gps.cxx

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// gps.cxx - distance-measuring equipment.
// Written by David Megginson, started 2003.
//
// This file is in the Public Domain and comes with no warranty.
 
#include <config.h>
 
#include "gps.hxx"
 
#include <memory>
#include <set>
#include <cstring>
#include <cstdio>
 
#include "Main/fg_props.hxx"
#include "Main/globals.hxx" // for get_subsystem
#include "Main/util.hxx" // for fgLowPass
#include "Navaids/positioned.hxx"
#include <Navaids/waypoint.hxx>
#include "Navaids/navrecord.hxx"
#include "Navaids/FlightPlan.hxx"
#include <Navaids/routePath.hxx>
#include <Instrumentation/rnav_waypt_controller.hxx>
 
#include "Airports/airport.hxx"
#include "Airports/runways.hxx"
#include "Autopilot/route_mgr.hxx"
 
#include <simgear/math/sg_random.hxx>
#include <simgear/sg_inlines.h>
#include <simgear/math/sg_geodesy.hxx>
#include <simgear/structure/exception.hxx>
 
using std::unique_ptr;
using std::string;
using namespace flightgear;
 
 
static const char* makeTTWString(double TTW)
{
  if ((TTW <= 0.0) || (TTW >= 356400.5)) { // 99 hours
    return "--:--:--";
  }
 
  unsigned TTW_seconds = (unsigned) (TTW + 0.5);
  unsigned TTW_minutes = 0;
  unsigned TTW_hours   = 0;
 
  TTW_hours   = TTW_seconds / 3600;
  TTW_minutes = (TTW_seconds / 60) % 60;
  TTW_seconds = TTW_seconds % 60;
 
  static char TTW_str[16];
  snprintf(TTW_str, 16, "%02u:%02u:%02u",
    TTW_hours, TTW_minutes, TTW_seconds);
 
  return TTW_str;
}

// configuration helper object
 
GPS::Config::Config() :
  _enableTurnAnticipation(false),
  _turnRate(3.0), // degrees-per-second, so 180 degree turn takes 60 seconds
  _overflightDistance(0.02),
  _overflightArmDistance(1.0),
  _overflightArmAngle(90.0),
  _waypointAlertTime(30.0),
  _requireHardSurface(true),
  _cdiMaxDeflectionNm(3.0), // linear mode, 3nm at the peg
  _driveAutopilot(true),
  _courseSelectable(false),
  _followLegTrackToFix(true)
{
}
 
void GPS::Config::bind(GPS* aOwner, SGPropertyNode* aCfg)
{
  aOwner->tie(aCfg, "turn-rate-deg-sec", SGRawValuePointer<double>(&_turnRate));
  aOwner->tie(aCfg, "enable-fly-by", SGRawValuePointer<bool>(&_enableTurnAnticipation));
  aOwner->tie(aCfg, "wpt-alert-time", SGRawValuePointer<double>(&_waypointAlertTime));
  aOwner->tie(aCfg, "hard-surface-runways-only", SGRawValuePointer<bool>(&_requireHardSurface));
  aOwner->tie(aCfg, "cdi-max-deflection-nm", SGRawValuePointer<double>(&_cdiMaxDeflectionNm));
  aOwner->tie(aCfg, "drive-autopilot", SGRawValuePointer<bool>(&_driveAutopilot));
  aOwner->tie(aCfg, "course-selectable", SGRawValuePointer<bool>(&_courseSelectable));
  aOwner->tie(aCfg, "follow-leg-track-to-fix", SGRawValuePointer<bool>(&_followLegTrackToFix));
  aOwner->tie(aCfg, "over-flight-distance-nm", SGRawValuePointer<double>(&_overflightDistance));
  aOwner->tie(aCfg, "over-flight-arm-distance-nm", SGRawValuePointer<double>(&_overflightArmDistance));
  aOwner->tie(aCfg, "over-flight-arm-angle-deg", SGRawValuePointer<double>(&_overflightArmAngle));
  aOwner->tie(aCfg, "delegate-sequencing", SGRawValuePointer<bool>(&_delegateSequencing));
  aOwner->tie(aCfg, "max-fly-by-turn-angle-deg", SGRawValueMethods<GPS, double>(*aOwner, &GPS::maxFlyByTurnAngleDeg, &GPS::setFlyByMaxTurnAngle));
}
 
void GPS::setFlyByMaxTurnAngle(double maxAngle)
{
    _config.setMaxFlyByTurnAngle(maxAngle);
    // keep the FlightPlan in sync, so RoutePath matches
    _route->setMaxFlyByTurnAngle(maxAngle);
}

 
GPS::GPS ( SGPropertyNode *node, bool defaultGPSMode) :
  _selectedCourse(0.0),
  _desiredCourse(0.0),
  _dataValid(false),
  _lastPosValid(false),
  _defaultGPSMode(defaultGPSMode),
  _mode("init"),
  _name(node->getStringValue("name", "gps")),
  _num(node->getIntValue("number", 0)),
  _callbackFlightPlanChanged(SGPropertyChangeCallback<GPS>(this,&GPS::routeManagerFlightPlanChanged,
                                                           fgGetNode("/autopilot/route-manager/signals/flightplan-changed", true))),
  _callbackRouteActivated(SGPropertyChangeCallback<GPS>(this,&GPS::routeActivated,
                                                        fgGetNode("/autopilot/route-manager/active", true)))
{
  string branch = "/instrumentation/" + _name;
  _gpsNode = fgGetNode(branch, _num, true );
  _scratchNode = _gpsNode->getChild("scratch", 0, true);
  
  SGPropertyNode *wp_node = _gpsNode->getChild("wp", 0, true);
  _currentWayptNode = wp_node->getChild("wp", 1, true);
    
#if FG_210_COMPAT
    _searchIsRoute = false;
    _searchHasNext = false;
    _searchType = FGPositioned::INVALID;
#endif
}
 
GPS::~GPS ()
{
}
 
void
GPS::init ()
{
  _magvar_node = fgGetNode("/environment/magnetic-variation-deg", true);
  _serviceable_node = _gpsNode->getChild("serviceable", 0, true);
  _serviceable_node->setBoolValue(true);
  _electrical_node = fgGetNode("/systems/electrical/outputs/gps", true);
 
// basic GPS outputs
  _raim_node = _gpsNode->getChild("raim", 0, true);
  _odometer_node = _gpsNode->getChild("odometer", 0, true);
  _trip_odometer_node = _gpsNode->getChild("trip-odometer", 0, true);
  _true_bug_error_node = _gpsNode->getChild("true-bug-error-deg", 0, true);
  _magnetic_bug_error_node = _gpsNode->getChild("magnetic-bug-error-deg", 0, true);
  _eastWestVelocity = _gpsNode->getChild("ew-velocity-msec", 0, true);
  _northSouthVelocity = _gpsNode->getChild("ns-velocity-msec", 0, true);
  
