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.- Version:
- 1.7
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Constructor Summary
Constructors Constructor Description MonotoneChain(Coordinate[] pts, int start, int end, java.lang.Object context)
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description private void
computeOverlaps(int start0, int end0, MonotoneChain mc, int start1, int end1, MonotoneChainOverlapAction mco)
void
computeOverlaps(MonotoneChain mc, MonotoneChainOverlapAction mco)
Determine all the line segments in two chains which may overlap, and process them.private void
computeSelect(Envelope searchEnv, int start0, int end0, MonotoneChainSelectAction mcs)
java.lang.Object
getContext()
Coordinate[]
getCoordinates()
Return the subsequence of coordinates forming this chain.int
getEndIndex()
Envelope
getEnvelope()
int
getId()
void
getLineSegment(int index, LineSegment ls)
Gets the line segment starting atindex
int
getStartIndex()
private boolean
overlaps(int start0, int end0, MonotoneChain mc, int start1, int end1)
Tests whether the envelopes of two chain sections overlap (intersect).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)
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Field Detail
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pts
private Coordinate[] pts
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start
private int start
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end
private int end
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env
private Envelope env
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context
private java.lang.Object context
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id
private int id
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Constructor Detail
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MonotoneChain
public MonotoneChain(Coordinate[] pts, int start, int end, java.lang.Object context)
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Method Detail
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setId
public void setId(int id)
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getId
public int getId()
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getContext
public java.lang.Object getContext()
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getEnvelope
public Envelope getEnvelope()
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getStartIndex
public int getStartIndex()
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getEndIndex
public int getEndIndex()
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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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computeSelect
private void computeSelect(Envelope searchEnv, int start0, int end0, MonotoneChainSelectAction mcs)
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computeOverlaps
public void computeOverlaps(MonotoneChain mc, MonotoneChainOverlapAction mco)
Determine all the line segments in two chains which may overlap, and process them.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:
searchEnv
- the search envelopemco
- the overlap action to execute on selected segments
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computeOverlaps
private void computeOverlaps(int start0, int end0, MonotoneChain mc, int start1, int end1, MonotoneChainOverlapAction mco)
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overlaps
private boolean overlaps(int start0, int end0, MonotoneChain mc, int start1, int end1)
Tests whether the envelopes of two chain sections overlap (intersect).- Parameters:
start0
-end0
-mc
-start1
-end1
-- Returns:
- true if the section envelopes overlap
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