1 // FGAIBase - abstract base class for AI objects
2 // Written by David Culp, started Nov 2003, based on
3 // David Luff's FGAIEntity class.
4 // - davidculp2@comcast.net
6 // With additions by Mathias Froehlich & Vivian Meazza 2004 -2007
8 // This program is free software; you can redistribute it and/or
9 // modify it under the terms of the GNU General Public License as
10 // published by the Free Software Foundation; either version 2 of the
11 // License, or (at your option) any later version.
13 // This program is distributed in the hope that it will be useful, but
14 // WITHOUT ANY WARRANTY; without even the implied warranty of
15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 // General Public License for more details.
18 // You should have received a copy of the GNU General Public License
19 // along with this program; if not, write to the Free Software
20 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
27 #include <simgear/compiler.h>
31 #include <osg/ref_ptr>
33 #include <osgDB/FileUtils>
35 #include <simgear/math/SGMath.hxx>
36 #include <simgear/misc/sg_path.hxx>
37 #include <simgear/scene/model/modellib.hxx>
38 #include <simgear/scene/util/SGNodeMasks.hxx>
39 #include <simgear/debug/logstream.hxx>
40 #include <simgear/props/props.hxx>
42 #include <Main/globals.hxx>
43 #include <Scenery/scenery.hxx>
44 #include <Scripting/NasalSys.hxx>
45 #include <Sound/fg_fx.hxx>
48 #include "AIManager.hxx"
50 const char *default_model = "Models/Geometry/glider.ac";
51 const double FGAIBase::e = 2.71828183;
52 const double FGAIBase::lbs_to_slugs = 0.031080950172; //conversion factor
54 using namespace simgear;
56 FGAIBase::FGAIBase(object_type ot, bool enableHot) :
61 model_removed( fgGetNode("/ai/models/model-removed", true) ),
72 _refID( _newAIModelID() ),
78 tgt_heading = hdg = tgt_altitude_ft = tgt_speed = 0.0;
79 tgt_roll = roll = tgt_pitch = tgt_yaw = tgt_vs = vs = pitch = 0.0;
80 bearing = elevation = range = rdot = 0.0;
81 x_shift = y_shift = rotation = 0.0;
87 _impact_reported = false;
88 _collision_reported = false;
89 _expiry_reported = false;
101 userpos = SGGeod::fromDeg(0, 0);
103 pos = SGGeod::fromDeg(0, 0);
106 speed_north_deg_sec = 0;
107 speed_east_deg_sec = 0;
127 // explicitly disable HOT for (most) AI models
129 aip.getSceneGraph()->setNodeMask(~SG_NODEMASK_TERRAIN_BIT);
132 FGAIBase::~FGAIBase() {
133 // Unregister that one at the scenery manager
137 SGPropertyNode* parent = props->getParent();
140 model_removed->setStringValue(props->getPath());
149 /** Cleanly remove the model
150 * and let the scenery database pager do the clean-up work.
153 FGAIBase::removeModel()
155 FGScenery* pSceneryManager = globals->get_scenery();
158 osg::ref_ptr<osg::Object> temp = _model.get();
159 pSceneryManager->get_scene_graph()->removeChild(aip.getSceneGraph());
160 // withdraw from SGModelPlacement and drop own reference (unref)
163 // pass it on to the pager, to be be deleted in the pager thread
164 pSceneryManager->getPagerSingleton()->queueDeleteRequest(temp);
168 SG_LOG(SG_AI, SG_ALERT, "AIBase: Could not unload model. Missing scenery manager!");
172 void FGAIBase::readFromScenario(SGPropertyNode* scFileNode)
177 setPath(scFileNode->getStringValue("model",
178 fgGetString("/sim/multiplay/default-model", default_model)));
180 setHeading(scFileNode->getDoubleValue("heading", 0.0));
181 setSpeed(scFileNode->getDoubleValue("speed", 0.0));
182 setAltitude(scFileNode->getDoubleValue("altitude", 0.0));
183 setLongitude(scFileNode->getDoubleValue("longitude", 0.0));
