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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  20 //
  21 // $Id$
  22
  23
  24 #ifdef HAVE_CONFIG_H
  25 #  include <config.h>
  26 #endif
  27
  28 #include <math.h>
  29
  30 #include <plib/sg.h>
  31
  32 #include <simgear/constants.h>
  33 #include <simgear/debug/logstream.hxx>
  34 #include <simgear/math/interpolater.hxx>
  35 #include <simgear/props/props.hxx>
  36 #include <simgear/environment/visual_enviro.hxx>
  37
  38 #include <Main/fg_props.hxx>
  39
  40 #include "environment.hxx"
  41
  42
  43 \f
  44 ////////////////////////////////////////////////////////////////////////
  45 // Atmosphere model.
  46 ////////////////////////////////////////////////////////////////////////
  47
  48 // Calculated based on the ISA standard day, as found at e.g.
  49 // http://www.av8n.com/physics/altimetry.htm
  50
  51 // Each line of data has 3 elements:
  52 //   Elevation (ft),
  53 //   temperature factor (dimensionless ratio of absolute temp),
  54 //   pressure factor (dimensionless ratio)
  55 static double atmosphere_data[][3] = {
  56  {  -3000.00,   1.021,  1.1133 },
  57  {      0.00,   1.000,  1.0000 },
  58  {   2952.76,   0.980,  0.8978 },
  59  {   5905.51,   0.959,  0.8042 },
  60  {   8858.27,   0.939,  0.7187 },
  61  {  11811.02,   0.919,  0.6407 },
  62  {  14763.78,   0.898,  0.5697 },
  63  {  17716.54,   0.878,  0.5052 },
  64  {  20669.29,   0.858,  0.4468 },
  65  {  23622.05,   0.838,  0.3940 },
  66  {  26574.80,   0.817,  0.3463 },
  67  {  29527.56,   0.797,  0.3034 },
  68  {  32480.31,   0.777,  0.2649 },
  69  {  35433.07,   0.756,  0.2305 },
  70  {  38385.83,   0.752,  0.2000 },
  71  {  41338.58,   0.752,  0.1736 },
  72  {  44291.34,   0.752,  0.1506 },
  73  {  47244.09,   0.752,  0.1307 },
  74  {  50196.85,   0.752,  0.1134 },
  75  {  53149.61,   0.752,  0.0984 },
  76  {  56102.36,   0.752,  0.0854 },
  77  {  59055.12,   0.752,  0.0741 },
  78  {  62007.87,   0.752,  0.0643 },
  79  {  65000.00,   0.752,  0.0557 },
  80  {  68000.00,   0.754,  0.0482 },
  81  {  71000.00,   0.758,  0.0418 },
  82  {  74000.00,   0.761,  0.0362 },
  83  {  77000.00,   0.764,  0.0314 },
  84  {  80000.00,   0.767,  0.0273 },
  85  {  83000.00,   0.770,  0.0237 },
  86  {  86000.00,   0.773,  0.0206 },
  87  {  89000.00,   0.777,  0.0179 },
  88  {  92000.00,   0.780,  0.0156 },
  89  {  95000.00,   0.783,  0.0135 },
  90  {  98000.00,   0.786,  0.0118 },
  91  { 101000.00,   0.789,  0.0103 },
  92  { -1, -1, -1 }
  93 };
  94
  95 static SGInterpTable * _temperature_degc_table = 0;
  96 static SGInterpTable * _pressure_inhg_table = 0;
  97
  98 static void
  99 _setup_tables ()
 100 {
 101   if (_temperature_degc_table != 0)
 102       return;
 103
 104   _temperature_degc_table = new SGInterpTable;
 105   _pressure_inhg_table = new SGInterpTable;
 106
 107   for (int i = 0; atmosphere_data[i][0] != -1; i++) {
 108     _temperature_degc_table->addEntry(atmosphere_data[i][0],
 109                                       atmosphere_data[i][1]);
 110     _pressure_inhg_table->addEntry(atmosphere_data[i][0],
 111                                    atmosphere_data[i][2]);
 112   }
 113 }
 114
 115
 116 \f
 117 ////////////////////////////////////////////////////////////////////////
 118 // Implementation of FGEnvironment.
