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.
29 #include <simgear/compiler.h>
31 #include <boost/foreach.hpp>
34 #include <osg/ref_ptr>
36 #include <osgDB/FileUtils>
38 #include <simgear/misc/sg_path.hxx>
39 #include <simgear/scene/model/modellib.hxx>
40 #include <simgear/scene/util/SGNodeMasks.hxx>
41 #include <simgear/debug/logstream.hxx>
42 #include <simgear/props/props.hxx>
44 #include <Main/globals.hxx>
45 #include <Scenery/scenery.hxx>
46 #include <Scripting/NasalSys.hxx>
47 #include <Scripting/NasalModelData.hxx>
48 #include <Sound/fg_fx.hxx>
51 #include "AIManager.hxx"
53 const char *default_model = "Models/Geometry/glider.ac";
54 const double FGAIBase::e = 2.71828183;
55 const double FGAIBase::lbs_to_slugs = 0.031080950172; //conversion factor
58 using namespace simgear;
60 class FGAIModelData : public simgear::SGModelData {
62 FGAIModelData(SGPropertyNode *root = NULL)
63 : _nasal( new FGNasalModelDataProxy(root) ),
66 _hasInteriorPath(false),
67 _interiorLoaded(false)
76 virtual FGAIModelData* clone() const { return new FGAIModelData(); }
78 /** osg callback, thread-safe */
79 void modelLoaded(const std::string& path, SGPropertyNode *prop, osg::Node *n)
81 // WARNING: Called in a separate OSG thread! Only use thread-safe stuff here...
85 if(prop->hasChild("interior-path")){
86 _interiorPath = prop->getStringValue("interior-path");
87 _hasInteriorPath = true;
90 _fxpath = prop->getStringValue("sound/path");
91 _nasal->modelLoaded(path, prop, n);
97 /** init hook to be called after model is loaded.
98 * Not thread-safe. Call from main thread only. */
99 void init(void) { _initialized = true; }
101 bool needInitilization(void) { return _ready && !_initialized;}
102 bool isInitialized(void) { return _initialized;}
103 inline std::string& get_sound_path() { return _fxpath;}
105 void setInteriorLoaded(const bool state) { _interiorLoaded = state;}
106 bool getInteriorLoaded(void) { return _interiorLoaded;}
107 bool hasInteriorPath(void) { return _hasInteriorPath;}
108 inline std::string& getInteriorPath() { return _interiorPath; }
110 std::auto_ptr<FGNasalModelDataProxy> _nasal;
115 std::string _interiorPath;
116 bool _hasInteriorPath;
117 bool _interiorLoaded;
120 FGAIBase::FGAIBase(object_type ot, bool enableHot) :
125 model_removed( fgGetNode("/ai/models/model-removed", true) ),
136 _refID( _newAIModelID() ),
142 tgt_heading = hdg = tgt_altitude_ft = tgt_speed = 0.0;
143 tgt_roll = roll = tgt_pitch = tgt_yaw = tgt_vs = vs = pitch = 0.0;
144 bearing = elevation = range = rdot = 0.0;
145 x_shift = y_shift = rotation = 0.0;
151 _impact_reported = false;
152 _collision_reported = false;
153 _expiry_reported = false;
165 pos = SGGeod::fromDeg(0, 0);
168 speed_north_deg_sec = 0;
169 speed_east_deg_sec = 0;
189 // explicitly disable HOT for (most) AI models
191 aip.getSceneGraph()->setNodeMask(~SG_NODEMASK_TERRAIN_BIT);
194 FGAIBase::~FGAIBase() {
195 // Unregister that one at the scenery manager
199 SGPropertyNode* parent = props->getParent();
202 model_removed->setStringValue(props->getPath());
212 /** Cleanly remove the model
213 * and let the scenery database pager do the clean-up work.
