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 \f
  45 ////////////////////////////////////////////////////////////////////////
  46 // Atmosphere model.
  47 ////////////////////////////////////////////////////////////////////////
  48
  49 // Copied from YASim Atmosphere.cxx, with m converted to ft, degK
  50 // converted to degC, Pa converted to inHG, and kg/m^3 converted to
  51 // slug/ft^3; they were then converted to deltas from the sea-level
  52 // defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).
  53
  54 // Original comment from YASim:
  55
  56 // Copied from McCormick, who got it from "The ARDC Model Atmosphere"
  57 // Note that there's an error in the text in the first entry,
  58 // McCormick lists 299.16/101325/1.22500, but those don't agree with
  59 // R=287.  I chose to correct the temperature to 288.20, since 79F is
  60 // pretty hot for a "standard" atmosphere.
  61
  62 // Elevation (ft), temperature factor (degK), pressure factor (inHG)
  63 static double atmosphere_data[][3] = {
  64  { 0.00, 1.00, 1.000 },
  65  { 2952.76, 0.98, 0.898 },
  66  { 5905.51, 0.96, 0.804 },
  67  { 8858.27, 0.94, 0.719 },
  68  { 11811.02, 0.92, 0.641 },
  69  { 14763.78, 0.90, 0.570 },
  70  { 17716.54, 0.88, 0.506 },
  71  { 20669.29, 0.86, 0.447 },
  72  { 23622.05, 0.84, 0.394 },
  73  { 26574.80, 0.82, 0.347 },
  74  { 29527.56, 0.80, 0.304 },
  75  { 32480.31, 0.78, 0.266 },
  76  { 35433.07, 0.76, 0.231 },
  77  { 38385.83, 0.75, 0.201 },
  78  { 41338.58, 0.75, 0.174 },
  79  { 44291.34, 0.75, 0.151 },
  80  { 47244.09, 0.75, 0.131 },
  81  { 50196.85, 0.75, 0.114 },
  82  { 53149.61, 0.75, 0.099 },
  83  { 56102.36, 0.75, 0.086 },
  84  { 59055.12, 0.75, 0.075 },
  85  { 62007.87, 0.75, 0.065 },
  86  { -1, -1, -1 }
  87 };
  88
  89 static SGInterpTable * _temperature_degc_table = 0;
  90 static SGInterpTable * _pressure_inhg_table = 0;
  91
  92 static void
  93 _setup_tables ()
  94 {
  95   if (_temperature_degc_table != 0)
  96       return;
  97
  98   _temperature_degc_table = new SGInterpTable;
  99   _pressure_inhg_table = new SGInterpTable;
 100
 101   for (int i = 0; atmosphere_data[i][0] != -1; i++) {
 102     _temperature_degc_table->addEntry(atmosphere_data[i][0],
 103                                       atmosphere_data[i][1]);
 104     _pressure_inhg_table->addEntry(atmosphere_data[i][0],
 105                                    atmosphere_data[i][2]);
 106   }
 107 }
 108
 109
 110 \f
 111 ////////////////////////////////////////////////////////////////////////
 112 // Implementation of FGEnvironment.
