Class Quadrant

1
2
3
4	/*
5	* Copyright (c) 2016 Vivid Solutions.
6	*
7	* All rights reserved. This program and the accompanying materials
8	* are made available under the terms of the Eclipse Public License 2.0
9	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
10	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
11	* and the Eclipse Distribution License is available at
12	*
13	* http://www.eclipse.org/org/documents/edl-v10.php.
14	*/
15	package org.locationtech.jts.geomgraph;
16
17	/**
18	* @version 1.7
19	*/
20	import org.locationtech.jts.geom.Coordinate;
21
22	/**
23	* Utility functions for working with quadrants, which are numbered as follows:
24	* <pre>
25	* 1 \| 0
26	* --+--
27	* 2 \| 3
28	* </pre>
29	*
30	* @version 1.7
31	*/
32	public class Quadrant
33	{
34	public static final int NE = 0;
35	public static final int NW = 1;
36	public static final int SW = 2;
37	public static final int SE = 3;
38
39	/**
40	* Returns the quadrant of a directed line segment (specified as x and y
41	* displacements, which cannot both be 0).
42	*
43	* @throws IllegalArgumentException if the displacements are both 0
44	*/
45	public static int quadrant(double dx, double dy)
46	{
47	if (dx == 0.0 && dy == 0.0)
48	throw new IllegalArgumentException("Cannot compute the quadrant for point ( "+ dx + ", " + dy + " )" );
49	if (dx >= 0.0) {
50	if (dy >= 0.0)
51	return NE;
52	else
53	return SE;
54	}
55	else {
56	if (dy >= 0.0)
57	return NW;
58	else
59	return SW;
60	}
61	}
62
63	/**
64	* Returns the quadrant of a directed line segment from p0 to p1.
65	*
66	* @throws IllegalArgumentException if the points are equal
67	*/
68	public static int quadrant(Coordinate p0, Coordinate p1)
69	{
70	if (p1.x == p0.x && p1.y == p0.y)
71	throw new IllegalArgumentException("Cannot compute the quadrant for two identical points " + p0);
72
73	if (p1.x >= p0.x) {
74	if (p1.y >= p0.y)
75	return NE;
76	else
77	return SE;
78	}
79	else {
80	if (p1.y >= p0.y)
81	return NW;
82	else
83	return SW;
84	}
85	}
86
87	/**
88	* Returns true if the quadrants are 1 and 3, or 2 and 4
89	*/
90	public static boolean isOpposite(int quad1, int quad2)
91	{
92	if (quad1 == quad2) return false;
93	int diff = (quad1 - quad2 + 4) % 4;
94	// if quadrants are not adjacent, they are opposite
95	if (diff == 2) return true;
96	return false;
97	}
98
99	/**
100	* Returns the right-hand quadrant of the halfplane defined by the two quadrants,
101	* or -1 if the quadrants are opposite, or the quadrant if they are identical.
102	*/
103	public static int commonHalfPlane(int quad1, int quad2)
104	{
105	// if quadrants are the same they do not determine a unique common halfplane.
106	// Simply return one of the two possibilities
107	if (quad1 == quad2) return quad1;
108	int diff = (quad1 - quad2 + 4) % 4;
109	// if quadrants are not adjacent, they do not share a common halfplane
110	if (diff == 2) return -1;
111	//
112	int min = (quad1 < quad2) ? quad1 : quad2;
113	int max = (quad1 > quad2) ? quad1 : quad2;
114	// for this one case, the righthand plane is NOT the minimum index;
115	if (min == 0 && max == 3) return 3;
116	// in general, the halfplane index is the minimum of the two adjacent quadrants
117	return min;
118	}
119
120	/**
121	* Returns whether the given quadrant lies within the given halfplane (specified
122	* by its right-hand quadrant).
123	*/
124	public static boolean isInHalfPlane(int quad, int halfPlane)
125	{
126	if (halfPlane == SE) {
127	return quad == SE \|\| quad == SW;
128	}
129	return quad == halfPlane \|\| quad == halfPlane + 1;
130	}
131
132	/**
133	* Returns true if the given quadrant is 0 or 1.
134	*/
135	public static boolean isNorthern(int quad)
136	{
137	return quad == NE \|\| quad == NW;
138	}
139	}
140