y.layout.router.polyline
Class PathSearch

java.lang.Object
  y.layout.router.polyline.PathSearch

public class PathSearch
extends java.lang.Object

This is a pathfinding algorithm that calculates the shortest (i.e., the cheapest) paths for a set of edges through a GraphPartition.

It is based on an A*-algorithm and uses PartitionCells as steps between source node and target node.

In each step, the algorithm takes a CellEntrance, that consists mainly of a PartitionCell and from where it was entered, from a queue with all seen CellEntrances, determines all possible neighbor cells and their enter intervals and enqueues the resulting CellEntrance. To influence the order in which the CellEntrances will be processed, the path search assigns real costs (like Dijkstra) as well as heuristic costs (A*-algorithm's heuristic) to the enqueued CellEntrances. The real costs arise from entering a neighbor cell, e.g., a bend has to be created, while the heuristic costs are an estimation of how expensive it will be to reach the target node continuing the path with this neighboring cell. Therefore, the path search prefers searching in the direction in which the target node lies. The CellEntrance with the lowest combined costs is processed next until the target cell is reached.

PathSearchExtensions modify the path search as they are able to add start entrances and weight them with costs. They also add real and heuristic costs to CellEntrances that are created for the currently entered PartitionCell and calculate shorter enter intervals that are less expensive to pass.

The algorithm gets a PathSearchContext which provides information about the graph and the currently routed edge. It stores the results of the path search that can then be retrieved calling PathSearchContext.getPathSearchResult().

See Also:

addPathSearchExtension(PathSearchExtension), addAdditionalEnterIntervalCalculator(EnterIntervalCalculator)

Constructor Summary

PathSearch()
Creates a new instance of PathSearch.

Method Summary

boolean	addAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator) Adds a new interval calculator to the list of registered EnterIntervalCalculators.
boolean	addPathSearchExtension(PathSearchExtension extension) Adds the given extension to the list of PathSearchExtensions.
protected void	calculateCosts(CellEntrance currentEntrance, PartitionCell enteredCell, OrthogonalInterval[] enterIntervals, EdgeCellInfo[] lastEdgeCellInfos, PathSearchContext context, double[] costs, double[] maxAllowedCosts) Calculates the costs for moving from the current CellEntrance to the neighboring PartitionCell using different enter intervals.
protected double	calculateHeuristicCosts(CellEntrance entrance, PathSearchContext context) Returns the estimated costs for the rest of the path when using the given CellEntrance for the next step in the path search.
void	clear() Resets all registered PathSearchExtensions and DataProviders added to this PathSearch.
protected void	decreasePenaltySettings(PenaltySettings penaltySettings, double decreaseFactor, PathSearchContext context) Decreases the given penalty settings for the current edge.
protected void	finalizePath(Path path) Informs all registered path search extensions about completing a path by calling their finalizePath(Path) method.
void	findPaths(PathSearchContext context) Finds paths for the edges in the given context and stores them in its PathSearchResult.
protected void	findPathsForCurrentEdge(PathSearchContext context) Finds the path for the current edge in the given context.
Path	getFinalizedPath(Edge edge) Returns the path for the given edge if it has already been finalized.
protected void	handleNeighbor(CellEntrance currentEntrance, PartitionCell neighborCell, PathSearchContext context) Adds CellEntrances for every interval through which the neighboring cell can be entered from the current entrance to the queue.
void	init(PathSearchConfiguration configuration) Initializes the fields of this PathSearch.
boolean	removeAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator) Removes the given interval calculator from the list of registered EnterIntervalCalculators.
boolean	removePathSearchExtension(PathSearchExtension extension) Removes the given extension from the list of PathSearchExtensions.

Methods inherited from class java.lang.Object

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

Constructor Detail

PathSearch

public PathSearch()

Creates a new instance of PathSearch.

Method Detail

addPathSearchExtension

public boolean addPathSearchExtension(PathSearchExtension extension)

Adds the given extension to the list of PathSearchExtensions.

An extension can influence the pathfinding process by adding costs for entering certain CellEntrances.