// waypoints
  // for compatibility, alias selected course down to wp/wp[1]/desired-course-deg
  SGPropertyNode* wp1Crs = _currentWayptNode->getChild("desired-course-deg", 0, true);
  wp1Crs->alias(_gpsNode->getChild("desired-course-deg", 0, true), true);
 
  _tracking_bug_node = _gpsNode->getChild("tracking-bug", 0, true);
    
// route properties
  // should these move to the route manager?
  _routeDistanceNm = _gpsNode->getChild("route-distance-nm", 0, true);
  _routeETE = _gpsNode->getChild("ETE", 0, true);
 
    
// navradio slaving properties
  SGPropertyNode* toFlag = _gpsNode->getChild("to-flag", 0, true);
  toFlag->alias(_currentWayptNode->getChild("to-flag"), true);
 
  SGPropertyNode* fromFlag = _gpsNode->getChild("from-flag", 0, true);
  fromFlag->alias(_currentWayptNode->getChild("from-flag"), true);
 
  // autopilot drive properties
  _apDrivingFlag = fgGetNode("/autopilot/settings/gps-driving-true-heading", true);
  _apTrueHeading = fgGetNode("/autopilot/settings/true-heading-deg",true);
 
  clearScratch();
  clearOutput();
}
 
void
GPS::reinit ()
{
  clearOutput();
}
 
void
GPS::bind()
{
  _config.bind(this, _gpsNode->getChild("config", 0, true));
 
// basic GPS outputs
  tie(_gpsNode, "selected-course-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getSelectedCourse, &GPS::setSelectedCourse));
 
  tie(_gpsNode, "desired-course-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getDesiredCourse, NULL));
  _desiredCourseNode = _gpsNode->getChild("desired-course-deg", 0, true);
    
  tieSGGeodReadOnly(_gpsNode, _indicated_pos, "indicated-longitude-deg", 
        "indicated-latitude-deg", "indicated-altitude-ft");
 
  tie(_gpsNode, "indicated-vertical-speed", SGRawValueMethods<GPS, double>
    (*this, &GPS::getVerticalSpeed, NULL));
  tie(_gpsNode, "indicated-track-true-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getTrueTrack, NULL));
  tie(_gpsNode, "indicated-track-magnetic-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getMagTrack, NULL));
  tie(_gpsNode, "indicated-ground-speed-kt", SGRawValueMethods<GPS, double>
    (*this, &GPS::getGroundspeedKts, NULL));
  
// command system
  tie(_gpsNode, "mode", SGRawValueMethods<GPS, const char*>(*this, &GPS::getMode, NULL));
  tie(_gpsNode, "command", SGRawValueMethods<GPS, const char*>(*this, &GPS::getCommand, &GPS::setCommand));
  tieSGGeod(_scratchNode, _scratchPos, "longitude-deg", "latitude-deg", "altitude-ft");
  
#if FG_210_COMPAT
    tie(_scratchNode, "valid", SGRawValueMethods<GPS, bool>(*this, &GPS::getScratchValid, NULL));
    tie(_scratchNode, "distance-nm", SGRawValueMethods<GPS, double>(*this, &GPS::getScratchDistance, NULL));
    tie(_scratchNode, "true-bearing-deg", SGRawValueMethods<GPS, double>(*this, &GPS::getScratchTrueBearing, NULL));
    tie(_scratchNode, "mag-bearing-deg", SGRawValueMethods<GPS, double>(*this, &GPS::getScratchMagBearing, NULL));
    tie(_scratchNode, "has-next", SGRawValueMethods<GPS, bool>(*this, &GPS::getScratchHasNext, NULL));
    _scratchValid = false;
    
    _scratchNode->setStringValue("type", "");
    _scratchNode->setStringValue("query", "");
#endif
    
  SGPropertyNode *wp_node = _gpsNode->getChild("wp", 0, true);
  SGPropertyNode* wp0_node = wp_node->getChild("wp", 0, true);
  tieSGGeodReadOnly(wp0_node, _wp0_position, "longitude-deg", "latitude-deg", "altitude-ft");
  tie(wp0_node, "ID", SGRawValueMethods<GPS, const char*>
      (*this, &GPS::getWP0Ident, NULL));
  tie(wp0_node, "name", SGRawValueMethods<GPS, const char*>
      (*this, &GPS::getWP0Name, NULL));
 
  tie(_currentWayptNode, "valid", SGRawValueMethods<GPS, bool>
       (*this, &GPS::getWP1IValid, NULL));
    
  tie(_currentWayptNode, "ID", SGRawValueMethods<GPS, const char*>
    (*this, &GPS::getWP1Ident, NULL));
  tie(_currentWayptNode, "name", SGRawValueMethods<GPS, const char*>
    (*this, &GPS::getWP1Name, NULL));
    
  tie(_currentWayptNode, "distance-nm", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1Distance, NULL));
  tie(_currentWayptNode, "bearing-true-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1Bearing, NULL));
  tie(_currentWayptNode, "bearing-mag-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1MagBearing, NULL));
  tie(_currentWayptNode, "TTW-sec", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1TTW, NULL));
  tie(_currentWayptNode, "TTW", SGRawValueMethods<GPS, const char*>
    (*this, &GPS::getWP1TTWString, NULL));
  
  tie(_currentWayptNode, "course-deviation-deg", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1CourseDeviation, NULL));
  tie(_currentWayptNode, "course-error-nm", SGRawValueMethods<GPS, double>
    (*this, &GPS::getWP1CourseErrorNm, NULL));
  tie(_currentWayptNode, "to-flag", SGRawValueMethods<GPS, bool>
    (*this, &GPS::getWP1ToFlag, NULL));
  tie(_currentWayptNode, "from-flag", SGRawValueMethods<GPS, bool>
    (*this, &GPS::getWP1FromFlag, NULL));
 
// leg properties (only valid in DTO/LEG modes, not OBS)
  tie(wp_node, "leg-distance-nm", SGRawValueMethods<GPS, double>(*this, &GPS::getLegDistance, NULL));
  tie(wp_node, "leg-true-course-deg", SGRawValueMethods<GPS, double>(*this, &GPS::getLegCourse, NULL));
  tie(wp_node, "leg-mag-course-deg", SGRawValueMethods<GPS, double>(*this, &GPS::getLegMagCourse, NULL));
 
// navradio slaving properties  
  tie(_gpsNode, "cdi-deflection", SGRawValueMethods<GPS,double>
    (*this, &GPS::getCDIDeflection));
 
