Class MonotoneChain
- java.lang.Object
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- org.locationtech.jts.index.chain.MonotoneChain
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public class MonotoneChain extends java.lang.Object
Monotone Chains are a way of partitioning the segments of a linestring to allow for fast searching of intersections. They have the following properties:- the segments within a monotone chain never intersect each other
- the envelope of any contiguous subset of the segments in a monotone chain is equal to the envelope of the endpoints of the subset.
Property 2 allows an efficient binary search to be used to find the intersection points of two monotone chains. For many types of real-world data, these properties eliminate a large number of segment comparisons, producing substantial speed gains.
One of the goals of this implementation of MonotoneChains is to be as space and time efficient as possible. One design choice that aids this is that a MonotoneChain is based on a subarray of a list of points. This means that new arrays of points (potentially very large) do not have to be allocated.
MonotoneChains support the following kinds of queries:
- Envelope select: determine all the segments in the chain which intersect a given envelope
- Overlap: determine all the pairs of segments in two chains whose envelopes overlap
MonotoneChainSelectAction
andMonotoneChainOverlapAction
) to return the results for queries. This has time and space advantages, since it is not necessary to build lists of instantiated objects to represent the segments returned by the query. Queries made in this manner are thread-safe.MonotoneChains support being assigned an integer id value to provide a total ordering for a set of chains. This can be used during some kinds of processing to avoid redundant comparisons (i.e. by comparing only chains where the first id is less than the second).
MonotoneChains support using an tolerance distance for overlap tests. This allows reporting overlap in situations where intersection snapping is being used. If this is used the chain envelope must be computed providing an expansion distance using
getEnvelope(double)
.- Version:
- 1.7
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Constructor Summary
Constructors Constructor Description MonotoneChain(Coordinate[] pts, int start, int end, java.lang.Object context)
Creates a new MonotoneChain based on the given array of points.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
computeOverlaps(MonotoneChain mc, double overlapTolerance, MonotoneChainOverlapAction mco)
Determines the line segments in two chains which may overlap, using an overlap distance tolerance, and passes them to an overlap action.void
computeOverlaps(MonotoneChain mc, MonotoneChainOverlapAction mco)
Determines the line segments in two chains which may overlap, and passes them to an overlap action.java.lang.Object
getContext()
Gets the user-defined context data value.Coordinate[]
getCoordinates()
Return the subsequence of coordinates forming this chain.int
getEndIndex()
Gets the index of the end of the monotone chain in the underlying array of points.Envelope
getEnvelope()
Gets the envelope of the chain.Envelope
getEnvelope(double expansionDistance)
Gets the envelope for this chain, expanded by a given distance.int
getId()
Gets the id of this chain.void
getLineSegment(int index, LineSegment ls)
Gets the line segment starting atindex
int
getStartIndex()
Gets the index of the start of the monotone chain in the underlying array of points.void
select(Envelope searchEnv, MonotoneChainSelectAction mcs)
Determine all the line segments in the chain whose envelopes overlap the searchEnvelope, and process them.void
setId(int id)
Sets the id of this chain.void
setOverlapDistance(double distance)
Sets the overlap distance used in overlap tests with other chains.
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Constructor Detail
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MonotoneChain
public MonotoneChain(Coordinate[] pts, int start, int end, java.lang.Object context)
Creates a new MonotoneChain based on the given array of points.- Parameters:
pts
- the points containing the chainstart
- the index of the first coordinate in the chainend
- the index of the last coordinate in the chaincontext
- a user-defined data object
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Method Detail
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setId
public void setId(int id)
Sets the id of this chain. Useful for assigning an ordering to a set of chains, which can be used to avoid redundant processing.- Parameters:
id
- an id value
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setOverlapDistance
public void setOverlapDistance(double distance)
Sets the overlap distance used in overlap tests with other chains.- Parameters:
distance
- the distance to buffer overlap tests by
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getId
public int getId()
Gets the id of this chain.- Returns:
- the id value
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getContext
public java.lang.Object getContext()
Gets the user-defined context data value.- Returns:
- a data value
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getEnvelope
public Envelope getEnvelope()
Gets the envelope of the chain.- Returns:
- the envelope of the chain
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getEnvelope
public Envelope getEnvelope(double expansionDistance)
Gets the envelope for this chain, expanded by a given distance.- Parameters:
expansionDistance
- distance to expand the envelope by- Returns:
- the expanded envelope of the chain
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getStartIndex
public int getStartIndex()
Gets the index of the start of the monotone chain in the underlying array of points.- Returns:
- the start index of the chain
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getEndIndex
public int getEndIndex()
Gets the index of the end of the monotone chain in the underlying array of points.- Returns:
- the end index of the chain
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getLineSegment
public void getLineSegment(int index, LineSegment ls)
Gets the line segment starting atindex
- Parameters:
index
- index of segmentls
- line segment to extract into
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getCoordinates
public Coordinate[] getCoordinates()
Return the subsequence of coordinates forming this chain. Allocates a new array to hold the Coordinates
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select
public void select(Envelope searchEnv, MonotoneChainSelectAction mcs)
Determine all the line segments in the chain whose envelopes overlap the searchEnvelope, and process them.The monotone chain search algorithm attempts to optimize performance by not calling the select action on chain segments which it can determine are not in the search envelope. However, it *may* call the select action on segments which do not intersect the search envelope. This saves on the overhead of checking envelope intersection each time, since clients may be able to do this more efficiently.
- Parameters:
searchEnv
- the search envelopemcs
- the select action to execute on selected segments
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computeOverlaps
public void computeOverlaps(MonotoneChain mc, MonotoneChainOverlapAction mco)
Determines the line segments in two chains which may overlap, and passes them to an overlap action.The monotone chain search algorithm attempts to optimize performance by not calling the overlap action on chain segments which it can determine do not overlap. However, it *may* call the overlap action on segments which do not actually interact. This saves on the overhead of checking intersection each time, since clients may be able to do this more efficiently.
- Parameters:
mc
- the chain to compare tomco
- the overlap action to execute on overlapping segments
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computeOverlaps
public void computeOverlaps(MonotoneChain mc, double overlapTolerance, MonotoneChainOverlapAction mco)
Determines the line segments in two chains which may overlap, using an overlap distance tolerance, and passes them to an overlap action.- Parameters:
mc
- the chain to compare tooverlapTolerance
- the distance tolerance for the overlap testmco
- the overlap action to execute on selected segments
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