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