    _currentWpLatNode = _currentWayptNode->getNode("latitude-deg", true);
    _currentWpLonNode = _currentWayptNode->getNode("longitude-deg", true);
    _currentWpAltNode = _currentWayptNode->getNode("altitude-ft", true);
}
 
void
GPS::unbind()
{
    // avoid shutdown crash during Untie(), due to invoking the getters to capture the
    // current value(s)
    _currentWaypt = _prevWaypt = nullptr;
 
    _tiedProperties.Untie();
    _gpsNode.clear();
    _currentWayptNode.clear();
    _currentWpLatNode.clear();
    _currentWpLonNode.clear();
    _currentWpAltNode.clear();
}
 
void
GPS::clearOutput()
{
  _dataValid = false;
  _last_speed_kts = 0.0;
  _last_pos = SGGeod();
  _lastPosValid = false;
  _indicated_pos = SGGeod();
  _last_vertical_speed = 0.0;
  _last_true_track = 0.0;
  _lastEWVelocity = _lastNSVelocity = 0.0;
  _currentWaypt = _prevWaypt = NULL;
  _legDistanceNm = -1.0;
  
  _raim_node->setDoubleValue(0.0);
  _indicated_pos = SGGeod();
  _odometer_node->setDoubleValue(0);
  _trip_odometer_node->setDoubleValue(0);
  _tracking_bug_node->setDoubleValue(0);
  _true_bug_error_node->setDoubleValue(0);
  _magnetic_bug_error_node->setDoubleValue(0);
  _northSouthVelocity->setDoubleValue(0.0);
  _eastWestVelocity->setDoubleValue(0.0);
}
 
void
GPS::update (double delta_time_sec)
{
  if (!_defaultGPSMode) {
    // If it's off, don't bother.
      // check if value is defined, since many aircraft don't define an output
      // for the GPS, but expect the default one to work.
      bool elecOn = !_electrical_node->hasValue() || _electrical_node->getBoolValue();
    if (!_serviceable_node->getBoolValue() || !elecOn) {
      clearOutput();
      return;
    }
  }
  
  if (delta_time_sec <= 0.0) {
    return; // paused, don't bother
  }    
  
  _raim_node->setDoubleValue(1.0);
  _indicated_pos = globals->get_aircraft_position();
  updateBasicData(delta_time_sec);
 
  if (_dataValid) {
    if (_wayptController.get()) {
      _wayptController->update(delta_time_sec);
        updateCurrentWpNode(_wayptController->position());
      _desiredCourse = getLegMagCourse();
      
      _gpsNode->setStringValue("rnav-controller-status", _wayptController->status());
        
      if (_wayptController->isDone()) {
        doSequence();
      }
      updateRouteData();
    }
 
    
    updateTrackingBug();
    driveAutopilot();
  }
  
  if (_dataValid && (_mode == "init")) {
    // will select LEG mode if the route is active
    routeManagerFlightPlanChanged(nullptr);
    auto routeMgr = globals->get_subsystem<FGRouteMgr>();
      
    if (!routeMgr || !routeMgr->isRouteActive()) {
      // initialise in OBS mode, with waypt set to the nearest airport.
      // keep in mind at this point, _dataValid is not set
      FGAirport::HardSurfaceFilter f;
      FGPositionedRef apt = FGPositioned::findClosest(_indicated_pos, 20.0, &f);
      if (apt) {
        selectOBSMode(new flightgear::NavaidWaypoint(apt, nullptr));
      } else {
        selectOBSMode(nullptr);
      }
    }
 
    if (_mode != "init")
    {
      // allow a realistic delay in the future, here
    }
  } // of init mode check
  
  _last_pos = _indicated_pos;
  _lastPosValid = !(_last_pos == SGGeod());
}
 
void GPS::shutdown()
{
    if (_route) {
        _route->removeDelegate(this);
        _route = nullptr;
    }
    _wayptController.reset();
}
 
void GPS::routeManagerFlightPlanChanged(SGPropertyNode*)
{
  if (_route) {
    _route->removeDelegate(this);
  }
  
  SG_LOG(SG_INSTR, SG_DEBUG, "GPS saw route-manager flight-plan replaced.");
  auto routeMgr = globals->get_subsystem<FGRouteMgr>();
  if (!routeMgr) {
    return;
  }
    
  _route = routeMgr->flightPlan();
  if (_route) {
    _route->addDelegate(this);
  }
  
  if (routeMgr->isRouteActive()) {
    selectLegMode();
  } else {
    selectOBSMode(_currentWaypt); // revert to OBS on current waypoint
  }
}
 
void GPS::routeActivated(SGPropertyNode* aNode)
{
    // if the delegate is handling this, don't do anything else ourselves
    if (_config.delegateDoesSequencing()) {
        return;
    }
    
    bool isActive = aNode->getBoolValue();
    if (isActive) {
        SG_LOG(SG_INSTR, SG_INFO, "GPS::route activated, switching to LEG mode");
        selectLegMode();
        
        // if we've already passed the current waypoint, sequence.
        if (_dataValid && getWP1FromFlag()) {
            SG_LOG(SG_INSTR, SG_INFO, "GPS::route activated, FROM wp1, sequencing");
            sequence();
        }
    } else if (_mode == "leg") {
        SG_LOG(SG_INSTR, SG_INFO, "GPS::route deactivated, switching to OBS mode");
        selectOBSMode(_currentWaypt);
    }
}
 

// implement the RNAV interface 
SGGeod GPS::position()
{
  if (!_dataValid) {
    return SGGeod();
  }
  
  return _indicated_pos;
}
 
double GPS::trackDeg()
{
  return _last_true_track;
}
 
double GPS::groundSpeedKts()
{
  return _last_speed_kts;
}
 
double GPS::vspeedFPM()
{
  return _last_vertical_speed;
}
 
double GPS::magvarDeg()
{
  return _magvar_node->getDoubleValue();
}
 
double GPS::overflightDistanceM()
{
  return _config.overflightDistanceNm() * SG_NM_TO_METER;
}
 
double GPS::overflightArmDistanceM()
{
  return _config.overflightArmDistanceNm() * SG_NM_TO_METER;
}
 
double GPS::overflightArmAngleDeg()
{
  return _config.overflightArmAngleDeg();
}
 
double GPS::selectedMagCourse()
{
  return _selectedCourse;
}
 
double GPS::maxFlyByTurnAngleDeg() const
{
    return _config.maxFlyByTurnAngleDeg();
}
 
std::optional<double> GPS::nextLegTrack()
{
    auto next = _route->nextLeg();
    if (!next)
        return {};
    
    return next->courseDeg();
}
 
std::optional<RNAV::LegData> GPS::previousLegData()
{
  // if the previous controller computed valid data,
  // use that. This ensures fly-by turns work out, especially
  if (_wp0Data.has_value())
    return _wp0Data;
  