 113 ////////////////////////////////////////////////////////////////////////
 114
 115 FGEnvironment::FGEnvironment()
 116   : elevation_ft(0),
 117     visibility_m(32000),
 118     temperature_sea_level_degc(15),
 119     temperature_degc(15),
 120     dewpoint_sea_level_degc(5), // guess
 121     dewpoint_degc(5),
 122     pressure_sea_level_inhg(29.92),
 123     pressure_inhg(29.92),
 124     wind_from_heading_deg(0),
 125     wind_speed_kt(0),
 126     wind_from_north_fps(0),
 127     wind_from_east_fps(0),
 128     wind_from_down_fps(0),
 129     turbulence_norm(0)
 130 {
 131   _setup_tables();
 132   _recalc_density();
 133 }
 134
 135 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 136 {
 137     FGEnvironment();
 138     copy(env);
 139 }
 140
 141 FGEnvironment::~FGEnvironment()
 142 {
 143 }
 144
 145 void
 146 FGEnvironment::copy (const FGEnvironment &env)
 147 {
 148     elevation_ft = env.elevation_ft;
 149     visibility_m = env.visibility_m;
 150     temperature_sea_level_degc = env.temperature_sea_level_degc;
 151     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 152     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 153     wind_from_heading_deg = env.wind_from_heading_deg;
 154     wind_speed_kt = env.wind_speed_kt;
 155     wind_from_north_fps = env.wind_from_north_fps;
 156     wind_from_east_fps = env.wind_from_east_fps;
 157     wind_from_down_fps = env.wind_from_down_fps;
 158     turbulence_norm = env.turbulence_norm;
 159 }
 160
 161 static inline bool
 162 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 163                   const char * name, void (FGEnvironment::*setter)(double))
 164 {
 165     const SGPropertyNode * child = node->getChild(name);
 166                                 // fragile: depends on not being typed
 167                                 // as a number
 168     if (child != 0 && child->getStringValue()[0] != '\0') {
 169         (env->*setter)(child->getDoubleValue());
 170         return true;
 171     } else {
 172         return false;
 173     }
 174 }
 175
 176 void
 177 FGEnvironment::read (const SGPropertyNode * node)
 178 {
 179     maybe_copy_value(this, node, "visibility-m",
 180                      &FGEnvironment::set_visibility_m);
 181
 182     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 183                           &FGEnvironment::set_temperature_sea_level_degc))
 184         maybe_copy_value(this, node, "temperature-degc",
 185                          &FGEnvironment::set_temperature_degc);
 186
 187     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 188                           &FGEnvironment::set_dewpoint_sea_level_degc))
 189         maybe_copy_value(this, node, "dewpoint-degc",
 190                          &FGEnvironment::set_dewpoint_degc);
 191
 192     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 193                           &FGEnvironment::set_pressure_sea_level_inhg))
 194         maybe_copy_value(this, node, "pressure-inhg",
 195                          &FGEnvironment::set_pressure_inhg);
 196
 197     maybe_copy_value(this, node, "wind-from-heading-deg",
 198                      &FGEnvironment::set_wind_from_heading_deg);
 199
 200     maybe_copy_value(this, node, "wind-speed-kt",
 201                      &FGEnvironment::set_wind_speed_kt);
 202
 203     maybe_copy_value(this, node, "elevation-ft",
 204                      &FGEnvironment::set_elevation_ft);
 205
 206     maybe_copy_value(this, node, "turbulence-norm",
 207                      &FGEnvironment::set_turbulence_norm);
 208 }
 209
 210
 211 double
 212 FGEnvironment::get_visibility_m () const
 213 {
 214   return visibility_m;
 215 }
 216
 217 double
 218 FGEnvironment::get_temperature_sea_level_degc () const
 219 {
 220   return temperature_sea_level_degc;
 221 }
 222
 223 double
 224 FGEnvironment::get_temperature_degc () const
 225 {
 226   return temperature_degc;
 227 }
 228
 229 double
 230 FGEnvironment::get_dewpoint_sea_level_degc () const
 231 {
 232   return dewpoint_sea_level_degc;
 233 }
 234
 235 double
 236 FGEnvironment::get_dewpoint_degc () const
 237 {
 238   return dewpoint_degc;
 239 }
 240
 241 double
 242 FGEnvironment::get_pressure_sea_level_inhg () const
 243 {
 244   return pressure_sea_level_inhg;
 245 }
 246
 247 double
 248 FGEnvironment::get_pressure_inhg () const
 249 {
 250   return pressure_inhg;
 251 }
 252
 253 double
 254 FGEnvironment::get_density_slugft3 () const
 255 {
 256   return density_slugft3;
 257 }
 258
 259 double
 260 FGEnvironment::get_wind_from_heading_deg () const
