Mathias Fr�hlich:

I have introduced the posibility to start directly on the carrier.

With that patch you will have a --carrrier=id argument where id can either be
the pennant number configured in the nimitz scenario or the carriers name
also configured in the carriers scenario.
Additionaly you can use --parkpos=id to select different positions on the
carrier. They are also configured in the scenario file.

That includes the switch of the whole FGInterface class to make use of the
groundcache.
That means that an aircraft no longer uses the current elevation value from
the scenery class. It rather has its own local cache of the aircrafts
environment which is setup in the common_init method of FGInterface and
updated either manually by calling
 FGInterface::get_groundlevel_m(lat, lon, alt_m);
or implicitly by calling the above method in the
 FGInterface::_updateGeo*Position(lat, lon, alt);
methods.
A call get_groundlevel_m rebuilds the groundcache if the request is outside
the range of the cache.

Note that for the real usage of the groundcache including the correct
information about the movement of objects and the velocity information, you
still need to set up the groundcache in the usual way like YASim and JSBSim
currently does.
If you use the native interface, you will get only static objects correctly.
But for FDM's only using one single ground level for a whole step this is IMO
sufficient.

The AIManager gets a way to return the location of a object which is placed
wrt an AI Object. At the moment it only honours AICarriers for that.
That method is a static one, which loads the scenario file for that reason and
throws it away afterwards. This looked like the aprioriate way, because the
AIManager is initialized much later in flightgears bootstrap, and I did not
find an easy way to reorder that for my needs. Since this additional load is
very small and does only happen if such a relative location is required, I
think that this is ok.

Note that moving on the carrier will only work correctly for JSBSim and YASim,
but you should now be able to start and move on every not itself moving
object with any FDM.

src/AIModel/AIBase.cxx

@@ -30,6 +30,7 @@
 #include <plib/ssg.h>
 
 #include <simgear/math/point3d.hxx>
+#include <simgear/math/sg_geodesy.hxx>
 #include <simgear/misc/sg_path.hxx>
 #include <simgear/scene/model/location.hxx>
 #include <simgear/scene/model/model.hxx>
@@ -70,9 +71,10 @@ FGAIBase::FGAIBase()
 
 FGAIBase::~FGAIBase() {
     // Unregister that one at the scenery manager
-    globals->get_scenery()->unregister_placement_transform(aip.getTransform());
+    if (globals->get_scenery()) {
-  
+        globals->get_scenery()->unregister_placement_transform(aip.getTransform());
-    globals->get_scenery()->get_scene_graph()->removeKid(aip.getSceneGraph());
+        globals->get_scenery()->get_scene_graph()->removeKid(aip.getSceneGraph());
+    }
     // unbind();
     SGPropertyNode *root = globals->get_props()->getNode("ai/models", true);
     root->removeChild(_type_str.c_str(), index);
@@ -322,6 +324,36 @@ double FGAIBase::UpdateRadar(FGAIManager* manager)
    return range_ft2;
 }
 
+Point3D
+FGAIBase::getCartPosAt(const Point3D& off) const
+{
+  // The offset converted to the usual body fixed coordinate system.
+  sgdVec3 sgdOff;
+  sgdSetVec3(sgdOff, -off.x(), off.z(), -off.y());
+
+  // Transform that one to the horizontal local coordinate system.
+  sgdMat4 hlTrans;
+  sgdMakeRotMat4(hlTrans, hdg, pitch, roll);
+  sgdXformPnt3(sgdOff, hlTrans);
+
+  // Now transform to the wgs84 earth centeres system.
+  Point3D pos2(pos.lon()* SGD_DEGREES_TO_RADIANS,
+               pos.lat() * SGD_DEGREES_TO_RADIANS,
+               pos.elev() * SG_FEET_TO_METER);
+  Point3D cartPos3D = sgGeodToCart(pos2);
+  sgdMat4 ecTrans;
+  sgdMakeCoordMat4(ecTrans, cartPos3D.x(), cartPos3D.y(), cartPos3D.z(),
+                   pos.lon(), 0, - 90 - pos.lat());
+  sgdXformPnt3(sgdOff, ecTrans);
+
+  return Point3D(sgdOff[0], sgdOff[1], sgdOff[2]);
+}
+
+Point3D
+FGAIBase::getGeocPosAt(const Point3D& off) const
+{
+  return sgCartToGeod(getCartPosAt(off));
+}
 
 /*
  * getters and Setters

src/AIModel/AIBase.hxx

@@ -36,6 +36,17 @@ SG_USING_STD(list);
 class FGAIManager;
 class FGAIFlightPlan;
 
