flightgear/src/Airports/groundnetwork.cxx

// groundnet.cxx - Implimentation of the FlightGear airport ground handling code
//
// Written by Durk Talsma, started June 2005.
//
// Copyright (C) 2004 Durk Talsma.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
//
// $Id$

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <math.h>
#include <algorithm>

//#include <plib/sg.h>
//#include <plib/ul.h>

//#include <Environment/environment_mgr.hxx>
//#include <Environment/environment.hxx>
//#include <simgear/misc/sg_path.hxx>
//#include <simgear/props/props.hxx>
//#include <simgear/structure/subsystem_mgr.hxx>
#include <simgear/debug/logstream.hxx>
#include <simgear/route/waypoint.hxx>
//#include <Main/globals.hxx>
//#include <Main/fg_props.hxx>
//#include <Airports/runways.hxx>

#include <AIModel/AIFlightPlan.hxx>

//#include STL_STRING

#include "groundnetwork.hxx"

/***************************************************************************
 * FGTaxiSegment
 **************************************************************************/
FGTaxiSegment::FGTaxiSegment()
{
  oppositeDirection = 0;
  isActive = true;
}

void FGTaxiSegment::setStart(FGTaxiNodeVector *nodes)
{
  FGTaxiNodeVectorIterator i = nodes->begin();
  while (i != nodes->end())
    {
      if ((*i)->getIndex() == startNode)
	{
	  start = (*i)->getAddress();
	  (*i)->addSegment(this);
	  return;
	}
      i++;
    }
}

void FGTaxiSegment::setEnd(FGTaxiNodeVector *nodes)
{
  FGTaxiNodeVectorIterator i = nodes->begin();
  while (i != nodes->end())
    {
      if ((*i)->getIndex() == endNode)
	{
	  end = (*i)->getAddress();
	  return;
	}
      i++;
    }
}



// There is probably a computationally cheaper way of 
// doing this.
void FGTaxiSegment::setTrackDistance()
{
  //double course;
  SGWayPoint first  (start->getLongitude(),
		     start->getLatitude(),
		     0);
  SGWayPoint second (end->getLongitude(),
		     end->getLatitude(),
		     0);
  first.CourseAndDistance(second, &course, &length);
}


void FGTaxiSegment::setCourseDiff(double crse)
{
  headingDiff = fabs(course-crse);
  
  if (headingDiff > 180)
    headingDiff = fabs(headingDiff - 360);
}


/***************************************************************************
 * FGTaxiRoute
 **************************************************************************/
bool FGTaxiRoute::next(int *nde) 
{ 
  //for (intVecIterator i = nodes.begin(); i != nodes.end(); i++)
  //  cerr << "FGTaxiRoute contains : " << *(i) << endl;
  //cerr << "Offset from end: " << nodes.end() - currNode << endl;
  //if (currNode != nodes.end())
  //  cerr << "true" << endl;
  //else
  //  cerr << "false" << endl;
  //if (nodes.size() != (routes.size()) +1)
  //  cerr << "ALERT: Misconfigured TaxiRoute : " << nodes.size() << " " << routes.size() << endl;
      
  if (currNode == nodes.end())
    return false;
  *nde = *(currNode); 
  if (currNode != nodes.begin()) // make sure route corresponds to the end node
    currRoute++;
  currNode++;
  return true;
};

bool FGTaxiRoute::next(int *nde, int *rte) 
{ 
  //for (intVecIterator i = nodes.begin(); i != nodes.end(); i++)
  //  cerr << "FGTaxiRoute contains : " << *(i) << endl;
  //cerr << "Offset from end: " << nodes.end() - currNode << endl;
  //if (currNode != nodes.end())
  //  cerr << "true" << endl;
  //else
  //  cerr << "false" << endl;
  if (nodes.size() != (routes.size()) +1) {
    SG_LOG(SG_GENERAL, SG_ALERT, "ALERT: Misconfigured TaxiRoute : " << nodes.size() << " " << routes.size());
    exit(1);
  }
  if (currNode == nodes.end())
    return false;
  *nde = *(currNode); 
  //*rte = *(currRoute);
  if (currNode != nodes.begin()) // Make sure route corresponds to the end node
    {
      *rte = *(currRoute);
      currRoute++;
    }
  else
    {
      // If currNode points to the first node, this means the aircraft is not on the taxi node
      // yet. Make sure to return a unique identifyer in this situation though, because otherwise
      // the speed adjust AI code may be unable to resolve whether two aircraft are on the same 
      // taxi route or not. the negative of the preceding route seems a logical choice, as it is 
      // unique for any starting location. 
      // Note that this is probably just a temporary fix until I get Parking / tower control working.
      *rte = -1 * *(currRoute); 
    }
  currNode++;
  return true;
};

void FGTaxiRoute::rewind(int route)
{
  int currPoint;
  int currRoute;
  first();
  do {
    if (!(next(&currPoint, &currRoute))) { 
      SG_LOG(SG_GENERAL,SG_ALERT, "Error in rewinding TaxiRoute: current" << currRoute 
	     << " goal " << route);
    }
  } while (currRoute != route);
}




/***************************************************************************
 * FGGroundNetwork()
 **************************************************************************/
bool compare_nodes(FGTaxiNode *a, FGTaxiNode *b) {
return (*a) < (*b);
}

bool compare_segments(FGTaxiSegment *a, FGTaxiSegment *b) {
return (*a) < (*b);
}

FGGroundNetwork::FGGroundNetwork()
{
  hasNetwork = false;
  foundRoute = false;
  totalDistance = 0;
  maxDistance = 0;
  //maxDepth    = 1000;
  count       = 0;
  currTraffic = activeTraffic.begin();

}

FGGroundNetwork::~FGGroundNetwork()
{
  for (FGTaxiNodeVectorIterator node = nodes.begin();
       node != nodes.end();
       node++)
    {
      delete (*node);
    }
  nodes.clear();
  for (FGTaxiSegmentVectorIterator seg = segments.begin();
       seg != segments.end();
       seg++)
    {
      delete (*seg);
    }
  segments.clear();
}

void FGGroundNetwork::addSegment(const FGTaxiSegment &seg)
{
  segments.push_back(new FGTaxiSegment(seg));
}

void FGGroundNetwork::addNode(const FGTaxiNode &node)
{
  nodes.push_back(new FGTaxiNode(node));
}

void FGGroundNetwork::addNodes(FGParkingVec *parkings)
{
  FGTaxiNode n;
  FGParkingVecIterator i = parkings->begin();
  while (i != parkings->end())
    {
      n.setIndex(i->getIndex());
      n.setLatitude(i->getLatitude());
      n.setLongitude(i->getLongitude());
      nodes.push_back(new FGTaxiNode(n));

      i++;
    }
}



void FGGroundNetwork::init()
{
  hasNetwork = true;
  int index = 1;
  sort(nodes.begin(), nodes.end(), compare_nodes);
  //sort(segments.begin(), segments.end(), compare_segments());
  FGTaxiSegmentVectorIterator i = segments.begin();
  while(i != segments.end()) {
    //cerr << "initializing node " << i->getIndex() << endl;
    (*i)->setStart(&nodes);
    (*i)->setEnd  (&nodes);
    (*i)->setTrackDistance();
    (*i)->setIndex(index);
    //cerr << "Track distance = " << i->getLength() << endl;
    //cerr << "Track ends at"      << i->getEnd()->getIndex() << endl;
    i++;
    index++;
  }
 
  i = segments.begin();
  while(i != segments.end()) {
    FGTaxiSegmentVectorIterator j = (*i)->getEnd()->getBeginRoute(); 
    while (j != (*i)->getEnd()->getEndRoute())
      {
	if ((*j)->getEnd()->getIndex() == (*i)->getStart()->getIndex())
	  {
	    int start1 = (*i)->getStart()->getIndex();
	    int end1   = (*i)->getEnd()  ->getIndex();
	    int start2 = (*j)->getStart()->getIndex();
	    int end2   = (*j)->getEnd()->getIndex();
	    int oppIndex = (*j)->getIndex();
	    //cerr << "Opposite of  " << (*i)->getIndex() << " (" << start1 << "," << end1 << ") "
	    //	 << "happens to be " << oppIndex      << " (" << start2 << "," << end2 << ") " << endl;
	    (*i)->setOpposite(*j);
	    break;
	  }
	  j++;
      }
    i++;
  }
  //cerr << "Done initializing ground network" << endl;
  //exit(1);
}



int FGGroundNetwork::findNearestNode(double lat, double lon)
{
  double minDist = HUGE_VAL;
  double dist;
  int index;
  SGWayPoint first  (lon,
		     lat,
		     0);
  
  for (FGTaxiNodeVectorIterator 
	 itr = nodes.begin();
       itr != nodes.end(); itr++)
    {
      double course;
      SGWayPoint second ((*itr)->getLongitude(),
			 (*itr)->getLatitude(),
			 0);
      first.CourseAndDistance(second, &course, &dist);
      if (dist < minDist)
	{
	  minDist = dist;
	  index = (*itr)->getIndex();
	  //cerr << "Minimum distance of " << minDist << " for index " << index << endl;
	}
    }
  return index;
}

FGTaxiNode *FGGroundNetwork::findNode(int idx)
{ /*
    for (FGTaxiNodeVectorIterator 
    itr = nodes.begin();
    itr != nodes.end(); itr++)
    {
    if (itr->getIndex() == idx)
    return itr->getAddress();
    }*/
  
  if ((idx >= 0) && (idx < nodes.size())) 
    return nodes[idx]->getAddress();
  else
    return 0;
}

FGTaxiSegment *FGGroundNetwork::findSegment(int idx)
{/*
  for (FGTaxiSegmentVectorIterator 
	 itr = segments.begin();
       itr != segments.end(); itr++)
    {
      if (itr->getIndex() == idx)
	return itr->getAddress();
    } 
 */
  if ((idx > 0) && (idx <= segments.size()))
    return segments[idx-1]->getAddress();
  else
    {
      //cerr << "Alert: trying to find invalid segment " << idx << endl;
      return 0;
    }
}


FGTaxiRoute FGGroundNetwork::findShortestRoute(int start, int end) 
{
//implements Dijkstra's algorithm to find shortest distance route from start to end
//taken from http://en.wikipedia.org/wiki/Dijkstra's_algorithm

    //double INFINITE = 100000000000.0;
    // initialize scoring values
    for (FGTaxiNodeVectorIterator
         itr = nodes.begin();
         itr != nodes.end(); itr++) {
            (*itr)->pathscore = HUGE_VAL; //infinity by all practical means
            (*itr)->previousnode = 0; //
            (*itr)->previousseg = 0; //
         }

    FGTaxiNode *firstNode = findNode(start);
    firstNode->pathscore = 0;

    FGTaxiNode *lastNode  = findNode(end);

    FGTaxiNodeVector unvisited(nodes); // working copy

    while (!unvisited.empty()) {
        FGTaxiNode* best = *(unvisited.begin());
        for (FGTaxiNodeVectorIterator
             itr = unvisited.begin();
             itr != unvisited.end(); itr++) {
                 if ((*itr)->pathscore < best->pathscore)
                     best = (*itr);
        }

        FGTaxiNodeVectorIterator newend = remove(unvisited.begin(), unvisited.end(), best);
        unvisited.erase(newend, unvisited.end());
        
        if (best == lastNode) { // found route or best not connected
            break;
        } else {
            for (FGTaxiSegmentVectorIterator
                 seg = best->getBeginRoute();
                 seg != best->getEndRoute(); seg++) {
                FGTaxiNode* tgt = (*seg)->getEnd();
                double alt = best->pathscore + (*seg)->getLength();
                if (alt < tgt->pathscore) {              // Relax (u,v)
                    tgt->pathscore = alt;
                    tgt->previousnode = best;
                    tgt->previousseg = *seg; //
                }
            }
        }
    }

    if (lastNode->pathscore == HUGE_VAL) {
        // no valid route found
        SG_LOG( SG_GENERAL, SG_ALERT, "Failed to find route from waypoint " << start << " to " << end << " at " <<
                parent->getId());
        exit(1); //TODO exit more gracefully, no need to stall the whole sim with broken GN's
    } else {
        // assemble route from backtrace information
        intVec nodes, routes;
        FGTaxiNode* bt = lastNode;
        while (bt->previousnode != 0) {
            nodes.push_back(bt->getIndex());
            routes.push_back(bt->previousseg->getIndex());
            bt = bt->previousnode;
        }
        nodes.push_back(start);
        reverse(nodes.begin(), nodes.end());
        reverse(routes.begin(), routes.end());

        return FGTaxiRoute(nodes, routes, lastNode->pathscore, 0);
    }
}


// void FGGroundNetwork::trace(FGTaxiNode *currNode, int end, int depth, double distance)
// {
//   // Just check some preconditions of the trace algorithm
//   if (nodesStack.size() != routesStack.size()) 
//     {
//       SG_LOG(SG_GENERAL, SG_ALERT, "size of nodesStack and routesStack is not equal. NodesStack :" 
// 	     << nodesStack.size() << ". RoutesStack : " << routesStack.size());
//     }
//   nodesStack.push_back(currNode->getIndex());
//   totalDistance += distance;
//   //cerr << "Starting trace " << currNode->getIndex() << " " << "total distance: " << totalDistance << endl;
//   //     << currNode->getIndex() << endl;
// 
//   // If the current route matches the required end point we found a valid route
//   // So we can add this to the routing table
//   if (currNode->getIndex() == end)
//     {
//       maxDepth = depth;
//       //cerr << "Found route : " <<  totalDistance << "" << " " << *(nodesStack.end()-1) << " Depth = " << depth << endl;
//       routes.push_back(FGTaxiRoute(nodesStack,routesStack,totalDistance, depth));
//       if (nodesStack.empty() || routesStack.empty())
// 	{
// 	  printRoutingError(string("while finishing route"));
// 	}
//       nodesStack.pop_back();
//       routesStack.pop_back();
//       if (!(foundRoute)) {
// 	maxDistance = totalDistance;
//       }
//       else
// 	if (totalDistance < maxDistance)
// 	  maxDistance = totalDistance;
//       foundRoute = true;
//       totalDistance -= distance;
//       return;
//     }
//  
// 
//   // search if the currentNode has been encountered before
//   // if so, we should step back one level, because it is
//   // rather rediculous to proceed further from here. 
//   // if the current node has not been encountered before,
//   // i should point to nodesStack.end()-1; and we can continue
//   // if i is not nodesStack.end, the previous node was found, 
//   // and we should return. 
//   // This only works at trace levels of 1 or higher though
//   if (depth > 0) {
//     intVecIterator i = nodesStack.begin();
//     while ((*i) != currNode->getIndex()) {
//       //cerr << "Route so far : " << (*i) << endl;
//       i++;
//     }
//     if (i != nodesStack.end()-1) {
//       if (nodesStack.empty() || routesStack.empty())
// 	{
// 	  printRoutingError(string("while returning from an already encountered node"));
// 	}
//       nodesStack.pop_back();
//       routesStack.pop_back();
//       totalDistance -= distance;
//       return;
//     }
//     if (depth >= maxDepth) {
//       count++;
//       if (!(count % 100000)) {
// 	maxDepth--; // Gradually decrease maxdepth, to prevent "eternal searches"
// 	//cerr << "Reducing maxdepth to " << maxDepth << endl;
//       }
//       nodesStack.pop_back();
//       routesStack.pop_back();
//       totalDistance -= distance;
//       return;
//     }
//     // If the total distance from start to the current waypoint
//     // is longer than that of a route we can also stop this trace 
//     // and go back one level. 
//     if ((totalDistance > maxDistance) && foundRoute)
//       //if (foundRoute)
//       {
// 	//cerr << "Stopping rediculously long trace: " << totalDistance << endl;
// 	if (nodesStack.empty() || routesStack.empty())
// 	{
// 	  printRoutingError(string("while returning from finding a rediculously long route"));
// 	}
// 	nodesStack.pop_back();
// 	routesStack.pop_back();
// 	totalDistance -= distance;
// 	return;
//       }
//   }
/*  
  //cerr << "2" << endl;
  if (currNode->getBeginRoute() != currNode->getEndRoute())
    {
      double course, length;
      //cerr << "3" << endl;
      // calculate distance and heading "as the crow flies" between starn and end points"
      SGWayPoint first(currNode->getLongitude(),
		       currNode->getLatitude(),
		       0);
      //SGWayPoint second (lastNode->getLongitude(),
      //		 lastNode->getLatitude(),
      //		     0);
  
      first.CourseAndDistance(destination, &course, &length);
      //for (FGTaxiSegmentVectorIterator 
      //	     itr = segments.begin();
      //	   itr != segments.end(); itr++)
      //	{
      //	  (*itr)->setCourseDiff(course);
      //	} 
      //FGTaxiNodeVectorIterator nde = nodes.begin();
      //while (nde != nodes.end()) {
      //(*nde)->sortEndSegments();
      //nde++;
      
      for (FGTaxiSegmentVectorIterator 
	     i = currNode->getBeginRoute();
	   i != currNode->getEndRoute();
	   i++)
	{
	  (*i)->setCourseDiff(course);
	}
      currNode->sortEndSegments(foundRoute);
      for (FGTaxiSegmentVectorIterator 
	     i = currNode->getBeginRoute();
	   i != currNode->getEndRoute();
	   i++)
	{
	  //cerr << (*i)->getLength() << endl;
	  //cerr << (*i)->getIndex() << endl;
	  int idx = (*i)->getIndex();
	  routesStack.push_back((*i)->getIndex());
	  trace((*i)->getEnd(), end, depth+1, (*i)->getLength());
	//  {
	//      // cerr << currNode -> getIndex() << " ";
	//      route.push_back(currNode->getIndex());
	//      return true;
	//    }
	}
    }
  else
    {
      //SG_LOG( SG_GENERAL, SG_DEBUG, "4" );
    }
  if (nodesStack.empty())
    {
      printRoutingError(string("while finishing trace"));
    }
  nodesStack.pop_back();
  // Make sure not to dump the level-zero routesStack entry, because that was never created.
  if (depth)
    {
      routesStack.pop_back();
      //cerr << "leaving trace " << routesStack.size() << endl;
    }
  totalDistance -= distance;
  return;
}*/

void FGGroundNetwork::printRoutingError(string mess)
{
  SG_LOG(SG_GENERAL, SG_ALERT,  "Error in ground network trace algorithm " << mess);
  if (nodesStack.empty())
    {
      SG_LOG(SG_GENERAL, SG_ALERT, " nodesStack is empty. Dumping routesStack");
      for (intVecIterator i = routesStack.begin() ; i != routesStack.end(); i++)
	SG_LOG(SG_GENERAL, SG_ALERT, "Route " << (*i));
    }
  if (routesStack.empty())
    {
      SG_LOG(SG_GENERAL, SG_ALERT, " routesStack is empty. Dumping nodesStack"); 
      for (intVecIterator i = nodesStack.begin() ; i != nodesStack.end(); i++)
	SG_LOG(SG_GENERAL, SG_ALERT, "Node " << (*i));
    }
  //exit(1);
}


void FGGroundNetwork::announcePosition(int id, FGAIFlightPlan *intendedRoute, int currentPosition,
				       double lat, double lon, double heading, 
				       double speed, double alt, double radius, int leg,
				       string callsign)
{
   TrafficVectorIterator i = activeTraffic.begin();
   // Search search if the current id alread has an entry
   // This might be faster using a map instead of a vector, but let's start by taking a safe route
   if (activeTraffic.size()) {
     //while ((i->getId() != id) && i != activeTraffic.end()) {
     while (i != activeTraffic.end()) {
       if (i->getId() == id) {
	 break;
       }
       i++;
     }
   }
   // Add a new TrafficRecord if no one exsists for this aircraft.
   if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
     FGTrafficRecord rec;
     rec.setId(id);
     rec.setPositionAndIntentions(currentPosition, intendedRoute);
     rec.setPositionAndHeading(lat, lon, heading, speed, alt);
     rec.setRadius(radius); // only need to do this when creating the record.
     rec.setCallSign(callsign);
     activeTraffic.push_back(rec);
   } else {
     i->setPositionAndIntentions(currentPosition, intendedRoute); 
     i->setPositionAndHeading(lat, lon, heading, speed, alt);
   }
}

void FGGroundNetwork::signOff(int id) {
  TrafficVectorIterator i = activeTraffic.begin();
   // Search search if the current id alread has an entry
   // This might be faster using a map instead of a vector, but let's start by taking a safe route
   if (activeTraffic.size()) {
     //while ((i->getId() != id) && i != activeTraffic.end()) {
     while (i != activeTraffic.end()) {
       if (i->getId() == id) {
	 break;
       }
       i++;
     }
   }
   if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
     SG_LOG(SG_GENERAL, SG_ALERT, "AI error: Aircraft without traffic record is signing off");
   } else {
       i = activeTraffic.erase(i);
   }
}

void FGGroundNetwork::update(int id, double lat, double lon, double heading, double speed, double alt, 
			     double dt) {
   TrafficVectorIterator i = activeTraffic.begin();
   // Search search if the current id has an entry
   // This might be faster using a map instead of a vector, but let's start by taking a safe route
   TrafficVectorIterator current, closest;
   if (activeTraffic.size()) {
     //while ((i->getId() != id) && i != activeTraffic.end()) {
     while (i != activeTraffic.end()) {
       if (i->getId() == id) {
	 break;
       }
       i++;
     }
   }
   // update position of the current aircraft
   if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
     SG_LOG(SG_GENERAL, SG_ALERT, "AI error: updating aircraft without traffic record");
   } else {
     i->setPositionAndHeading(lat, lon, heading, speed, alt);
     current = i;
   }
  
   setDt(getDt() + dt);
  
   // Update every three secs, but add some randomness
   // to prevent all IA objects doing this in synchrony
   //if (getDt() < (3.0) + (rand() % 10))
   //  return;
   //else
   //  setDt(0);
   current->clearResolveCircularWait();
   current->setWaitsForId(0);
   checkSpeedAdjustment(id, lat, lon, heading, speed, alt);
   checkHoldPosition   (id, lat, lon, heading, speed, alt);
   if (checkForCircularWaits(id)) {
       i->setResolveCircularWait();
   }
}

/**
   Scan for a speed adjustment change. Find the nearest aircraft that is in front
   and adjust speed when we get too close. Only do this when current position and/or
   intentions of the current aircraft match current taxiroute position of the proximate
   aircraft. For traffic that is on other routes we need to issue a "HOLD Position"
   instruction. See below for the hold position instruction.

   Note that there currently still is one flaw in the logic that needs to be addressed. 
   can be situations where one aircraft is in front of the current aircraft, on a separate
   route, but really close after an intersection coming off the current route. This
   aircraft is still close enough to block the current aircraft. This situation is currently
   not addressed yet, but should be.
*/

void FGGroundNetwork::checkSpeedAdjustment(int id, double lat, 
					   double lon, double heading, 
					   double speed, double alt)
{
  
  TrafficVectorIterator current, closest;
  TrafficVectorIterator i = activeTraffic.begin();
  bool otherReasonToSlowDown = false;
  bool previousInstruction;
  if (activeTraffic.size()) 
    {
      //while ((i->getId() != id) && (i != activeTraffic.end()))
      while (i != activeTraffic.end()) {
	if (i->getId() == id) {
	  break;
	}
	i++;
      }
    }
  else
    {
      return;
    }
  if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
    SG_LOG(SG_GENERAL, SG_ALERT, "AI error: Trying to access non-existing aircraft in FGGroundNetwork::checkSpeedAdjustment");
  }
  current = i;
  //closest = current;
  
  previousInstruction = current->getSpeedAdjustment();
  double mindist = HUGE;
  if (activeTraffic.size()) 
    {
      double course, dist, bearing, minbearing;
      SGWayPoint curr  (lon,
			lat,
			alt);
      //TrafficVector iterator closest;
      closest = current;
      for (TrafficVectorIterator i = activeTraffic.begin(); 
   	   i != activeTraffic.end(); i++)
   	{
   	  if (i != current) {
   	    //SGWayPoint curr  (lon,
  	    //	      lat,
  	    //	      alt);
   	    SGWayPoint other    (i->getLongitude  (),
   				 i->getLatitude (),
   				 i->getAltitude  ());
   	    other.CourseAndDistance(curr, &course, &dist);
   	    bearing = fabs(heading-course);
   	    if (bearing > 180)
   	      bearing = 360-bearing;
   	    if ((dist < mindist) && (bearing < 60.0))
   	      {
   		mindist = dist;
   		closest = i;
   		minbearing = bearing;
   	      }
   	  }
   	}
      //Check traffic at the tower controller
      if (towerController->hasActiveTraffic())
	{
	  for (TrafficVectorIterator i = towerController->getActiveTraffic().begin(); 
	       i != towerController->getActiveTraffic().end(); i++)
	    {
	      //cerr << "Comparing " << current->getId() << " and " << i->getId() << endl;
	      //SGWayPoint curr  (lon,
	      //		  lat,
	      //		  alt);
	      SGWayPoint other    (i->getLongitude  (),
				   i->getLatitude (),
				   i->getAltitude  ());
	      other.CourseAndDistance(curr, &course, &dist);
	      bearing = fabs(heading-course);
	      if (bearing > 180)
		bearing = 360-bearing;
	      if ((dist < mindist) && (bearing < 60.0))
		{
		  mindist = dist;
		  closest = i;
		  minbearing = bearing;
		  otherReasonToSlowDown = true;
		}
	    }
	}
      // Finally, check UserPosition
      double userLatitude  = fgGetDouble("/position/latitude-deg");
      double userLongitude = fgGetDouble("/position/longitude-deg");
      SGWayPoint user    (userLongitude,
			  userLatitude,
			  alt); // Alt is not really important here. 
      user.CourseAndDistance(curr, &course, &dist);
      bearing = fabs(heading-course);
      if (bearing > 180)
	bearing = 360-bearing;
      if ((dist < mindist) && (bearing < 60.0))
	{
	  mindist = dist;
	  //closest = i;
	  minbearing = bearing;
	  otherReasonToSlowDown = true;
	}
      
      // 	if (closest == current) {
      // 	  //SG_LOG(SG_GENERAL, SG_ALERT, "AI error: closest and current match");
      // 	  //return;
      // 	}      
      //cerr << "Distance : " << dist << " bearing : " << bearing << " heading : " << heading 
      //   << " course : " << course << endl;
      current->clearSpeedAdjustment();
    
      if (current->checkPositionAndIntentions(*closest) || otherReasonToSlowDown) 
	{
	   double maxAllowableDistance = (1.1*current->getRadius()) + (1.1*closest->getRadius());
	   if (mindist < 2*maxAllowableDistance)
	     {
	       if (current->getId() == closest->getWaitsForId())
		 return;
	       else 
		 current->setWaitsForId(closest->getId());
	       if (closest != current)
		 current->setSpeedAdjustment(closest->getSpeed()* (mindist/100));
	       else
		 current->setSpeedAdjustment(0); // This can only happen when the user aircraft is the one closest
	       if (mindist < maxAllowableDistance)
		 {
		   //double newSpeed = (maxAllowableDistance-mindist);
		   //current->setSpeedAdjustment(newSpeed);
		   //if (mindist < 0.5* maxAllowableDistance)
		   //  {
		       current->setSpeedAdjustment(0);
		       //  }
		 }
	     }
	}
    }
}

/**
   Check for "Hold position instruction".
   The hold position should be issued under the following conditions:
   1) For aircraft entering or crossing a runway with active traffic on it, or landing aircraft near it
   2) For taxiing aircraft that use one taxiway in opposite directions
   3) For crossing or merging taxiroutes.
*/

void FGGroundNetwork::checkHoldPosition(int id, double lat, 
					double lon, double heading, 
					double speed, double alt)
{
  
  TrafficVectorIterator current;
  TrafficVectorIterator i = activeTraffic.begin();
  if (activeTraffic.size()) 
    {
      //while ((i->getId() != id) && i != activeTraffic.end()) 
      while (i != activeTraffic.end()) {
	if (i->getId() == id) {
	  break;
	}
	i++;
      }
    }
  else
    {
      return ;
    } 
  if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
    SG_LOG(SG_GENERAL, SG_ALERT, "AI error: Trying to access non-existing aircraft in FGGroundNetwork::checkHoldPosition");
  }
  current = i;
  current->setHoldPosition(false);
  SGWayPoint curr  (lon,
		    lat,
		    alt);
  double course, dist, bearing, minbearing;
  for (i = activeTraffic.begin(); 
       i != activeTraffic.end(); i++)
    {
      if (i != current) 
  	{
  	  int node = current->crosses(this, *i);
  	  if (node != -1)
  	    {
  	      // Determine whether it's save to continue or not. 
  	      // If we have a crossing route, there are two possibilities:
  	      // 1) This is an interestion
  	      // 2) This is oncoming two-way traffic, using the same taxiway.
  	      //cerr << "Hold check 1 : " << id << " has common node " << node << endl;
  	      SGWayPoint nodePos(findNode(node)->getLongitude  (),
  				 findNode(node)->getLatitude   (),
  				 alt);

  	      SGWayPoint other    (i->getLongitude  (),
  				   i->getLatitude (),
  				   i->getAltitude  ());
  	      //other.CourseAndDistance(curr, &course, &dist);
  	      bool needsToWait;
	      bool opposing;
  	      if (current->isOpposing(this, *i, node))
  		{
  		  needsToWait = true;
		  opposing    = true;
  		  //cerr << "Hold check 2 : " << node << "  has opposing segment " << endl;
  		  // issue a "Hold Position" as soon as we're close to the offending node
  		  // For now, I'm doing this as long as the other aircraft doesn't
 		  // have a hold instruction as soon as we're within a reasonable 
  		  // distance from the offending node.
  		  // This may be a bit of a conservative estimate though, as it may
  		  // be well possible that both aircraft can both continue to taxi 
  		  // without crashing into each other.
  		} 
  	      else 
  		{
		  opposing = false;
  		  other.CourseAndDistance(nodePos, &course, &dist);
  		  if (dist > 200) // 2.0*i->getRadius())
  		    {
  		      needsToWait = false; 
  		      //cerr << "Hold check 3 : " << id <<"  Other aircraft approaching node is still far away. (" << dist << " nm). Can safely continue " 
  		      //	   << endl;
  		    }
  		  else 
  		    {
  		      needsToWait = true;
  		      //cerr << "Hold check 4: " << id << "  Would need to wait for other aircraft : distance = " << dist << " meters" << endl;
  		    }
  		}
  	      curr.CourseAndDistance(nodePos, &course, &dist);
  	      if (!(i->hasHoldPosition()))
  		{
		  
  		  if ((dist < 200) && //2.5*current->getRadius()) && 
  		      (needsToWait) &&
		      (i->onRoute(this, *current)) &&
		      //((i->onRoute(this, *current)) || ((!(i->getSpeedAdjustment())))) &&
  		      (!(current->getId() == i->getWaitsForId())))
		      //(!(i->getSpeedAdjustment()))) // &&
  		      //(!(current->getSpeedAdjustment())))
		    
  		    {
  		      current->setHoldPosition(true);
		      current->setWaitsForId(i->getId());
  		      //cerr << "Hold check 5: " << current->getCallSign() <<"  Setting Hold Position: distance to node ("  << node << ") "
		      //	   << dist << " meters. Waiting for " << i->getCallSign();
		      //if (opposing)
		      //cerr <<" [opposing] " << endl;
		      //else
		      //	cerr << "[non-opposing] " << endl;
		      //if (i->hasSpeefAdjustment())
		      //	{
		      //	  cerr << " (which in turn waits for ) " << i->
  		    }
  		  else
  		    {
  		      //cerr << "Hold check 6: " << id << "  No need to hold yet: Distance to node : " << dist << " nm"<< endl;
  		    }
  		}
  	    }
  	}
    }
}

/**
 * Check whether situations occur where the current aircraft is waiting for itself
 * due to higher order interactions. 
 * A 'circular' wait is a situation where a waits for b, b waits for c, and c waits
 * for a. Ideally each aircraft only waits for one other aircraft, so by tracing 
 * through this list of waiting aircraft, we can check if we'd eventually end back 
 * at the current aircraft.
 *
 * Note that we should consider the situation where we are actually checking aircraft
 * d, which is waiting for aircraft a. d is not part of the loop, but is held back by
 * the looping aircraft. If we don't check for that, this function will get stuck into
 * endless loop.
 */

bool FGGroundNetwork::checkForCircularWaits(int id)
{  
   //cerr << "Performing Wait check " << id << endl;
   int target = 0;
   TrafficVectorIterator current, other;
   TrafficVectorIterator i = activeTraffic.begin();
   int trafficSize = activeTraffic.size();
   if (trafficSize)  {
        while (i != activeTraffic.end()) {
        if (i->getId() == id) {
	    break;
	}
	i++;
    }
  }
  else {
      return false;
  }
  if (i == activeTraffic.end() || (trafficSize == 0)) {
    SG_LOG(SG_GENERAL, SG_ALERT, "AI error: Trying to access non-existing aircraft in FGGroundNetwork::checkForCircularWaits");
  }
   
   current = i;
   target = current->getWaitsForId();
   //bool printed = false; // Note that this variable is for debugging purposes only.
   int counter = 0;

   if (id == target) {
       //cerr << "aircraft waits for user" << endl;
       return false;
   }


   while ((target > 0) && (target != id) && counter++ < trafficSize) {
    //printed = true;
     TrafficVectorIterator i = activeTraffic.begin();
     if (trafficSize)  {
          //while ((i->getId() != id) && i != activeTraffic.end()) 
          while (i != activeTraffic.end()) {
          if (i->getId() == target) {
	      break;
	  }
	  i++;
        }
      }
      else {
        return false;
    } 
    if (i == activeTraffic.end() || (trafficSize == 0)) {
	//cerr << "[Waiting for traffic at Runway: DONE] " << endl << endl;;
      // The target id is not found on the current network, which means it's at the tower
      //SG_LOG(SG_GENERAL, SG_ALERT, "AI error: Trying to access non-existing aircraft in FGGroundNetwork::checkForCircularWaits");
      return false;
    }
    other = i;
    target = other->getWaitsForId();

    // actually this trap isn't as impossible as it first seemed:
    // the setWaitsForID(id) is set to current when the aircraft
    // is waiting for the user controlled aircraft. 
    //if (current->getId() == other->getId()) {
    //    cerr << "Caught the impossible trap" << endl;
    //    cerr << "Current = " << current->getId() << endl;
    //    cerr << "Other   = " << other  ->getId() << endl;
    //    for (TrafficVectorIterator at = activeTraffic.begin();
    //          at != activeTraffic.end();
    //          at++) {
    //        cerr << "currently active aircraft : " << at->getCallSign() << " with Id " << at->getId() << " waits for " << at->getWaitsForId() << endl;
    //    }
    //    exit(1);
    if (current->getId() == other->getId())
	return false;
    //}
    //cerr << current->getCallSign() << " (" << current->getId()  << ") " << " -> " << other->getCallSign() 
    //     << " (" << other->getId()  << "); " << endl;;
    //current = other;
   }






   //if (printed)
   //   cerr << "[done] " << endl << endl;;
   if (id == target) {
       SG_LOG(SG_GENERAL, SG_ALERT, "Detected circular wait condition");
       cerr << "Id = " << id << endl;
       cerr << "target = " << target << endl;
       return true;
   } else {
   return false;
   }
}

// Note that this function is probably obsolete...
bool FGGroundNetwork::hasInstruction(int id)
{
    TrafficVectorIterator i = activeTraffic.begin();
   // Search search if the current id has an entry
   // This might be faster using a map instead of a vector, but let's start by taking a safe route
   if (activeTraffic.size()) 
     {
       //while ((i->getId() != id) && i != activeTraffic.end()) {
       while (i != activeTraffic.end()) {
	 if (i->getId() == id) {
	   break;
	 }
	 i++;
       }
     }
   if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
     SG_LOG(SG_GENERAL, SG_ALERT, "AI error: checking ATC instruction for aircraft without traffic record");
   } else {
     return i->hasInstruction();
   }
  return false;
}

FGATCInstruction FGGroundNetwork::getInstruction(int id)
{
  TrafficVectorIterator i = activeTraffic.begin();
  // Search search if the current id has an entry
   // This might be faster using a map instead of a vector, but let's start by taking a safe route
   if (activeTraffic.size()) {
     //while ((i->getId() != id) && i != activeTraffic.end()) {
     while (i != activeTraffic.end()) {
       if (i->getId() == id) {
	 break;
       }
       i++;
     }
   }
   if (i == activeTraffic.end() || (activeTraffic.size() == 0)) {
     SG_LOG(SG_GENERAL, SG_ALERT, "AI error: requesting ATC instruction for aircraft without traffic record");
   } else {
     return i->getInstruction();
   }
  return FGATCInstruction();
}