  // if we did not get data from the previous controller (eg, waypoint
  // jumped or first waypoint), just compute the position
  FlightPlan::Leg* leg = _route->previousLeg();
  if (!leg) {
    return {}; // no data
  }
  
  LegData legData;
  Waypt* waypt = leg->waypoint();
  legData.position = waypt->position();
  
   // ensure computations use runway end, not threshold
   if (waypt->type() == "runway") {
       RunwayWaypt* rwpt = static_cast<RunwayWaypt*>(waypt);
       legData.position =  rwpt->runway()->end();
   }
 
  return legData;
}
 
bool GPS::canFlyBy() const
{
    return _config.turnAnticipationEnabled();
}

 
void
GPS::updateBasicData(double dt)
{
  if (!_lastPosValid) {
    return;
  }
  
  double distance_m;
  double track2_deg;
  SGGeodesy::inverse(_last_pos, _indicated_pos, _last_true_track, track2_deg, distance_m );
    
// detect repositions
// setting this value high enough hypersonic aircraft but not spaceships
  if ((distance_m / dt) > 100000.0) {
    SG_LOG(SG_INSTR, SG_DEBUG, "GPS detected reposition, resetting data");
    _dataValid = false;
    return;
  }
    
  double speed_kt = ((distance_m * SG_METER_TO_NM) * ((1 / dt) * 3600.0));
  double vertical_speed_mpm = ((_indicated_pos.getElevationM() - _last_pos.getElevationM()) * 60 / dt);
  _last_vertical_speed = vertical_speed_mpm * SG_METER_TO_FEET;
  
  speed_kt = fgGetLowPass(_last_speed_kts, speed_kt, dt/5.0);
  _last_speed_kts = speed_kt;
  
  SGGeod g = _indicated_pos;
  g.setLongitudeDeg(_last_pos.getLongitudeDeg());
  double northSouthM = dist(SGVec3d::fromGeod(_last_pos), SGVec3d::fromGeod(g));
  northSouthM = copysign(northSouthM, _indicated_pos.getLatitudeDeg() - _last_pos.getLatitudeDeg());
  
  double nsMSec = fgGetLowPass(_lastNSVelocity, northSouthM / dt, dt/2.0);
  _lastNSVelocity = nsMSec;
  _northSouthVelocity->setDoubleValue(nsMSec);
 
  g = _indicated_pos;
  g.setLatitudeDeg(_last_pos.getLatitudeDeg());
  double eastWestM = dist(SGVec3d::fromGeod(_last_pos), SGVec3d::fromGeod(g));
  eastWestM = copysign(eastWestM, _indicated_pos.getLongitudeDeg() - _last_pos.getLongitudeDeg());
  
  double ewMSec = fgGetLowPass(_lastEWVelocity, eastWestM / dt, dt/2.0);
  _lastEWVelocity = ewMSec;
  _eastWestVelocity->setDoubleValue(ewMSec);
  
  double odometer = _odometer_node->getDoubleValue();
  _odometer_node->setDoubleValue(odometer + distance_m * SG_METER_TO_NM);
  odometer = _trip_odometer_node->getDoubleValue();
  _trip_odometer_node->setDoubleValue(odometer + distance_m * SG_METER_TO_NM);
  
  if (!_dataValid) {
    _dataValid = true;
  }
}
 
void
GPS::updateTrackingBug()
{
  double tracking_bug = _tracking_bug_node->getDoubleValue();
  double true_bug_error = tracking_bug - getTrueTrack();
  double magnetic_bug_error = tracking_bug - getMagTrack();
 
  // Get the errors into the (-180,180) range.
  SG_NORMALIZE_RANGE(true_bug_error, -180.0, 180.0);
  SG_NORMALIZE_RANGE(magnetic_bug_error, -180.0, 180.0);
 
  _true_bug_error_node->setDoubleValue(true_bug_error);
  _magnetic_bug_error_node->setDoubleValue(magnetic_bug_error);
}
 
void GPS::currentWaypointChanged()
{
  _wp0Data.reset();
  if (!_route) {
    return;
  }
  
  int index = _route->currentIndex(),
    count = _route->numLegs();
  if ((index < 0) || (index >= count)) {
    _currentWaypt=nullptr;
    _prevWaypt=nullptr;
    // no active leg on the route
    return;
  }
    
  if (index > 0) {
    _prevWaypt = _route->previousLeg()->waypoint();
    if (_prevWaypt->flag(WPT_DYNAMIC)) {
      _wp0_position = _indicated_pos;
    } else {
      _wp0_position = _prevWaypt->position();
    }
  }
  
  _currentWaypt = _route->currentLeg()->waypoint();
  if (_wayptController && (_wayptController->waypoint() == _prevWaypt)) {
    // capture leg data form the controller, before we destroy it
    _wp0Data = _wayptController->legData();
  }
  
  wp1Changed(); // rebuild the active controller
  _desiredCourse = getLegMagCourse();
  _desiredCourseNode->fireValueChanged();
}
 
 
void GPS::waypointsChanged()
{
  if (_mode != "leg") {
    return;
  }
  
  SG_LOG(SG_INSTR, SG_DEBUG, "GPS route edited while in LEG mode, updating waypoints");
  currentWaypointChanged();
}
 
void GPS::doSequence()
{
    if (!_route) {
        return;
    }
  
    if (_config.delegateDoesSequencing()) {
        // new style behaviour : let the delegate handle it
        _route->sequence();
    } else {
        // backwards compatible behaviour : we do it ourselves
        if (_mode == "dto") {
            SG_LOG(SG_INSTR, SG_INFO, "GPS DTO reached destination point");
            if (_route && _route->isActive()) {
                // check if our destination point is on the active route,
                // in which case resume leg mode
                const int index = _route->findWayptIndex(_currentWaypt->position());
                if (index >= 0) {
                    SG_LOG(SG_INSTR, SG_INFO, "GPS DTO resuming LEG mode at " << _route->legAtIndex(index)->waypoint()->ident());
                    _mode = "leg";
                    _route->setCurrentIndex(index);
                    return;
                }
            }
            
            // if we didn't enter LEG mode, drop back to OBS
            selectOBSMode(_currentWaypt);
        } else if (_mode == "leg") {
            const int nextIndex = _route->currentIndex() + 1;
            if (nextIndex >= _route->numLegs()) {
                SG_LOG(SG_INSTR, SG_INFO, "GPS built-in sequencing, reached end of route,");
                _route->finish();
                selectOBSMode(_currentWaypt);
            } else {
                // sequence ourselves
                _route->setCurrentIndex(nextIndex);
            }
        }
    }
}
 
void GPS::cleared()
{
    // if the aircraft delegates handle sequencing, don't do
    // anything here
    if (_config.delegateDoesSequencing()) {
        return;
    }
    
