// 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <math.h>
#include <boost/tuple/tuple.hpp>
#include <simgear/props/props.hxx>
#include <Main/fg_props.hxx>
#include "environment.hxx"
#include "atmosphere.hxx"
////////////////////////////////////////////////////////////////////////
// Atmosphere model.
////////////////////////////////////////////////////////////////////////
#ifdef USING_TABLES
// Calculated based on the ISA standard day, as found at e.g.
// http://www.av8n.com/physics/altimetry.htm
// Each line of data has 3 elements:
// Elevation (ft),
// temperature factor (dimensionless ratio of absolute temp),
// pressure factor (dimensionless ratio)
static double atmosphere_data[][3] = {
{ -3000.00, 1.021, 1.1133 },
{ 0.00, 1.000, 1.0000 },
{ 2952.76, 0.980, 0.8978 },
{ 5905.51, 0.959, 0.8042 },
{ 8858.27, 0.939, 0.7187 },
{ 11811.02, 0.919, 0.6407 },
{ 14763.78, 0.898, 0.5697 },
{ 17716.54, 0.878, 0.5052 },
{ 20669.29, 0.858, 0.4468 },
{ 23622.05, 0.838, 0.3940 },
{ 26574.80, 0.817, 0.3463 },
{ 29527.56, 0.797, 0.3034 },
{ 32480.31, 0.777, 0.2649 },
{ 35433.07, 0.756, 0.2305 },
{ 38385.83, 0.752, 0.2000 },
{ 41338.58, 0.752, 0.1736 },
{ 44291.34, 0.752, 0.1506 },
{ 47244.09, 0.752, 0.1307 },
{ 50196.85, 0.752, 0.1134 },
{ 53149.61, 0.752, 0.0984 },
{ 56102.36, 0.752, 0.0854 },
{ 59055.12, 0.752, 0.0741 },
{ 62007.87, 0.752, 0.0643 },
{ 65000.00, 0.752, 0.0557 },
{ 68000.00, 0.754, 0.0482 },
{ 71000.00, 0.758, 0.0418 },
{ 74000.00, 0.761, 0.0362 },
{ 77000.00, 0.764, 0.0314 },
{ 80000.00, 0.767, 0.0273 },
{ 83000.00, 0.770, 0.0237 },
{ 86000.00, 0.773, 0.0206 },
{ 89000.00, 0.777, 0.0179 },
{ 92000.00, 0.780, 0.0156 },
{ 95000.00, 0.783, 0.0135 },
{ 98000.00, 0.786, 0.0118 },
{ 101000.00, 0.789, 0.0103 },
{ -1, -1, -1 }
};
static SGInterpTable * _temperature_degc_table = 0;
static SGInterpTable * _pressure_inhg_table = 0;
static void
_setup_tables ()
{
if (_temperature_degc_table != 0)
return;
_temperature_degc_table = new SGInterpTable;
_pressure_inhg_table = new SGInterpTable;
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]);
}
}
#endif
////////////////////////////////////////////////////////////////////////
// Implementation of FGEnvironment.
////////////////////////////////////////////////////////////////////////
void FGEnvironment::_init()
{
elevation_ft = 0;
visibility_m = 32000;
temperature_sea_level_degc = 15;
temperature_degc = 15;
dewpoint_sea_level_degc = 5; // guess
dewpoint_degc = 5;
pressure_sea_level_inhg = 29.92;
pressure_inhg = 29.92;
turbulence_magnitude_norm = 0;
turbulence_rate_hz = 1;
wind_from_heading_deg = 0;
wind_speed_kt = 0;
wind_from_north_fps = 0;
wind_from_east_fps = 0;
wind_from_down_fps = 0;
altitude_half_to_sun_m = 1000;
altitude_tropo_top_m = 10000;
#ifdef USING_TABLES
_setup_tables();
#endif
_recalc_density();
_recalc_relative_humidity();
live_update = true;
}
FGEnvironment::FGEnvironment()
{
_init();
}
FGEnvironment::FGEnvironment (const FGEnvironment &env)
{
_init();
copy(env);
}
FGEnvironment::~FGEnvironment()
{
Untie();
}
FGEnvironment & FGEnvironment::operator = ( const FGEnvironment & other )
{
copy( other );
return *this;
}
void
FGEnvironment::copy (const FGEnvironment &env)
{
elevation_ft = env.elevation_ft;
visibility_m = env.visibility_m;
temperature_sea_level_degc = env.temperature_sea_level_degc;
temperature_degc = env.temperature_degc;
dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
dewpoint_degc = env.dewpoint_degc;
pressure_sea_level_inhg = env.pressure_sea_level_inhg;
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;
turbulence_magnitude_norm = env.turbulence_magnitude_norm;
turbulence_rate_hz = env.turbulence_rate_hz;
}
static inline bool
maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
const char * name, void (FGEnvironment::*setter)(double))
{
const SGPropertyNode * child = node->getNode(name);
// fragile: depends on not being typed
// as a number
if (child != 0 && child->hasValue() &&
child->getStringValue()[0] != '\0') {
(env->*setter)(child->getDoubleValue());
return true;
} else {
return false;
}
}
void
FGEnvironment::read (const SGPropertyNode * node)
{
bool live_update = set_live_update( false );
