1 // FGGround - a class to provide ground control at larger airports.
3 // Written by David Luff, started March 2002.
5 // Copyright (C) 2002 David C. Luff - david.luff@nottingham.ac.uk
7 // This program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License as
9 // published by the Free Software Foundation; either version 2 of the
10 // License, or (at your option) any later version.
12 // This program is distributed in the hope that it will be useful, but
13 // WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
27 #include <simgear/misc/sg_path.hxx>
28 #include <simgear/math/sg_random.h>
29 #include <simgear/debug/logstream.hxx>
30 #include <simgear/misc/sgstream.hxx>
31 #include <simgear/constants.h>
32 #include <Main/globals.hxx>
38 #include "ATCutils.hxx"
39 #include "AILocalTraffic.hxx"
49 for(unsigned int i=0; i < arcs.size(); ++i) {
54 // Make sure that a_path.cost += distance is safe from the moment it's created.
59 FGGround::FGGround() {
60 ATCmgr = globals->get_ATC_mgr();
62 networkLoadOK = false;
63 ground_traffic.erase(ground_traffic.begin(), ground_traffic.end());
64 ground_traffic_itr = ground_traffic.begin();
66 // Init the property nodes - TODO - need to make sure we're getting surface winds.
67 wind_from_hdg = fgGetNode("/environment/wind-from-heading-deg", true);
68 wind_speed_knots = fgGetNode("/environment/wind-speed-kt", true);
70 // TODO - get the actual airport elevation
74 FGGround::FGGround(const string& id) {
75 ATCmgr = globals->get_ATC_mgr();
76 networkLoadOK = false;
77 ground_traffic.erase(ground_traffic.begin(), ground_traffic.end());
78 ground_traffic_itr = ground_traffic.begin();
81 // Init the property nodes - TODO - need to make sure we're getting surface winds.
82 wind_from_hdg = fgGetNode("/environment/wind-from-heading-deg", true);
83 wind_speed_knots = fgGetNode("/environment/wind-speed-kt", true);
85 // TODO - get the actual airport elevation
89 FGGround::~FGGround() {
92 void FGGround::ParseRwyExits(node* np, char* es) {
96 const char delimiters[] = "-";
97 token = strtok(estr, delimiters);
98 while(token != NULL) {
100 //cout << "token = " << token << endl;
101 //cout << "rwy number = " << i << endl;
102 //runways[(atoi(token))].exits.push_back(np);
103 runways[i].exits.push_back(np);
104 //cout << "token = " << token << '\n';
105 token = strtok(NULL, delimiters);
110 // Load the ground logical network of the current instances airport
111 // Return true if successfull.
112 // TODO - currently the file is assumed to reside in the base/ATC directory.
113 // This might change to something more thought out in the future.
114 // NOTE - currently it is assumed that all nodes are loaded before any arcs.
115 // It won't work ATM if this doesn't hold true.
116 bool FGGround::LoadNetwork() {
121 int gateCount = 0; // This is used to allocate gateID's from zero upwards
122 // This may well change in the future - probably to reading in the real-world
123 // gate numbers from file.
126 SGPath path = globals->get_fg_root();
127 //string taxiPath = "ATC/" + ident + ".taxi";
128 string taxiPath = "ATC/KEMT.taxi"; // FIXME - HARDWIRED FOR TESTING
129 path.append(taxiPath);
131 SG_LOG(SG_ATC, SG_INFO, "Trying to read taxiway data for " << ident << "...");
132 //cout << "Trying to read taxiway data for " << ident << "..." << endl;
133 fin.open(path.c_str(), ios::in);
135 SG_LOG(SG_ATC, SG_ALERT, "Unable to open taxiway data input file " << path.c_str());
136 //cout << "Unable to open taxiway data input file " << path.c_str() << endl;
144 // Node, arc, or [End]?
