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 void FGEnvironment::_init()
 122 {
 123     elevation_ft = 0;
 124     visibility_m = 32000;
 125     temperature_sea_level_degc = 15;
 126     temperature_degc = 15;
 127     dewpoint_sea_level_degc = 5; // guess
 128     dewpoint_degc = 5;
 129     pressure_sea_level_inhg = 29.92;
 130     pressure_inhg = 29.92;
 131     turbulence_magnitude_norm = 0;
 132     turbulence_rate_hz = 1;
 133     wind_from_heading_deg = 0;
 134     wind_speed_kt = 0;
 135     wind_from_north_fps = 0;
 136     wind_from_east_fps = 0;
 137     wind_from_down_fps = 0;
 138     altitude_half_to_sun_m = 1000;
 139     altitude_tropo_top_m = 10000;
 140     _setup_tables();
 141     _recalc_density();
 142     _recalc_relative_humidity();
 143
 144 }
 145
 146 FGEnvironment::FGEnvironment()
 147 {
 148     _init();
 149 }
 150
 151 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 152 {
 153     _init();
 154     copy(env);
 155 }
 156
 157 FGEnvironment::~FGEnvironment()
 158 {
 159 }
 160
 161 void
 162 FGEnvironment::copy (const FGEnvironment &env)
 163 {
 164     elevation_ft = env.elevation_ft;
 165     visibility_m = env.visibility_m;
 166     temperature_sea_level_degc = env.temperature_sea_level_degc;
 167     temperature_degc = env.temperature_degc;
 168     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 169     dewpoint_degc = env.dewpoint_degc;
 170     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 171     wind_from_heading_deg = env.wind_from_heading_deg;
 172     wind_speed_kt = env.wind_speed_kt;
 173     wind_from_north_fps = env.wind_from_north_fps;
 174     wind_from_east_fps = env.wind_from_east_fps;
 175     wind_from_down_fps = env.wind_from_down_fps;
 176     turbulence_magnitude_norm = env.turbulence_magnitude_norm;
 177     turbulence_rate_hz = env.turbulence_rate_hz;
 178 }
 179
 180 static inline bool
 181 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 182                   const char * name, void (FGEnvironment::*setter)(double))
 183 {
 184     const SGPropertyNode * child = node->getNode(name);
 185                                 // fragile: depends on not being typed
 186                                 // as a number
 187     if (child != 0 && child->hasValue() &&
 188         child->getStringValue()[0] != '\0') {
 189         (env->*setter)(child->getDoubleValue());
 190         return true;
 191     } else {
 192         return false;
 193     }
 194 }
 195
 196 void
 197 FGEnvironment::read (const SGPropertyNode * node)
 198 {
 199     maybe_copy_value(this, node, "visibility-m",
 200                      &FGEnvironment::set_visibility_m);
 201
 202     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 203                           &FGEnvironment::set_temperature_sea_level_degc))
 204         maybe_copy_value(this, node, "temperature-degc",
 205                          &FGEnvironment::set_temperature_degc);
 206
 207     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 208                           &FGEnvironment::set_dewpoint_sea_level_degc))
 209         maybe_copy_value(this, node, "dewpoint-degc",
 210                          &FGEnvironment::set_dewpoint_degc);
 211
 212     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 213                           &FGEnvironment::set_pressure_sea_level_inhg))
 214         maybe_copy_value(this, node, "pressure-inhg",
 215                          &FGEnvironment::set_pressure_inhg);
 216
 217     maybe_copy_value(this, node, "wind-from-heading-deg",
 218                      &FGEnvironment::set_wind_from_heading_deg);
 219
 220     maybe_copy_value(this, node, "wind-speed-kt",
 221                      &FGEnvironment::set_wind_speed_kt);
 222
 223     maybe_copy_value(this, node, "elevation-ft",
 224                      &FGEnvironment::set_elevation_ft);
 225
 226     maybe_copy_value(this, node, "turbulence/magnitude-norm",
 227                      &FGEnvironment::set_turbulence_magnitude_norm);
 228
 229     maybe_copy_value(this, node, "turbulence/rate-hz",
 230                      &FGEnvironment::set_turbulence_rate_hz);
 231 }
 232
 233
 234 double
 235 FGEnvironment::get_visibility_m () const
 236 {
 237   return visibility_m;
 238 }
 239
 240 double
 241 FGEnvironment::get_temperature_sea_level_degc () const
 242 {
 243   return temperature_sea_level_degc;
 244 }
 245
 246 double