maybe_copy_value(this, node, "visibility-m",
&FGEnvironment::set_visibility_m);
maybe_copy_value(this, node, "elevation-ft",
&FGEnvironment::set_elevation_ft);
if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
&FGEnvironment::set_temperature_sea_level_degc)) {
if( maybe_copy_value(this, node, "temperature-degc",
&FGEnvironment::set_temperature_degc)) {
_recalc_sl_temperature();
}
}
if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
&FGEnvironment::set_dewpoint_sea_level_degc)) {
if( maybe_copy_value(this, node, "dewpoint-degc",
&FGEnvironment::set_dewpoint_degc)) {
_recalc_sl_dewpoint();
}
}
if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
&FGEnvironment::set_pressure_sea_level_inhg)) {
if( maybe_copy_value(this, node, "pressure-inhg",
&FGEnvironment::set_pressure_inhg)) {
_recalc_sl_pressure();
}
}
maybe_copy_value(this, node, "wind-from-heading-deg",
&FGEnvironment::set_wind_from_heading_deg);
maybe_copy_value(this, node, "wind-speed-kt",
&FGEnvironment::set_wind_speed_kt);
maybe_copy_value(this, node, "turbulence/magnitude-norm",
&FGEnvironment::set_turbulence_magnitude_norm);
maybe_copy_value(this, node, "turbulence/rate-hz",
&FGEnvironment::set_turbulence_rate_hz);
// calculate derived properties here to avoid duplicate expensive computations
_recalc_ne();
_recalc_alt_pt();
_recalc_alt_dewpoint();
_recalc_density();
_recalc_relative_humidity();
set_live_update(live_update);
}
void FGEnvironment::Tie( SGPropertyNode_ptr base, bool archivable )
{
_tiedProperties.setRoot( base );
_tiedProperties.Tie( "visibility-m", this,
&FGEnvironment::get_visibility_m,
&FGEnvironment::set_visibility_m)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("temperature-sea-level-degc", this,
&FGEnvironment::get_temperature_sea_level_degc,
&FGEnvironment::set_temperature_sea_level_degc)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("temperature-degc", this,
&FGEnvironment::get_temperature_degc,
&FGEnvironment::set_temperature_degc)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("temperature-degf", this,
&FGEnvironment::get_temperature_degf);
_tiedProperties.Tie("dewpoint-sea-level-degc", this,
&FGEnvironment::get_dewpoint_sea_level_degc,
&FGEnvironment::set_dewpoint_sea_level_degc)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("dewpoint-degc", this,
&FGEnvironment::get_dewpoint_degc,
&FGEnvironment::set_dewpoint_degc)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("pressure-sea-level-inhg", this,
&FGEnvironment::get_pressure_sea_level_inhg,
&FGEnvironment::set_pressure_sea_level_inhg)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("pressure-inhg", this,
&FGEnvironment::get_pressure_inhg,
&FGEnvironment::set_pressure_inhg)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("density-slugft3", this,
&FGEnvironment::get_density_slugft3); // read-only
_tiedProperties.Tie("relative-humidity", this,
&FGEnvironment::get_relative_humidity); //ro
_tiedProperties.Tie("atmosphere/density-tropo-avg", this,
&FGEnvironment::get_density_tropo_avg_kgm3); //ro
_tiedProperties.Tie("atmosphere/altitude-half-to-sun", this,
&FGEnvironment::get_altitude_half_to_sun_m,
&FGEnvironment::set_altitude_half_to_sun_m)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("atmosphere/altitude-troposphere-top", this,
&FGEnvironment::get_altitude_tropo_top_m,
&FGEnvironment::set_altitude_tropo_top_m)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("wind-from-heading-deg", this,
&FGEnvironment::get_wind_from_heading_deg,
&FGEnvironment::set_wind_from_heading_deg)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("wind-speed-kt", this,
&FGEnvironment::get_wind_speed_kt,
&FGEnvironment::set_wind_speed_kt)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("wind-from-north-fps", this,
&FGEnvironment::get_wind_from_north_fps,
&FGEnvironment::set_wind_from_north_fps)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("wind-from-east-fps", this,
&FGEnvironment::get_wind_from_east_fps,
&FGEnvironment::set_wind_from_east_fps)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("wind-from-down-fps", this,
&FGEnvironment::get_wind_from_down_fps,
&FGEnvironment::set_wind_from_down_fps)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("turbulence/magnitude-norm", this,
