Class Octant

1	/*
2	* Copyright (c) 2016 Vivid Solutions.
3	*
4	* All rights reserved. This program and the accompanying materials
5	* are made available under the terms of the Eclipse Public License 2.0
6	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
7	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
8	* and the Eclipse Distribution License is available at
9	*
10	* http://www.eclipse.org/org/documents/edl-v10.php.
11	*/
12
13	package org.locationtech.jts.noding;
14
15	import org.locationtech.jts.geom.Coordinate;
16	/**
17	* Methods for computing and working with octants of the Cartesian plane
18	* Octants are numbered as follows:
19	* <pre>
20	* \2\|1/
21	* 3 \\|/ 0
22	* ---+--
23	* 4 /\|\ 7
24	* /5\|6\
25	* </pre>
26	* If line segments lie along a coordinate axis, the octant is the lower of the two
27	* possible values.
28	*
29	* @version 1.7
30	*/
31	public class Octant {
32
33	/**
34	* Returns the octant of a directed line segment (specified as x and y
35	* displacements, which cannot both be 0).
36	*/
37	public static int octant(double dx, double dy)
38	{
39	if (dx == 0.0 && dy == 0.0)
40	throw new IllegalArgumentException("Cannot compute the octant for point ( "+ dx + ", " + dy + " )" );
41
42	double adx = Math.abs(dx);
43	double ady = Math.abs(dy);
44
45	if (dx >= 0) {
46	if (dy >= 0) {
47	if (adx >= ady)
48	return 0;
49	else
50	return 1;
51	}
52	else { // dy < 0
53	if (adx >= ady)
54	return 7;
55	else
56	return 6;
57	}
58	}
59	else { // dx < 0
60	if (dy >= 0) {
61	if (adx >= ady)
62	return 3;
63	else
64	return 2;
65	}
66	else { // dy < 0
67	if (adx >= ady)
68	return 4;
69	else
70	return 5;
71	}
72	}
73	}
74
75	/**
76	* Returns the octant of a directed line segment from p0 to p1.
77	*/
78	public static int octant(Coordinate p0, Coordinate p1)
79	{
80	double dx = p1.x - p0.x;
81	double dy = p1.y - p0.y;
82	if (dx == 0.0 && dy == 0.0)
83	throw new IllegalArgumentException("Cannot compute the octant for two identical points " + p0);
84	return octant(dx, dy);
85	}
86
87	private Octant() {
88	}
89	}
90