org.apache.commons.math3.geometry.euclidean.twod.hull

Class MonotoneChain

java.lang.Object

org.apache.commons.math3.geometry.euclidean.twod.hull.MonotoneChain

All Implemented Interfaces:

ConvexHullGenerator2D, ConvexHullGenerator<Euclidean2D,Vector2D>

public class MonotoneChain
extends Object

Implements Andrew's monotone chain method to generate the convex hull of a finite set of points in the two-dimensional euclidean space.

The runtime complexity is O(n log n), with n being the number of input points. If the point set is already sorted (by x-coordinate), the runtime complexity is O(n).

The implementation is not sensitive to collinear points on the hull. The parameter includeCollinearPoints allows to control the behavior with regard to collinear points. If true, all points on the boundary of the hull will be added to the hull vertices, otherwise only the extreme points will be present. By default, collinear points are not added as hull vertices.

The tolerance parameter (default: 1e-10) is used as epsilon criteria to determine identical and collinear points.

Since:

3.3

See Also:

Andrew's monotone chain algorithm (Wikibooks)

Constructor Summary

Constructors

Constructor and Description
MonotoneChain() Create a new MonotoneChain instance.
MonotoneChain(boolean includeCollinearPoints) Create a new MonotoneChain instance.
MonotoneChain(boolean includeCollinearPoints, double tolerance) Create a new MonotoneChain instance.

Method Summary

Modifier and Type	Method and Description
Collection<Vector2D>	findHullVertices(Collection<Vector2D> points) Find the convex hull vertices from the set of input points.
ConvexHull2D	generate(Collection<Vector2D> points) Builds the convex hull from the set of input points.
double	getTolerance() Get the tolerance below which points are considered identical.
boolean	isIncludeCollinearPoints() Returns if collinear points on the hull will be added as hull vertices.

Methods inherited from class java.lang.Object

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

Constructor Detail

MonotoneChain

public MonotoneChain()

Create a new MonotoneChain instance.

MonotoneChain

public MonotoneChain(boolean includeCollinearPoints)

Create a new MonotoneChain instance.

Parameters:

includeCollinearPoints - whether collinear points shall be added as hull vertices

MonotoneChain

public MonotoneChain(boolean includeCollinearPoints,
                     double tolerance)

Create a new MonotoneChain instance.

Parameters:

includeCollinearPoints - whether collinear points shall be added as hull vertices

tolerance - tolerance below which points are considered identical

Method Detail

findHullVertices

public Collection<Vector2D> findHullVertices(Collection<Vector2D> points)

Find the convex hull vertices from the set of input points.

Parameters:

points - the set of input points

Returns:

the convex hull vertices in CCW winding

getTolerance

public double getTolerance()

Get the tolerance below which points are considered identical.

Returns:

the tolerance below which points are considered identical

isIncludeCollinearPoints

public boolean isIncludeCollinearPoints()

Returns if collinear points on the hull will be added as hull vertices.

Returns:

true if collinear points are added as hull vertices, or false if only extreme points are present.

generate

public ConvexHull2D generate(Collection<Vector2D> points)
                      throws NullArgumentException,
                             ConvergenceException

Builds the convex hull from the set of input points.

Specified by:

generate in interface ConvexHullGenerator2D

Specified by:

generate in interface ConvexHullGenerator<Euclidean2D,Vector2D>

Parameters:

points - the set of input points

Returns:

the convex hull

Throws:

NullArgumentException - if the input collection is null

ConvergenceException - if generator fails to generate a convex hull for the given set of input points