1 // environment.cxx -- routines to model the natural environment
3 // Written by David Megginson, started February 2002.
5 // Copyright (C) 2002 David Megginson - david@megginson.com
7 // This program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License as
9 // published by the Free Software Foundation; either version 2 of the
10 // License, or (at your option) any later version.
12 // This program is distributed in the hope that it will be useful, but
13 // WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
36 #include <simgear/constants.h>
37 #include <simgear/debug/logstream.hxx>
38 #include <simgear/math/interpolater.hxx>
40 #include <Main/fg_props.hxx>
41 #include "environment.hxx"
44 FGEnvironment::FGEnvironment()
45 : _temperature_degc_table(new SGInterpTable),
46 _pressure_inhg_table(new SGInterpTable),
49 temperature_sea_level_degc(15),
51 dewpoint_sea_level_degc(5), // guess
53 pressure_sea_level_inhg(29.92),
55 wind_from_heading_deg(0),
57 wind_from_north_fps(0),
58 wind_from_east_fps(0),
64 FGEnvironment::FGEnvironment (const FGEnvironment &env)
65 : _temperature_degc_table(new SGInterpTable),
66 _pressure_inhg_table(new SGInterpTable),
67 elevation_ft(env.elevation_ft),
68 visibility_m(env.visibility_m),
69 temperature_sea_level_degc(env.temperature_sea_level_degc),
70 dewpoint_sea_level_degc(env.dewpoint_sea_level_degc),
71 pressure_sea_level_inhg(env.pressure_sea_level_inhg),
72 wind_from_heading_deg(env.wind_from_heading_deg),
73 wind_speed_kt(env.wind_speed_kt),
74 wind_from_north_fps(env.wind_from_north_fps),
75 wind_from_east_fps(env.wind_from_east_fps),
76 wind_from_down_fps(env.wind_from_down_fps)
81 FGEnvironment::~FGEnvironment()
83 delete _temperature_degc_table;
84 delete _pressure_inhg_table;
89 FGEnvironment::get_visibility_m () const
95 FGEnvironment::get_temperature_sea_level_degc () const
97 return temperature_sea_level_degc;
101 FGEnvironment::get_temperature_degc () const
103 return temperature_degc;
107 FGEnvironment::get_dewpoint_sea_level_degc () const
109 return dewpoint_sea_level_degc;
113 FGEnvironment::get_dewpoint_degc () const
115 return dewpoint_degc;
119 FGEnvironment::get_pressure_sea_level_inhg () const
121 return pressure_sea_level_inhg;
125 FGEnvironment::get_pressure_inhg () const
127 return pressure_inhg;
131 FGEnvironment::get_density_slugft3 () const
133 return density_slugft3;
137 FGEnvironment::get_wind_from_heading_deg () const
139 return wind_from_heading_deg;
143 FGEnvironment::get_wind_speed_kt () const
145 return wind_speed_kt;
149 FGEnvironment::get_wind_from_north_fps () const
151 return wind_from_north_fps;
155 FGEnvironment::get_wind_from_east_fps () const
157 return wind_from_east_fps;
161 FGEnvironment::get_wind_from_down_fps () const
163 return wind_from_down_fps;
167 FGEnvironment::get_elevation_ft () const
173 FGEnvironment::set_visibility_m (double v)
179 FGEnvironment::set_temperature_sea_level_degc (double t)
181 temperature_sea_level_degc = t;
182 _recalc_alt_temperature();
187 FGEnvironment::set_temperature_degc (double t)
189 temperature_degc = t;
190 _recalc_sl_temperature();
195 FGEnvironment::set_dewpoint_sea_level_degc (double t)
197 dewpoint_sea_level_degc = t;
198 _recalc_alt_dewpoint();
203 FGEnvironment::set_dewpoint_degc (double t)
206 _recalc_sl_dewpoint();
211 FGEnvironment::set_pressure_sea_level_inhg (double p)
213 pressure_sea_level_inhg = p;
214 _recalc_alt_pressure();
219 FGEnvironment::set_pressure_inhg (double p)
222 _recalc_sl_pressure();
227 FGEnvironment::set_wind_from_heading_deg (double h)
229 wind_from_heading_deg = h;
234 FGEnvironment::set_wind_speed_kt (double s)
241 FGEnvironment::set_wind_from_north_fps (double n)
243 wind_from_north_fps = n;
248 FGEnvironment::set_wind_from_east_fps (double e)
250 wind_from_east_fps = e;
255 FGEnvironment::set_wind_from_down_fps (double d)
257 wind_from_down_fps = d;
262 FGEnvironment::set_elevation_ft (double e)
265 _recalc_alt_temperature();
266 _recalc_alt_dewpoint();
267 _recalc_alt_pressure();
273 // Copied from YASim Atmosphere.cxx, with m converted to ft, degK
274 // converted to degC, Pa converted to inHG, and kg/m^3 converted to
275 // slug/ft^3; they were then converted to deltas from the sea-level
276 // defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).
