89 lines
2.4 KiB
C++
89 lines
2.4 KiB
C++
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// gravity.cxx -- interface for earth gravitational model
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//
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// Written by Torsten Dreyer, June 2011
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//
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// Copyright (C) 2011 Torsten Dreyer - torsten (at) t3r _dot_ de
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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//
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#include "gravity.hxx"
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#include <simgear/structure/exception.hxx>
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namespace Environment {
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/*
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http://de.wikipedia.org/wiki/Normalschwereformel
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*/
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class Somigliana : public Gravity {
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public:
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Somigliana();
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virtual ~Somigliana();
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virtual double getGravity( const SGGeod & position ) const;
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};
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Somigliana::Somigliana()
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{
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}
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Somigliana::~Somigliana()
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{
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}
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double Somigliana::getGravity( const SGGeod & position ) const
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{
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// Geodetic Reference System 1980 parameter
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#define A 6378137.0 // equatorial radius of earth
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#define B 6356752.3141 // semiminor axis
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#define AGA (A*9.7803267715) // A times normal gravity at equator
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#define BGB (B*9.8321863685) // B times normal gravity at pole
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// forumla of Somigliana
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double cosphi = ::cos(position.getLatitudeRad());
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double cos2phi = cosphi*cosphi;
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double sinphi = ::sin(position.getLatitudeRad());
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double sin2phi = sinphi*sinphi;
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double g0 = (AGA * cos2phi + BGB * sin2phi) / sqrt( A*A*cos2phi+B*B*sin2phi );
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static const double k1 = 3.15704e-7;
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static const double k2 = 2.10269e-9;
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static const double k3 = 7.37452e-14;
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double h = position.getElevationM();
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return g0*(1-(k1-k2*sin2phi)*h+k3*h*h);
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}
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static Somigliana _somigliana;
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/* --------------------- Gravity implementation --------------------- */
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Gravity * Gravity::_instance = NULL;
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Gravity::~Gravity()
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{
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}
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//double Gravity::getGravity( const SGGeoc & position ) = 0;
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const Gravity * Gravity::instance()
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{
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if( _instance == NULL )
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_instance = &_somigliana;
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return _instance;
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}
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} // namespace
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