184 setLatitude(scFileNode->getDoubleValue("latitude", 0.0));
185 setBank(scFileNode->getDoubleValue("roll", 0.0));
187 SGPropertyNode* submodels = scFileNode->getChild("submodels");
190 setServiceable(submodels->getBoolValue("serviceable", false));
191 setSMPath(submodels->getStringValue("path", ""));
196 void FGAIBase::update(double dt) {
198 if (_otype == otStatic)
201 if (_otype == otBallistic)
204 ft_per_deg_lat = 366468.96 - 3717.12 * cos(pos.getLatitudeRad());
205 ft_per_deg_lon = 365228.16 * cos(pos.getLatitudeRad());
209 // update model's audio sample values
210 _fx->set_position_geod( pos );
212 SGQuatd orient = SGQuatd::fromYawPitchRollDeg(hdg, pitch, roll);
213 _fx->set_orientation( orient );
216 velocity = SGVec3d( speed_north_deg_sec, speed_east_deg_sec, pitch*speed );
217 _fx->set_velocity( velocity );
221 /** update LOD properties of the model */
222 void FGAIBase::updateLOD()
224 double maxRangeDetail = fgGetDouble("/sim/rendering/static-lod/ai-detailed", 10000.0);
225 double maxRangeBare = fgGetDouble("/sim/rendering/static-lod/ai-bare", 20000.0);
228 if( maxRangeDetail == 0.0 )
231 _model->setRange(0, 0.0, FLT_MAX);
232 _model->setRange(1, FLT_MAX, FLT_MAX);
236 _model->setRange(0, 0.0, maxRangeDetail);
237 _model->setRange(1, maxRangeDetail,maxRangeBare);
242 void FGAIBase::Transform() {
245 aip.setVisible(true);
246 aip.setPosition(pos);
249 aip.setOrientation(0.0, pitch, hdg);
251 aip.setOrientation(roll, pitch, hdg);
255 aip.setVisible(false);
261 bool FGAIBase::init(bool search_in_AI_path) {
264 if(search_in_AI_path)
266 // setup a modified Options structure, with only the $fg-root/AI defined;
267 // we'll check that first, then give the normal search logic a chance.
268 // this ensures that models in AI/ are preferred to normal models, where
270 osg::ref_ptr<osgDB::ReaderWriter::Options>
271 opt(osg::clone(osgDB::Registry::instance()->getOptions(), osg::CopyOp::SHALLOW_COPY));
273 SGPath ai_path(globals->get_fg_root(), "AI");
274 opt->setDatabasePath(ai_path.str());
276 f = osgDB::findDataFile(model_path, opt.get());
280 f = simgear::SGModelLib::findDataFile(model_path);
284 f = fgGetString("/sim/multiplay/default-model", default_model);
288 osg::Node * mdl = SGModelLib::loadDeferredModel(f, props, new FGNasalModelData(props));
292 // reinit, dump the old model
296 _model = new osg::LOD;
297 _model->setName("AI-model range animation node");
299 _model->addChild( mdl, 0, FLT_MAX );
300 _model->setCenterMode(osg::LOD::USE_BOUNDING_SPHERE_CENTER);
301 _model->setRangeMode(osg::LOD::DISTANCE_FROM_EYE_POINT);
302 // We really need low-resolution versions of AI/MP aircraft.
303 // Or at least dummy "stubs" with some default silhouette.
304 // _model->addChild( SGModelLib::loadPagedModel(fgGetString("/sim/multiplay/default-model", default_model),
305 // props, new FGNasalModelData(props)), FLT_MAX, FLT_MAX);
309 if (_model.valid() && _initialized == false) {
310 aip.init( _model.get() );
311 aip.setVisible(true);
313 globals->get_scenery()->get_scene_graph()->addChild(aip.getSceneGraph());
315 // Get the sound-path tag from the configuration file and store it
316 // in the property tree.
317 string fxpath = props->getStringValue("sim/sound/path");
318 if ( !fxpath.empty() )
320 props->setStringValue("sim/sound/path", fxpath.c_str());
322 // initialize the sound configuration
323 SGSoundMgr *smgr = globals->get_soundmgr();
324 _fx = new FGFX(smgr, "aifx:"+f, props);
330 } else if (!model_path.empty()) {
331 SG_LOG(SG_AI, SG_WARN, "AIBase: Could not load model " << model_path);
332 // not properly installed...
