src/AIModel/AIGroundVehicle.cxx

   1 // FGAIGroundVehicle - FGAIShip-derived class creates an AI Ground Vehicle
   2 // by adding a ground following utility
   3 //
   4 // Written by Vivian Meazza, started August 2009.
   5 // - vivian.meazza at lineone.net
   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 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <simgear/sg_inlines.h>
  26
  27 #include <Main/viewer.hxx>
  28 #include <Scenery/scenery.hxx>
  29 #include <Scenery/tilemgr.hxx>
  30 #include <Airports/dynamics.hxx>
  31
  32 #include "AIGroundVehicle.hxx"
  33
  34 FGAIGroundVehicle::FGAIGroundVehicle() :
  35 FGAIShip(otGroundVehicle),
  36
  37 _pitch(0),
  38 _pitch_deg(0),
  39 _speed_kt(0),
  40 _range_ft(0),
  41 _relbrg (0),
  42 _parent_speed(0),
  43 _parent_x_offset(0),
  44 _parent_y_offset(0),
  45 _parent_z_offset(0),
  46 _dt_count(0),
  47 _next_run(0),
  48 _break_count(0)
  49
  50 {
  51     invisible = false;
  52     _parent = "";
  53 }
  54
  55 FGAIGroundVehicle::~FGAIGroundVehicle() {}
  56
  57 void FGAIGroundVehicle::readFromScenario(SGPropertyNode* scFileNode) {
  58     if (!scFileNode)
  59         return;
  60
  61     FGAIShip::readFromScenario(scFileNode);
  62
  63     setName(scFileNode->getStringValue("name", "groundvehicle"));
  64     setParentName(scFileNode->getStringValue("parent", ""));
  65     setNoRoll(scFileNode->getBoolValue("no-roll", true));
  66     setContactX1offset(scFileNode->getDoubleValue("contact-x1-offset", 0.0));
  67     setContactX2offset(scFileNode->getDoubleValue("contact-x2-offset", 0.0));
  68     setXOffset(scFileNode->getDoubleValue("hitch-x-offset", 35.0));
  69     setYOffset(scFileNode->getDoubleValue("hitch-y-offset", 0.0));
  70     setZOffset(scFileNode->getDoubleValue("hitch-z-offset", 0.0));
  71     setPitchoffset(scFileNode->getDoubleValue("pitch-offset", 0.0));
  72     setRolloffset(scFileNode->getDoubleValue("roll-offset", 0.0));
  73     setYawoffset(scFileNode->getDoubleValue("yaw-offset", 0.0));
  74     setPitchCoeff(scFileNode->getDoubleValue("pitch-coefficient", 0.1));
  75     setElevCoeff(scFileNode->getDoubleValue("elevation-coefficient", 0.25));
  76     setTowAngleGain(scFileNode->getDoubleValue("tow-angle-gain", 1.0));
  77     setTowAngleLimit(scFileNode->getDoubleValue("tow-angle-limit-deg", 2.0));
  78     setInitialTunnel(scFileNode->getBoolValue("tunnel", false));
  79     //we may need these later for towed vehicles
  80     //    setSubID(scFileNode->getIntValue("SubID", 0));
  81     //    setGroundOffset(scFileNode->getDoubleValue("ground-offset", 0.0));
  82     //    setFormate(scFileNode->getBoolValue("formate", true));
  83 }
  84
  85 void FGAIGroundVehicle::bind() {
  86     FGAIShip::bind();
  87
  88     props->tie("controls/constants/elevation-coeff",
  89         SGRawValuePointer<double>(&_elevation_coeff));
  90     props->tie("controls/constants/pitch-coeff",
  91         SGRawValuePointer<double>(&_pitch_coeff));
  92     props->tie("position/ht-AGL-ft",
  93         SGRawValuePointer<double>(&_ht_agl_ft));
  94     props->tie("hitch/rel-bearing-deg",
  95          SGRawValuePointer<double>(&_relbrg));
  96     props->tie("hitch/tow-angle-deg",
  97          SGRawValuePointer<double>(&_tow_angle));
  98     props->tie("hitch/range-ft",
  99         SGRawValuePointer<double>(&_range_ft));
 100     props->tie("hitch/x-offset-ft",
 101         SGRawValuePointer<double>(&_x_offset));
 102     props->tie("hitch/y-offset-ft",
