com.vividsolutions.jts.geom
Class Triangle

java.lang.Object
  com.vividsolutions.jts.geom.Triangle

public class Triangle
extends java.lang.Object

Represents a planar triangle, and provides methods for calculating various properties of triangles.

Version:

1.7

Field Summary

Coordinate	p0 The coordinates of the vertices of the triangle
Coordinate	p1 The coordinates of the vertices of the triangle
Coordinate	p2 The coordinates of the vertices of the triangle

Constructor Summary

Triangle(Coordinate p0, Coordinate p1, Coordinate p2)
Creates a new triangle with the given vertices.

Method Summary

static Coordinate	angleBisector(Coordinate a, Coordinate b, Coordinate c) Computes the point at which the bisector of the angle ABC cuts the segment AC.
static double	area(Coordinate a, Coordinate b, Coordinate c) Computes the 2D area of a triangle.
static double	area3D(Coordinate a, Coordinate b, Coordinate c) Computes the 3D area of a triangle.
static Coordinate	centroid(Coordinate a, Coordinate b, Coordinate c) Computes the centroid (centre of mass) of a triangle.
static Coordinate	circumcentre(Coordinate a, Coordinate b, Coordinate c) Computes the circumcentre of a triangle.
Coordinate	inCentre() Computes the incentre of a triangle.
static Coordinate	inCentre(Coordinate a, Coordinate b, Coordinate c) Computes the incentre of a triangle.
static boolean	isAcute(Coordinate a, Coordinate b, Coordinate c) Tests whether a triangle is acute.
static double	longestSideLength(Coordinate a, Coordinate b, Coordinate c) Computes the length of the longest side of a triangle
static HCoordinate	perpendicularBisector(Coordinate a, Coordinate b) Computes the line which is the perpendicular bisector of the line segment a-b.
static double	signedArea(Coordinate a, Coordinate b, Coordinate c) Computes the signed 2D area of a triangle.

Methods inherited from class java.lang.Object

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

Field Detail

p0

public Coordinate p0

The coordinates of the vertices of the triangle

p1

public Coordinate p1

The coordinates of the vertices of the triangle

p2

public Coordinate p2

The coordinates of the vertices of the triangle

Constructor Detail

Triangle

public Triangle(Coordinate p0,
                Coordinate p1,
                Coordinate p2)

Creates a new triangle with the given vertices.

Parameters:

p0 - a vertex

p1 - a vertex

p2 - a vertex

Method Detail

isAcute

public static boolean isAcute(Coordinate a,
                              Coordinate b,
                              Coordinate c)

Tests whether a triangle is acute. A triangle is acute iff all interior angles are acute. This is a strict test - right triangles will return false A triangle which is not acute is either right or obtuse.

Note: this implementation is not robust for angles very close to 90 degrees.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

true if the triangle is acute

perpendicularBisector

public static HCoordinate perpendicularBisector(Coordinate a,
                                                Coordinate b)

Computes the line which is the perpendicular bisector of the line segment a-b.

Parameters:

a - a point

b - another point

Returns:

the perpendicular bisector, as an HCoordinate

circumcentre

public static Coordinate circumcentre(Coordinate a,
                                      Coordinate b,
                                      Coordinate c)

Computes the circumcentre of a triangle. The circumcentre is the centre of the circumcircle, the smallest circle which encloses the triangle. It is also the common intersection point of the perpendicular bisectors of the sides of the triangle, and is the only point which has equal distance to all three vertices of the triangle.

The circumcentre does not necessarily lie within the triangle.

This method uses an algorithm due to J.R.Shewchuk which uses normalization to the origin to improve the accuracy of computation. (See Lecture Notes on Geometric Robustness, Jonathan Richard Shewchuk, 1999).

Parameters:

a - a vertx of the triangle

b - a vertx of the triangle

c - a vertx of the triangle

Returns:

the circumcentre of the triangle

inCentre

public static Coordinate inCentre(Coordinate a,
                                  Coordinate b,
                                  Coordinate c)

Computes the incentre of a triangle. The inCentre of a triangle is the point which is equidistant from the sides of the triangle. It is also the point at which the bisectors of the triangle's angles meet. It is the centre of the triangle's incircle, which is the unique circle that is tangent to each of the triangle's three sides.

The incentre always lies within the triangle.

Parameters:

a - a vertx of the triangle

b - a vertx of the triangle

c - a vertx of the triangle

Returns:

the point which is the incentre of the triangle

centroid

public static Coordinate centroid(Coordinate a,
                                  Coordinate b,
                                  Coordinate c)

Computes the centroid (centre of mass) of a triangle. This is also the point at which the triangle's three medians intersect (a triangle median is the segment from a vertex of the triangle to the midpoint of the opposite side). The centroid divides each median in a ratio of 2:1.

The centroid always lies within the triangle.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the centroid of the triangle

longestSideLength

public static double longestSideLength(Coordinate a,
                                       Coordinate b,
                                       Coordinate c)

Computes the length of the longest side of a triangle

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the length of the longest side of the triangle

angleBisector

public static Coordinate angleBisector(Coordinate a,
                                       Coordinate b,
                                       Coordinate c)

Computes the point at which the bisector of the angle ABC cuts the segment AC.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the angle bisector cut point

area

public static double area(Coordinate a,
                          Coordinate b,
                          Coordinate c)

Computes the 2D area of a triangle. The area value is always non-negative.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the area of the triangle

See Also:

signedArea(Coordinate, Coordinate, Coordinate)

signedArea

public static double signedArea(Coordinate a,
                                Coordinate b,
                                Coordinate c)

Computes the signed 2D area of a triangle. The area value is positive if the triangle is oriented CW, and negative if it is oriented CCW.

The signed area value can be used to determine point orientation, but the implementation in this method is susceptible to round-off errors. Use CGAlgorithms.orientationIndex(Coordinate, Coordinate, Coordinate) for robust orientation calculation.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the signed 2D area of the triangle

See Also:

CGAlgorithms.orientationIndex(Coordinate, Coordinate, Coordinate)

area3D

public static double area3D(Coordinate a,
                            Coordinate b,
                            Coordinate c)

Computes the 3D area of a triangle. The value computed is alway non-negative.

Parameters:

a - a vertex of the triangle

b - a vertex of the triangle

c - a vertex of the triangle

Returns:

the 3D area of the triangle

inCentre

public Coordinate inCentre()

Computes the incentre of a triangle. The incentre of a triangle is the point which is equidistant from the sides of the triangle. It is also the point at which the bisectors of the triangle's angles meet. It is the centre of the triangle's incircle, which is the unique circle that is tangent to each of the triangle's three sides.

Returns:

the point which is the inCentre of the triangle