X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FFDM%2Fflight.cxx;h=43b5aa03b62d6b21084263e2717e0c9c82e92403;hb=1e3f0f0050cd4860b8bf2b6ecb59ba040f8b934f;hp=9b1c089060c602a44f1bbd1a52a0f72957132ee0;hpb=485230b443de22c97d5c4ddfda98598fb52ce98a;p=flightgear.git

diff --git a/src/FDM/flight.cxx b/src/FDM/flight.cxx
index 9b1c08906..43b5aa03b 100644
--- a/src/FDM/flight.cxx
+++ b/src/FDM/flight.cxx
@@ -1,8 +1,8 @@
-// flight.c -- a general interface to the various flight models
+// flight.cxx -- a general interface to the various flight models
 //
 // Written by Curtis Olson, started May 1997.
 //
-// Copyright (C) 1997  Curtis L. Olson  - curt@infoplane.com
+// Copyright (C) 1997  Curtis L. Olson  - http://www.flightgear.org/~curt
 //
 // This program is free software; you can redistribute it and/or
 // modify it under the terms of the GNU General Public License as
@@ -23,19 +23,20 @@
 
 #include <stdio.h>
 
-#include <simgear/logstream.hxx>
+#include <plib/sg.h>
+
 #include <simgear/constants.h>
-#include <simgear/fg_geodesy.hxx>
+#include <simgear/debug/logstream.hxx>
+#include <simgear/math/sg_geodesy.hxx>
+#include <simgear/scene/model/placement.hxx>
+#include <simgear/timing/timestamp.hxx>
 
-#include <FDM/LaRCsim/ls_interface.h>
-#include <Main/options.hxx>
-#include <Time/timestamp.hxx>
+#include <Scenery/scenery.hxx>
+#include <Main/globals.hxx>
+#include <Main/fg_props.hxx>
+#include <FDM/groundcache.hxx>
 
-#include "External.hxx"
 #include "flight.hxx"
-#include "JSBsim.hxx"
-#include "LaRCsim.hxx"
-#include "Balloon.h"
 
 
 // base_fdm_state is the internal state that is updated in integer
@@ -43,21 +44,530 @@
 // world time, so we introduce cur_fdm_state which is extrapolated by
 // the difference between sim time and real world time
 
-FGInterface *cur_fdm_state;
+FGInterface *cur_fdm_state = 0;
 FGInterface base_fdm_state;
 
+inline void init_vec(FG_VECTOR_3 vec) {
+    vec[0] = 0.0; vec[1] = 0.0; vec[2] = 0.0;
+}
 
-int FGInterface::init( double dt ) {
-    cout << "dummy init() ... SHOULDN'T BE CALLED!" << endl;
-    return 0;
+// Constructor
+FGInterface::FGInterface()
+  : remainder(0)
+{
+    _setup();
 }
 
-int FGInterface::update( int multi_loop ) {
-    cout << "dummy update() ... SHOULDN'T BE CALLED!" << endl;
-    return 0;
+FGInterface::FGInterface( double dt )
+  : remainder(0)
+{
+    _setup();
 }
 