 103         SGRawValuePointer<double>(&_y_offset));
 104     props->tie("hitch/z-offset-ft",
 105         SGRawValuePointer<double>(&_z_offset));
 106     props->tie("hitch/parent-x-offset-ft",
 107         SGRawValuePointer<double>(&_parent_x_offset));
 108     props->tie("hitch/parent-y-offset-ft",
 109         SGRawValuePointer<double>(&_parent_y_offset));
 110     props->tie("hitch/parent-z-offset-ft",
 111         SGRawValuePointer<double>(&_parent_z_offset));
 112     props->tie("controls/constants/tow-angle/gain",
 113         SGRawValuePointer<double>(&_tow_angle_gain));
 114     props->tie("controls/constants/tow-angle/limit-deg",
 115         SGRawValuePointer<double>(&_tow_angle_limit));
 116     props->tie("controls/contact-x1-offset-ft",
 117         SGRawValuePointer<double>(&_contact_x1_offset));
 118     props->tie("controls/contact-x2-offset-ft",
 119         SGRawValuePointer<double>(&_contact_x2_offset));
 120 }
 121
 122 void FGAIGroundVehicle::unbind() {
 123     FGAIShip::unbind();
 124
 125     props->untie("controls/constants/elevation-coeff");
 126     props->untie("controls/constants/pitch-coeff");
 127     props->untie("position/ht-AGL-ft");
 128     props->untie("hitch/rel-bearing-deg");
 129     props->untie("hitch/tow-angle-deg");
 130     props->untie("hitch/range-ft");
 131     props->untie("hitch/x-offset-ft");
 132     props->untie("hitch/y-offset-ft");
 133     props->untie("hitch/z-offset-ft");
 134     props->untie("hitch/parent-x-offset-ft");
 135     props->untie("hitch/parent-y-offset-ft");
 136     props->untie("hitch/parent-y-offset-ft");
 137     props->untie("controls/constants/tow-angle/gain");
 138     props->untie("controls/constants/tow-angle/limit-deg");
 139     props->untie("controls/contact-x1-offset-ft");
 140     props->untie("controls/contact-x2-offset-ft");
 141 }
 142
 143 bool FGAIGroundVehicle::init(bool search_in_AI_path) {
 144     if (!FGAIShip::init(search_in_AI_path))
 145         return false;
 146
 147     invisible = false;
 148     _limit = 200;
 149     no_roll = true;
 150
 151     props->setStringValue("controls/parent-name", _parent.c_str());
 152
 153     if (setParentNode()){
 154         _parent_x_offset = _selected_ac->getDoubleValue("hitch/x-offset-ft");
 155         _parent_y_offset = _selected_ac->getDoubleValue("hitch/y-offset-ft");
 156         _parent_z_offset = _selected_ac->getDoubleValue("hitch/z-offset-ft");
 157         _hitch_x_offset_m = _selected_ac->getDoubleValue("hitch/x-offset-ft")
 158             * SG_FEET_TO_METER;
 159         _hitch_y_offset_m = _selected_ac->getDoubleValue("hitch/y-offset-ft")
 160             * SG_FEET_TO_METER;
 161         _hitch_z_offset_m = _selected_ac->getDoubleValue("hitch/z-offset-ft")
 162             * SG_FEET_TO_METER;
 163         setParent();
 164     }
 165
 166     return true;
 167 }
 168
 169 void FGAIGroundVehicle::update(double dt) {
 170     //    SG_LOG(SG_GENERAL, SG_ALERT, "updating GroundVehicle: " << _name );
 171     FGAIShip::update(dt);
 172
 173     RunGroundVehicle(dt);
 174 }
 175
 176 void FGAIGroundVehicle::setNoRoll(bool nr) {
 177     no_roll = nr;
 178 }
 179
 180 void FGAIGroundVehicle::setContactX1offset(double x1) {
 181     _contact_x1_offset = x1;
 182 }
 183
 184 void FGAIGroundVehicle::setContactX2offset(double x2) {
 185     _contact_x2_offset = x2;
 186 }
 187
 188 void FGAIGroundVehicle::setXOffset(double x) {
 189     _x_offset = x;
 190 }
 191
 192 void FGAIGroundVehicle::setYOffset(double y) {
 193     _y_offset = y;
 194 }
 195