Parameters:

extension - the extension to add to this path search

Returns:

true if the extension has been added, false otherwise

removePathSearchExtension

public boolean removePathSearchExtension(PathSearchExtension extension)

Removes the given extension from the list of PathSearchExtensions.

Parameters:

extension - the extension to remove from the path search

Returns:

true if an extension was removed as a result of this call, false if the given extension was not contained in the list

addAdditionalEnterIntervalCalculator

public boolean addAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator)

Adds a new interval calculator to the list of registered EnterIntervalCalculators.

EnterIntervalCalculators may add CellEntrances with narrowed intervals to the queue. The interval is more specific and will be judged with lower costs.

Parameters:

enterIntervalCalculator - the calculator to add

Returns:

true if the calculator was successfully added, false otherwise

removeAdditionalEnterIntervalCalculator

public boolean removeAdditionalEnterIntervalCalculator(EnterIntervalCalculator enterIntervalCalculator)

Removes the given interval calculator from the list of registered EnterIntervalCalculators.

Parameters:

enterIntervalCalculator - the calculator to remove

Returns:

true if an interval calculator was removed as a result of this call, false if the given calculator was not part of the list

init

public void init(PathSearchConfiguration configuration)

Initializes the fields of this PathSearch.

This method also calls PathSearchExtension.initialize(PathSearchConfiguration) for all registered path search extensions.

Parameters:

configuration - the configuration that the path search shall use

clear

public void clear()

Resets all registered PathSearchExtensions and DataProviders added to this PathSearch. So, PathSearch is ready to calculate paths for a new layout.

See Also:

PathSearchExtension.cleanup()

getFinalizedPath

public Path getFinalizedPath(Edge edge)

Returns the path for the given edge if it has already been finalized.

The path is finalized if the PathSearch chose it as the best result for the edge.

Parameters:

edge - the edge for which the path is returned

Returns:

the finalized path for the given edge or null if no path has been found and finalized

findPathsForCurrentEdge

protected void findPathsForCurrentEdge(PathSearchContext context)

Finds the path for the current edge in the given context. This method:

• Calls PathSearchExtension.initializeCurrentEdge(PathSearchContext) for all extensions.
• Collects and enqueues all start entrances.
• Iteratively processes the next cheapest cell entrance and
  • adds a path result after a finalizePath(Path) call if it is a valid target entrance and/or
  • calls handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) for all neighbor cells of the entered cell.
• Calls PathSearchExtension.finalizeCurrentEdge(PathSearchContext) for all extensions.

It is called by findPaths(PathSearchContext) and may be overridden to skip certain edges or implement a custom path search.

Parameters:

context - the context information needed for finding a path

decreasePenaltySettings

protected void decreasePenaltySettings(PenaltySettings penaltySettings,
                                       double decreaseFactor,
                                       PathSearchContext context)

Decreases the given penalty settings for the current edge.

If finding a path for the current edge takes too long according to the maximum duration of the edge routing algorithm, the path search for the current edge is canceled and restarted using decreased penalties. The decreaseFactor indicates, how much the penalties shall be reduced.

This method is called by findPathsForCurrentEdge(PathSearchContext). If overriding this method, note that the penalty for creating bends should not be reduced as this results in more possible turns of the edge path and, therefore, a longer runtime of the path search. Furthermore, not all penalties should be decreased equally as these decreases would neutralize each other.

The decreaseFactor takes values from [0,1], where 0 means no reduction while 1 means the strongest reduction.

Parameters:

penaltySettings - the penalty settings whose penalties shall be reduced

decreaseFactor - the factor with values between 0 and 1 that indicates how strong to reduce the penalties

context - the context information of the current path search

findPaths

public void findPaths(PathSearchContext context)

Finds paths for the edges in the given context and stores them in its PathSearchResult. This is the main method of PathSearch.

It initializes its extensions using PathSearchExtension.initializeEdges(PathSearchContext) and delegates the path search for each edge to findPathsForCurrentEdge(PathSearchContext).

The path calculations for all edges are finalized by calling the extensions' PathSearchExtension.finalizeEdges(PathSearchContext) method and, after that, the path search result is filled with the path for each edge.