145 //cout << "Read in ground network element type = " << buf << endl;
146 if(!strcmp(buf, "[End]")) { // TODO - maybe make this more robust to spelling errors by just looking for '['
147 SG_LOG(SG_ATC, SG_INFO, "Done reading " << path.c_str() << endl);
149 } else if(!strcmp(buf, "N")) {
152 np->struct_type = NODE;
154 np->nodeID = atoi(buf);
156 np->pos.setLongitudeDeg(atof(buf));
158 np->pos.setLatitudeDeg(atof(buf));
160 np->pos.setElevationM(atof(buf));
161 fin >> buf; // node type
162 if(!strcmp(buf, "J")) {
164 } else if(!strcmp(buf, "T")) {
165 np->type = TJUNCTION;
166 } else if(!strcmp(buf, "H")) {
169 SG_LOG(SG_ATC, SG_ALERT, "**** ERROR ***** Unknown node type in taxi network...\n");
173 fin >> buf; // rwy exit information - gets parsed later - FRAGILE - will break if buf is reused.
175 fin >> ch; // strip the leading " off
178 fin.unsetf(ios::skipws);
180 if((ch == '"') || (ch == 0x0A)) {
182 } // we shouldn't need the 0x0A but it makes a nice safely in case someone leaves off the "
185 fin.setf(ios::skipws);
186 network.push_back(np);
187 // FIXME - fragile - replies on buf not getting modified from exits read to here
188 // see if we also need to push it onto the runway exit list
189 //cout << "strlen(buf) = " << strlen(buf) << endl;
190 if(strlen(buf) > 2) {
191 //cout << "Calling ParseRwyExits for " << buf << endl;
192 ParseRwyExits(np, buf);
194 } else if(!strcmp(buf, "A")) {
196 ap->struct_type = ARC;
202 if(!strcmp(buf, "R")) {
204 } else if(!strcmp(buf, "T")) {
207 SG_LOG(SG_ATC, SG_ALERT, "**** ERROR ***** Unknown arc type in taxi network...\n");
213 if(!strcmp(buf, "Y")) {
215 } else if(!strcmp(buf, "N")) {
216 ap->directed = false;
218 SG_LOG(SG_ATC, SG_ALERT, "**** ERROR ***** Unknown arc directed value in taxi network - should be Y/N !!!\n");
225 fin.unsetf(ios::skipws);
228 if((ch == '"') || (ch == 0x0A)) {
230 } // we shouldn't need the 0x0A but it makes a nice safely in case someone leaves off the "
232 fin.setf(ios::skipws);
233 ap->distance = (int)dclGetHorizontalSeparation(network[ap->n1]->pos, network[ap->n2]->pos);
234 //cout << "Distance = " << ap->distance << '\n';
235 network[ap->n1]->arcs.push_back(ap);
236 network[ap->n2]->arcs.push_back(ap);
237 } else if(!strcmp(buf, "G")) {
239 gp->struct_type = NODE;
242 gp->nodeID = atoi(buf);
244 gp->pos.setLongitudeDeg(atof(buf));
246 gp->pos.setLatitudeDeg(atof(buf));
248 gp->pos.setElevationM(atof(buf));
249 fin >> buf; // gate type - ignore this for now
250 fin >> buf; // gate heading
251 gp->heading = atoi(buf);
255 fin.unsetf(ios::skipws);
258 if((ch == '"') || (ch == 0x0A)) {
260 } // we shouldn't need the 0x0A but it makes a nice safely in case someone leaves off the "
262 fin.setf(ios::skipws);
263 gp->id = gateCount; // Warning - this will likely change in the future.
265 network.push_back(gp);
266 gates[gateCount] = gp;
269 // Something has gone seriously pear-shaped
270 SG_LOG(SG_ATC, SG_ALERT, "********* ERROR - unknown ground network element type... aborting read of " << path.c_str() << '\n');
279 void FGGround::Init() {
282 // Figure out which is the active runway - TODO - it would be better to have ground call tower
283 // for runway operation details, but at the moment we can't guarantee that tower control at a given airport
284 // will be initialised before ground so we can't do that.
286 //cout << "In FGGround::Init, active rwy is " << activeRwy << '\n';
287 ortho.Init(rwy.threshold_pos, rwy.hdg);
289 networkLoadOK = LoadNetwork();
292 void FGGround::Update(double dt) {
293 // Each time step, what do we need to do?
294 // We need to go through the list of outstanding requests and acknowedgements
295 // and process at least one of them.
296 // We need to go through the list of planes under our control and check if
297 // any need to be addressed.
298 // We need to check for planes not under our control coming within our
299 // control area and address if necessary.