340 void FGAIBase::initModel(osg::Node *node)
342 if (_model.valid()) {
345 props->setStringValue("submodels/path", _path.c_str());
346 SG_LOG(SG_AI, SG_DEBUG, "AIBase: submodels/path " << _path);
350 props->setStringValue("parent-name", _parent.c_str());
353 fgSetString("/ai/models/model-added", props->getPath().c_str());
354 } else if (!model_path.empty()) {
355 SG_LOG(SG_AI, SG_WARN, "AIBase: Could not load model " << model_path);
362 bool FGAIBase::isa( object_type otype ) {
363 return otype == _otype;
367 void FGAIBase::bind() {
368 props->tie("id", SGRawValueMethods<FGAIBase,int>(*this,
370 props->tie("velocities/true-airspeed-kt", SGRawValuePointer<double>(&speed));
371 props->tie("velocities/vertical-speed-fps",
372 SGRawValueMethods<FGAIBase,double>(*this,
373 &FGAIBase::_getVS_fps,
374 &FGAIBase::_setVS_fps));
376 props->tie("position/altitude-ft",
377 SGRawValueMethods<FGAIBase,double>(*this,
378 &FGAIBase::_getAltitude,
379 &FGAIBase::_setAltitude));
380 props->tie("position/latitude-deg",
381 SGRawValueMethods<FGAIBase,double>(*this,
382 &FGAIBase::_getLatitude,
383 &FGAIBase::_setLatitude));
384 props->tie("position/longitude-deg",
385 SGRawValueMethods<FGAIBase,double>(*this,
386 &FGAIBase::_getLongitude,
387 &FGAIBase::_setLongitude));
389 props->tie("position/global-x",
390 SGRawValueMethods<FGAIBase,double>(*this,
391 &FGAIBase::_getCartPosX,
393 props->tie("position/global-y",
394 SGRawValueMethods<FGAIBase,double>(*this,
395 &FGAIBase::_getCartPosY,
397 props->tie("position/global-z",
398 SGRawValueMethods<FGAIBase,double>(*this,
399 &FGAIBase::_getCartPosZ,
401 props->tie("callsign",
402 SGRawValueMethods<FGAIBase,const char*>(*this,
403 &FGAIBase::_getCallsign,
406 props->tie("orientation/pitch-deg", SGRawValuePointer<double>(&pitch));
407 props->tie("orientation/roll-deg", SGRawValuePointer<double>(&roll));
408 props->tie("orientation/true-heading-deg", SGRawValuePointer<double>(&hdg));
410 props->tie("radar/in-range", SGRawValuePointer<bool>(&in_range));
411 props->tie("radar/bearing-deg", SGRawValuePointer<double>(&bearing));
412 props->tie("radar/elevation-deg", SGRawValuePointer<double>(&elevation));
413 props->tie("radar/range-nm", SGRawValuePointer<double>(&range));
414 props->tie("radar/h-offset", SGRawValuePointer<double>(&horiz_offset));
415 props->tie("radar/v-offset", SGRawValuePointer<double>(&vert_offset));
416 props->tie("radar/x-shift", SGRawValuePointer<double>(&x_shift));
417 props->tie("radar/y-shift", SGRawValuePointer<double>(&y_shift));
418 props->tie("radar/rotation", SGRawValuePointer<double>(&rotation));
419 props->tie("radar/ht-diff-ft", SGRawValuePointer<double>(&ht_diff));
420 props->tie("subID", SGRawValuePointer<int>(&_subID));
421 props->tie("controls/lighting/nav-lights",
422 SGRawValueFunctions<bool>(_isNight));
423 props->setBoolValue("controls/lighting/beacon", true);
424 props->setBoolValue("controls/lighting/strobe", true);
425 props->setBoolValue("controls/glide-path", true);
427 props->setStringValue("controls/flight/lateral-mode", "roll");
428 props->setDoubleValue("controls/flight/target-hdg", hdg);
429 props->setDoubleValue("controls/flight/target-roll", roll);
431 props->setStringValue("controls/flight/longitude-mode", "alt");
432 props->setDoubleValue("controls/flight/target-alt", altitude_ft);
