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Thomas Foerster: Replaced AI network route tracing algorithm by a much more

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efficiently performing "Dijkstra algorithm".

Durk Talsma: Added the detection of "circular" wait situations in the AI
ground network. A circular wait is a situation where aircraft a waits for
b; b waits for c; and c (in turn) waits for a. The checkCircularWaits
function detects these situations.

The current "solution" to a circular wait is rather crude: Remove the
aircraft from the scene. A proper solution needs a lot more work, however,
and at least this patch stops the AI system from clogging up. in case of a
circular wait.
This commit is contained in:
durk 2007-06-28 07:54:39 +00:00
parent 1613d7e63e
commit 54ef3b77d5
4 changed files with 308 additions and 177 deletions
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454
src/Airports/groundnetwork.cxx
View file

@ -232,7 +232,7 @@ FGGroundNetwork::FGGroundNetwork()
foundRoute = false; foundRoute = false;
totalDistance = 0; totalDistance = 0;
maxDistance = 0; maxDistance = 0;
maxDepth = 1000; //maxDepth = 1000;
count = 0; count = 0;
currTraffic = activeTraffic.begin(); currTraffic = activeTraffic.begin();
@ -392,172 +392,172 @@ FGTaxiSegment *FGGroundNetwork::findSegment(int idx)
} }
} }
FGTaxiRoute FGGroundNetwork::findShortestRoute(int start, int end) FGTaxiRoute FGGroundNetwork::findShortestRoute(int start, int end)
{ {
double course; //implements Dijkstra's algorithm to find shortest distance route from start to end
double length; //taken from http://en.wikipedia.org/wiki/Dijkstra's_algorithm
foundRoute = false;
totalDistance = 0;
FGTaxiNode *firstNode = findNode(start);
FGTaxiNode *lastNode = findNode(end);
//prevNode = prevPrevNode = -1;
//prevNode = start;
routes.clear();
nodesStack.clear();
routesStack.clear();
// calculate distance and heading "as the crow flies" between starn and end points"
SGWayPoint first(firstNode->getLongitude(),
firstNode->getLatitude(),
0);
destination = SGWayPoint(lastNode->getLongitude(),
lastNode->getLatitude(),
0);
first.CourseAndDistance(destination, &course, &length); //double INFINITE = 100000000000.0;
for (FGTaxiSegmentVectorIterator // initialize scoring values
itr = segments.begin(); for (FGTaxiNodeVectorIterator
itr != segments.end(); itr++) itr = nodes.begin();
{ itr != nodes.end(); itr++) {
(*itr)->setCourseDiff(course); (*itr)->pathscore = HUGE_VAL; //infinity by all practical means
} (*itr)->previousnode = 0; //
//FGTaxiNodeVectorIterator nde = nodes.begin(); (*itr)->previousseg = 0; //
//while (nde != nodes.end()) { }
// (*nde)->sortEndSegments();
// nde++;
//}
maxDepth = 1000;
//do
// {
// cerr << "Begin of Trace " << start << " to "<< end << " maximum depth = " << maxDepth << endl;
trace(firstNode, end, 0, 0);
// maxDepth--;
// }
//while ((routes.size() != 0) && (maxDepth > 0));
//cerr << "End of Trace" << endl;
FGTaxiRoute empty;
if (!foundRoute) FGTaxiNode *firstNode = findNode(start);
{ firstNode->pathscore = 0;
SG_LOG( SG_GENERAL, SG_ALERT, "Failed to find route from waypoint " << start << " to " << end << " at " <<
parent->getId());
exit(1);
}
sort(routes.begin(), routes.end());
//for (intVecIterator i = route.begin(); i != route.end(); i++)
// {
// rte->push_back(*i);
// }
if (routes.begin() != routes.end()) FGTaxiNode *lastNode = findNode(end);
{
// if ((routes.begin()->getDepth() < 0.5 * maxDepth) && (maxDepth > 1)) FGTaxiNodeVector unvisited(nodes); // working copy
// {
// maxDepth--; while (!unvisited.empty()) {
// cerr << "Max search depth decreased to : " << maxDepth; FGTaxiNode* best = *(unvisited.begin());
// } for (FGTaxiNodeVectorIterator
// else itr = unvisited.begin();
// { itr != unvisited.end(); itr++) {
// maxDepth++; if ((*itr)->pathscore < best->pathscore)
// cerr << "Max search depth increased to : " << maxDepth; best = (*itr);
// } }
return *(routes.begin());
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);
} }
else
return empty;
} }
void FGGroundNetwork::trace(FGTaxiNode *currNode, int end, int depth, double distance) // void FGGroundNetwork::trace(FGTaxiNode *currNode, int end, int depth, double distance)
{ // {
// Just check some preconditions of the trace algorithm // // Just check some preconditions of the trace algorithm
if (nodesStack.size() != routesStack.size()) // if (nodesStack.size() != routesStack.size())
{ // {
SG_LOG(SG_GENERAL, SG_ALERT, "size of nodesStack and routesStack is not equal. NodesStack :" // SG_LOG(SG_GENERAL, SG_ALERT, "size of nodesStack and routesStack is not equal. NodesStack :"
<< nodesStack.size() << ". RoutesStack : " << routesStack.size()); // << nodesStack.size() << ". RoutesStack : " << routesStack.size());
} // }
nodesStack.push_back(currNode->getIndex()); // nodesStack.push_back(currNode->getIndex());
totalDistance += distance; // totalDistance += distance;
//cerr << "Starting trace " << currNode->getIndex() << " " << "total distance: " << totalDistance << endl; // //cerr << "Starting trace " << currNode->getIndex() << " " << "total distance: " << totalDistance << endl;
// << currNode->getIndex() << endl; // // << currNode->getIndex() << endl;
//
// If the current route matches the required end point we found a valid route // // If the current route matches the required end point we found a valid route
// So we can add this to the routing table // // So we can add this to the routing table
if (currNode->getIndex() == end) // if (currNode->getIndex() == end)
{ // {
maxDepth = depth; // maxDepth = depth;
//cerr << "Found route : " << totalDistance << "" << " " << *(nodesStack.end()-1) << " Depth = " << depth << endl; // //cerr << "Found route : " << totalDistance << "" << " " << *(nodesStack.end()-1) << " Depth = " << depth << endl;
routes.push_back(FGTaxiRoute(nodesStack,routesStack,totalDistance, depth)); // routes.push_back(FGTaxiRoute(nodesStack,routesStack,totalDistance, depth));
if (nodesStack.empty() || routesStack.empty()) // if (nodesStack.empty() || routesStack.empty())
{ // {
printRoutingError(string("while finishing route")); // printRoutingError(string("while finishing route"));
} // }
nodesStack.pop_back(); // nodesStack.pop_back();
routesStack.pop_back(); // routesStack.pop_back();
if (!(foundRoute)) { // if (!(foundRoute)) {
maxDistance = totalDistance; // maxDistance = totalDistance;
} // }
else // else
if (totalDistance < maxDistance) // if (totalDistance < maxDistance)
maxDistance = totalDistance; // maxDistance = totalDistance;
foundRoute = true; // foundRoute = true;
totalDistance -= distance; // totalDistance -= distance;
return; // return;
} // }
//
//
// search if the currentNode has been encountered before // // search if the currentNode has been encountered before
// if so, we should step back one level, because it is // // if so, we should step back one level, because it is
// rather rediculous to proceed further from here. // // rather rediculous to proceed further from here.
// if the current node has not been encountered before, // // if the current node has not been encountered before,
// i should point to nodesStack.end()-1; and we can continue // // i should point to nodesStack.end()-1; and we can continue
// if i is not nodesStack.end, the previous node was found, // // if i is not nodesStack.end, the previous node was found,
// and we should return. // // and we should return.
// This only works at trace levels of 1 or higher though // // This only works at trace levels of 1 or higher though
if (depth > 0) { // if (depth > 0) {
intVecIterator i = nodesStack.begin(); // intVecIterator i = nodesStack.begin();
while ((*i) != currNode->getIndex()) { // while ((*i) != currNode->getIndex()) {
//cerr << "Route so far : " << (*i) << endl; // //cerr << "Route so far : " << (*i) << endl;
i++; // i++;
} // }
if (i != nodesStack.end()-1) { // if (i != nodesStack.end()-1) {
if (nodesStack.empty() || routesStack.empty()) // if (nodesStack.empty() || routesStack.empty())
{ // {
printRoutingError(string("while returning from an already encountered node")); // printRoutingError(string("while returning from an already encountered node"));
} // }
nodesStack.pop_back(); // nodesStack.pop_back();
routesStack.pop_back(); // routesStack.pop_back();
totalDistance -= distance; // totalDistance -= distance;
return; // return;
} // }
if (depth >= maxDepth) { // if (depth >= maxDepth) {
count++; // count++;
if (!(count % 100000)) { // if (!(count % 100000)) {
maxDepth--; // Gradually decrease maxdepth, to prevent "eternal searches" // maxDepth--; // Gradually decrease maxdepth, to prevent "eternal searches"
//cerr << "Reducing maxdepth to " << maxDepth << endl; // //cerr << "Reducing maxdepth to " << maxDepth << endl;
} // }
nodesStack.pop_back(); // nodesStack.pop_back();
routesStack.pop_back(); // routesStack.pop_back();
totalDistance -= distance; // totalDistance -= distance;
return; // return;
} // }
// If the total distance from start to the current waypoint // // If the total distance from start to the current waypoint
// is longer than that of a route we can also stop this trace // // is longer than that of a route we can also stop this trace
// and go back one level. // // and go back one level.
if ((totalDistance > maxDistance) && foundRoute) // if ((totalDistance > maxDistance) && foundRoute)
//if (foundRoute) // //if (foundRoute)
{ // {
//cerr << "Stopping rediculously long trace: " << totalDistance << endl; // //cerr << "Stopping rediculously long trace: " << totalDistance << endl;
if (nodesStack.empty() || routesStack.empty()) // if (nodesStack.empty() || routesStack.empty())
{ // {
printRoutingError(string("while returning from finding a rediculously long route")); // printRoutingError(string("while returning from finding a rediculously long route"));
} // }
nodesStack.pop_back(); // nodesStack.pop_back();
routesStack.pop_back(); // routesStack.pop_back();
totalDistance -= distance; // totalDistance -= distance;
return; // return;
} // }
} // }
/*
//cerr << "2" << endl; //cerr << "2" << endl;
if (currNode->getBeginRoute() != currNode->getEndRoute()) if (currNode->getBeginRoute() != currNode->getEndRoute())
{ {
@ -625,7 +625,7 @@ void FGGroundNetwork::trace(FGTaxiNode *currNode, int end, int depth, double dis
} }
totalDistance -= distance; totalDistance -= distance;
return; return;
} }*/
void FGGroundNetwork::printRoutingError(string mess) void FGGroundNetwork::printRoutingError(string mess)
{ {
@ -729,20 +729,34 @@ void FGGroundNetwork::update(int id, double lat, double lon, double heading, dou
// return; // return;
//else //else
// setDt(0); // setDt(0);
current->clearResolveCircularWait();
current->setWaitsForId(0);
checkSpeedAdjustment(id, lat, lon, heading, speed, alt); checkSpeedAdjustment(id, lat, lon, heading, speed, alt);
checkHoldPosition (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, void FGGroundNetwork::checkSpeedAdjustment(int id, double lat,
double lon, double heading, double lon, double heading,
double speed, double alt) double speed, double alt)
{ {
// 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.
TrafficVectorIterator current, closest; TrafficVectorIterator current, closest;
TrafficVectorIterator i = activeTraffic.begin(); TrafficVectorIterator i = activeTraffic.begin();
bool otherReasonToSlowDown = false; bool otherReasonToSlowDown = false;
@ -766,6 +780,7 @@ void FGGroundNetwork::checkSpeedAdjustment(int id, double lat,
} }
current = i; current = i;
//closest = current; //closest = current;
previousInstruction = current->getSpeedAdjustment(); previousInstruction = current->getSpeedAdjustment();
double mindist = HUGE; double mindist = HUGE;
if (activeTraffic.size()) if (activeTraffic.size())
@ -877,15 +892,18 @@ void FGGroundNetwork::checkSpeedAdjustment(int id, double lat,
} }
} }
/**
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, void FGGroundNetwork::checkHoldPosition(int id, double lat,
double lon, double heading, double lon, double heading,
double speed, double alt) double speed, double alt)
{ {
// 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.
TrafficVectorIterator current; TrafficVectorIterator current;
TrafficVectorIterator i = activeTraffic.begin(); TrafficVectorIterator i = activeTraffic.begin();
@ -929,7 +947,6 @@ void FGGroundNetwork::checkHoldPosition(int id, double lat,
findNode(node)->getLatitude (), findNode(node)->getLatitude (),
alt); alt);
SGWayPoint other (i->getLongitude (), SGWayPoint other (i->getLongitude (),
i->getLatitude (), i->getLatitude (),
i->getAltitude ()); i->getAltitude ());
@ -979,6 +996,7 @@ void FGGroundNetwork::checkHoldPosition(int id, double lat,
{ {
current->setHoldPosition(true); current->setHoldPosition(true);
current->setWaitsForId(i->getId());
//cerr << "Hold check 5: " << current->getCallSign() <<" Setting Hold Position: distance to node (" << node << ") " //cerr << "Hold check 5: " << current->getCallSign() <<" Setting Hold Position: distance to node (" << node << ") "
// << dist << " meters. Waiting for " << i->getCallSign(); // << dist << " meters. Waiting for " << i->getCallSign();
//if (opposing) //if (opposing)
@ -999,6 +1017,101 @@ void FGGroundNetwork::checkHoldPosition(int id, double lat,
} }
} }
/**
* 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->getId() != id) && i != activeTraffic.end())
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;
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_INFO, "Detected circular wait condition");
return true;
} else {
return false;
}
}
// Note that this function is probably obsolete... // Note that this function is probably obsolete...
bool FGGroundNetwork::hasInstruction(int id) bool FGGroundNetwork::hasInstruction(int id)
{ {
@ -1045,3 +1158,4 @@ FGATCInstruction FGGroundNetwork::getInstruction(int id)
return FGATCInstruction(); return FGATCInstruction();
} }

12
src/Airports/groundnetwork.hxx
View file

@ -81,6 +81,12 @@ public:
bool operator<(const FGTaxiNode &other) const { return index < other.index; }; bool operator<(const FGTaxiNode &other) const { return index < other.index; };
void sortEndSegments(bool); void sortEndSegments(bool);
// used in way finding
double pathscore;
FGTaxiNode* previousnode;
FGTaxiSegment* previousseg;
}; };
typedef vector<FGTaxiNode*> FGTaxiNodeVector; typedef vector<FGTaxiNode*> FGTaxiNodeVector;
@ -190,7 +196,7 @@ class FGGroundNetwork : public FGATCController
{ {
private: private:
bool hasNetwork; bool hasNetwork;
int maxDepth; //int maxDepth;
int count; int count;
FGTaxiNodeVector nodes; FGTaxiNodeVector nodes;
FGTaxiSegmentVector segments; FGTaxiSegmentVector segments;
@ -230,7 +236,7 @@ public:
FGTaxiNode *findNode(int idx); FGTaxiNode *findNode(int idx);
FGTaxiSegment *findSegment(int idx); FGTaxiSegment *findSegment(int idx);
FGTaxiRoute findShortestRoute(int start, int end); FGTaxiRoute findShortestRoute(int start, int end);
void trace(FGTaxiNode *, int, int, double dist); //void trace(FGTaxiNode *, int, int, double dist);
void setParent(FGAirport *par) { parent = par; }; void setParent(FGAirport *par) { parent = par; };
@ -241,6 +247,8 @@ public:
virtual void update(int id, double lat, double lon, double heading, double speed, double alt, double dt); virtual void update(int id, double lat, double lon, double heading, double speed, double alt, double dt);
virtual bool hasInstruction(int id); virtual bool hasInstruction(int id);
virtual FGATCInstruction getInstruction(int id); virtual FGATCInstruction getInstruction(int id);
bool checkForCircularWaits(int id);
}; };

3
src/Airports/trafficcontrol.cxx
View file

@ -300,6 +300,7 @@ FGATCInstruction::FGATCInstruction()
changeSpeed = false; changeSpeed = false;
changeHeading = false; changeHeading = false;
changeAltitude = false; changeAltitude = false;
resolveCircularWait = false;
double speed = 0; double speed = 0;
double heading = 0; double heading = 0;
@ -308,7 +309,7 @@ FGATCInstruction::FGATCInstruction()
bool FGATCInstruction::hasInstruction() bool FGATCInstruction::hasInstruction()
{ {
return (holdPattern || holdPosition || changeSpeed || changeHeading || changeAltitude); return (holdPattern || holdPosition || changeSpeed || changeHeading || changeAltitude || resolveCircularWait);
} }

10
src/Airports/trafficcontrol.hxx
View file

@ -58,6 +58,7 @@ private:
bool changeSpeed; bool changeSpeed;
bool changeHeading; bool changeHeading;
bool changeAltitude; bool changeAltitude;
bool resolveCircularWait;
double speed; double speed;
double heading; double heading;
@ -76,19 +77,23 @@ public:
double getHeading () { return heading; }; double getHeading () { return heading; };
double getAlt () { return alt; }; double getAlt () { return alt; };
bool getCheckForCircularWait() { return resolveCircularWait; };
void setHoldPattern (bool val) { holdPattern = val; }; void setHoldPattern (bool val) { holdPattern = val; };
void setHoldPosition (bool val) { holdPosition = val; }; void setHoldPosition (bool val) { holdPosition = val; };
void setChangeSpeed (bool val) { changeSpeed = val; }; void setChangeSpeed (bool val) { changeSpeed = val; };
void setChangeHeading (bool val) { changeHeading = val; }; void setChangeHeading (bool val) { changeHeading = val; };
void setChangeAltitude(bool val) { changeAltitude = val; }; void setChangeAltitude(bool val) { changeAltitude = val; };
void setResolveCircularWait (bool val) { resolveCircularWait = val; };
void setSpeed (double val) { speed = val; }; void setSpeed (double val) { speed = val; };
void setHeading (double val) { heading = val; }; void setHeading (double val) { heading = val; };
void setAlt (double val) { alt = val; }; void setAlt (double val) { alt = val; };
}; };
/************************************************************************************** /**
* class FGATCController * class FGATCController
* NOTE: this class serves as an abstraction layer for all sorts of ATC controller. * NOTE: this class serves as an abstraction layer for all sorts of ATC controller.
*************************************************************************************/ *************************************************************************************/
@ -170,6 +175,9 @@ public:
void setWaitsForId(int id) { waitsForId = id; }; void setWaitsForId(int id) { waitsForId = id; };
void setResolveCircularWait() { instruction.setResolveCircularWait(true); };
void clearResolveCircularWait() { instruction.setResolveCircularWait(false); };
string getRunway() { return runway; }; string getRunway() { return runway; };
void setCallSign(string clsgn) { callsign = clsgn; }; void setCallSign(string clsgn) { callsign = clsgn; };
string getCallSign() { return callsign; }; string getCallSign() { return callsign; };