 247 FGEnvironment::get_temperature_degc () const
 248 {
 249   return temperature_degc;
 250 }
 251
 252 double
 253 FGEnvironment::get_temperature_degf () const
 254 {
 255   return (temperature_degc * 9.0 / 5.0) + 32.0;
 256 }
 257
 258 double
 259 FGEnvironment::get_dewpoint_sea_level_degc () const
 260 {
 261   return dewpoint_sea_level_degc;
 262 }
 263
 264 double
 265 FGEnvironment::get_dewpoint_degc () const
 266 {
 267   return dewpoint_degc;
 268 }
 269
 270 double
 271 FGEnvironment::get_pressure_sea_level_inhg () const
 272 {
 273   return pressure_sea_level_inhg;
 274 }
 275
 276 double
 277 FGEnvironment::get_pressure_inhg () const
 278 {
 279   return pressure_inhg;
 280 }
 281
 282 double
 283 FGEnvironment::get_density_slugft3 () const
 284 {
 285   return density_slugft3;
 286 }
 287
 288 double
 289 FGEnvironment::get_relative_humidity () const
 290 {
 291   return relative_humidity;
 292 }
 293
 294 double
 295 FGEnvironment::get_density_tropo_avg_kgm3 () const
 296 {
 297   return density_tropo_avg_kgm3;
 298 }
 299
 300 double
 301 FGEnvironment::get_altitude_half_to_sun_m () const
 302 {
 303   return altitude_half_to_sun_m;
 304 }
 305
 306 double
 307 FGEnvironment::get_altitude_tropo_top_m () const
 308 {
 309   return altitude_tropo_top_m;
 310 }
 311
 312 double
 313 FGEnvironment::get_wind_from_heading_deg () const
 314 {
 315   return wind_from_heading_deg;
 316 }
 317
 318 double
 319 FGEnvironment::get_wind_speed_kt () const
 320 {
 321   return wind_speed_kt;
 322 }
 323
 324 double
 325 FGEnvironment::get_wind_from_north_fps () const
 326 {
 327   return wind_from_north_fps;
 328 }
 329
 330 double
 331 FGEnvironment::get_wind_from_east_fps () const
 332 {
 333   return wind_from_east_fps;
 334 }
 335
 336 double
 337 FGEnvironment::get_wind_from_down_fps () const
 338 {
 339   return wind_from_down_fps;
 340 }
 341
 342 double
 343 FGEnvironment::get_turbulence_magnitude_norm () const
 344 {
 345   if( sgEnviro.get_turbulence_enable_state() )
 346     if (fgGetBool("/environment/params/real-world-weather-fetch") == true)
 347       return sgEnviro.get_cloud_turbulence();
 348   return turbulence_magnitude_norm;
 349 }
 350
 351 double
 352 FGEnvironment::get_turbulence_rate_hz () const
 353 {
 354   return turbulence_rate_hz;
 355 }
 356
 357 double
 358 FGEnvironment::get_elevation_ft () const
 359 {
 360   return elevation_ft;
 361 }
 362
 363 void
 364 FGEnvironment::set_visibility_m (double v)
 365 {
 366   visibility_m = v;
 367 }
 368
 369 void
 370 FGEnvironment::set_temperature_sea_level_degc (double t)
 371 {
 372   temperature_sea_level_degc = t;
 373   if (dewpoint_sea_level_degc > t)
 374       dewpoint_sea_level_degc = t;
 375   _recalc_alt_temperature();
 376   _recalc_density();
 377 }
 378
 379 void
 380 FGEnvironment::set_temperature_degc (double t)
 381 {
 382   temperature_degc = t;
 383   _recalc_sl_temperature();
 384   _recalc_density();
 385   _recalc_relative_humidity();
 386 }
 387
 388 void
 389 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 390 {
 391   dewpoint_sea_level_degc = t;
 392   if (temperature_sea_level_degc < t)
 393       temperature_sea_level_degc = t;
 394   _recalc_alt_dewpoint();
 395   _recalc_density();
 396 }
 397
 398 void
 399 FGEnvironment::set_dewpoint_degc (double t)
 400 {
 401   dewpoint_degc = t;
 402   _recalc_sl_dewpoint();
 403   _recalc_density();
 404   _recalc_relative_humidity();
 405 }
 406
 407 void
 408 FGEnvironment::set_pressure_sea_level_inhg (double p)
 409 {
 410   pressure_sea_level_inhg = p;
 411   _recalc_alt_pressure();
 412   _recalc_density();
 413 }
 414
 415 void
 416 FGEnvironment::set_pressure_inhg (double p)
 417 {
 418   pressure_inhg = p;
 419   _recalc_sl_pressure();
 420   _recalc_density();
 421 }
 422
 423 void
 424 FGEnvironment::set_wind_from_heading_deg (double h)
 425 {
 426   wind_from_heading_deg = h;
 427   _recalc_ne();
 428 }
 429
 430 void
 431 FGEnvironment::set_wind_speed_kt (double s)
 432 {
 433   wind_speed_kt = s;
 434   _recalc_ne();
 435 }
 436
 437 void
 438 FGEnvironment::set_wind_from_north_fps (double n)
 439 {
 440   wind_from_north_fps = n;
 441   _recalc_hdgspd();
 442 }
 443
 444 void
 445 FGEnvironment::set_wind_from_east_fps (double e)
 446 {
 447   wind_from_east_fps = e;
 448   _recalc_hdgspd();
 449 }
 450
 451 void
 452 FGEnvironment::set_wind_from_down_fps (double d)
 453 {
 454   wind_from_down_fps = d;
