/* * The JTS Topology Suite is a collection of Java classes that * implement the fundamental operations required to validate a given * geo-spatial data set to a known topological specification. * * Copyright (C) 2001 Vivid Solutions * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * For more information, contact: * * Vivid Solutions * Suite #1A * 2328 Government Street * Victoria BC V8T 5G5 * Canada * * (250)385-6040 * www.vividsolutions.com */ package com.vividsolutions.jts.index.quadtree; import com.vividsolutions.jts.geom.Coordinate; import com.vividsolutions.jts.geom.Envelope; /** * A Key is a unique identifier for a node in a quadtree. * It contains a lower-left point and a level number. The level number * is the power of two for the size of the node envelope * * @version 1.7 */ public class Key { public static int computeQuadLevel(Envelope env) { double dx = env.getWidth(); double dy = env.getHeight(); double dMax = dx > dy ? dx : dy; int level = DoubleBits.exponent(dMax) + 1; return level; } // the fields which make up the key private Coordinate pt = new Coordinate(); private int level = 0; // auxiliary data which is derived from the key for use in computation private Envelope env = null; public Key(Envelope itemEnv) { computeKey(itemEnv); } public Coordinate getPoint() { return pt; } public int getLevel() { return level; } public Envelope getEnvelope() { return env; } public Coordinate getCentre() { return new Coordinate( (env.getMinX() + env.getMaxX()) / 2, (env.getMinY() + env.getMaxY()) / 2 ); } /** * return a square envelope containing the argument envelope, * whose extent is a power of two and which is based at a power of 2 */ public void computeKey(Envelope itemEnv) { level = computeQuadLevel(itemEnv); env = new Envelope(); computeKey(level, itemEnv); // MD - would be nice to have a non-iterative form of this algorithm while (! env.contains(itemEnv)) { level += 1; computeKey(level, itemEnv); } } private void computeKey(int level, Envelope itemEnv) { double quadSize = DoubleBits.powerOf2(level); pt.x = Math.floor(itemEnv.getMinX() / quadSize) * quadSize; pt.y = Math.floor(itemEnv.getMinY() / quadSize) * quadSize; env.init(pt.x, pt.x + quadSize, pt.y, pt.y + quadSize); } }