917 lines
24 KiB
C++
917 lines
24 KiB
C++
// environment.cxx -- routines to model the natural environment
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//
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// Written by David Megginson, started February 2002.
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//
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// Copyright (C) 2002 David Megginson - david@megginson.com
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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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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include <cmath>
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#include <boost/tuple/tuple.hpp>
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#include <simgear/props/props.hxx>
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#include <simgear/math/SGMath.hxx>
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#include <Main/fg_props.hxx>
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#include "environment.hxx"
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#include "atmosphere.hxx"
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////////////////////////////////////////////////////////////////////////
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// Atmosphere model.
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////////////////////////////////////////////////////////////////////////
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#ifdef USING_TABLES
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// Calculated based on the ISA standard day, as found at e.g.
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// http://www.av8n.com/physics/altimetry.htm
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// Each line of data has 3 elements:
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// Elevation (ft),
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// temperature factor (dimensionless ratio of absolute temp),
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// pressure factor (dimensionless ratio)
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static double atmosphere_data[][3] = {
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{ -3000.00, 1.021, 1.1133 },
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{ 0.00, 1.000, 1.0000 },
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{ 2952.76, 0.980, 0.8978 },
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{ 5905.51, 0.959, 0.8042 },
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{ 8858.27, 0.939, 0.7187 },
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{ 11811.02, 0.919, 0.6407 },
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{ 14763.78, 0.898, 0.5697 },
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{ 17716.54, 0.878, 0.5052 },
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{ 20669.29, 0.858, 0.4468 },
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{ 23622.05, 0.838, 0.3940 },
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{ 26574.80, 0.817, 0.3463 },
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{ 29527.56, 0.797, 0.3034 },
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{ 32480.31, 0.777, 0.2649 },
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{ 35433.07, 0.756, 0.2305 },
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{ 38385.83, 0.752, 0.2000 },
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{ 41338.58, 0.752, 0.1736 },
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{ 44291.34, 0.752, 0.1506 },
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{ 47244.09, 0.752, 0.1307 },
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{ 50196.85, 0.752, 0.1134 },
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{ 53149.61, 0.752, 0.0984 },
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{ 56102.36, 0.752, 0.0854 },
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{ 59055.12, 0.752, 0.0741 },
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{ 62007.87, 0.752, 0.0643 },
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{ 65000.00, 0.752, 0.0557 },
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{ 68000.00, 0.754, 0.0482 },
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{ 71000.00, 0.758, 0.0418 },
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{ 74000.00, 0.761, 0.0362 },
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{ 77000.00, 0.764, 0.0314 },
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{ 80000.00, 0.767, 0.0273 },
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{ 83000.00, 0.770, 0.0237 },
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{ 86000.00, 0.773, 0.0206 },
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{ 89000.00, 0.777, 0.0179 },
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{ 92000.00, 0.780, 0.0156 },
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{ 95000.00, 0.783, 0.0135 },
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{ 98000.00, 0.786, 0.0118 },
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{ 101000.00, 0.789, 0.0103 },
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{ -1, -1, -1 }
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};
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static SGInterpTable * _temperature_degc_table = 0;
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static SGInterpTable * _pressure_inhg_table = 0;
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static void
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_setup_tables ()
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{
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if (_temperature_degc_table != 0)
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return;
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_temperature_degc_table = new SGInterpTable;
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_pressure_inhg_table = new SGInterpTable;
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for (int i = 0; atmosphere_data[i][0] != -1; i++) {
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_temperature_degc_table->addEntry(atmosphere_data[i][0],
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atmosphere_data[i][1]);
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_pressure_inhg_table->addEntry(atmosphere_data[i][0],
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atmosphere_data[i][2]);
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}
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}
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#endif
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////////////////////////////////////////////////////////////////////////
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// Implementation of FGEnvironment.