&FGEnvironment::get_turbulence_magnitude_norm,
&FGEnvironment::set_turbulence_magnitude_norm)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
_tiedProperties.Tie("turbulence/rate-hz", this,
&FGEnvironment::get_turbulence_rate_hz,
&FGEnvironment::set_turbulence_rate_hz)
->setAttribute( SGPropertyNode::ARCHIVE, archivable );
}
void FGEnvironment::Untie()
{
_tiedProperties.Untie();
}
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_temperature_degf () const
{
return (temperature_degc * 9.0 / 5.0) + 32.0;
}
double
FGEnvironment::get_dewpoint_sea_level_degc () const
{
return dewpoint_sea_level_degc;
}
double
FGEnvironment::get_dewpoint_degc () const
{
return dewpoint_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_slugft3 () const
{
return density_slugft3;
}
double
FGEnvironment::get_relative_humidity () const
{
return relative_humidity;
}
double
FGEnvironment::get_density_tropo_avg_kgm3 () const
{
return density_tropo_avg_kgm3;
}
double
FGEnvironment::get_altitude_half_to_sun_m () const
{
return altitude_half_to_sun_m;
}
double
FGEnvironment::get_altitude_tropo_top_m () const
{
return altitude_tropo_top_m;
}
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_turbulence_magnitude_norm () const
{
return turbulence_magnitude_norm;
}
double
FGEnvironment::get_turbulence_rate_hz () const
{
return turbulence_rate_hz;
}
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;
if (dewpoint_sea_level_degc > t)
dewpoint_sea_level_degc = t;
if( live_update ) {
_recalc_alt_pt();
_recalc_density();
}
}
void
FGEnvironment::set_temperature_degc (double t)
{
temperature_degc = t;
if( live_update ) {
_recalc_sl_temperature();
_recalc_sl_pressure();
_recalc_alt_pt();
_recalc_density();
_recalc_relative_humidity();
}
}
void
FGEnvironment::set_dewpoint_sea_level_degc (double t)
{
dewpoint_sea_level_degc = t;
if (temperature_sea_level_degc < t)
temperature_sea_level_degc = t;
if( live_update ) {
_recalc_alt_dewpoint();
_recalc_density();
}
}
void
FGEnvironment::set_dewpoint_degc (double t)
{
dewpoint_degc = t;
if( live_update ) {
_recalc_sl_dewpoint();
_recalc_density();
_recalc_relative_humidity();
}
}
void
FGEnvironment::set_pressure_sea_level_inhg (double p)
{
pressure_sea_level_inhg = p;
if( live_update ) {
_recalc_alt_pt();
_recalc_density();
}
}
void
FGEnvironment::set_pressure_inhg (double p)
{
pressure_inhg = p;
if( live_update ) {
_recalc_sl_pressure();
_recalc_density();
}
}
void
FGEnvironment::set_wind_from_heading_deg (double h)
{
wind_from_heading_deg = h;
if( live_update ) {
_recalc_ne();
}
}
void
FGEnvironment::set_wind_speed_kt (double s)
{
wind_speed_kt = s;
if( live_update ) {
_recalc_ne();
}
}
void
FGEnvironment::set_wind_from_north_fps (double n)
{
wind_from_north_fps = n;
if( live_update ) {
_recalc_hdgspd();
}
}
void
FGEnvironment::set_wind_from_east_fps (double e)
{
wind_from_east_fps = e;
if( live_update ) {
_recalc_hdgspd();
}
}
void
FGEnvironment::set_wind_from_down_fps (double d)
{
wind_from_down_fps = d;
if( live_update ) {
_recalc_hdgspd();
}
}
void
FGEnvironment::set_turbulence_magnitude_norm (double t)
{
turbulence_magnitude_norm = t;
}
void
FGEnvironment::set_turbulence_rate_hz (double r)
{
turbulence_rate_hz = r;
}
void
FGEnvironment::set_elevation_ft (double e)
{
elevation_ft = e;
if( live_update ) {
_recalc_alt_pt();
_recalc_alt_dewpoint();
_recalc_density();
_recalc_relative_humidity();
}
}
void
FGEnvironment::set_altitude_half_to_sun_m (double alt)
{
altitude_half_to_sun_m = alt;
if( live_update ) {
_recalc_density_tropo_avg_kgm3();
}
}
void
FGEnvironment::set_altitude_tropo_top_m (double alt)
{
altitude_tropo_top_m = alt;
if( live_update ) {
_recalc_density_tropo_avg_kgm3();
}
}
void
FGEnvironment::_recalc_hdgspd ()
{
wind_from_heading_deg =
atan2(wind_from_east_fps, wind_from_north_fps) * SGD_RADIANS_TO_DEGREES;
if( wind_from_heading_deg < 0 )
wind_from_heading_deg += 360.0;
wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
wind_from_east_fps * wind_from_east_fps)
* 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);
}
// Intended to help with the interpretation of METAR data,
// not for random in-flight outside-air temperatures.
