geotools的最短路径实现
Geotools提供了一个Graph的扩展包,使用它可以实现最短路径的查找,提供的算法有Dijkstra和AStar。Api的功能非常强大,只需要提供line的features对象,即可创建graph,然后调用算法即可实现最短路径查找,权重可以自由设置,对于不懂算法的人用起来也毫不费力。
Dijkstra的使用
String filePath = "E:\\gis资料\\测试数据\\道路中心线.shp";
//读取shp数据
DataStore dataStore = readShapeFile(filePath);
SimpleFeatureSource featureSource = dataStore.getFeatureSource(dataStore.getTypeNames()[0]);
SimpleFeatureCollection simFeatureCollect =featureSource.getFeatures();
final Integer num = new Integer(0);
System.out.println("shp文件原始线的个数:" + simFeatureCollect.size());
//创建graph数据结构
Graph graph = buildGraph(simFeatureCollect);
//这里是定义权重
DijkstraIterator.EdgeWeighter weighter = new DijkstraIterator.EdgeWeighter(){
@Override
public double getWeight(Edge edge) {
//这个方法返回的值就是权重,这里使用的最简单的线的长度
//如果有路况、限速等信息,可以做的更复杂一些
SimpleFeature feature = (SimpleFeature)edge.getObject();
Geometry geometry = (Geometry)feature.getDefaultGeometry();
return geometry.getLength();
}
};
Date startT = new Date();
//初始化查找器
DijkstraShortestPathFinder pf = new DijkstraShortestPathFinder(graph,start,weighter);
pf.calculate();
//传入终点,得到最短路径
Path path = pf.getPath(destination);
Date end = new Date();
System.out.println("迪杰斯特拉算法耗时:" +(end.getTime() - startT.getTime()));
System.out.println("迪杰斯特拉算法距离:"+getPathLength(path));
System.out.println(destination.getID()+""+start.equals(destination));
//AStar算法
public static void AStarShortestPath(Graph graph,Node startNode,Node endNode){
AStarIterator.AStarFunctions aStarFunction = new AStarIterator.AStarFunctions(endNode){
@Override
public double cost(AStarIterator.AStarNode aStarNode, AStarIterator.AStarNode aStarNode1) {
Edge edge = aStarNode.getNode().getEdge(aStarNode1.getNode());
SimpleFeature feature = (SimpleFeature)edge.getObject();
Geometry geometry = (Geometry)feature.getDefaultGeometry();
//System.out.println(aStarNode.getH());
return geometry.getLength();
}
@Override
public double h(Node node) {
return -10;
}
};
Date start = new Date();
AStarShortestPathFinder aStarPf = new AStarShortestPathFinder(graph,startNode,endNode,aStarFunction);
try {
aStarPf.calculate();
Date end = new Date();
System.out.println("AStar算法耗时:" +(end.getTime() - start.getTime()));
System.out.println("AStar算法距离:" + getPathLength(aStarPf.getPath()));
} catch (Exception e) {
e.printStackTrace();
}
}
AStar算法使用也很简单,可参考api使用文档。两个算法效率比较下来,AStar算法效率更好。算法验证和效率比较:
使用同样的起点和终点,分别调用上面两个算法,计算结果如下:
shp文件原始线段的个数:67749
AStar算法耗时:84ms
AStar距离:0.2307215100346536
迪杰斯特拉耗时:188ms
迪杰斯特拉距离:0.2307215100346536