 119 ////////////////////////////////////////////////////////////////////////
 120
 121 FGEnvironment::FGEnvironment()
 122   : elevation_ft(0),
 123     visibility_m(32000),
 124     temperature_sea_level_degc(15),
 125     temperature_degc(15),
 126     dewpoint_sea_level_degc(5), // guess
 127     dewpoint_degc(5),
 128     pressure_sea_level_inhg(29.92),
 129     pressure_inhg(29.92),
 130     turbulence_magnitude_norm(0),
 131     turbulence_rate_hz(1),
 132     wind_from_heading_deg(0),
 133     wind_speed_kt(0),
 134     wind_from_north_fps(0),
 135     wind_from_east_fps(0),
 136     wind_from_down_fps(0),
 137     altitude_half_to_sun_m(1000),
 138     altitude_tropo_top_m(10000)
 139 {
 140   _setup_tables();
 141   _recalc_density();
 142   _recalc_relative_humidity();
 143 }
 144
 145 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 146 {
 147     FGEnvironment();
 148     copy(env);
 149 }
 150
 151 FGEnvironment::~FGEnvironment()
 152 {
 153 }
 154
 155 void
 156 FGEnvironment::copy (const FGEnvironment &env)
 157 {
 158     elevation_ft = env.elevation_ft;
 159     visibility_m = env.visibility_m;
 160     temperature_sea_level_degc = env.temperature_sea_level_degc;
 161     temperature_degc = env.temperature_degc;
 162     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 163     dewpoint_degc = env.dewpoint_degc;
 164     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 165     wind_from_heading_deg = env.wind_from_heading_deg;
 166     wind_speed_kt = env.wind_speed_kt;
 167     wind_from_north_fps = env.wind_from_north_fps;
 168     wind_from_east_fps = env.wind_from_east_fps;
 169     wind_from_down_fps = env.wind_from_down_fps;
 170     turbulence_magnitude_norm = env.turbulence_magnitude_norm;
 171     turbulence_rate_hz = env.turbulence_rate_hz;
 172 }
 173
 174 static inline bool
 175 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 176                   const char * name, void (FGEnvironment::*setter)(double))
 177 {
 178     const SGPropertyNode * child = node->getNode(name);
 179                                 // fragile: depends on not being typed
 180                                 // as a number
 181     if (child != 0 && child->hasValue() &&
 182         child->getStringValue()[0] != '\0') {
 183         (env->*setter)(child->getDoubleValue());
 184         return true;
 185     } else {
 186         return false;
 187     }
 188 }
 189
 190 void
 191 FGEnvironment::read (const SGPropertyNode * node)
 192 {
 193     maybe_copy_value(this, node, "visibility-m",
 194                      &FGEnvironment::set_visibility_m);
 195
 196     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 197                           &FGEnvironment::set_temperature_sea_level_degc))
 198         maybe_copy_value(this, node, "temperature-degc",
 199                          &FGEnvironment::set_temperature_degc);
 200
 201     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 202                           &FGEnvironment::set_dewpoint_sea_level_degc))
 203         maybe_copy_value(this, node, "dewpoint-degc",
 204                          &FGEnvironment::set_dewpoint_degc);
 205
 206     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 207                           &FGEnvironment::set_pressure_sea_level_inhg))
 208         maybe_copy_value(this, node, "pressure-inhg",
 209                          &FGEnvironment::set_pressure_inhg);
 210
 211     maybe_copy_value(this, node, "wind-from-heading-deg",
 212                      &FGEnvironment::set_wind_from_heading_deg);
 213
 214     maybe_copy_value(this, node, "wind-speed-kt",
 215                      &FGEnvironment::set_wind_speed_kt);
 216
 217     maybe_copy_value(this, node, "elevation-ft",
 218                      &FGEnvironment::set_elevation_ft);
 219
 220     maybe_copy_value(this, node, "turbulence/magnitude-norm",
 221                      &FGEnvironment::set_turbulence_magnitude_norm);
 222
 223     maybe_copy_value(this, node, "turbulence/rate-hz",
 224                      &FGEnvironment::set_turbulence_rate_hz);
 225 }
 226
 227
 228 double
 229 FGEnvironment::get_visibility_m () const
 230 {
 231   return visibility_m;
 232 }
 233
 234 double
 235 FGEnvironment::get_temperature_sea_level_degc () const
 236 {
 237   return temperature_sea_level_degc;
 238 }
 239
 240 double
 241 FGEnvironment::get_temperature_degc () const
 242 {