+// Destructor
 FGInterface::~FGInterface() {
+    // unbind();                   // FIXME: should be called explicitly
+}
+
+
+int
+FGInterface::_calc_multiloop (double dt)
+{
+  int hz = fgGetInt("/sim/model-hz");
+  int speedup = fgGetInt("/sim/speed-up");
+
+  dt += remainder;
+  remainder = 0;
+  double ml = dt * hz;
+  // Avoid roundoff problems by adding the roundoff itself.
+  // ... ok, two times the roundoff to have enough room.
+  int multiloop = int(floor(ml * (1.0 + 2.0*DBL_EPSILON)));
+  remainder = (ml - multiloop) / hz;
+  return (multiloop * speedup);
+}
+
+
+/**
+ * Set default values for the state of the FDM.
+ *
+ * This method is invoked by the constructors.
+ */
+void
+FGInterface::_setup ()
+{
+    inited = false;
+    bound = false;
+
+    init_vec( d_pilot_rp_body_v );
+    init_vec( d_cg_rp_body_v );
+    init_vec( f_body_total_v );
+    init_vec( f_local_total_v );
+    init_vec( f_aero_v );
+    init_vec( f_engine_v );
+    init_vec( f_gear_v );
+    init_vec( m_total_rp_v );
+    init_vec( m_total_cg_v );
+    init_vec( m_aero_v );
+    init_vec( m_engine_v );
+    init_vec( m_gear_v );
+    init_vec( v_dot_local_v );
+    init_vec( v_dot_body_v );
+    init_vec( a_cg_body_v );
+    init_vec( a_pilot_body_v );
+    init_vec( n_cg_body_v );
+    init_vec( n_pilot_body_v );
+    init_vec( omega_dot_body_v );
+    init_vec( v_local_v );
+    init_vec( v_local_rel_ground_v );
+    init_vec( v_local_airmass_v );
+    init_vec( v_local_rel_airmass_v );
+    init_vec( v_local_gust_v );
+    init_vec( v_wind_body_v );
+    init_vec( omega_body_v );
+    init_vec( omega_local_v );
+    init_vec( omega_total_v );
+    init_vec( euler_rates_v );
+    init_vec( geocentric_rates_v );
+    init_vec( geocentric_position_v );
+    init_vec( geodetic_position_v );
+    init_vec( euler_angles_v );
+    init_vec( d_cg_rwy_local_v );
+    init_vec( d_cg_rwy_rwy_v );
+    init_vec( d_pilot_rwy_local_v );
+    init_vec( d_pilot_rwy_rwy_v );
+    init_vec( t_local_to_body_m[0] );
+    init_vec( t_local_to_body_m[1] );
+    init_vec( t_local_to_body_m[2] );
+
+    mass=i_xx=i_yy=i_zz=i_xz=0;
+    nlf=0;
+    v_rel_wind=v_true_kts=v_rel_ground=v_inertial=0;
+    v_ground_speed=v_equiv=v_equiv_kts=0;
+    v_calibrated=v_calibrated_kts=0;
+    gravity=0;
+    centrifugal_relief=0;
+    alpha=beta=alpha_dot=beta_dot=0;
+    cos_alpha=sin_alpha=cos_beta=sin_beta=0;
+    cos_phi=sin_phi=cos_theta=sin_theta=cos_psi=sin_psi=0;
+    gamma_vert_rad=gamma_horiz_rad=0;
+    sigma=density=v_sound=mach_number=0;
+    static_pressure=total_pressure=impact_pressure=0;
+    dynamic_pressure=0;
+    static_temperature=total_temperature=0;
+    sea_level_radius=earth_position_angle=0;
+    runway_altitude=runway_latitude=runway_longitude=0;
+    runway_heading=0;
+    radius_to_rwy=0;
+    climb_rate=0;
+    sin_lat_geocentric=cos_lat_geocentric=0;
+    sin_latitude=cos_latitude=0;
+    sin_longitude=cos_longitude=0;
+    altitude_agl=0;
+}
+
+void
+FGInterface::init () {}
+
+/**
+ * Initialize the state of the FDM.
+ *
+ * Subclasses of FGInterface may do their own, additional initialization,
+ * but there is some that is common to all.  Normally, they should call
+ * this before they begin their own init to make sure the basic structures
+ * are set up properly.
+ */
+void
+FGInterface::common_init ()
+{
+    SG_LOG( SG_FLIGHT, SG_INFO, "Start common FDM init" );
+
+    set_inited( true );
+
+//     stamp();
+//     set_remainder( 0 );
+
+    // Set initial position
+    SG_LOG( SG_FLIGHT, SG_INFO, "...initializing position..." );
+    double lon = fgGetDouble("/sim/presets/longitude-deg")
+      * SGD_DEGREES_TO_RADIANS;
+    double lat = fgGetDouble("/sim/presets/latitude-deg")
+      * SGD_DEGREES_TO_RADIANS;
