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 #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 #include <simgear/environment/visual_enviro.hxx>
  40
  41 #include <Main/fg_props.hxx>
  42 #include "environment.hxx"
  43
  44
  45 \f
  46 ////////////////////////////////////////////////////////////////////////
  47 // Atmosphere model.
  48 ////////////////////////////////////////////////////////////////////////
  49
  50 // Copied from YASim Atmosphere.cxx, with m converted to ft, degK
  51 // converted to degC, Pa converted to inHG, and kg/m^3 converted to
  52 // slug/ft^3; they were then converted to deltas from the sea-level
  53 // defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).
  54
  55 // Original comment from YASim:
  56
  57 // Copied from McCormick, who got it from "The ARDC Model Atmosphere"
  58 // Note that there's an error in the text in the first entry,
  59 // McCormick lists 299.16/101325/1.22500, but those don't agree with
  60 // R=287.  I chose to correct the temperature to 288.20, since 79F is
  61 // pretty hot for a "standard" atmosphere.
  62
  63 // Elevation (ft), temperature factor (degK), pressure factor (inHG)
  64 static double atmosphere_data[][3] = {
  65  { 0.00, 1.00, 1.000 },
  66  { 2952.76, 0.98, 0.898 },
  67  { 5905.51, 0.96, 0.804 },
  68  { 8858.27, 0.94, 0.719 },
  69  { 11811.02, 0.92, 0.641 },
  70  { 14763.78, 0.90, 0.570 },
  71  { 17716.54, 0.88, 0.506 },
  72  { 20669.29, 0.86, 0.447 },
  73  { 23622.05, 0.84, 0.394 },
  74  { 26574.80, 0.82, 0.347 },
  75  { 29527.56, 0.80, 0.304 },
  76  { 32480.31, 0.78, 0.266 },
  77  { 35433.07, 0.76, 0.231 },
  78  { 38385.83, 0.75, 0.201 },
  79  { 41338.58, 0.75, 0.174 },
  80  { 44291.34, 0.75, 0.151 },
  81  { 47244.09, 0.75, 0.131 },
  82  { 50196.85, 0.75, 0.114 },
  83  { 53149.61, 0.75, 0.099 },
  84  { 56102.36, 0.75, 0.086 },
  85  { 59055.12, 0.75, 0.075 },
  86  { 62007.87, 0.75, 0.065 },
  87  { -1, -1, -1 }
  88 };
  89
  90 static SGInterpTable * _temperature_degc_table = 0;
  91 static SGInterpTable * _pressure_inhg_table = 0;
  92
  93 static void
  94 _setup_tables ()
  95 {
  96   if (_temperature_degc_table != 0)
  97       return;
  98
  99   _temperature_degc_table = new SGInterpTable;
 100   _pressure_inhg_table = new SGInterpTable;
 101
 102   for (int i = 0; atmosphere_data[i][0] != -1; i++) {
 103     _temperature_degc_table->addEntry(atmosphere_data[i][0],
 104                                       atmosphere_data[i][1]);
 105     _pressure_inhg_table->addEntry(atmosphere_data[i][0],
 106                                    atmosphere_data[i][2]);
 107   }
 108 }
 109
 110
 111 \f
 112 ////////////////////////////////////////////////////////////////////////
 113 // Implementation of FGEnvironment.
