MonotoneChainI class

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 ({@link MonotoneChainSelectAction} and {@link 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).

@version 1.7

Constructors

MonotoneChainI(List<Coordinate> pts, int start, int end, Object? context)
Creates a new MonotoneChain based on the given array of points. @param pts the points containing the chain @param start the index of the first coordinate in the chain @param end the index of the last coordinate in the chain @param context a user-defined data object

Properties

context ↔ Object?
getter/setter pair
end ↔ int
getter/setter pair
env ↔ Envelope?
getter/setter pair
hashCode → int
The hash code for this object.
no setterinherited
id ↔ int
getter/setter pair
pts ↔ List<Coordinate>
getter/setter pair
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
start ↔ int
getter/setter pair

Methods

computeOverlaps3(MonotoneChainI mc, MonotoneChainOverlapAction mco) → void
Determine all the line segments in two chains which may overlap, and process them.
computeOverlaps6(int start0, int end0, MonotoneChainI mc, int start1, int end1, MonotoneChainOverlapAction mco) → void
Uses an efficient mutual binary search strategy to determine which pairs of chain segments may overlap, and calls the given overlap action on them.
computeSelect(Envelope searchEnv, int start0, int end0, MonotoneChainSelectAction mcs) → void
getContext() → Object?
Gets the user-defined context data value.
getCoordinates() → List<Coordinate>
Return the subsequence of coordinates forming this chain. Allocates a new array to hold the Coordinates
getEndIndex() → int
Gets the index of the end of the monotone chain in the underlying array of points.
getEnvelope() → Envelope
Gets the envelope of the chain.
getId() → int
Gets the id of this chain.
getLineSegment(int index, LineSegment ls) → void
Gets the line segment starting at index
getStartIndex() → int
Gets the index of the start of the monotone chain in the underlying array of points.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
overlaps(int start0, int end0, MonotoneChainI mc, int start1, int end1) → bool
Tests whether the envelope of a section of the chain overlaps (intersects) the envelope of a section of another target chain. This test is efficient due to the monotonicity property of the sections (i.e. the envelopes can be are determined from the section endpoints rather than a full scan).
select(Envelope searchEnv, MonotoneChainSelectAction mcs) → void
Determine all the line segments in the chain whose envelopes overlap the searchEnvelope, and process them.
setId(int id) → void
Sets the id of this chain. Useful for assigning an ordering to a set of chains, which can be used to avoid redundant processing.
toString() → String
A string representation of this object.
inherited

Operators

operator ==(Object other) → bool
The equality operator.
inherited