    // backwards compatability : select OBS mode
    if (_mode == "leg") {
        selectOBSMode(_currentWaypt);
    }
}
 
void GPS::endOfFlightPlan()
{
    // backwards compatability - same logic as 'cleared', revert to OBS mode
    // if we're in leg mode
    cleared();
}
 
double GPS::turnRadiusNm(double groundSpeedKts)
{
    return computeTurnRadiusNm(groundSpeedKts);
}
 
double GPS::computeTurnRadiusNm(double aGroundSpeedKts) const
{
        // turn time is seconds to execute a 360 turn. 
  double turnTime = 360.0 / _config.turnRateDegSec();
  
  // c is ground distance covered in that time (circumference of the circle)
        double c = turnTime * (aGroundSpeedKts / 3600.0); // convert knts to nm/sec
  
  // divide by 2PI to go from circumference -> radius
        return c / (2 * M_PI);
}
 
void GPS::updateRouteData()
{
    double totalDistance = 0.0;
    // waypt controller might be null: Sentry-Id: FLIGHTGEAR-FFX
    if (_wayptController) {
        totalDistance = _wayptController->distanceToWayptM() * SG_METER_TO_NM;
    }
 
    if (_route) {
        // walk all waypoints from wp2 to route end, and sum
        for (int i=_route->currentIndex()+1; i<_route->numLegs(); ++i) {
            auto leg = _route->legAtIndex(i);
            // omit missed-approach waypoints in distance calculation
            if (leg->waypoint()->flag(WPT_MISS))
                continue;
            
            totalDistance += leg->distanceNm();
        }
    }
  
  _routeDistanceNm->setDoubleValue(totalDistance * SG_METER_TO_NM);
  if (_last_speed_kts > 1.0) {
    double TTW = ((totalDistance * SG_METER_TO_NM) / _last_speed_kts) * 3600.0;
    _routeETE->setStringValue(makeTTWString(TTW));    
  }
}
 
void GPS::driveAutopilot()
{
  if (!_config.driveAutopilot() || !_defaultGPSMode) {
    _apDrivingFlag->setBoolValue(false);
    return;
  }
 
  // compatibility feature - allow the route-manager / GPS to drive the
  // generic autopilot heading hold *in leg mode only* 
  
  bool drive = _mode == "leg";
  _apDrivingFlag->setBoolValue(drive);
  
  if (drive) {
    // FIXME: we want to set desired track, not heading, here
    _apTrueHeading->setDoubleValue(getWP1Bearing());
  }
}
 
void GPS::wp1Changed()
{
  if (!_currentWaypt)
    return;
  
  if (_mode == "leg") {
    _wayptController.reset(WayptController::createForWaypt(this, _currentWaypt));
    if (_currentWaypt->type() == "hold") {
      // pass the hold count through
      auto leg = _route->currentLeg();
      auto holdCtl = static_cast<flightgear::HoldCtl*>(_wayptController.get());
      holdCtl->setHoldCount(leg->holdCount());
    }
  } else if (_mode == "obs") {
    _wayptController.reset(new OBSController(this, _currentWaypt));
  } else if (_mode == "dto") {
    _wayptController.reset(new DirectToController(this, _currentWaypt, _wp0_position));
  }
 
  const bool ok = _wayptController && _wayptController->init();
  if (!ok) {
      SG_LOG(SG_AUTOPILOT, SG_WARN, "GPS failed to init RNAV controller for waypoint " << _currentWaypt->ident());
      _wayptController.reset();
      _mode.clear();
      _gpsNode->setStringValue("rnav-controller-status", "");
      return;
  }
 
  _gpsNode->setStringValue("rnav-controller-status", _wayptController->status());
  
  if (_mode == "obs") {
    _legDistanceNm = -1.0;
  } else {
    _wayptController->update(0.0);
    _gpsNode->setStringValue("rnav-controller-status", _wayptController->status());
    
    _legDistanceNm = _wayptController->distanceToWayptM() * SG_METER_TO_NM;
    
    // synchronise these properties immediately
      updateCurrentWpNode(_wayptController->position());
    
    _desiredCourse = getLegMagCourse();
  }
}
 
void GPS::updateCurrentWpNode(const SGGeod& p)
{
    _currentWpLatNode->setDoubleValue(p.getLatitudeDeg());
    _currentWpLonNode->setDoubleValue(p.getLongitudeDeg());
    _currentWpAltNode->setDoubleValue(p.getElevationFt());
}

// property getter/setters
 
void GPS::setSelectedCourse(double crs)
{
  if (_selectedCourse == crs) {
    return;
  }
  
  _selectedCourse = crs;
  if ((_mode == "obs") || _config.courseSelectable()) {
    _desiredCourse = _selectedCourse;
    _desiredCourseNode->fireValueChanged();
  }
}
 
double GPS::getLegDistance() const
{
  if (!_dataValid || (_mode == "obs")) {
    return -1;
  }
  
  return _legDistanceNm;
}
 
double GPS::getLegCourse() const
{
  if (!_dataValid || !_wayptController.get()) {
    return -9999.0;
  }
  
  return _wayptController->targetTrackDeg();
}
 
double GPS::getLegMagCourse() const
{
  if (!_dataValid) {
    return 0.0;
  }
  
  double m = getLegCourse() - _magvar_node->getDoubleValue();
  SG_NORMALIZE_RANGE(m, 0.0, 360.0);
  return m;
}
 
double GPS::getMagTrack() const
{
  if (!_dataValid) {
    return 0.0;
  }
  
  double m = getTrueTrack() - _magvar_node->getDoubleValue();
  SG_NORMALIZE_RANGE(m, 0.0, 360.0);
  return m;
}
 
double GPS::getCDIDeflection() const
{
  if (!_dataValid) {
    return 0.0;
  }
  
  double defl;
  if (_config.cdiDeflectionIsAngular()) {
    defl = getWP1CourseDeviation();
    SG_CLAMP_RANGE(defl, -10.0, 10.0); // as in navradio.cxx
  } else {
    double fullScale = _config.cdiDeflectionLinearPeg();
    double normError = getWP1CourseErrorNm() / fullScale;
    SG_CLAMP_RANGE(normError, -1.0, 1.0);
    defl = normError * 10.0; // re-scale to navradio limits, i.e [-10.0 .. 10.0]
  }
  
  return defl;
}
 
const char* GPS::getWP0Ident() const
{
  if (!_dataValid || (_mode != "leg") || !_prevWaypt) {
    return "";
  }
  
// work around std::string::c_str() storage lifetime with libc++
// real fix is to allow tie-ing with std::string instead of char*
  static char identBuf[16];
  strncpy(identBuf, _prevWaypt->ident().c_str(), 15);
 
  return identBuf;
}
 
const char* GPS::getWP0Name() const
{
    if (!_dataValid || !_prevWaypt || !_prevWaypt->source()) {
        return "";
    }
    
    return _prevWaypt->source()->name().c_str();
}
 
bool GPS::getWP1IValid() const
{
    return _dataValid && _currentWaypt.get();
}
 
const char* GPS::getWP1Ident() const
{
  if (!_dataValid || !_currentWaypt) {
    return "";
  }
  
// work around std::string::c_str() storage lifetime with libc++
// real fix is to allow tie-ing with std::string instead of char*
  static char identBuf[16];
  strncpy(identBuf, _currentWaypt->ident().c_str(), 15);
    
  return identBuf;
}
 
const char* GPS::getWP1Name() const
{
    if (!_dataValid || !_currentWaypt || !_currentWaypt->source()) {
        return "";
    }
    
    return _currentWaypt->source()->name().c_str();
}
 
double GPS::getWP1Distance() const
{
  if (!_dataValid || !_wayptController.get()) {
    return -1.0;
  }
  
  return _wayptController->distanceToWayptM() * SG_METER_TO_NM;
}
 
double GPS::getWP1TTW() const
{
  if (!_dataValid || !_wayptController.get()) {
    return -1.0;
  }
  
  return _wayptController->timeToWaypt();
}
 
const char* GPS::getWP1TTWString() const
{
  double t = getWP1TTW();
  if (t <= 0.0) {
    return "";
  }
  
  return makeTTWString(t);
}
 
double GPS::getWP1Bearing() const
{
  if (!_dataValid || !_wayptController.get()) {
    return -9999.0;
  }
  
  return _wayptController->trueBearingDeg();
}
 
double GPS::getWP1MagBearing() const
{
  if (!_dataValid || !_wayptController.get()) {
    return -9999.0;
  }
 
  double magBearing =  _wayptController->trueBearingDeg() - _magvar_node->getDoubleValue();
  SG_NORMALIZE_RANGE(magBearing, 0.0, 360.0);
  return magBearing;
}
 
double GPS::getWP1CourseDeviation() const
{
  if (!_dataValid || !_wayptController.get()) {
    return 0.0;
  }
 
  return _wayptController->courseDeviationDeg();
}
 
double GPS::getWP1CourseErrorNm() const
{
  if (!_dataValid || !_wayptController.get()) {
    return 0.0;
  }
  
  return _wayptController->xtrackErrorNm();
}
 
bool GPS::getWP1ToFlag() const
{
  if (!_dataValid || !_wayptController.get()) {
    return false;
  }
  
  return _wayptController->toFlag();
}
 
bool GPS::getWP1FromFlag() const
{
  if (!_dataValid || !_wayptController.get()) {
    return false;
  }
  
  return !getWP1ToFlag();
}
 
#if FG_210_COMPAT
double GPS::getScratchDistance() const
{
    if (!_scratchValid) {
        return 0.0;
    }
    
    return SGGeodesy::distanceNm(_indicated_pos, _scratchPos);
}
 
double GPS::getScratchTrueBearing() const
{
    if (!_scratchValid) {
        return 0.0;
    }
    
    return SGGeodesy::courseDeg(_indicated_pos, _scratchPos);
}
 
double GPS::getScratchMagBearing() const
{
    if (!_scratchValid) {
        return 0.0;
    }
    
    double crs = getScratchTrueBearing() - _magvar_node->getDoubleValue();
    SG_NORMALIZE_RANGE(crs, 0.0, 360.0);
    return crs;
}
 
#endif

// scratch system
 
void GPS::setCommand(const char* aCmd)
{
  SG_LOG(SG_INSTR, SG_DEBUG, "GPS command:" << aCmd);
  
  if (!strcmp(aCmd, "direct")) {
    directTo();
  } else if (!strcmp(aCmd, "obs")) {
      // valid scratch data is always used, if it's not valid we will
      // use the current waypoint if one exists
      selectOBSMode(isScratchPositionValid() ? nullptr : _currentWaypt);
  } else if (!strcmp(aCmd, "leg")) {
      selectLegMode();
  } else if (!strcmp(aCmd, "exit-hold")) {
      commandExitHold();
#if FG_210_COMPAT
  } else if (!strcmp(aCmd, "load-route-wpt")) {
      loadRouteWaypoint();
  } else if (!strcmp(aCmd, "nearest")) {
      loadNearest();
  } else if (!strcmp(aCmd, "search")) {
      _searchNames = false;
      search();
  } else if (!strcmp(aCmd, "search-names")) {
      _searchNames = true;
      search();
  } else if (!strcmp(aCmd, "next")) {
      nextResult();
  } else if (!strcmp(aCmd, "previous")) {
      previousResult();
  } else if (!strcmp(aCmd, "define-user-wpt")) {
      defineWaypoint();
  } else if (!strcmp(aCmd, "route-insert-before")) {
      int index = _scratchNode->getIntValue("index");
      if (index < 0 || (_route->numLegs() == 0)) {
          index = _route->numLegs();
      } else if (index >= _route->numLegs()) {
          SG_LOG(SG_INSTR, SG_WARN, "GPS:route-insert-before, bad index:" << index);
          return;
      }
      
      insertWaypointAtIndex(index);
  } else if (!strcmp(aCmd, "route-insert-after")) {
      int index = _scratchNode->getIntValue("index");
      if (index < 0 || (_route->numLegs() == 0)) {
          index = _route->numLegs();
      } else if (index >= _route->numLegs()) {
          SG_LOG(SG_INSTR, SG_WARN, "GPS:route-insert-after, bad index:" << index);
          return;
      } else {
          ++index;
      }
      
      insertWaypointAtIndex(index);
  } else if (!strcmp(aCmd, "route-delete")) {
      int index = _scratchNode->getIntValue("index");
      if (index < 0) {
          index = _route->numLegs();
      } else if (index >= _route->numLegs()) {
          SG_LOG(SG_INSTR, SG_WARN, "GPS:route-delete, bad index:" << index);
          return;
      }
      
      removeWaypointAtIndex(index);
#endif
  } else {
    SG_LOG(SG_INSTR, SG_WARN, "GPS:unrecognized command:" << aCmd);
  }
}
 
void GPS::clearScratch()
{
  _scratchPos = SGGeod::fromDegFt(-9999.0, -9999.0, -9999.0);
  _scratchNode->setBoolValue("valid", false);
#if FG_210_COMPAT
    _scratchNode->setStringValue("type", "");
    _scratchNode->setStringValue("query", "");
#endif
}
 
bool GPS::isScratchPositionValid() const
{
  if ((_scratchPos.getLongitudeDeg() < -9990.0) ||
      (_scratchPos.getLatitudeDeg() < -9990.0)) {
   return false;   
  }
  
  return true;
}
 
FGPositionedRef GPS::positionedFromScratch() const
{
    if (!isScratchPositionValid()) {
        return NULL;
    }
    
    std::string ident(_scratchNode->getStringValue("ident"));
    return FGPositioned::findClosestWithIdent(ident, _scratchPos);
}
 
void GPS::directTo()
{  
  if (!isScratchPositionValid()) {
    return;
  }
  
  _prevWaypt = NULL;
  _wp0_position = _indicated_pos;
    