 114 ////////////////////////////////////////////////////////////////////////
 115
 116 FGEnvironment::FGEnvironment()
 117   : elevation_ft(0),
 118     visibility_m(32000),
 119     temperature_sea_level_degc(15),
 120     temperature_degc(15),
 121     dewpoint_sea_level_degc(5), // guess
 122     dewpoint_degc(5),
 123     pressure_sea_level_inhg(29.92),
 124     pressure_inhg(29.92),
 125     turbulence_magnitude_norm(0),
 126     turbulence_rate_hz(1),
 127     wind_from_heading_deg(0),
 128     wind_speed_kt(0),
 129     wind_from_north_fps(0),
 130     wind_from_east_fps(0),
 131     wind_from_down_fps(0),
 132     altitude_half_to_sun_m(1000),
 133     altitude_tropo_top_m(10000)
 134 {
 135   _setup_tables();
 136   _recalc_density();
 137   _recalc_relative_humidity();
 138 }
 139
 140 FGEnvironment::FGEnvironment (const FGEnvironment &env)
 141 {
 142     FGEnvironment();
 143     copy(env);
 144 }
 145
 146 FGEnvironment::~FGEnvironment()
 147 {
 148 }
 149
 150 void
 151 FGEnvironment::copy (const FGEnvironment &env)
 152 {
 153     elevation_ft = env.elevation_ft;
 154     visibility_m = env.visibility_m;
 155     temperature_sea_level_degc = env.temperature_sea_level_degc;
 156     temperature_degc = env.temperature_degc;
 157     dewpoint_sea_level_degc = env.dewpoint_sea_level_degc;
 158     dewpoint_degc = env.dewpoint_degc;
 159     pressure_sea_level_inhg = env.pressure_sea_level_inhg;
 160     wind_from_heading_deg = env.wind_from_heading_deg;
 161     wind_speed_kt = env.wind_speed_kt;
 162     wind_from_north_fps = env.wind_from_north_fps;
 163     wind_from_east_fps = env.wind_from_east_fps;
 164     wind_from_down_fps = env.wind_from_down_fps;
 165     turbulence_magnitude_norm = env.turbulence_magnitude_norm;
 166     turbulence_rate_hz = env.turbulence_rate_hz;
 167 }
 168
 169 static inline bool
 170 maybe_copy_value (FGEnvironment * env, const SGPropertyNode * node,
 171                   const char * name, void (FGEnvironment::*setter)(double))
 172 {
 173     const SGPropertyNode * child = node->getNode(name);
 174                                 // fragile: depends on not being typed
 175                                 // as a number
 176     if (child != 0 && child->hasValue() &&
 177         child->getStringValue()[0] != '\0') {
 178         (env->*setter)(child->getDoubleValue());
 179         return true;
 180     } else {
 181         return false;
 182     }
 183 }
 184
 185 void
 186 FGEnvironment::read (const SGPropertyNode * node)
 187 {
 188     maybe_copy_value(this, node, "visibility-m",
 189                      &FGEnvironment::set_visibility_m);
 190
 191     if (!maybe_copy_value(this, node, "temperature-sea-level-degc",
 192                           &FGEnvironment::set_temperature_sea_level_degc))
 193         maybe_copy_value(this, node, "temperature-degc",
 194                          &FGEnvironment::set_temperature_degc);
 195
 196     if (!maybe_copy_value(this, node, "dewpoint-sea-level-degc",
 197                           &FGEnvironment::set_dewpoint_sea_level_degc))
 198         maybe_copy_value(this, node, "dewpoint-degc",
 199                          &FGEnvironment::set_dewpoint_degc);
 200
 201     if (!maybe_copy_value(this, node, "pressure-sea-level-inhg",
 202                           &FGEnvironment::set_pressure_sea_level_inhg))
 203         maybe_copy_value(this, node, "pressure-inhg",
 204                          &FGEnvironment::set_pressure_inhg);