433 props->setDoubleValue("controls/flight/target-pitch", pitch);
435 props->setDoubleValue("controls/flight/target-spd", speed);
437 props->setBoolValue("sim/sound/avionics/enabled", false);
438 props->setDoubleValue("sim/sound/avionics/volume", 0.0);
439 props->setBoolValue("sim/sound/avionics/external-view", false);
440 props->setBoolValue("sim/current-view/internal", false);
444 void FGAIBase::unbind() {
446 props->untie("velocities/true-airspeed-kt");
447 props->untie("velocities/vertical-speed-fps");
449 props->untie("position/altitude-ft");
450 props->untie("position/latitude-deg");
451 props->untie("position/longitude-deg");
452 props->untie("position/global-x");
453 props->untie("position/global-y");
454 props->untie("position/global-z");
455 props->untie("callsign");
457 props->untie("orientation/pitch-deg");
458 props->untie("orientation/roll-deg");
459 props->untie("orientation/true-heading-deg");
461 props->untie("radar/in-range");
462 props->untie("radar/bearing-deg");
463 props->untie("radar/elevation-deg");
464 props->untie("radar/range-nm");
465 props->untie("radar/h-offset");
466 props->untie("radar/v-offset");
467 props->untie("radar/x-shift");
468 props->untie("radar/y-shift");
469 props->untie("radar/rotation");
470 props->untie("radar/ht-diff-ft");
472 props->untie("controls/lighting/nav-lights");
474 props->setBoolValue("/sim/controls/radar/", true);
478 double FGAIBase::UpdateRadar(FGAIManager* manager) {
479 bool control = fgGetBool("/sim/controls/radar", true);
481 if(!control) return 0;
483 double radar_range_ft2 = fgGetDouble("/instrumentation/radar/range");
484 bool force_on = fgGetBool("/instrumentation/radar/debug-mode", false);
485 radar_range_ft2 *= SG_NM_TO_METER * SG_METER_TO_FEET * 1.1; // + 10%
486 radar_range_ft2 *= radar_range_ft2;
488 double user_latitude = manager->get_user_latitude();
489 double user_longitude = manager->get_user_longitude();
490 double lat_range = fabs(pos.getLatitudeDeg() - user_latitude) * ft_per_deg_lat;
491 double lon_range = fabs(pos.getLongitudeDeg() - user_longitude) * ft_per_deg_lon;
492 double range_ft2 = lat_range*lat_range + lon_range*lon_range;
495 // Test whether the target is within radar range.
497 in_range = (range_ft2 && (range_ft2 <= radar_range_ft2));
499 if ( in_range || force_on ) {
500 props->setBoolValue("radar/in-range", true);
502 // copy values from the AIManager
503 double user_altitude = manager->get_user_altitude();
504 double user_heading = manager->get_user_heading();
505 double user_pitch = manager->get_user_pitch();
506 //double user_yaw = manager->get_user_yaw();
507 //double user_speed = manager->get_user_speed();
509 // calculate range to target in feet and nautical miles
510 double range_ft = sqrt( range_ft2 );
511 range = range_ft / 6076.11549;
513 // calculate bearing to target
514 if (pos.getLatitudeDeg() >= user_latitude) {
515 bearing = atan2(lat_range, lon_range) * SG_RADIANS_TO_DEGREES;
516 if (pos.getLongitudeDeg() >= user_longitude) {
517 bearing = 90.0 - bearing;
519 bearing = 270.0 + bearing;
522 bearing = atan2(lon_range, lat_range) * SG_RADIANS_TO_DEGREES;
523 if (pos.getLongitudeDeg() >= user_longitude) {
524 bearing = 180.0 - bearing;
526 bearing = 180.0 + bearing;
530 // This is an alternate way to compute bearing and distance which
531 // agrees with the original scheme within about 0.1 degrees.
