Re: [Geotools-gt2-users] Reg AStarShortestPathFinder in Geotools

Harshad S Sun, 02 Oct 2011 22:07:14 -0700

Hi,

I am using the 'FeatureGraphGenerator' to store all my features(which in my case are all linesegments). Post this, I use the 'getGraph()' function to get the graph. Then, I provide this graph, the source node and dest node(both are objects of BasicXYNode class) to the AStar function. Am i doing it correctly?
My primary doubt is if the nodes in the derived graph will be simple X,Y points or something else. Please clarify.

Thank You.
Harshad Shrikhande
Researcher R&D
TCS Innovations Infra Lab, Chennai
Tata Consultancy Services
Cell:- 7200605821
Mailto: harsha...@tcs.com
Website: http://www.tcs.com
____________________________________________
Experience certainty. IT Services
Business Solutions
Outsourcing
____________________________________________

-----Jody Garnett <jody.garn...@gmail.com> wrote: -----

To: Harshad S <harsha...@tcs.com>
From: Jody Garnett <jody.garn...@gmail.com>
Date: 09/30/2011 06:39PM
cc: geotools-gt2-users@lists.sourceforge.net
Subject: Re: [Geotools-gt2-users] Reg AStarShortestPathFinder in Geotools

I think you (when you supply the generator) get to choose what to store where.

* The graph is just a data structure; if you look at the example of the docs you can see the edgeWeighter accessing the edge to get the associated Feature.
* If you were making a graph out of polygons (with the relationship touches) it would make more sense to store the feature on the Nodes.

Note: It is very difficult to get a quality dataset that can be used for navigation; so disconnected graphs are pretty common (and a good way to perform QA on your dataset).

There are two implementations of LineGraphGenerator which one are you using?

The BasicLineGraphGenerator has the following:

public Graphable add(Object obj) {
LineSegment line = (LineSegment)obj;
Coordinate c;
Node n1, n2;

//check first coordinate
c = line.p0;
if ((n1 = (Node)m_coord2node.get(c)) == null) {
//first time coordinate seen, create node for it
n1 = getGraphBuilder().buildNode();

//set underlying object to coordinate
//n1.setObject(c);
setObject(n1, c);

getGraphBuilder().addNode(n1);
m_coord2node.put(c,n1);
}

//check second coordinate
c = line.p1;
if ((n2 = (Node)m_coord2node.get(c)) == null) {
//first time coordinate seen, create node for it
n2 = getGraphBuilder().buildNode();

//set underlying object to coordiante
//n2.setObject(c);
setObject(n2,c);

getGraphBuilder().addNode(n2);
m_coord2node.put(c,n2);
}

//build the edge setting underlying object to line
Edge e = getGraphBuilder().buildEdge(n1,n2);
//e.setObject(line);
setObject(e, line);

getGraphBuilder().addEdge(e);

//return the created edge
return(e);
}

You can see that setObject( n1, c) is called ... does the source code offer enough clarification for you?
--
Jody Garnett

On Friday, 30 September 2011 at 9:37 PM, Harshad S wrote:

Hi,

        Once the graph is formed as a line network from the shapefile, what is stored exactly in a Node which we obtain from the 'getNodes()' function. I am guessing the 'Node' will store the X,Y coordinates of a point. Can anyone provide some clarification on this because irrespective of which 2 points I select, they always seem to be disconnected on the graph. Please suggest.

Thank You.
Harshad Shrikhande
Researcher R&D
TCS Innovations Infra Lab, Chennai
Tata Consultancy Services
Cell:- 7200605821
Mailto: harsha...@tcs.com
Website: http://www.tcs.com
____________________________________________
Experience certainty.     IT Services
               Business Solutions
               Outsourcing
____________________________________________

-----Harshad S/TVM/TCS wrote: -----
To: Harshad S/TVM/TCS
From: Harshad S/TVM/TCS
Date: 09/30/2011 03:49PM
cc: geotools-gt2-users@lists.sourceforge.net
Subject: Re: [Geotools-gt2-users] Reg AStarShortestPathFinder in Geotools

Hi,

         I guess if this is because the last node in the path is not the same as the first node. Is this a bug with the graph or I am missing something.

Thank You.
Harshad Shrikhande
Researcher R&D
TCS Innovations Infra Lab, Chennai
Tata Consultancy Services
Cell:- 7200605821
Mailto: harsha...@tcs.com
Website: http://www.tcs.com
____________________________________________
Experience certainty.     IT Services
               Business Solutions
               Outsourcing
____________________________________________

-----Harshad S wrote: -----
To: geotools-gt2-users@lists.sourceforge.net
From: Harshad S <harsha...@tcs.com>
Date: 09/30/2011 02:22PM
Subject: [Geotools-gt2-users] Reg AStarShortestPathFinder in Geotools

Hey folks ,

             I just needed to confirm one thing about 'AStarShortestPathFinder' class and its functions .   I have a graph and I run the following code on it .

          1) AStarShortestPathFinder astar = new AStarShortestPathFinder(graph, source, dest, afuncs)

          2) astar.calculate()    ( I am assuming the path gets stored in astar)

          3) Path p = astar.getPath();

           For one of the shapefiles that I am using, the graph is constructed with all the nodes. But, there is an error that comes up in the 3rd line saying that 'The path doesn't begin correctly'.

             Please suggest a fix for this .

Thank You.
Harshad Shrikhande
Researcher R&D
TCS Innovations Infra Lab, Chennai
Tata Consultancy Services
Cell:- 7200605821
Mailto: harsha...@tcs.com
Website: http://www.tcs.com
____________________________________________
Experience certainty.     IT Services
               Business Solutions
               Outsourcing
____________________________________________
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Re: [Geotools-gt2-users] Reg AStarShortestPathFinder in Geotools

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