216 FGAIBase::removeModel()
221 FGScenery* pSceneryManager = globals->get_scenery();
224 osg::ref_ptr<osg::Object> temp = _model.get();
225 pSceneryManager->get_models_branch()->removeChild(aip.getSceneGraph());
226 // withdraw from SGModelPlacement and drop own reference (unref)
231 // pass it on to the pager, to be be deleted in the pager thread
232 pSceneryManager->getPager()->queueDeleteRequest(temp);
236 SG_LOG(SG_AI, SG_ALERT, "AIBase: Could not unload model. Missing scenery manager!");
240 void FGAIBase::readFromScenario(SGPropertyNode* scFileNode)
245 setPath(scFileNode->getStringValue("model",
246 fgGetString("/sim/multiplay/default-model", default_model)));
248 setHeading(scFileNode->getDoubleValue("heading", 0.0));
249 setSpeed(scFileNode->getDoubleValue("speed", 0.0));
250 setAltitude(scFileNode->getDoubleValue("altitude", 0.0));
251 setLongitude(scFileNode->getDoubleValue("longitude", 0.0));
252 setLatitude(scFileNode->getDoubleValue("latitude", 0.0));
253 setBank(scFileNode->getDoubleValue("roll", 0.0));
255 SGPropertyNode* submodels = scFileNode->getChild("submodels");
258 setServiceable(submodels->getBoolValue("serviceable", false));
259 setSMPath(submodels->getStringValue("path", ""));
264 void FGAIBase::update(double dt) {
266 if (_otype == otStatic)
269 if (_otype == otBallistic)
272 ft_per_deg_lat = 366468.96 - 3717.12 * cos(pos.getLatitudeRad());
273 ft_per_deg_lon = 365228.16 * cos(pos.getLatitudeRad());
277 // update model's audio sample values
278 _fx->set_position_geod( pos );
280 SGQuatd orient = SGQuatd::fromYawPitchRollDeg(hdg, pitch, roll);
281 _fx->set_orientation( orient );
284 velocity = SGVec3d( speed_north_deg_sec, speed_east_deg_sec,
286 _fx->set_velocity( velocity );
288 else if ((_modeldata)&&(_modeldata->needInitilization()))
290 // process deferred nasal initialization,
291 // which must be done in main thread
294 // sound initialization
295 if (fgGetBool("/sim/sound/aimodels/enabled",false))
297 const string& fxpath = _modeldata->get_sound_path();
300 props->setStringValue("sim/sound/path", fxpath.c_str());
302 // initialize the sound configuration
303 std::stringstream name;
306 _fx = new FGFX(name.str(), props);
315 void FGAIBase::updateInterior()
317 if(!_modeldata || !_modeldata->hasInteriorPath())
320 if(!_modeldata->getInteriorLoaded()){ // interior is not yet load
321 double d2 = dist(SGVec3d::fromGeod(pos), globals->get_aircraft_position_cart());
322 if(d2 <= _maxRangeInterior){ // if the AI is in-range we load the interior
323 _interior = SGModelLib::loadPagedModel(_modeldata->getInteriorPath(), props, _modeldata);
324 if(_interior.valid()){
325 _interior->setRange(0, 0.0, _maxRangeInterior);
326 aip.add(_interior.get());
327 _modeldata->setInteriorLoaded(true);
328 SG_LOG(SG_AI, SG_INFO, "AIBase: Loaded interior model " << _interior->getName());
334 /** update LOD properties of the model */
335 void FGAIBase::updateLOD()
337 double maxRangeDetail = fgGetDouble("/sim/rendering/static-lod/ai-detailed", 10000.0);
338 // double maxRangeBare = fgGetDouble("/sim/rendering/static-lod/ai-bare", 20000.0);
340 _maxRangeInterior = fgGetDouble("/sim/rendering/static-lod/ai-interior", 50.0);
343 if( maxRangeDetail == 0.0 )
346 _model->setRange(0, 0.0, FLT_MAX);
347 _model->setRange(1, FLT_MAX, FLT_MAX);
351 if( fgGetBool("/sim/rendering/static-lod/ai-range-mode-pixel", false ) )
353 _model->setRangeMode( osg::LOD::PIXEL_SIZE_ON_SCREEN );
354 _model->setRange(0, maxRangeDetail, 100000 );
356 _model->setRangeMode( osg::LOD:: DISTANCE_FROM_EYE_POINT);
357 _model->setRange(0, 0.0, maxRangeDetail);
363 void FGAIBase::Transform() {
366 aip.setVisible(true);
367 aip.setPosition(pos);
370 aip.setOrientation(0.0, pitch, hdg);
372 aip.setOrientation(roll, pitch, hdg);
376 aip.setVisible(false);
382 bool FGAIBase::init(bool search_in_AI_path)
386 SG_LOG(SG_AI, SG_ALERT, "AIBase: Cannot initialize a model multiple times! " << model_path);
391 if(search_in_AI_path)
393 BOOST_FOREACH(SGPath p, globals->get_data_paths("AI")) {
394 p.append(model_path);
399 } // of AI data paths iteration
400 } // of search in AI path
403 f = simgear::SGModelLib::findDataFile(model_path);
407 f = fgGetString("/sim/multiplay/default-model", default_model);
411 props->addChild("type")->setStringValue("AI");
412 _modeldata = new FGAIModelData(props);
413 _model= SGModelLib::loadPagedModel(f, props, _modeldata);
415 _model->setName("AI-model range animation node");
417 // _model->setCenterMode(osg::LOD::USE_BOUNDING_SPHERE_CENTER);
418 // _model->setRangeMode(osg::LOD::DISTANCE_FROM_EYE_POINT);
420 // We really need low-resolution versions of AI/MP aircraft.