+struct ParkPosition {
+  ParkPosition(const ParkPosition& pp)
+    : name(pp.name), offset(pp.offset), heading_deg(pp.heading_deg)
+  {}
+  ParkPosition(const string& n, const Point3D& off = Point3D(), double heading = 0)
+    : name(n), offset(off), heading_deg(heading)
+  {}
+  string name;
+  Point3D offset;
+  double heading_deg;
+};
 
 typedef struct {
    string callsign;
@@ -73,7 +84,7 @@ typedef struct {
    list<string> solid_objects;    // List of solid object names
    list<string> wire_objects;     // List of wire object names
    list<string> catapult_objects; // List of catapult object names
-   list<Point3D> ppositions;  // List of positions on a carrier where an aircraft can start.
+   list<ParkPosition> ppositions; // List of positions on a carrier where an aircraft can start.
    Point3D flols_offset;      // used by carrier objects, in meters
    double radius;             // used by ship objects, in feet
    string name;               // used by carrier objects
@@ -117,6 +128,9 @@ public:
     void setDie( bool die );
     bool getDie();
 
+    Point3D getCartPosAt(const Point3D& off) const;
+    Point3D getGeocPosAt(const Point3D& off) const;
+
 protected:
 
     SGPropertyNode_ptr props;

src/AIModel/AICarrier.cxx

@@ -33,6 +33,9 @@
 #include "AICarrier.hxx"
 
 
+#include "AIScenario.hxx"
+
+
 FGAICarrier::FGAICarrier(FGAIManager* mgr) : FGAIShip(mgr) {
   _type_str = "carrier";
   _otype = otCarrier;
@@ -53,7 +56,7 @@ void FGAICarrier::setCatapultObjects(const list<string>& co) {
   catapult_objects = co;
 }
 
-void FGAICarrier::setParkingPositions(const list<Point3D>& p) {
+void FGAICarrier::setParkingPositions(const list<ParkPosition>& p) {
   ppositions = p;
 }
 
@@ -135,6 +138,28 @@ void FGAICarrier::unbind() {
     props->untie("controls/flols/angle-degs");
 }
 
+bool FGAICarrier::getParkPosition(const string& id, Point3D& geodPos,
+                                  double& hdng, sgdVec3 uvw)
+{
+  list<ParkPosition>::iterator it = ppositions.begin();
+  while (it != ppositions.end()) {
+    // Take either the specified one or the first one ...
+    if ((*it).name == id || id.empty()) {
+      ParkPosition ppos = *it;
+      geodPos = getGeocPosAt(ppos.offset);
+      hdng = hdg + ppos.heading_deg;
+      double shdng = sin(ppos.heading_deg * SGD_DEGREES_TO_RADIANS);
+      double chdng = cos(ppos.heading_deg * SGD_DEGREES_TO_RADIANS);
+      double speed_fps = speed*1.6878099;
+      sgdSetVec3(uvw, chdng*speed_fps, shdng*speed_fps, 0);
+      return true;
+    }
+    ++it;
+  }
+
+  return false;
+}
+
 void FGAICarrier::mark_nohot(ssgEntity* e) {
   if (e->isAKindOf(ssgTypeBranch())) {
     ssgBranch* br = (ssgBranch*)e;

src/AIModel/AICarrier.hxx

@@ -78,7 +78,7 @@ public:
         void setSolidObjects(const list<string>& solid_objects);
         void setWireObjects(const list<string>& wire_objects);
         void setCatapultObjects(const list<string>& catapult_objects);
-        void setParkingPositions(const list<Point3D>& p);
+        void setParkingPositions(const list<ParkPosition>& p);
         void setSign(const string& );
         void setFlolsOffset(const Point3D& off);
 
@@ -89,7 +89,8 @@ public:
 	
 	bool init();
 
-        static SGPropertyNode* getStartPosition(const string& id);
+        bool getParkPosition(const string& id, Point3D& geodPos,
+                             double& hdng, sgdVec3 uvw);
 
 private:
 
@@ -102,7 +103,7 @@ private:
 	list<string> solid_objects;       // List of solid object names
 	list<string> wire_objects;        // List of wire object names
 	list<string> catapult_objects;    // List of catapult object names
-	list<Point3D> ppositions;         // List of positions where an aircraft can start.
+	list<ParkPosition> ppositions;    // List of positions where an aircraft can start.
 	string sign;                      // The sign of this carrier.
 