278 // Original comment from YASim:
280 // Copied from McCormick, who got it from "The ARDC Model Atmosphere"
281 // Note that there's an error in the text in the first entry,
282 // McCormick lists 299.16/101325/1.22500, but those don't agree with
283 // R=287. I chose to correct the temperature to 288.20, since 79F is
284 // pretty hot for a "standard" atmosphere.
286 // Elevation (ft), temperature factor (degK), pressure factor (inHG)
287 static double atmosphere_data[][3] = {
288 { 0.00, 1.00, 1.000 },
289 { 2952.76, 0.98, 0.898 },
290 { 5905.51, 0.96, 0.804 },
291 { 8858.27, 0.94, 0.719 },
292 { 11811.02, 0.92, 0.641 },
293 { 14763.78, 0.90, 0.570 },
294 { 17716.54, 0.88, 0.506 },
295 { 20669.29, 0.86, 0.447 },
296 { 23622.05, 0.84, 0.394 },
297 { 26574.80, 0.82, 0.347 },
298 { 29527.56, 0.80, 0.304 },
299 { 32480.31, 0.78, 0.266 },
300 { 35433.07, 0.76, 0.231 },
301 { 38385.83, 0.75, 0.201 },
302 { 41338.58, 0.75, 0.174 },
303 { 44291.34, 0.75, 0.151 },
304 { 47244.09, 0.75, 0.131 },
305 { 50196.85, 0.75, 0.114 },
306 { 53149.61, 0.75, 0.099 },
307 { 56102.36, 0.75, 0.086 },
308 { 59055.12, 0.75, 0.075 },
309 { 62007.87, 0.75, 0.065 },
314 FGEnvironment::_setup_tables ()
316 for (int i = 0; atmosphere_data[i][0] != -1; i++) {
317 _temperature_degc_table->addEntry(atmosphere_data[i][0],
318 atmosphere_data[i][1]);
319 _pressure_inhg_table->addEntry(atmosphere_data[i][0],
320 atmosphere_data[i][2]);
325 FGEnvironment::_recalc_hdgspd ()
329 if (wind_from_east_fps == 0) {
330 angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
332 angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
334 wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
335 if (wind_from_east_fps >= 0)
336 wind_from_heading_deg = 90 - wind_from_heading_deg;
338 wind_from_heading_deg = 270 - wind_from_heading_deg;
340 wind_speed_kt = fabs(wind_from_east_fps
341 * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
343 wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
344 * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
348 FGEnvironment::_recalc_ne ()
351 wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
353 wind_from_north_fps = speed_fps *
354 cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
355 wind_from_east_fps = speed_fps *
356 sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
360 FGEnvironment::_recalc_sl_temperature ()
362 // If we're in the stratosphere, leave sea-level temp alone
363 if (elevation_ft < 38000) {
364 temperature_sea_level_degc =
365 (temperature_degc + 273.15)
366 /_temperature_degc_table->interpolate(elevation_ft)
372 FGEnvironment::_recalc_alt_temperature ()
374 if (elevation_ft < 38000) {
376 (temperature_sea_level_degc + 273.15) *
377 _temperature_degc_table->interpolate(elevation_ft) - 273.15;
379 temperature_degc = -56.49; // Stratosphere is constant
384 FGEnvironment::_recalc_sl_dewpoint ()
387 // FIXME: this will work only for low
389 dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
390 if (dewpoint_sea_level_degc > temperature_sea_level_degc)
391 dewpoint_sea_level_degc = temperature_sea_level_degc;
395 FGEnvironment::_recalc_alt_dewpoint ()
398 // FIXME: this will work only for low
400 dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
401 if (dewpoint_degc > temperature_degc)
402 dewpoint_degc = temperature_degc;
406 FGEnvironment::_recalc_sl_pressure ()
408 pressure_sea_level_inhg =
409 pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
413 FGEnvironment::_recalc_alt_pressure ()
416 pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
420 FGEnvironment::_recalc_density ()
422 double pressure_psf = pressure_inhg * 70.7487;
424 // adjust for humidity
425 // calculations taken from USA Today (oops!) at
426 // http://www.usatoday.com/weather/basics/density-calculations.htm
427 double temperature_degk = temperature_degc + 273.15;
428 double pressure_mb = pressure_inhg * 33.86;
429 double vapor_pressure_mb =
430 6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
431 double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
432 double virtual_temperature_degr = virtual_temperature_degk * 1.8;
434 density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
437 // end of environment.cxx