+    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;
+    _set_Runway_altitude ( ground_elev_ft );
+    if ( fgGetBool("/sim/presets/onground") || alt_ft < ground_elev_ft ) {
+        fgSetDouble("/position/altitude-ft", ground_elev_ft + 0.1);
+        set_Altitude( ground_elev_ft + 0.1);
+    } else {
+        set_Altitude( alt_ft );
+    }
+
+    // Set ground elevation
+    SG_LOG( SG_FLIGHT, SG_INFO,
+            "...initializing ground elevation to " << ground_elev_ft
+            << "ft..." );
+
+    // Set sea-level radius
+    SG_LOG( SG_FLIGHT, SG_INFO, "...initializing sea-level radius..." );
+    SG_LOG( SG_FLIGHT, SG_INFO, " lat = "
+            << fgGetDouble("/sim/presets/latitude-deg")
+            << " alt = " << get_Altitude() );
+    double sea_level_radius_meters;
+    double lat_geoc;
+    sgGeodToGeoc( fgGetDouble("/sim/presets/latitude-deg")
+                    * SGD_DEGREES_TO_RADIANS,
+                  get_Altitude() * SG_FEET_TO_METER,
+                  &sea_level_radius_meters, &lat_geoc );
+    _set_Sea_level_radius( sea_level_radius_meters * SG_METER_TO_FEET );
+
+    // Set initial velocities
+    SG_LOG( SG_FLIGHT, SG_INFO, "...initializing velocities..." );
+    if ( !fgHasNode("/sim/presets/speed-set") ) {
+        set_V_calibrated_kts(0.0);
+    } else {
+        const string speedset = fgGetString("/sim/presets/speed-set");
+        if ( speedset == "knots" || speedset == "KNOTS" ) {
+            set_V_calibrated_kts( fgGetDouble("/sim/presets/airspeed-kt") );
+        } else if ( speedset == "mach" || speedset == "MACH" ) {
+            set_Mach_number( fgGetDouble("/sim/presets/mach") );
+        } else if ( speedset == "UVW" || speedset == "uvw" ) {
+            set_Velocities_Wind_Body(
+                                     fgGetDouble("/sim/presets/uBody-fps"),
+                                     fgGetDouble("/sim/presets/vBody-fps"),
+                                     fgGetDouble("/sim/presets/wBody-fps") );
+        } else if ( speedset == "NED" || speedset == "ned" ) {
+            set_Velocities_Local(
+                                 fgGetDouble("/sim/presets/speed-north-fps"),
+                                 fgGetDouble("/sim/presets/speed-east-fps"),
+                                 fgGetDouble("/sim/presets/speed-down-fps") );
+        } else {
+            SG_LOG( SG_FLIGHT, SG_ALERT,
+                    "Unrecognized value for /sim/presets/speed-set: "
+                    << speedset);
+            set_V_calibrated_kts( 0.0 );
+        }
+    }
+
+    // Set initial Euler angles
+    SG_LOG( SG_FLIGHT, SG_INFO, "...initializing Euler angles..." );
+    set_Euler_Angles( fgGetDouble("/sim/presets/roll-deg")
+                        * SGD_DEGREES_TO_RADIANS,
+                      fgGetDouble("/sim/presets/pitch-deg")
+                        * SGD_DEGREES_TO_RADIANS,
+                      fgGetDouble("/sim/presets/heading-deg")
+                        * SGD_DEGREES_TO_RADIANS );
+
+    SG_LOG( SG_FLIGHT, SG_INFO, "End common FDM init" );
+}
+
+
+/**
+ * Bind getters and setters to properties.
+ *
+ * The bind() method will be invoked after init().  Note that unlike
+ * the usual implementations of FGSubsystem::bind(), this method does
+ * not automatically pick up existing values for the properties at
+ * bind time; instead, all values are set explicitly in the init()
+ * method.
+ */
+void
+FGInterface::bind ()
+{
+  bound = true;
+
+                                // Time management (read-only)
+//   fgTie("/fdm/time/delta_t", this,
+//         &FGInterface::get_delta_t); // read-only
+//   fgTie("/fdm/time/elapsed", this,
+//         &FGInterface::get_elapsed); // read-only
+//   fgTie("/fdm/time/remainder", this,
+//         &FGInterface::get_remainder); // read-only
