Simplifies a buffer input line to remove concavities with shallow depth. More...

#include <BufferInputLineSimplifier.h>

Collaboration diagram for geos::operation::buffer::BufferInputLineSimplifier:

Public Member Functions
	BufferInputLineSimplifier (const geom::CoordinateSequence &input)

std::unique_ptr< geom::CoordinateSequence >	simplify (double distanceTol)

Static Public Member Functions
static std::unique_ptr< geom::CoordinateSequence >	simplify (const geom::CoordinateSequence &inputLine, double distanceTol)

Private Member Functions
bool	deleteShallowConcavities ()

size_t	findNextNonDeletedIndex (size_t index) const

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

bool	isDeletable (size_t i0, size_t i1, size_t i2, double distanceTol) const

bool	isShallowConcavity (const geom::Coordinate &p0, const geom::Coordinate &p1, const geom::Coordinate &p2, double distanceTol) const

bool	isShallowSampled (const geom::Coordinate &p0, const geom::Coordinate &p2, size_t i0, size_t i2, double distanceTol) const

bool	isShallow (const geom::Coordinate &p0, const geom::Coordinate &p1, const geom::Coordinate &p2, double distanceTol) const

bool	isConcave (const geom::Coordinate &p0, const geom::Coordinate &p1, const geom::Coordinate &p2) const

	BufferInputLineSimplifier (const BufferInputLineSimplifier &other)=delete

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

Private Attributes
const geom::CoordinateSequence &	inputLine

double	distanceTol

std::vector< int >	isDeleted

int	angleOrientation

Static Private Attributes
static const int	NUM_PTS_TO_CHECK = 10

static const int	INIT = 0

static const int	DELETE = 1

static const int	KEEP = 1

Detailed Description

Simplifies a buffer input line to remove concavities with shallow depth.

The most important benefit of doing this is to reduce the number of points and the complexity of shape which will be buffered. It also reduces the risk of gores created by the quantized fillet arcs (although this issue should be eliminated in any case by the offset curve generation logic).

A key aspect of the simplification is that it affects inside (concave or inward) corners only. Convex (outward) corners are preserved, since they are required to ensure that the generated buffer curve lies at the correct distance from the input geometry.

Another important heuristic used is that the end segments of the input are never simplified. This ensures that the client buffer code is able to generate end caps faithfully.

No attempt is made to avoid self-intersections in the output. This is acceptable for use for generating a buffer offset curve, since the buffer algorithm is insensitive to invalid polygonal geometry. However, this means that this algorithm cannot be used as a general-purpose polygon simplification technique.

Author: Martin Davis

Definition at line 72 of file BufferInputLineSimplifier.h.

Constructor & Destructor Documentation

geos::operation::buffer::BufferInputLineSimplifier::BufferInputLineSimplifier ( const geom::CoordinateSequence & input )

geos::operation::buffer::BufferInputLineSimplifier::BufferInputLineSimplifier ( const BufferInputLineSimplifier & other )

privatedelete

Member Function Documentation

std::unique_ptr<geom::CoordinateSequence> geos::operation::buffer::BufferInputLineSimplifier::collapseLine ( ) const

private

bool geos::operation::buffer::BufferInputLineSimplifier::deleteShallowConcavities ( )

private

Uses a sliding window containing 3 vertices to detect shallow angles in which the middle vertex can be deleted, since it does not affect the shape of the resulting buffer in a significant way.

Returns

size_t geos::operation::buffer::BufferInputLineSimplifier::findNextNonDeletedIndex ( size_t index ) const

private

Finds the next non-deleted index, or the end of the point array if none

Parameters

index

Returns: the next non-deleted index, if any; inputLine.size() if there are no more non-deleted indices

bool geos::operation::buffer::BufferInputLineSimplifier::isConcave	(	const geom::Coordinate &	p0,
		const geom::Coordinate &	p1,
		const geom::Coordinate &	p2
	)		const

private

bool geos::operation::buffer::BufferInputLineSimplifier::isDeletable	(	size_t	i0,
		size_t	i1,
		size_t	i2,
		double	distanceTol
	)		const

private

bool geos::operation::buffer::BufferInputLineSimplifier::isShallow	(	const geom::Coordinate &	p0,
		const geom::Coordinate &	p1,
		const geom::Coordinate &	p2,
		double	distanceTol
	)		const

private

bool geos::operation::buffer::BufferInputLineSimplifier::isShallowConcavity	(	const geom::Coordinate &	p0,
		const geom::Coordinate &	p1,
		const geom::Coordinate &	p2,
		double	distanceTol
	)		const

private

bool geos::operation::buffer::BufferInputLineSimplifier::isShallowSampled	(	const geom::Coordinate &	p0,
		const geom::Coordinate &	p2,
		size_t	i0,
		size_t	i2,
		double	distanceTol
	)		const

private

Checks for shallowness over a sample of points in the given section.

This helps prevents the siplification from incrementally "skipping" over points which are in fact non-shallow.

Parameters

p0	start coordinate of section
p2	end coordinate of section
i0	start index of section
i2	end index of section
distanceTol	distance tolerance

Returns

BufferInputLineSimplifier& geos::operation::buffer::BufferInputLineSimplifier::operator= ( const BufferInputLineSimplifier & rhs )

privatedelete

static std::unique_ptr<geom::CoordinateSequence> geos::operation::buffer::BufferInputLineSimplifier::simplify	(	const geom::CoordinateSequence &	inputLine,
		double	distanceTol
	)

static

Simplify the input coordinate list.

If the distance tolerance is positive, concavities on the LEFT side of the line are simplified. If the supplied distance tolerance is negative, concavities on the RIGHT side of the line are simplified.

Parameters

inputLine	the coordinate sequence to simplify
distanceTol	simplification distance tolerance to use

Returns: a simplified version of the coordinate sequence

std::unique_ptr<geom::CoordinateSequence> geos::operation::buffer::BufferInputLineSimplifier::simplify ( double distanceTol )

Simplify the input coordinate list. If the distance tolerance is positive, concavities on the LEFT side of the line are simplified. If the supplied distance tolerance is negative, concavities on the RIGHT side of the line are simplified.

Parameters

distanceTol simplification distance tolerance to use