geos::algorithm::Centroid Class Reference

Computes the centroid of a Geometry of any dimension. More...

#include <Centroid.h>

Collaboration diagram for geos::algorithm::Centroid:

Public Member Functions
	Centroid (const geom::Geometry &geom)
	Creates a new instance for computing the centroid of a geometry. More...
bool	getCentroid (geom::Coordinate &cent) const
	Gets the computed centroid. More...

Static Public Member Functions
static bool	getCentroid (const geom::Geometry &geom, geom::Coordinate &cent)
	Computes the centroid point of a geometry. More...

Private Member Functions
void	add (const geom::Geometry &geom)
void	setAreaBasePoint (const geom::Coordinate &basePt)
void	add (const geom::Polygon &poly)
void	addShell (const geom::CoordinateSequence &pts)
void	addHole (const geom::CoordinateSequence &pts)
void	addTriangle (const geom::Coordinate &p0, const geom::Coordinate &p1, const geom::Coordinate &p2, bool isPositiveArea)
void	addLineSegments (const geom::CoordinateSequence &pts)
void	addPoint (const geom::Coordinate &pt)

Static Private Member Functions
static void	centroid3 (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &p3, geom::Coordinate &c)
static double	area2 (const geom::Coordinate &p1, const geom::Coordinate &p2, const geom::Coordinate &p3)

Private Attributes
std::unique_ptr< geom::Coordinate >	areaBasePt
geom::Coordinate	triangleCent3
geom::Coordinate	cg3
geom::Coordinate	lineCentSum
geom::Coordinate	ptCentSum
double	areasum2
double	totalLength
int	ptCount

Detailed Description

Computes the centroid of a Geometry of any dimension.

If the geometry is nomimally of higher dimension, but contains only components having a lower effective dimension (i.e. zero length or area), the centroid will be computed appropriately.

Algorithm

• Dimension = 2 - Based on the usual algorithm for calculating the centroid as a weighted sum of the centroids of a decomposition of the area into (possibly overlapping) triangles. The algorithm has been extended to handle holes and multi-polygons. See http://www.faqs.org/faqs/graphics/algorithms-faq/ for further details of the basic approach.
• Dimension = 1 - Computes the average of the midpoints of all line segments weighted by the segment length.
• Dimension = 0 - Compute the average coordinate over all points.

If the input geometries are empty, a null Coordinate is returned.

Definition at line 61 of file Centroid.h.

Constructor & Destructor Documentation

geos::algorithm::Centroid::Centroid ( const geom::Geometry &  geom )

inline

Creates a new instance for computing the centroid of a geometry.

Definition at line 79 of file Centroid.h.

Member Function Documentation

void geos::algorithm::Centroid::add ( const geom::Geometry &  geom )

private

Adds a Geometry to the centroid total.

Parameters

geom	the geometry to add

void geos::algorithm::Centroid::add ( const geom::Polygon &  poly )

private

void geos::algorithm::Centroid::addHole ( const geom::CoordinateSequence &  pts )

private

void geos::algorithm::Centroid::addLineSegments ( const geom::CoordinateSequence &  pts )

private

Adds the line segments defined by an array of coordinates to the linear centroid accumulators.

Parameters

pts	an array of Coordinates

void geos::algorithm::Centroid::addPoint ( const geom::Coordinate &  pt )

private

Adds a point to the point centroid accumulator.

Parameters

pt	a Coordinate

void geos::algorithm::Centroid::addShell ( const geom::CoordinateSequence &  pts )

private

void geos::algorithm::Centroid::addTriangle ( const geom::Coordinate &  p0, const geom::Coordinate &  p1, const geom::Coordinate &  p2, bool  isPositiveArea  )

private

static double geos::algorithm::Centroid::area2 ( const geom::Coordinate &  p1, const geom::Coordinate &  p2, const geom::Coordinate &  p3  )

staticprivate

Returns twice the signed area of the triangle p1-p2-p3. The area is positive if the triangle is oriented CCW, and negative if CW.

static void geos::algorithm::Centroid::centroid3 ( const geom::Coordinate &  p1, const geom::Coordinate &  p2, const geom::Coordinate &  p3, geom::Coordinate &  c  )

staticprivate

Computes three times the centroid of the triangle p1-p2-p3. The factor of 3 is left in to permit division to be avoided until later.

static bool geos::algorithm::Centroid::getCentroid ( const geom::Geometry &  geom, geom::Coordinate &  cent  )

static

Computes the centroid point of a geometry.

Parameters

geom	the geometry to use
cent	will be set to the centroid point, if any

Returns

true if a centroid could be computed, false otherwise (empty geom)

bool geos::algorithm::Centroid::getCentroid

(

geom::Coordinate &

cent

)

const

Gets the computed centroid.

Parameters

cent	will be set to the centroid point, if any

Returns

true if a centroid could be computed, false otherwise (empty geom)

void geos::algorithm::Centroid::setAreaBasePoint ( const geom::Coordinate &  basePt )

private

Member Data Documentation

std::unique_ptr<geom::Coordinate> geos::algorithm::Centroid::areaBasePt

private

Definition at line 100 of file Centroid.h.

double geos::algorithm::Centroid::areasum2

private

Definition at line 105 of file Centroid.h.

geom::Coordinate geos::algorithm::Centroid::cg3

private

Definition at line 102 of file Centroid.h.

geom::Coordinate geos::algorithm::Centroid::lineCentSum

private

Definition at line 103 of file Centroid.h.

geom::Coordinate geos::algorithm::Centroid::ptCentSum

private

Definition at line 104 of file Centroid.h.

int geos::algorithm::Centroid::ptCount

private

Definition at line 107 of file Centroid.h.

double geos::algorithm::Centroid::totalLength

private

Definition at line 106 of file Centroid.h.

geom::Coordinate geos::algorithm::Centroid::triangleCent3

private

Definition at line 101 of file Centroid.h.

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

• Centroid.h