flightgear/src/Main/positioninit.cxx

// positioninit.cxx - helpers relating to setting initial aircraft position
//
// Copyright (C) 2012 James Turner  zakalawe@mac.com
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

#include "positioninit.hxx"

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include <boost/tuple/tuple.hpp>

// simgear
#include <simgear/props/props_io.hxx>
#include <simgear/structure/exception.hxx>
#include <simgear/structure/event_mgr.hxx>

#include "globals.hxx"
#include "fg_props.hxx"

#include <Navaids/navlist.hxx>
#include <Airports/runways.hxx>
#include <Airports/airport.hxx>
#include <Airports/dynamics.hxx>
#include <Airports/groundnetwork.hxx>
#include <AIModel/AIManager.hxx>
#include <GUI/MessageBox.hxx>


using std::endl;
using std::string;

namespace flightgear
{
    
/// to avoid blocking when metar-fetch is enabled, but the network is
/// unresponsive, we need a timeout value. This value is reset on initPosition,
/// and tracked through each call to finalizePosition.
static SGTimeStamp global_finalizeTime;
static bool global_callbackRegistered = false;

static void finalizePosition();
  
// Set current tower position lon/lat given an airport id
static bool fgSetTowerPosFromAirportID( const string& id) {
  const FGAirport *a = fgFindAirportID( id);
  if (a) {
    SGGeod tower = a->getTowerLocation();
    fgSetDouble("/sim/tower/longitude-deg",  tower.getLongitudeDeg());
    fgSetDouble("/sim/tower/latitude-deg",  tower.getLatitudeDeg());
    fgSetDouble("/sim/tower/altitude-ft", tower.getElevationFt());
    return true;
  } else {
    return false;
  }
  
}

class FGTowerLocationListener : public SGPropertyChangeListener {
    
  void valueChanged(SGPropertyNode* node) {
    string id(node->getStringValue());
    if (fgGetBool("/sim/tower/auto-position",true))
    {
      // enforce using closest airport when auto-positioning is enabled
      const char* closest_airport = fgGetString("/sim/airport/closest-airport-id", "");
      if (closest_airport && (id != closest_airport))
      {
        id = closest_airport;
        node->setStringValue(id);
      }
    }
    fgSetTowerPosFromAirportID(id);
  }
};

class FGClosestTowerLocationListener : public SGPropertyChangeListener
{
  void valueChanged(SGPropertyNode* )
  {
    // closest airport has changed
    if (fgGetBool("/sim/tower/auto-position",true))
    {
      // update tower position
      const char* id = fgGetString("/sim/airport/closest-airport-id", "");
      if (id && *id!=0)
        fgSetString("/sim/tower/airport-id", id);
    }
  }
};

void initTowerLocationListener() {
    
  SGPropertyChangeListener* tll = new FGTowerLocationListener();
  globals->addListenerToCleanup(tll);
  fgGetNode("/sim/tower/airport-id",  true)
  ->addChangeListener( tll, true );
    
  FGClosestTowerLocationListener* ntcl = new FGClosestTowerLocationListener();
  globals->addListenerToCleanup(ntcl);
  fgGetNode("/sim/airport/closest-airport-id", true)
  ->addChangeListener(ntcl , true );
  fgGetNode("/sim/tower/auto-position", true)
  ->addChangeListener(ntcl, true );
}

static void setInitialPosition(const SGGeod& aPos, double aHeadingDeg)
{
    // presets
    fgSetDouble("/sim/presets/longitude-deg", aPos.getLongitudeDeg() );
    fgSetDouble("/sim/presets/latitude-deg", aPos.getLatitudeDeg() );
    fgSetDouble("/sim/presets/heading-deg", aHeadingDeg );

    // other code depends on the actual values being set ...
    fgSetDouble("/position/longitude-deg",  aPos.getLongitudeDeg() );
    fgSetDouble("/position/latitude-deg",  aPos.getLatitudeDeg() );
    fgSetDouble("/orientation/heading-deg", aHeadingDeg );
}

static bool isMPEnabled()
{
    // crude test, but sufficient for what we need
    std::string txAddress = fgGetString("/sim/multiplay/txhost");
    return !txAddress.empty();
}

static void fgApplyStartOffset(const SGGeod& aStartPos, double aHeading, double aTargetHeading = HUGE_VAL)
{
  SGGeod startPos(aStartPos);
  if (aTargetHeading == HUGE_VAL) {
    aTargetHeading = aHeading;
  }
  
