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