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////////////////////////////////////////////////////////////////////////
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void FGEnvironment::_init()
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{
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live_update = false;
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elevation_ft = 0;
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visibility_m = 32000;
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temperature_sea_level_degc = 15;
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temperature_degc = 15;
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dewpoint_sea_level_degc = 5; // guess
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dewpoint_degc = 5;
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pressure_sea_level_inhg = 29.92;
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pressure_inhg = 29.92;
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density_slugft3 = 0;
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turbulence_magnitude_norm = 0;
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turbulence_rate_hz = 1;
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wind_from_heading_deg = 0;
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wind_speed_kt = 0;
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wind_from_north_fps = 0;
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wind_from_east_fps = 0;
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wind_from_down_fps = 0;
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altitude_half_to_sun_m = 1000;
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altitude_tropo_top_m = 10000;
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#ifdef USING_TABLES
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_setup_tables();
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#endif
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_recalc_density();
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_recalc_relative_humidity();
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live_update = true;
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}
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FGEnvironment::FGEnvironment()
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{
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_init();
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}
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FGEnvironment::FGEnvironment (const FGEnvironment &env)
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{
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_init();
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copy(env);
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}
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FGEnvironment::~FGEnvironment()
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{
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Untie();
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}
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FGEnvironment & FGEnvironment::operator = ( const FGEnvironment & other )
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{
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copy( other );
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return *this;
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}
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void
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FGEnvironment::copy (const FGEnvironment &env)
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{
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elevation_ft = env.elevation_ft;
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visibility_m = env.visibility_m;
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temperature_sea_level_degc = env.temperature_sea_level_degc;
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temperature_degc = env.temperature_degc;
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dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
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dewpoint_degc = env.dewpoint_degc;
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pressure_sea_level_inhg = env.pressure_sea_level_inhg;
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wind_from_heading_deg = env.wind_from_heading_deg;
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wind_speed_kt = env.wind_speed_kt;
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wind_from_north_fps = env.wind_from_north_fps;
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wind_from_east_fps = env.wind_from_east_fps;
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wind_from_down_fps = env.wind_from_down_fps;
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turbulence_magnitude_norm = env.turbulence_magnitude_norm;
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turbulence_rate_hz = env.turbulence_rate_hz;
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pressure_inhg = env.pressure_inhg;
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density_slugft3 = env.density_slugft3;
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density_tropo_avg_kgm3 = env.density_tropo_avg_kgm3;
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relative_humidity = env.relative_humidity;
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altitude_half_to_sun_m = env.altitude_half_to_sun_m;
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altitude_tropo_top_m = env.altitude_tropo_top_m;
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live_update = env.live_update;
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}
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static inline bool
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maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
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const char * name, void (FGEnvironment::*setter)(double))
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{
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const SGPropertyNode * child = node->getNode(name);
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// fragile: depends on not being typed
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// as a number
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if (child != 0 && child->hasValue() &&
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child->getStringValue()[0] != '\0') {
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(env->*setter)(child->getDoubleValue());
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return true;
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} else {
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return false;
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}
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}
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void
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FGEnvironment::read (const SGPropertyNode * node)
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{
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bool live_update = set_live_update( false );
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maybe_copy_value(this, node, "visibility-m",
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&FGEnvironment::set_visibility_m);
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maybe_copy_value(this, node, "elevation-ft",
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&FGEnvironment::set_elevation_ft);
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if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
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&FGEnvironment::set_temperature_sea_level_degc)) {
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if( maybe_copy_value(this, node, "temperature-degc",
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&FGEnvironment::set_temperature_degc)) {
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_recalc_sl_temperature();
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}
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}
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if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
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&FGEnvironment::set_dewpoint_sea_level_degc)) {
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if( maybe_copy_value(this, node, "dewpoint-degc",