void
FGEnvironment::_recalc_sl_temperature ()
{
#if 0
{
SG_LOG(SG_GENERAL, SG_DEBUG, "recalc_sl_temperature: using "
<< temperature_degc << " @ " << elevation_ft << " :: " << this);
}
#endif
if (elevation_ft * atmodel::foot >= ISA_def[1].height) {
SG_LOG(SG_GENERAL, SG_ALERT, "recalc_sl_temperature: "
<< "valid only in troposphere, not " << elevation_ft);
return;
}
// Clamp: temperature of the stratosphere, in degrees C:
double t_strato = ISA_def[1].temp - atmodel::freezing;
if (temperature_degc < t_strato) temperature_sea_level_degc = t_strato;
else temperature_sea_level_degc =
temperature_degc + elevation_ft * atmodel::foot * ISA_def[0].lapse;
// Alternative implemenation:
// else temperature_sea_level_inhg = T_layer(0., elevation_ft * foot,
// pressure_inhg * inHg, temperature_degc + freezing, ISA_def[0].lapse) - freezing;
}
void
FGEnvironment::_recalc_sl_dewpoint ()
{
// 0.2degC/1000ft
// FIXME: this will work only for low
// elevations
dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
if (dewpoint_sea_level_degc > temperature_sea_level_degc)
dewpoint_sea_level_degc = temperature_sea_level_degc;
}
void
FGEnvironment::_recalc_alt_dewpoint ()
{
// 0.2degC/1000ft
// FIXME: this will work only for low
// elevations
dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
if (dewpoint_degc > temperature_degc)
dewpoint_degc = temperature_degc;
}
void
FGEnvironment::_recalc_sl_pressure ()
{
using namespace atmodel;
#if 0
{
SG_LOG(SG_GENERAL, SG_ALERT, "recalc_sl_pressure: using "
<< pressure_inhg << " and "
<< temperature_degc << " @ " << elevation_ft << " :: " << this);
}
#endif
pressure_sea_level_inhg = P_layer(0., elevation_ft * foot,
pressure_inhg * inHg, temperature_degc + freezing, ISA_def[0].lapse) / inHg;
}
// This gets called at frame rate, to account for the aircraft's
// changing altitude.