301 // Lets take the example of a plane which has just contacted ground
302 // following landing - presumably requesting where to go?
303 // First we need to establish the position of the plane within the logical network.
304 // Next we need to decide where its going.
306 if(ground_traffic.size()) {
307 if(ground_traffic_itr == ground_traffic.end()) {
308 ground_traffic_itr = ground_traffic.begin();
311 //Process(*ground_traffic_itr);
312 GroundRec* g = *ground_traffic_itr;
313 if(g->taxiRequestOutstanding) {
314 double responseTime = 10.0; // seconds - this should get more sophisticated at some point
315 if(g->clearanceCounter > responseTime) {
317 // TODO - move the mechanics of making up the transmission out of the main Update(...) routine.
319 trns += g->plane.callsign;
320 trns += " taxi holding point runway "; // TODO - add the holding point name
321 // eg " taxi holding point G2 runway "
322 trns += ConvertRwyNumToSpokenString(activeRwy);
324 fgSetString("/sim/messages/ground", trns.c_str());
326 g->planePtr->RegisterTransmission(1); // cleared to taxi
327 g->clearanceCounter = 0.0;
328 g->taxiRequestOutstanding = false;
330 g->clearanceCounter += (dt * ground_traffic.size());
332 } else if(((FGAILocalTraffic*)(g->planePtr))->AtHoldShort()) { // That's a hack - eventually we should monitor actual position
333 // HACK ALERT - the automatic cast to AILocalTraffic has to go once we have other sorts working!!!!! FIXME TODO
334 // NOTE - we don't need to do the contact tower bit unless we have separate tower and ground
335 string trns = g->plane.callsign;
336 trns += " contact Tower ";
337 double f = globals->get_ATC_mgr()->GetFrequency(ident, TOWER) / 100.0;
339 sprintf(buf, "%.2f", f);
342 fgSetString("/sim/messages/ground", trns.c_str());
344 g->planePtr->RegisterTransmission(2); // contact tower
345 delete *ground_traffic_itr;
346 ground_traffic.erase(ground_traffic_itr);
347 ground_traffic_itr = ground_traffic.begin();
349 ++ground_traffic_itr;
352 // Call the base class update for the response time handling.
356 // Figure out which runways are active.
357 // For now we'll just be simple and do one active runway - eventually this will get much more complex
358 // Copied from FGTower - TODO - it would be better to implement this just once, and have ground call tower
359 // for runway operation details, but at the moment we can't guarantee that tower control at a given airport
360 // will be initialised before ground so we can't do that.
361 void FGGround::DoRwyDetails() {
362 //cout << "GetRwyDetails called" << endl;
364 const FGAirport* apt = fgFindAirportID(ident);
366 SG_LOG(SG_ATC, SG_WARN, "FGGround::DoRwyDetails: unknown ICAO:" << ident);
370 FGRunway* runway = apt->getActiveRunwayForUsage();
372 activeRwy = runway->ident();
373 rwy.rwyID = runway->ident();
374 SG_LOG(SG_ATC, SG_INFO, "In FGGround, active runway for airport " << ident << " is " << activeRwy);
376 // Get the threshold position
377 double other_way = runway->headingDeg() - 180.0;
378 while(other_way <= 0.0) {
381 // move to the +l end/center of the runway
382 //cout << "Runway center is at " << runway._lon << ", " << runway._lat << '\n';
383 double tshlon = 0.0, tshlat = 0.0, tshr = 0.0;
384 double tolon = 0.0, tolat = 0.0, tor = 0.0;
385 rwy.length = runway->lengthM();
386 geo_direct_wgs_84 ( aptElev, runway->latitude(), runway->longitude(), other_way,
387 rwy.length / 2.0 - 25.0, &tshlat, &tshlon, &tshr );
388 geo_direct_wgs_84 ( aptElev, runway->latitude(), runway->longitude(), runway->headingDeg(),
389 rwy.length / 2.0 - 25.0, &tolat, &tolon, &tor );
390 // Note - 25 meters in from the runway end is a bit of a hack to put the plane ahead of the user.
