src/Environment/environment.cxx

   1 // environment.cxx -- routines to model the natural environment
   2 //
   3 // Written by David Megginson, started February 2002.
   4 //
   5 // Copyright (C) 2002  David Megginson - david@megginson.com
   6 //
   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.
  11 //
  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.
  16 //
  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.
  20 //
  21 // $Id$
  22
  23
  24 #ifdef HAVE_CONFIG_H
  25 #  include <config.h>
  26 #endif
  27
  28 #ifdef HAVE_WINDOWS_H
  29 #  include <windows.h>
  30 #endif
  31
  32 #include <math.h>
  33
  34 #include <plib/sg.h>
  35
  36 #include <simgear/constants.h>
  37 #include <simgear/debug/logstream.hxx>
  38 #include <simgear/math/interpolater.hxx>
  39
  40 #include <Main/fg_props.hxx>
  41 #include "environment.hxx"
  42
  43
  44 FGEnvironment::FGEnvironment()
  45   : _temperature_degc_table(new SGInterpTable),
  46     _pressure_inhg_table(new SGInterpTable),
  47     elevation_ft(0),
  48     visibility_m(32000),
  49     temperature_sea_level_degc(15),
  50     temperature_degc(15),
  51     dewpoint_sea_level_degc(5), // guess
  52     dewpoint_degc(5),
  53     pressure_sea_level_inhg(29.92),
  54     pressure_inhg(29.92),
  55     wind_from_heading_deg(0),
  56     wind_speed_kt(0),
  57     wind_from_north_fps(0),
  58     wind_from_east_fps(0),
  59     wind_from_down_fps(0)
  60 {
  61   _setup_tables();
  62 }
  63
  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)
  77 {
  78   _setup_tables();
  79 }
  80
  81 FGEnvironment::~FGEnvironment()
  82 {
  83   delete _temperature_degc_table;
  84   delete _pressure_inhg_table;
  85 }
  86
  87
  88 double
  89 FGEnvironment::get_visibility_m () const
  90 {
  91   return visibility_m;
  92 }
  93
  94 double
  95 FGEnvironment::get_temperature_sea_level_degc () const
  96 {
  97   return temperature_sea_level_degc;
  98 }
  99
 100 double
 101 FGEnvironment::get_temperature_degc () const
 102 {
 103   return temperature_degc;
 104 }
 105
 106 double
 107 FGEnvironment::get_dewpoint_sea_level_degc () const
 108 {
 109   return dewpoint_sea_level_degc;
 110 }
 111
 112 double
 113 FGEnvironment::get_dewpoint_degc () const
 114 {
 115   return dewpoint_degc;
 116 }
 117
 118 double
 119 FGEnvironment::get_pressure_sea_level_inhg () const
 120 {
 121   return pressure_sea_level_inhg;
 122 }
 123
 124 double
 125 FGEnvironment::get_pressure_inhg () const
 126 {
 127   return pressure_inhg;
 128 }
 129
 130 double
 131 FGEnvironment::get_density_slugft3 () const
 132 {
 133   return density_slugft3;
 134 }
 135
 136 double
 137 FGEnvironment::get_wind_from_heading_deg () const
 138 {
 139   return wind_from_heading_deg;
 140 }
 141
 142 double
 143 FGEnvironment::get_wind_speed_kt () const
 144 {
 145   return wind_speed_kt;
 146 }
 147
 148 double
 149 FGEnvironment::get_wind_from_north_fps () const
 150 {
 151   return wind_from_north_fps;
 152 }
 153
 154 double
 155 FGEnvironment::get_wind_from_east_fps () const
 156 {
 157   return wind_from_east_fps;
 158 }
 159
 160 double
 161 FGEnvironment::get_wind_from_down_fps () const
 162 {
 163   return wind_from_down_fps;
 164 }
 165
 166 double
 167 FGEnvironment::get_elevation_ft () const
 168 {
 169   return elevation_ft;
 170 }
 171
 172 void
 173 FGEnvironment::set_visibility_m (double v)
 174 {
 175   visibility_m = v;
 176 }
 177
 178 void
 179 FGEnvironment::set_temperature_sea_level_degc (double t)
 180 {
 181   temperature_sea_level_degc = t;
 182   _recalc_alt_temperature();
 183   _recalc_density();
 184 }
 185
 186 void
 187 FGEnvironment::set_temperature_degc (double t)
 188 {
 189   temperature_degc = t;
 190   _recalc_sl_temperature();
 191   _recalc_density();
 192 }
 193
 194 void
 195 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 196 {
 197   dewpoint_sea_level_degc = t;
 198   _recalc_alt_dewpoint();
 199   _recalc_density();
 200 }
 201
 202 void
 203 FGEnvironment::set_dewpoint_degc (double t)
 204 {
 205   dewpoint_degc = t;
 206   _recalc_sl_dewpoint();
 207   _recalc_density();
 208 }
 209
 210 void
 211 FGEnvironment::set_pressure_sea_level_inhg (double p)
 212 {
 213   pressure_sea_level_inhg = p;
 214   _recalc_alt_pressure();