+//   fgTie("/fdm/time/multi_loop", this,
+//         &FGInterface::get_multi_loop); // read-only
+
+			// Aircraft position
+  fgTie("/position/latitude-deg", this,
+        &FGInterface::get_Latitude_deg,
+        &FGInterface::set_Latitude_deg,
+        false);
+  fgSetArchivable("/position/latitude-deg");
+  fgTie("/position/longitude-deg", this,
+        &FGInterface::get_Longitude_deg,
+        &FGInterface::set_Longitude_deg,
+        false);
+  fgSetArchivable("/position/longitude-deg");
+  fgTie("/position/altitude-ft", this,
+        &FGInterface::get_Altitude,
+        &FGInterface::set_Altitude,
+        false);
+  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
+  fgTie("/environment/ground-elevation-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,
+	&FGInterface::get_Phi_deg,
+	&FGInterface::set_Phi_deg);
+  fgSetArchivable("/orientation/roll-deg");
+  fgTie("/orientation/pitch-deg", this,
+	&FGInterface::get_Theta_deg,
+	&FGInterface::set_Theta_deg);
+  fgSetArchivable("/orientation/pitch-deg");
+  fgTie("/orientation/heading-deg", this,
+	&FGInterface::get_Psi_deg,
+	&FGInterface::set_Psi_deg);
+  fgSetArchivable("/orientation/heading-deg");
+
+  // Body-axis "euler rates" (rotation speed, but in a funny
+  // representation).
+  fgTie("/orientation/roll-rate-degps", this,
+	&FGInterface::get_Phi_dot_degps);
+  fgTie("/orientation/pitch-rate-degps", this,
+	&FGInterface::get_Theta_dot_degps);
+  fgTie("/orientation/yaw-rate-degps", this,
+	&FGInterface::get_Psi_dot_degps);
+
+				// Calibrated airspeed
+  fgTie("/velocities/airspeed-kt", this,
+	&FGInterface::get_V_calibrated_kts,
+	&FGInterface::set_V_calibrated_kts,
+	false);
+
+				// Mach number
+  fgTie("/velocities/mach", this,
+	&FGInterface::get_Mach_number,
+	&FGInterface::set_Mach_number,
+	false);
+
+				// Local velocities
+//   fgTie("/velocities/speed-north-fps", this,
+// 	&FGInterface::get_V_north,
+// 	&FGInterface::set_V_north);
+//   fgSetArchivable("/velocities/speed-north-fps");
+//   fgTie("/velocities/speed-east-fps", this,
+// 	&FGInterface::get_V_east,
+// 	&FGInterface::set_V_east);
+//   fgSetArchivable("/velocities/speed-east-fps");
+//   fgTie("/velocities/speed-down-fps", this,
+// 	&FGInterface::get_V_down,
+// 	&FGInterface::set_V_down);
+//   fgSetArchivable("/velocities/speed-down-fps");
+				// FIXME: Temporarily read-only, until the
+				// incompatibilities between JSBSim and
+				// LaRCSim are fixed (LaRCSim adds the
+				// earth's rotation to the east velocity).
+  fgTie("/velocities/speed-north-fps", this,
+	&FGInterface::get_V_north);
+  fgTie("/velocities/speed-east-fps", this,
+	&FGInterface::get_V_east);
+  fgTie("/velocities/speed-down-fps", this,
+	&FGInterface::get_V_down);
+
+				// Relative wind
+				// FIXME: temporarily archivable, until
+				// the NED problem is fixed.
+  fgTie("/velocities/uBody-fps", this,
+	&FGInterface::get_uBody,
+	&FGInterface::set_uBody,
+	false);
+  fgSetArchivable("/velocities/uBody-fps");
+  fgTie("/velocities/vBody-fps", this,
+	&FGInterface::get_vBody,
+	&FGInterface::set_vBody,
+	false);
+  fgSetArchivable("/velocities/vBody-fps");
+  fgTie("/velocities/wBody-fps", this,
+	&FGInterface::get_wBody,
+	&FGInterface::set_wBody,
+	false);
+  fgSetArchivable("/velocities/wBody-fps");
+
+				// Climb and slip (read-only)
+  fgTie("/velocities/vertical-speed-fps", this,
+	&FGInterface::get_Climb_Rate,
+  &FGInterface::set_Climb_Rate ); 
+  fgTie("/velocities/glideslope", this,
+  &FGInterface::get_Gamma_vert_rad,
+  &FGInterface::set_Gamma_vert_rad );
+  fgTie("/orientation/side-slip-rad", this,
+	&FGInterface::get_Beta); // read-only
+  fgTie("/orientation/side-slip-deg", this,
+  &FGInterface::get_Beta_deg); // read-only
+  fgTie("/orientation/alpha-deg", this,