533 // Point3D start( user_longitude * SGD_DEGREES_TO_RADIANS,
534 // user_latitude * SGD_DEGREES_TO_RADIANS, 0 );
535 // Point3D dest( pos.getLongitudeRad(), pos.getLatitudeRad(), 0 );
536 // double gc_bearing, gc_range;
537 // calc_gc_course_dist( start, dest, &gc_bearing, &gc_range );
538 // gc_range *= SG_METER_TO_NM;
539 // gc_bearing *= SGD_RADIANS_TO_DEGREES;
540 // printf("orig b = %.3f %.2f gc b= %.3f, %.2f\n",
541 // bearing, range, gc_bearing, gc_range);
543 // calculate look left/right to target, without yaw correction
544 horiz_offset = bearing - user_heading;
545 if (horiz_offset > 180.0) horiz_offset -= 360.0;
546 if (horiz_offset < -180.0) horiz_offset += 360.0;
548 // calculate elevation to target
549 elevation = atan2( altitude_ft - user_altitude, range_ft ) * SG_RADIANS_TO_DEGREES;
551 // calculate look up/down to target
552 vert_offset = elevation - user_pitch;
554 /* this calculation needs to be fixed, but it isn't important anyway
555 // calculate range rate
556 double recip_bearing = bearing + 180.0;
557 if (recip_bearing > 360.0) recip_bearing -= 360.0;
558 double my_horiz_offset = recip_bearing - hdg;
559 if (my_horiz_offset > 180.0) my_horiz_offset -= 360.0;
560 if (my_horiz_offset < -180.0) my_horiz_offset += 360.0;
561 rdot = (-user_speed * cos( horiz_offset * SG_DEGREES_TO_RADIANS ))
562 +(-speed * 1.686 * cos( my_horiz_offset * SG_DEGREES_TO_RADIANS ));
565 // now correct look left/right for yaw
566 // horiz_offset += user_yaw; // FIXME: WHY WOULD WE WANT TO ADD IN SIDE-SLIP HERE?
568 // calculate values for radar display
569 y_shift = range * cos( horiz_offset * SG_DEGREES_TO_RADIANS);
570 x_shift = range * sin( horiz_offset * SG_DEGREES_TO_RADIANS);
571 rotation = hdg - user_heading;
572 if (rotation < 0.0) rotation += 360.0;
573 ht_diff = altitude_ft - user_altitude;
581 * Getters and Setters
584 SGVec3d FGAIBase::getCartPosAt(const SGVec3d& _off) const {
585 // Transform that one to the horizontal local coordinate system.
586 SGQuatd hlTrans = SGQuatd::fromLonLat(pos);
588 // and postrotate the orientation of the AIModel wrt the horizontal
590 hlTrans *= SGQuatd::fromYawPitchRollDeg(hdg, pitch, roll);
592 // The offset converted to the usual body fixed coordinate system
593 // rotated to the earth fixed coordinates axis
594 SGVec3d off = hlTrans.backTransform(_off);
596 // Add the position offset of the AIModel to gain the earth centered position
597 SGVec3d cartPos = SGVec3d::fromGeod(pos);
599 return cartPos + off;
602 SGVec3d FGAIBase::getCartPos() const {
603 SGVec3d cartPos = SGVec3d::fromGeod(pos);
607 bool FGAIBase::getGroundElevationM(const SGGeod& pos, double& elev,
608 const SGMaterial** material) const {
609 return globals->get_scenery()->get_elevation_m(pos, elev, material,
613 double FGAIBase::_getCartPosX() const {
614 SGVec3d cartPos = getCartPos();
618 double FGAIBase::_getCartPosY() const {
619 SGVec3d cartPos = getCartPos();
623 double FGAIBase::_getCartPosZ() const {
624 SGVec3d cartPos = getCartPos();
628 void FGAIBase::_setLongitude( double longitude ) {
629 pos.setLongitudeDeg(longitude);
632 void FGAIBase::_setLatitude ( double latitude ) {
633 pos.setLatitudeDeg(latitude);
636 void FGAIBase::_setUserPos(){
637 userpos.setLatitudeDeg(manager->get_user_latitude());
638 userpos.setLongitudeDeg(manager->get_user_longitude());
639 userpos.setElevationM(manager->get_user_altitude() * SG_FEET_TO_METER);
642 void FGAIBase::_setSubID( int s ) {
646 bool FGAIBase::setParentNode() {
649 SG_LOG(SG_AI, SG_ALERT, "AIBase: " << _name
650 << " parent not set ");
654 const SGPropertyNode_ptr ai = fgGetNode("/ai/models", true);
656 for (int i = ai->nChildren() - 1; i >= -1; i--) {
657 SGPropertyNode_ptr model;
659 if (i < 0) { // last iteration: selected model
660 model = _selected_ac;
662 model = ai->getChild(i);
663 string path = ai->getPath();