 215   _recalc_density();
 216 }
 217
 218 void
 219 FGEnvironment::set_pressure_inhg (double p)
 220 {
 221   pressure_inhg = p;
 222   _recalc_sl_pressure();
 223   _recalc_density();
 224 }
 225
 226 void
 227 FGEnvironment::set_wind_from_heading_deg (double h)
 228 {
 229   wind_from_heading_deg = h;
 230   _recalc_ne();
 231 }
 232
 233 void
 234 FGEnvironment::set_wind_speed_kt (double s)
 235 {
 236   wind_speed_kt = s;
 237   _recalc_ne();
 238 }
 239
 240 void
 241 FGEnvironment::set_wind_from_north_fps (double n)
 242 {
 243   wind_from_north_fps = n;
 244   _recalc_hdgspd();
 245 }
 246
 247 void
 248 FGEnvironment::set_wind_from_east_fps (double e)
 249 {
 250   wind_from_east_fps = e;
 251   _recalc_hdgspd();
 252 }
 253
 254 void
 255 FGEnvironment::set_wind_from_down_fps (double d)
 256 {
 257   wind_from_down_fps = d;
 258   _recalc_hdgspd();
 259 }
 260
 261 void
 262 FGEnvironment::set_elevation_ft (double e)
 263 {
 264   elevation_ft = e;
 265   _recalc_alt_temperature();
 266   _recalc_alt_dewpoint();
 267   _recalc_alt_pressure();
 268   _recalc_density();
 269 }
 270
 271 // Atmosphere model.
 272
 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).
 277
 278 // Original comment from YASim:
 279
 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.
 285
 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 },
 310  { -1, -1, -1 }
 311 };
 312
 313 void
 314 FGEnvironment::_setup_tables ()
 315 {
 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]);
 321   }
 322 }
 323
 324 void
 325 FGEnvironment::_recalc_hdgspd ()
 326 {
 327   double angle_rad;
 328
 329   if (wind_from_east_fps == 0) {
 330     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
 331   } else {
 332     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 333   }
 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;
 337   else
 338     wind_from_heading_deg = 270 - wind_from_heading_deg;
 339   if (angle_rad == 0)
 340     wind_speed_kt = fabs(wind_from_east_fps
 341                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 342   else
 343     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 344       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 345 }
 346
 347 void
 348 FGEnvironment::_recalc_ne ()
 349 {
 350   double speed_fps =
 351     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 352
 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);
 357 }
 358
 359 void
 360 FGEnvironment::_recalc_sl_temperature ()
 361 {
 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)
 367       - 273.15;
 368   }
 369 }
 370
 371 void
 372 FGEnvironment::_recalc_alt_temperature ()
 373 {
 374   if (elevation_ft < 38000) {
 375     temperature_degc =
 376       (temperature_sea_level_degc + 273.15) *
 377       _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 378   } else {
 379     temperature_degc = -56.49;  // Stratosphere is constant
 380   }
 381 }
 382
 383 void
 384 FGEnvironment::_recalc_sl_dewpoint ()
 385 {
 386                                 // 0.2degC/1000ft
 387                                 // FIXME: this will work only for low
 388                                 // elevations
 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;
 392 }
 393
 394 void
 395 FGEnvironment::_recalc_alt_dewpoint ()
 396 {
 397                                 // 0.2degC/1000ft
 398                                 // FIXME: this will work only for low
 399                                 // elevations
 400   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 401   if (dewpoint_degc > temperature_degc)
 402     dewpoint_degc = temperature_degc;
 403 }
 404
 405 void
 406 FGEnvironment::_recalc_sl_pressure ()
 407 {
 408   pressure_sea_level_inhg =
 409     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 410 }
 411
 412 void
 413 FGEnvironment::_recalc_alt_pressure ()
 414 {
 415   pressure_inhg =
 416     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 417 }
 418
 419 void
 420 FGEnvironment::_recalc_density ()
 421 {
 422   double pressure_psf = pressure_inhg * 70.7487;
 423
 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;
 433
 434   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 435 }
 436
 437 // end of environment.cxx