edu.ie3.util.geo

Class GrahamScan

java.lang.Object

edu.ie3.util.geo.GrahamScan

public final class GrahamScan
extends java.lang.Object

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	GrahamScan.Turn An enum denoting a directional-turn between 3 points (vectors).

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	GrahamScan()

Method Summary

Modifier and Type	Method and Description
protected static boolean	areAllCollinear(java.util.List<java.awt.Point> points) Returns true iff all points in points are collinear.
static java.util.List<java.awt.Point>	getConvexHull(int[] xs, int[] ys) Returns the convex hull of the points created from xs and ys.
static java.util.List<java.awt.Point>	getConvexHull(java.util.List<java.awt.Point> points) Returns the convex hull of the points created from the list points.
protected static java.awt.Point	getLowestPoint(java.util.List<java.awt.Point> points) Returns the points with the lowest y coordinate.
protected static java.util.Set<java.awt.Point>	getSortedPointSet(java.util.List<java.awt.Point> points) Returns a sorted set of points from the list points.
protected static GrahamScan.Turn	getTurn(java.awt.Point a, java.awt.Point b, java.awt.Point c) Returns the GrahamScan#Turn formed by traversing through the ordered points a, b and c.

Methods inherited from class java.lang.Object

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

Constructor Detail

GrahamScan

protected GrahamScan()

Method Detail

areAllCollinear

protected static boolean areAllCollinear(java.util.List<java.awt.Point> points)

Returns true iff all points in points are collinear.

Parameters:

points - the list of points.

Returns:

true iff all points in points are collinear.

getConvexHull

public static java.util.List<java.awt.Point> getConvexHull(int[] xs,
                                                           int[] ys)

Returns the convex hull of the points created from xs and ys. Note that the first and last point in the returned List<java.awt.Point> are the same point.

Parameters:

xs - the x coordinates.

ys - the y coordinates.

Returns:

the convex hull of the points created from xs and ys.

Throws:

java.lang.IllegalArgumentException - if xs and ys don't have the same size, if all points are collinear or if there are less than 3 unique points present.

getConvexHull

public static java.util.List<java.awt.Point> getConvexHull(java.util.List<java.awt.Point> points)

Returns the convex hull of the points created from the list points. Note that the first and last point in the returned List<java.awt.Point> are the same point.

Parameters:

points - the list of points.

Returns:

the convex hull of the points created from the list points.

Throws:

java.lang.IllegalArgumentException - if all points are collinear or if there are less than 3 unique points present.

getLowestPoint

protected static java.awt.Point getLowestPoint(java.util.List<java.awt.Point> points)

Returns the points with the lowest y coordinate. In case more than 1 such point exists, the one with the lowest x coordinate is returned.

Parameters:

points - the list of points to return the lowest point from.

Returns:

the points with the lowest y coordinate. In case more than 1 such point exists, the one with the lowest x coordinate is returned.

getSortedPointSet

protected static java.util.Set<java.awt.Point> getSortedPointSet(java.util.List<java.awt.Point> points)

Returns a sorted set of points from the list points. The set of points are sorted in increasing order of the angle they and the lowest point P make with the x-axis. If tow (or more) points form the same angle towards P, the one closest to P comes first.

Parameters:

points - the list of points to sort.

Returns:

a sorted set of points from the list points.

See Also:

getLowestPoint(java.util.List)

getTurn

protected static GrahamScan.Turn getTurn(java.awt.Point a,
                                         java.awt.Point b,
                                         java.awt.Point c)

Returns the GrahamScan#Turn formed by traversing through the ordered points a, b and c. More specifically, the cross product C between the 3 points (vectors) is calculated: (b.x-a.x * c.y-a.y) - (b.y-a.y * c.x-a.x) and if C is less than 0, the turn is CLOCKWISE, if C is more than 0, the turn is COUNTER_CLOCKWISE, else the three points are COLLINEAR.

Parameters:

a - the starting point.

b - the second point.

c - the end point.

Returns:

the GrahamScan#Turn formed by traversing through the ordered points a, b and c.