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MonotoneChain(Coordinate[], int, int, Object)
setId(int): void
getId(): int
getContext(): Object
getEnvelope(): Envelope
getStartIndex(): int
getEndIndex(): int
getLineSegment(int, LineSegment): void
getCoordinates(): Coordinate[]
select(Envelope, MonotoneChainSelectAction): void
computeOverlaps(MonotoneChain, MonotoneChainOverlapAction): void
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Class MonotoneChain

Hierarchy: Object , MonotoneChain
public class MonotoneChain
Monotone Chains are a way of partitioning the segments of a linestring to allow for fast searching of intersections. They have the following properties:
  1. the segments within a monotone chain never intersect each other
  2. 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 1 means that there is no need to test pairs of segments from within the same monotone chain for intersection.

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
This implementation of MonotoneChains uses the concept of internal iterators ( MonotoneChainSelectAction and MonotoneChainOverlapAction) 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).

Other

  • version: 1.7
public MonotoneChain(Coordinate[] pts, int start, int end, Object context)
Creates a new MonotoneChain based on the given array of points.
Parameters:
pts - pts the points containing the chain
start - start the index of the first coordinate in the chain
end - end the index of the last coordinate in the chain
context - context a user-defined data object
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 - id an id value
public int getId()
Gets the id of this chain.
Returns:
the id value
public Object getContext()
Gets the user-defined context data value.
Returns:
a data value
public Envelope getEnvelope()
Gets the envelope of the chain.
Returns:
the envelope of the chain
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
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
public void getLineSegment(int index, LineSegment ls)
Gets the line segment starting at index
Parameters:
index - index index of segment
ls - ls line segment to extract into
public Coordinate[] getCoordinates()
Return the subsequence of coordinates forming this chain. Allocates a new array to hold the Coordinates
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 - searchEnv the search envelope
mcs - mcs the select action to execute on selected segments
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 - searchEnv the search envelope
mco - mco the overlap action to execute on selected segments