 205
 206     maybe_copy_value(this, node, "wind-from-heading-deg",
 207                      &FGEnvironment::set_wind_from_heading_deg);
 208
 209     maybe_copy_value(this, node, "wind-speed-kt",
 210                      &FGEnvironment::set_wind_speed_kt);
 211
 212     maybe_copy_value(this, node, "elevation-ft",
 213                      &FGEnvironment::set_elevation_ft);
 214
 215     maybe_copy_value(this, node, "turbulence/magnitude-norm",
 216                      &FGEnvironment::set_turbulence_magnitude_norm);
 217
 218     maybe_copy_value(this, node, "turbulence/rate-hz",
 219                      &FGEnvironment::set_turbulence_rate_hz);
 220 }
 221
 222
 223 double
 224 FGEnvironment::get_visibility_m () const
 225 {
 226   return visibility_m;
 227 }
 228
 229 double
 230 FGEnvironment::get_temperature_sea_level_degc () const
 231 {
 232   return temperature_sea_level_degc;
 233 }
 234
 235 double
 236 FGEnvironment::get_temperature_degc () const
 237 {
 238   return temperature_degc;
 239 }
 240
 241 double
 242 FGEnvironment::get_temperature_degf () const
 243 {
 244   return (temperature_degc * 9.0 / 5.0) + 32.0;
 245 }
 246
 247 double
 248 FGEnvironment::get_dewpoint_sea_level_degc () const
 249 {
 250   return dewpoint_sea_level_degc;
 251 }
 252
 253 double
 254 FGEnvironment::get_dewpoint_degc () const
 255 {
 256   return dewpoint_degc;
 257 }
 258
 259 double
 260 FGEnvironment::get_pressure_sea_level_inhg () const
 261 {
 262   return pressure_sea_level_inhg;
 263 }
 264
 265 double
 266 FGEnvironment::get_pressure_inhg () const
 267 {
 268   return pressure_inhg;
 269 }
 270
 271 double
 272 FGEnvironment::get_density_slugft3 () const
 273 {
 274   return density_slugft3;
 275 }
 276
 277 double
 278 FGEnvironment::get_relative_humidity () const
 279 {
 280   return relative_humidity;
 281 }
 282
 283 double
 284 FGEnvironment::get_density_tropo_avg_kgm3 () const
 285 {
 286   return density_tropo_avg_kgm3;
 287 }
 288
 289 double
 290 FGEnvironment::get_altitude_half_to_sun_m () const
 291 {
 292   return altitude_half_to_sun_m;
 293 }
 294
 295 double
 296 FGEnvironment::get_altitude_tropo_top_m () const
 297 {
 298   return altitude_tropo_top_m;
 299 }
 300
 301 double
 302 FGEnvironment::get_wind_from_heading_deg () const
 303 {
 304   return wind_from_heading_deg;
 305 }
 306
 307 double
 308 FGEnvironment::get_wind_speed_kt () const
 309 {
 310   return wind_speed_kt;
 311 }
 312
 313 double
 314 FGEnvironment::get_wind_from_north_fps () const
 315 {
 316   return wind_from_north_fps;
 317 }
 318
 319 double
 320 FGEnvironment::get_wind_from_east_fps () const
 321 {
 322   return wind_from_east_fps;
 323 }
 324
 325 double
 326 FGEnvironment::get_wind_from_down_fps () const
 327 {
 328   return wind_from_down_fps;
 329 }
 330
 331 double
 332 FGEnvironment::get_turbulence_magnitude_norm () const
 333 {
 334   if( sgEnviro.get_turbulence_enable_state() )
 335     if (fgGetBool("/environment/params/real-world-weather-fetch") == true)
 336       return sgEnviro.get_cloud_turbulence();
 337   return turbulence_magnitude_norm;
 338 }
 339
 340 double
 341 FGEnvironment::get_turbulence_rate_hz () const
 342 {
 343   return turbulence_rate_hz;
 344 }
 345
 346 double
 347 FGEnvironment::get_elevation_ft () const
 348 {
 349   return elevation_ft;
 350 }
 351
 352 void
 353 FGEnvironment::set_visibility_m (double v)
 354 {
 355   visibility_m = v;
 356 }
 357
 358 void
