Class Key

1
2	/*
3	* Copyright (c) 2016 Vivid Solutions.
4	*
5	* All rights reserved. This program and the accompanying materials
6	* are made available under the terms of the Eclipse Public License 2.0
7	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
8	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
9	* and the Eclipse Distribution License is available at
10	*
11	* http://www.eclipse.org/org/documents/edl-v10.php.
12	*/
13	package org.locationtech.jts.index.quadtree;
14
15	import org.locationtech.jts.geom.Coordinate;
16	import org.locationtech.jts.geom.Envelope;
17
18	/**
19	* A Key is a unique identifier for a node in a quadtree.
20	* It contains a lower-left point and a level number. The level number
21	* is the power of two for the size of the node envelope
22	*
23	* @version 1.7
24	*/
25	public class Key {
26
27	public static int computeQuadLevel(Envelope env)
28	{
29	double dx = env.getWidth();
30	double dy = env.getHeight();
31	double dMax = dx > dy ? dx : dy;
32	int level = DoubleBits.exponent(dMax) + 1;
33	return level;
34	}
35
36	// the fields which make up the key
37	private Coordinate pt = new Coordinate();
38	private int level = 0;
39	// auxiliary data which is derived from the key for use in computation
40	private Envelope env = null;
41
42	public Key(Envelope itemEnv)
43	{
44	computeKey(itemEnv);
45	}
46
47	public Coordinate getPoint() { return pt; }
48	public int getLevel() { return level; }
49	public Envelope getEnvelope() { return env; }
50
51	public Coordinate getCentre()
52	{
53	return new Coordinate(
54	(env.getMinX() + env.getMaxX()) / 2,
55	(env.getMinY() + env.getMaxY()) / 2
56	);
57	}
58	/**
59	* return a square envelope containing the argument envelope,
60	* whose extent is a power of two and which is based at a power of 2
61	*/
62	public void computeKey(Envelope itemEnv)
63	{
64	level = computeQuadLevel(itemEnv);
65	env = new Envelope();
66	computeKey(level, itemEnv);
67	// MD - would be nice to have a non-iterative form of this algorithm
68	while (! env.contains(itemEnv)) {
69	level += 1;
70	computeKey(level, itemEnv);
71	}
72	}
73
74	private void computeKey(int level, Envelope itemEnv)
75	{
76	double quadSize = DoubleBits.powerOf2(level);
77	pt.x = Math.floor(itemEnv.getMinX() / quadSize) * quadSize;
78	pt.y = Math.floor(itemEnv.getMinY() / quadSize) * quadSize;
79	env.init(pt.x, pt.x + quadSize, pt.y, pt.y + quadSize);
80	}
81	}
82