 	// Velocity wrt earth.

src/AIModel/AIManager.cxx

@@ -370,7 +370,7 @@ void FGAIManager::processThermal( FGAIThermal* thermal ) {
 }
 
 
-void FGAIManager::processScenario( string &filename ) {
+void FGAIManager::processScenario( const string &filename ) {
   FGAIScenario* s = new FGAIScenario( filename );
   for (int i=0;i<s->nEntries();i++) {
     FGAIModelEntity* en = s->getNextEntry();
@@ -423,5 +423,42 @@ void FGAIManager::setModel(const string& path, ssgBranch *model)
   loadedModels.push_back(FGModelID(path,model));
 }
 
+bool FGAIManager::getStartPosition(const string& id, const string& pid,
+                                   Point3D& geodPos, double& heading,
+                                   sgdVec3 uvw)
+{
+  SGPropertyNode* root = fgGetNode("sim/ai", true);
+  if (!root->getNode("enabled", true)->getBoolValue())
+      return 0;
+
+  bool found = false;
+  string filename = root->getNode("scenario", true)->getStringValue();
+  FGAIScenario* s = new FGAIScenario( filename );
+  for (int i=0; i<s->nEntries(); i++) {
+    FGAIModelEntity* en = s->getNextEntry();
+    if (en && en->m_type == "carrier" &&
+        (en->pennant_number == id || en->name == id)) {
+      FGAICarrier* ai_carrier = new FGAICarrier(0);
+      ai_carrier->setHeading(en->heading);
+      ai_carrier->setSpeed(en->speed);
+      ai_carrier->setAltitude(en->altitude);
+      ai_carrier->setLongitude(en->longitude);
+      ai_carrier->setLatitude(en->latitude);
+      ai_carrier->setBank(en->rudder);
+      ai_carrier->setParkingPositions(en->ppositions);
+
+      if (ai_carrier->getParkPosition(pid, geodPos, heading, uvw)) {
+        delete ai_carrier;
+        found = true;
+        break;
+      }
+
+      delete ai_carrier;
+    }
+  }
+  delete s;
+
+  return found;
+}
 
 //end AIManager.cxx

src/AIModel/AIManager.hxx

@@ -103,11 +103,14 @@ public:
       return (0 < ot && ot < FGAIBase::MAX_OBJECTS) ? numObjects[ot] : numObjects[0];
     }
 
-    void processScenario( string &filename );
+    void processScenario( const string &filename );
 
   ssgBranch * getModel(const string& path);
   void setModel(const string& path, ssgBranch *model);
 
+  static bool getStartPosition(const string& id, const string& pid,
+                               Point3D& geodPos, double& hdng, sgdVec3 uvw);
+
 private:
 
     bool initDone;

src/AIModel/AIScenario.cxx

@@ -35,10 +35,10 @@
 
 static list<string>
 getAllStringNodeVals(const char* name, SGPropertyNode * entry_node);
-static list<Point3D>
+static list<ParkPosition>
 getAllOffsetNodeVals(const char* name, SGPropertyNode * entry_node);
 
-FGAIScenario::FGAIScenario(string &filename)
+FGAIScenario::FGAIScenario(const string &filename)
 {
   int i;
   SGPath path( globals->get_fg_root() );
@@ -105,8 +105,8 @@ FGAIScenario::FGAIScenario(string &filename)
      en->catapult_objects = getAllStringNodeVals("catapult", entry_node);
      en->solid_objects    = getAllStringNodeVals("solid", entry_node);
      en->ppositions       = getAllOffsetNodeVals("parking-pos", entry_node);
-     list<Point3D> flolspos = getAllOffsetNodeVals("flols-pos", entry_node);
+     list<ParkPosition> flolspos = getAllOffsetNodeVals("flols-pos", entry_node);
-     en->flols_offset     = flolspos.front();
+     en->flols_offset     = flolspos.front().offset;
 
      en->fp             = NULL;
      if (en->flightplan != ""){
@@ -161,18 +161,21 @@ getAllStringNodeVals(const char* name, SGPropertyNode * entry_node)
   return retval;
 }
 