 243   return temperature_degc;
 244 }
 245
 246 double
 247 FGEnvironment::get_temperature_degf () const
 248 {
 249   return (temperature_degc * 9.0 / 5.0) + 32.0;
 250 }
 251
 252 double
 253 FGEnvironment::get_dewpoint_sea_level_degc () const
 254 {
 255   return dewpoint_sea_level_degc;
 256 }
 257
 258 double
 259 FGEnvironment::get_dewpoint_degc () const
 260 {
 261   return dewpoint_degc;
 262 }
 263
 264 double
 265 FGEnvironment::get_pressure_sea_level_inhg () const
 266 {
 267   return pressure_sea_level_inhg;
 268 }
 269
 270 double
 271 FGEnvironment::get_pressure_inhg () const
 272 {
 273   return pressure_inhg;
 274 }
 275
 276 double
 277 FGEnvironment::get_density_slugft3 () const
 278 {
 279   return density_slugft3;
 280 }
 281
 282 double
 283 FGEnvironment::get_relative_humidity () const
 284 {
 285   return relative_humidity;
 286 }
 287
 288 double
 289 FGEnvironment::get_density_tropo_avg_kgm3 () const
 290 {
 291   return density_tropo_avg_kgm3;
 292 }
 293
 294 double
 295 FGEnvironment::get_altitude_half_to_sun_m () const
 296 {
 297   return altitude_half_to_sun_m;
 298 }
 299
 300 double
 301 FGEnvironment::get_altitude_tropo_top_m () const
 302 {
 303   return altitude_tropo_top_m;
 304 }
 305
 306 double
 307 FGEnvironment::get_wind_from_heading_deg () const
 308 {
 309   return wind_from_heading_deg;
 310 }
 311
 312 double
 313 FGEnvironment::get_wind_speed_kt () const
 314 {
 315   return wind_speed_kt;
 316 }
 317
 318 double
 319 FGEnvironment::get_wind_from_north_fps () const
 320 {
 321   return wind_from_north_fps;
 322 }
 323
 324 double
 325 FGEnvironment::get_wind_from_east_fps () const
 326 {
 327   return wind_from_east_fps;
 328 }
 329
 330 double
 331 FGEnvironment::get_wind_from_down_fps () const
 332 {
 333   return wind_from_down_fps;
 334 }
 335
 336 double
 337 FGEnvironment::get_turbulence_magnitude_norm () const
 338 {
 339   if( sgEnviro.get_turbulence_enable_state() )
 340     if (fgGetBool("/environment/params/real-world-weather-fetch") == true)
 341       return sgEnviro.get_cloud_turbulence();
 342   return turbulence_magnitude_norm;
 343 }
 344
 345 double
 346 FGEnvironment::get_turbulence_rate_hz () const
 347 {
 348   return turbulence_rate_hz;
 349 }
 350
 351 double
 352 FGEnvironment::get_elevation_ft () const
 353 {
 354   return elevation_ft;
 355 }
 356
 357 void
 358 FGEnvironment::set_visibility_m (double v)
 359 {
 360   visibility_m = v;
 361 }
 362
 363 void
 364 FGEnvironment::set_temperature_sea_level_degc (double t)
 365 {
 366   temperature_sea_level_degc = t;
 367   if (dewpoint_sea_level_degc > t)
 368       dewpoint_sea_level_degc = t;
 369   _recalc_alt_temperature();
 370   _recalc_density();
 371 }
 372
 373 void
 374 FGEnvironment::set_temperature_degc (double t)
 375 {
 376   temperature_degc = t;
 377   _recalc_sl_temperature();
 378   _recalc_density();
 379   _recalc_relative_humidity();
 380 }
 381
 382 void
 383 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 384 {
 385   dewpoint_sea_level_degc = t;
 386   if (temperature_sea_level_degc < t)
 387       temperature_sea_level_degc = t;
 388   _recalc_alt_dewpoint();
 389   _recalc_density();
 390 }
 391
 392 void
 393 FGEnvironment::set_dewpoint_degc (double t)
 394 {
 395   dewpoint_degc = t;
 396   _recalc_sl_dewpoint();
 397   _recalc_density();
 398   _recalc_relative_humidity();
 399 }
 400
 401 void
 402 FGEnvironment::set_pressure_sea_level_inhg (double p)
 403 {
 404   pressure_sea_level_inhg = p;
 405   _recalc_alt_pressure();
 406   _recalc_density();
 407 }
 408
 409 void
 410 FGEnvironment::set_pressure_inhg (double p)
 411 {
 412   pressure_inhg = p;
 413   _recalc_sl_pressure();
 414   _recalc_density();
 415 }
 416
 417 void
 418 FGEnvironment::set_wind_from_heading_deg (double h)
 419 {
 420   wind_from_heading_deg = h;
 421   _recalc_ne();
 422 }
 423
 424 void
 425 FGEnvironment::set_wind_speed_kt (double s)
 426 {
 427   wind_speed_kt = s;
 428   _recalc_ne();
 429 }
 430
 431 void
 432 FGEnvironment::set_wind_from_north_fps (double n)
 433 {
 434   wind_from_north_fps = n;
 435   _recalc_hdgspd();
 436 }
 437
 438 void
 439 FGEnvironment::set_wind_from_east_fps (double e)
 440 {
 441   wind_from_east_fps = e;
 442   _recalc_hdgspd();
 443 }
 444
 445 void
 446 FGEnvironment::set_wind_from_down_fps (double d)
 447 {
 448   wind_from_down_fps = d;
 449   _recalc_hdgspd();
 450 }
 451