391 // now copy what we need out of runway into rwy
392 rwy.threshold_pos = SGGeod::fromDegM(tshlon, tshlat, aptElev);
393 SGGeod takeoff_end = SGGeod::fromDegM(tolon, tolat, aptElev);
394 //cout << "Threshold position = " << tshlon << ", " << tshlat << ", " << aptElev << '\n';
395 //cout << "Takeoff position = " << tolon << ", " << tolat << ", " << aptElev << '\n';
396 rwy.hdg = runway->headingDeg();
397 // Set the projection for the local area based on this active runway
398 ortho.Init(rwy.threshold_pos, rwy.hdg);
399 rwy.end1ortho = ortho.ConvertToLocal(rwy.threshold_pos); // should come out as zero
400 rwy.end2ortho = ortho.ConvertToLocal(takeoff_end);
403 // Return a random gate ID of an unused gate.
404 // Two error values may be returned and must be checked for by the calling function:
405 // -2 signifies that no gates exist at this airport.
406 // -1 signifies that all gates are currently full.
407 int FGGround::GetRandomGateID() {
408 // Check that this airport actually has some gates!!
413 gate_vec_type gateVec;
418 gatesItr = gates.begin();
419 while(gatesItr != gates.end()) {
420 if((gatesItr->second)->used == false) {
421 gateVec.push_back(gatesItr->second);
427 // Check that there are some unused gates!
428 if(!gateVec.size()) {
432 // Randomly select one from the list
434 thenum = (int)(sg_random() * gateVec.size());
435 ID = gateVec[thenum]->id;
440 // Return a pointer to an unused gate node
441 Gate* FGGround::GetGateNode() {
442 int id = GetRandomGateID();
451 node* FGGround::GetHoldShortNode(const string& rwyID) {
452 return(NULL); // TODO - either implement me or remove me!!!
456 // WARNING - This is hardwired to my prototype logical network format
457 // and will almost certainly change when Bernie's stuff comes on-line.
458 // Returns NULL if it can't find a valid node.
459 node* FGGround::GetThresholdNode(const string& rwyID) {
460 // For now go through all the nodes and parse their names
461 // Maybe in the future we'll map threshold nodes by ID
462 //cout << "Size of network is " << network.size() << '\n';
463 for(unsigned int i=0; i<network.size(); ++i) {
464 //cout << "Name = " << network[i]->name << '\n';
465 if(network[i]->name.size()) {
466 string s = network[i]->name;
467 // Warning - the next bit is fragile and dependent on my current naming scheme
468 //cout << "substr = " << s.substr(0,3) << '\n';
469 //cout << "size of s = " << s.size() << '\n';
470 if(s.substr(0,3) == "rwy") {
471 //cout << "subsubstr = " << s.substr(4, s.size() - 4) << '\n';
472 if(s.substr(4, s.size() - 4) == rwyID) {
482 // Get a path from a point on a runway to a gate
485 // Get a path from a node to another node
486 // Eventually we will need complex algorithms for this taking other traffic,
487 // shortest path and suitable paths into accout.
488 // For now we'll just call the shortest path algorithm.
489 ground_network_path_type FGGround::GetPath(node* A, node* B) {
490 return(GetShortestPath(A, B));
493 // Get a path from a node to a runway threshold
494 ground_network_path_type FGGround::GetPath(node* A, const string& rwyID) {
495 node* b = GetThresholdNode(rwyID);
497 SG_LOG(SG_ATC, SG_ALERT, "ERROR - unable to find path to runway theshold in ground.cxx for airport " << ident << '\n');
498 ground_network_path_type emptyPath;
499 emptyPath.erase(emptyPath.begin(), emptyPath.end());
502 return GetShortestPath(A, b);
505 // Get a path from a node to a runway hold short point
506 // Bit of a hack this at the moment!
507 ground_network_path_type FGGround::GetPathToHoldShort(node* A, const string& rwyID) {
508 ground_network_path_type path = GetPath(A, rwyID);
509 path.pop_back(); // That should be the threshold stripped of
510 path.pop_back(); // and that should be the arc from hold short to threshold
511 // This isn't robust though - TODO - implement properly!
515 // A shortest path algorithm from memory (ie. I can't find the bl&*dy book again!)
516 // I'm sure there must be enchancements that we can make to this, such as biasing the
517 // order in which the nodes are searched out from in favour of those geographically
518 // closer to the destination.
