Package org.locationtech.jts.algorithm

Class Centroid

java.lang.Object

org.locationtech.jts.algorithm.Centroid

public class Centroid
extends java.lang.Object

Computes the centroid of a Geometry of any dimension. If the geometry is nominally of higher dimension, but has lower effective dimension (i.e. contains only components having zero length or area), the centroid will be computed as for the equivalent lower-dimension geometry. If the input geometry is empty, a null Coordinate is returned.

Algorithm

• Dimension 2 - the centroid is computed as the weighted sum of the centroids of a decomposition of the area into (possibly overlapping) triangles. Holes and multipolygons are handled correctly. 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. Zero-length lines are treated as points.
• Dimension 0 - Compute the average coordinate for all points. Repeated points are all included in the average.

Version:

1.7

Field Summary

Fields

Modifier and Type	Field	Description
private Coordinate	areaBasePt
private double	areasum2
private Coordinate	cg3
private Coordinate	lineCentSum
private Coordinate	ptCentSum
private int	ptCount
private double	totalLength
private Coordinate	triangleCent3

Constructor Summary

Constructors

Constructor	Description
Centroid(Geometry geom)	Creates a new instance for computing the centroid of a geometry

Method Summary

Modifier and Type	Method	Description
private void	add(Geometry geom)	Adds a Geometry to the centroid total.
private void	add(Polygon poly)
private void	addHole(Coordinate[] pts)
private void	addLineSegments(Coordinate[] pts)	Adds the line segments defined by an array of coordinates to the linear centroid accumulators.
private void	addPoint(Coordinate pt)	Adds a point to the point centroid accumulator.
private void	addShell(Coordinate[] pts)
private void	addTriangle(Coordinate p0, Coordinate p1, Coordinate p2, boolean isPositiveArea)
private static double	area2(Coordinate p1, Coordinate p2, Coordinate p3)	Returns twice the signed area of the triangle p1-p2-p3.
private static void	centroid3(Coordinate p1, Coordinate p2, Coordinate p3, Coordinate c)	Computes three times the centroid of the triangle p1-p2-p3.
Coordinate	getCentroid()	Gets the computed centroid.
static Coordinate	getCentroid(Geometry geom)	Computes the centroid point of a geometry.
private void	setAreaBasePoint(Coordinate basePt)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

areaBasePt

private Coordinate areaBasePt

triangleCent3

private Coordinate triangleCent3

areasum2

private double areasum2

cg3

private Coordinate cg3

lineCentSum

private Coordinate lineCentSum

totalLength

private double totalLength

ptCount

private int ptCount

ptCentSum

private Coordinate ptCentSum

Constructor Detail

Centroid

public Centroid(Geometry geom)

Creates a new instance for computing the centroid of a geometry

Method Detail

getCentroid

public static Coordinate getCentroid(Geometry geom)

Computes the centroid point of a geometry.

Parameters:

geom - the geometry to use

Returns:

the centroid point, or null if the geometry is empty

add

private void add(Geometry geom)

Adds a Geometry to the centroid total.

Parameters:

geom - the geometry to add

getCentroid

public Coordinate getCentroid()

Gets the computed centroid.

Returns:

the computed centroid, or null if the input is empty

setAreaBasePoint

private void setAreaBasePoint(Coordinate basePt)

add

private void add(Polygon poly)

addShell

private void addShell(Coordinate[] pts)

addHole

private void addHole(Coordinate[] pts)

addTriangle

private void addTriangle(Coordinate p0,
                         Coordinate p1,
                         Coordinate p2,
                         boolean isPositiveArea)

centroid3

private static void centroid3(Coordinate p1,
                              Coordinate p2,
                              Coordinate p3,
                              Coordinate c)

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.

area2

private static double area2(Coordinate p1,
                            Coordinate p2,
                            Coordinate p3)

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.

addLineSegments

private void addLineSegments(Coordinate[] pts)

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

Parameters:

pts - an array of Coordinates

addPoint

private void addPoint(Coordinate pt)

Adds a point to the point centroid accumulator.

Parameters:

pt - a Coordinate