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