/* * 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.geomgraph; /** * @version 1.7 */ import com.vividsolutions.jts.geom.Coordinate; /** * Utility functions for working with quadrants, which are numbered as follows: * <pre> * 1 | 0 * --+-- * 2 | 3 * <pre> * * @version 1.7 */ public class Quadrant { public static final int NE = 0; public static final int NW = 1; public static final int SW = 2; public static final int SE = 3; /** * Returns the quadrant of a directed line segment (specified as x and y * displacements, which cannot both be 0). * * @throws IllegalArgumentException if the displacements are both 0 */ public static int quadrant(double dx, double dy) { if (dx == 0.0 && dy == 0.0) throw new IllegalArgumentException("Cannot compute the quadrant for point ( "+ dx + ", " + dy + " )" ); if (dx >= 0.0) { if (dy >= 0.0) return NE; else return SE; } else { if (dy >= 0.0) return NW; else return SW; } } /** * Returns the quadrant of a directed line segment from p0 to p1. * * @throws IllegalArgumentException if the points are equal */ public static int quadrant(Coordinate p0, Coordinate p1) { if (p1.x == p0.x && p1.y == p0.y) throw new IllegalArgumentException("Cannot compute the quadrant for two identical points " + p0); if (p1.x >= p0.x) { if (p1.y >= p0.y) return NE; else return SE; } else { if (p1.y >= p0.y) return NW; else return SW; } } /** * Returns true if the quadrants are 1 and 3, or 2 and 4 */ public static boolean isOpposite(int quad1, int quad2) { if (quad1 == quad2) return false; int diff = (quad1 - quad2 + 4) % 4; // if quadrants are not adjacent, they are opposite if (diff == 2) return true; return false; } /** * Returns the right-hand quadrant of the halfplane defined by the two quadrants, * or -1 if the quadrants are opposite, or the quadrant if they are identical. */ public static int commonHalfPlane(int quad1, int quad2) { // if quadrants are the same they do not determine a unique common halfplane. // Simply return one of the two possibilities if (quad1 == quad2) return quad1; int diff = (quad1 - quad2 + 4) % 4; // if quadrants are not adjacent, they do not share a common halfplane if (diff == 2) return -1; // int min = (quad1 < quad2) ? quad1 : quad2; int max = (quad1 > quad2) ? quad1 : quad2; // for this one case, the righthand plane is NOT the minimum index; if (min == 0 && max == 3) return 3; // in general, the halfplane index is the minimum of the two adjacent quadrants return min; } /** * Returns whether the given quadrant lies within the given halfplane (specified * by its right-hand quadrant). */ public static boolean isInHalfPlane(int quad, int halfPlane) { if (halfPlane == SE) { return quad == SE || quad == SW; } return quad == halfPlane || quad == halfPlane + 1; } /** * Returns true if the given quadrant is 0 or 1. */ public static boolean isNorthern(int quad) { return quad == NE || quad == NW; } }