    FGPositionedRef pos = positionedFromScratch();
    if (pos) {
        _currentWaypt = new NavaidWaypoint(pos, NULL);
    } else {
        _currentWaypt = new BasicWaypt(_scratchPos, _scratchNode->getStringValue("ident"), NULL);
    }
    
    _mode = "dto";
  wp1Changed();
}
 
void GPS::selectOBSMode(flightgear::Waypt* waypt)
{
  if (!waypt && isScratchPositionValid()) {
    FGPositionedRef pos = positionedFromScratch();
    if (pos) {
        waypt = new NavaidWaypoint(pos, NULL);
    } else {
        waypt = new BasicWaypt(_scratchPos, _scratchNode->getStringValue("ident"), NULL);
    }
  }
  
  _mode = "obs";
  _prevWaypt = NULL;
  _wp0_position = _indicated_pos;
  _currentWaypt = waypt;
  wp1Changed();
}
 
void GPS::selectLegMode()
{
  if (_mode == "leg") {
    return;
  }
  
  if (!_route) {
    SG_LOG(SG_INSTR, SG_WARN, "GPS:selectLegMode: no active route");
    return;
  }
 
  _mode = "leg";  
 
// clear any previous leg data which might be hanging around
// note this means you can mess up fly-by by toggling into and out LEG
// mode, but this seems reasonable
  _wp0Data.reset();
 
  // depending on the situation, this will either get over-written 
  // in routeManagerSequenced or not; either way it does no harm to
  // set it here.
  _wp0_position = _indicated_pos;
 
  // not really sequenced, but does all the work of updating wp0/1
  currentWaypointChanged();
}
 
#if FG_210_COMPAT
 
void GPS::loadRouteWaypoint()
{
    _scratchValid = false;    
    int index = _scratchNode->getIntValue("index", -9999);
    clearScratch();
    
    if ((index < 0) || (index >= _route->numLegs())) { // no index supplied, use current wp
        index = _route->currentIndex();
    }
    
    _searchIsRoute = true;
    setScratchFromRouteWaypoint(index);
}
 
void GPS::setScratchFromRouteWaypoint(int aIndex)
{
    assert(_searchIsRoute);
    if ((aIndex < 0) || (aIndex >= _route->numLegs())) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:setScratchFromRouteWaypoint: route-index out of bounds");
        return;
    }
    
    _searchResultIndex = aIndex;
    WayptRef wp = _route->legAtIndex(aIndex)->waypoint();
    _scratchNode->setStringValue("ident", wp->ident());
    _scratchPos = wp->position();
    _scratchValid = true;
    _scratchNode->setIntValue("index", aIndex);
}
 
void GPS::loadNearest()
{
    string sty(_scratchNode->getStringValue("type"));
    FGPositioned::Type ty = FGPositioned::typeFromName(sty);
    if (ty == FGPositioned::INVALID) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:loadNearest: request type is invalid:" << sty);
        return;
    }
    
    unique_ptr<FGPositioned::Filter> f(createFilter(ty));
    int limitCount = _scratchNode->getIntValue("max-results", 1);
    double cutoffDistance = _scratchNode->getDoubleValue("cutoff-nm", 400.0);
    
    SGGeod searchPos = _indicated_pos;
    if (isScratchPositionValid()) {
        searchPos = _scratchPos;
    }
    
    clearScratch(); // clear now, regardless of whether we find a match or not
    
    _searchResults =
    FGPositioned::findClosestN(searchPos, limitCount, cutoffDistance, f.get());
    _searchResultIndex = 0;
    _searchIsRoute = false;
    
    if (_searchResults.empty()) {
        return;
    }
    
    setScratchFromCachedSearchResult();
}
 
bool GPS::SearchFilter::pass(FGPositioned* aPos) const
{
    switch (aPos->type()) {
        case FGPositioned::AIRPORT:
            // heliport and seaport too?
        case FGPositioned::VOR:
        case FGPositioned::NDB:
        case FGPositioned::FIX:
        case FGPositioned::TACAN:
        case FGPositioned::WAYPOINT:
            return true;
        default:
            return false;
    }
}
 
FGPositioned::Type GPS::SearchFilter::minType() const
{
    return FGPositioned::AIRPORT;
}
 
FGPositioned::Type GPS::SearchFilter::maxType() const
{
    return FGPositioned::VOR;
}
 
FGPositioned::Filter* GPS::createFilter(FGPositioned::Type aTy)
{
    if (aTy == FGPositioned::AIRPORT) {
        return new FGAirport::HardSurfaceFilter();
    }
    
    // if we were passed INVALID, assume it means 'all types interesting to a GPS'
    if (aTy == FGPositioned::INVALID) {
        return new SearchFilter;
    }
    
    return new FGPositioned::TypeFilter(aTy);
}
 
void GPS::search()
{
    // parse search terms into local members, and exec the first search
    string sty(_scratchNode->getStringValue("type"));
    _searchType = FGPositioned::typeFromName(sty);
    _searchQuery = _scratchNode->getStringValue("query");
    if (_searchQuery.empty()) {
        SG_LOG(SG_INSTR, SG_WARN, "empty GPS search query");
        clearScratch();
        return;
    }
    
    _searchExact = _scratchNode->getBoolValue("exact", true);
    _searchResultIndex = 0;
    _searchIsRoute = false;
    
    unique_ptr<FGPositioned::Filter> f(createFilter(_searchType));
    if (_searchNames) {
        _searchResults = FGPositioned::findAllWithName(_searchQuery, f.get(), _searchExact);
    } else {
        _searchResults = FGPositioned::findAllWithIdent(_searchQuery, f.get(), _searchExact);
    }
    
    bool orderByRange = _scratchNode->getBoolValue("order-by-distance", true);
    if (orderByRange) {
        FGPositioned::sortByRange(_searchResults, _indicated_pos);
    }
    
    if (_searchResults.empty()) {
        clearScratch();
        return;
    }
    
    setScratchFromCachedSearchResult();
}
 
bool GPS::getScratchHasNext() const
{
    int lastResult;
    if (_searchIsRoute) {
        lastResult = _route->numLegs() - 1;
    } else {
        lastResult = (int) _searchResults.size() - 1;
    }
    
    if (lastResult < 0) { // search array might be empty
        return false;
    }
    
    return (_searchResultIndex < lastResult);
}
 
void GPS::setScratchFromCachedSearchResult()
{
    int index = _searchResultIndex;
    
    if ((index < 0) || (index >= (int) _searchResults.size())) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:setScratchFromCachedSearchResult: index out of bounds:" << index);
        return;
    }
    
    setScratchFromPositioned(_searchResults[index], index);
}
 
void GPS::setScratchFromPositioned(FGPositioned* aPos, int aIndex)
{
    clearScratch();
    assert(aPos);
    