 196 void FGAIGroundVehicle::setZOffset(double z) {
 197     _z_offset = z;
 198 }
 199
 200 void FGAIGroundVehicle::setPitchCoeff(double pc) {
 201     _pitch_coeff = pc;
 202 }
 203
 204 void FGAIGroundVehicle::setElevCoeff(double ec) {
 205     _elevation_coeff = ec;
 206 }
 207
 208 void FGAIGroundVehicle::setTowAngleGain(double g) {
 209     _tow_angle_gain = g;
 210 }
 211
 212 void FGAIGroundVehicle::setTowAngleLimit(double l) {
 213     _tow_angle_limit = l;
 214 }
 215
 216 void FGAIGroundVehicle::setElevation(double h, double dt, double coeff){
 217     double c = dt / (coeff + dt);
 218     _elevation_ft = (h * c) + (_elevation_ft * (1 - c));
 219 }
 220
 221 void FGAIGroundVehicle::setPitch(double p, double dt, double coeff){
 222     double c = dt / (coeff + dt);
 223     _pitch_deg = (p * c) + (_pitch_deg * (1 - c));
 224 }
 225
 226 void FGAIGroundVehicle::setTowAngle(double ta, double dt, double coeff){
 227     ta *= _tow_angle_gain;
 228     double factor = -0.0045 * speed + 1;
 229     double limit = _tow_angle_limit * factor;
 230 //      cout << "speed "<< speed << " _factor " << _factor<<" " <<_tow_angle_limit<< endl;
 231      _tow_angle = pow(ta,2) * sign(ta) * factor;
 232     SG_CLAMP_RANGE(_tow_angle, -limit, limit);
 233 }
 234
 235 bool FGAIGroundVehicle::getPitch() {
 236
 237     if (!_tunnel){
 238         double vel = props->getDoubleValue("velocities/true-airspeed-kt", 0);
 239         double contact_offset_x1_m = _contact_x1_offset * SG_FEET_TO_METER;
 240         double contact_offset_x2_m = _contact_x2_offset * SG_FEET_TO_METER;
 241         double _z_offset_m = _parent_z_offset * SG_FEET_TO_METER;
 242
 243         SGVec3d front(-contact_offset_x1_m, 0, 0);
 244         SGVec3d rear(-contact_offset_x2_m, 0, 0);
 245         SGVec3d Front = getCartPosAt(front);
 246         SGVec3d Rear = getCartPosAt(rear);
 247
 248         SGGeod geodFront = SGGeod::fromCart(Front);
 249         SGGeod geodRear = SGGeod::fromCart(Rear);
 250
 251         double front_elev_m = 0;
 252         double rear_elev_m = 0;
 253         double elev_front = 0;
 254         double elev_rear = 0;
 255         //double max_alt = 10000;
 256
 257         if (globals->get_scenery()->get_elevation_m(SGGeod::fromGeodM(geodFront, 3000),
 258             elev_front, &_material, 0)){
 259                 front_elev_m = elev_front + _z_offset_m;
 260         } else
 261             return false;
 262
 263         if (globals->get_scenery()->get_elevation_m(SGGeod::fromGeodM(geodRear, 3000),
 264             elev_rear, &_material, 0)){
 265                 rear_elev_m = elev_rear;
 266         } else
 267             return false;
 268
 269         if (vel >= 0){
 270             double diff = front_elev_m - rear_elev_m;
 271             _pitch = atan2 (diff,
 272                 fabs(contact_offset_x1_m) + fabs(contact_offset_x2_m)) * SG_RADIANS_TO_DEGREES;
 273             _elevation = (rear_elev_m + diff/2) * SG_METER_TO_FEET;
 274         } else {
 275             double diff = rear_elev_m - front_elev_m;
 276             _pitch = atan2 (diff,
 277                 fabs(contact_offset_x1_m) + fabs(contact_offset_x2_m)) * SG_RADIANS_TO_DEGREES;
 278             _elevation = (front_elev_m + diff/2) * SG_METER_TO_FEET;
 279             _pitch = -_pitch;
 280         }
 281
 282     } else {
 283
 284         if (prev->altitude == 0 || curr->altitude == 0) return false;
 285
 286         static double distance;
 287         static double d_alt;
 288         static double curr_alt;
