/*
 *    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.util.algorithm2D;

import org.geotools.geometry.iso.topograph2D.Coordinate;


/**
 * Represents a homogeneous coordinate in a 2-D coordinate space. In JTS
 * {@link HCoordinate}s are used as a clean way of computing intersections
 * between line segments.
 *
 *
 *
 * @source $URL$
 */
public class HCoordinate {

	/**
	 * Computes the (approximate) intersection point between two line segments
	 * using homogeneous coordinates.
	 * <p>
	 * Note that this algorithm is not numerically stable; i.e. it can produce
	 * intersection points which lie outside the envelope of the line segments
	 * themselves. In order to increase the precision of the calculation input
	 * points should be normalized before passing them to this routine.
	 */
	public static Coordinate intersection(Coordinate p1, Coordinate p2,
			Coordinate q1, Coordinate q2) throws NotRepresentableException {
		HCoordinate l1 = new HCoordinate(new HCoordinate(p1), new HCoordinate(
				p2));
		HCoordinate l2 = new HCoordinate(new HCoordinate(q1), new HCoordinate(
				q2));
		HCoordinate intHCoord = new HCoordinate(l1, l2);
		Coordinate intPt = intHCoord.getCoordinate();
		return intPt;
	}

	public double x, y, w;

	public HCoordinate() {
		x = 0.0;
		y = 0.0;
		w = 1.0;
	}

	public HCoordinate(double _x, double _y, double _w) {
		x = _x;
		y = _y;
		w = _w;
	}

	public HCoordinate(double _x, double _y) {
		x = _x;
		y = _y;
		w = 1.0;
	}

	public HCoordinate(Coordinate p) {
		x = p.x;
		y = p.y;
		w = 1.0;
	}

	public HCoordinate(HCoordinate p1, HCoordinate p2) {
		x = p1.y * p2.w - p2.y * p1.w;
		y = p2.x * p1.w - p1.x * p2.w;
		w = p1.x * p2.y - p2.x * p1.y;
	}

	public double getX() throws NotRepresentableException {
		double a = x / w;
		if ((Double.isNaN(a)) || (Double.isInfinite(a))) {
			throw new NotRepresentableException();
		}
		return a;
	}

	public double getY() throws NotRepresentableException {
		double a = y / w;
		if ((Double.isNaN(a)) || (Double.isInfinite(a))) {
			throw new NotRepresentableException();
		}
		return a;
	}

	public Coordinate getCoordinate() throws NotRepresentableException {
		Coordinate p = new Coordinate();
		p.x = getX();
		p.y = getY();
		return p;
	}
}