421 // Or at least dummy "stubs" with some default silhouette.
422 // _model->addChild( SGModelLib::loadPagedModel(fgGetString("/sim/multiplay/default-model", default_model),
423 // props, new FGNasalModelData(props)), FLT_MAX, FLT_MAX);
427 if (_model.valid() && _initialized == false) {
428 aip.init( _model.get() );
429 aip.setVisible(true);
431 globals->get_scenery()->get_models_branch()->addChild(aip.getSceneGraph());
434 SG_LOG(SG_AI, SG_DEBUG, "AIBase: Loaded model " << model_path);
436 } else if (!model_path.empty()) {
437 SG_LOG(SG_AI, SG_WARN, "AIBase: Could not load model " << model_path);
438 // not properly installed...
446 void FGAIBase::initModel()
448 if (_model.valid()) {
451 props->setStringValue("submodels/path", _path.c_str());
452 SG_LOG(SG_AI, SG_DEBUG, "AIBase: submodels/path " << _path);
456 props->setStringValue("parent-name", _parent.c_str());
459 fgSetString("/ai/models/model-added", props->getPath().c_str());
460 } else if (!model_path.empty()) {
461 SG_LOG(SG_AI, SG_WARN, "AIBase: Could not load model " << model_path);
468 bool FGAIBase::isa( object_type otype ) {
469 return otype == _otype;
473 void FGAIBase::bind() {
474 _tiedProperties.setRoot(props);
475 tie("id", SGRawValueMethods<FGAIBase,int>(*this,
477 tie("velocities/true-airspeed-kt", SGRawValuePointer<double>(&speed));
478 tie("velocities/vertical-speed-fps",
479 SGRawValueMethods<FGAIBase,double>(*this,
480 &FGAIBase::_getVS_fps,
481 &FGAIBase::_setVS_fps));
483 tie("position/altitude-ft",
484 SGRawValueMethods<FGAIBase,double>(*this,
485 &FGAIBase::_getAltitude,
486 &FGAIBase::_setAltitude));
487 tie("position/latitude-deg",
488 SGRawValueMethods<FGAIBase,double>(*this,
489 &FGAIBase::_getLatitude,
490 &FGAIBase::_setLatitude));
491 tie("position/longitude-deg",
492 SGRawValueMethods<FGAIBase,double>(*this,
493 &FGAIBase::_getLongitude,
494 &FGAIBase::_setLongitude));
496 tie("position/global-x",
497 SGRawValueMethods<FGAIBase,double>(*this,
498 &FGAIBase::_getCartPosX,
500 tie("position/global-y",
501 SGRawValueMethods<FGAIBase,double>(*this,
502 &FGAIBase::_getCartPosY,
504 tie("position/global-z",
505 SGRawValueMethods<FGAIBase,double>(*this,
506 &FGAIBase::_getCartPosZ,
509 SGRawValueMethods<FGAIBase,const char*>(*this,
510 &FGAIBase::_getCallsign,
513 tie("orientation/pitch-deg", SGRawValuePointer<double>(&pitch));
514 tie("orientation/roll-deg", SGRawValuePointer<double>(&roll));
515 tie("orientation/true-heading-deg", SGRawValuePointer<double>(&hdg));
517 tie("radar/in-range", SGRawValuePointer<bool>(&in_range));
518 tie("radar/bearing-deg", SGRawValuePointer<double>(&bearing));
519 tie("radar/elevation-deg", SGRawValuePointer<double>(&elevation));
520 tie("radar/range-nm", SGRawValuePointer<double>(&range));
521 tie("radar/h-offset", SGRawValuePointer<double>(&horiz_offset));
522 tie("radar/v-offset", SGRawValuePointer<double>(&vert_offset));
523 tie("radar/x-shift", SGRawValuePointer<double>(&x_shift));
524 tie("radar/y-shift", SGRawValuePointer<double>(&y_shift));
525 tie("radar/rotation", SGRawValuePointer<double>(&rotation));
526 tie("radar/ht-diff-ft", SGRawValuePointer<double>(&ht_diff));
527 tie("subID", SGRawValuePointer<int>(&_subID));
528 tie("controls/lighting/nav-lights", SGRawValueFunctions<bool>(_isNight));
