Computes the buffer of a geometry, for both positive and negative buffer distances. More...

#include <BufferOp.h>

Collaboration diagram for geos::operation::buffer::BufferOp:

Public Types
enum	{ CAP_ROUND = BufferParameters::CAP_ROUND, CAP_BUTT = BufferParameters::CAP_FLAT, CAP_SQUARE = BufferParameters::CAP_SQUARE }

Public Member Functions
	BufferOp (const geom::Geometry *g)
	Initializes a buffer computation for the given geometry. More...

	BufferOp (const geom::Geometry *g, const BufferParameters &params)
	Initializes a buffer computation for the given geometry with the given set of parameters. More...

void	setEndCapStyle (int nEndCapStyle)
	Specifies the end cap style of the generated buffer. More...

void	setQuadrantSegments (int nQuadrantSegments)
	Sets the number of segments used to approximate a angle fillet. More...

void	setSingleSided (bool isSingleSided)
	Sets whether the computed buffer should be single-sided. More...

geom::Geometry *	getResultGeometry (double nDistance)
	Returns the buffer computed for a geometry for a given buffer distance. More...

Static Public Member Functions
static geom::Geometry *	bufferOp (const geom::Geometry *g, double distance, int quadrantSegments=BufferParameters::DEFAULT_QUADRANT_SEGMENTS, int endCapStyle=BufferParameters::CAP_ROUND)
	Computes the buffer for a geometry for a given buffer distance and accuracy of approximation. More...

Private Member Functions
void	computeGeometry ()

void	bufferOriginalPrecision ()

void	bufferReducedPrecision (int precisionDigits)

void	bufferReducedPrecision ()

void	bufferFixedPrecision (const geom::PrecisionModel &fixedPM)

Static Private Member Functions
static double	precisionScaleFactor (const geom::Geometry *g, double distance, int maxPrecisionDigits)

Private Attributes
const geom::Geometry *	argGeom

util::TopologyException	saveException

double	distance

BufferParameters	bufParams

geom::Geometry *	resultGeometry

Static Private Attributes
static const int	MAX_PRECISION_DIGITS = 12
	A number of digits of precision which leaves some computational "headroom" for floating point operations. More...

Detailed Description

Computes the buffer of a geometry, for both positive and negative buffer distances.

In GIS, the positive (or negative) buffer of a geometry is defined as the Minkowski sum (or difference) of the geometry with a circle with radius equal to the absolute value of the buffer distance. In the CAD/CAM world buffers are known as offset curves. In morphological analysis the operation of positive and negative buffering is referred to as erosion and dilation.

The buffer operation always returns a polygonal result. The negative or zero-distance buffer of lines and points is always an empty Polygon.

Since true buffer curves may contain circular arcs, computed buffer polygons can only be approximations to the true geometry. The user can control the accuracy of the curve approximation by specifying the number of linear segments with which to approximate a curve.

The end cap style of a linear buffer may be specified. The following end cap styles are supported:

CAP_ROUND - the usual round end caps
CAP_BUTT - end caps are truncated flat at the line ends
CAP_SQUARE - end caps are squared off at the buffer distance beyond the line ends

Definition at line 78 of file BufferOp.h.

Member Enumeration Documentation

anonymous enum

Enumerator

CAP_ROUND

Specifies a round line buffer end cap style.

Deprecated:: use BufferParameters

CAP_BUTT

Specifies a butt (or flat) line buffer end cap style.

Deprecated:: use BufferParameters

CAP_SQUARE

Specifies a square line buffer end cap style.

Deprecated:: use BufferParameters

Definition at line 134 of file BufferOp.h.

Constructor & Destructor Documentation

geos::operation::buffer::BufferOp::BufferOp ( const geom::Geometry * g )

inline

Initializes a buffer computation for the given geometry.

Parameters

g	the geometry to buffer

Definition at line 171 of file BufferOp.h.

geos::operation::buffer::BufferOp::BufferOp	(	const geom::Geometry *	g,
		const BufferParameters &	params
	)

inline

Initializes a buffer computation for the given geometry with the given set of parameters.

Parameters

g	the geometry to buffer
params	the buffer parameters to use. This class will copy it to private memory.

Definition at line 187 of file BufferOp.h.

