/*
* 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;
}
}