Yes, the relationship among features is customizable. For linestrings,
the relationship is sharing an endpoint. This is a natural relationship
as the nodes in your graph will correspond to the nodes in your road
network. The downfall with this approach is that if your roadnetwork is
not properly noded, then their will be no relationship in the graph.
As for routing, you are correct, the structure of the graph will dictate
the routing. However, it is mostly dependent on how you define "weights"
on edges in the graph. The graph package contains a number of pathing
algorithms, the most populate being dijkstra. For linestrings the weight
defaults to the length of the line, however this could be easily
extended to use an attribute on the feature (speed limit perhaps).
Hope this helps, if you supply me with more information about your
problem I can better direct you on how to implement it.
Justin
jgarnett wrote:
The graphing package is not specific to roads. Indeed the "relationship"
is up to you to define. You could define it as "touches" with JTS, or
simply compare linestring endpoints, if you need it to inspect the
intersections (and if they are built or not) you can do that as well.
Justin is the developer on this one (for both JUMP and GeoTools) - and
should be able to answer with the exact classes you need to implement.
JOdy
Jase wrote:
Hi Satya,
Thanks for the heads on. I did more reading on graphing and have a
better understanding now on some of the concepts.My intention is to
load the graph once into memory and route from there. It has
approximately 15000 features.
Before I dwell further, I've got a question. I looked through the
LineStringGraphGenerator class on how the graph network is built and
have some questions.
I would like to know if the graph network takes into consideration
road intersections during built? I'm asking this as I'm thinking it
would affect routing as the shortest path might be taking a turn into
another road before the road ends rather than travesing the entire
road. Correct me if I'm wrong.
Thanks
On 9 Nov 2005 07:49:56 -0000, *Satyanarayana Murty Pindiproli*
<[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>
wrote:
Hi jason,
Considering your Queries I think you have just begun the Work.
here is Somehting that i can Help you out with.
Do U want to Load the Graph Network at all times and Create a
route for
Points A and B ?
This is the most Optimum way of Doing that cause ur Data Change
would be minimum and Loading the graph in memory( provided its not
so huge ) would remove the overhead of Data reading and Graph
Creating Everythime for every request for a Route.
Go through the Pathgenerators class which Allow you to find a Path
based on Constraints.Constrains can be Distance or Customized on
Various Parameters based on an interface. I think u will get
better idea of this when you look at the API's provided.
This Shoudl Solve your problem.Implementation of Routing
Algorithms is also there in geo-tools like Dijkstra's et all
..making your job more simpler.
Am Providing a Sample Code for ur Understanding :
Graph g = lsg.getGraph(); // ge tthe Graph from the Data. or from
ur global variable.
MEdgeWeighterImpl mwi = new MEdgeWeighterImpl(); //Cost based
Implementaion that u need to refer to from the API depending on
your needs ..Someitmes if Trafic data present then even that is to
be Consiered ..et all..
mwi.setEdgeCostMap(hmEdgeCost);
DijkstraShortestPathFinder dspf = new
DijkstraShortestPathFinder(g, srcNode, mwi);
dspf.calculate();
Path p = dspf.getPath(destNode);
if (p != null) {
return p.getEdges();
// actual Rooute Edges .
} else
{
return null;
//No Route found Case .
}
Good Luck Dude ..happy Routing .
Bye.
On Tue, 08 Nov 2005 Jase wrote :
>My current research involves using open source libraries to create
an online
>vehicle routing system for taxis or any vehicles as a matter of
fact. I have
>done some research and identified Geotools & Geoserver as the best
libraries
>for building such a system. After going through the mailing list,
it seems
>that the question I am going to ask is quite a common one afterall
but there
>is a lack of solution.
>
>I have a PostGIS database of roads in LineStrings. After
following the
>tutorials on graphing, I have managed to create the graph network
using the
>LineStringGraphGenerator. What I did was to load the entire
PostGIS database
>into the linestringgraphgenerator the and the output that I have
obtained
>using getGraph() is as follows:-
>
>V = [14042, 3162, 2002, 12968 … ]
>E = [20301 (6097, 20300) … ]
>Is it right to build the entire line network first before
traversing even
>though I do not know the points I would like to use?
>
>I understand I should traverse the graph but I am a bit stuck as
to how I
>should proceed. Say, if I would like to route from Point A to
Point B, how
>would I do that? As a matter of fact, I would like to locate the
closest
>vehicle in a particular area and find the quickest route to that
point. I
>see that there are many classes that are in the org.geotools.graph
package
>but I'm unsure on how to proceed.
>
>I appreciate if anyone can offer an insight to this.
>
>Thanks
>
>Jason
<http://adworks.rediff.com/cgi-bin/AdWorks/sigclick.cgi/www.rediff.com/signature-home.htm/[EMAIL PROTECTED]>
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