At last, the extensions are asked to finalize the path search result using their PathSearchExtension.finalizePathSearchResult(PathSearchResult) callback.

Parameters:

context - the context to use during the path search

See Also:

PathSearchContext.getEdges(), PathSearchContext.getPathSearchResult()

finalizePath

protected void finalizePath(Path path)

Informs all registered path search extensions about completing a path by calling their finalizePath(Path) method. That way, extensions can collect data about this path to use it later during path search.

This method is called by findPathsForCurrentEdge(PathSearchContext) and may be overridden to use a custom finalization step.

Parameters:

path - the path to finalize

handleNeighbor

protected void handleNeighbor(CellEntrance currentEntrance,
                              PartitionCell neighborCell,
                              PathSearchContext context)

Adds CellEntrances for every interval through which the neighboring cell can be entered from the current entrance to the queue. The algorithm calls this method in every step for each neighbor of the current cell to collect all next possible entrances for the current path. This path consists of several entrances where each knows the entrance through which it has been entered.

After calculating all possible enter intervals to the given neighboring cell, each interval gets rated with costs. If there is already an entrance for the neighboring cell whose interval is the same with one of these intervals, this entrance will be used and re-enqueued, so that the path search can still reach it. The current entrance is set as its predecessor within the current path and its enter interval and costs will be updated.

If there is an entrance for the neighboring cell whose interval is intersected by a current interval, new entrances will be created with the new enter intervals and enqueued. The same happens if there is no entrance that has been matched with one of the current intervals, yet. Costs will be added. If there are some entries afterwards that are intersected by the current interval and have higher costs, they will be removed from the queue.

This method is called during cost calculation. It may be overridden to change the interval handling for the CellEntrances.

Parameters:

currentEntrance - the current cell entrance

neighborCell - the neighboring cell that is handled.

context - the context information

See Also:

calculateCosts(CellEntrance, PartitionCell, OrthogonalInterval[], EdgeCellInfo[], PathSearchContext, double[], double[]), calculateHeuristicCosts(CellEntrance, PathSearchContext)

calculateCosts

protected void calculateCosts(CellEntrance currentEntrance,
                              PartitionCell enteredCell,
                              OrthogonalInterval[] enterIntervals,
                              EdgeCellInfo[] lastEdgeCellInfos,
                              PathSearchContext context,
                              double[] costs,
                              double[] maxAllowedCosts)

Calculates the costs for moving from the current CellEntrance to the neighboring PartitionCell using different enter intervals. It is called by handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) to determine the costs for all CellEntrances that it will create and enqueue afterwards.

The costs for the given enter intervals are retrieved from all registered PathSearchExtensions. The calculation stops when it reaches the given maximum cost value.

Parameters:

currentEntrance - the current cell entrance

enteredCell - the partition cell to enter

enterIntervals - the different entering intervals of the entered cell

lastEdgeCellInfos - the information about how the last cell was crossed

context - the context information

costs - the array in which the calculated costs for entering the neighbor cell via the according enter intervals shall be written

maxAllowedCosts - the maximum costs an enter interval may induce. If this cost is exceeded, no further additional costs for this interval are calculated. Note that the entries in this array get modified during cost calculation

See Also:

PathSearchExtension.calculateCosts(CellEntrance, PartitionCell, OrthogonalInterval, EdgeCellInfo, double)

calculateHeuristicCosts

protected double calculateHeuristicCosts(CellEntrance entrance,
                                         PathSearchContext context)

Returns the estimated costs for the rest of the path when using the given CellEntrance for the next step in the path search. It is called by handleNeighbor(CellEntrance, PartitionCell, PathSearchContext) to determine the heuristic part of the costs with which the entrance will be enqueued.

The heuristic costs for the given entrance are retrieved from all registered PathSearchExtensions.

Parameters:

entrance - the current entrance

context - the context information

Returns:

the heuristic costs for the rest of the path if the given entrance is used

See Also:

PathSearchExtension.calculateHeuristicCosts(CellEntrance)