 289         static double prev_alt;
 290
 291         if (_new_waypoint){
 292             //cout << "new waypoint, calculating pitch " << endl;
 293             curr_alt = curr->altitude;
 294             prev_alt = prev->altitude;
 295             //cout << "prev_alt" <<prev_alt << endl;
 296             d_alt = (curr_alt - prev_alt) * SG_METER_TO_FEET;
 297             //_elevation = prev->altitude;
 298             distance = SGGeodesy::distanceM(SGGeod::fromDeg(prev->longitude, prev->latitude),
 299             SGGeod::fromDeg(curr->longitude, curr->latitude));
 300             _pitch = atan2(d_alt, distance * SG_METER_TO_FEET) * SG_RADIANS_TO_DEGREES;
 301             //cout << "new waypoint, calculating pitch " <<  _pitch <<
 302             //    " " << _pitch_offset << " " << _elevation <<endl;
 303         }
 304
 305         double distance_to_go = SGGeodesy::distanceM(SGGeod::fromDeg(pos.getLongitudeDeg(), pos.getLatitudeDeg()),
 306             SGGeod::fromDeg(curr->longitude, curr->latitude));
 307
 308         /*cout << "tunnel " << _tunnel
 309              << " distance prev & curr " << prev->name << " " << curr->name << " " << distance * SG_METER_TO_FEET
 310              << " distance to go " << distance_to_go * SG_METER_TO_FEET
 311              << " d_alt ft " << d_alt
 312              << endl;*/
 313
 314         if (distance_to_go > distance)
 315             _elevation = prev_alt;
 316         else
 317             _elevation = curr_alt - (tan(_pitch * SG_DEGREES_TO_RADIANS) * distance_to_go * SG_METER_TO_FEET);
 318
 319     }
 320
 321     return true;
 322 }
 323
 324 void FGAIGroundVehicle::setParent(){
 325
 326     double lat = _selected_ac->getDoubleValue("position/latitude-deg");
 327     double lon = _selected_ac->getDoubleValue("position/longitude-deg");
 328     double elevation = _selected_ac->getDoubleValue("position/altitude-ft");
 329
 330     _selectedpos.setLatitudeDeg(lat);
 331     _selectedpos.setLongitudeDeg(lon);
 332     _selectedpos.setElevationFt(elevation);
 333
 334     _parent_speed = _selected_ac->getDoubleValue("velocities/true-airspeed-kt");
 335
 336     SGVec3d rear_hitch(-_hitch_x_offset_m, _hitch_y_offset_m, 0);
 337     SGVec3d RearHitch = getCartHitchPosAt(rear_hitch);
 338
 339     SGGeod rearpos = SGGeod::fromCart(RearHitch);
 340
 341     double user_lat = rearpos.getLatitudeDeg();
 342     double user_lon = rearpos.getLongitudeDeg();
 343
 344     double range, bearing;
 345
 346     calcRangeBearing(pos.getLatitudeDeg(), pos.getLongitudeDeg(),
 347         user_lat, user_lon, range, bearing);
 348     _range_ft = range * 6076.11549;
 349     _relbrg = calcRelBearingDeg(bearing, hdg);
 350 }
 351
 352 void FGAIGroundVehicle::calcRangeBearing(double lat, double lon, double lat2, double lon2,
 353                             double &range, double &bearing) const
 354 {
 355     // calculate the bearing and range of the second pos from the first
 356     double az2, distance;
 357     geo_inverse_wgs_84(lat, lon, lat2, lon2, &bearing, &az2, &distance);
 358     range = distance * SG_METER_TO_NM;
 359 }
 360
 361
 362 SGVec3d FGAIGroundVehicle::getCartHitchPosAt(const SGVec3d& _off) const {
 363     double hdg = _selected_ac->getDoubleValue("orientation/true-heading-deg");
 364     double pitch = _selected_ac->getDoubleValue("orientation/pitch-deg");
 365     double roll = _selected_ac->getDoubleValue("orientation/roll-deg");
 366
 367     // Transform that one to the horizontal local coordinate system.
 368     SGQuatd hlTrans = SGQuatd::fromLonLat(_selectedpos);
 369
 370     // and postrotate the orientation of the AIModel wrt the horizontal
 371     // local frame
 372     hlTrans *= SGQuatd::fromYawPitchRollDeg(hdg, pitch, roll);
 373
 374     // The offset converted to the usual body fixed coordinate system
 375     // rotated to the earth fiexed coordinates axis
 376     SGVec3d off = hlTrans.backTransform(_off);
 377
 378     // Add the position offset of the AIModel to gain the earth centered position
 379     SGVec3d cartPos = SGVec3d::fromGeod(_selectedpos);
 380
 381     return cartPos + off;
 382 }
 383
 384 void FGAIGroundVehicle::AdvanceFP(){
 385
 386     double count = 0;
 387     string parent_next_name =_selected_ac->getStringValue("waypoint/name-next");
 388
 389     while(fp->getNextWaypoint() != 0 && fp->getNextWaypoint()->name != "END" && count < 5){
 390         SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 391             <<" advancing waypoint to: " << parent_next_name);
 392
 393         if (fp->getNextWaypoint()->name == parent_next_name){
 394             SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 395                 << " not setting waypoint already at: " << fp->getNextWaypoint()->name);
 396             return;
 397         }
 398
 399         prev = curr;
 400         fp->IncrementWaypoint(false);
 401         curr = fp->getCurrentWaypoint();
 402         next = fp->getNextWaypoint();
 403
 404         if (fp->getNextWaypoint()->name == parent_next_name){
 405             SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 406             << " waypoint set to: " << fp->getNextWaypoint()->name);
 407             return;
 408         }
 409
 410         count++;
 411
 412     }// end while loop
 413
 414     while(fp->getPreviousWaypoint() != 0 && fp->getPreviousWaypoint()->name != "END"
 415         && count > -10){
 416             SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 417             << " retreating waypoint to: " << parent_next_name
 418             << " at: " << fp->getNextWaypoint()->name);
 419
 420         if (fp->getNextWaypoint()->name == parent_next_name){
 421             SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 422                 << " not setting waypoint already at:" << fp->getNextWaypoint()->name );
 423             return;
 424         }
 425
 426         prev = curr;
 427         fp->DecrementWaypoint(false);
 428         curr = fp->getCurrentWaypoint();
 429         next = fp->getNextWaypoint();
 430
 431         if (fp->getNextWaypoint()->name == parent_next_name){
 432             SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 433             << " waypoint set to: " << fp->getNextWaypoint()->name);
 434             return;
 435         }
 436
 437         count--;
 438
 439     }// end while loop
 440 }
 441
 442 void FGAIGroundVehicle::setTowSpeed(){
 443
 444     //double diff = _range_ft - _x_offset;
 445     double  x = 0;
 446
 447     if (_range_ft > _x_offset * 3) x = 50;
 448
 449     if (_relbrg < -90 || _relbrg > 90){
 450         setSpeed(_parent_speed - 5 - x);
 451         //cout << _name << " case 1r _relbrg spd - 5 " << _relbrg << " " << diff << endl;
 452     }else if (_range_ft > _x_offset + 0.25 && _relbrg >= -90 && _relbrg <= 90){
 453         setSpeed(_parent_speed + 1 + x);
 454         //cout << _name << " case 2r _relbrg spd + 1 " << _relbrg << " "
 455         //    << diff << " range " << _range_ft << endl;
 456     } else if (_range_ft < _x_offset - 0.25 && _relbrg >= -90 && _relbrg <= 90){
 457         setSpeed(_parent_speed - 1 - x);
 458         //cout << _name << " case 3r _relbrg spd - 2 " << _relbrg << " "
 459         //    << diff << " " << _range_ft << endl;
 460     } else {
 461         setSpeed(_parent_speed);
 462         //cout << _name << " else r _relbrg " << _relbrg << " " << diff << endl;
 463     }
 464
 465 }
 466
 467 void FGAIGroundVehicle::RunGroundVehicle(double dt){
 468
 469     _dt_count += dt;
 470
 471     ///////////////////////////////////////////////////////////////////////////
 472     // Check execution time (currently once every 0.05 sec or 20 fps)
 473     // Add a bit of randomization to prevent the execution of all flight plans
 474     // in synchrony, which can add significant periodic framerate flutter.
 475     // Randomization removed to get better appearance
 476     ///////////////////////////////////////////////////////////////////////////
 477
 478     //cout << "_start_sec " << _start_sec << " time_sec " << time_sec << endl;
 479     if (_dt_count < _next_run)
 480         return;
 481
 482     _next_run = 0.05 /*+ (0.015 * sg_random())*/;
 483
 484     if (getPitch()){
 485         setElevation(_elevation, _dt_count, _elevation_coeff);
 486         ClimbTo(_elevation_ft);
 487         setPitch(_pitch, _dt_count, _pitch_coeff);
 488         PitchTo(_pitch_deg);
 489     }
 490
 491     if(_parent == ""){
 492         AccelTo(prev->speed);
 493         _dt_count = 0;
 494         return;
 495     }
 496
 497     setParent();
 498
 499     string parent_next_name = _selected_ac->getStringValue("waypoint/name-next");
 500     bool parent_waiting = _selected_ac->getBoolValue("waypoint/waiting");
 501     //bool parent_restart = _selected_ac->getBoolValue("controls/restart");
 502
 503     if (parent_next_name == "END" && fp->getNextWaypoint()->name != "END" ){
 504         SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 505             << " setting END: getting new waypoints ");
 506         AdvanceFP();
 507         setWPNames();
 508         setTunnel(_initial_tunnel);
 509         if(_restart) _missed_count = 200;
 510         /*} else if (parent_next_name == "WAIT" && fp->getNextWaypoint()->name != "WAIT" ){*/
 511     } else if (parent_waiting && !_waiting){
 512         SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 513             << " setting WAIT/WAITUNTIL: getting new waypoints ");
 514         AdvanceFP();
 515         setWPNames();
 516         _waiting = true;
 517     } else if (parent_next_name != "WAIT" && fp->getNextWaypoint()->name == "WAIT"){
 518         SG_LOG(SG_GENERAL, SG_DEBUG, "AIGroundVeh1cle: " << _name
 519             << " wait done: getting new waypoints ");
 520         _waiting = false;
 521         _wait_count = 0;
 522         fp->IncrementWaypoint(false);
 523         next = fp->getNextWaypoint();
 524
 525         if (next->name == "WAITUNTIL" || next->name == "WAIT"
 526             || next->name == "END"){
 527         } else {
 528             prev = curr;
 529             fp->IncrementWaypoint(false);
 530             curr = fp->getCurrentWaypoint();
 531             next = fp->getNextWaypoint();
 532         }
 533
 534         setWPNames();
 535     } else if (_range_ft > (_x_offset +_parent_x_offset)* 4
 536         ){
 537         SG_LOG(SG_GENERAL, SG_ALERT, "AIGroundVeh1cle: " << _name
 538             << " rescue: reforming train " << _range_ft
 539             );
 540
 541         setTowAngle(0, dt, 1);
 542         setSpeed(_parent_speed + (10 * sign(_parent_speed)));
 543
 544     } else if (_parent_speed > 1){
 545
 546         setTowSpeed();
 547         setTowAngle(_relbrg, dt, 1);
 548
 549     } else if (_parent_speed < -1){
 550
 551         setTowSpeed();
 552
 553         if (_relbrg < 0)
 554             setTowAngle(-(180 - (360 + _relbrg)), dt, 1);
 555         else
 556             setTowAngle(-(180 - _relbrg), dt, 1);
 557
 558     } else
 559         setSpeed(_parent_speed);
 560
 561 //    FGAIShip::update(_dt_count);
 562     _dt_count = 0;
 563
 564 }
 565
 566 // end AIGroundvehicle