/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2001-2006 Vivid Solutions
* (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
*
* 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;
* version 2.1 of the License.
*
* 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.
*/
package org.geotools.geometry.iso.topograph2D;
/**
* Utility functions for working with quadrants, which are numbered as follows:
*
* <pre>
* 1 | 0
* --+--
* 2 | 3
* <pre>
*
*
*
*
* @source $URL$
*/
public class Quadrant {
/**
* Returns the quadrant of a directed line segment (specified as x and y
* displacements, which cannot both be 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) {
if (dy >= 0)
return 0;
else
return 3;
} else {
if (dy >= 0)
return 1;
else
return 2;
}
}
/**
* Returns the quadrant of a directed line segment from p0 to p1.
*/
public static int quadrant(Coordinate p0, Coordinate p1) {
double dx = p1.x - p0.x;
double dy = p1.y - p0.y;
if (dx == 0.0 && dy == 0.0)
throw new IllegalArgumentException(
"Cannot compute the quadrant for two identical points "
+ p0);
return quadrant(dx, dy);
}
/**
* 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 == 3) {
return quad == 3 || quad == 0;
}
return quad == halfPlane || quad == halfPlane + 1;
}
/**
* Returns true if the given quadrant is 0 or 1.
*/
public static boolean isNorthern(int quad) {
return quad == 0 || quad == 1;
}
}