[Geotools-gt2-users] Graph Traversal in GeoTools 2.1.x

[Suneet K. <sun...@ho...>]

Hi.

I've been trying to get the Graph Traversal algorithm to work with a =
shapefile of a road network. This is my first experience with GeoTools =
and have quite a few questions.

The graph examples in the tutorials do not work with the 2.1.M4 version =
of GeoTools.

So i tried to modify the example code but was not very successful. Here =
is the code and some output

1. the conversion of Multilinestring to Linestring.
   FeatureCollection fc =3D featureSource.getFeatures().collection();
   LineStringGraphGenerator lgb =3D new LineStringGraphGenerator();

   FeatureIterator f =3D fc.features();
   while (f.hasNext()) {
    Feature feature =3D f.next();
    GeometryCollectionIterator gci =3D new =
GeometryCollectionIterator((GeometryCollection) =
feature.getDefaultGeometry());

        gci.next(); // since the first iterator element is the original =
MULTILINESTRING feature itself
    while (gci.hasNext()) {
     Geometry geo =3D (Geometry) gci.next();
     System.out.println("\t" + geo);
     lgb.add(geo);
    }
   }
   Graph g =3D lgb.getGraph();

Partial Output :=20
MULTILINESTRING ((324939 672627, 324944 672561, 324899 672481))

LINESTRING (324939 672627, 324944 672561, 324899 672481)

Is it possible to modify the codebase to accept MultiLineString's while =
building the  as well (although I am not sure of how to go about doing =
this). I found several users having similar problems having to deal with =
conversion of MULTILINESTRING TO LINESTRING.

2. The Graph Traversal code

   Graph g =3D lgb.getGraph();
   System.out.println(g);

   class PrintVisitor implements GraphVisitor {
    public int visit(Graphable element) {
     System.out.println(element);
     return GraphTraversal.CONTINUE;
    }
   }
   PrintVisitor pv =3D new PrintVisitor();
   SimpleGraphWalker sgv =3D new SimpleGraphWalker(pv);
   BasicGraphTraversal bgt =3D new BasicGraphTraversal(g, sgv,
     new BreadthFirstIterator());
   bgt.traverse();      //I get a java.lang.NullPointerException here

Partial Output :=20

V=3D[103, 355, 661, 334, 219, 296,............
E=3D[746 (678,700), 92 (90,91), 19...........


Based on the two outputs shown I was wondering how the graphs get built =
as there seems to be completely different values than the =
Multilinestrings values when comparing the two outputs, assuming that =
the code works as I expect it to.

What I would like to be able to do is take a ShapeFile road network and =
have a graph structure in memory that can be acessed easily. I would =
also like to experiment with weights/cost functions and traversal =
algorithms. I have seen some mails in the lists referring to code being =
mailed by Marc Andre and Justin but these were mailed as attachments and =
are not accessible in the mailing lists.=20

Another problem is that I tried working the same examples with the =
GeoTools 2.1.RC1 before trying it with 2.1.M4 and noticed that the API's =
are constantly eveolving. In that case I feel I should be using the =
latest version to ensure not having to rewrite code. Is there anyone who =
has worked the graph examples with the latest version. (Was also =
wondering why some of the class method calls in 2.1.RC1 return Object.

Lastly I noticed some demo code and a report of which demos failed. Is =
it possible to start including the graph demos as part of the build. =
Also is the only way to get API documentation for versions like the =
2.1.M5 by building from the source.

This is work towards a Master's thesis. Any help and example code would =
be greatly appreciated in the area of graph traversal, shortest path =
algorithms and cost functions.=20

Thanks in advance

Suneet Kamath