[GRASS-user] How to assign costs to nodes using v.net.distance
Markus Metz
markus.metz.giswork at gmail.com
Tue Apr 2 07:17:41 PDT 2013
On Mon, Apr 1, 2013 at 6:20 PM, דור פרידמן <dof1985 at gmail.com> wrote:
> Thanks Markus.
>
> I will appreciate if you could direct me to the place I can ask for an
> improvement of the v.net.distance tool.
https://trac.osgeo.org/grass/
>
> Regarding to the current analysis, I have though of two solutions and would
> like to get your (and all others) idea about it:
>
> Follow Markus's original suggestion to perform the analysis using
> v.net.allpairs
That was Moritz.
> 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.
In this case, don't assign costs to nodes. The attribute table of the
output of v.net.distance includes the category of the nearest 'to'
node. You can then add a new column to the table and add node costs to
the reported distance for each 'to' node separately.
Node costs are only considered when a node is crossed, not when a node
is reached: pass through the gate vs. arrive at the gate. I understand
that you would like to give different preferences to destination nodes
which is a different problem and would require an additional option to
the module.
First of all, v.net.distance needs to be updated to consider node
costs in general, and also to consider backward travelling costs for
arcs. This applies also to some other of the new v.net.* modules.
Markus M
>
> 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
>> >> >
>> >
>> >
More information about the grass-user
mailing list