Plane3D.java

/*
* 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.math;

import com.vividsolutions.jts.geom.Coordinate;

/**
 * Models a plane in 3-dimensional Cartesian space.
 * 
 * @author mdavis
 *
 */
public class Plane3D {
	
	/**
	 * Enums for the 3 coordinate planes
	 */
	public static final int XY_PLANE = 1;
	public static final int YZ_PLANE = 2;
	public static final int XZ_PLANE = 3;
	
	private Vector3D normal;
	private Coordinate basePt;

	public Plane3D(Vector3D normal, Coordinate basePt)
	{
		this.normal = normal;
		this.basePt = basePt;
	}
	
	/**
	 * Computes the oriented distance from a point to the plane.
	 * The distance is:
	 * <ul>
	 * <li><b>positive</b> if the point lies above the plane (relative to the plane normal)
	 * <li><b>zero</b> if the point is on the plane
	 * <li><b>negative</b> if the point lies below the plane (relative to the plane normal)
	 * </ul> 
	 * 
	 * @param p the point to compute the distance for
	 * @return the oriented distance to the plane
	 */
	public double orientedDistance(Coordinate p) {
		Vector3D pb = new Vector3D(p, basePt);
		double pbdDotNormal = pb.dot(normal);
		if (Double.isNaN(pbdDotNormal)) 
			throw new IllegalArgumentException("3D Coordinate has NaN ordinate");
		double d = pbdDotNormal / normal.length();
		return d;
	}

	/**
	 * Computes the axis plane that this plane lies closest to.
	 * <p>
	 * Geometries lying in this plane undergo least distortion
	 * (and have maximum area)
	 * when projected to the closest axis plane.
	 * This provides optimal conditioning for
	 * computing a Point-in-Polygon test.
	 *  
	 * @return the index of the closest axis plane.
	 */
	public int closestAxisPlane() {
		double xmag = Math.abs(normal.getX());
		double ymag = Math.abs(normal.getY());
		double zmag = Math.abs(normal.getZ());
		if (xmag > ymag) {
			if (xmag > zmag)
				return YZ_PLANE;
			else
				return XY_PLANE;
		}
		// y >= x
		else if (zmag > ymag) {
			return XY_PLANE;
		}
		// y >= z
		return XZ_PLANE;
	}

}