centralendpointintersector.h

在Linux下做的QuadTree的程序

/**********************************************************************
 * $Id: LineIntersector.h 1820 2006-09-06 16:54:23Z mloskot $
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.refractions.net
 *
 * Copyright (C) 2006 Refractions Research Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU Lesser General Public Licence as published
 * by the Free Software Foundation. 
 * See the COPYING file for more information.
 *
 **********************************************************************
 *
 * Last port: algorithm/CentralEndpointIntersector.java rev. 1.1
 *
 **********************************************************************/

#ifndef GEOS_ALGORITHM_CENTRALENDPOINTINTERSECTOR_H
#define GEOS_ALGORITHM_CENTRALENDPOINTINTERSECTOR_H

#include <geos/geom/Coordinate.h>

#include <string>
#include <limits>

// Forward declarations
namespace geos {
	namespace geom {
		//class PrecisionModel;
	}
}

namespace geos {
namespace algorithm { // geos::algorithm

/** \brief
 * Computes an approximate intersection of two line segments
 * by taking the most central of the endpoints of the segments.
 *
 * This is effective in cases where the segments are nearly parallel
 * and should intersect at an endpoint.
 * It is also a reasonable strategy for cases where the 
 * endpoint of one segment lies on or almost on the interior of another one.
 * Taking the most central endpoint ensures that the computed intersection
 * point lies in the envelope of the segments.
 * Also, by always returning one of the input points, this should result 
 * in reducing segment fragmentation.
 * Intended to be used as a last resort for 
 * computing ill-conditioned intersection situations which 
 * cause other methods to fail.
 *
 * @author Martin Davis
 * @version 1.8
 */
class CentralEndpointIntersector {

public:	

	static const geom::Coordinate& getIntersection(const geom::Coordinate& p00,
			const geom::Coordinate& p01, const geom::Coordinate& p10,
			const geom::Coordinate& p11)
	{
		CentralEndpointIntersector intor(p00, p01, p10, p11);
		return intor.getIntersection();
	}

	CentralEndpointIntersector(const geom::Coordinate& p00,
			const geom::Coordinate& p01,
			const geom::Coordinate& p10,
			const geom::Coordinate& p11)
		:
		_pts(4)
	{
		_pts[0]=p00;
		_pts[1]=p01;
		_pts[2]=p10;
		_pts[3]=p11;
		compute();
	}

	const geom::Coordinate& getIntersection() const
	{
		return _intPt;
	}


private:

	// This is likely overkill.. we'll be allocating heap
	// memory at every call !
	std::vector<geom::Coordinate> _pts;

	geom::Coordinate _intPt;

	void compute()
	{
		geom::Coordinate centroid = average(_pts);
		_intPt = findNearestPoint(centroid, _pts);
	}

	static geom::Coordinate average(
			const std::vector<geom::Coordinate>& pts)
	{
		geom::Coordinate avg(0, 0);
		size_t n = pts.size();
		if ( ! n ) return avg;
		for (size_t i=0; i<n; ++i)
		{
			avg.x += pts[i].x;
			avg.y += pts[i].y;
		}
		avg.x /= n;
		avg.y /= n;
		return avg;
	}

	/**
	 * Determines a point closest to the given point.
	 * 
	 * @param p the point to compare against
	 * @param p1 a potential result point
	 * @param p2 a potential result point
	 * @param q1 a potential result point
	 * @param q2 a potential result point
	 * @return the point closest to the input point p
	 */
	geom::Coordinate findNearestPoint(const geom::Coordinate& p,
			const std::vector<geom::Coordinate>& pts) const
	{
		double minDist = std::numeric_limits<double>::max();
		geom::Coordinate result = geom::Coordinate::getNull();
		for (size_t i = 0, n=pts.size(); i < n; ++i) {
			double dist = p.distance(pts[i]);
			if (dist < minDist) {
				minDist = dist;
				result = pts[i];
			}
		}
		return result;
	}
  


};

} // namespace geos::algorithm
} // namespace geos


#endif // GEOS_ALGORITHM_CENTRALENDPOINTINTERSECTOR_H

/**********************************************************************
 * $Log$
 **********************************************************************/