519 // Note that we are working with the master set of nodes and arcs so we mustn't change
520 // or delete them - we only delete the paths that we create during the algorithm.
521 ground_network_path_type FGGround::GetShortestPath(node* A, node* B) {
523 shortest_path_map_type pathMap;
524 node_array_type nodesLeft;
527 int pathsCreated = 0;
529 // Initialise the algorithm
530 nodesLeft.push_back(A);
531 pathPtr = new a_path;
533 pathPtr->path.push_back(A);
535 pathMap[A->nodeID] = pathPtr;
536 bool solution_found = false; // Flag to indicate that at least one candidate path has been found
537 int solution_cost = -1; // Cost of current best cost solution. -1 indicates no solution found yet.
538 a_path solution_path;
540 node* nPtr; // nPtr is used to point to the node we are currently working with
542 while(nodesLeft.size()) {
543 //cout << "\n*****nodesLeft*****\n";
544 //for(unsigned int i=0; i<nodesLeft.size(); ++i) {
545 //cout << nodesLeft[i]->nodeID << '\n';
547 //cout << "*******************\n\n";
548 nPtr = *nodesLeft.begin(); // Thought - definate optimization possibilities here in the choice of which nodes we process first.
549 nodesLeft.erase(nodesLeft.begin());
550 //cout << "Walking out from node " << nPtr->nodeID << '\n';
551 for(unsigned int i=0; i<nPtr->arcs.size(); ++i) {
552 //cout << "ARC TO " << ((nPtr->arcs[i]->n1 == nPtr->nodeID) ? nPtr->arcs[i]->n2 : nPtr->arcs[i]->n1) << '\n';
554 if((solution_found) && (solution_cost <= pathMap[nPtr->nodeID]->cost)) {
555 // Do nothing - we've already found a solution and this partial path is already more expensive
557 // This path could still be better than the current solution - check it out
558 for(unsigned int i=0; i<(nPtr->arcs.size()); i++) {
559 // Map the new path against the end node, ie. *not* the one we just started with.
560 unsigned int end_nodeID = ((nPtr->arcs[i]->n1 == nPtr->nodeID) ? nPtr->arcs[i]->n2 : nPtr->arcs[i]->n1);
561 //cout << "end_nodeID = " << end_nodeID << '\n';
562 //cout << "pathMap size is " << pathMap.size() << '\n';
563 if(end_nodeID == nPtr->nodeID) {
564 //cout << "Circular arc!\n";
565 // Then its a circular arc - don't bother!!
566 //nPtr->arcs.erase(nPtr->arcs.begin() + i);
568 // see if the end node is already in the map or not
569 if(pathMap.find(end_nodeID) == pathMap.end()) {
570 //cout << "Not in the map" << endl;;
571 // Not in the map - easy!
572 pathPtr = new a_path;
574 *pathPtr = *pathMap[nPtr->nodeID]; // *copy* the path
575 pathPtr->path.push_back(nPtr->arcs[i]);
576 pathPtr->path.push_back(network[end_nodeID]);
577 pathPtr->cost += nPtr->arcs[i]->distance;
578 pathMap[end_nodeID] = pathPtr;
579 nodesLeft.push_back(network[end_nodeID]); // By definition this can't be in the list already, or
580 // it would also have been in the map and hence OR'd with this one.
581 if(end_nodeID == B->nodeID) {
582 //cout << "Solution found!!!" << endl;
583 // Since this node wasn't in the map this is by definition the first solution
584 solution_cost = pathPtr->cost;
585 solution_path = *pathPtr;
586 solution_found = true;
589 //cout << "Already in the map" << endl;
590 // In the map - not so easy - need to get rid of an arc from the higher cost one.
591 //cout << "Current cost of node " << end_nodeID << " is " << pathMap[end_nodeID]->cost << endl;
592 int newCost = pathMap[nPtr->nodeID]->cost + nPtr->arcs[i]->distance;
593 //cout << "New cost is of node " << nPtr->nodeID << " is " << newCost << endl;
594 if(newCost >= pathMap[end_nodeID]->cost) {
595 // No need to do anything.