  if ( fabs( fgGetDouble("/sim/presets/offset-distance-nm") ) > SG_EPSILON ) {
    double offsetDistance = fgGetDouble("/sim/presets/offset-distance-nm");
    offsetDistance *= SG_NM_TO_METER;
    double offsetAzimuth = aHeading;
    if ( fabs(fgGetDouble("/sim/presets/offset-azimuth-deg")) > SG_EPSILON ) {
      offsetAzimuth = fgGetDouble("/sim/presets/offset-azimuth-deg");
      aHeading = aTargetHeading;
    }
    
    SGGeod offset;
    double az2; // dummy
    SGGeodesy::direct(startPos, offsetAzimuth + 180, offsetDistance, offset, az2);
    startPos = offset;
  }
  
    setInitialPosition(startPos, aHeading);
}

boost::tuple<SGGeod, double> runwayStartPos(FGRunwayRef runway)
{
    fgSetString("/sim/atc/runway", runway->ident().c_str());
    double offsetNm = fgGetDouble("/sim/presets/offset-distance-nm");
    double startOffset = fgGetDouble("/sim/airport/runways/start-offset-m", 5.0);
    SGGeod pos = runway->pointOnCenterline(startOffset);

    if (isMPEnabled() && (fabs(offsetNm) <0.1)) {
        SG_LOG( SG_GENERAL, SG_WARN, "Requested to start on " << runway->airport()->ident() << "/" <<
               runway->ident() << ", MP is enabled so computing hold short position to avoid runway incursion");

        FGGroundNetwork* groundNet = runway->airport()->groundNetwork();
        // add a margin, try to keep the entire aeroplane comfortable off the
        // runway. 
        double margin = startOffset + (runway->widthM() * 1.5);
        FGTaxiNodeRef taxiNode = groundNet ? groundNet->findNearestNodeOffRunway(pos, runway, margin) : 0;
        if (taxiNode) {
            // set this so multiplayer.nas can inform the user
            fgSetBool("/sim/presets/avoided-mp-runway", true);
            return boost::make_tuple(taxiNode->geod(), SGGeodesy::courseDeg(taxiNode->geod(), pos));
        }

        // if we couldn't find a suitable taxi-node, give up. Guessing a position
        // causes too much pain (starting in the water or similar bad things)
    }

    return boost::make_tuple(pos, runway->headingDeg());
}

// Set current_options lon/lat given an airport id and heading (degrees)
static bool setPosFromAirportIDandHdg( const string& id, double tgt_hdg ) {
  if ( id.empty() )
    return false;
  
  // set initial position from runway and heading
  SG_LOG( SG_GENERAL, SG_INFO,
         "Attempting to set starting position from airport code "
         << id << " heading " << tgt_hdg );
  
  const FGAirport* apt = fgFindAirportID(id);
  if (!apt) return false;

  SGGeod startPos;
  double heading = tgt_hdg;
  if (apt->type() == FGPositioned::HELIPORT) {
    if (apt->numHelipads() > 0) {
      startPos = apt->getHelipadByIndex(0)->geod();
    } else {
      startPos = apt->geod();
    }
  } else {
    FGRunway* r = apt->findBestRunwayForHeading(tgt_hdg);
      boost::tie(startPos, heading) = runwayStartPos(r);
  }

    fgApplyStartOffset(startPos, heading);
    return true;
}

// Set current_options lon/lat given an airport id and parkig position name
static bool fgSetPosFromAirportIDandParkpos( const string& id, const string& parkpos )
{
  string fltType;
  string acOperator;
  string acType; // Currently not used by findAvailable parking, so safe to leave empty.
  SGPath acData;
  if ( id.empty() )
    return false;
  
  const FGAirport* apt = fgFindAirportID(id);
  if (!apt) {
    SG_LOG( SG_GENERAL, SG_ALERT, "Failed to find airport " << id );
    return false;
  }

  FGAirportDynamicsRef dcs = apt->getDynamics();
  if (!dcs) {
      // this happens during initPosition(), because the dynamics manager and
      // ATC manager aren't running yet. We want to set an interim position
      // so METAR and tile-loading can proceed, and then we're set the final
      // position by call this this function again during finalizePosition
      setInitialPosition(apt->geod(), 0.0);
      return true;
  }
  
