flightgear/src/Environment/environment.cxx

// environment.cxx -- routines to model the natural environment
//
// 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., 675 Mass Ave, Cambridge, MA 02139, USA.
//
// $Id$


#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#ifdef HAVE_WINDOWS_H
#  include <windows.h>                     
#endif

#include <math.h>

#include <plib/sg.h>

#include <simgear/constants.h>
#include <simgear/debug/logstream.hxx>
#include <simgear/math/interpolater.hxx>

#include <Main/fg_props.hxx>
#include "environment.hxx"


FGEnvironment::FGEnvironment()
  : _temperature_degc_table(new SGInterpTable),
    _pressure_inhg_table(new SGInterpTable),
    _density_slugft3_table(new SGInterpTable),
    visibility_m(32000),
    temperature_sea_level_degc(20),
    pressure_sea_level_inhg(29.92),
    density_sea_level_slugft3(0.00237),
    wind_from_heading_deg(0),
    wind_speed_kt(0),
    wind_from_north_fps(0),
    wind_from_east_fps(0),
    wind_from_down_fps(0)
{
  _setup_tables();
}

FGEnvironment::FGEnvironment (const FGEnvironment &env)
  : _temperature_degc_table(new SGInterpTable),
    _pressure_inhg_table(new SGInterpTable),
    _density_slugft3_table(new SGInterpTable),
    elevation_ft(env.elevation_ft),
    visibility_m(env.visibility_m),
    temperature_sea_level_degc(env.temperature_sea_level_degc),
    pressure_sea_level_inhg(env.pressure_sea_level_inhg),
    density_sea_level_slugft3(env.density_sea_level_slugft3),
    wind_from_heading_deg(env.wind_from_heading_deg),
    wind_speed_kt(env.wind_speed_kt),
    wind_from_north_fps(env.wind_from_north_fps),
    wind_from_east_fps(env.wind_from_east_fps),
    wind_from_down_fps(env.wind_from_down_fps)
{
  _setup_tables();
}

FGEnvironment::~FGEnvironment()
{
  delete _temperature_degc_table;
  delete _pressure_inhg_table;
  delete _density_slugft3_table;
}


double
FGEnvironment::get_visibility_m () const
{
  return visibility_m;
}

double
FGEnvironment::get_temperature_sea_level_degc () const
{
  return temperature_sea_level_degc;
}

double
FGEnvironment::get_temperature_degc () const
{
  return temperature_degc;
}

double
FGEnvironment::get_pressure_sea_level_inhg () const
{
  return pressure_sea_level_inhg;
}

double
FGEnvironment::get_pressure_inhg () const
{
  return pressure_inhg;
}

double
FGEnvironment::get_density_sea_level_slugft3 () const
{
  return density_sea_level_slugft3;
}

double
FGEnvironment::get_density_slugft3 () const
{
  return density_slugft3;
}

double
FGEnvironment::get_wind_from_heading_deg () const
{
  return wind_from_heading_deg;
}

double
FGEnvironment::get_wind_speed_kt () const
{
  return wind_speed_kt;
}

double
FGEnvironment::get_wind_from_north_fps () const
{
  return wind_from_north_fps;
}

double
FGEnvironment::get_wind_from_east_fps () const
{
  return wind_from_east_fps;
}

double
FGEnvironment::get_wind_from_down_fps () const
{
  return wind_from_down_fps;
}

double
FGEnvironment::get_elevation_ft () const
{
  return elevation_ft;
}

void
FGEnvironment::set_visibility_m (double v)
{
  visibility_m = v;
}

void
FGEnvironment::set_temperature_sea_level_degc (double t)
{
  temperature_sea_level_degc = t;
  _recalc_alt_temperature();
}

void
FGEnvironment::set_temperature_degc (double t)
{
  temperature_degc = t;
  _recalc_sl_temperature();
}

void
FGEnvironment::set_pressure_sea_level_inhg (double p)
{
  pressure_sea_level_inhg = p;
  _recalc_alt_pressure();
}

void
FGEnvironment::set_pressure_inhg (double p)
{
  pressure_inhg = p;
  _recalc_sl_pressure();
}

void
FGEnvironment::set_density_sea_level_slugft3 (double d)
{
  density_sea_level_slugft3 = d;
  _recalc_alt_density();
}

void
FGEnvironment::set_density_slugft3 (double d)
{
  density_slugft3 = d;
  _recalc_sl_density();
}

void
FGEnvironment::set_wind_from_heading_deg (double h)
{
  wind_from_heading_deg = h;
  _recalc_ne();
}

void
FGEnvironment::set_wind_speed_kt (double s)
{
  wind_speed_kt = s;
  _recalc_ne();
}

void
FGEnvironment::set_wind_from_north_fps (double n)
{
  wind_from_north_fps = n;
  _recalc_hdgspd();
}

void
FGEnvironment::set_wind_from_east_fps (double e)
{
  wind_from_east_fps = e;
  _recalc_hdgspd();
}

void
FGEnvironment::set_wind_from_down_fps (double d)
{
  wind_from_down_fps = d;
  _recalc_hdgspd();
}

void
FGEnvironment::set_elevation_ft (double e)
{
  elevation_ft = e;
  _recalc_alt_temperature();
  _recalc_alt_pressure();
  _recalc_alt_density();
}

// Atmosphere model.