664 const string name = model->getStringValue("name");
666 if (!model->nChildren()){
669 if (name == _parent) {
670 _selected_ac = model; // save selected model for last iteration
680 if (_selected_ac != 0){
681 const string name = _selected_ac->getStringValue("name");
684 SG_LOG(SG_AI, SG_ALERT, "AIBase: " << _name
685 << " parent not found: dying ");
692 double FGAIBase::_getLongitude() const {
693 return pos.getLongitudeDeg();
696 double FGAIBase::_getLatitude() const {
697 return pos.getLatitudeDeg();
700 double FGAIBase::_getElevationFt() const {
701 return pos.getElevationFt();
704 double FGAIBase::_getRdot() const {
708 double FGAIBase::_getVS_fps() const {
712 double FGAIBase::_get_speed_east_fps() const {
713 return speed_east_deg_sec * ft_per_deg_lon;
716 double FGAIBase::_get_speed_north_fps() const {
717 return speed_north_deg_sec * ft_per_deg_lat;
720 void FGAIBase::_setVS_fps( double _vs ) {
724 double FGAIBase::_getAltitude() const {
728 double FGAIBase::_getAltitudeAGL(SGGeod inpos, double start){
729 getGroundElevationM(SGGeod::fromGeodM(inpos, start),
730 _elevation_m, &_material);
731 return inpos.getElevationFt() - _elevation_m * SG_METER_TO_FEET;
734 bool FGAIBase::_getServiceable() const {
738 SGPropertyNode* FGAIBase::_getProps() const {
742 void FGAIBase::_setAltitude( double _alt ) {
746 bool FGAIBase::_isNight() {
747 return (fgGetFloat("/sim/time/sun-angle-rad") > 1.57);
750 bool FGAIBase::_getCollisionData() {
751 return _collision_reported;
754 bool FGAIBase::_getExpiryData() {
755 return _expiry_reported;
758 bool FGAIBase::_getImpactData() {
759 return _impact_reported;
762 double FGAIBase::_getImpactLat() const {
766 double FGAIBase::_getImpactLon() const {
770 double FGAIBase::_getImpactElevFt() const {
771 return _impact_elev * SG_METER_TO_FEET;
774 double FGAIBase::_getImpactPitch() const {
775 return _impact_pitch;
778 double FGAIBase::_getImpactRoll() const {
782 double FGAIBase::_getImpactHdg() const {
786 double FGAIBase::_getImpactSpeed() const {
787 return _impact_speed;
790 int FGAIBase::getID() const {
794 int FGAIBase::_getSubID() const {
798 double FGAIBase::_getSpeed() const {
802 double FGAIBase::_getRoll() const {
806 double FGAIBase::_getPitch() const {
810 double FGAIBase::_getHeading() const {
814 double FGAIBase::_getXOffset() const {
818 double FGAIBase::_getYOffset() const {
822 double FGAIBase::_getZOffset() const {
826 const char* FGAIBase::_getPath() const {
827 return model_path.c_str();
830 const char* FGAIBase::_getSMPath() const {
831 return _path.c_str();
834 const char* FGAIBase::_getName() const {
835 return _name.c_str();
838 const char* FGAIBase::_getCallsign() const {
839 return _callsign.c_str();
842 const char* FGAIBase::_getSubmodel() const {
843 return _submodel.c_str();
846 void FGAIBase::CalculateMach() {
847 // Calculate rho at altitude, using standard atmosphere
848 // For the temperature T and the pressure p,
849 double altitude = altitude_ft;
851 if (altitude < 36152) { // curve fits for the troposphere
852 T = 59 - 0.00356 * altitude;
853 p = 2116 * pow( ((T + 459.7) / 518.6) , 5.256);
854 } else if ( 36152 < altitude && altitude < 82345 ) { // lower stratosphere
856 p = 473.1 * pow( e , 1.73 - (0.000048 * altitude) );
857 } else { // upper stratosphere
858 T = -205.05 + (0.00164 * altitude);
859 p = 51.97 * pow( ((T + 459.7) / 389.98) , -11.388);
862 rho = p / (1718 * (T + 459.7));
864 // calculate the speed of sound at altitude
865 // a = sqrt ( g * R * (T + 459.7))
867 // a = speed of sound [ft/s]
868 // g = specific heat ratio, which is usually equal to 1.4
869 // R = specific gas constant, which equals 1716 ft-lb/slug/R
870 a = sqrt ( 1.4 * 1716 * (T + 459.7));
872 // calculate Mach number
875 // cout << "Speed(ft/s) "<< speed <<" Altitude(ft) "<< altitude << " Mach " << Mach << endl;
878 int FGAIBase::_newAIModelID() {
882 id++; // id = 0 is not allowed.