com.graphhopper.routing

Class AStarBidirection

java.lang.Object

com.graphhopper.routing.AbstractRoutingAlgorithm

com.graphhopper.routing.AbstractBidirAlgo

com.graphhopper.routing.AStarBidirection

All Implemented Interfaces:

RecalculationHook, RoutingAlgorithm

Direct Known Subclasses:

AlternativeRoute.AlternativeBidirSearch, AStarBidirectionCH

public class AStarBidirection
extends AbstractBidirAlgo
implements RecalculationHook

This class implements a bidirectional A* algorithm. It is interesting to note that a bidirectional dijkstra is far more efficient than a single direction one. The same does not hold for a bidirectional A* as the heuristic can not be as tight.

See http://research.microsoft.com/apps/pubs/default.aspx?id=64511 http://i11www.iti.uni-karlsruhe.de/_media/teaching/sommer2012/routenplanung/vorlesung4.pdf http://research.microsoft.com/pubs/64504/goldberg-sofsem07.pdf http://www.cs.princeton.edu/courses/archive/spr06/cos423/Handouts/EPP%20shortest%20path%20algorithms.pdf

and

1. Ikeda, T., Hsu, M.-Y., Imai, H., Nishimura, S., Shimoura, H., Hashimoto, T., Tenmoku, K., and Mitoh, K. (1994). A fast algorithm for finding better routes by ai search techniques. In VNIS, pages 291–296.

2. Whangbo, T. K. (2007). Efficient modified bidirectional a* algorithm for optimal route- finding. In IEA/AIE, volume 4570, pages 344–353. Springer.

or could we even use this three phase approach? www.lix.polytechnique.fr/~giacomon/papers/bidirtimedep.pdf

Author:

Peter Karich, jansoe

Field Summary

Fields inherited from class com.graphhopper.routing.AbstractBidirAlgo

bestPath, bestWeightMapFrom, bestWeightMapOther, bestWeightMapTo, currFrom, currTo, finishedFrom, finishedTo, from, to

Fields inherited from class com.graphhopper.routing.AbstractRoutingAlgorithm

additionalEdgeFilter, flagEncoder, graph, inEdgeExplorer, maxVisitedNodes, nodeAccess, outEdgeExplorer, traversalMode, weighting

Constructor Summary

Constructors

Constructor and Description
AStarBidirection(Graph graph, Weighting weighting, TraversalMode tMode)

Method Summary

Modifier and Type	Method and Description
void	afterHeuristicChange(boolean forward, boolean backward) Call this method after the heuristic has changed and graph exploration should continue.
protected double	calcWeight(EdgeIteratorState iter, SPTEntry currEdge, boolean reverse)
protected SPTEntry	createEntry(EdgeIteratorState edge, int incEdge, double weight, SPTEntry parent, boolean reverse) Creates a new entry of the shortest path tree (a SPTEntry or one of its subclasses) during a dijkstra expansion.
protected SPTEntry	createStartEntry(int node, double weight, boolean reverse) Creates the root shortest path tree entry for the forward or backward search.
WeightApproximator	getApproximation()
String	getName()
AStarBidirection	setApproximation(WeightApproximator approx)
protected void	updateEntry(SPTEntry entry, EdgeIteratorState edge, int edgeId, double weight, SPTEntry parent, boolean reverse)

Methods inherited from class com.graphhopper.routing.AbstractBidirAlgo

accept, bwdSearchCanBeStopped, calcPath, createAndInitPath, extractPath, finished, fromEntryCanBeSkipped, fwdSearchCanBeStopped, getCurrentFromWeight, getCurrentToWeight, getIncomingEdge, getOrigEdgeId, getTraversalId, getVisitedNodes, initCollections, initFrom, initTo, postInit, postInitFrom, postInitTo, runAlgo, setUpdateBestPath, toEntryCanBeSkipped, updateBestPath

Methods inherited from class com.graphhopper.routing.AbstractRoutingAlgorithm

accept, calcPaths, checkAlreadyRun, createEmptyPath, isMaxVisitedNodesExceeded, setEdgeFilter, setMaxVisitedNodes, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.graphhopper.routing.RecalculationHook

getVisitedNodes

Constructor Detail

AStarBidirection

public AStarBidirection(Graph graph,
                        Weighting weighting,
                        TraversalMode tMode)

Method Detail

createStartEntry

protected SPTEntry createStartEntry(int node,
                                    double weight,
                                    boolean reverse)

Description copied from class: AbstractBidirAlgo

Creates the root shortest path tree entry for the forward or backward search.

Specified by:

createStartEntry in class AbstractBidirAlgo

createEntry

protected SPTEntry createEntry(EdgeIteratorState edge,
                               int incEdge,
                               double weight,
                               SPTEntry parent,
                               boolean reverse)

Description copied from class: AbstractBidirAlgo

Creates a new entry of the shortest path tree (a SPTEntry or one of its subclasses) during a dijkstra expansion.

Specified by:

createEntry in class AbstractBidirAlgo

Parameters:

edge - the edge that is currently processed for the expansion

incEdge - the id of the edge that is incoming to the node the edge is pointed at. usually this is the same as edge.getEdge(), but for edge-based CH and in case edge is a shortcut incEdge is the original edge that is incoming to the node

weight - the weight the shortest path three entry should carry

parent - the parent entry of in the shortest path tree

reverse - true if we are currently looking at the backward search, false otherwise

updateEntry

protected void updateEntry(SPTEntry entry,
                           EdgeIteratorState edge,
                           int edgeId,
                           double weight,
                           SPTEntry parent,
                           boolean reverse)

Overrides:

updateEntry in class AbstractBidirAlgo

calcWeight

protected double calcWeight(EdgeIteratorState iter,
                            SPTEntry currEdge,
                            boolean reverse)

Overrides:

calcWeight in class AbstractBidirAlgo

getApproximation

public WeightApproximator getApproximation()

setApproximation

public AStarBidirection setApproximation(WeightApproximator approx)

Parameters:

approx - if true it enables approximate distance calculation from lat,lon values

afterHeuristicChange

public void afterHeuristicChange(boolean forward,
                                 boolean backward)

Description copied from interface: RecalculationHook

Call this method after the heuristic has changed and graph exploration should continue.

Specified by:

afterHeuristicChange in interface RecalculationHook

getName

public String getName()

Specified by:

getName in interface RoutingAlgorithm

Overrides:

getName in class AbstractRoutingAlgorithm

Returns:

name of this algorithm