I managed to create a DirectedGraph using the
DirectedLineStringGraphGenerator and FeatureGraphGenerator as follows:
public static DirectedGraph getDirectedGraph(SimpleFeatureCollection
features) {
final GeometryOperations geomOps = new GeometryOperations();
final DirectedLineStringGraphGenerator lineStrGen = new
DirectedLineStringGraphGenerator();
SimpleFeatureIterator iterator = merged_features.features();
try {
while(iterator.hasNext()) {
SimpleFeature feature = iterator.next();
String bidirectional =
feature.getAttribute("TYPE").toString();
Coordinate[] featureCoords =
((Geometry)feature.getDefaultGeometry()).getCoordinates();
Coordinate[] coords;
Geometry directedLineSegment;
DirectedEdge e;
//build edge based on feature type of segment
if (bidirectional == "No") {
//create new lineString segment to add as directed edge
coords = new Coordinate[]{featureCoords[1],
featureCoords[0]};
directedLineSegment =
geomOps.coordinatesToLineGeometry(coords);
e = (DirectedEdge)lineStrGen.add(directedLineSegment);
e.setObject(feature);
if
(!((Geometry)e.getInNode().getObject()).equals(geomOps.coordinateToPointGeometry(coords[0]))
||
!((Geometry)e.getOutNode().getObject()).equals(geomOps.coordinateToPointGeometry(coords[1])))
{
System.err.println("Slope segment " +
((SimpleFeature)e.getObject()).getAttribute("r_id") + " was falsely entered
in directed graph");
}
} else {
coords = new Coordinate[]{featureCoords[1],
featureCoords[0]};
directedLineSegment =
geomOps.coordinatesToLineGeometry(coords);
e = (DirectedEdge)lineStrGen.add(directedLineSegment);
e.setObject((SimpleFeature) feature);
coords = new Coordinate[]{featureCoords[0],
featureCoords[1]};
directedLineSegment =
geomOps.coordinatesToLineGeometry(coords);
e = (DirectedEdge)lineStrGen.add(directedLineSegment);
e.setObject((SimpleFeature) feature);
}
catch (Exception e) {
Logger.getLogger(Logger.GLOBAL_LOGGER_NAME).log(Level.SEVERE, "Directed
graph generation aborted: " + e);
}
finally {
iterator.close();
}
DirectedGraph graph = (DirectedGraph)featureGen.getGraph();
return graph;
}
I realised that using a FeatureGraphGenerator to wrap the
DirectedLineStringGraphGenerator and adding the features through the
FeatureGraphGenerator like this : featureGen.add(feature)
won't result to directed edges somehow.
After having created the Directed graph I want to query some paths using the
Dijkstra algorithm. To force the path finder to use a
DirectedDijkstraIterator I realised I had to explicitly instantiate a
PathFinder by providing a DirectedDijkstraIterator in the constructor
parameters and set the source directly in the iterator object, as such:
DirectedDijkstraIterator iterator = new
DirectedDijkstraIterator(new
DijkstraIterator.EdgeWeighter() {
public double getWeight(Edge e) {
SimpleFeature feature = (SimpleFeature) e.getObject();
LineString geometry = (LineString)
feature.getDefaultGeometry();
return geometry.getLength();
}
});
iterator.setSource(start);
DijkstraShortestPathFinder pf = new
DijkstraShortestPathFinder(directedGraph, iterator);
pf.calculate();
Path shortestPath = pf.getPath( destination );
Any other alternative I tried failed. This way it seems that the
DijkstraShortestPathFinder is providing the right results.
Please correct, if I have done something wrong.
Regards,
Thomas
thKous wrote
> Hi everybody,
>
> I have a FeatureCollection loaded from a shapefile and create an
> undirected Graph out of it, using the code provided in:
> http://docs.geotools.org/stable/userguide.old/extension/graph/index.html
> <http://docs.geotools.org/stable/userguide.old/extension/graph/index.html>
>
> To investigate if my Graph is connected I use a DijkstraShortestPathFinder
> as shown in the same link to fetch a path to each other node from a
> hand-picked start node. At the same time I can confirm that all nodes in
> my Graph have been visited.
>
> The structure of my data though is so that some features can only be
> traversed in one direction and for the DijkstraShortestPathFinder to
> fetch reasonable results I need to create a directed Graph from my
> FeatureCollection based on an attribute value in each feature.
>
> Is there any example to provide as help on how to create a directed graph?
>
> Thanks,
> Thomas
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