meter). I would like to include a cost for landfill (gate fee) which
> will be measured with the same currency. MY attempt to use ncolumn (cost for
> nodes) didn't go well. I have opened a new column (double precision) in
> layer 2 and named it gatefee. I have assigned 0 to all cats, except cat=3
> which I have assigned with 60. My expectation was that at least some of the
> settlements that were allocated to cat=3 on layer 2 will be allocated to
> another one. However after running v.net.distance again with ncolumn=gatefee
> I have found out that more settlements were allocated to cat=3 of layer 2.

If I understand the code of v.net.distance correctly, node costs are ignored.

Markus M

>
> Did I misused that option? I can't find any guide to how to use it in the
> manual or tutorials and will appreciate an explanation or a reference to
> such guide or tutorial.
>
> Best,
>
> Dor
>
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