// Called by set_elevation_ft() which is called by FGEnvironmentMgr::update
void
FGEnvironment::_recalc_alt_pt ()
{
using namespace atmodel;
#if 0
{
static int count(0);
if (++count % 1000 == 0) {
SG_LOG(SG_GENERAL, SG_ALERT,
"recalc_alt_pt for: " << elevation_ft
<< " using " << pressure_sea_level_inhg
<< " and " << temperature_sea_level_degc
<< " :: " << this
<< " # " << count);
}
}
#endif
double press = pressure_inhg * inHg;
double temp = temperature_degc + freezing;
boost::tie(press, temp) = PT_vs_hpt(elevation_ft * foot,
pressure_sea_level_inhg * inHg, temperature_sea_level_degc + freezing);
temperature_degc = temp - freezing;
pressure_inhg = press / inHg;
}
void
FGEnvironment::_recalc_density ()
{
double pressure_psf = pressure_inhg * 70.7487;
// adjust for humidity
// calculations taken from USA Today (oops!) at
// http://www.usatoday.com/weather/basics/density-calculations.htm
double temperature_degk = temperature_degc + 273.15;
double pressure_mb = pressure_inhg * 33.86;
double vapor_pressure_mb =
6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
double virtual_temperature_degr = virtual_temperature_degk * 1.8;
density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
_recalc_density_tropo_avg_kgm3();
}
// This is used to calculate the average density on the path
// of sunlight to the observer for calculating sun-color
void
FGEnvironment::_recalc_density_tropo_avg_kgm3 ()
{
double pressure_mb = pressure_inhg * 33.86;
double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / (237.7 + dewpoint_degc)));
double virtual_temp = (temperature_degc + 273.15) / (1 - 0.379 * (vaporpressure/pressure_mb));
double density_half = (100 * pressure_mb * exp(-altitude_half_to_sun_m / 8000))
/ (287.05 * virtual_temp);
double density_tropo = (100 * pressure_mb * exp((-1 * altitude_tropo_top_m) / 8000))
/ ( 287.05 * virtual_temp);
density_tropo_avg_kgm3 = ((density_slugft3 * 515.379) + density_half + density_tropo) / 3;
}
void
FGEnvironment::_recalc_relative_humidity ()
{
/*
double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / ( 237.7 + dewpoint_degc)));
double sat_vaporpressure = 6.11 * pow(10.0, ((7.5 * temperature_degc)
/ ( 237.7 + temperature_degc)) );
relative_humidity = 100 * vaporpressure / sat_vaporpressure ;
with a little algebra, this gets the same result and spares two multiplications and one pow()
*/
double a = (7.5 * dewpoint_degc) / ( 237.7 + dewpoint_degc);
double b = (7.5 * temperature_degc) / ( 237.7 + temperature_degc);
relative_humidity = 100 * pow(10.0,a-b);
}
bool
FGEnvironment::set_live_update( bool _live_update )
{
bool b = live_update;
live_update = _live_update;
return b;
}
////////////////////////////////////////////////////////////////////////
// Functions.
////////////////////////////////////////////////////////////////////////
static inline double
do_interp (double a, double b, double fraction)
{
double retval = (a + ((b - a) * fraction));
return retval;
}
static inline double
do_interp_deg (double a, double b, double fraction)
{
a = fmod(a, 360);
b = fmod(b, 360);
if (fabs(b-a) > 180) {
if (a < b)
a += 360;
else
b += 360;
}
return fmod(do_interp(a, b, fraction), 360);
}
FGEnvironment &
FGEnvironment::interpolate( const FGEnvironment & env2,
double fraction, FGEnvironment * result) const
{
// don't calculate each internal property every time we set a single value
// we trigger that at the end of the interpolation process
bool live_update = result->set_live_update( false );
result->set_visibility_m
(do_interp(get_visibility_m(),
env2.get_visibility_m(),
fraction));
result->set_temperature_sea_level_degc
(do_interp(get_temperature_sea_level_degc(),
env2.get_temperature_sea_level_degc(),
fraction));
result->set_dewpoint_sea_level_degc
(do_interp(get_dewpoint_sea_level_degc(),
env2.get_dewpoint_sea_level_degc(),
fraction));
result->set_pressure_sea_level_inhg
(do_interp(get_pressure_sea_level_inhg(),
env2.get_pressure_sea_level_inhg(),
fraction));
result->set_wind_from_heading_deg
(do_interp_deg(get_wind_from_heading_deg(),
env2.get_wind_from_heading_deg(),
fraction));
result->set_wind_speed_kt
(do_interp(get_wind_speed_kt(),
env2.get_wind_speed_kt(),
fraction));
result->set_elevation_ft
(do_interp(get_elevation_ft(),
env2.get_elevation_ft(),
fraction));
result->set_turbulence_magnitude_norm
(do_interp(get_turbulence_magnitude_norm(),
env2.get_turbulence_magnitude_norm(),
fraction));
result->set_turbulence_rate_hz
(do_interp(get_turbulence_rate_hz(),
env2.get_turbulence_rate_hz(),
fraction));
// calculate derived properties here to avoid duplicate expensive computations
result->_recalc_ne();
result->_recalc_alt_pt();
result->_recalc_alt_dewpoint();
result->_recalc_density();
result->_recalc_relative_humidity();
result->set_live_update(live_update);
return *result;
}
// end of environment.cxx