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 #include <simgear/environment/visual_enviro.hxx>
  40
  41 #include <Main/fg_props.hxx>
  42 #include "environment.hxx"
  43
  44
  45 \f
  46 ////////////////////////////////////////////////////////////////////////
  47 // Atmosphere model.
  48 ////////////////////////////////////////////////////////////////////////
  49
  50 // Copied from YASim Atmosphere.cxx, with m converted to ft, degK
  51 // converted to degC, Pa converted to inHG, and kg/m^3 converted to
  52 // slug/ft^3; they were then converted to deltas from the sea-level
  53 // defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).
  54
  55 // Original comment from YASim:
  56
  57 // Copied from McCormick, who got it from "The ARDC Model Atmosphere"
  58 // Note that there's an error in the text in the first entry,
  59 // McCormick lists 299.16/101325/1.22500, but those don't agree with
  60 // R=287.  I chose to correct the temperature to 288.20, since 79F is
  61 // pretty hot for a "standard" atmosphere.
  62
  63 // Elevation (ft), temperature factor (degK), pressure factor (inHG)
  64 static double atmosphere_data[][3] = {
  65  { 0.00, 1.00, 1.000 },
  66  { 2952.76, 0.98, 0.898 },
  67  { 5905.51, 0.96, 0.804 },
  68  { 8858.27, 0.94, 0.719 },
  69  { 11811.02, 0.92, 0.641 },
  70  { 14763.78, 0.90, 0.570 },
  71  { 17716.54, 0.88, 0.506 },
  72  { 20669.29, 0.86, 0.447 },
  73  { 23622.05, 0.84, 0.394 },
  74  { 26574.80, 0.82, 0.347 },
  75  { 29527.56, 0.80, 0.304 },
  76  { 32480.31, 0.78, 0.266 },
  77  { 35433.07, 0.76, 0.231 },
  78  { 38385.83, 0.75, 0.201 },
  79  { 41338.58, 0.75, 0.174 },
  80  { 44291.34, 0.75, 0.151 },
  81  { 47244.09, 0.75, 0.131 },
  82  { 50196.85, 0.75, 0.114 },
  83  { 53149.61, 0.75, 0.099 },
  84  { 56102.36, 0.75, 0.086 },
  85  { 59055.12, 0.75, 0.075 },
  86  { 62007.87, 0.75, 0.065 },
  87  { -1, -1, -1 }
  88 };
  89
  90 static SGInterpTable * _temperature_degc_table = 0;
  91 static SGInterpTable * _pressure_inhg_table = 0;
  92
  93 static void
  94 _setup_tables ()
  95 {
  96   if (_temperature_degc_table != 0)
  97       return;
  98
  99   _temperature_degc_table = new SGInterpTable;
 100   _pressure_inhg_table = new SGInterpTable;
 101
 102   for (int i = 0; atmosphere_data[i][0] != -1; i++) {
 103     _temperature_degc_table->addEntry(atmosphere_data[i][0],
 104                                       atmosphere_data[i][1]);
 105     _pressure_inhg_table->addEntry(atmosphere_data[i][0],
 106                                    atmosphere_data[i][2]);
 107   }
 108 }
 109
 110
 111 \f
 112 ////////////////////////////////////////////////////////////////////////
 113 // Implementation of FGEnvironment.
 114 ////////////////////////////////////////////////////////////////////////
 115
 116 FGEnvironment::FGEnvironment()
 117   : elevation_ft(0),
 118     visibility_m(32000),
 119     temperature_sea_level_degc(15),
 120     temperature_degc(15),
 121     dewpoint_sea_level_degc(5), // guess
 122     dewpoint_degc(5),
 123     pressure_sea_level_inhg(29.92),
 124     pressure_inhg(29.92),
 125     turbulence_magnitude_norm(0),
 126     turbulence_rate_hz(1),
 127     wind_from_heading_deg(0),
 128     wind_speed_kt(0),
 129     wind_from_north_fps(0),
 130     wind_from_east_fps(0),
 131     wind_from_down_fps(0)
 132 {
 133   _setup_tables();
 134   _recalc_density();
 135 }
 136
 137 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 138 {
 139     FGEnvironment();
 140     copy(env);
 141 }
 142
 143 FGEnvironment::~FGEnvironment()
 144 {
 145 }
 146
 147 void
 148 FGEnvironment::copy (const FGEnvironment &env)
 149 {
 150     elevation_ft = env.elevation_ft;
 151     visibility_m = env.visibility_m;
 152     temperature_sea_level_degc = env.temperature_sea_level_degc;
 153     temperature_degc = env.temperature_degc;
 154     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 155     dewpoint_degc = env.dewpoint_degc;