 452 void
 453 FGEnvironment::set_turbulence_magnitude_norm (double t)
 454 {
 455   turbulence_magnitude_norm = t;
 456 }
 457
 458 void
 459 FGEnvironment::set_turbulence_rate_hz (double r)
 460 {
 461   turbulence_rate_hz = r;
 462 }
 463
 464 void
 465 FGEnvironment::set_elevation_ft (double e)
 466 {
 467   elevation_ft = e;
 468   _recalc_alt_temperature();
 469   _recalc_alt_dewpoint();
 470   _recalc_alt_pressure();
 471   _recalc_density();
 472   _recalc_relative_humidity();
 473 }
 474
 475 void
 476 FGEnvironment::set_altitude_half_to_sun_m (double alt)
 477 {
 478  altitude_half_to_sun_m = alt;
 479  _recalc_density_tropo_avg_kgm3();
 480 }
 481
 482 void
 483 FGEnvironment::set_altitude_tropo_top_m (double alt)
 484 {
 485  altitude_tropo_top_m = alt;
 486  _recalc_density_tropo_avg_kgm3();
 487 }
 488
 489
 490 void
 491 FGEnvironment::_recalc_hdgspd ()
 492 {
 493   double angle_rad;
 494
 495   if (wind_from_east_fps == 0) {
 496     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI_2 : -SGD_PI_2);
 497   } else {
 498     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 499   }
 500   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 501   if (wind_from_east_fps >= 0)
 502     wind_from_heading_deg = 90 - wind_from_heading_deg;
 503   else
 504     wind_from_heading_deg = 270 - wind_from_heading_deg;
 505
 506 #if 0
 507   // FIXME: Windspeed can become negative with these formulas.
 508   //        which can cause problems for animations that rely
 509   //        on the windspeed property.
 510   if (angle_rad == 0)
 511     wind_speed_kt = fabs(wind_from_east_fps
 512                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 513   else
 514     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 515       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 516 #else
 517   wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
 518                        wind_from_east_fps * wind_from_east_fps)
 519                   * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 520 #endif
 521 }
 522
 523 void
 524 FGEnvironment::_recalc_ne ()
 525 {
 526   double speed_fps =
 527     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 528
 529   wind_from_north_fps = speed_fps *
 530     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 531   wind_from_east_fps = speed_fps *
 532     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 533 }
 534
 535 void
 536 FGEnvironment::_recalc_sl_temperature ()
 537 {
 538   // If we're in the stratosphere, leave sea-level temp alone
 539   if (elevation_ft < 38000) {
 540     temperature_sea_level_degc = (temperature_degc + 273.15)
 541         / _temperature_degc_table->interpolate(elevation_ft)
 542       - 273.15;
 543   }
 544 }
 545
 546 void
 547 FGEnvironment::_recalc_alt_temperature ()
 548 {
 549   if (elevation_ft < 38000) {
 550     temperature_degc = (temperature_sea_level_degc + 273.15) *
 551         _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 552   } else {
 553     temperature_degc = -56.49;  // Stratosphere is constant
 554   }
 555 }
 556
 557 void
 558 FGEnvironment::_recalc_sl_dewpoint ()
 559 {
 560                                 // 0.2degC/1000ft
 561                                 // FIXME: this will work only for low
 562                                 // elevations
 563   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 564   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 565     dewpoint_sea_level_degc = temperature_sea_level_degc;
 566 }
 567
 568 void
 569 FGEnvironment::_recalc_alt_dewpoint ()
 570 {
 571                                 // 0.2degC/1000ft
 572                                 // FIXME: this will work only for low
 573                                 // elevations
 574   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 575   if (dewpoint_degc > temperature_degc)
 576     dewpoint_degc = temperature_degc;
 577 }
 578
 579 void
 580 FGEnvironment::_recalc_sl_pressure ()
 581 {
 582   pressure_sea_level_inhg =
 583     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 584 }
 585
 586 void
 587 FGEnvironment::_recalc_alt_pressure ()
 588 {
 589   pressure_inhg =
 590     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 591 }
 592
 593 void
 594 FGEnvironment::_recalc_density ()
 595 {
 596   double pressure_psf = pressure_inhg * 70.7487;
 597
 598   // adjust for humidity
