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

Modifier and Type	Field and Description
protected PathBidirRef	bestPath
protected com.carrotsearch.hppc.IntObjectMap<AStar.AStarEntry>	bestWeightMapFrom
protected com.carrotsearch.hppc.IntObjectMap<AStar.AStarEntry>	bestWeightMapTo
protected AStar.AStarEntry	currFrom
protected AStar.AStarEntry	currTo

Fields inherited from class com.graphhopper.routing.AbstractBidirAlgo

finishedFrom, finishedTo

Fields inherited from class com.graphhopper.routing.AbstractRoutingAlgorithm

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 Path	createAndInitPath()
protected SPTEntry	createSPTEntry(int node, double weight)
protected Path	extractPath() To be overwritten from extending class.
protected boolean	finished() To be overwritten from extending class.
WeightApproximator	getApproximation()
protected double	getCurrentFromWeight()
protected double	getCurrentToWeight()
String	getName()
protected void	initCollections(int size)
void	initFrom(int from, double weight)
void	initTo(int to, double weight)
AStarBidirection	setApproximation(WeightApproximator approx)
void	updateBestPath(EdgeIteratorState edgeState, AStar.AStarEntry entryCurrent, int currLoc)

Methods inherited from class com.graphhopper.routing.AbstractBidirAlgo

calcPath, getVisitedNodes, runAlgo

Methods inherited from class com.graphhopper.routing.AbstractRoutingAlgorithm

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

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

Field Detail

currFrom

protected AStar.AStarEntry currFrom

currTo

protected AStar.AStarEntry currTo

bestPath

protected PathBidirRef bestPath

bestWeightMapFrom

protected com.carrotsearch.hppc.IntObjectMap<AStar.AStarEntry> bestWeightMapFrom

bestWeightMapTo

protected com.carrotsearch.hppc.IntObjectMap<AStar.AStarEntry> bestWeightMapTo

Constructor Detail

AStarBidirection

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

Method Detail

initCollections

protected void initCollections(int size)

setApproximation

public AStarBidirection setApproximation(WeightApproximator approx)

Parameters:

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

getApproximation

public WeightApproximator getApproximation()

createSPTEntry

protected SPTEntry createSPTEntry(int node,
                                  double weight)

Overrides:

createSPTEntry in class AbstractRoutingAlgorithm

initFrom

public void initFrom(int from,
                     double weight)

initTo

public void initTo(int to,
                   double weight)

createAndInitPath

protected Path createAndInitPath()

Specified by:

createAndInitPath in class AbstractBidirAlgo

extractPath

protected Path extractPath()

Description copied from class: AbstractRoutingAlgorithm

To be overwritten from extending class. Should we make this available in RoutingAlgorithm interface?

Specified by:

extractPath in class AbstractRoutingAlgorithm

Returns:

true if finished.

getCurrentFromWeight

protected double getCurrentFromWeight()

Specified by:

getCurrentFromWeight in class AbstractBidirAlgo

getCurrentToWeight

protected double getCurrentToWeight()

Specified by:

getCurrentToWeight in class AbstractBidirAlgo

finished

protected boolean finished()

Description copied from class: AbstractRoutingAlgorithm

To be overwritten from extending class. Should we make this available in RoutingAlgorithm interface?

Specified by:

finished in class AbstractRoutingAlgorithm

Returns:

true if finished.

updateBestPath

public void updateBestPath(EdgeIteratorState edgeState,
                           AStar.AStarEntry entryCurrent,
                           int currLoc)

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