-static list<Point3D>
+static list<ParkPosition>
 getAllOffsetNodeVals(const char* name, SGPropertyNode * entry_node)
 {
-  list<Point3D> retval;
+  list<ParkPosition> retval;
 
   vector<SGPropertyNode_ptr>::iterator it;
   vector<SGPropertyNode_ptr> children = entry_node->getChildren(name);
   for (it = children.begin(); it != children.end(); ++it) {
+    string name = (*it)->getStringValue("name", "unnamed");
     double offset_x = (*it)->getDoubleValue("x-offset-m", 0);
     double offset_y = (*it)->getDoubleValue("y-offset-m", 0);
     double offset_z = (*it)->getDoubleValue("z-offset-m", 0);
-    retval.push_back(Point3D(offset_x, offset_y, offset_z));
+    double hd = (*it)->getDoubleValue("heading-offset-deg", 0);
+    ParkPosition pp(name, Point3D(offset_x, offset_y, offset_z), hd);
+    retval.push_back(pp);
   }
 
   return retval;

src/AIModel/AIScenario.hxx

@@ -34,7 +34,7 @@ class FGAIScenario {
 
 public:
 
-   FGAIScenario(string &filename);
+   FGAIScenario(const string &filename);
    ~FGAIScenario();
 
    FGAIModelEntity* getNextEntry( void );

src/FDM/ExternalPipe/ExternalPipe.cxx

@@ -431,7 +431,7 @@ static void process_set_command( const string_list &tokens ) {
         cur_fdm_state->_updateGeodeticPosition( lat_rad, lon_rad,
                                                 alt_m * SG_METER_TO_FEET );
 
-        double agl_m = alt_m - globals->get_scenery()->get_cur_elev();
+        double agl_m = alt_m - cur_fdm_state->get_Runway_altitude_m();
         cur_fdm_state->_set_Altitude_AGL( agl_m * SG_METER_TO_FEET );
     } else if ( tokens[1] == "euler_angles" ) {
         double phi_rad   = atof( tokens[2].c_str() );

src/FDM/LaRCsim/LaRCsim.cxx

@@ -285,8 +285,10 @@ void FGLaRCsim::update( double dt ) {
     Brake_pct[1] = globals->get_controls()->get_brake_left();
 
     // Inform LaRCsim of the local terrain altitude
-    // Runway_altitude = get_Runway_altitude();
+    Runway_altitude
-    Runway_altitude = fgGetDouble("/position/ground-elev-m") * SG_METER_TO_FEET;
+      = get_groundlevel_m(Latitude, Longitude, Altitude * SG_FEET_TO_METER)
+      * SG_METER_TO_FEET;
+
     // Weather
     /* V_north_airmass = get_V_north_airmass();
        V_east_airmass =  get_V_east_airmass();

src/FDM/flight.cxx

@@ -188,20 +188,23 @@ FGInterface::common_init ()
 
     // Set initial position
     SG_LOG( SG_FLIGHT, SG_INFO, "...initializing position..." );
-    set_Longitude( fgGetDouble("/sim/presets/longitude-deg")
+    double lon = fgGetDouble("/sim/presets/longitude-deg")
-                   * SGD_DEGREES_TO_RADIANS );
+      * SGD_DEGREES_TO_RADIANS;
-    set_Latitude( fgGetDouble("/sim/presets/latitude-deg")
+    double lat = fgGetDouble("/sim/presets/latitude-deg")
-                  * SGD_DEGREES_TO_RADIANS );
+      * SGD_DEGREES_TO_RADIANS;
-    double ground_elev_m = globals->get_scenery()->get_cur_elev();
+    double alt_ft = fgGetDouble("/sim/presets/altitude-ft");
+    double alt_m = alt_ft * SG_FEET_TO_METER;
+    set_Longitude( lon );
+    set_Latitude( lat );
+
+    double ground_elev_m = get_groundlevel_m(lat, lon, alt_m);
     double ground_elev_ft = ground_elev_m * SG_METER_TO_FEET;
-    fgSetDouble("/position/ground-elev-m", ground_elev_m);
     _set_Runway_altitude ( ground_elev_ft );
-    if ( fgGetBool("/sim/presets/onground")
+    if ( fgGetBool("/sim/presets/onground") || alt_ft < ground_elev_ft ) {
-         || fgGetDouble("/sim/presets/altitude-ft") < ground_elev_ft ) {
+        fgSetDouble("/position/altitude-ft", ground_elev_ft + 0.1);
-        fgSetDouble("/position/altitude-ft", ground_elev_ft);
+        set_Altitude( ground_elev_ft + 0.1);
-        set_Altitude( ground_elev_ft );
     } else {
-        set_Altitude( fgGetDouble("/sim/presets/altitude-ft") );
+        set_Altitude( alt_ft );
     }
 
     // Set ground elevation
@@ -305,6 +308,15 @@ FGInterface::bind ()
   fgSetArchivable("/position/altitude-ft");
   fgTie("/position/altitude-agl-ft", this,
         &FGInterface::get_Altitude_AGL); // read-only
+  fgSetArchivable("/position/ground-elev-ft");
+  fgTie("/position/ground-elev-ft", this,
+        &FGInterface::get_Runway_altitude); // read-only
+  fgSetArchivable("/position/ground-elev-m");
+  fgTie("/position/ground-elev-m", this,
+        &FGInterface::get_Runway_altitude_m); // read-only
+  fgSetArchivable("/position/sea-level-radius-ft");
+  fgTie("/position/sea-level-radius-ft", this,
+        &FGInterface::get_Sea_level_radius); // read-only
 
 				// Orientation
   fgTie("/orientation/roll-deg", this,
@@ -438,6 +450,9 @@ FGInterface::unbind ()
   fgUntie("/position/longitude-deg");
   fgUntie("/position/altitude-ft");
   fgUntie("/position/altitude-agl-ft");
+  fgUntie("/position/ground-elev-ft");
+  fgUntie("/position/ground-elev-m");
+  fgUntie("/position/sea-level-radius-ft");
   fgUntie("/orientation/roll-deg");
   fgUntie("/orientation/pitch-deg");
   fgUntie("/orientation/heading-deg");
@@ -497,7 +512,9 @@ void FGInterface::_updateGeodeticPosition( double lat, double lon, double alt )
     _set_Geodetic_Position( lat, lon, alt );
 
     _set_Sea_level_radius( sl_radius * SG_METER_TO_FEET );
-    _set_Runway_altitude( fgGetDouble("/position/ground-elev-m") * SG_METER_TO_FEET );
+    double alt_m = alt*SG_FEET_TO_METER;
+    double groundlevel_m = get_groundlevel_m(lat, lon, alt_m);
+    _set_Runway_altitude( groundlevel_m * SG_METER_TO_FEET );
 
     _set_sin_lat_geocentric( lat_geoc );
     _set_cos_lat_geocentric( lat_geoc );
@@ -505,25 +522,6 @@ void FGInterface::_updateGeodeticPosition( double lat, double lon, double alt )
     _set_sin_cos_longitude( lon );
 
     _set_sin_cos_latitude( lat );
-
-    /* Norman's code for slope of the terrain */
-    /* needs to be tested -- get it on the HUD and taxi around */
-    /* double *tnorm = scenery.cur_normal;
-
-       double sy = sin ( -get_Psi() ) ;
-       double cy = cos ( -get_Psi() ) ;
-
-       double phitb, thetatb, psitb;
-       if ( tnorm[1] != 0.0 ) {
-           psitb = -atan2 ( tnorm[0], tnorm[1] );
-       }
-       if ( tnorm[2] != 0.0 ) {	
-	   thetatb =  atan2 ( tnorm[0] * cy - tnorm[1] * sy, tnorm[2] );
-	   phitb = -atan2 ( tnorm[1] * cy + tnorm[0] * sy, tnorm[2] );  
-       }	
-	
-       _set_terrain_slope(phitb, thetatb, psitb) 
-     */
 }
 
 
@@ -553,7 +551,9 @@ void FGInterface::_updateGeocentricPosition( double lat_geoc, double lon,
     _set_Geodetic_Position( lat_geod, lon, alt );
 
     _set_Sea_level_radius( sl_radius2 * SG_METER_TO_FEET );
-    _set_Runway_altitude(  fgGetDouble("/position/ground-elev-m") * SG_METER_TO_FEET );
+    double alt_m = alt*SG_FEET_TO_METER;
+    double groundlevel_m = get_groundlevel_m(lat_geod, lon, alt_m);
+    _set_Runway_altitude( groundlevel_m * SG_METER_TO_FEET );
 
     _set_sin_lat_geocentric( lat_geoc );
     _set_cos_lat_geocentric( lat_geoc );
@@ -561,25 +561,6 @@ void FGInterface::_updateGeocentricPosition( double lat_geoc, double lon,
     _set_sin_cos_longitude( lon );
 
     _set_sin_cos_latitude( lat_geod );
-
-    /* Norman's code for slope of the terrain */
-    /* needs to be tested -- get it on the HUD and taxi around */
-    /* double *tnorm = scenery.cur_normal;
-
-       double sy = sin ( -get_Psi() ) ;
-       double cy = cos ( -get_Psi() ) ;
-
-       double phitb, thetatb, psitb;
-       if ( tnorm[1] != 0.0 ) {
-           psitb = -atan2 ( tnorm[0], tnorm[1] );
-       }
-       if ( tnorm[2] != 0.0 ) {	
-	   thetatb =  atan2 ( tnorm[0] * cy - tnorm[1] * sy, tnorm[2] );
-	   phitb = -atan2 ( tnorm[1] * cy + tnorm[0] * sy, tnorm[2] );  
-       }	
-	
-       _set_terrain_slope(phitb, thetatb, psitb) 
-     */
 }
 