 359 FGEnvironment::set_temperature_sea_level_degc (double t)
 360 {
 361   temperature_sea_level_degc = t;
 362   if (dewpoint_sea_level_degc > t)
 363       dewpoint_sea_level_degc = t;
 364   _recalc_alt_temperature();
 365   _recalc_density();
 366 }
 367
 368 void
 369 FGEnvironment::set_temperature_degc (double t)
 370 {
 371   temperature_degc = t;
 372   _recalc_sl_temperature();
 373   _recalc_density();
 374   _recalc_relative_humidity();
 375 }
 376
 377 void
 378 FGEnvironment::set_dewpoint_sea_level_degc (double t)
 379 {
 380   dewpoint_sea_level_degc = t;
 381   if (temperature_sea_level_degc < t)
 382       temperature_sea_level_degc = t;
 383   _recalc_alt_dewpoint();
 384   _recalc_density();
 385 }
 386
 387 void
 388 FGEnvironment::set_dewpoint_degc (double t)
 389 {
 390   dewpoint_degc = t;
 391   _recalc_sl_dewpoint();
 392   _recalc_density();
 393   _recalc_relative_humidity();
 394 }
 395
 396 void
 397 FGEnvironment::set_pressure_sea_level_inhg (double p)
 398 {
 399   pressure_sea_level_inhg = p;
 400   _recalc_alt_pressure();
 401   _recalc_density();
 402 }
 403
 404 void
 405 FGEnvironment::set_pressure_inhg (double p)
 406 {
 407   pressure_inhg = p;
 408   _recalc_sl_pressure();
 409   _recalc_density();
 410 }
 411
 412 void
 413 FGEnvironment::set_wind_from_heading_deg (double h)
 414 {
 415   wind_from_heading_deg = h;
 416   _recalc_ne();
 417 }
 418
 419 void
 420 FGEnvironment::set_wind_speed_kt (double s)
 421 {
 422   wind_speed_kt = s;
 423   _recalc_ne();
 424 }
 425
 426 void
 427 FGEnvironment::set_wind_from_north_fps (double n)
 428 {
 429   wind_from_north_fps = n;
 430   _recalc_hdgspd();
 431 }
 432
 433 void
 434 FGEnvironment::set_wind_from_east_fps (double e)
 435 {
 436   wind_from_east_fps = e;
 437   _recalc_hdgspd();
 438 }
 439
 440 void
 441 FGEnvironment::set_wind_from_down_fps (double d)
 442 {
 443   wind_from_down_fps = d;
 444   _recalc_hdgspd();
 445 }
 446
 447 void
 448 FGEnvironment::set_turbulence_magnitude_norm (double t)
 449 {
 450   turbulence_magnitude_norm = t;
 451 }
 452
 453 void
 454 FGEnvironment::set_turbulence_rate_hz (double r)
 455 {
 456   turbulence_rate_hz = r;
 457 }
 458
 459 void
 460 FGEnvironment::set_elevation_ft (double e)
 461 {
 462   elevation_ft = e;
 463   _recalc_alt_temperature();
 464   _recalc_alt_dewpoint();
 465   _recalc_alt_pressure();
 466   _recalc_density();
 467   _recalc_relative_humidity();
 468 }
 469
 470 void
 471 FGEnvironment::set_altitude_half_to_sun_m (double alt)
 472 {
 473  altitude_half_to_sun_m = alt;
 474  _recalc_density_tropo_avg_kgm3();
 475 }
 476
 477 void
 478 FGEnvironment::set_altitude_tropo_top_m (double alt)
 479 {
 480  altitude_tropo_top_m = alt;
 481  _recalc_density_tropo_avg_kgm3();
 482 }
 483
 484
 485 void
 486 FGEnvironment::_recalc_hdgspd ()
 487 {
 488   double angle_rad;
 489
 490   if (wind_from_east_fps == 0) {
 491     angle_rad = (wind_from_north_fps >= 0 ? SGD_PI_2 : -SGD_PI_2);
 492   } else {
 493     angle_rad = atan(wind_from_north_fps/wind_from_east_fps);
 494   }
 495   wind_from_heading_deg = angle_rad * SGD_RADIANS_TO_DEGREES;
 496   if (wind_from_east_fps >= 0)
 497     wind_from_heading_deg = 90 - wind_from_heading_deg;
 498   else
 499     wind_from_heading_deg = 270 - wind_from_heading_deg;
 500
 501 #if 0
 502   // FIXME: Windspeed can become negative with these formulas.
 503   //        which can cause problems for animations that rely
 504   //        on the windspeed property.
