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.bintree;
14
15
16
17	import org.locationtech.jts.index.quadtree.DoubleBits;
18
19	/**
20	* A Key is a unique identifier for a node in a tree.
21	* It contains a lower-left point and a level number. The level number
22	* is the power of two for the size of the node envelope
23	*
24	* @version 1.7
25	*/
26	public class Key {
27
28	public static int computeLevel(Interval interval)
29	{
30	double dx = interval.getWidth();
31	//int level = BinaryPower.exponent(dx) + 1;
32	int level = DoubleBits.exponent(dx) + 1;
33	return level;
34	}
35
36
37	// the fields which make up the key
38	private double pt = 0.0;
39	private int level = 0;
40	// auxiliary data which is derived from the key for use in computation
41	private Interval interval;
42
43	public Key(Interval interval)
44	{
45	computeKey(interval);
46	}
47
48	public double getPoint() { return pt; }
49	public int getLevel() { return level; }
50	public Interval getInterval() { return interval; }
51
52	/**
53	* return a square envelope containing the argument envelope,
54	* whose extent is a power of two and which is based at a power of 2
55	*/
56	public void computeKey(Interval itemInterval)
57	{
58	level = computeLevel(itemInterval);
59	interval = new Interval();
60	computeInterval(level, itemInterval);
61	// MD - would be nice to have a non-iterative form of this algorithm
62	while (! interval.contains(itemInterval)) {
63	level += 1;
64	computeInterval(level, itemInterval);
65	}
66	}
67
68	private void computeInterval(int level, Interval itemInterval)
69	{
70	double size = DoubleBits.powerOf2(level);
71	//double size = pow2.power(level);
72	pt = Math.floor(itemInterval.getMin() / size) * size;
73	interval.init(pt, pt + size);
74	}
75	}
76