 
@@ -848,7 +829,7 @@ FGInterface::get_agl_m(double t, const double pt[3],
                        int *type, double *loadCapacity,
                        double *frictionFactor, double *agl)
 {
-  return ground_cache.get_agl(t, pt, contact, normal, vel, type,
+  return ground_cache.get_agl(t, pt, 2.0, contact, normal, vel, type,
                               loadCapacity, frictionFactor, agl);
 }
 
@@ -861,7 +842,7 @@ FGInterface::get_agl_ft(double t, const double pt[3],
   // Convert units and do the real work.
   sgdVec3 pt_m;
   sgdScaleVec3( pt_m, pt, SG_FEET_TO_METER );
-  bool ret = ground_cache.get_agl(t, pt_m, contact, normal, vel,
+  bool ret = ground_cache.get_agl(t, pt_m, 2.0, contact, normal, vel,
                                   type, loadCapacity, frictionFactor, agl);
   // Convert units back ...
   sgdScaleVec3( contact, SG_METER_TO_FEET );
@@ -872,6 +853,63 @@ FGInterface::get_agl_ft(double t, const double pt[3],
   return ret;
 }
 
+bool
+FGInterface::get_agl_m(double t, const double pt[3], double max_altoff,
+                       double contact[3], double normal[3], double vel[3],
+                       int *type, double *loadCapacity,
+                       double *frictionFactor, double *agl)
+{
+  return ground_cache.get_agl(t, pt, max_altoff, contact, normal, vel, type,
+                              loadCapacity, frictionFactor, agl);
+}
+
+bool
+FGInterface::get_agl_ft(double t, const double pt[3], double max_altoff,
+                        double contact[3], double normal[3], double vel[3],
+                        int *type, double *loadCapacity,
+                        double *frictionFactor, double *agl)
+{
+  // Convert units and do the real work.
+  sgdVec3 pt_m;
+  sgdScaleVec3( pt_m, pt, SG_FEET_TO_METER );
+  bool ret = ground_cache.get_agl(t, pt_m, SG_FEET_TO_METER * max_altoff,
+                                  contact, normal, vel,
+                                  type, loadCapacity, frictionFactor, agl);
+  // Convert units back ...
+  sgdScaleVec3( contact, SG_METER_TO_FEET );
+  sgdScaleVec3( vel, SG_METER_TO_FEET );
+  *agl *= SG_METER_TO_FEET;
+  // FIXME: scale the load limit to something in the english unit system.
+  // Be careful with the DBL_MAX which is returned by default.
+  return ret;
+}
+
+
+double
+FGInterface::get_groundlevel_m(double lat, double lon, double alt)
+{
+  // First compute the sea level radius,
+  sgdVec3 pos, cpos;
+  sgGeodToCart(lat, lon, 0, pos);
+  double slr = sgdLengthVec3(pos);
+  // .. then the cartesian position of the given lat/lon/alt.
+  sgGeodToCart(lat, lon, alt, pos);
+
+  // FIXME: how to handle t - ref_time differences ???
+  double ref_time, radius;
+  // Prepare the ground cache for that position.
+  if (!is_valid_m(&ref_time, cpos, &radius))
+    prepare_ground_cache_m(ref_time, pos, 10);
+  else if (radius*radius <= sgdDistanceSquaredVec3(pos, cpos))
+    prepare_ground_cache_m(ref_time, pos, radius);
+  
+  double contact[3], normal[3], vel[3], lc, ff, agl;
+  int type;
+  get_agl_m(ref_time, pos, 2.0, contact, normal, vel, &type, &lc, &ff, &agl);
+
+  return sgdLengthVec3(contact) - slr;
+}
+  
 bool
 FGInterface::caught_wire_m(double t, const double pt[4][3])
 {