 455   _recalc_hdgspd();
 456 }
 457
 458 void
 459 FGEnvironment::set_turbulence_magnitude_norm (double t)
 460 {
 461   turbulence_magnitude_norm = t;
 462 }
 463
 464 void
 465 FGEnvironment::set_turbulence_rate_hz (double r)
 466 {
 467   turbulence_rate_hz = r;
 468 }
 469
 470 void
 471 FGEnvironment::set_elevation_ft (double e)
 472 {
 473   elevation_ft = e;
 474   _recalc_alt_temperature();
 475   _recalc_alt_dewpoint();
 476   _recalc_alt_pressure();
 477   _recalc_density();
 478   _recalc_relative_humidity();
 479 }
 480
 481 void
 482 FGEnvironment::set_altitude_half_to_sun_m (double alt)
 483 {
 484  altitude_half_to_sun_m = alt;
 485  _recalc_density_tropo_avg_kgm3();
 486 }
 487
 488 void
 489 FGEnvironment::set_altitude_tropo_top_m (double alt)
 490 {
 491  altitude_tropo_top_m = alt;
 492  _recalc_density_tropo_avg_kgm3();
 493 }
 494
 495
 496 void
 497 FGEnvironment::_recalc_hdgspd ()
 498 {
 499   double angle_rad;
 500
 501   if (wind_from_east_fps == 0) {
 502     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI_2 : -SGD_PI_2);
 503   } else {
 504     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 505   }
 506   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 507   if (wind_from_east_fps >= 0)
 508     wind_from_heading_deg = 90 - wind_from_heading_deg;
 509   else
 510     wind_from_heading_deg = 270 - wind_from_heading_deg;
 511
 512 #if 0
 513   // FIXME: Windspeed can become negative with these formulas.
 514   //        which can cause problems for animations that rely
 515   //        on the windspeed property.
 516   if (angle_rad == 0)
 517     wind_speed_kt = fabs(wind_from_east_fps
 518                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 519   else
 520     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 521       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 522 #else
 523   wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
 524                        wind_from_east_fps * wind_from_east_fps)
 525                   * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 526 #endif
 527 }
 528
 529 void
 530 FGEnvironment::_recalc_ne ()
 531 {
 532   double speed_fps =
 533     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 534
 535   wind_from_north_fps = speed_fps *
 536     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 537   wind_from_east_fps = speed_fps *
 538     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 539 }
 540
 541 void
 542 FGEnvironment::_recalc_sl_temperature ()
 543 {
 544   // If we're in the stratosphere, leave sea-level temp alone
 545   if (elevation_ft < 38000) {
 546     temperature_sea_level_degc = (temperature_degc + 273.15)
 547         / _temperature_degc_table->interpolate(elevation_ft)
 548       - 273.15;
 549   }
 550 }
 551
 552 void
 553 FGEnvironment::_recalc_alt_temperature ()
 554 {
 555   if (elevation_ft < 38000) {
 556     temperature_degc = (temperature_sea_level_degc + 273.15) *
 557         _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 558   } else {
 559     temperature_degc = -56.49;  // Stratosphere is constant
 560   }
 561 }
 562
 563 void
 564 FGEnvironment::_recalc_sl_dewpoint ()
 565 {
 566                                 // 0.2degC/1000ft
 567                                 // FIXME: this will work only for low
 568                                 // elevations
 569   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 570   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 571     dewpoint_sea_level_degc = temperature_sea_level_degc;
 572 }
 573
 574 void
 575 FGEnvironment::_recalc_alt_dewpoint ()
 576 {
 577                                 // 0.2degC/1000ft
 578                                 // FIXME: this will work only for low
 579                                 // elevations
 580   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 581   if (dewpoint_degc > temperature_degc)
 582     dewpoint_degc = temperature_degc;
 583 }
 584
 585 void
 586 FGEnvironment::_recalc_sl_pressure ()
 587 {
 588   pressure_sea_level_inhg =
 589     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 590 }
 591
 592 void
 593 FGEnvironment::_recalc_alt_pressure ()
 594 {
 595   pressure_inhg =
 596     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 597 }
 598
 599 void
 600 FGEnvironment::_recalc_density ()
 601 {
 602   double pressure_psf = pressure_inhg * 70.7487;
 603
 604   // adjust for humidity