 505   if (angle_rad == 0)
 506     wind_speed_kt = fabs(wind_from_east_fps
 507                          * SG_METER_TO_NM * SG_FEET_TO_METER * 3600);
 508   else
 509     wind_speed_kt = (wind_from_north_fps / sin(angle_rad))
 510       * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 511 #else
 512   wind_speed_kt = sqrt(wind_from_north_fps * wind_from_north_fps +
 513                        wind_from_east_fps * wind_from_east_fps)
 514                   * SG_METER_TO_NM * SG_FEET_TO_METER * 3600;
 515 #endif
 516 }
 517
 518 void
 519 FGEnvironment::_recalc_ne ()
 520 {
 521   double speed_fps =
 522     wind_speed_kt * SG_NM_TO_METER * SG_METER_TO_FEET * (1.0/3600);
 523
 524   wind_from_north_fps = speed_fps *
 525     cos(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 526   wind_from_east_fps = speed_fps *
 527     sin(wind_from_heading_deg * SGD_DEGREES_TO_RADIANS);
 528 }
 529
 530 void
 531 FGEnvironment::_recalc_sl_temperature ()
 532 {
 533   // If we're in the stratosphere, leave sea-level temp alone
 534   if (elevation_ft < 38000) {
 535     temperature_sea_level_degc =
 536       (temperature_degc + 273.15)
 537       /_temperature_degc_table->interpolate(elevation_ft)
 538       - 273.15;
 539   }
 540 }
 541
 542 void
 543 FGEnvironment::_recalc_alt_temperature ()
 544 {
 545   if (elevation_ft < 38000) {
 546     temperature_degc =
 547       (temperature_sea_level_degc + 273.15) *
 548       _temperature_degc_table->interpolate(elevation_ft) - 273.15;
 549   } else {
 550     temperature_degc = -56.49;  // Stratosphere is constant
 551   }
 552 }
 553
 554 void
 555 FGEnvironment::_recalc_sl_dewpoint ()
 556 {
 557                                 // 0.2degC/1000ft
 558                                 // FIXME: this will work only for low
 559                                 // elevations
 560   dewpoint_sea_level_degc = dewpoint_degc + (elevation_ft * .0002);
 561   if (dewpoint_sea_level_degc > temperature_sea_level_degc)
 562     dewpoint_sea_level_degc = temperature_sea_level_degc;
 563 }
 564
 565 void
 566 FGEnvironment::_recalc_alt_dewpoint ()
 567 {
 568                                 // 0.2degC/1000ft
 569                                 // FIXME: this will work only for low
 570                                 // elevations
 571   dewpoint_degc = dewpoint_sea_level_degc + (elevation_ft * .0002);
 572   if (dewpoint_degc > temperature_degc)
 573     dewpoint_degc = temperature_degc;
 574 }
 575
 576 void
 577 FGEnvironment::_recalc_sl_pressure ()
 578 {
 579   pressure_sea_level_inhg =
 580     pressure_inhg / _pressure_inhg_table->interpolate(elevation_ft);
 581 }
 582
 583 void
 584 FGEnvironment::_recalc_alt_pressure ()
 585 {
 586   pressure_inhg =
 587     pressure_sea_level_inhg * _pressure_inhg_table->interpolate(elevation_ft);
 588 }
 589
 590 void
 591 FGEnvironment::_recalc_density ()
 592 {
 593   double pressure_psf = pressure_inhg * 70.7487;
 594
 595   // adjust for humidity
 596   // calculations taken from USA Today (oops!) at
 597   // http://www.usatoday.com/weather/basics/density-calculations.htm
 598   double temperature_degk = temperature_degc + 273.15;
 599   double pressure_mb = pressure_inhg * 33.86;
 600   double vapor_pressure_mb =
 601     6.11 * pow(10.0, 7.5 * dewpoint_degc / (237.7 + dewpoint_degc));
 602   double virtual_temperature_degk = temperature_degk / (1 - (vapor_pressure_mb / pressure_mb) * (1.0 - 0.622));
 603   double virtual_temperature_degr = virtual_temperature_degk * 1.8;
 604
 605   density_slugft3 = pressure_psf / (virtual_temperature_degr * 1718);
 606   _recalc_density_tropo_avg_kgm3();
 607 }
 608
 609 // This is used to calculate the average density on the path