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&FGEnvironment::set_dewpoint_degc)) {
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_recalc_sl_dewpoint();
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}
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}
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if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
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&FGEnvironment::set_pressure_sea_level_inhg)) {
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if( maybe_copy_value(this, node, "pressure-inhg",
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&FGEnvironment::set_pressure_inhg)) {
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_recalc_sl_pressure();
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}
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}
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maybe_copy_value(this, node, "wind-from-heading-deg",
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&FGEnvironment::set_wind_from_heading_deg);
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maybe_copy_value(this, node, "wind-speed-kt",
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&FGEnvironment::set_wind_speed_kt);
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maybe_copy_value(this, node, "turbulence/magnitude-norm",
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&FGEnvironment::set_turbulence_magnitude_norm);
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maybe_copy_value(this, node, "turbulence/rate-hz",
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&FGEnvironment::set_turbulence_rate_hz);
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// calculate derived properties here to avoid duplicate expensive computations
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_recalc_ne();
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_recalc_alt_pt();
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_recalc_alt_dewpoint();
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_recalc_density();
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_recalc_relative_humidity();
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set_live_update(live_update);
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}
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void FGEnvironment::Tie( SGPropertyNode_ptr base, bool archivable )
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{
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_tiedProperties.setRoot( base );
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_tiedProperties.Tie( "visibility-m", this,
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&FGEnvironment::get_visibility_m,
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&FGEnvironment::set_visibility_m);
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_tiedProperties.Tie("temperature-sea-level-degc", this,
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&FGEnvironment::get_temperature_sea_level_degc,
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&FGEnvironment::set_temperature_sea_level_degc);
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_tiedProperties.Tie("temperature-degc", this,
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&FGEnvironment::get_temperature_degc,
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&FGEnvironment::set_temperature_degc);
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_tiedProperties.Tie("dewpoint-sea-level-degc", this,
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&FGEnvironment::get_dewpoint_sea_level_degc,
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&FGEnvironment::set_dewpoint_sea_level_degc);
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_tiedProperties.Tie("dewpoint-degc", this,
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&FGEnvironment::get_dewpoint_degc,
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&FGEnvironment::set_dewpoint_degc);
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_tiedProperties.Tie("pressure-sea-level-inhg", this,
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&FGEnvironment::get_pressure_sea_level_inhg,
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&FGEnvironment::set_pressure_sea_level_inhg);
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_tiedProperties.Tie("pressure-inhg", this,
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&FGEnvironment::get_pressure_inhg,
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&FGEnvironment::set_pressure_inhg);
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_tiedProperties.Tie("atmosphere/altitude-half-to-sun", this,
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&FGEnvironment::get_altitude_half_to_sun_m,
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&FGEnvironment::set_altitude_half_to_sun_m);
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_tiedProperties.Tie("atmosphere/altitude-troposphere-top", this,
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&FGEnvironment::get_altitude_tropo_top_m,
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&FGEnvironment::set_altitude_tropo_top_m);
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_tiedProperties.Tie("wind-from-heading-deg", this,
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&FGEnvironment::get_wind_from_heading_deg,
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&FGEnvironment::set_wind_from_heading_deg);
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_tiedProperties.Tie("wind-speed-kt", this,
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&FGEnvironment::get_wind_speed_kt,
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&FGEnvironment::set_wind_speed_kt);
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_tiedProperties.Tie("wind-from-north-fps", this,
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&FGEnvironment::get_wind_from_north_fps,
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&FGEnvironment::set_wind_from_north_fps);
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_tiedProperties.Tie("wind-from-east-fps", this,
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&FGEnvironment::get_wind_from_east_fps,
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&FGEnvironment::set_wind_from_east_fps);
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_tiedProperties.Tie("wind-from-down-fps", this,
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&FGEnvironment::get_wind_from_down_fps,
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&FGEnvironment::set_wind_from_down_fps);
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_tiedProperties.Tie("turbulence/magnitude-norm", this,
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&FGEnvironment::get_turbulence_magnitude_norm,
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&FGEnvironment::set_turbulence_magnitude_norm);
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_tiedProperties.Tie("turbulence/rate-hz", this,
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&FGEnvironment::get_turbulence_rate_hz,
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&FGEnvironment::set_turbulence_rate_hz);
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_tiedProperties.setAttribute( SGPropertyNode::ARCHIVE, archivable );
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_tiedProperties.Tie("temperature-degf", this,
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&FGEnvironment::get_temperature_degf);
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_tiedProperties.Tie("density-slugft3", this,
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&FGEnvironment::get_density_slugft3); // read-only
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_tiedProperties.Tie("relative-humidity", this,
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&FGEnvironment::get_relative_humidity); //ro
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_tiedProperties.Tie("atmosphere/density-tropo-avg", this,
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&FGEnvironment::get_density_tropo_avg_kgm3); //ro
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}
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void FGEnvironment::Untie()
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{
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_tiedProperties.Untie();
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}
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double
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FGEnvironment::get_visibility_m () const