// Copied from YASim Atmosphere.cxx, with m converted to ft, degK
// converted to degC, Pa converted to inHG, and kg/m^3 converted to
// slug/ft^3; they were then converted to deltas from the sea-level
// defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).

// Original comment from YASim:

// Copied from McCormick, who got it from "The ARDC Model Atmosphere"
// Note that there's an error in the text in the first entry,
// McCormick lists 299.16/101325/1.22500, but those don't agree with
// R=287.  I chose to correct the temperature to 288.20, since 79F is
// pretty hot for a "standard" atmosphere.

// Elevation (ft), temperature factor (degK), pressure factor (inHG),
// density factor (slug/ft^3)
static double atmosphere_data[][4] = {
  0.00, 1.00, 1.000, 1.000000,
  2952.76, 0.98, 0.898, 0.916408,
  5905.51, 0.96, 0.804, 0.838286,
  8858.27, 0.94, 0.719, 0.765429,
  11811.02, 0.92, 0.641, 0.697510,
  14763.78, 0.90, 0.570, 0.634318,
  17716.54, 0.88, 0.506, 0.575616,
  20669.29, 0.86, 0.447, 0.521184,
  23622.05, 0.84, 0.394, 0.470784,
  26574.80, 0.82, 0.347, 0.424220,
  29527.56, 0.80, 0.304, 0.381273,
  32480.31, 0.78, 0.266, 0.341747,
  35433.07, 0.76, 0.231, 0.305445,
  38385.83, 0.75, 0.201, 0.266931,
  41338.58, 0.75, 0.174, 0.231739,
  44291.34, 0.75, 0.151, 0.201192,
  47244.09, 0.75, 0.131, 0.174686,
  50196.85, 0.75, 0.114, 0.151673,
  53149.61, 0.75, 0.099, 0.131698,
  56102.36, 0.75, 0.086, 0.114359,
  59055.12, 0.75, 0.075, 0.099306,
  62007.87, 0.75, 0.065, 0.086237,
  -1, -1, -1, -1
};

void
FGEnvironment::_setup_tables ()
{
  for (int i = 0; atmosphere_data[i][0] != -1; i++) {
    _temperature_degc_table->addEntry(atmosphere_data[i][0],
				      atmosphere_data[i][1]);
    _pressure_inhg_table->addEntry(atmosphere_data[i][0],
				   atmosphere_data[i][2]);
    _density_slugft3_table->addEntry(atmosphere_data[i][0],
				     atmosphere_data[i][3]);
  }
}

void
FGEnvironment::_recalc_hdgspd ()
{
  double angle_rad;

  if (wind_from_east_fps == 0) {
    angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
  } else {
    angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
  }
  wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
  if (wind_from_east_fps >= 0)
    wind_from_heading_deg = 90 - wind_from_heading_deg;
  else
    wind_from_heading_deg = 270 - wind_from_heading_deg;
  if (angle_rad == 0)
    wind_speed_kt = fabs(wind_from_east_fps
			 * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
  else
    wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
      * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
}

void
FGEnvironment::_recalc_ne ()
{
  double speed_fps =
    wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);

  wind_from_north_fps = speed_fps *
    cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
  wind_from_east_fps = speed_fps *
    sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
}

void
FGEnvironment::_recalc_sl_temperature ()
{
  // If we're in the stratosphere, leave sea-level temp alone
  if (elevation_ft < 38000) {
    temperature_sea_level_degc =
      (temperature_degc + 273.15)
      /_temperature_degc_table->interpolate(elevation_ft)
      - 273.15;
  }
}

void
FGEnvironment::_recalc_alt_temperature ()
{
  if (elevation_ft < 38000) {
    temperature_degc =
      (temperature_sea_level_degc + 273.15) *
      _temperature_degc_table->interpolate(elevation_ft) - 273.15;
  } else {
    temperature_degc = -56.49;	// Stratosphere is constant
  }
}

void
FGEnvironment::_recalc_sl_pressure ()
{
  pressure_sea_level_inhg =
    pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
}

void
FGEnvironment::_recalc_alt_pressure ()
{
  pressure_inhg =
    pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
}

void
FGEnvironment::_recalc_sl_density ()
{
  density_sea_level_slugft3 =
    density_slugft3 / _density_slugft3_table->interpolate(elevation_ft);
}

void
FGEnvironment::_recalc_alt_density ()
{
  density_slugft3 =
    density_sea_level_slugft3 *
    _density_slugft3_table->interpolate(elevation_ft);
}

// end of environment.cxx