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

[דור פרידמן]

Hi Markus,

I was very surprised to read your comment about v.net.distance since the
manual indicates the following:

> "v.net.distance - Computes shortest distance via the network between the
> given sets of features.
> Finds the shortest paths from each 'from' point to the nearest 'to'
> feature and various information about this relation are uploaded to the
> attribute table"
>

Is it possible that you had a mistake, or is it that the manual is
incorrect?
Is the manual *is* correct? How can I assign costs to the destination nodes
to receive the "lowest cost" (shortest) path from each origin node to the
nearest (cheapest) target node?


Best,

Dor


2013/3/29 Markus Metz <markus.metz.giswork at gmail.com>

> 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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> > grass-user at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-user
> >
>
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