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     turbulence_magnitude_norm(0),
 125     turbulence_rate_hz(1),
 126     wind_from_heading_deg(0),
 127     wind_speed_kt(0),
 128     wind_from_north_fps(0),
 129     wind_from_east_fps(0),
 130     wind_from_down_fps(0)
 131 {
 132   _setup_tables();
 133   _recalc_density();
 134 }
 135
 136 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 137 {
 138     FGEnvironment();
 139     copy(env);
 140 }
 141
 142 FGEnvironment::~FGEnvironment()
 143 {
 144 }
 145
 146 void
 147 FGEnvironment::copy (const FGEnvironment &env)
 148 {
 149     elevation_ft = env.elevation_ft;
 150     visibility_m = env.visibility_m;
 151     temperature_sea_level_degc = env.temperature_sea_level_degc;
 152     temperature_degc = env.temperature_degc;
 153     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 154     dewpoint_degc = env.dewpoint_degc;
 155     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 156     wind_from_heading_deg = env.wind_from_heading_deg;
 157     wind_speed_kt = env.wind_speed_kt;
 158     wind_from_north_fps = env.wind_from_north_fps;
 159     wind_from_east_fps = env.wind_from_east_fps;
 160     wind_from_down_fps = env.wind_from_down_fps;
 161     turbulence_magnitude_norm = env.turbulence_magnitude_norm;
 162     turbulence_rate_hz = env.turbulence_rate_hz;
 163 }
 164
 165 static inline bool
 166 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 167                   const char * name, void (FGEnvironment::*setter)(double))
 168 {
 169     const SGPropertyNode * child = node->getNode(name);
 170                                 // fragile: depends on not being typed
 171                                 // as a number
 172     if (child != 0 && child->hasValue() &&
 173         child->getStringValue()[0] != '\0') {
 174         (env->*setter)(child->getDoubleValue());
 175         return true;
 176     } else {
 177         return false;
 178     }
 179 }
 180
 181 void
 182 FGEnvironment::read (const SGPropertyNode * node)
 183 {
 184     maybe_copy_value(this, node, "visibility-m",
 185                      &FGEnvironment::set_visibility_m);
 186
 187     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 188                           &FGEnvironment::set_temperature_sea_level_degc))
 189         maybe_copy_value(this, node, "temperature-degc",
 190                          &FGEnvironment::set_temperature_degc);
 191
 192     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 193                           &FGEnvironment::set_dewpoint_sea_level_degc))
 194         maybe_copy_value(this, node, "dewpoint-degc",
 195                          &FGEnvironment::set_dewpoint_degc);
 196
 197     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 198                           &FGEnvironment::set_pressure_sea_level_inhg))
 199         maybe_copy_value(this, node, "pressure-inhg",
 200                          &FGEnvironment::set_pressure_inhg);
 201
 202     maybe_copy_value(this, node, "wind-from-heading-deg",
 203                      &FGEnvironment::set_wind_from_heading_deg);
 204
 205     maybe_copy_value(this, node, "wind-speed-kt",
 206                      &FGEnvironment::set_wind_speed_kt);
 207
 208     maybe_copy_value(this, node, "elevation-ft",
 209                      &FGEnvironment::set_elevation_ft);
 210
 211     maybe_copy_value(this, node, "turbulence/magnitude-norm",
 212                      &FGEnvironment::set_turbulence_magnitude_norm);
 213
 214     maybe_copy_value(this, node, "turbulence/rate-hz",
 215                      &FGEnvironment::set_turbulence_rate_hz);
 216 }
 217
 218
 219 double
 220 FGEnvironment::get_visibility_m () const
 221 {
 222   return visibility_m;
 223 }
 224
 225 double
 226 FGEnvironment::get_temperature_sea_level_degc () const
 227 {
 228   return temperature_sea_level_degc;
 229 }
 230
 231 double
 232 FGEnvironment::get_temperature_degc () const
 233 {
 234   return temperature_degc;
 235 }
 236
 237 double
 238 FGEnvironment::get_dewpoint_sea_level_degc () const
 239 {
 240   return dewpoint_sea_level_degc;
 241 }
 242
 243 double
 244 FGEnvironment::get_dewpoint_degc () const
 245 {
 246   return dewpoint_degc;
 247 }
 248
 249 double
 250 FGEnvironment::get_pressure_sea_level_inhg () const
 251 {
 252   return pressure_sea_level_inhg;
 253 }
 254
 255 double
 256 FGEnvironment::get_pressure_inhg () const
 257 {
 258   return pressure_inhg;
 259 }
 260
 261 double
 262 FGEnvironment::get_density_slugft3 () const
 263 {
 264   return density_slugft3;
 265 }
 266
 267 double
 268 FGEnvironment::get_wind_from_heading_deg () const
 269 {
 270   return wind_from_heading_deg;
 271 }
 272
 273 double
 274 FGEnvironment::get_wind_speed_kt () const
 275 {
 276   return wind_speed_kt;
 277 }
 278
 279 double
 280 FGEnvironment::get_wind_from_north_fps () const
 281 {
 282   return wind_from_north_fps;
 283 }
 284
 285 double
 286 FGEnvironment::get_wind_from_east_fps () const
 287 {
 288   return wind_from_east_fps;
 289 }
 290
 291 double
 292 FGEnvironment::get_wind_from_down_fps () const
 293 {
 294   return wind_from_down_fps;
 295 }
 296
 297 double
 298 FGEnvironment::get_turbulence_magnitude_norm () const
 299 {
 300   return turbulence_magnitude_norm;
 301 }
 302
 303 double
 304 FGEnvironment::get_turbulence_rate_hz () const
 305 {
 306   return turbulence_rate_hz;
 307 }
 308
 309 double
 310 FGEnvironment::get_elevation_ft () const
 311 {
 312   return elevation_ft;
 313 }
 314
 315 void
 316 FGEnvironment::set_visibility_m (double v)
 317 {
 318   visibility_m = v;
 319 }
 320
 321 void
 322 FGEnvironment::set_temperature_sea_level_degc (double t)
 323 {
 324   temperature_sea_level_degc = t;
 325   if (dewpoint_sea_level_degc > t)
 326       dewpoint_sea_level_degc = t;
 327   _recalc_alt_temperature();
 328   _recalc_density();
 329 }
 330
 331 void
 332 FGEnvironment::set_temperature_degc (double t)
 333 {
 334   temperature_degc = t;
 335   _recalc_sl_temperature();
 336   _recalc_density();
 337 }
 338
 339 void
 340 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 341 {
 342   dewpoint_sea_level_degc = t;
 343   if (temperature_sea_level_degc < t)
 344       temperature_sea_level_degc = t;
 345   _recalc_alt_dewpoint();
 346   _recalc_density();
 347 }
 348
 349 void
 350 FGEnvironment::set_dewpoint_degc (double t)
 351 {
 352   dewpoint_degc = t;
 353   _recalc_sl_dewpoint();
 354   _recalc_density();
 355 }
 356
 357 void
 358 FGEnvironment::set_pressure_sea_level_inhg (double p)
 359 {
 360   pressure_sea_level_inhg = p;
 361   _recalc_alt_pressure();
 362   _recalc_density();
 363 }
 364
 365 void
 366 FGEnvironment::set_pressure_inhg (double p)
 367 {
 368   pressure_inhg = p;
 369   _recalc_sl_pressure();
 370   _recalc_density();
 371 }
 372
 373 void
 374 FGEnvironment::set_wind_from_heading_deg (double h)
 375 {
 376   wind_from_heading_deg = h;
 377   _recalc_ne();
 378 }
 379
 380 void
 381 FGEnvironment::set_wind_speed_kt (double s)
 382 {
 383   wind_speed_kt = s;
 384   _recalc_ne();
 385 }
 386
 387 void
 388 FGEnvironment::set_wind_from_north_fps (double n)
 389 {
 390   wind_from_north_fps = n;
 391   _recalc_hdgspd();
 392 }
 393
 394 void
 395 FGEnvironment::set_wind_from_east_fps (double e)
 396 {
 397   wind_from_east_fps = e;
 398   _recalc_hdgspd();
 399 }
 400
 401 void
 402 FGEnvironment::set_wind_from_down_fps (double d)
 403 {
 404   wind_from_down_fps = d;
 405   _recalc_hdgspd();
 406 }
 407
 408 void
 409 FGEnvironment::set_turbulence_magnitude_norm (double t)
 410 {
 411   turbulence_magnitude_norm = t;
 412 }
 413
 414 void
 415 FGEnvironment::set_turbulence_rate_hz (double r)
 416 {
 417   turbulence_rate_hz = r;
 418 }
 419
 420 void
 421 FGEnvironment::set_elevation_ft (double e)
 422 {
 423   elevation_ft = e;
 424   _recalc_alt_temperature();
 425   _recalc_alt_dewpoint();
 426   _recalc_alt_pressure();
 427   _recalc_density();
 428 }
 429
 430 void
 431 FGEnvironment::_recalc_hdgspd ()
 432 {
 433   double angle_rad;
 434
 435   if (wind_from_east_fps == 0) {
 436     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI/2 : -SGD_PI/2);
 437   } else {
 438     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 439   }
 440   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 441   if (wind_from_east_fps >= 0)
 442     wind_from_heading_deg = 90 - wind_from_heading_deg;
 443   else
 444     wind_from_heading_deg = 270 - wind_from_heading_deg;
 445
 446 #if 0
 447   // FIXME: Windspeed can become negative with these formulas.
 448   //        which can cause problems for animations that rely
 449   //        on the windspeed property.
 450   if (angle_rad == 0)
 451     wind_speed_kt = fabs(wind_from_east_fps
 452                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 453   else
 454     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 455       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 456 #else
 457   wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
 458                        wind_from_east_fps * wind_from_east_fps)
 459                   * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 460 #endif
 461 }
 462
 463 void
 464 FGEnvironment::_recalc_ne ()
 465 {
 466   double speed_fps =
 467     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 468
 469   wind_from_north_fps = speed_fps *
 470     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 471   wind_from_east_fps = speed_fps *
 472     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 473 }
 474
 475 void
 476 FGEnvironment::_recalc_sl_temperature ()
 477 {
 478   // If we're in the stratosphere, leave sea-level temp alone
 479   if (elevation_ft < 38000) {
 480     temperature_sea_level_degc =
 481       (temperature_degc + 273.15)
 482       /_temperature_degc_table->interpolate(elevation_ft)
 483       - 273.15;
 484   }
 485 }
 486
 487 void
 488 FGEnvironment::_recalc_alt_temperature ()
 489 {
 490   if (elevation_ft < 38000) {
 491     temperature_degc =
 492       (temperature_sea_level_degc + 273.15) *
 493       _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 494   } else {
 495     temperature_degc = -56.49;  // Stratosphere is constant
 496   }
 497 }
 498
 499 void
 500 FGEnvironment::_recalc_sl_dewpoint ()
 501 {
 502                                 // 0.2degC/1000ft
 503                                 // FIXME: this will work only for low
 504                                 // elevations
 505   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 506   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 507     dewpoint_sea_level_degc = temperature_sea_level_degc;
 508 }
 509
 510 void
 511 FGEnvironment::_recalc_alt_dewpoint ()
 512 {
 513                                 // 0.2degC/1000ft
 514                                 // FIXME: this will work only for low
 515                                 // elevations
 516   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 517   if (dewpoint_degc > temperature_degc)
 518     dewpoint_degc = temperature_degc;
 519 }
 520
 521 void
 522 FGEnvironment::_recalc_sl_pressure ()
 523 {
 524   pressure_sea_level_inhg =
 525     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 526 }
 527
 528 void
 529 FGEnvironment::_recalc_alt_pressure ()
 530 {
 531   pressure_inhg =
 532     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 533 }
 534
 535 void
 536 FGEnvironment::_recalc_density ()
 537 {
 538   double pressure_psf = pressure_inhg * 70.7487;
 539
 540   // adjust for humidity
 541   // calculations taken from USA Today (oops!) at
 542   // http://www.usatoday.com/weather/basics/density-calculations.htm
 543   double temperature_degk = temperature_degc + 273.15;
 544   double pressure_mb = pressure_inhg * 33.86;
 545   double vapor_pressure_mb =
 546     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 547   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 548   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 549
 550   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 551 }
 552
 553
 554 \f
 555 ////////////////////////////////////////////////////////////////////////
 556 // Functions.
 557 ////////////////////////////////////////////////////////////////////////
 558
 559 static inline double
 560 do_interp (double a, double b, double fraction)
 561 {
 562     double retval = (a + ((b - a) * fraction));
 563     return retval;
 564 }
 565
 566 static inline double
 567 do_interp_deg (double a, double b, double fraction)
 568 {
 569     a = fmod(a, 360);
 570     b = fmod(b, 360);
 571     if (fabs(b-a) > 180) {
 572         if (a < b)
 573             a += 360;
 574         else
 575             b += 360;
 576     }
 577     return fmod(do_interp(a, b, fraction), 360);
 578 }
 579
 580 void
 581 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 582              double fraction, FGEnvironment * result)
 583 {
 584     result->set_visibility_m
 585         (do_interp(env1->get_visibility_m(),
 586                    env2->get_visibility_m(),
 587                    fraction));
 588
 589     result->set_temperature_sea_level_degc
 590         (do_interp(env1->get_temperature_sea_level_degc(),
 591                    env2->get_temperature_sea_level_degc(),
 592                    fraction));
 593
 594     result->set_dewpoint_degc
 595         (do_interp(env1->get_dewpoint_sea_level_degc(),
 596                    env2->get_dewpoint_sea_level_degc(),
 597                    fraction));
 598
 599     result->set_pressure_sea_level_inhg
 600         (do_interp(env1->get_pressure_sea_level_inhg(),
 601                    env2->get_pressure_sea_level_inhg(),
 602                    fraction));
 603
 604     result->set_wind_from_heading_deg
 605         (do_interp_deg(env1->get_wind_from_heading_deg(),
 606                        env2->get_wind_from_heading_deg(),
 607                        fraction));
 608
 609     result->set_wind_speed_kt
 610         (do_interp(env1->get_wind_speed_kt(),
 611                    env2->get_wind_speed_kt(),
 612                    fraction));
 613
 614     result->set_elevation_ft
 615         (do_interp(env1->get_elevation_ft(),
 616                    env2->get_elevation_ft(),
 617                    fraction));
 618
 619     result->set_turbulence_magnitude_norm
 620         (do_interp(env1->get_turbulence_magnitude_norm(),
 621                    env2->get_turbulence_magnitude_norm(),
 622                    fraction));
 623
 624     result->set_turbulence_rate_hz
 625         (do_interp(env1->get_turbulence_rate_hz(),
 626                    env2->get_turbulence_rate_hz(),
 627                    fraction));
 628 }
 629
 630 // end of environment.cxx