com.vividsolutions.jts.index.chain
Class MonotoneChain
java.lang.Object
com.vividsolutions.jts.index.chain.MonotoneChain
public class MonotoneChain
extends java.lang.Object
MonotoneChains 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 will 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 1 means that there is no need to test pairs of segments from within
the same monotone chain for intersection.
Property 2 allows
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
to return the resultsets for the above 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.
However, it does mean that the queries are not thread-safe.
MonotoneChain
public MonotoneChain(Coordinate[] pts,
int start,
int end,
Object context)
getContext
public Object getContext()
getCoordinates
public Coordinate[] getCoordinates()
Return the subsequence of coordinates forming this chain.
Allocates a new array to hold the Coordinates
getEndIndex
public int getEndIndex()
getEnvelope
public Envelope getEnvelope()
getLineSegment
public void getLineSegment(int index,
LineSegment ls)
getStartIndex
public int getStartIndex()
select
public void select(Envelope searchEnv,
MonotoneChainSelectAction mcs)
Determine all the line segments in the chain whose envelopes overlap
the searchEnvelope, and process them
setId
public void setId(int id)