 156     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 157     wind_from_heading_deg = env.wind_from_heading_deg;
 158     wind_speed_kt = env.wind_speed_kt;
 159     wind_from_north_fps = env.wind_from_north_fps;
 160     wind_from_east_fps = env.wind_from_east_fps;
 161     wind_from_down_fps = env.wind_from_down_fps;
 162     turbulence_magnitude_norm = env.turbulence_magnitude_norm;
 163     turbulence_rate_hz = env.turbulence_rate_hz;
 164 }
 165
 166 static inline bool
 167 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 168                   const char * name, void (FGEnvironment::*setter)(double))
 169 {
 170     const SGPropertyNode * child = node->getNode(name);
 171                                 // fragile: depends on not being typed
 172                                 // as a number
 173     if (child != 0 && child->hasValue() &&
 174         child->getStringValue()[0] != '\0') {
 175         (env->*setter)(child->getDoubleValue());
 176         return true;
 177     } else {
 178         return false;
 179     }
 180 }
 181
 182 void
 183 FGEnvironment::read (const SGPropertyNode * node)
 184 {
 185     maybe_copy_value(this, node, "visibility-m",
 186                      &FGEnvironment::set_visibility_m);
 187
 188     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 189                           &FGEnvironment::set_temperature_sea_level_degc))
 190         maybe_copy_value(this, node, "temperature-degc",
 191                          &FGEnvironment::set_temperature_degc);
 192
 193     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 194                           &FGEnvironment::set_dewpoint_sea_level_degc))
 195         maybe_copy_value(this, node, "dewpoint-degc",
 196                          &FGEnvironment::set_dewpoint_degc);
 197
 198     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 199                           &FGEnvironment::set_pressure_sea_level_inhg))
 200         maybe_copy_value(this, node, "pressure-inhg",
 201                          &FGEnvironment::set_pressure_inhg);
 202
 203     maybe_copy_value(this, node, "wind-from-heading-deg",
 204                      &FGEnvironment::set_wind_from_heading_deg);
 205
 206     maybe_copy_value(this, node, "wind-speed-kt",
 207                      &FGEnvironment::set_wind_speed_kt);
 208
 209     maybe_copy_value(this, node, "elevation-ft",
 210                      &FGEnvironment::set_elevation_ft);
 211
 212     maybe_copy_value(this, node, "turbulence/magnitude-norm",
 213                      &FGEnvironment::set_turbulence_magnitude_norm);
 214
 215     maybe_copy_value(this, node, "turbulence/rate-hz",
 216                      &FGEnvironment::set_turbulence_rate_hz);
 217 }
 218
 219
 220 double
 221 FGEnvironment::get_visibility_m () const
 222 {
 223   return visibility_m;
 224 }
 225
 226 double
 227 FGEnvironment::get_temperature_sea_level_degc () const
 228 {
 229   return temperature_sea_level_degc;
 230 }
 231
 232 double
 233 FGEnvironment::get_temperature_degc () const
 234 {
 235   return temperature_degc;
 236 }
 237
 238 double
 239 FGEnvironment::get_dewpoint_sea_level_degc () const
 240 {
 241   return dewpoint_sea_level_degc;
 242 }
 243
 244 double
 245 FGEnvironment::get_dewpoint_degc () const
 246 {
 247   return dewpoint_degc;
 248 }
 249
 250 double
 251 FGEnvironment::get_pressure_sea_level_inhg () const
 252 {
 253   return pressure_sea_level_inhg;
 254 }
 255
 256 double
 257 FGEnvironment::get_pressure_inhg () const
 258 {
 259   return pressure_inhg;
 260 }
 261
 262 double
 263 FGEnvironment::get_density_slugft3 () const
 264 {
 265   return density_slugft3;
 266 }
 267
 268 double
 269 FGEnvironment::get_wind_from_heading_deg () const
 270 {
 271   return wind_from_heading_deg;
 272 }
 273
 274 double
 275 FGEnvironment::get_wind_speed_kt () const
 276 {
 277   return wind_speed_kt;
 278 }
 279
 280 double
 281 FGEnvironment::get_wind_from_north_fps () const
 282 {
 283   return wind_from_north_fps;
 284 }
 285
 286 double
 287 FGEnvironment::get_wind_from_east_fps () const
 288 {
 289   return wind_from_east_fps;
 290 }
 291
 292 double
 293 FGEnvironment::get_wind_from_down_fps () const
 294 {
 295   return wind_from_down_fps;
 296 }
 297
 298 double
 299 FGEnvironment::get_turbulence_magnitude_norm () const
 300 {
 301   if( sgEnviro.get_turbulence_enable_state() )
 302     if (fgGetBool("/environment/params/real-world-weather-fetch") == true)
 303       return sgEnviro.get_cloud_turbulence();
 304   return turbulence_magnitude_norm;
 305 }
 306
 307 double
 308 FGEnvironment::get_turbulence_rate_hz () const
 309 {
 310   return turbulence_rate_hz;
 311 }
 312
 313 double
 314 FGEnvironment::get_elevation_ft () const
 315 {
 316   return elevation_ft;
 317 }
 318
 319 void
 320 FGEnvironment::set_visibility_m (double v)
 321 {
 322   visibility_m = v;
 323 }
 324
 325 void
 326 FGEnvironment::set_temperature_sea_level_degc (double t)
 327 {
 328   temperature_sea_level_degc = t;
 329   if (dewpoint_sea_level_degc > t)
 330       dewpoint_sea_level_degc = t;
 331   _recalc_alt_temperature();
 332   _recalc_density();
 333 }
 334
 335 void
 336 FGEnvironment::set_temperature_degc (double t)
 337 {
 338   temperature_degc = t;
 339   _recalc_sl_temperature();
 340   _recalc_density();
 341 }
 342
 343 void
 344 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 345 {
 346   dewpoint_sea_level_degc = t;
 347   if (temperature_sea_level_degc < t)
 348       temperature_sea_level_degc = t;
 349   _recalc_alt_dewpoint();
 350   _recalc_density();
 351 }
 352
 353 void
 354 FGEnvironment::set_dewpoint_degc (double t)
 355 {
 356   dewpoint_degc = t;
 357   _recalc_sl_dewpoint();
 358   _recalc_density();
 359 }
 360
 361 void
 362 FGEnvironment::set_pressure_sea_level_inhg (double p)
 363 {
 364   pressure_sea_level_inhg = p;
 365   _recalc_alt_pressure();
 366   _recalc_density();
 367 }
 368
 369 void
 370 FGEnvironment::set_pressure_inhg (double p)
 371 {
 372   pressure_inhg = p;
 373   _recalc_sl_pressure();
 374   _recalc_density();
 375 }
 376
 377 void
 378 FGEnvironment::set_wind_from_heading_deg (double h)
 379 {
 380   wind_from_heading_deg = h;
 381   _recalc_ne();
 382 }
 383
 384 void
 385 FGEnvironment::set_wind_speed_kt (double s)
 386 {
 387   wind_speed_kt = s;
 388   _recalc_ne();
 389 }
 390
 391 void
 392 FGEnvironment::set_wind_from_north_fps (double n)
 393 {
 394   wind_from_north_fps = n;
 395   _recalc_hdgspd();
 396 }
 397
 398 void
 399 FGEnvironment::set_wind_from_east_fps (double e)
 400 {
 401   wind_from_east_fps = e;
 402   _recalc_hdgspd();
 403 }
 404
 405 void
 406 FGEnvironment::set_wind_from_down_fps (double d)
 407 {
 408   wind_from_down_fps = d;
 409   _recalc_hdgspd();
 410 }
 411
 412 void
 413 FGEnvironment::set_turbulence_magnitude_norm (double t)
 414 {
 415   turbulence_magnitude_norm = t;
 416 }
 417
 418 void
 419 FGEnvironment::set_turbulence_rate_hz (double r)
 420 {
 421   turbulence_rate_hz = r;
 422 }
 423
 424 void
 425 FGEnvironment::set_elevation_ft (double e)
 426 {
 427   elevation_ft = e;
 428   _recalc_alt_temperature();
 429   _recalc_alt_dewpoint();
 430   _recalc_alt_pressure();
 431   _recalc_density();
 432 }
 433
 434 void
 435 FGEnvironment::_recalc_hdgspd ()
 436 {
 437   double angle_rad;
 438
 439   if (wind_from_east_fps == 0) {
 440     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
 441   } else {
 442     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 443   }
 444   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 445   if (wind_from_east_fps >= 0)
 446     wind_from_heading_deg = 90 - wind_from_heading_deg;
 447   else
 448     wind_from_heading_deg = 270 - wind_from_heading_deg;
 449
 450 #if 0
 451   // FIXME: Windspeed can become negative with these formulas.
 452   //        which can cause problems for animations that rely
 453   //        on the windspeed property.
 454   if (angle_rad == 0)
 455     wind_speed_kt = fabs(wind_from_east_fps
 456                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 457   else
 458     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 459       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 460 #else
 461   wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
 462                        wind_from_east_fps * wind_from_east_fps)
 463                   * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 464 #endif
 465 }
 466
 467 void
 468 FGEnvironment::_recalc_ne ()
 469 {
 470   double speed_fps =
 471     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 472
 473   wind_from_north_fps = speed_fps *
 474     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 475   wind_from_east_fps = speed_fps *
 476     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 477 }
 478
 479 void
 480 FGEnvironment::_recalc_sl_temperature ()
 481 {
 482   // If we're in the stratosphere, leave sea-level temp alone
 483   if (elevation_ft < 38000) {
 484     temperature_sea_level_degc =
 485       (temperature_degc + 273.15)
 486       /_temperature_degc_table->interpolate(elevation_ft)
 487       - 273.15;
 488   }
 489 }
 490
 491 void
 492 FGEnvironment::_recalc_alt_temperature ()
 493 {
 494   if (elevation_ft < 38000) {
 495     temperature_degc =
 496       (temperature_sea_level_degc + 273.15) *
 497       _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 498   } else {
 499     temperature_degc = -56.49;  // Stratosphere is constant
 500   }
 501 }
 502
 503 void
 504 FGEnvironment::_recalc_sl_dewpoint ()
 505 {
 506                                 // 0.2degC/1000ft
 507                                 // FIXME: this will work only for low
 508                                 // elevations
 509   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 510   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 511     dewpoint_sea_level_degc = temperature_sea_level_degc;
 512 }
 513
 514 void
 515 FGEnvironment::_recalc_alt_dewpoint ()
 516 {
 517                                 // 0.2degC/1000ft
 518                                 // FIXME: this will work only for low
 519                                 // elevations
 520   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 521   if (dewpoint_degc > temperature_degc)
 522     dewpoint_degc = temperature_degc;
 523 }
 524
 525 void
 526 FGEnvironment::_recalc_sl_pressure ()
 527 {
 528   pressure_sea_level_inhg =
 529     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 530 }
 531
 532 void
 533 FGEnvironment::_recalc_alt_pressure ()
 534 {
 535   pressure_inhg =
 536     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 537 }
 538
 539 void
 540 FGEnvironment::_recalc_density ()
 541 {
 542   double pressure_psf = pressure_inhg * 70.7487;
 543
 544   // adjust for humidity
 545   // calculations taken from USA Today (oops!) at
 546   // http://www.usatoday.com/weather/basics/density-calculations.htm
 547   double temperature_degk = temperature_degc + 273.15;
 548   double pressure_mb = pressure_inhg * 33.86;
 549   double vapor_pressure_mb =
 550     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 551   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 552   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 553
 554   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 555 }
 556
 557
 558 \f
 559 ////////////////////////////////////////////////////////////////////////
 560 // Functions.
 561 ////////////////////////////////////////////////////////////////////////
 562
 563 static inline double
 564 do_interp (double a, double b, double fraction)
 565 {
 566     double retval = (a + ((b - a) * fraction));
 567     return retval;
 568 }
 569
 570 static inline double
 571 do_interp_deg (double a, double b, double fraction)
 572 {
 573     a = fmod(a, 360);
 574     b = fmod(b, 360);
 575     if (fabs(b-a) > 180) {
 576         if (a < b)
 577             a += 360;
 578         else
 579             b += 360;
 580     }
 581     return fmod(do_interp(a, b, fraction), 360);
 582 }
 583
 584 void
 585 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 586              double fraction, FGEnvironment * result)
 587 {
 588     result->set_visibility_m
 589         (do_interp(env1->get_visibility_m(),
 590                    env2->get_visibility_m(),
 591                    fraction));
 592
 593     result->set_temperature_sea_level_degc
 594         (do_interp(env1->get_temperature_sea_level_degc(),
 595                    env2->get_temperature_sea_level_degc(),
 596                    fraction));
 597
 598     result->set_dewpoint_degc
 599         (do_interp(env1->get_dewpoint_sea_level_degc(),
 600                    env2->get_dewpoint_sea_level_degc(),
 601                    fraction));
 602
 603     result->set_pressure_sea_level_inhg
 604         (do_interp(env1->get_pressure_sea_level_inhg(),
 605                    env2->get_pressure_sea_level_inhg(),
 606                    fraction));
 607
 608     result->set_wind_from_heading_deg
 609         (do_interp_deg(env1->get_wind_from_heading_deg(),
 610                        env2->get_wind_from_heading_deg(),
 611                        fraction));
 612
 613     result->set_wind_speed_kt
 614         (do_interp(env1->get_wind_speed_kt(),
 615                    env2->get_wind_speed_kt(),
 616                    fraction));
 617
 618     result->set_elevation_ft
 619         (do_interp(env1->get_elevation_ft(),
 620                    env2->get_elevation_ft(),
 621                    fraction));
 622
 623     result->set_turbulence_magnitude_norm
 624         (do_interp(env1->get_turbulence_magnitude_norm(),
 625                    env2->get_turbulence_magnitude_norm(),
 626                    fraction));
 627
 628     result->set_turbulence_rate_hz
 629         (do_interp(env1->get_turbulence_rate_hz(),
 630                    env2->get_turbulence_rate_hz(),
 631                    fraction));
 632 }
 633
 634 // end of environment.cxx