530 props->setBoolValue("controls/lighting/beacon", true);
531 props->setBoolValue("controls/lighting/strobe", true);
532 props->setBoolValue("controls/glide-path", true);
534 props->setStringValue("controls/flight/lateral-mode", "roll");
535 props->setDoubleValue("controls/flight/target-hdg", hdg);
536 props->setDoubleValue("controls/flight/target-roll", roll);
538 props->setStringValue("controls/flight/longitude-mode", "alt");
539 props->setDoubleValue("controls/flight/target-alt", altitude_ft);
540 props->setDoubleValue("controls/flight/target-pitch", pitch);
542 props->setDoubleValue("controls/flight/target-spd", speed);
544 props->setBoolValue("sim/sound/avionics/enabled", false);
545 props->setDoubleValue("sim/sound/avionics/volume", 0.0);
546 props->setBoolValue("sim/sound/avionics/external-view", false);
547 props->setBoolValue("sim/current-view/internal", false);
550 void FGAIBase::unbind() {
551 _tiedProperties.Untie();
553 props->setBoolValue("/sim/controls/radar", true);
558 void FGAIBase::removeSoundFx() {
559 // drop reference to sound effects now
562 // must remove explicitly - since the sound manager also keeps a reference
564 // now drop last reference - kill the object
569 double FGAIBase::UpdateRadar(FGAIManager* manager)
571 bool control = fgGetBool("/sim/controls/radar", true);
573 if(!control) return 0;
575 double radar_range_m = fgGetDouble("/instrumentation/radar/range");
576 bool force_on = fgGetBool("/instrumentation/radar/debug-mode", false);
577 radar_range_m *= SG_NM_TO_METER * 1.1; // + 10%
578 radar_range_m *= radar_range_m; // squared
580 double d2 = distSqr(SGVec3d::fromGeod(pos), globals->get_aircraft_position_cart());
581 double range_ft = sqrt(d2) * SG_METER_TO_FEET;
583 if (!force_on && (d2 > radar_range_m)) {
584 return range_ft * range_ft;
587 props->setBoolValue("radar/in-range", true);
589 // copy values from the AIManager
590 double user_heading = manager->get_user_heading();
591 double user_pitch = manager->get_user_pitch();
593 range = range_ft * SG_FEET_TO_METER * SG_METER_TO_NM;
595 // calculate bearing to target
596 bearing = SGGeodesy::courseDeg(globals->get_aircraft_position(), pos);
598 // calculate look left/right to target, without yaw correction
599 horiz_offset = bearing - user_heading;
600 SG_NORMALIZE_RANGE(horiz_offset, -180.0, 180.0);
602 // calculate elevation to target
603 ht_diff = altitude_ft - globals->get_aircraft_position().getElevationFt();
604 elevation = atan2( ht_diff, range_ft ) * SG_RADIANS_TO_DEGREES;
606 // calculate look up/down to target
607 vert_offset = elevation - user_pitch;
609 /* this calculation needs to be fixed, but it isn't important anyway
610 // calculate range rate
611 double recip_bearing = bearing + 180.0;
612 if (recip_bearing > 360.0) recip_bearing -= 360.0;
613 double my_horiz_offset = recip_bearing - hdg;
614 if (my_horiz_offset > 180.0) my_horiz_offset -= 360.0;
615 if (my_horiz_offset < -180.0) my_horiz_offset += 360.0;
616 rdot = (-user_speed * cos( horiz_offset * SG_DEGREES_TO_RADIANS ))
617 +(-speed * 1.686 * cos( my_horiz_offset * SG_DEGREES_TO_RADIANS ));
620 // now correct look left/right for yaw
621 // horiz_offset += user_yaw; // FIXME: WHY WOULD WE WANT TO ADD IN SIDE-SLIP HERE?