  ParkingAssignment pka;
  double radius = fgGetDouble("/sim/dimensions/radius-m");
  if ((parkpos == "AVAILABLE") && (radius > 0)) {
    
    try {
      acData = globals->get_fg_home();
      acData.append("aircraft-data");
      string acfile = fgGetString("/sim/aircraft") + string(".xml");
      acData.append(acfile);
      SGPropertyNode root;
      readProperties(acData, &root);
      SGPropertyNode * node = root.getNode("sim");
      fltType    = node->getStringValue("aircraft-class", "NONE"     );
      acOperator = node->getStringValue("aircraft-operator", "NONE"     );
    } catch (const sg_exception &) {
      SG_LOG(SG_GENERAL, SG_INFO,
             "Could not load aircraft aircrat type and operator information from: " << acData << ". Using defaults");
      
      // cout << path.str() << endl;
    }
    if (fltType.empty() || fltType == "NONE") {
      SG_LOG(SG_GENERAL, SG_INFO,
             "Aircraft type information not found in: " << acData << ". Using default value");
      fltType = fgGetString("/sim/aircraft-class"   );
    }
    if (acOperator.empty() || fltType == "NONE") {
      SG_LOG(SG_GENERAL, SG_INFO,
             "Aircraft operator information not found in: " << acData << ". Using default value");
      acOperator = fgGetString("/sim/aircraft-operator"   );
    }
    
    
    pka = dcs->getAvailableParking(radius, fltType, acType, acOperator);
    if (pka.isValid()) {
        // why is the following line necessary?
      fgGetString("/sim/presets/parkpos");
      fgSetString("/sim/presets/parkpos", pka.parking()->getName());
    } else {
      SG_LOG( SG_GENERAL, SG_ALERT,
             "Failed to find a suitable parking at airport " << id );
      return false;
    }
  } else {
      
    pka = dcs->getParkingByName(parkpos);
    if (!pka.isValid()) {
      SG_LOG( SG_GENERAL, SG_ALERT,
               "Failed to find a parking at airport " << id << ":" << parkpos);
      return false;
    }
  }
  // Why is the following line necessary?
  fgGetString("/sim/presets/parkpos");
  fgSetString("/sim/presets/parkpos", pka.parking()->getName());
  // The problem is, this line doesn't work because the ParkingAssignment's refcounting mechanism:
  // The parking will be released after this function returns. 
  // As a temporary measure, I'll try to reserve the parking via the atc_manager, which should work, because it uses the same 
  // mechanism as the AI traffic code. 
  dcs->setParkingAvailable(pka.parking(), false);
  fgApplyStartOffset(pka.parking()->geod(), pka.parking()->getHeading());
  return true;
}


// Set current_options lon/lat given an airport id and runway number
static bool fgSetPosFromAirportIDandRwy( const string& id, const string& rwy, bool rwy_req ) {
  if ( id.empty() )
    return false;
  
  // set initial position from airport and runway number
  SG_LOG( SG_GENERAL, SG_INFO,
         "Attempting to set starting position for "
         << id << ":" << rwy );
  
  const FGAirport* apt = fgFindAirportID(id);
  if (!apt) {
    SG_LOG( SG_GENERAL, SG_ALERT, "Failed to find airport:" << id);
    return false;
  }

  if (apt->hasRunwayWithIdent(rwy)) {
      FGRunway* r(apt->getRunwayByIdent(rwy));
      SGGeod startPos;
      double heading;
      boost::tie(startPos, heading) = runwayStartPos(r);
      fgApplyStartOffset(startPos, heading);
      return true;
  } else if (apt->hasHelipadWithIdent(rwy)) {
      FGHelipad* h(apt->getHelipadByIdent(rwy));
      fgApplyStartOffset(h->geod(), h->headingDeg());
      return true;
  }

  if (rwy_req) {
      flightgear::modalMessageBox("Runway not available", "Runway/helipad "
                                   + rwy + " not found at airport " + apt->getId()
                                   + " - " + apt->getName() );
  } else {
    SG_LOG( SG_GENERAL, SG_INFO,
           "Failed to find runway/helipad " << rwy <<
           " at airport " << id << ". Using default runway." );
  }
  return false;
}


static void fgSetDistOrAltFromGlideSlope() {
  // cout << "fgSetDistOrAltFromGlideSlope()" << endl;
  string apt_id = fgGetString("/sim/presets/airport-id");
  double gs = fgGetDouble("/sim/presets/glideslope-deg")
  * SG_DEGREES_TO_RADIANS ;
  double od = fgGetDouble("/sim/presets/offset-distance-nm");
  double alt = fgGetDouble("/sim/presets/altitude-ft");
  
  double apt_elev = 0.0;
  if ( ! apt_id.empty() ) {
    apt_elev = fgGetAirportElev( apt_id );
    if ( apt_elev < -9990.0 ) {
      apt_elev = 0.0;
    }
  } else {
    apt_elev = 0.0;
  }
  
  if( fabs(gs) > 0.01 && fabs(od) > 0.1 && alt < -9990 ) {
    // set altitude from glideslope and offset-distance
    od *= SG_NM_TO_METER * SG_METER_TO_FEET;
    alt = fabs(od*tan(gs)) + apt_elev;
    fgSetDouble("/sim/presets/altitude-ft", alt);
    fgSetBool("/sim/presets/onground", false);
    SG_LOG( SG_GENERAL, SG_INFO, "Calculated altitude as: "
           << alt  << " ft" );
  } else if( fabs(gs) > 0.01 && alt > 0 && fabs(od) < 0.1) {
    // set offset-distance from glideslope and altitude
    od  = (alt - apt_elev) / tan(gs);
    od *= -1*SG_FEET_TO_METER * SG_METER_TO_NM;
    fgSetDouble("/sim/presets/offset-distance-nm", od);
    fgSetBool("/sim/presets/onground", false);
    SG_LOG( SG_GENERAL, SG_INFO, "Calculated offset distance as: "
           << od  << " nm" );
  } else if( fabs(gs) > 0.01 ) {
    SG_LOG( SG_GENERAL, SG_ALERT,
           "Glideslope given but not altitude or offset-distance." );
    SG_LOG( SG_GENERAL, SG_ALERT, "Resetting glideslope to zero" );
    fgSetDouble("/sim/presets/glideslope-deg", 0);
    fgSetBool("/sim/presets/onground", true);
  }
}


// Set current_options lon/lat given an airport id and heading (degrees)
static bool fgSetPosFromNAV( const string& id,
                             const double& freq,
                             FGPositioned::Type type,
                             PositionedID guid)
{
    FGNavRecord* nav = 0;


    if (guid != 0) {
        nav = FGPositioned::loadById<FGNavRecord>(guid);
        if (!nav)
            return false;
    } else {
        FGNavList::TypeFilter filter(type);
        const nav_list_type navlist = FGNavList::findByIdentAndFreq( id.c_str(), freq, &filter );

        if (navlist.empty()) {
          SG_LOG( SG_GENERAL, SG_ALERT, "Failed to locate NAV = "
                 << id << ":" << freq );
          return false;
        }

        if( navlist.size() > 1 ) {
          std::ostringstream buf;
          buf << "Ambigous NAV-ID: '" << id << "'. Specify id and frequency. Available stations:" << endl;
          for( nav_list_type::const_iterator it = navlist.begin(); it != navlist.end(); ++it ) {
            // NDB stored in kHz, VOR stored in MHz * 100 :-P
            double factor = (*it)->type() == FGPositioned::NDB ? 1.0 : 1/100.0;
            string unit = (*it)->type() == FGPositioned::NDB ? "kHz" : "MHz";
            buf << (*it)->ident() << " "
            << std::setprecision(5) << (double)((*it)->get_freq() * factor) << " "
            << (*it)->get_lat() << "/" << (*it)->get_lon()
            << endl;
          }

          SG_LOG( SG_GENERAL, SG_ALERT, buf.str() );
          return false;
        }

        // nav list must be of length 1
        nav = navlist[0];
    }

    fgApplyStartOffset(nav->geod(), fgGetDouble("/sim/presets/heading-deg"));
    return true;
}

// Set current_options lon/lat given an aircraft carrier id
static bool fgSetPosFromCarrier( const string& carrier, const string& posid ) {
  
  // set initial position from runway and heading
  SGGeod geodPos;
  double heading;
  SGVec3d uvw;
  if (FGAIManager::getStartPosition(carrier, posid, geodPos, heading, uvw)) {
    double lon = geodPos.getLongitudeDeg();
    double lat = geodPos.getLatitudeDeg();
    double alt = geodPos.getElevationFt();
    
    SG_LOG( SG_GENERAL, SG_INFO, "Attempting to set starting position for "
           << carrier << " at lat = " << lat << ", lon = " << lon
           << ", alt = " << alt << ", heading = " << heading);
    
    fgSetDouble("/sim/presets/longitude-deg",  lon);
    fgSetDouble("/sim/presets/latitude-deg",  lat);
    fgSetDouble("/sim/presets/altitude-ft", alt);
    fgSetDouble("/sim/presets/heading-deg", heading);
    fgSetDouble("/position/longitude-deg",  lon);
    fgSetDouble("/position/latitude-deg",  lat);
    fgSetDouble("/position/altitude-ft", alt);
    fgSetDouble("/orientation/heading-deg", heading);
    
    fgSetString("/sim/presets/speed-set", "UVW");
    fgSetDouble("/velocities/uBody-fps", uvw(0));
    fgSetDouble("/velocities/vBody-fps", uvw(1));
    fgSetDouble("/velocities/wBody-fps", uvw(2));
    fgSetDouble("/sim/presets/uBody-fps", uvw(0));
    fgSetDouble("/sim/presets/vBody-fps", uvw(1));
    fgSetDouble("/sim/presets/wBody-fps", uvw(2));
    
    fgSetBool("/sim/presets/onground", true);
    
    return true;
  } else {
    SG_LOG( SG_GENERAL, SG_ALERT, "Failed to locate aircraft carrier = "
           << carrier );
    return false;
  }
}

// Set current_options lon/lat given a fix ident and GUID
static bool fgSetPosFromFix( const string& id, PositionedID guid )
{
    FGPositioned* fix = NULL;
    if (guid != 0) {
        fix = FGPositioned::loadById<FGPositioned>(guid);
    } else {
        FGPositioned::TypeFilter fixFilter(FGPositioned::FIX);
        fix = FGPositioned::findFirstWithIdent(id, &fixFilter);
    }

  if (!fix) {
    SG_LOG( SG_GENERAL, SG_ALERT, "Failed to locate fix = " << id );
    return false;
  }
  
  fgApplyStartOffset(fix->geod(), fgGetDouble("/sim/presets/heading-deg"));
  return true;
}

// Set the initial position based on presets (or defaults)
bool initPosition()
{
  global_finalizeTime = SGTimeStamp(); // reset to invalid
  if (!global_callbackRegistered) {
    globals->get_event_mgr()->addTask("finalizePosition", &finalizePosition, 0.1);
    global_callbackRegistered = true;
  }
    
  double gs = fgGetDouble("/sim/presets/glideslope-deg")
  * SG_DEGREES_TO_RADIANS ;
  double od = fgGetDouble("/sim/presets/offset-distance-nm");
  double alt = fgGetDouble("/sim/presets/altitude-ft");
  
  bool set_pos = false;
  
  // If glideslope is specified, then calculate offset-distance or
  // altitude relative to glide slope if either of those was not
  // specified.
  if ( fabs( gs ) > 0.01 ) {
    fgSetDistOrAltFromGlideSlope();
  }
  
  
  // If we have an explicit, in-range lon/lat, don't change it, just use it.
  // If not, check for an airport-id and use that.
  // If not, default to the middle of the KSFO field.
  // The default values for lon/lat are deliberately out of range
  // so that the airport-id can take effect; valid lon/lat will
  // override airport-id, however.
  double lon_deg = fgGetDouble("/sim/presets/longitude-deg");
  double lat_deg = fgGetDouble("/sim/presets/latitude-deg");
  if ( lon_deg >= -180.0 && lon_deg <= 180.0
      && lat_deg >= -90.0 && lat_deg <= 90.0 )
  {
    set_pos = true;
  }
  
  string apt = fgGetString("/sim/presets/airport-id");
  string rwy_no = fgGetString("/sim/presets/runway");
  bool rwy_req = fgGetBool("/sim/presets/runway-requested");
  string vor = fgGetString("/sim/presets/vor-id");
  double vor_freq = fgGetDouble("/sim/presets/vor-freq");
  string ndb = fgGetString("/sim/presets/ndb-id");
  double ndb_freq = fgGetDouble("/sim/presets/ndb-freq");
  string carrier = fgGetString("/sim/presets/carrier");
  string parkpos = fgGetString("/sim/presets/parkpos");
  string fix = fgGetString("/sim/presets/fix");

  // the launcher sets this to precisely identify a navaid
    PositionedID navaidId = fgGetInt("/sim/presets/navaid-id");

  SGPropertyNode *hdg_preset = fgGetNode("/sim/presets/heading-deg", true);
  double hdg = hdg_preset->getDoubleValue();
  
  // save some start parameters, so that we can later say what the
  // user really requested. TODO generalize that and move it to options.cxx
  static bool start_options_saved = false;
  if (!start_options_saved) {
    start_options_saved = true;
    SGPropertyNode *opt = fgGetNode("/sim/startup/options", true);
    
    opt->setDoubleValue("latitude-deg", lat_deg);
    opt->setDoubleValue("longitude-deg", lon_deg);
    opt->setDoubleValue("heading-deg", hdg);
    opt->setStringValue("airport", apt.c_str());
    opt->setStringValue("runway", rwy_no.c_str());
  }
  
  if (hdg > 9990.0)
    hdg = fgGetDouble("/environment/config/boundary/entry/wind-from-heading-deg", 270);
  
  if ( !set_pos && !apt.empty() && !parkpos.empty() ) {
    // An airport + parking position is requested
    // since this depends on parking, which is part of dynamics, and hence
    // also depends on ATC (the ground controller), we need to defer this
    // until position finalisation
    if ( fgSetPosFromAirportIDandParkpos( apt, parkpos ) ) {
      // set tower position
      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
      fgSetString("/sim/tower/airport-id",  apt.c_str());
      set_pos = true;
    }
  }
  
  if ( !set_pos && !apt.empty() && !rwy_no.empty() ) {
    // An airport + runway is requested
    if ( fgSetPosFromAirportIDandRwy( apt, rwy_no, rwy_req ) ) {
      // set tower position (a little off the heading for single
      // runway airports)
      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
      fgSetString("/sim/tower/airport-id",  apt.c_str());
      set_pos = true;
    }
  }
  
  if ( !set_pos && !apt.empty() ) {
    // An airport is requested (find runway closest to hdg)
    if ( setPosFromAirportIDandHdg( apt, hdg ) ) {
      // set tower position (a little off the heading for single
      // runway airports)
      fgSetString("/sim/airport/closest-airport-id",  apt.c_str());
      fgSetString("/sim/tower/airport-id",  apt.c_str());
      set_pos = true;
    }
  }
  
  if (hdg_preset->getDoubleValue() > 9990.0)
    hdg_preset->setDoubleValue(hdg);
  
  if ( !set_pos && !vor.empty() ) {
    // a VOR is requested
    if ( fgSetPosFromNAV( vor, vor_freq, FGPositioned::VOR, navaidId ) ) {
      set_pos = true;
    }
  }
  
  if ( !set_pos && !ndb.empty() ) {
    // an NDB is requested
    if ( fgSetPosFromNAV( ndb, ndb_freq, FGPositioned::NDB, navaidId ) ) {
      set_pos = true;
    }
  }
  
  if ( !set_pos && !carrier.empty() ) {
    // an aircraft carrier is requested
    if ( fgSetPosFromCarrier( carrier, parkpos ) ) {
      set_pos = true;
    }
  }
  
  if ( !set_pos && !fix.empty() ) {
    // a Fix is requested
    if ( fgSetPosFromFix( fix, navaidId ) ) {
      set_pos = true;
    }
  }
  
  if ( !set_pos ) {
    // No lon/lat specified, no airport specified, use the default airport
    // TODO: don't hardcode this. Really.
    const FGAirport* airport = fgFindAirportID("ENBR");
    if( airport ) {
      const SGGeod & airportGeod = airport->geod();
      fgSetDouble("/sim/presets/longitude-deg", airportGeod.getLongitudeDeg());
      fgSetDouble("/sim/presets/latitude-deg", airportGeod.getLatitudeDeg());
    } else {
      // So, the default airport is unknown? We are in serious trouble. 
      // Let's hope KSFO still exists somehow
      fgSetDouble("/sim/presets/longitude-deg", -122.374843);
      fgSetDouble("/sim/presets/latitude-deg", 37.619002);
      SG_LOG(SG_GENERAL, SG_ALERT, "Sorry, the default airport seems to be unknown.");
    }
  }
  
  fgSetDouble( "/position/longitude-deg",
              fgGetDouble("/sim/presets/longitude-deg") );
  fgSetDouble( "/position/latitude-deg",
              fgGetDouble("/sim/presets/latitude-deg") );
  fgSetDouble( "/orientation/heading-deg", hdg_preset->getDoubleValue());
  
  // determine if this should be an on-ground or in-air start
  if ((fabs(gs) > 0.01 || fabs(od) > 0.1 || alt > 0.1) && carrier.empty()) {
    fgSetBool("/sim/presets/onground", false);
  } else {
    fgSetBool("/sim/presets/onground", true);
  }
  
  fgSetBool("/sim/position-finalized", false);

// Initialize the longitude, latitude and altitude to the initial position
    fgSetDouble("/position/altitude-ft", fgGetDouble("/sim/presets/altitude-ft"));
    fgSetDouble("/position/longitude-deg", fgGetDouble("/sim/presets/longitude-deg"));
    fgSetDouble("/position/latitude-deg", fgGetDouble("/sim/presets/latitude-deg"));
    
  return true;
}
  
bool finalizeMetar()
{
  if (!fgGetBool("/environment/realwx/enabled")) {
    return true;
  }
  
  double hdg = fgGetDouble( "/environment/metar/base-wind-dir-deg", 9999.0 );
  string apt = fgGetString("/sim/presets/airport-id");
  string rwy = fgGetString("/sim/presets/runway");
  double strthdg = fgGetDouble( "/sim/startup/options/heading-deg", 9999.0 );
  string parkpos = fgGetString( "/sim/presets/parkpos" );
  bool onground = fgGetBool( "/sim/presets/onground", false );
  // this logic is taken from former startup.nas
  bool needMetar = (hdg < 360.0) && !apt.empty() && (strthdg > 360.0) &&
  rwy.empty() && onground && parkpos.empty();
  
  if (needMetar) {
    // timeout so we don't spin forever if the network is down
    if (global_finalizeTime.elapsedMSec() > fgGetInt("/sim/startup/metar-fetch-timeout-msec", 6000)) {
      SG_LOG(SG_GENERAL, SG_WARN, "finalizePosition: timed out waiting for METAR fetch");
      return true;
    }
    
    if (fgGetBool( "/environment/metar/failure" )) {
      SG_LOG(SG_ENVIRONMENT, SG_INFO, "metar download failed, not waiting");
      return true;
    }

    if (!fgGetBool( "/environment/metar/valid" )) {
      return false;
    }
    
    SG_LOG(SG_ENVIRONMENT, SG_INFO,
           "Using METAR for runway selection: '" << fgGetString("/environment/metar/data") << "'" );
    setPosFromAirportIDandHdg( apt, hdg );
    // fall through to return true
  } // of need-metar case
  
  return true;
}
  
void finalizePosition()
{
  // first call to finalize after an initPosition call
  if (global_finalizeTime.get_usec() == 0) {
    global_finalizeTime = SGTimeStamp::now();
  }
  
  bool done = true;
  
    /* Scenarios require Nasal, so FGAIManager loads the scenarios,
     * including its models such as a/c carriers, in its 'postinit',
     * which is the very last thing we do.
     * flightgear::initPosition is called very early in main.cxx/fgIdleFunction,
     * one of the first things we do, long before scenarios/carriers are
     * loaded. => When requested "initial preset position" relates to a
     * carrier, recalculate the 'initial' position here 
     */
    std::string carrier = fgGetString("/sim/presets/carrier");
    std::string parkpos = fgGetString("/sim/presets/parkpos");
    std::string apt = fgGetString("/sim/presets/airport-id");

    if (!carrier.empty())
    {
        SG_LOG(SG_GENERAL, SG_INFO, "finalizePositioned: re-init-ing position on carrier");
        // clear preset location and re-trigger position setup
        fgSetDouble("/sim/presets/longitude-deg", 9999);
        fgSetDouble("/sim/presets/latitude-deg", 9999);
        initPosition();
    } else if (!apt.empty() && !parkpos.empty()) {
        // parking position depends on ATC / dynamics code to assign spaces,
        // so we wait until this point to initialise
        fgSetPosFromAirportIDandParkpos(apt, parkpos);
    } else {
        done = finalizeMetar();
    }
  
    fgSetBool("/sim/position-finalized", done);
    if (done) {
        globals->get_event_mgr()->removeTask("finalizePosition");
        global_callbackRegistered = false;
    }
}
    
} // of namespace flightgear