mapnik/src/distance.cpp

/*****************************************************************************
 * 
 * This file is part of Mapnik (c++ mapping toolkit)
 *
 * Copyright (C) 2006 Artem Pavlenko
 *
 * 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 *****************************************************************************/

//$Id$
#include <mapnik/distance.hpp>

#include <mapnik/ellipsoid.hpp>
#include <cmath>

// When using Sun's C++ compiler, use the `std` namespace to get the math routines.
#ifdef __SUNPRO_CC
using std::atan2;
using std::cos;
using std::pow;
using std::sin;
using std::sqrt;
#endif

namespace mapnik {
    
    static const double deg2rad = 0.0174532925199432958;
    static const double R = 6372795.0; // average great-circle radius of the earth
    
    double great_circle_distance::operator() (coord2d const& pt0, 
                                              coord2d const& pt1) const
    {
        double lon0 = pt0.x * deg2rad;
        double lat0 = pt0.y * deg2rad;
        double lon1 = pt1.x * deg2rad;
        double lat1 = pt1.y * deg2rad;
        
        double dlat = lat1 - lat0;
        double dlon = lon1 - lon0;
        
        double sin_dlat = sin(0.5 * dlat);
        double sin_dlon = sin(0.5 * dlon);
        
        double a = pow(sin_dlat,2.0) + cos(lat0)*cos(lat1)*pow(sin_dlon,2.0);
        double c = 2 * atan2(sqrt(a),sqrt(1 - a));
        return R * c; 
    }
    
}