flightgear/src/WeatherCM/FGAirPressureItem.h

/*****************************************************************************

 Header:       FGAirPressureItem.h	
 Author:       Christian Mayer
 Date started: 28.05.99

 ---------- Copyright (C) 1999  Christian Mayer (vader@t-online.de) ----------

 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., 59 Temple
 Place - Suite 330, Boston, MA  02111-1307, USA.

 Further information about the GNU General Public License can also be found on
 the world wide web at http://www.gnu.org.

FUNCTIONAL DESCRIPTION
------------------------------------------------------------------------------
Air pressure item that is stored in the micro weather class

HISTORY
------------------------------------------------------------------------------
28.05.1999 Christian Mayer      Created
08.06.1999 Christian Mayer      Added international air preasure formula
16.06.1999 Durk Talsma		Portability for Linux
20.06.1999 Christian Mayer	added lots of consts
*****************************************************************************/

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/* SENTRY                                                                   */
/****************************************************************************/
#ifndef FGAirPressureItem_H
#define FGAirPressureItem_H

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/* INCLUDES								    */
/****************************************************************************/
#include "FGWeatherDefs.h"
#include <math.h>
		
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/* DEFINES								    */
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class FGAirPressureItem;
FGAirPressureItem operator-(const FGAirPressureItem& arg);

/****************************************************************************/
/* CLASS DECLARATION							    */
/* NOTE: The value stored in 'value' is the air preasure that we'd have at  */
/*       an altitude of 0.0 The correct airpreasure at the stored altitude  */
/*       gets calulated when getValue() is called.			    */
/****************************************************************************/
class FGAirPressureItem
{
private:
    WeatherPrecition value;
protected:
public:

    FGAirPressureItem(const WeatherPrecition& v)    {value = v;}
    FGAirPressureItem()				    {value = FG_WEATHER_DEFAULT_AIRPRESSURE;}

    //WeatherPrecition getValue(WeatherPrecition alt) { return value * pow(1.0 - 0.0065*alt/288.0, 5.255); };

    WeatherPrecition getValue(const WeatherPrecition& alt) const
    { 
	return (WeatherPrecition)((value / 101325.0) *
	    (
	    1.01325e5 + alt * (-1.19459535223623e1 + alt * (5.50461110007561e-4 + alt * (-1.13574703113648e-8 + alt * 8.61601726143988e-14)))
	    ));
    };
   
    FGAirPressureItem& operator*=(const WeatherPrecition& arg);
    FGAirPressureItem& operator+=(const FGAirPressureItem& arg);
    FGAirPressureItem& operator-=(const FGAirPressureItem& arg);

    friend FGAirPressureItem operator-(const FGAirPressureItem& arg);
};

inline FGAirPressureItem& FGAirPressureItem::operator*= (const WeatherPrecition& arg)
{
  value *= arg;
  return *this;
}

inline FGAirPressureItem& FGAirPressureItem::operator+= (const FGAirPressureItem& arg)
{
  value += arg.value;
  return *this;
}

inline FGAirPressureItem& FGAirPressureItem::operator-= (const FGAirPressureItem& arg)
{
  value -= arg.value;
  return *this;
}

inline FGAirPressureItem operator-(const FGAirPressureItem& arg)
{
    return FGAirPressureItem(-arg.value);
}

/****************************************************************************/
#endif /*FGAirPressureItem_H*/