src/FDM/flight.hxx

@@ -977,6 +977,7 @@ public:
     }
 
     inline double get_Runway_altitude() const { return runway_altitude; }
+    inline double get_Runway_altitude_m() const { return SG_FEET_TO_METER * runway_altitude; }
     // inline double get_Runway_latitude() const { return runway_latitude; }
     // inline void set_Runway_latitude( double lat ) { runway_latitude = lat; }
     // inline double get_Runway_longitude() const { return runway_longitude; }
@@ -1132,6 +1133,15 @@ public:
                     double contact[3], double normal[3], double vel[3],
                     int *type, double *loadCapacity,
                     double *frictionFactor, double *agl);
+    bool get_agl_m(double t, const double pt[3], double max_altoff,
+                   double contact[3], double normal[3], double vel[3],
+                   int *type, double *loadCapacity,
+                   double *frictionFactor, double *agl);
+    bool get_agl_ft(double t, const double pt[3], double max_altoff,
+                    double contact[3], double normal[3], double vel[3],
+                    int *type, double *loadCapacity,
+                    double *frictionFactor, double *agl);
+    double get_groundlevel_m(double lat, double lon, double alt);
 
 
     // Return 1 if the hook intersects with a wire.

src/FDM/groundcache.cxx

@@ -583,10 +583,10 @@ FGGroundCache::get_cat(double t, const double dpt[3],
 }
 
 bool
-FGGroundCache::get_agl(double t, const double dpt[3],
+FGGroundCache::get_agl(double t, const double dpt[3], double max_altoff,
-                         double contact[3], double normal[3], double vel[3],
+                       double contact[3], double normal[3], double vel[3],
-                         int *type, double *loadCapacity,
+                       int *type, double *loadCapacity,
-                         double *frictionFactor, double *agl)
+                       double *frictionFactor, double *agl)
 {
   bool ret = false;
 
@@ -608,9 +608,10 @@ FGGroundCache::get_agl(double t, const double dpt[3],
   // The search direction
   sgdVec3 dir;
   sgdSetVec3( dir, -dpt[0], -dpt[1], -dpt[2] );
+  sgdNormaliseVec3( dir );
 
   // Initialize to something sensible
-  double sqdist = DBL_MAX;
+  double current_radius = 0.0;
 
   size_t sz = triangles.size();
   for (size_t i = 0; i < sz; ++i) {
@@ -623,28 +624,33 @@ FGGroundCache::get_agl(double t, const double dpt[3],
     sgdVec3 isecpoint;
     if ( sgdIsectInfLinePlane( isecpoint, pt, dir, triangle.plane ) &&
          sgdPointInTriangle( isecpoint, triangle.vertices ) ) {
-
+      // Transform to the wgs system
-      // Check for the closest intersection point.
+      sgdAddVec3( isecpoint, cache_center );
-      // FIXME: is this the right one?
+      // compute the radius, good enough approximation to take the geocentric radius
-      SGDfloat newSqdist = sgdDistanceSquaredVec3( isecpoint, pt );
+      SGDfloat radius = sgdLengthSquaredVec3(isecpoint);
-      if ( newSqdist < sqdist ) {
+      if (current_radius < radius) {
-        sqdist = newSqdist;
+        // Compute the vector from pt to the intersection point ...
-        ret = true;
+        sgdVec3 off;
-        // Save the new potential intersection point.
+        sgdSubVec3(off, pt, isecpoint);
-        sgdCopyVec3( contact, isecpoint );
+        // ... and check if it is too high or not
-        sgdAddVec3( contact, cache_center );
+        if (-max_altoff < sgdScalarProductVec3( off, dir )) {
-        // The first three values in the vector are the plane normal.
+          current_radius = radius;
-        sgdCopyVec3( normal, triangle.plane );
+          ret = true;
-        // The velocity wrt earth.
+          // Save the new potential intersection point.
-        /// FIXME: only true for non rotating objects!!!!
+          sgdCopyVec3( contact, isecpoint );
-        sgdCopyVec3( vel, triangle.velocity );
+          // The first three values in the vector are the plane normal.
-        // Save the ground type.
+          sgdCopyVec3( normal, triangle.plane );
-        *type = triangle.type;
+          // The velocity wrt earth.
-        // FIXME: figure out how to get that sign ...
+          /// FIXME: only true for non rotating objects!!!!
+          sgdCopyVec3( vel, triangle.velocity );
+          // Save the ground type.
+          *type = triangle.type;
+          // FIXME: figure out how to get that sign ...
 //           *agl = sqrt(sqdist);
-        *agl = sgdLengthVec3( dpt ) - sgdLengthVec3( contact );
+          *agl = sgdLengthVec3( dpt ) - sgdLengthVec3( contact );
 //           *loadCapacity = DBL_MAX;
 //           *frictionFactor = 1.0;
+        }
       }
     }
   }

src/FDM/groundcache.hxx

@@ -56,17 +56,16 @@ public:
   