Member Function Documentation

void geos::operation::buffer::BufferOp::bufferFixedPrecision ( const geom::PrecisionModel & fixedPM )

private

static geom::Geometry* geos::operation::buffer::BufferOp::bufferOp	(	const geom::Geometry *	g,
		double	distance,
		int	quadrantSegments = `BufferParameters::DEFAULT_QUADRANT_SEGMENTS`,
		int	endCapStyle = `BufferParameters::CAP_ROUND`
	)

static

Computes the buffer for a geometry for a given buffer distance and accuracy of approximation.

Parameters

g	the geometry to buffer
distance	the buffer distance
quadrantSegments	the number of segments used to approximate a quarter circle
endCapStyle	line buffer end cap style (default: BufferParameters::CAP_ROUND)

Returns: the buffer of the input geometry

void geos::operation::buffer::BufferOp::bufferOriginalPrecision ( )

private

void geos::operation::buffer::BufferOp::bufferReducedPrecision ( int precisionDigits )

private

void geos::operation::buffer::BufferOp::bufferReducedPrecision ( )

private

void geos::operation::buffer::BufferOp::computeGeometry ( )

private

geom::Geometry* geos::operation::buffer::BufferOp::getResultGeometry ( double nDistance )

Returns the buffer computed for a geometry for a given buffer distance.

Parameters

nDistance the buffer distance

Returns: the buffer of the input geometry

static double geos::operation::buffer::BufferOp::precisionScaleFactor	(	const geom::Geometry *	g,
		double	distance,
		int	maxPrecisionDigits
	)

staticprivate

Compute a reasonable scale factor to limit the precision of a given combination of Geometry and buffer distance. The scale factor is based on a heuristic.

Parameters

g	the Geometry being buffered
distance	the buffer distance
maxPrecisionDigits	the mzx # of digits that should be allowed by the precision determined by the computed scale factor

Returns: a scale factor that allows a reasonable amount of precision for the buffer computation

void geos::operation::buffer::BufferOp::setEndCapStyle ( int nEndCapStyle )

inline

Specifies the end cap style of the generated buffer.

The styles supported are CAP_ROUND, CAP_BUTT, and CAP_SQUARE. The default is CAP_ROUND.

Parameters

nEndCapStyle the end cap style to specify

Definition at line 253 of file BufferOp.h.

void geos::operation::buffer::BufferOp::setQuadrantSegments ( int nQuadrantSegments )

inline

Sets the number of segments used to approximate a angle fillet.

Parameters

nQuadrantSegments the number of segments in a fillet for a quadrant

Definition at line 247 of file BufferOp.h.

void geos::operation::buffer::BufferOp::setSingleSided ( bool isSingleSided )

inline

Sets whether the computed buffer should be single-sided.

A single-sided buffer is constructed on only one side of each input line.

The side used is determined by the sign of the buffer distance:

a positive distance indicates the left-hand side
a negative distance indicates the right-hand side

The single-sided buffer of point geometries is the same as the regular buffer.

The End Cap Style for single-sided buffers is always ignored, and forced to the equivalent of CAP_FLAT.

Parameters

isSingleSided true if a single-sided buffer should be constructed

Definition at line 259 of file BufferOp.h.

Member Data Documentation

const geom::Geometry* geos::operation::buffer::BufferOp::argGeom

private

Definition at line 110 of file BufferOp.h.

BufferParameters geos::operation::buffer::BufferOp::bufParams

private

Definition at line 118 of file BufferOp.h.

double geos::operation::buffer::BufferOp::distance

private

Definition at line 114 of file BufferOp.h.

const int geos::operation::buffer::BufferOp::MAX_PRECISION_DIGITS = 12

staticprivate

A number of digits of precision which leaves some computational "headroom" for floating point operations.

This value should be less than the decimal precision of double-precision values (16).

Definition at line 89 of file BufferOp.h.

geom::Geometry* geos::operation::buffer::BufferOp::resultGeometry

private

Definition at line 120 of file BufferOp.h.

util::TopologyException geos::operation::buffer::BufferOp::saveException

private

Definition at line 112 of file BufferOp.h.

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

BufferOp.h

Public Types

Public Member Functions

Static Public Member Functions

Private Member Functions

Static Private Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation