LineSegment.java

/* (c) 2014 Open Source Geospatial Foundation - all rights reserved
 * (c) 2001 - 2013 OpenPlans
 * This code is licensed under the GPL 2.0 license, available at the root
 * application directory.
 */
package org.vfny.geoserver.wms.responses.map.htmlimagemap.holes;

import javax.vecmath.GVector;

import com.vividsolutions.jts.geom.Coordinate;

/**
 * Represents a segment. It has the 2 ending points as properties
 * (A,B).
 * @author m.bartolomeoli
 *
 */
public class LineSegment {
	public Vertex A;
	public Vertex B;

	public LineSegment() {
		
	}
	
	public LineSegment(Vertex a, Vertex b)
	{
		A = a;
		B = b;
	}

	/**
	 * Checks if the segment intersects a "ray "starting from the
	 * given origin and "going" in the given direction.
	 * 
	 * @param origin
	 * @param direction
	 *
	 */
	public Float intersectsWithRay(Coordinate origin, Coordinate direction)
	{
		float largestDistance = Math.max((float)(A.getPosition().x - origin.x), (float)(B.getPosition().x - origin.x)) * 2f;
		GVector v=new GVector(new double[] {origin.x,origin.y});
		GVector d=new GVector(new double[] {direction.x,direction.y});
		d.scale(largestDistance);
		v.add(d);
		LineSegment raySegment = new LineSegment(new Vertex(origin, 0), new Vertex(new Coordinate(v.getElement(0),v.getElement(1)), 0));
		Coordinate intersection= findIntersection(this, raySegment);
		Float value = null;
		
		if (intersection != null) {
			v=new GVector(new double[] {origin.x,origin.y});
			v.sub(new GVector(new double[] {intersection.x,intersection.y}));
			double dist=v.norm();
			value = new Float(dist);
		}

		return value;
	}

	/**
	 * Gets the intersection point of the 2 given segments
	 * (null if they don't intersect).
	 * @param a
	 * @param b
	 *
	 */
	public static Coordinate findIntersection(LineSegment a, LineSegment b)
	{
		double x1 = a.A.getPosition().x;
		double y1 = a.A.getPosition().y;
		double x2 = a.B.getPosition().x;
		double y2 = a.B.getPosition().y;
		double x3 = b.A.getPosition().x;
		double y3 = b.A.getPosition().y;
		double x4 = b.B.getPosition().x;
		double y4 = b.B.getPosition().y;

		double denom = (y4 - y3) * (x2 - x1) - (x4 - x3) * (y2 - y1);

		double uaNum = (x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3);
		double ubNum = (x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3);

		double ua = uaNum / denom;
		double ub = ubNum / denom;

		if (clamp(ua, 0f, 1f) != ua || clamp(ub, 0f, 1f) != ub)
			return null;
		GVector v=new GVector(new double[] {a.A.getPosition().x,a.A.getPosition().y});
		GVector d=new GVector(new double[] {a.B.getPosition().x,a.B.getPosition().y});
		d.sub(v);
		d.scale(ua);
		d.add(v);
		return new Coordinate(d.getElement(0),d.getElement(1));		
	}
	
	/**
	 * Restricts a value to be in the given range (min - max).
	 * @param value
	 * @param min
	 * @param max
	 *
	 */
	public static double clamp(double value,double min,double max) {
		if(value>max)
			return max;
		if(value<min)
			return min;
		return value;
	
	}
}