01: /*
02: * The JTS Topology Suite is a collection of Java classes that
03: * implement the fundamental operations required to validate a given
04: * geo-spatial data set to a known topological specification.
05: *
06: * Copyright (C) 2001 Vivid Solutions
07: *
08: * This library is free software; you can redistribute it and/or
09: * modify it under the terms of the GNU Lesser General Public
10: * License as published by the Free Software Foundation; either
11: * version 2.1 of the License, or (at your option) any later version.
12: *
13: * This library is distributed in the hope that it will be useful,
14: * but WITHOUT ANY WARRANTY; without even the implied warranty of
15: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16: * Lesser General Public License for more details.
17: *
18: * You should have received a copy of the GNU Lesser General Public
19: * License along with this library; if not, write to the Free Software
20: * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
21: *
22: * For more information, contact:
23: *
24: * Vivid Solutions
25: * Suite #1A
26: * 2328 Government Street
27: * Victoria BC V8T 5G5
28: * Canada
29: *
30: * (250)385-6040
31: * www.vividsolutions.com
32: */
33: package com.vividsolutions.jts.index.bintree;
34:
35: import com.vividsolutions.jts.index.quadtree.DoubleBits;
36:
37: /**
38: * A Key is a unique identifier for a node in a tree.
39: * It contains a lower-left point and a level number. The level number
40: * is the power of two for the size of the node envelope
41: *
42: * @version 1.7
43: */
44: public class Key {
45:
46: public static int computeLevel(Interval interval) {
47: double dx = interval.getWidth();
48: //int level = BinaryPower.exponent(dx) + 1;
49: int level = DoubleBits.exponent(dx) + 1;
50: return level;
51: }
52:
53: // the fields which make up the key
54: private double pt = 0.0;
55: private int level = 0;
56: // auxiliary data which is derived from the key for use in computation
57: private Interval interval;
58:
59: public Key(Interval interval) {
60: computeKey(interval);
61: }
62:
63: public double getPoint() {
64: return pt;
65: }
66:
67: public int getLevel() {
68: return level;
69: }
70:
71: public Interval getInterval() {
72: return interval;
73: }
74:
75: /**
76: * return a square envelope containing the argument envelope,
77: * whose extent is a power of two and which is based at a power of 2
78: */
79: public void computeKey(Interval itemInterval) {
80: level = computeLevel(itemInterval);
81: interval = new Interval();
82: computeInterval(level, itemInterval);
83: // MD - would be nice to have a non-iterative form of this algorithm
84: while (!interval.contains(itemInterval)) {
85: level += 1;
86: computeInterval(level, itemInterval);
87: }
88: }
89:
90: private void computeInterval(int level, Interval itemInterval) {
91: double size = DoubleBits.powerOf2(level);
92: //double size = pow2.power(level);
93: pt = Math.floor(itemInterval.getMin() / size) * size;
94: interval.init(pt, pt + size);
95: }
96: }
|