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