// atmo.hxx -- routines to model the air column
//
// Written by David Megginson, started February 2002.
//
// Copyright (C) 2002  David Megginson - david@megginson.com
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program 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
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
//
// $Id: atmodel.hxx,v 1.1 2007/02/16 03:54:09 jsd Exp jsd $


#ifndef _ATMODEL_HXX
#define _ATMODEL_HXX

#include <simgear/compiler.h>
#include <simgear/math/interpolater.hxx>

#ifdef SG_HAVE_STD_INCLUDES
#  include <cmath>
#else
#  include <math.h>
#endif

#include <iomanip>
using namespace std;

/**
 * Model the atmosphere in a way consistent with the laws
 * of physics.
 *
 * Each instance of this class models a particular air mass.
 * You may freely move up, down, or sideways in the air mass.
 * In contrast, if you want to compare different air masses,
 * you should use a separate instance for each one.
 *
 * See also ./environment.hxx
 */

#define SCD(name,val) const double name(val)
namespace atmodel {
  SCD(g, 9.80665);		// [m/s/s] acceleration of gravity
  SCD(mm, .0289644);		// [kg/mole] molar mass of air (dry?)
  SCD(Rgas, 8.31432);		// [J/K/mole] gas constant
  SCD(inch, 0.0254);		// [m] definition of inch
  SCD(foot, 12 * inch);		// [m]
  SCD(inHg, 101325.0 / 760 * 1000 * inch);  // [Pa] definition of inHg
  SCD(freezing, 273.15);	// [K] centigrade - kelvin offset
  SCD(nm, 1852);		// [m] nautical mile (NIST)
  SCD(sm, 5280*foot);		// [m] nautical mile (NIST)

  namespace ISA {
    SCD(P0, 101325.0); 		// [pascals] ISA sea-level pressure
    SCD(T0, 15. + freezing);	// [K] ISA sea-level temperature
    SCD(lam0, .0065);		// [K/m] ISA troposphere lapse rate
  }
}
#undef SCD

// The base class is little more than a namespace.
// It has no constructor, no destructor, and no variables.
class FGatmo{
public:
  double p_vs_a(const double height, const double Psl = atmodel::ISA::P0);
  double a_vs_p(const double press, const double qnh = atmodel::ISA::P0);
  double fake_t_vs_a_us(const double h_ft);
  double fake_dp_vs_a_us(const double dpsl, const double h_ft);
  double P_layer(const double height, const double href, 
	const double Pref, const double Tref, 
	const double lapse );
  void check_one(const double height);
  double qnh(const double field_ft, const double press_in);
};

class FGatmocache : FGatmo {

  friend class FGaltimetry;
  SGInterpTable * a_tvs_p;	// _tvs_ means "tabulated versus"

public: 

  FGatmocache();
  ~FGatmocache();
  void tabulate();
  void cache();
#ifdef ATMO_TEST
  void check_model();
#endif
};

class FGaltimetry : public FGatmocache {
  double kset;
  double kft;
public:  
  FGaltimetry();
  inline double press_alt_ft(const double p_inHg){return a_tvs_p->interpolate(p_inHg);}
  inline double kollsman_ft(const double set_inHg){
    if (set_inHg == kset) return kft;
    kset = set_inHg;
    return kft = a_tvs_p->interpolate(kset);
  }
  inline double reading_ft(const double p_inHg, 
  		const double set_inHg = atmodel::ISA::P0/atmodel::inHg){
    return press_alt_ft(p_inHg) - kollsman_ft(set_inHg);		  
  }

#ifdef ATMO_TEST
  void stack();
  void stack1(const double Tref);
#endif
};

#endif // _ATMODEL_HXX