596 //cout << "Not doing anything!" << endl;
598 delete pathMap[end_nodeID];
601 pathPtr = new a_path;
603 *pathPtr = *pathMap[nPtr->nodeID]; // *copy* the path
604 pathPtr->path.push_back(nPtr->arcs[i]);
605 pathPtr->path.push_back(network[end_nodeID]);
606 pathPtr->cost += nPtr->arcs[i]->distance;
607 pathMap[end_nodeID] = pathPtr;
609 // We need to add this node to the list-to-do again to force a recalculation
610 // onwards from this node with the new lower cost to node cost.
611 nodesLeft.push_back(network[end_nodeID]);
613 if(end_nodeID == B->nodeID) {
614 //cout << "Solution found!!!" << endl;
615 // Need to check if there is a previous better solution
616 if((solution_cost < 0) || (pathPtr->cost < solution_cost)) {
617 solution_cost = pathPtr->cost;
618 solution_path = *pathPtr;
619 solution_found = true;
629 // delete all the paths before returning
630 shortest_path_map_iterator spItr = pathMap.begin();
631 while(spItr != pathMap.end()) {
632 if(spItr->second != NULL) {
633 delete spItr->second;
639 //cout << "pathsCreated = " << pathsCreated << '\n';
640 if(pathsCreated > 0) {
641 SG_LOG(SG_ATC, SG_ALERT, "WARNING - Possible memory leak in FGGround::GetShortestPath\n\
642 Please report to flightgear-devel@flightgear.org\n");
645 //cout << (solution_found ? "Result: solution found\n" : "Result: no solution found\n");
646 return(solution_path.path); // TODO - we really ought to have a fallback position incase a solution isn't found.
651 // Randomly or otherwise populate some of the gates with parked planes
652 // (might eventually be done by the AIMgr if and when lots of AI traffic is generated)
654 // Return a list of exits from a given runway
655 // It is up to the calling function to check for non-zero size of returned array before use
656 node_array_type FGGround::GetExits(const string& rwyID) {
657 // FIXME - get a 07L or similar in here and we're stuffed!!!
658 return(runways[atoi(rwyID.c_str())].exits);
661 void FGGround::RequestDeparture(const PlaneRec& plane, FGAIEntity* requestee) {
662 // For now we'll just automatically clear all planes to the runway hold.
663 // This communication needs to be delayed 20 sec or so from receiving the request.
664 // Even if display=false we still need to start the timer in case display=true when communication starts.
665 // We also need to bear in mind we also might have other outstanding communications, although for now we'll punt that issue!
666 // FIXME - sort the above!
668 // HACK - assume that anything requesting departure is new for now - FIXME LATER
669 GroundRec* g = new GroundRec;
671 g->planePtr = requestee;
672 g->taxiRequestOutstanding = true;
673 g->clearanceCounter = 0;
676 // TODO - need to handle the next 3 as well
678 //node* last_clearance;
680 ground_traffic.push_back(g);
684 void FGGround::NewArrival(plane_rec plane) {
685 // What are we going to do here?
686 // We need to start a new ground_rec and add the plane_rec to it
687 // We need to decide what gate we are going to clear it to.
688 // Then we need to add clearing it to that gate to the pending transmissions queue? - or simply transmit?
689 // Probably simply transmit for now and think about a transmission queue later if we need one.
690 // We might need one though in order to add a little delay for response time.
691 ground_rec* g = new ground_rec;
692 g->plane_rec = plane;
693 g->current_pos = ConvertWGS84ToXY(plane.pos);
694 g->node = GetNode(g->current_pos); // TODO - might need to sort out node/arc here
697 ground_traffic.push_back(g);
701 void FGGround::NewContact(plane_rec plane) {
702 // This is a bit of a convienience function at the moment and is likely to change.
703 if(at a gate or apron)
709 void FGGround::NextClearance(ground_rec &g) {
710 // Need to work out where we can clear g to.
711 // Assume the pilot doesn't need progressive instructions
712 // We *should* already have a gate or holding point assigned by the time we get here
713 // but it wouldn't do any harm to check.
715 // For now though we will hardwire it to clear to the final destination.
718 void FGGround::AssignGate(ground_rec &g) {
719 // We'll cheat for now - since we only have the user's aircraft and a couple of airports implemented
720 // we'll hardwire the gate!
721 // In the long run the logic of which gate or area to send the plane to could be somewhat non-trivial.