 610 // of sunlight to the observer for calculating sun-color
 611 void
 612 FGEnvironment::_recalc_density_tropo_avg_kgm3 ()
 613 {
 614   double pressure_mb = pressure_inhg * 33.86;
 615   double vaporpressure = 6.11 * pow ( 10, ((7.5 * dewpoint_degc) /( 237.7 + dewpoint_degc)));
 616
 617   double virtual_temp = (temperature_degc + 273.15) / (1 - 0.379 * (vaporpressure/pressure_mb));
 618
 619   double density_half = (100* pressure_mb * exp (-altitude_half_to_sun_m / 8000)) / (287.05 * virtual_temp);
 620   double density_tropo = (100* pressure_mb * exp ((-1 * altitude_tropo_top_m) / 8000)) /( 287.05 * virtual_temp);
 621
 622   density_tropo_avg_kgm3 = ((density_slugft3 * 515.379) + density_half + density_tropo) / 3;
 623 }
 624
 625 void
 626 FGEnvironment::_recalc_relative_humidity ()
 627 {
 628   double vaporpressure = 6.11 * pow ( 10, ((7.5 * dewpoint_degc) /( 237.7 + dewpoint_degc)));
 629   double sat_vaporpressure = 6.11 * pow ( 10, ((7.5 * temperature_degc) /( 237.7 + temperature_degc)) );
 630   relative_humidity = 100 *vaporpressure / sat_vaporpressure ;
 631 }
 632
 633
 634
 635 ////////////////////////////////////////////////////////////////////////
 636 // Functions.
 637 ////////////////////////////////////////////////////////////////////////
 638
 639 static inline double
 640 do_interp (double a, double b, double fraction)
 641 {
 642     double retval = (a + ((b - a) * fraction));
 643     return retval;
 644 }
 645
 646 static inline double
 647 do_interp_deg (double a, double b, double fraction)
 648 {
 649     a = fmod(a, 360);
 650     b = fmod(b, 360);
 651     if (fabs(b-a) > 180) {
 652         if (a < b)
 653             a += 360;
 654         else
 655             b += 360;
 656     }
 657     return fmod(do_interp(a, b, fraction), 360);
 658 }
 659
 660 void
 661 interpolate (const FGEnvironment * env1, const FGEnvironment * env2,
 662              double fraction, FGEnvironment * result)
 663 {
 664     result->set_visibility_m
 665         (do_interp(env1->get_visibility_m(),
 666                    env2->get_visibility_m(),
 667                    fraction));
 668
 669     result->set_temperature_sea_level_degc
 670         (do_interp(env1->get_temperature_sea_level_degc(),
 671                    env2->get_temperature_sea_level_degc(),
 672                    fraction));
 673
 674     result->set_dewpoint_degc
 675         (do_interp(env1->get_dewpoint_sea_level_degc(),
 676                    env2->get_dewpoint_sea_level_degc(),
 677                    fraction));
 678
 679     result->set_pressure_sea_level_inhg
 680         (do_interp(env1->get_pressure_sea_level_inhg(),
 681                    env2->get_pressure_sea_level_inhg(),
 682                    fraction));
 683
 684     result->set_wind_from_heading_deg
 685         (do_interp_deg(env1->get_wind_from_heading_deg(),
 686                        env2->get_wind_from_heading_deg(),
 687                        fraction));
 688
 689     result->set_wind_speed_kt
 690         (do_interp(env1->get_wind_speed_kt(),
 691                    env2->get_wind_speed_kt(),
 692                    fraction));
 693
 694     result->set_elevation_ft
 695         (do_interp(env1->get_elevation_ft(),
 696                    env2->get_elevation_ft(),
 697                    fraction));
 698
 699     result->set_turbulence_magnitude_norm
 700         (do_interp(env1->get_turbulence_magnitude_norm(),
 701                    env2->get_turbulence_magnitude_norm(),
 702                    fraction));
 703
 704     result->set_turbulence_rate_hz
 705         (do_interp(env1->get_turbulence_rate_hz(),
 706                    env2->get_turbulence_rate_hz(),
 707                    fraction));
 708 }
 709
 710 // end of environment.cxx