 261 {
 262   return wind_from_heading_deg;
 263 }
 264
 265 double
 266 FGEnvironment::get_wind_speed_kt () const
 267 {
 268   return wind_speed_kt;
 269 }
 270
 271 double
 272 FGEnvironment::get_wind_from_north_fps () const
 273 {
 274   return wind_from_north_fps;
 275 }
 276
 277 double
 278 FGEnvironment::get_wind_from_east_fps () const
 279 {
 280   return wind_from_east_fps;
 281 }
 282
 283 double
 284 FGEnvironment::get_wind_from_down_fps () const
 285 {
 286   return wind_from_down_fps;
 287 }
 288
 289 double
 290 FGEnvironment::get_turbulence_norm () const
 291 {
 292   return turbulence_norm;
 293 }
 294
 295 double
 296 FGEnvironment::get_elevation_ft () const
 297 {
 298   return elevation_ft;
 299 }
 300
 301 void
 302 FGEnvironment::set_visibility_m (double v)
 303 {
 304   visibility_m = v;
 305 }
 306
 307 void
 308 FGEnvironment::set_temperature_sea_level_degc (double t)
 309 {
 310   temperature_sea_level_degc = t;
 311   if (dewpoint_sea_level_degc > t)
 312       dewpoint_sea_level_degc = t;
 313   _recalc_alt_temperature();
 314   _recalc_density();
 315 }
 316
 317 void
 318 FGEnvironment::set_temperature_degc (double t)
 319 {
 320   temperature_degc = t;
 321   _recalc_sl_temperature();
 322   _recalc_density();
 323 }
 324
 325 void
 326 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 327 {
 328   dewpoint_sea_level_degc = t;
 329   if (temperature_sea_level_degc < t)
 330       temperature_sea_level_degc = t;
 331   _recalc_alt_dewpoint();
 332   _recalc_density();
 333 }
 334
 335 void
 336 FGEnvironment::set_dewpoint_degc (double t)
 337 {
 338   dewpoint_degc = t;
 339   _recalc_sl_dewpoint();
 340   _recalc_density();
 341 }
 342
 343 void
 344 FGEnvironment::set_pressure_sea_level_inhg (double p)
 345 {
 346   pressure_sea_level_inhg = p;
 347   _recalc_alt_pressure();
 348   _recalc_density();
 349 }
 350
 351 void
 352 FGEnvironment::set_pressure_inhg (double p)
 353 {
 354   pressure_inhg = p;
 355   _recalc_sl_pressure();
 356   _recalc_density();
 357 }
 358
 359 void
 360 FGEnvironment::set_wind_from_heading_deg (double h)
 361 {
 362   wind_from_heading_deg = h;
 363   _recalc_ne();
 364 }
 365
 366 void
 367 FGEnvironment::set_wind_speed_kt (double s)
 368 {
 369   wind_speed_kt = s;
 370   _recalc_ne();
 371 }
 372
 373 void
 374 FGEnvironment::set_wind_from_north_fps (double n)
 375 {
 376   wind_from_north_fps = n;
 377   _recalc_hdgspd();
 378 }
 379
 380 void
 381 FGEnvironment::set_wind_from_east_fps (double e)
 382 {
 383   wind_from_east_fps = e;
 384   _recalc_hdgspd();
 385 }
 386
 387 void
 388 FGEnvironment::set_wind_from_down_fps (double d)
 389 {
 390   wind_from_down_fps = d;
 391   _recalc_hdgspd();
 392 }
 393
 394 void
 395 FGEnvironment::set_turbulence_norm (double t)
 396 {
 397   turbulence_norm = t;
 398 }
 399
 400 void
 401 FGEnvironment::set_elevation_ft (double e)
 402 {
 403   elevation_ft = e;
 404   _recalc_alt_temperature();
 405   _recalc_alt_dewpoint();
 406   _recalc_alt_pressure();
 407   _recalc_density();
 408 }
 409
 410 void
 411 FGEnvironment::_recalc_hdgspd ()
 412 {
 413   double angle_rad;
 414
 415   if (wind_from_east_fps == 0) {
 416     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
 417   } else {
 418     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 419   }
 420   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 421   if (wind_from_east_fps >= 0)
 422     wind_from_heading_deg = 90 - wind_from_heading_deg;
 423   else
 424     wind_from_heading_deg = 270 - wind_from_heading_deg;
 425   if (angle_rad == 0)
 426     wind_speed_kt = fabs(wind_from_east_fps
 427                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 428   else
 429     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 430       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 431 }
 432
 433 void
 434 FGEnvironment::_recalc_ne ()
 435 {
 436   double speed_fps =
 437     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 438
 439   wind_from_north_fps = speed_fps *
 440     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 441   wind_from_east_fps = speed_fps *
 442     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 443 }
 444
 445 void
 446 FGEnvironment::_recalc_sl_temperature ()
 447 {
 448   // If we're in the stratosphere, leave sea-level temp alone
 449   if (elevation_ft < 38000) {
 450     temperature_sea_level_degc =
 451       (temperature_degc + 273.15)
 452       /_temperature_degc_table->interpolate(elevation_ft)
 453       - 273.15;
 454   }
 455 }
 456
 457 void
 458 FGEnvironment::_recalc_alt_temperature ()
 459 {
 460   if (elevation_ft < 38000) {
 461     temperature_degc =
 462       (temperature_sea_level_degc + 273.15) *
 463       _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 464   } else {
 465     temperature_degc = -56.49;  // Stratosphere is constant
 466   }
 467 }
 468
 469 void
 470 FGEnvironment::_recalc_sl_dewpoint ()
 471 {
 472                                 // 0.2degC/1000ft
 473                                 // FIXME: this will work only for low
 474                                 // elevations
 475   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 476   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 477     dewpoint_sea_level_degc = temperature_sea_level_degc;
 478 }
 479
 480 void
 481 FGEnvironment::_recalc_alt_dewpoint ()
 482 {
 483                                 // 0.2degC/1000ft
 484                                 // FIXME: this will work only for low
 485                                 // elevations
 486   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 487   if (dewpoint_degc > temperature_degc)
 488     dewpoint_degc = temperature_degc;
 489 }
 490
 491 void
 492 FGEnvironment::_recalc_sl_pressure ()
 493 {
 494   pressure_sea_level_inhg =
 495     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 496 }
 497
 498 void
 499 FGEnvironment::_recalc_alt_pressure ()
 500 {
 501   pressure_inhg =
 502     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 503 }
 504
 505 void
 506 FGEnvironment::_recalc_density ()
 507 {
 508   double pressure_psf = pressure_inhg * 70.7487;
 509
 510   // adjust for humidity
 511   // calculations taken from USA Today (oops!) at
 512   // http://www.usatoday.com/weather/basics/density-calculations.htm
 513   double temperature_degk = temperature_degc + 273.15;
 514   double pressure_mb = pressure_inhg * 33.86;
 515   double vapor_pressure_mb =
 516     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 517   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 518   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 519
 520   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 521 }
 522
 523
 524 \f
 525 ////////////////////////////////////////////////////////////////////////
 526 // Functions.
 527 ////////////////////////////////////////////////////////////////////////
 528
 529 static inline double
 530 do_interp (double a, double b, double fraction)
 531 {
 532     double retval = (a + ((b - a) * fraction));
 533     return retval;
 534 }
 535
 536 static inline double
 537 do_interp_deg (double a, double b, double fraction)
 538 {
 539     a = fmod(a, 360);
 540     b = fmod(b, 360);
 541     if (fabs(b-a) > 180) {
 542         if (a < b)
 543             a += 360;
 544         else
 545             b += 360;
 546     }
 547     return fmod(do_interp(a, b, fraction), 360);
 548 }
 549
 550 void
 551 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 552              double fraction, FGEnvironment * result)
 553 {
 554     result->set_visibility_m
 555         (do_interp(env1->get_visibility_m(),
 556                    env2->get_visibility_m(),
 557                    fraction));
 558
 559     result->set_temperature_sea_level_degc
 560         (do_interp(env1->get_temperature_sea_level_degc(),
 561                    env2->get_temperature_sea_level_degc(),
 562                    fraction));
 563
 564     result->set_dewpoint_sea_level_degc
 565         (do_interp(env1->get_dewpoint_sea_level_degc(),
 566                    env2->get_dewpoint_sea_level_degc(),
 567                    fraction));
 568
 569     result->set_pressure_sea_level_inhg
 570         (do_interp(env1->get_pressure_sea_level_inhg(),
 571                    env2->get_pressure_sea_level_inhg(),
 572                    fraction));
 573
 574     result->set_wind_from_heading_deg
 575         (do_interp_deg(env1->get_wind_from_heading_deg(),
 576                        env2->get_wind_from_heading_deg(),
 577                        fraction));
 578
 579     result->set_wind_speed_kt
 580         (do_interp(env1->get_wind_speed_kt(),
 581                    env2->get_wind_speed_kt(),
 582                    fraction));
 583
 584     result->set_elevation_ft
 585         (do_interp(env1->get_elevation_ft(),
 586                    env2->get_elevation_ft(),
 587                    fraction));
 588
 589     result->set_turbulence_norm
 590         (do_interp(env1->get_turbulence_norm(),
 591                    env2->get_turbulence_norm(),
 592                    fraction));
 593 }
 594
 595 // end of environment.cxx