 599   // calculations taken from USA Today (oops!) at
 600   // http://www.usatoday.com/weather/basics/density-calculations.htm
 601   double temperature_degk = temperature_degc + 273.15;
 602   double pressure_mb = pressure_inhg * 33.86;
 603   double vapor_pressure_mb =
 604     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 605   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 606   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 607
 608   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 609   _recalc_density_tropo_avg_kgm3();
 610 }
 611
 612 // This is used to calculate the average density on the path
 613 // of sunlight to the observer for calculating sun-color
 614 void
 615 FGEnvironment::_recalc_density_tropo_avg_kgm3 ()
 616 {
 617   double pressure_mb = pressure_inhg * 33.86;
 618   double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / (237.7 + dewpoint_degc)));
 619
 620   double virtual_temp = (temperature_degc + 273.15) / (1 - 0.379 * (vaporpressure/pressure_mb));
 621
 622   double density_half = (100 * pressure_mb * exp(-altitude_half_to_sun_m / 8000))
 623       / (287.05 * virtual_temp);
 624   double density_tropo = (100 * pressure_mb * exp((-1 * altitude_tropo_top_m) / 8000))
 625       / ( 287.05 * virtual_temp);
 626
 627   density_tropo_avg_kgm3 = ((density_slugft3 * 515.379) + density_half + density_tropo) / 3;
 628 }
 629
 630 void
 631 FGEnvironment::_recalc_relative_humidity ()
 632 {
 633   double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / ( 237.7 + dewpoint_degc)));
 634   double sat_vaporpressure = 6.11 * pow(10.0, ((7.5 * temperature_degc)
 635       / ( 237.7 + temperature_degc)) );
 636   relative_humidity = 100 * vaporpressure / sat_vaporpressure ;
 637 }
 638
 639
 640
 641 ////////////////////////////////////////////////////////////////////////
 642 // Functions.
 643 ////////////////////////////////////////////////////////////////////////
 644
 645 static inline double
 646 do_interp (double a, double b, double fraction)
 647 {
 648     double retval = (a + ((b - a) * fraction));
 649     return retval;
 650 }
 651
 652 static inline double
 653 do_interp_deg (double a, double b, double fraction)
 654 {
 655     a = fmod(a, 360);
 656     b = fmod(b, 360);
 657     if (fabs(b-a) > 180) {
 658         if (a < b)
 659             a += 360;
 660         else
 661             b += 360;
 662     }
 663     return fmod(do_interp(a, b, fraction), 360);
 664 }
 665
 666 void
 667 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 668              double fraction, FGEnvironment * result)
 669 {
 670     result->set_visibility_m
 671         (do_interp(env1->get_visibility_m(),
 672                    env2->get_visibility_m(),
 673                    fraction));
 674
 675     result->set_temperature_sea_level_degc
 676         (do_interp(env1->get_temperature_sea_level_degc(),
 677                    env2->get_temperature_sea_level_degc(),
 678                    fraction));
 679
 680     result->set_dewpoint_degc
 681         (do_interp(env1->get_dewpoint_sea_level_degc(),
 682                    env2->get_dewpoint_sea_level_degc(),
 683                    fraction));
 684
 685     result->set_pressure_sea_level_inhg
 686         (do_interp(env1->get_pressure_sea_level_inhg(),
 687                    env2->get_pressure_sea_level_inhg(),
 688                    fraction));
 689
 690     result->set_wind_from_heading_deg
 691         (do_interp_deg(env1->get_wind_from_heading_deg(),
 692                        env2->get_wind_from_heading_deg(),
 693                        fraction));
 694
 695     result->set_wind_speed_kt
 696         (do_interp(env1->get_wind_speed_kt(),
 697                    env2->get_wind_speed_kt(),
 698                    fraction));
 699
 700     result->set_elevation_ft
 701         (do_interp(env1->get_elevation_ft(),
 702                    env2->get_elevation_ft(),
 703                    fraction));
 704
 705     result->set_turbulence_magnitude_norm
 706         (do_interp(env1->get_turbulence_magnitude_norm(),
 707                    env2->get_turbulence_magnitude_norm(),
 708                    fraction));
 709
 710     result->set_turbulence_rate_hz
 711         (do_interp(env1->get_turbulence_rate_hz(),
 712                    env2->get_turbulence_rate_hz(),
 713                    fraction));
 714 }
 715
 716 // end of environment.cxx