623 // calculate values for radar display
624 y_shift = range * cos( horiz_offset * SG_DEGREES_TO_RADIANS);
625 x_shift = range * sin( horiz_offset * SG_DEGREES_TO_RADIANS);
627 rotation = hdg - user_heading;
628 SG_NORMALIZE_RANGE(rotation, 0.0, 360.0);
630 return range_ft * range_ft;
634 * Getters and Setters
637 SGVec3d FGAIBase::getCartPosAt(const SGVec3d& _off) const {
638 // Transform that one to the horizontal local coordinate system.
639 SGQuatd hlTrans = SGQuatd::fromLonLat(pos);
641 // and postrotate the orientation of the AIModel wrt the horizontal
643 hlTrans *= SGQuatd::fromYawPitchRollDeg(hdg, pitch, roll);
645 // The offset converted to the usual body fixed coordinate system
646 // rotated to the earth fixed coordinates axis
647 SGVec3d off = hlTrans.backTransform(_off);
649 // Add the position offset of the AIModel to gain the earth centered position
650 SGVec3d cartPos = SGVec3d::fromGeod(pos);
652 return cartPos + off;
655 SGVec3d FGAIBase::getCartPos() const {
656 SGVec3d cartPos = SGVec3d::fromGeod(pos);
660 bool FGAIBase::getGroundElevationM(const SGGeod& pos, double& elev,
661 const simgear::BVHMaterial** material) const {
662 return globals->get_scenery()->get_elevation_m(pos, elev, material,
666 double FGAIBase::_getCartPosX() const {
667 SGVec3d cartPos = getCartPos();
671 double FGAIBase::_getCartPosY() const {
672 SGVec3d cartPos = getCartPos();
676 double FGAIBase::_getCartPosZ() const {
677 SGVec3d cartPos = getCartPos();
681 void FGAIBase::_setLongitude( double longitude ) {
682 pos.setLongitudeDeg(longitude);
685 void FGAIBase::_setLatitude ( double latitude ) {
686 pos.setLatitudeDeg(latitude);
689 void FGAIBase::_setSubID( int s ) {
693 bool FGAIBase::setParentNode() {
696 SG_LOG(SG_AI, SG_ALERT, "AIBase: " << _name
697 << " parent not set ");
701 const SGPropertyNode_ptr ai = fgGetNode("/ai/models", true);
703 for (int i = ai->nChildren() - 1; i >= -1; i--) {
704 SGPropertyNode_ptr model;
706 if (i < 0) { // last iteration: selected model
707 model = _selected_ac;
709 model = ai->getChild(i);
710 //const string& path = ai->getPath();
711 const string name = model->getStringValue("name");
713 if (!model->nChildren()){
716 if (name == _parent) {
717 _selected_ac = model; // save selected model for last iteration
727 if (_selected_ac != 0){
728 const string name = _selected_ac->getStringValue("name");
731 SG_LOG(SG_AI, SG_ALERT, "AIBase: " << _name
732 << " parent not found: dying ");
739 double FGAIBase::_getLongitude() const {
740 return pos.getLongitudeDeg();
743 double FGAIBase::_getLatitude() const {
744 return pos.getLatitudeDeg();
747 double FGAIBase::_getElevationFt() const {
748 return pos.getElevationFt();
751 double FGAIBase::_getRdot() const {
755 double FGAIBase::_getVS_fps() const {
759 double FGAIBase::_get_speed_east_fps() const {
760 return speed_east_deg_sec * ft_per_deg_lon;
763 double FGAIBase::_get_speed_north_fps() const {
764 return speed_north_deg_sec * ft_per_deg_lat;
767 void FGAIBase::_setVS_fps( double _vs ) {
771 double FGAIBase::_getAltitude() const {
