/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2002-2008, Open Source Geospatial Foundation (OSGeo)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*/
package org.geotools.graph.path;
import org.geotools.graph.structure.Graph;
import org.geotools.graph.structure.Graphable;
import org.geotools.graph.structure.Node;
import org.geotools.graph.traverse.GraphTraversal;
import org.geotools.graph.traverse.GraphWalker;
import org.geotools.graph.traverse.basic.BasicGraphTraversal;
import org.geotools.graph.traverse.standard.AStarIterator;
import org.geotools.graph.traverse.standard.AStarIterator.AStarFunctions;
/**
* Calculates the shortest path between two nodes using the A Star algorithm
* (for details see http://en.wikipedia.org/wiki/A_star)
* @see AStarIterator
* @author Germán E. Trouillet, Francisco G. Malbrán. Universidad Nacional de Córdoba (UNC)
*
*
*
* @source $URL$
*/
public class AStarShortestPathFinder implements GraphWalker {
/** Graphs to calculate paths for **/
private Graph m_graph;
/** Graph traversal used for the A Star iteration **/
private GraphTraversal m_traversal;
/** Underling A Star iterator **/
private AStarIterator m_iterator;
/** */
private Node m_target;
/**
* Constructs a new path finder
*
* @param graph Graph where we will perform the search.
* @param source Node to calculate path from.
* @param target Node to calculate path to.
* @param weighter Associates weights with edges in the graph.
*/
public AStarShortestPathFinder (
Graph graph, Node source, Node target, AStarFunctions afuncs
) {
m_graph = graph;
m_target = target;
m_iterator = new AStarIterator(source, afuncs);
m_traversal = new BasicGraphTraversal(graph,this,m_iterator);
}
/**
* Performs the graph traversal and calculates the shortest path from
* the source node to destiny node in the graph.
*/
public void calculate() {
m_traversal.init();
m_traversal.traverse();
}
/**
*
* @see GraphWalker#visit(Graphable, GraphTraversal)
*/
public int visit(Graphable element, GraphTraversal traversal) {
if (element.equals(m_target)) {
return(GraphTraversal.STOP);
} else {
return(GraphTraversal.CONTINUE);
}
}
/**
* Returns a path <B>from</B> the target <B>to</B> the source. If the desired path is
* the opposite (from the source to the target), the <i>reverse</i> or the <i>riterator</i>
* methods from the <b>Path<b> class can be used.
*
* @see Path#riterator()
* @see Path#reverse()
*
* @return A path from the target to the source.
* @throws WrongPathException
*/
public Path getPath() throws WrongPathException {
Path path = new Path();
path.add(m_target);
Node parent = m_iterator.getParent(m_target);
while ( parent != null ) {
path.add(parent);
parent = m_iterator.getParent(parent);
}
if (!path.getLast().equals(m_iterator.getSource())) {
throw new WrongPathException("getPath: The path obtained doesn't begin correctly");
}
return(path);
}
/**
* Does nothing.
*
* @see GraphWalker#finish()
*/
public void finish() {}
}
class WrongPathException extends Exception{
String message;
public WrongPathException(String msj){
message = msj;
}
public String getMessage(){
return message;
}
}