RIF: R: [postgis-users] routing and network analysis
Robin Chauhan
robin.chauhan at gmail.com
Thu Jan 20 13:20:57 PST 2005
In case anyone is not aware, GRASS is open source and now has basic
network analysis capabilities:
http://grass.baylor.edu/grass57/tutorial/network.html#shortestpath
It seems there is (some level of) connectivity between GRASS and
PostGIS. The network analysis is done using DGLib (document suggests
its not very mature, but the document is old):
http://www.grass.itc.it/dglib/
I asked for other approaches because I wanted to have more background
before deciding on one. (I might try the GRASS mailing lists next.)
Thanks,
-Robin Chauhan
Justin Deoliveira <jdeolive at refractions.net> wrote:
> Date: Thu, 20 Jan 2005 11:04:38 -0800
> From: Justin Deoliveira <jdeolive at refractions.net>
> Subject: Re: RIF: R: [postgis-users] routing and network analysis
> To: "Paolo PP. Pulli" <Ppulli at edinform.it>, PostGIS Users Discussion
> <postgis-users at postgis.refractions.net>
> Message-ID: <41F000C6.7050701 at refractions.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Does the routing have to be done in real time? on-demand? etc.
>
> If not you could calculate all paths, store them in postgis and then
> just publish them out with a mapserver layer.
>
> If you do have such a requirement then you will need a middle layer of
> processing that will do the network analysis.
>
> The ideal solution would be to have postgis do the network analysis. I
> have thought about how this could be accomlished, and at first glance it
> is not a trivial amount of work. It involves getting down and dirty with
> postgres and developing a new access method.
>
> Justin
>
> Paolo PP. Pulli wrote:
> > Many thanks for your code. I'm going to try it.
> >
> > Are you never develop a web gis with shorter path functionality? Have you any idea?
> > I'm explain my self:
> > Data in PostGis
> > Webserver Apache/Mapserver
> > Language Php or other
> >
> > Thanks
> > Paolo
> >
> >
> > -----Messaggio originale-----
> > Da: Justin Deoliveira [mailto:jdeolive at refractions.net]
> > Inviato: mer 19/01/2005 18.17
> > A: Paolo PP. Pulli
> > Cc:
> > Oggetto: Re: R: [postgis-users] routing and network analysis
> >
> >
> >
> > Hi Paulo, Here is some sample code to solve the routing problem, as for
> > data, just run it on any line string data that you have. As for thread
> > safety, the frame work is not thread safe. If you have any more
> > questions please let me know.
> >
> > Justin
> >
> > //read a feature collection of LineString geomtries
> > FeatureCollection fc = ...
> >
> > //create a graph generator
> > LineStringFeatureGraphGenerator g = new LineStringFeatureGraphGenerator();
> >
> > //add all the features to the graph
> > for (Iterator itr = fc.iterator(); itr.hasNext();) g.add(itr.next());
> >
> > //get any node in the graph, we will choose the first
> > Node source = (Node)g.getGraph().getNodes().iterator().next();
> >
> > //create a cost function for the edges of the graph
> > DijkstraIterator.EdgeWeighter ew = new DijsktraIterator.EdgeWeighter() {
> >
> > public double getWeight(Edge e) {
> > //just return the length of the line
> > Feature f = (Feature)e.getObject();
> > LineString l = (LineString)f.getGeometry();
> > return l.getLength();
> > }
> > };
> >
> >
> > //create a shortest path finder
> > DijsktraShortestPathFinder p = new
> > DijsktraShortestPathFinder(g.getGraph(),source,ew);
> >
> > //for each other node in the graph find the shortest path
> > for (Iterator itr = g.getGraph().getNodes().iterator(); itr.hasNext();) {
> > Node n = (Node)itr.next();
> > if (n.equals(source)) continue;
> >
> > Path p = p.getPath(n);
> > }
> >
> >
> >
> > Paolo PP. Pulli wrote:
> > >
> > >
> > >>Hi Robin,
> > >>
> > >>I have built a network building/walking framework that is precisley
> > >
> > > for
> > >
> > >>solving problems like the one you describe. It is part of the geotools
> > >>project, in a module called "graph". See http://www.geotools.org/
> > >>
> > >>The way it works is you pull all of the relevant geometries (in your
> > >>case road linestrings) out of the database and build a graph. Then
> > >
> > > walk
> > >
> > >>the graph to answer questions like give me the shortest path from node
> > >
> > > 1
> > >
> > >>to node 2.
> > >>
> > >>The main drawback is that the entire graph has to be stored in main
> > >>memory. So if you are working with mass amounts of data then you might
> > >>need something a bit more elegant.
> > >>
> > >>Let me know if you are interested and I can send you some sample code.
> > >
> > >
> > > I'm apologize.
> > > I'm very interesting about routing and network analysis.
> > > Could you send me your sample code (with data!?), please.
> > >
> > >
> > >>>a) I have access to road network data. I've heard the new GRASS can
> > >>>be used to do network analysis. anyone heard if it would be
> > >
> > > promising
> > >
> > >>>in combination with postGIS, or could suggest another package?
> > >
> > > Yes, Grass is powerful to do network analysis but, for my knowledge and
> > > my needed, is not thread safe therefore it's not suitable for example in
> > > webGis and it is to prefer(?) PostGIS sql-procedure (any idea on it?)
> > >
> > >
> > >>>b) as an alternative, can anyone suggest or point to an efficient
> > >>>approach for computing the shortest path between two points which
> > >
> > > does
> > >
> > >>>not go through, say, water polygons?
> > >
> > > Justin, your solution solve this question?
> > >
> > > Thanks
> > > Paolo
> > > ICQ: 254248one23
> > >
> > > PS.
> > > I'm just download GeoTools and I'm going to study it!
> > >
> > > _______________________________________________
> > > postgis-users mailing list
> > > postgis-users at postgis.refractions.net
> > > http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> > --
> > Justin Deoliveira
> > Refractions Research Inc.
> > jdeolive at refractions.net
> > (250) 885-4387
> >
> >
>
> --
> Justin Deoliveira
> Refractions Research Inc.
> jdeolive at refractions.net
> (250) 885-4387
>
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