 
     // Return the altitude above ground below the wgs84 point pt
-    // Search for the nearest triangle to pt.
+    // Search for highest triangle not higher than pt + max_altoff.
     // Return ground properties like the ground type, the maximum load
     // this kind kind of ground can carry, the friction factor between
     // 0 and 1 which can be used to model lower friction with wet runways
     // and finally the altitude above ground.
-    bool get_agl(double t, const double pt[3],
+    bool get_agl(double t, const double pt[3], double max_altoff,
                  double contact[3], double normal[3], double vel[3],
                  int *type, double *loadCapacity,
                  double *frictionFactor, double *agl);
 
-
     // Return 1 if the hook intersects with a wire.
     // That test is done by checking if the quad spanned by the points pt*
     // intersects with the line representing the wire.

src/Main/fg_init.cxx

@@ -68,6 +68,7 @@
 #include <Airports/apt_loader.hxx>
 #include <Airports/runways.hxx>
 #include <Airports/simple.hxx>
+#include <AIModel/AIManager.hxx>
 #include <ATC/ATCdisplay.hxx>
 #include <ATC/ATCmgr.hxx>
 #include <ATC/AIMgr.hxx>
@@ -954,7 +955,49 @@ static bool fgSetPosFromNAV( const string& id, const double& freq ) {
     }
 }
 
+// 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
+    Point3D geodPos;
+    double heading;
+    sgdVec3 uvw;
+    if (FGAIManager::getStartPosition(carrier, posid, geodPos, heading, uvw)) {
+        double lon = geodPos.lon() * SGD_RADIANS_TO_DEGREES;
+        double lat = geodPos.lat() * SGD_RADIANS_TO_DEGREES;
+        double alt = geodPos.elev() * SG_METER_TO_FEET;
+
+        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 carroer = "
+                << carrier );
+        return false;
+    }
+}
+ 
 // Set current_options lon/lat given an airport id and heading (degrees)
 static bool fgSetPosFromFix( const string& id ) {
     FGFix fix;
@@ -1127,6 +1170,8 @@ bool fgInitPosition() {
     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");
 
     if ( !set_pos && !apt.empty() && !rwy_no.empty() ) {
@@ -1163,6 +1208,13 @@ bool fgInitPosition() {
         }
     }
 
+    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 ) ) {
@@ -1185,7 +1237,7 @@ bool fgInitPosition() {
                  fgGetDouble("/sim/presets/heading-deg") );
 
     // determine if this should be an on-ground or in-air start
-    if ( fabs(gs) > 0.01 || fabs(od) > 0.1 || alt > 0.1 ) {
+    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);

src/Main/options.cxx

@@ -597,6 +597,8 @@ clearLocation ()
     fgSetString("/sim/presets/airport-id", "");
     fgSetString("/sim/presets/vor-id", "");
     fgSetString("/sim/presets/ndb-id", "");
+    fgSetString("/sim/presets/carrier", "");
+    fgSetString("/sim/presets/parkpos", "");
     fgSetString("/sim/presets/fix", "");
 }
 
@@ -616,6 +618,21 @@ fgOptNDB( const char * arg )
     return FG_OPTIONS_OK;
 }
 
+static int
+fgOptCarrier( const char * arg )
+{
+    clearLocation();
+    fgSetString("/sim/presets/carrier", arg);
+    return FG_OPTIONS_OK;
+}
+
+static int
+fgOptParkpos( const char * arg )
+{
+    fgSetString("/sim/presets/parkpos", arg);
+    return FG_OPTIONS_OK;
+}
+
 static int
 fgOptFIX( const char * arg )
 {
@@ -1215,6 +1232,8 @@ struct OptionDesc {
     {"runway",                       true,  OPTION_STRING, "/sim/presets/runway", false, "", 0 },
     {"vor",                          true,  OPTION_FUNC,   "", false, "", fgOptVOR },
     {"ndb",                          true,  OPTION_FUNC,   "", false, "", fgOptNDB },
+    {"carrier",                      true,  OPTION_FUNC,   "", false, "", fgOptCarrier },
+    {"parkpos",                      true,  OPTION_FUNC,   "", false, "", fgOptParkpos },
     {"fix",                          true,  OPTION_FUNC,   "", false, "", fgOptFIX },
     {"offset-distance",              true,  OPTION_DOUBLE, "/sim/presets/offset-distance", false, "", 0 },
     {"offset-azimuth",               true,  OPTION_DOUBLE, "/sim/presets/offset-azimuth", false, "", 0 },