775 double FGAIBase::_getAltitudeAGL(SGGeod inpos, double start){
776 getGroundElevationM(SGGeod::fromGeodM(inpos, start),
778 return inpos.getElevationFt() - _elevation_m * SG_METER_TO_FEET;
781 bool FGAIBase::_getServiceable() const {
785 SGPropertyNode* FGAIBase::_getProps() const {
789 void FGAIBase::_setAltitude( double _alt ) {
793 bool FGAIBase::_isNight() {
794 return (fgGetFloat("/sim/time/sun-angle-rad") > 1.57);
797 bool FGAIBase::_getCollisionData() {
798 return _collision_reported;
801 bool FGAIBase::_getExpiryData() {
802 return _expiry_reported;
805 bool FGAIBase::_getImpactData() {
806 return _impact_reported;
809 double FGAIBase::_getImpactLat() const {
813 double FGAIBase::_getImpactLon() const {
817 double FGAIBase::_getImpactElevFt() const {
818 return _impact_elev * SG_METER_TO_FEET;
821 double FGAIBase::_getImpactPitch() const {
822 return _impact_pitch;
825 double FGAIBase::_getImpactRoll() const {
829 double FGAIBase::_getImpactHdg() const {
833 double FGAIBase::_getImpactSpeed() const {
834 return _impact_speed;
837 int FGAIBase::getID() const {
841 int FGAIBase::_getSubID() const {
845 double FGAIBase::_getSpeed() const {
849 double FGAIBase::_getRoll() const {
853 double FGAIBase::_getPitch() const {
857 double FGAIBase::_getHeading() const {
861 double FGAIBase::_getXOffset() const {
865 double FGAIBase::_getYOffset() const {
869 double FGAIBase::_getZOffset() const {
873 const char* FGAIBase::_getPath() const {
874 return model_path.c_str();
877 const char* FGAIBase::_getSMPath() const {
878 return _path.c_str();
881 const char* FGAIBase::_getName() const {
882 return _name.c_str();
885 const char* FGAIBase::_getCallsign() const {
886 return _callsign.c_str();
889 const char* FGAIBase::_getSubmodel() const {
890 return _submodel.c_str();
893 void FGAIBase::CalculateMach() {
894 // Calculate rho at altitude, using standard atmosphere
895 // For the temperature T and the pressure p,
896 double altitude = altitude_ft;
898 if (altitude < 36152) { // curve fits for the troposphere
899 T = 59 - 0.00356 * altitude;
900 p = 2116 * pow( ((T + 459.7) / 518.6) , 5.256);
901 } else if ( 36152 < altitude && altitude < 82345 ) { // lower stratosphere
903 p = 473.1 * pow( e , 1.73 - (0.000048 * altitude) );
904 } else { // upper stratosphere
905 T = -205.05 + (0.00164 * altitude);
906 p = 51.97 * pow( ((T + 459.7) / 389.98) , -11.388);
909 rho = p / (1718 * (T + 459.7));
911 // calculate the speed of sound at altitude
912 // a = sqrt ( g * R * (T + 459.7))
914 // a = speed of sound [ft/s]
915 // g = specific heat ratio, which is usually equal to 1.4
916 // R = specific gas constant, which equals 1716 ft-lb/slug/R
917 a = sqrt ( 1.4 * 1716 * (T + 459.7));
919 // calculate Mach number
922 // cout << "Speed(ft/s) "<< speed <<" Altitude(ft) "<< altitude << " Mach " << Mach << endl;
925 int FGAIBase::_newAIModelID() {
929 id++; // id = 0 is not allowed.
934 bool FGAIBase::isValid() {
935 //Either no flightplan or it is valid
936 return !fp || fp->isValidPlan();