GEOS  3.8.0dev
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geos::index::chain::MonotoneChain Class Reference

Monotone Chains are a way of partitioning the segments of a linestring to allow for fast searching of intersections. More...

#include <MonotoneChain.h>

Public Member Functions

 MonotoneChain (const geom::CoordinateSequence &pts, std::size_t start, std::size_t end, void *context)
const geom::EnvelopegetEnvelope () const
 Returned envelope is owned by this class.
size_t getStartIndex () const
size_t getEndIndex () const
void getLineSegment (std::size_t index, geom::LineSegment &ls) const
 Set given LineSegment with points of the segment starting at the given index.
< geom::CoordinateSequence
getCoordinates () const
void select (const geom::Envelope &searchEnv, MonotoneChainSelectAction &mcs)
void computeOverlaps (MonotoneChain *mc, MonotoneChainOverlapAction *mco)
void setId (int nId)
int getId () const
void * getContext ()

Detailed Description

Monotone Chains are a way of partitioning the segments of a linestring to allow for fast searching of intersections.

They have the following properties:

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:

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.

Constructor & Destructor Documentation

geos::index::chain::MonotoneChain::MonotoneChain ( const geom::CoordinateSequence pts,
std::size_t  start,
std::size_t  end,
void *  context 
ptsOwnership left to caller, this class holds a reference.
contextOwnership left to caller, this class holds a reference.

Member Function Documentation

std::unique_ptr<geom::CoordinateSequence> geos::index::chain::MonotoneChain::getCoordinates ( ) const

Return the subsequence of coordinates forming this chain. Allocates a new CoordinateSequence to hold the Coordinates

void geos::index::chain::MonotoneChain::select ( const geom::Envelope searchEnv,
MonotoneChainSelectAction mcs 

Determine all the line segments in the chain whose envelopes overlap the searchEnvelope, and process them

The documentation for this class was generated from the following file: