flightgear/src/ATC/tower.cxx

// FGTower - a class to provide tower control at towered airports.
//
// Written by David Luff, started March 2002.
//
// Copyright (C) 2002  David C. Luff - david.luff@nottingham.ac.uk
//
// 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., 675 Mass Ave, Cambridge, MA 02139, USA.

#include <Main/globals.hxx>
#include <Airports/runways.hxx>
#include <simgear/math/sg_geodesy.hxx>
#include <simgear/debug/logstream.hxx>

#include "tower.hxx"
#include "ATCdisplay.hxx"
#include "ATCmgr.hxx"
#include "ATCutils.hxx"
#include "commlist.hxx"
#include "AILocalTraffic.hxx"

SG_USING_STD(cout);

// TowerPlaneRec

TowerPlaneRec::TowerPlaneRec() :
clearedToLand(false),
clearedToLineUp(false),
clearedToTakeOff(false),
holdShortReported(false),
longFinalReported(false),
longFinalAcknowledged(false),
finalReported(false),
finalAcknowledged(false),
onRwy(false),
nextOnRwy(false),
opType(TTT_UNKNOWN),
leg(LEG_UNKNOWN),
landingType(AIP_LT_UNKNOWN),
isUser(false)
{
	plane.callsign = "UNKNOWN";
}

TowerPlaneRec::TowerPlaneRec(PlaneRec p) :
clearedToLand(false),
clearedToLineUp(false),
clearedToTakeOff(false),
holdShortReported(false),
longFinalReported(false),
longFinalAcknowledged(false),
finalReported(false),
finalAcknowledged(false),
onRwy(false),
nextOnRwy(false),
opType(TTT_UNKNOWN),
leg(LEG_UNKNOWN),
landingType(AIP_LT_UNKNOWN),
isUser(false)
{
	plane = p;
}

TowerPlaneRec::TowerPlaneRec(Point3D pt) :
clearedToLand(false),
clearedToLineUp(false),
clearedToTakeOff(false),
holdShortReported(false),
longFinalReported(false),
longFinalAcknowledged(false),
finalReported(false),
finalAcknowledged(false),
onRwy(false),
nextOnRwy(false),
opType(TTT_UNKNOWN),
leg(LEG_UNKNOWN),
landingType(AIP_LT_UNKNOWN),
isUser(false)
{
	plane.callsign = "UNKNOWN";
	pos = pt;
}

TowerPlaneRec::TowerPlaneRec(PlaneRec p, Point3D pt) :
clearedToLand(false),
clearedToLineUp(false),
clearedToTakeOff(false),
holdShortReported(false),
longFinalReported(false),
longFinalAcknowledged(false),
finalReported(false),
finalAcknowledged(false),
onRwy(false),
nextOnRwy(false),
opType(TTT_UNKNOWN),
leg(LEG_UNKNOWN),
landingType(AIP_LT_UNKNOWN),
isUser(false)
{
	plane = p;
	pos = pt;
}


// FGTower

FGTower::FGTower() {
	ATCmgr = globals->get_ATC_mgr();
	
	// Init the property nodes - TODO - need to make sure we're getting surface winds.
	wind_from_hdg = fgGetNode("/environment/wind-from-heading-deg", true);
	wind_speed_knots = fgGetNode("/environment/wind-speed-kt", true);
	
	update_count = 0;
	update_count_max = 15;
	
	holdListItr = holdList.begin();
	appListItr = appList.begin();
	depListItr = depList.begin();
	rwyListItr = rwyList.begin();
	circuitListItr = circuitList.begin();
	trafficListItr = trafficList.begin();
	
	freqClear = true;
	
	timeSinceLastDeparture = 9999;
	departed = false;
}

FGTower::~FGTower() {
	if(!separateGround) {
		delete ground;
	}
}

void FGTower::Init() {
    display = false;
	
	// Pointers to user's position
	user_lon_node = fgGetNode("/position/longitude-deg", true);
	user_lat_node = fgGetNode("/position/latitude-deg", true);
	user_elev_node = fgGetNode("/position/altitude-ft", true);
	user_hdg_node = fgGetNode("/orientation/heading-deg", true);
	
	// Need some way to initialise rwyOccupied flag correctly if the user is on the runway and to know its the user.
	// I'll punt the startup issue for now though!!!
	rwyOccupied = false;
	
	// Setup the ground control at this airport
	AirportATC a;
	//cout << "Tower ident = " << ident << '\n';
	if(ATCmgr->GetAirportATCDetails(ident, &a)) {
		if(a.ground_freq) {		// Ground control
			ground = (FGGround*)ATCmgr->GetATCPointer(ident, GROUND);
			separateGround = true;
			if(ground == NULL) {
				// Something has gone wrong :-(
				SG_LOG(SG_ATC, SG_WARN, "ERROR - ground has frequency but can't get ground pointer :-(");
				ground = new FGGround(ident);
				separateGround = false;
				ground->Init();
				if(display) {
					ground->SetDisplay();
				} else {
					ground->SetNoDisplay();
				}
			}
		} else {
			// Initialise ground anyway to do the shortest path stuff!
			// Note that we're now responsible for updating and deleting this - NOT the ATCMgr.
			ground = new FGGround(ident);
			separateGround = false;
			ground->Init();
			if(display) {
				ground->SetDisplay();
			} else {
				ground->SetNoDisplay();
			}
		}
	} else {
		SG_LOG(SG_ATC, SG_ALERT, "Unable to find airport details for " << ident << " in FGTower::Init()");
		// Initialise ground anyway to avoid segfault later
		ground = new FGGround(ident);
		separateGround = false;
		ground->Init();
		if(display) {
			ground->SetDisplay();
		} else {
			ground->SetNoDisplay();
		}
	}
	
	// Get the airport elevation
	aptElev = dclGetAirportElev(ident.c_str()) * SG_FEET_TO_METER;
	
	DoRwyDetails();
	
	// FIXME - this currently assumes use of the active rwy by the user.
	rwyOccupied = OnAnyRunway(Point3D(user_lon_node->getDoubleValue(), user_lat_node->getDoubleValue(), 0.0));
	if(rwyOccupied) {
		// Assume the user is started at the threshold ready to take-off
		TowerPlaneRec* t = new TowerPlaneRec;
		t->plane.callsign = "Charlie Foxtrot Sierra";	// C-FGFS !!! - fixme - this is a bit hardwired
		t->plane.type = GA_SINGLE;
		t->opType = TTT_UNKNOWN;	// We don't know if the user wants to do circuits or a departure...
		t->landingType = AIP_LT_UNKNOWN;
		t->leg = TAKEOFF_ROLL;
		t->isUser = true;
		t->planePtr = NULL;
		t->clearedToTakeOff = true;
		rwyList.push_back(t);
		departed = false;
	}
}

void FGTower::Update(double dt) {
	//cout << "T" << flush;
	// Each time step, what do we need to do?
	// We need to go through the list of outstanding requests and acknowedgements
	// and process at least one of them.
	// We need to go through the list of planes under our control and check if
	// any need to be addressed.
	// We need to check for planes not under our control coming within our 
	// control area and address if necessary.
	
	// TODO - a lot of the below probably doesn't need to be called every frame and should be staggered.
	
	// Sort the arriving planes
	
	/*
	if(ident == "KEMT") {
		cout << update_count << "\ttL: " << trafficList.size() << "  cL: " << circuitList.size() << "  hL: " << holdList.size() << "  aL: " << appList.size() << '\n';
	}
	*/
	
	if(departed != false) {
		timeSinceLastDeparture += dt;
		//if(ident == "KEMT") 
		//	cout << "  dt = " << dt << "  timeSinceLastDeparture = " << timeSinceLastDeparture << '\n';
	}
	
	// Calculate the eta of each plane to the threshold.
	// For ground traffic this is the fastest they can get there.
	// For air traffic this is the middle approximation.
	if(update_count == 1) {
		doThresholdETACalc();
	}
	
	// Order the list of traffic as per expected threshold use and flag any conflicts
	if(update_count == 2) {
		//bool conflicts = doThresholdUseOrder();
		doThresholdUseOrder();
	}
	
	// sortConficts() !!!
	
	if(update_count == 4) {
		CheckHoldList(dt);
	}
	
	// Uggh - HACK - why have we got rwyOccupied - wouldn't simply testing rwyList.size() do?
	if(rwyList.size()) {
		rwyOccupied = true;
	} else {
		rwyOccupied = false;
	}
	
	if(update_count == 5 && rwyOccupied) {
		CheckRunwayList(dt);
	}
		
	if(update_count == 6) {
		CheckCircuitList(dt);
	}
	
	if(update_count == 7) {
		CheckApproachList(dt);
	}
	
	// TODO - do one plane from the departure list and set departed = false when out of consideration
	
	//doCommunication();
	
	if(!separateGround) {
		// The display stuff might have to get more clever than this when not separate 
		// since the tower and ground might try communicating simultaneously even though
		// they're mean't to be the same contoller/frequency!!
		if(display) {
			ground->SetDisplay();
		} else {
			ground->SetNoDisplay();
		}
		ground->Update(dt);
	}
	
	++update_count;
	// How big should ii get - ie how long should the update cycle interval stretch?
	if(update_count >= update_count_max) {
		update_count = 0;
	}
	
	// Call the base class update for the response time handling.
	FGATC::Update(dt);

	if(ident == "KEMT") {	
		// For AI debugging convienience - may be removed
		Point3D user_pos;
		user_pos.setlon(user_lon_node->getDoubleValue());
		user_pos.setlat(user_lat_node->getDoubleValue());
		user_pos.setelev(user_elev_node->getDoubleValue());
		Point3D user_ortho_pos = ortho.ConvertToLocal(user_pos);
		fgSetDouble("/AI/user/ortho-x", user_ortho_pos.x());
		fgSetDouble("/AI/user/ortho-y", user_ortho_pos.y());
		fgSetDouble("/AI/user/elev", user_elev_node->getDoubleValue());
	}
}

// Do one plane from the hold list
void FGTower::CheckHoldList(double dt) {
	//cout << "ug\n";
	if(holdList.size()) {
		//cout << "*holdListItr = " << *holdListItr << endl;
		if(holdListItr == holdList.end()) {
			holdListItr = holdList.begin();
		}
		//cout << "*holdListItr = " << *holdListItr << endl;
		//Process(*holdListItr);
		TowerPlaneRec* t = *holdListItr;
		//cout << "t = " << t << endl;
		if(t->holdShortReported) {
			//cout << "ding\n";
			double responseTime = 10.0;		// seconds - this should get more sophisticated at some point
			if(t->clearanceCounter > responseTime) {
				if(t->nextOnRwy) {
					if(rwyOccupied) {	// TODO - ought to add a sanity check that it isn't this plane only on the runway (even though it shouldn't be!!)
						// Do nothing for now - consider acknowloging hold short eventually
					} else {
						// Lets Roll !!!!
						string trns = t->plane.callsign;
						//if(departed plane < some threshold in time away) {
						if(0) {		// FIXME
							trns += " line up";
							t->clearedToLineUp = true;
							t->planePtr->RegisterTransmission(3);	// cleared to line-up
							t->leg = TAKEOFF_ROLL;
						//} else if(arriving plane < some threshold away) {
						} else if(GetTrafficETA(2) < 150.0) {
							trns += " cleared immediate take-off";
							if(trafficList.size()) {
								tower_plane_rec_list_iterator trfcItr = trafficList.begin();
								trfcItr++;	// At the moment the holding plane should be first in trafficList.
								// Note though that this will break if holding planes aren't put in trafficList in the future.
								TowerPlaneRec* trfc = *trfcItr;
								trns += "... traffic is";
								switch(trfc->plane.type) {
								case UNKNOWN:
									break;
								case GA_SINGLE:
									trns += " a Cessna";	// TODO - add ability to specify actual plane type somewhere
									break;
								case GA_HP_SINGLE:
									trns += " a Piper";
									break;
								case GA_TWIN:
									trns += " a King-air";
									break;
								case GA_JET:
									trns += " a Learjet";
									break;
								case MEDIUM:
									trns += " a Regional";
									break;
								case HEAVY:
									trns += " a Heavy";
									break;
								case MIL_JET:
									trns += " Military";
									break;
								}
								if(trfc->opType == STRAIGHT_IN || trfc->opType == TTT_UNKNOWN) {
									double miles_out = CalcDistOutMiles(trfc);
									if(miles_out < 2) {
										trns += " on final";
									} else {
										trns += " on ";
										trns += ConvertNumToSpokenDigits((int)miles_out);
										trns += " mile final";
									}
								} else if(trfc->opType == CIRCUIT) {
									switch(trfc->leg) {
									case FINAL:
										trns += " on final";
										break;
									case TURN4:
										trns += " turning final";
										break;
									case BASE:
										trns += " on base";
										break;
									case TURN3:
										trns += " turning base";
										break;
									case DOWNWIND:
										trns += " in circuit";
										break;
									// And to eliminate compiler warnings...
									case TAKEOFF_ROLL: break;
									case CLIMBOUT:     break;
									case TURN1:        break;
									case CROSSWIND:    break;
									case TURN2:        break;
									case LANDING_ROLL: break;
									case LEG_UNKNOWN:  break;
									}
								}
							} else {
								// By definition there should be some arriving traffic if we're cleared for immediate takeoff
								SG_LOG(SG_ATC, SG_WARN, "Warning: Departing traffic cleared for *immediate* take-off despite no arriving traffic in FGTower");
							}
							t->clearedToTakeOff = true;
							t->planePtr->RegisterTransmission(4);	// cleared to take-off - TODO differentiate between immediate and normal take-off
							t->leg = TAKEOFF_ROLL;
							departed = false;
							timeSinceLastDeparture = 0.0;
						} else {
							trns += " cleared for take-off";
							// TODO - add traffic is... ?
							t->clearedToTakeOff = true;
							t->planePtr->RegisterTransmission(4);	// cleared to take-off
							t->leg = TAKEOFF_ROLL;
							departed = false;
							timeSinceLastDeparture = 0.0;
						}
						if(display) {
							globals->get_ATC_display()->RegisterSingleMessage(trns, 0);
						}
						t->holdShortReported = false;
						t->clearanceCounter = 0;
						rwyList.push_back(t);
						rwyOccupied = true;
						holdList.erase(holdListItr);
						holdListItr = holdList.begin();
					}
				} else {
					// Tell him to hold and what position he is.
					// Not currently sure under which circumstances we do or don't bother transmitting this.
					string trns = t->plane.callsign;
					trns += " hold position";
					if(display) {
						globals->get_ATC_display()->RegisterSingleMessage(trns, 0);
					}
					t->holdShortReported = false;
					t->clearanceCounter = 0;
					// TODO - add some idea of what traffic is blocking him.
				}
			} else {
				t->clearanceCounter += (dt * holdList.size() * update_count_max);
			}
		} else {	// not responding to report, but still need to clear if clear
			//cout << "dong\n";
			if(t->nextOnRwy) {
				//cout << "departed = " << departed << '\n';
				//cout << "timeSinceLastDeparture = " << timeSinceLastDeparture << '\n';
				if(rwyOccupied) {
					// Do nothing for now - consider acknowloging hold short eventually
				} else if(timeSinceLastDeparture <= 60.0 && departed == true) {
					// Do nothing - this is a bit of a hack - should maybe do line up be ready here
				} else {
					// Lets Roll !!!!
					string trns = t->plane.callsign;
					//cout << "******************* squaggle\n";
					//cout << "departed = " << departed << '\n';
					//cout << "timeSinceLastDeparture = " << timeSinceLastDeparture << '\n';
					//if(departed plane < some threshold in time away) {
						if(0) {		// FIXME
							//cout << "A\n";
							trns += " line up";
							t->clearedToLineUp = true;
							t->planePtr->RegisterTransmission(3);	// cleared to line-up
							t->leg = TAKEOFF_ROLL;
					//} else if(arriving plane < some threshold away) {
						} else if(GetTrafficETA(2) < 150.0 && (timeSinceLastDeparture > 60.0 || departed == false)) {	// Hack - hardwired time
							//cout << "B\n";
							trns += " cleared immediate take-off";
							// TODO - add traffic is... ?
							t->clearedToTakeOff = true;
							t->planePtr->RegisterTransmission(4);	// cleared to take-off - TODO differentiate between immediate and normal take-off
							t->leg = TAKEOFF_ROLL;
							departed = false;
							timeSinceLastDeparture = 0.0;
						} else if(timeSinceLastDeparture > 60.0 || departed == false) {	// Hack - test for timeSinceLastDeparture should be in lineup block eventually
							//cout << "C\n";
							trns += " cleared for take-off";
							// TODO - add traffic is... ?
							t->clearedToTakeOff = true;
							t->planePtr->RegisterTransmission(4);	// cleared to take-off
							t->leg = TAKEOFF_ROLL;
							departed = false;
							timeSinceLastDeparture = 0.0;
						} else {
							//cout << "D\n";
						}
						if(display) {
							globals->get_ATC_display()->RegisterSingleMessage(trns, 0);
						}
						rwyList.push_back(t);
						rwyOccupied = true;
						holdList.erase(holdListItr);
						holdListItr = holdList.begin();
				}
			}
			// TODO - rationalise the considerable code duplication above!
		}
		++holdListItr;
	}
}

// do the ciruit list
void FGTower::CheckCircuitList(double dt) {
	// Clear the constraints - we recalculate here.
	base_leg_pos = 0.0;
	downwind_leg_pos = 0.0;
	crosswind_leg_pos = 0.0;
	
	if(circuitList.size()) {	// Do one plane from the circuit
		if(circuitListItr == circuitList.end()) {
			circuitListItr = circuitList.begin();
		}
		TowerPlaneRec* t = *circuitListItr;
		if(t->isUser) {
			t->pos.setlon(user_lon_node->getDoubleValue());
			t->pos.setlat(user_lat_node->getDoubleValue());
			t->pos.setelev(user_elev_node->getDoubleValue());
		} else {
			t->pos = t->planePtr->GetPos();		// We should probably only set the pos's on one walk through the traffic list in the update function, to save a few CPU should we end up duplicating this.
			t->landingType = t->planePtr->GetLandingOption();
			//cout << "AI plane landing option is " << t->landingType << '\n';
		}
		Point3D tortho = ortho.ConvertToLocal(t->pos);
		if(t->isUser) {
			// Need to figure out which leg he's on
			//cout << "rwy.hdg = " << rwy.hdg << " user hdg = " << user_hdg_node->getDoubleValue();
			double ho = GetAngleDiff_deg(user_hdg_node->getDoubleValue(), rwy.hdg);
			//cout << " ho = " << ho << '\n';
			// TODO FIXME - get the wind and convert this to track, or otherwise use track somehow!!!
			// If it's gusty might need to filter the value, although we are leaving 30 degrees each way leeway!
			if(abs(ho) < 30) {
				// could be either takeoff, climbout or landing - check orthopos.y
				//cout << "tortho.y = " << tortho.y() << '\n';
				if((tortho.y() < 0) || (t->leg == TURN4) || (t->leg == FINAL)) {
					t->leg = FINAL;
					//cout << "Final\n";
				} else {
					t->leg = CLIMBOUT;	// TODO - check elev wrt. apt elev to differentiate takeoff roll and climbout
					//cout << "Climbout\n";
					// If it's the user we may be unsure of his/her intentions.
					// (Hopefully the AI planes won't try confusing the sim!!!)
					if(t->opType == TTT_UNKNOWN) {
						if(tortho.y() > 5000) {
							// 5 km out from threshold - assume it's a departure
							t->opType = OUTBOUND;	// TODO - could check if the user has climbed significantly above circuit altitude as well.
							// Since we are unknown operation we should be in depList already.
							circuitList.erase(circuitListItr);
							RemoveFromTrafficList(t->plane.callsign);
							circuitListItr = circuitList.begin();
						}
					} else if(t->opType == CIRCUIT) {
						if(tortho.y() > 10000) {
							// 10 km out - assume the user has abandoned the circuit!!
							t->opType = OUTBOUND;
							depList.push_back(t);
							circuitList.erase(circuitListItr);
							circuitListItr = circuitList.begin();
						}
					}
				}
			} else if(abs(ho) < 60) {
				// turn1 or turn 4
				// TODO - either fix or doublecheck this hack by looking at heading and pattern direction
				if((t->leg == CLIMBOUT) || (t->leg == TURN1)) {
					t->leg = TURN1;
					//cout << "Turn1\n";
				} else {
					t->leg = TURN4;
					//cout << "Turn4\n";
				}
			} else if(abs(ho) < 120) {
				// crosswind or base
				// TODO - either fix or doublecheck this hack by looking at heading and pattern direction
				if((t->leg == TURN1) || (t->leg == CROSSWIND)) {
					t->leg = CROSSWIND;
					//cout << "Crosswind\n";
				} else {
					t->leg = BASE;
					//cout << "Base\n";
				}
			} else if(abs(ho) < 150) {
				// turn2 or turn 3
				// TODO - either fix or doublecheck this hack by looking at heading and pattern direction
				if((t->leg == CROSSWIND) || (t->leg == TURN2)) {
					t->leg = TURN2;
					//cout << "Turn2\n";
				} else {
					t->leg = TURN3;
					// Probably safe now to assume the user is flying a circuit
					t->opType = CIRCUIT;
					//cout << "Turn3\n";
				}
			} else {
				// downwind
				t->leg = DOWNWIND;
				//cout << "Downwind\n";
			}
			if(t->leg == FINAL) {
				if(OnActiveRunway(t->pos)) {
					t->leg = LANDING_ROLL;
				}
			}
		} else {
			t->leg = t->planePtr->GetLeg();
		}
		
		// Set the constraints IF this is the first plane in the circuit
		// TODO - at the moment we're constraining plane 2 based on plane 1 - this won't (or might not) work for 3 planes in the circuit!!
		if(circuitListItr == circuitList.begin()) {
			switch(t->leg) {
			case FINAL:
				// Base leg must be at least as far out as the plane is - actually possibly not necessary for separation, but we'll use that for now.
				base_leg_pos = tortho.y();
				//cout << "base_leg_pos = " << base_leg_pos << '\n';
				break;
			case TURN4:
				// Fall through to base
			case BASE:
				base_leg_pos = tortho.y();
				//cout << "base_leg_pos = " << base_leg_pos << '\n';
				break;
			case TURN3:
				// Fall through to downwind
			case DOWNWIND:
				// Only have the downwind leg pos as turn-to-base constraint if more negative than we already have.
				base_leg_pos = (tortho.y() < base_leg_pos ? tortho.y() : base_leg_pos);
				//cout << "base_leg_pos = " << base_leg_pos;
				downwind_leg_pos = tortho.x();		// Assume that a following plane can simply be constrained by the immediately in front downwind plane
				//cout << " downwind_leg_pos = " << downwind_leg_pos << '\n';
				break;
			case TURN2:
				// Fall through to crosswind
			case CROSSWIND:
				crosswind_leg_pos = tortho.y();
				//cout << "crosswind_leg_pos = " << crosswind_leg_pos << '\n';
				break;
			case TURN1:
				// Fall through to climbout
			case CLIMBOUT:
				// Only use current by constraint as largest
				crosswind_leg_pos = (tortho.y() > crosswind_leg_pos ? tortho.y() : crosswind_leg_pos);
				//cout << "crosswind_leg_pos = " << crosswind_leg_pos << '\n';
				break;
			case TAKEOFF_ROLL:
				break;
			case LEG_UNKNOWN:
				break;
			case LANDING_ROLL:
				break;
			default:
				break;
			}
		}
		
		if(t->leg == FINAL) {
			if(t->landingType == FULL_STOP) t->opType = INBOUND;
		} else if(t->leg == LANDING_ROLL) {
			rwyList.push_front(t);
			RemoveFromTrafficList(t->plane.callsign);
			if(t->isUser) {
				t->opType = TTT_UNKNOWN;
			}	// TODO - allow the user to specify opType via ATC menu
			circuitListItr = circuitList.erase(circuitListItr);
			if(circuitListItr == circuitList.end() ) {
				circuitListItr = circuitList.begin();
			}
		}
		++circuitListItr;
	}
}

// Do the runway list - we'll do the whole runway list since it's important and there'll never be many planes on the rwy at once!!
// FIXME - at the moment it looks like we're only doing the first plane from the rwy list.
// (However, at the moment there should only be one airplane on the rwy at once, until we
// start allowing planes to line up whilst previous arrival clears the rwy.)
void FGTower::CheckRunwayList(double dt) {
	if(rwyOccupied) {
		if(!rwyList.size()) {
			rwyOccupied = false;
		} else {
			rwyListItr = rwyList.begin();
			TowerPlaneRec* t = *rwyListItr;
			if(t->isUser) {
				t->pos.setlon(user_lon_node->getDoubleValue());
				t->pos.setlat(user_lat_node->getDoubleValue());
				t->pos.setelev(user_elev_node->getDoubleValue());
			} else {
				t->pos = t->planePtr->GetPos();		// We should probably only set the pos's on one walk through the traffic list in the update function, to save a few CPU should we end up duplicating this.
			}
			bool on_rwy = OnActiveRunway(t->pos);
			if(!on_rwy) {
				if((t->opType == INBOUND) || (t->opType == STRAIGHT_IN)) {
					rwyList.pop_front();
					delete t;
					// TODO - tell it to taxi / contact ground / don't delete it etc!
				} else if(t->opType == OUTBOUND) {
					depList.push_back(t);
					rwyList.pop_front();
					departed = true;
					timeSinceLastDeparture = 0.0;
				} else if(t->opType == CIRCUIT) {
					circuitList.push_back(t);
					AddToTrafficList(t);
					rwyList.pop_front();
					departed = true;
					timeSinceLastDeparture = 0.0;
				} else if(t->opType == TTT_UNKNOWN) {
					depList.push_back(t);
					circuitList.push_back(t);
					AddToTrafficList(t);
					rwyList.pop_front();
					departed = true;
					timeSinceLastDeparture = 0.0;	// TODO - we need to take into account that the user might taxi-in when flagged opType UNKNOWN - check speed/altitude etc to make decision as to what user is up to.
				} else {
					// HELP - we shouldn't ever get here!!!
				}
			}
		}
	}
}

// Do one plane from the approach list
void FGTower::CheckApproachList(double dt) {
	if(appList.size()) {
		if(appListItr == appList.end()) {
			appListItr = appList.begin();
		}
		TowerPlaneRec* t = *appListItr;
		//cout << "t = " << t << endl;
		if(t->isUser) {
			t->pos.setlon(user_lon_node->getDoubleValue());
			t->pos.setlat(user_lat_node->getDoubleValue());
			t->pos.setelev(user_elev_node->getDoubleValue());
		} else {
			// TODO - set/update the position if it's an AI plane
		}				
		if(t->nextOnRwy && !(t->clearedToLand)) {
			// check distance away and whether runway occupied
			// and schedule transmission if necessary
		}				
		++appListItr;
	}
}

// Returns true if positions of crosswind/downwind/base leg turns should be constrained by previous traffic
// plus the constraint position as a rwy orientated orthopos (meters)
bool FGTower::GetCrosswindConstraint(double& cpos) {
	if(crosswind_leg_pos != 0.0) {
		cpos = crosswind_leg_pos;
		return(true);
	} else {
		cpos = 0.0;
		return(false);
	}
}
bool FGTower::GetDownwindConstraint(double& dpos) {
	if(downwind_leg_pos != 0.0) {
		dpos = downwind_leg_pos;
		return(true);
	} else {
		dpos = 0.0;
		return(false);
	}
}
bool FGTower::GetBaseConstraint(double& bpos) {
	if(base_leg_pos != 0.0) {
		bpos = base_leg_pos;
		return(true);
	} else {
		bpos = 0.0;
		return(false);
	}
}


// Figure out which runways are active.
// For now we'll just be simple and do one active runway - eventually this will get much more complex
// This is a private function - public interface to the results of this is through GetActiveRunway
void FGTower::DoRwyDetails() {
	//cout << "GetRwyDetails called" << endl;
	
	// Based on the airport-id and wind get the active runway
	
	//wind
	double hdg = wind_from_hdg->getDoubleValue();
	double speed = wind_speed_knots->getDoubleValue();
	hdg = (speed == 0.0 ? 270.0 : hdg);
	//cout << "Heading = " << hdg << '\n';
	
	FGRunway runway;
	bool rwyGood = globals->get_runways()->search(ident, int(hdg), &runway);
	if(rwyGood) {
		activeRwy = runway.rwy_no;
		rwy.rwyID = runway.rwy_no;
		SG_LOG(SG_ATC, SG_INFO, "Active runway for airport " << ident << " is " << activeRwy);
		
		// Get the threshold position
		double other_way = runway.heading - 180.0;
		while(other_way <= 0.0) {
			other_way += 360.0;
		}
    	// move to the +l end/center of the runway
		//cout << "Runway center is at " << runway.lon << ", " << runway.lat << '\n';
    	Point3D origin = Point3D(runway.lon, runway.lat, aptElev);
		Point3D ref = origin;
    	double tshlon, tshlat, tshr;
		double tolon, tolat, tor;
		rwy.length = runway.length * SG_FEET_TO_METER;
		rwy.width = runway.width * SG_FEET_TO_METER;
    	geo_direct_wgs_84 ( aptElev, ref.lat(), ref.lon(), other_way, 
        	                rwy.length / 2.0 - 25.0, &tshlat, &tshlon, &tshr );
    	geo_direct_wgs_84 ( aptElev, ref.lat(), ref.lon(), runway.heading, 
        	                rwy.length / 2.0 - 25.0, &tolat, &tolon, &tor );
		// Note - 25 meters in from the runway end is a bit of a hack to put the plane ahead of the user.
		// now copy what we need out of runway into rwy
    	rwy.threshold_pos = Point3D(tshlon, tshlat, aptElev);
		Point3D takeoff_end = Point3D(tolon, tolat, aptElev);
		//cout << "Threshold position = " << tshlon << ", " << tshlat << ", " << aptElev << '\n';
		//cout << "Takeoff position = " << tolon << ", " << tolat << ", " << aptElev << '\n';
		rwy.hdg = runway.heading;
		// Set the projection for the local area based on this active runway
		ortho.Init(rwy.threshold_pos, rwy.hdg);	
		rwy.end1ortho = ortho.ConvertToLocal(rwy.threshold_pos);	// should come out as zero
		rwy.end2ortho = ortho.ConvertToLocal(takeoff_end);
	} else {
		SG_LOG(SG_ATC, SG_ALERT, "Help  - can't get good runway in FGTower!!");
		activeRwy = "NN";
	}
}


// Figure out if a given position lies on the active runway
// Might have to change when we consider more than one active rwy.
bool FGTower::OnActiveRunway(Point3D pt) {
	// TODO - check that the centre calculation below isn't confused by displaced thesholds etc.
	Point3D xyc((rwy.end1ortho.x() + rwy.end2ortho.x())/2.0, (rwy.end1ortho.y() + rwy.end2ortho.y())/2.0, 0.0);
	Point3D xyp = ortho.ConvertToLocal(pt);
	
	//cout << "Length offset = " << fabs(xyp.y() - xyc.y()) << '\n';
	//cout << "Width offset = " << fabs(xyp.x() - xyc.x()) << '\n';

	double rlen = rwy.length/2.0 + 5.0;
	double rwidth = rwy.width/2.0;
	double ldiff = fabs(xyp.y() - xyc.y());
	double wdiff = fabs(xyp.x() - xyc.x());

	return((ldiff < rlen) && (wdiff < rwidth));
}	


// Figure out if a given position lies on any runway or not
// Only call this at startup - reading the runways database is expensive and needs to be fixed!
bool FGTower::OnAnyRunway(Point3D pt) {
	ATCData ad;
	double dist = current_commlist->FindClosest(lon, lat, elev, ad, TOWER, 10.0);
	if(dist < 0.0) {
		return(false);
	}
	// Based on the airport-id, go through all the runways and check for a point in them
	
	// TODO - do we actually need to search for the airport - surely we already know our ident and
	// can just search runways of our airport???
	//cout << "Airport ident is " << ad.ident << '\n';
	FGRunway runway;
	bool rwyGood = globals->get_runways()->search(ad.ident, &runway);
	if(!rwyGood) {
		SG_LOG(SG_ATC, SG_WARN, "Unable to find any runways for airport ID " << ad.ident << " in FGTower");
	}
	bool on = false;
	while(runway.id == ad.ident) {		
		on = OnRunway(pt, runway);
		//cout << "Runway " << runway.rwy_no << ": On = " << (on ? "true\n" : "false\n");
		if(on) return(true);
		globals->get_runways()->next(&runway);		
	}
	return(on);
}


// Returns true if successful
bool FGTower::RemoveFromTrafficList(string id) {
	tower_plane_rec_list_iterator twrItr;
	for(twrItr = trafficList.begin(); twrItr != trafficList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		if(tpr->plane.callsign == id) {
			trafficList.erase(twrItr);
			return(true);
		}
	}	
	SG_LOG(SG_ATC, SG_WARN, "Warning - unable to remove aircraft " << id << " from trafficList in FGTower");
	return(false);
}


// Add a tower plane rec with ETA to the traffic list in the correct position ETA-wise
// and set nextOnRwy if so.
// Returns true if this could cause a threshold ETA conflict with other traffic, false otherwise.
// For planes holding they are put in the first position with time to go, and the return value is
// true if in the first position (nextOnRwy) and false otherwise.
// See the comments in FGTower::doThresholdUseOrder for notes on the ordering
bool FGTower::AddToTrafficList(TowerPlaneRec* t, bool holding) {
	//cout << "ADD: " << trafficList.size();
	//cout << "AddToTrafficList called, currently size = " << trafficList.size() << ", holding = " << holding << '\n';
	double separation_time = 90.0;	// seconds - this is currently a guess for light plane separation, and includes a few seconds for a holding plane to taxi onto the rwy.
	double departure_sep_time = 60.0;	// Separation time behind departing airplanes.  Comments above also apply.
	bool conflict = false;
	double lastETA = 0.0;
	bool firstTime = true;
	// FIXME - make this more robust for different plane types eg. light following heavy.
	tower_plane_rec_list_iterator twrItr;
	//twrItr = trafficList.begin();
	//while(1) {
	for(twrItr = trafficList.begin(); twrItr != trafficList.end(); twrItr++) {
		//if(twrItr == trafficList.end()) {
		//	cout << "  END  ";
		//	trafficList.push_back(t);
		//	return(holding ? firstTime : conflict);
		//} else {
			TowerPlaneRec* tpr = *twrItr;
			if(holding) {
				//cout << (tpr->isUser ? "USER!\n" : "NOT user\n");
				//cout << "tpr->eta - lastETA = " << tpr->eta - lastETA << '\n';
				double dep_allowance = (timeSinceLastDeparture < departure_sep_time ? departure_sep_time - timeSinceLastDeparture : 0.0); 
				double slot_time = (firstTime ? separation_time + dep_allowance : separation_time + departure_sep_time);
				// separation_time + departure_sep_time in the above accounts for the fact that the arrival could be touch and go,
				// and if not needs time to clear the rwy anyway.
				if(tpr->eta  - lastETA > slot_time) {
					t->nextOnRwy = firstTime;
					trafficList.insert(twrItr, t);
					//cout << "\tH\t" << trafficList.size() << '\n';
					return(firstTime);
				}
				firstTime = false;
			} else {
				if(t->eta < tpr->eta) {
					// Ugg - this one's tricky.
					// It depends on what the two planes are doing and whether there's a conflict what we do.
					if(tpr->eta - t->eta > separation_time) {	// No probs, plane 2 can squeeze in before plane 1 with no apparent conflict
						if(tpr->nextOnRwy) {
							tpr->nextOnRwy = false;
							t->nextOnRwy = true;
						}
						trafficList.insert(twrItr, t);
					} else {	// Ooops - this ones tricky - we have a potential conflict!
						conflict = true;
						// HACK - just add anyway for now and flag conflict - TODO - FIX THIS using CIRCUIT/STRAIGHT_IN and VFR/IFR precedence rules.
						if(tpr->nextOnRwy) {
							tpr->nextOnRwy = false;
							t->nextOnRwy = true;
						}
						trafficList.insert(twrItr, t);
					}
					//cout << "\tC\t" << trafficList.size() << '\n';
					return(conflict);
				}
			}
		//}
		//++twrItr;
	}
	// If we get here we must be at the end of the list, or maybe the list is empty.
	if(!trafficList.size()) {
		t->nextOnRwy = true;
		// conflict and firstTime should be false and true respectively in this case anyway.
	}
	trafficList.push_back(t);
	//cout << "\tE\t" << trafficList.size() << '\n';
	return(holding ? firstTime : conflict);
}


// Calculate the eta of a plane to the threshold.
// For ground traffic this is the fastest they can get there.
// For air traffic this is the middle approximation.
void FGTower::CalcETA(TowerPlaneRec* tpr, bool printout) {
	// For now we'll be very crude and hardwire expected speeds to C172-like values
	// The speeds below are specified in knots IAS and then converted to m/s
	double app_ias = 100.0 * 0.514444;			// Speed during straight-in approach
	double circuit_ias = 80.0 * 0.514444;		// Speed around circuit
	double final_ias = 70.0 * 0.514444;		// Speed during final approach
	
	//if(printout) {
	//	cout << "In CalcETA, airplane ident = " << tpr->plane.callsign << '\n';
	//	cout << (tpr->isUser ? "USER\n" : "AI\n");
	//}
	
	// Sign convention - dist_out is -ve for approaching planes and +ve for departing planes
	// dist_across is +ve in the pattern direction - ie a plane correctly on downwind will have a +ve dist_across
	
	Point3D op = ortho.ConvertToLocal(tpr->pos);
	//if(printout) {
	//	cout << "Orthopos is " << op.x() << ", " << op.y() << '\n';
	//	cout << "opType is " << tpr->opType << '\n';
	//}
	double dist_out_m = op.y();
	double dist_across_m = fabs(op.x());	// FIXME = the fabs is a hack to cope with the fact that we don't know the circuit direction yet
	//cout << "Doing ETA calc for " << tpr->plane.callsign << '\n';
	
	if(tpr->opType == STRAIGHT_IN) {
		double dist_to_go_m = sqrt((dist_out_m * dist_out_m) + (dist_across_m * dist_across_m));
		if(dist_to_go_m < 1000) {
			tpr->eta = dist_to_go_m / final_ias;
		} else {
			tpr->eta = (1000.0 / final_ias) + ((dist_to_go_m - 1000.0) / app_ias);
		}
	} else if(tpr->opType == CIRCUIT || tpr->opType == TTT_UNKNOWN) {	// Hack alert - UNKNOWN has sort of been added here as a temporary hack.
		// It's complicated - depends on if base leg is delayed or not
		//if(printout) {
		//	cout << "Leg = " << tpr->leg << '\n';
		//}
		if(tpr->leg == LANDING_ROLL) {
			tpr->eta = 0;
		} else if((tpr->leg == FINAL) || (tpr->leg == TURN4)) {
			tpr->eta = fabs(dist_out_m) / final_ias;
		} else if((tpr->leg == BASE) || (tpr->leg == TURN3)) {
			tpr->eta = (fabs(dist_out_m) / final_ias) + (dist_across_m / circuit_ias);
		} else {
			// Need to calculate where base leg is likely to be
			// FIXME - for now I'll hardwire it to 1000m which is what AILocalTraffic uses!!!
			// TODO - as a matter of design - AILocalTraffic should get the nominal no-traffic base turn distance from Tower, since in real life the published pattern might differ from airport to airport
			double nominal_base_dist_out_m = -1000;
			double current_base_dist_out_m;
			if(!GetBaseConstraint(current_base_dist_out_m)) {
				current_base_dist_out_m = nominal_base_dist_out_m;
			}
			double nominal_dist_across_m = 1000;	// Hardwired value from AILocalTraffic
			double current_dist_across_m;
			if(!GetDownwindConstraint(current_dist_across_m)) {
				current_dist_across_m = nominal_dist_across_m;
			}
			double nominal_cross_dist_out_m = 2000;	// Bit of a guess - AI plane turns to crosswind at 600ft agl.
			tpr->eta = fabs(current_base_dist_out_m) / final_ias;	// final
			//if(printout) cout << "a = " << tpr->eta << '\n';
			if((tpr->leg == DOWNWIND) || (tpr->leg == TURN2)) {
				tpr->eta += dist_across_m / circuit_ias;
				//if(printout) cout << "b = " << tpr->eta << '\n';
				tpr->eta += fabs(current_base_dist_out_m - dist_out_m) / circuit_ias;
				//if(printout) cout << "c = " << tpr->eta << '\n';
			} else if((tpr->leg == CROSSWIND) || (tpr->leg == TURN1)) {
				if(dist_across_m > nominal_dist_across_m) {
					tpr->eta += dist_across_m / circuit_ias;
				} else {
					tpr->eta += nominal_dist_across_m / circuit_ias;
				}
				// should we use the dist across of the previous plane if there is previous still on downwind?
				//if(printout) cout << "bb = " << tpr->eta << '\n';
				if(dist_out_m > nominal_cross_dist_out_m) {
					tpr->eta += fabs(current_base_dist_out_m - dist_out_m) / circuit_ias;
				} else {
					tpr->eta += fabs(current_base_dist_out_m - nominal_cross_dist_out_m) / circuit_ias;
				}
				//if(printout) cout << "cc = " << tpr->eta << '\n';
				if(nominal_dist_across_m > dist_across_m) {
					tpr->eta += (nominal_dist_across_m - dist_across_m) / circuit_ias;
				} else {
					// Nothing to add
				}
				//if(printout) cout << "dd = " << tpr->eta << '\n';
			} else {
				// We've only just started - why not use a generic estimate?
				tpr->eta = 240.0;
			}
		}
		//if(printout) {
		//	cout << "ETA = " << tpr->eta << '\n';
		//}
	} else {
		tpr->eta = 99999;
	}	
}


// Calculate the distance of a plane to the threshold in meters
// TODO - Modify to calculate flying distance of a plane in the circuit
double FGTower::CalcDistOutM(TowerPlaneRec* tpr) {
	return(dclGetHorizontalSeparation(rwy.threshold_pos, tpr->pos));
}


// Calculate the distance of a plane to the threshold in miles
// TODO - Modify to calculate flying distance of a plane in the circuit
double FGTower::CalcDistOutMiles(TowerPlaneRec* tpr) {
	return(CalcDistOutM(tpr) / 1600.0);		// FIXME - use a proper constant if possible.
}


// Iterate through all the lists and call CalcETA for all the planes.
void FGTower::doThresholdETACalc() {
	tower_plane_rec_list_iterator twrItr;
	// Do the approach list first
	for(twrItr = appList.begin(); twrItr != appList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		CalcETA(tpr);
	}	
	// Then the circuit list
	for(twrItr = circuitList.begin(); twrItr != circuitList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		CalcETA(tpr);
	}
}
		

// Check that the planes in traffic list are correctly ordered,
// that the nearest (timewise) is flagged next on rwy, and return
// true if any threshold use conflicts are detected, false otherwise.
bool FGTower::doThresholdUseOrder() {
	bool conflict = false;
	
	// Wipe out traffic list, go through circuit, app and hold list, and reorder them in traffic list.
	// Here's the rather simplistic assumptions we're using:
	// Currently all planes are assumed to be GA light singles with corresponding speeds and separation times.
	// In order of priority for runway use:
	// STRAIGHT_IN > CIRCUIT > HOLDING_FOR_DEPARTURE
	// No modification of planes speeds occurs - conflicts are resolved by delaying turn for base,
	// and holding planes until a space.
	// When calculating if a holding plane can use the runway, time clearance from last departure
	// as well as time clearance to next arrival must be considered.
	
	trafficList.clear();
	
	tower_plane_rec_list_iterator twrItr;
	// Do the approach list first
	for(twrItr = appList.begin(); twrItr != appList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		conflict = AddToTrafficList(tpr);
	}	
	// Then the circuit list
	for(twrItr = circuitList.begin(); twrItr != circuitList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		conflict = AddToTrafficList(tpr);
	}
	// And finally the hold list
	for(twrItr = holdList.begin(); twrItr != holdList.end(); twrItr++) {
		TowerPlaneRec* tpr = *twrItr;
		AddToTrafficList(tpr, true);
	}
	
	if(0) {
	//if(ident == "KEMT") {
		for(twrItr = trafficList.begin(); twrItr != trafficList.end(); twrItr++) {
			TowerPlaneRec* tpr = *twrItr;
			cout << tpr->plane.callsign << '\t' << tpr->eta << '\t';
		}
		cout << '\n';
	}
	
	return(conflict);
}

/*
void FGTower::doCommunication() {
}
*/

// Return the ETA of plane no. list_pos (1-based) in the traffic list.
// i.e. list_pos = 1 implies next to use runway.
double FGTower::GetTrafficETA(unsigned int list_pos, bool printout) {
	if(trafficList.size() < list_pos) {
		return(99999);
	}

	tower_plane_rec_list_iterator twrItr;
	twrItr = trafficList.begin();
	for(unsigned int i = 1; i < list_pos; i++, twrItr++);
	TowerPlaneRec* tpr = *twrItr;
	CalcETA(tpr, printout);
	//cout << "ETA returned = " << tpr->eta << '\n';
	return(tpr->eta);
}
	

void FGTower::ContactAtHoldShort(PlaneRec plane, FGAIPlane* requestee, tower_traffic_type operation) {
	// HACK - assume that anything contacting at hold short is new for now - FIXME LATER
	TowerPlaneRec* t = new TowerPlaneRec;
	t->plane = plane;
	t->planePtr = requestee;
	t->holdShortReported = true;
	t->clearanceCounter = 0;
	t->clearedToLineUp = false;
	t->clearedToTakeOff = false;
	t->opType = operation;
	
	//cout << "Hold Short reported by " << plane.callsign << '\n';
	
	bool next = AddToTrafficList(t, true);
	
	if(next) {
		//cout << "Next to take off - respond with clearance\n";
		double teta = GetTrafficETA(2);
		if(teta < 150.0) {
			t->clearanceCounter = 7.0;	// This reduces the delay before response to 3 secs if an immediate takeoff is reqd
			//cout << "Reducing response time to request due imminent traffic\n";
		}
	} else {
		//cout << "Not next to take off - respond with hold\n";
	}
	
	//cout << "t = " << t << '\n';
	
	holdList.push_back(t);
}

void FGTower::RequestLandingClearance(string ID) {
	//cout << "Request Landing Clearance called...\n";
	
	// Assume this comes from the user - have another function taking a pointer to the AIplane for the AI traffic.
	// For now we'll also assume that the user is a light plane and can get him/her to join the circuit if necessary.
	
	TowerPlaneRec* t = new TowerPlaneRec;
	t->isUser = true;
	t->clearedToLand = false;
	t->pos.setlon(user_lon_node->getDoubleValue());
	t->pos.setlat(user_lat_node->getDoubleValue());
	t->pos.setelev(user_elev_node->getDoubleValue());
	
	// TODO
	// Calculate where the user is in relation to the active runway and it's circuit
	// and set the op-type as appropriate.
	
	// HACK - to get up and running I'm going to assume that the user contacts tower on a staight-in final for now.
	t->opType = STRAIGHT_IN;
	
	t->plane.type = GA_SINGLE;	// FIXME - Another assumption!
	t->plane.callsign = ID;
	
	appList.push_back(t);	// Not necessarily permanent
	AddToTrafficList(t);
}

void FGTower::RequestDepartureClearance(string ID) {
	//cout << "Request Departure Clearance called...\n";
}	
//void FGTower::ReportFinal(string ID);
//void FGTower::ReportLongFinal(string ID);
//void FGTower::ReportOuterMarker(string ID);
//void FGTower::ReportMiddleMarker(string ID);
//void FGTower::ReportInnerMarker(string ID);
//void FGTower::ReportGoingAround(string ID);
void FGTower::ReportRunwayVacated(string ID) {
	//cout << "Report Runway Vacated Called...\n";
}

void FGTower::ReportDownwind(string ID) {
	// Tell the plane reporting what number she is in the circuit
}

ostream& operator << (ostream& os, tower_traffic_type ttt) {
	switch(ttt) {
	case(CIRCUIT):      return(os << "CIRCUIT");
	case(INBOUND):      return(os << "INBOUND");
	case(OUTBOUND):     return(os << "OUTBOUND");
	case(TTT_UNKNOWN):  return(os << "UNKNOWN");
	case(STRAIGHT_IN):  return(os << "STRAIGHT_IN");
	}
	return(os << "ERROR - Unknown switch in tower_traffic_type operator << ");
}