 605   // calculations taken from USA Today (oops!) at
 606   // http://www.usatoday.com/weather/basics/density-calculations.htm
 607   double temperature_degk = temperature_degc + 273.15;
 608   double pressure_mb = pressure_inhg * 33.86;
 609   double vapor_pressure_mb =
 610     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 611   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 612   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 613
 614   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 615   _recalc_density_tropo_avg_kgm3();
 616 }
 617
 618 // This is used to calculate the average density on the path
 619 // of sunlight to the observer for calculating sun-color
 620 void
 621 FGEnvironment::_recalc_density_tropo_avg_kgm3 ()
 622 {
 623   double pressure_mb = pressure_inhg * 33.86;
 624   double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / (237.7 + dewpoint_degc)));
 625
 626   double virtual_temp = (temperature_degc + 273.15) / (1 - 0.379 * (vaporpressure/pressure_mb));
 627
 628   double density_half = (100 * pressure_mb * exp(-altitude_half_to_sun_m / 8000))
 629       / (287.05 * virtual_temp);
 630   double density_tropo = (100 * pressure_mb * exp((-1 * altitude_tropo_top_m) / 8000))
 631       / ( 287.05 * virtual_temp);
 632
 633   density_tropo_avg_kgm3 = ((density_slugft3 * 515.379) + density_half + density_tropo) / 3;
 634 }
 635
 636 void
 637 FGEnvironment::_recalc_relative_humidity ()
 638 {
 639   double vaporpressure = 6.11 * pow(10.0, ((7.5 * dewpoint_degc) / ( 237.7 + dewpoint_degc)));
 640   double sat_vaporpressure = 6.11 * pow(10.0, ((7.5 * temperature_degc)
 641       / ( 237.7 + temperature_degc)) );
 642   relative_humidity = 100 * vaporpressure / sat_vaporpressure ;
 643 }
 644
 645
 646
 647 ////////////////////////////////////////////////////////////////////////
 648 // Functions.
 649 ////////////////////////////////////////////////////////////////////////
 650
 651 static inline double
 652 do_interp (double a, double b, double fraction)
 653 {
 654     double retval = (a + ((b - a) * fraction));
 655     return retval;
 656 }
 657
 658 static inline double
 659 do_interp_deg (double a, double b, double fraction)
 660 {
 661     a = fmod(a, 360);
 662     b = fmod(b, 360);
 663     if (fabs(b-a) > 180) {
 664         if (a < b)
 665             a += 360;
 666         else
 667             b += 360;
 668     }
 669     return fmod(do_interp(a, b, fraction), 360);
 670 }
 671
 672 void
 673 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 674              double fraction, FGEnvironment * result)
 675 {
 676     result->set_visibility_m
 677         (do_interp(env1->get_visibility_m(),
 678                    env2->get_visibility_m(),
 679                    fraction));
 680
 681     result->set_temperature_sea_level_degc
 682         (do_interp(env1->get_temperature_sea_level_degc(),
 683                    env2->get_temperature_sea_level_degc(),
 684                    fraction));
 685
 686     result->set_dewpoint_degc
 687         (do_interp(env1->get_dewpoint_sea_level_degc(),
 688                    env2->get_dewpoint_sea_level_degc(),
 689                    fraction));
 690
 691     result->set_pressure_sea_level_inhg
 692         (do_interp(env1->get_pressure_sea_level_inhg(),
 693                    env2->get_pressure_sea_level_inhg(),
 694                    fraction));
 695
 696     result->set_wind_from_heading_deg
 697         (do_interp_deg(env1->get_wind_from_heading_deg(),
 698                        env2->get_wind_from_heading_deg(),
 699                        fraction));
 700
 701     result->set_wind_speed_kt
 702         (do_interp(env1->get_wind_speed_kt(),
 703                    env2->get_wind_speed_kt(),
 704                    fraction));
 705
 706     result->set_elevation_ft
 707         (do_interp(env1->get_elevation_ft(),
 708                    env2->get_elevation_ft(),
 709                    fraction));
 710
 711     result->set_turbulence_magnitude_norm
 712         (do_interp(env1->get_turbulence_magnitude_norm(),
 713                    env2->get_turbulence_magnitude_norm(),
 714                    fraction));
 715
 716     result->set_turbulence_rate_hz
 717         (do_interp(env1->get_turbulence_rate_hz(),
 718                    env2->get_turbulence_rate_hz(),
 719                    fraction));
 720 }
 721
 722 // end of environment.cxx