    _scratchPos = aPos->geod();
    _scratchNode->setStringValue("name", aPos->name());
    _scratchNode->setStringValue("ident", aPos->ident());
    _scratchNode->setStringValue("type", FGPositioned::nameForType(aPos->type()));
    
    if (aIndex >= 0) {
        _scratchNode->setIntValue("index", aIndex);
    }
    
    _scratchValid = true;
    _scratchNode->setIntValue("result-count", _searchResults.size());
    
    switch (aPos->type()) {
        case FGPositioned::VOR:
            _scratchNode->setDoubleValue("frequency-mhz", static_cast<FGNavRecord*>(aPos)->get_freq() / 100.0);
            break;
            
        case FGPositioned::NDB:
            _scratchNode->setDoubleValue("frequency-khz", static_cast<FGNavRecord*>(aPos)->get_freq() / 100.0);
            break;
            
        case FGPositioned::AIRPORT:
            addAirportToScratch((FGAirport*)aPos);
            break;
            
        default:
            // no-op
            break;
    }
    
    // look for being on the route and set?
}
 
void GPS::addAirportToScratch(FGAirport* aAirport)
{
    for (unsigned int r=0; r<aAirport->numRunways(); ++r) {
        SGPropertyNode* rwyNd = _scratchNode->getChild("runways", r, true);
        FGRunway* rwy = aAirport->getRunwayByIndex(r);
        // TODO: filter out unsuitable runways in the future
        // based on config again
        
        rwyNd->setStringValue("id", rwy->ident().c_str());
        rwyNd->setIntValue("length-ft", rwy->lengthFt());
        rwyNd->setIntValue("width-ft", rwy->widthFt());
        rwyNd->setIntValue("heading-deg", rwy->headingDeg());
        // map surface code to a string
        // TODO: lighting information
        
        if (rwy->ILS()) {
            rwyNd->setDoubleValue("ils-frequency-mhz", rwy->ILS()->get_freq() / 100.0);
        }
    } // of runways iteration
}
 
void GPS::nextResult()
{
    if (!getScratchHasNext()) {
        return;
    }
    
    clearScratch();
    if (_searchIsRoute) {
        setScratchFromRouteWaypoint(++_searchResultIndex);
    } else {
        ++_searchResultIndex;
        setScratchFromCachedSearchResult();
    }
}
 
void GPS::previousResult()
{
    if (_searchResultIndex <= 0) {
        return;
    }
    
    clearScratch();
    --_searchResultIndex;
    
    if (_searchIsRoute) {
        setScratchFromRouteWaypoint(_searchResultIndex);
    } else {
        setScratchFromCachedSearchResult();
    }
}
 
void GPS::defineWaypoint()
{
    if (!isScratchPositionValid()) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:defineWaypoint: invalid lat/lon");
        return;
    }
    
    string ident = _scratchNode->getStringValue("ident");
    if (ident.size() < 2) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:defineWaypoint: waypoint identifier must be at least two characters");
        return;
    }
    
    // check for duplicate idents
    FGPositioned::TypeFilter f(FGPositioned::WAYPOINT);
    FGPositionedList dups = FGPositioned::findAllWithIdent(ident, &f);
    if (!dups.empty()) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:defineWaypoint: non-unique waypoint identifier, ho-hum");
    }
    
    SG_LOG(SG_INSTR, SG_INFO, "GPS:defineWaypoint: creating waypoint:" << ident);
    FGPositionedRef wpt = FGPositioned::createWaypoint(FGPositioned::WAYPOINT, ident, _scratchPos, false);
    _searchResults.clear();
    _searchResults.push_back(wpt);
    setScratchFromPositioned(wpt.get(), -1);
}
 
void GPS::insertWaypointAtIndex(int aIndex)
{
    // note we do allow index = routeMgr->size(), that's an append
    if ((aIndex < 0) || (aIndex > _route->numLegs())) {
        throw sg_range_exception("GPS::insertWaypointAtIndex: index out of bounds");
    }
    
    if (!isScratchPositionValid()) {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:insertWaypointAtIndex: invalid lat/lon");
        return;
    }
    
    string ident = _scratchNode->getStringValue("ident");
    
    WayptRef wpt = new BasicWaypt(_scratchPos, ident, NULL);
    _route->insertWayptAtIndex(wpt, aIndex);
}
 
void GPS::removeWaypointAtIndex(int aIndex)
{
    if ((aIndex < 0) || (aIndex >= _route->numLegs())) {
        throw sg_range_exception("GPS::removeWaypointAtIndex: index out of bounds");
    }
    
    _route->deleteIndex(aIndex);
}
 
 
#endif // of FG_210_COMPAT
 
void GPS::tieSGGeod(SGPropertyNode* aNode, SGGeod& aRef, 
  const char* lonStr, const char* latStr, const char* altStr)
{
  tie(aNode, lonStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getLongitudeDeg, &SGGeod::setLongitudeDeg));
  tie(aNode, latStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getLatitudeDeg, &SGGeod::setLatitudeDeg));
  
  if (altStr) {
    tie(aNode, altStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getElevationFt, &SGGeod::setElevationFt));
  }
}
 
void GPS::tieSGGeodReadOnly(SGPropertyNode* aNode, SGGeod& aRef, 
  const char* lonStr, const char* latStr, const char* altStr)
{
  tie(aNode, lonStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getLongitudeDeg, NULL));
  tie(aNode, latStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getLatitudeDeg, NULL));
  
  if (altStr) {
    tie(aNode, altStr, SGRawValueMethods<SGGeod, double>(aRef, &SGGeod::getElevationFt, NULL));
  }
}
 
void GPS::commandExitHold()
{
    if (_currentWaypt && (_currentWaypt->type() == "hold")) {
        auto holdCtl = static_cast<flightgear::HoldCtl*>(_wayptController.get());
        holdCtl->exitHold();
    } else {
        SG_LOG(SG_INSTR, SG_WARN, "GPS:exit hold requested, but not currently in a hold");
    }
}
 
 
// Register the subsystem.
#if 0
SGSubsystemMgr::InstancedRegistrant<GPS> registrantGPS(
    SGSubsystemMgr::FDM,
    {{"instrumentation", SGSubsystemMgr::Dependency::HARD}});
#endif
 
// end of gps.cxx