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{
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return visibility_m;
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}
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double
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FGEnvironment::get_temperature_sea_level_degc () const
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{
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return temperature_sea_level_degc;
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}
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double
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FGEnvironment::get_temperature_degc () const
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{
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return temperature_degc;
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}
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double
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FGEnvironment::get_temperature_degf () const
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{
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return (temperature_degc * 9.0 / 5.0) + 32.0;
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}
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double
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FGEnvironment::get_dewpoint_sea_level_degc () const
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{
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return dewpoint_sea_level_degc;
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}
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double
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FGEnvironment::get_dewpoint_degc () const
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{
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return dewpoint_degc;
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}
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double
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FGEnvironment::get_pressure_sea_level_inhg () const
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{
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return pressure_sea_level_inhg;
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}
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double
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FGEnvironment::get_pressure_inhg () const
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{
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return pressure_inhg;
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}
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double
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FGEnvironment::get_density_slugft3 () const
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{
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return density_slugft3;
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}
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double
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FGEnvironment::get_relative_humidity () const
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{
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return relative_humidity;
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}
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double
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FGEnvironment::get_density_tropo_avg_kgm3 () const
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{
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return density_tropo_avg_kgm3;
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}
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double
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FGEnvironment::get_altitude_half_to_sun_m () const
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{
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return altitude_half_to_sun_m;
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}
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double
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FGEnvironment::get_altitude_tropo_top_m () const
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{
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return altitude_tropo_top_m;
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}
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double
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FGEnvironment::get_wind_from_heading_deg () const
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{
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return wind_from_heading_deg;
|
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}
|
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|
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double
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FGEnvironment::get_wind_speed_kt () const
|
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{
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return wind_speed_kt;
|
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}
|
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|
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double
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FGEnvironment::get_wind_from_north_fps () const
|
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{
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return wind_from_north_fps;
|
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}
|
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|
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double
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FGEnvironment::get_wind_from_east_fps () const
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{
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return wind_from_east_fps;
|
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}
|
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|
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double
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FGEnvironment::get_wind_from_down_fps () const
|
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{
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return wind_from_down_fps;
|
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}
|
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|
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double
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FGEnvironment::get_turbulence_magnitude_norm () const
|
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{
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return turbulence_magnitude_norm;
|
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}
|
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|
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double
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FGEnvironment::get_turbulence_rate_hz () const
|
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{
|
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return turbulence_rate_hz;
|
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}
|
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|
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double
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FGEnvironment::get_elevation_ft () const
|
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{
|
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return elevation_ft;
|
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}
|
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|
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void
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FGEnvironment::set_visibility_m (double v)
|
||
{
|
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visibility_m = v;
|
||
}
|
||
|
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void
|
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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_ENVIRONMENT, SG_DEBUG, "recalc_sl_temperature: using "
|
||
<< temperature_degc << " @ " << elevation_ft << " :: " << this);
|
||
}
|
||
#endif
|
||
|
||
if (elevation_ft * atmodel::foot >= ISA_def[1].height) {
|
||
SG_LOG(SG_ENVIRONMENT, 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_ENVIRONMENT, 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_ENVIRONMENT, 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
|