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

Class MonotoneChain

java.lang.Object

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

All Implemented Interfaces:

ConvexHullGenerator<Vector2D>, ConvexHullGenerator2D

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.

See Also:

Andrew's monotone chain algorithm (Wikibooks)

Constructor Summary

Constructors

Constructor and Description
MonotoneChain(boolean includeCollinearPoints, DoublePrecisionContext precision) Create a new instance with the given parameters.
MonotoneChain(DoublePrecisionContext precision) Create a new instance that only includes extreme points as hull vertices.

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) Build a convex hull from the set of input points.
DoublePrecisionContext	getPrecision() Get the object used to determine floating point equality for this region.
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(DoublePrecisionContext precision)

Create a new instance that only includes extreme points as hull vertices.

Parameters:

precision - precision context used to compare floating point numbers

MonotoneChain

public MonotoneChain(boolean includeCollinearPoints,
                     DoublePrecisionContext precision)

Create a new instance with the given parameters.

Parameters:

includeCollinearPoints - whether collinear points shall be added as hull vertices

precision - precision context used to compare floating point numbers

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

getPrecision

public DoublePrecisionContext getPrecision()

Get the object used to determine floating point equality for this region.

Returns:

the floating point precision context for the instance

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)

Build a convex hull from the set of input points.

Specified by:

generate in interface ConvexHullGenerator<Vector2D>

Specified by:

generate in interface ConvexHullGenerator2D

Parameters:

points - the set of input points

Returns:

the convex hull