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

#include <MonotoneChain.h>

Collaboration diagram for geos::index::chain::MonotoneChain:

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Public Member Functions
	MonotoneChain (const geom::CoordinateSequence &pts, std::size_t start, std::size_t end, void *context)

	~MonotoneChain ()=default

const geom::Envelope &	getEnvelope ()
	Returned envelope is owned by this class. More...

const geom::Envelope &	getEnvelope (double expansionDistance)

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. More...

std::unique_ptr< geom::CoordinateSequence >	getCoordinates () const

void	select (const geom::Envelope &searchEnv, MonotoneChainSelectAction &mcs)

void	computeOverlaps (MonotoneChain mc, MonotoneChainOverlapAction mco)

void	computeOverlaps (MonotoneChain mc, double overlapTolerance, MonotoneChainOverlapAction mco)

void	setId (int nId)

int	getId () const

void *	getContext ()

Private Member Functions
void	computeSelect (const geom::Envelope &searchEnv, size_t start0, size_t end0, MonotoneChainSelectAction &mcs)

void	computeOverlaps (std::size_t start0, std::size_t end0, MonotoneChain &mc, std::size_t start1, std::size_t end1, double overlapTolerance, MonotoneChainOverlapAction &mco)

bool	overlaps (size_t start0, size_t end0, const MonotoneChain &mc, size_t start1, size_t end1, double overlapTolerance) const

bool	overlaps (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &q1, const geom::Coordinate &q2, double overlapTolerance) const

	MonotoneChain (const MonotoneChain &other)=delete

MonotoneChain &	operator= (const MonotoneChain &rhs)=delete

Private Attributes
const geom::CoordinateSequence &	pts
	Externally owned. More...

void *	context
	user-defined information More...

size_t	start
	Index of chain start vertex into the CoordinateSequence, 0 based. More...

size_t	end
	Index of chain end vertex into the CoordinateSequence, 0 based. More...

geom::Envelope	env
	Owned by this class. More...

bool	envIsSet

int	id
	useful for optimizing chain comparisons More...

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:

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 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 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.

Definition at line 84 of file index/chain/MonotoneChain.h.

Constructor & Destructor Documentation

geos::index::chain::MonotoneChain::MonotoneChain	(	const geom::CoordinateSequence &	pts,
		std::size_t	start,
		std::size_t	end,
		void *	context
	)

Parameters

pts	Ownership left to caller, this class holds a reference.
start
end
context	Ownership left to caller, this class holds a reference.

geos::index::chain::MonotoneChain::~MonotoneChain ( )

default

geos::index::chain::MonotoneChain::MonotoneChain ( const MonotoneChain & other )

privatedelete

Member Function Documentation

void geos::index::chain::MonotoneChain::computeOverlaps	(	MonotoneChain *	mc,
		MonotoneChainOverlapAction *	mco
	)

void geos::index::chain::MonotoneChain::computeOverlaps	(	MonotoneChain *	mc,
		double	overlapTolerance,
		MonotoneChainOverlapAction *	mco
	)

void geos::index::chain::MonotoneChain::computeOverlaps	(	std::size_t	start0,
		std::size_t	end0,
		MonotoneChain &	mc,
		std::size_t	start1,
		std::size_t	end1,
		double	overlapTolerance,
		MonotoneChainOverlapAction &	mco
	)

private

void geos::index::chain::MonotoneChain::computeSelect	(	const geom::Envelope &	searchEnv,
		size_t	start0,
		size_t	end0,
		MonotoneChainSelectAction &	mcs
	)

private

void* geos::index::chain::MonotoneChain::getContext ( )

inline

Definition at line 157 of file index/chain/MonotoneChain.h.

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

size_t geos::index::chain::MonotoneChain::getEndIndex ( ) const

inline

Definition at line 113 of file index/chain/MonotoneChain.h.

const geom::Envelope& geos::index::chain::MonotoneChain::getEnvelope ( )

Returned envelope is owned by this class.

const geom::Envelope& geos::index::chain::MonotoneChain::getEnvelope ( double expansionDistance )

int geos::index::chain::MonotoneChain::getId ( ) const

inline

Definition at line 151 of file index/chain/MonotoneChain.h.

void geos::index::chain::MonotoneChain::getLineSegment	(	std::size_t	index,
		geom::LineSegment &	ls
	)		const

Set given LineSegment with points of the segment starting at the given index.

size_t geos::index::chain::MonotoneChain::getStartIndex ( ) const

inline

Definition at line 107 of file index/chain/MonotoneChain.h.

MonotoneChain& geos::index::chain::MonotoneChain::operator= ( const MonotoneChain & rhs )

privatedelete

bool geos::index::chain::MonotoneChain::overlaps	(	size_t	start0,
		size_t	end0,
		const MonotoneChain &	mc,
		size_t	start1,
		size_t	end1,
		double	overlapTolerance
	)		const

private

bool geos::index::chain::MonotoneChain::overlaps	(	const geom::Coordinate &	p1,
		const geom::Coordinate &	p2,
		const geom::Coordinate &	q1,
		const geom::Coordinate &	q2,
		double	overlapTolerance
	)		const