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

[דור פרידמן]

Thanks Markus.

It might be valuable to add an option to assign costs to the destination
nodes, either for my purpose when there is an actual gate fee that
influence the total cost (e.g. waste management, national parks and
reserves) or when the "gate fee" or nodes cost represent other factors that
influence an individual decisions, i.e. external costs that describe
socio-environmental parameters, such as: level of crime, general
maintenance, scenery, number of shops in a commercial center, hospitals
reliability and quality etc.

I will appreciate if you could direct me to the place I can ask for an
improvement of the v.net.distance tool.

Regarding to the current analysis, I have though of two solutions and would
like to get your (and all others) idea about it:


   1. Follow Markus's original suggestion to perform the analysis using
   v.net.allpairs - which will be easy to the empirical anlysis using excel,
   but more complex to create a map for the final shortest distance.
   2. Try to assign costs to the nodes that connect each arc (formed by
   v.net) to the original network. My fear is that instead of assign cost
   just to the path to the destination node, it will also include those who
   attempt to use the original network to arrive to another destination. I'm
   also not sure about how to locate the nodes I'm looking for.

Any advice?


Thanks


Dor


2013/4/1 Markus Metz <markus.metz.giswork at gmail.com>

>
>
> On Mon, Apr 1, 2013 at 10:23 AM, דור פרידמן <dof1985 at gmail.com> wrote:
> >
> > 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?
>
> I wrote:
>
> 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.
>
> From the manual:
>
> ...the table has three columns: *cat*, *tcat* and *dist* storing category
> of each *from* feature, category of the nearest *to* feature and the
> distance between them respectively.
>
> No contradiction AFAICT.
>
>
> > How can I assign costs to the destination nodes
> That does not make sense because destination nodes are usually not
> crossed. Assigning costs to nodes makes more sense for nodes between the
> start and the end node.
>
>
> > to receive the "lowest cost" (shortest) path from each origin node to
> the nearest (cheapest) target node?
>
> The shortest path for each 'from' node to the nearest 'to' node is
> included in the output map. See also the example in the manual.
>
> Markus M
>
> >
> >
> > 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
> >> >
> >> > _______________________________________________
> >> > grass-user mailing list
> >> > grass-user at lists.osgeo.org
> >> > http://lists.osgeo.org/mailman/listinfo/grass-user
> >> >
> >
> >
>
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