+  &FGInterface::get_Alpha_deg); // read-only
+  fgTie("/accelerations/nlf", this,
+  &FGInterface::get_Nlf); // read-only
+
+                                // NED accelerations
+  fgTie("/accelerations/ned/north-accel-fps_sec",
+        this, &FGInterface::get_V_dot_north);
+  fgTie("/accelerations/ned/east-accel-fps_sec",
+        this, &FGInterface::get_V_dot_east);
+  fgTie("/accelerations/ned/down-accel-fps_sec",
+        this, &FGInterface::get_V_dot_down);
+
+                                // Pilot accelerations
+  fgTie("/accelerations/pilot/x-accel-fps_sec",
+        this, &FGInterface::get_A_X_pilot);
+  fgTie("/accelerations/pilot/y-accel-fps_sec",
+        this, &FGInterface::get_A_Y_pilot);
+  fgTie("/accelerations/pilot/z-accel-fps_sec",
+        this, &FGInterface::get_A_Z_pilot);
+
+}
+
+
+/**
+ * Unbind any properties bound to this FDM.
+ *
+ * This method allows the FDM to release properties so that a new
+ * FDM can bind them instead.
+ */
+void
+FGInterface::unbind ()
+{
+  bound = false;
+
+  // fgUntie("/fdm/time/delta_t");
+  // fgUntie("/fdm/time/elapsed");
+  // fgUntie("/fdm/time/remainder");
+  // fgUntie("/fdm/time/multi_loop");
+  fgUntie("/position/latitude-deg");
+  fgUntie("/position/longitude-deg");
+  fgUntie("/position/altitude-ft");
+  fgUntie("/position/altitude-agl-ft");
+  fgUntie("/position/ground-elev-ft");
+  fgUntie("/position/ground-elev-m");
+  fgUntie("/environment/ground-elevation-m");
+  fgUntie("/position/sea-level-radius-ft");
+  fgUntie("/orientation/roll-deg");
+  fgUntie("/orientation/pitch-deg");
+  fgUntie("/orientation/heading-deg");
+  fgUntie("/orientation/roll-rate-degps");
+  fgUntie("/orientation/pitch-rate-degps");
+  fgUntie("/orientation/yaw-rate-degps");
+  fgUntie("/orientation/side-slip-rad");
+  fgUntie("/orientation/side-slip-deg");
+  fgUntie("/orientation/alpha-deg");
+  fgUntie("/velocities/airspeed-kt");
+  fgUntie("/velocities/mach");
+  fgUntie("/velocities/speed-north-fps");
+  fgUntie("/velocities/speed-east-fps");
+  fgUntie("/velocities/speed-down-fps");
+  fgUntie("/velocities/uBody-fps");
+  fgUntie("/velocities/vBody-fps");
+  fgUntie("/velocities/wBody-fps");
+  fgUntie("/velocities/vertical-speed-fps");
+  fgUntie("/velocities/glideslope");
+  fgUntie("/accelerations/nlf");
+  fgUntie("/accelerations/pilot/x-accel-fps_sec");
+  fgUntie("/accelerations/pilot/y-accel-fps_sec");
+  fgUntie("/accelerations/pilot/z-accel-fps_sec");
+  fgUntie("/accelerations/ned/north-accel-fps_sec");
+  fgUntie("/accelerations/ned/east-accel-fps_sec");
+  fgUntie("/accelerations/ned/down-accel-fps_sec");
+}
+
+/**
+ * Update the state of the FDM (i.e. run the equations of motion).
+ */
+void
+FGInterface::update (double dt)
+{
+    SG_LOG(SG_FLIGHT, SG_ALERT, "dummy update() ... SHOULDN'T BE CALLED!");
+}
+
+
+void FGInterface::_updateGeodeticPosition( double lat, double lon, double alt )
+{
+    double lat_geoc, sl_radius;
+
+    // cout << "starting sea level rad = " << get_Sea_level_radius() << endl;
+
+    sgGeodToGeoc( lat, alt * SG_FEET_TO_METER, &sl_radius, &lat_geoc );
+
+    SG_LOG( SG_FLIGHT, SG_DEBUG, "lon = " << lon 
+	    << " lat_geod = " << lat
+	    << " lat_geoc = " << lat_geoc
+	    << " alt = " << alt 
+	    << " sl_radius = " << sl_radius * SG_METER_TO_FEET
+	    << " Equator = " << SG_EQUATORIAL_RADIUS_FT );
+
+    _set_Geocentric_Position( lat_geoc, lon, 
+			      sl_radius * SG_METER_TO_FEET + alt );
+	
+    _set_Geodetic_Position( lat, lon, alt );
+
+    _set_Sea_level_radius( sl_radius * SG_METER_TO_FEET );
+    _update_ground_elev_at_pos();
+
+    _set_sin_lat_geocentric( lat_geoc );
+    _set_cos_lat_geocentric( lat_geoc );
+
+    _set_sin_cos_longitude( lon );
+
+    _set_sin_cos_latitude( lat );
+}
+
+
+void FGInterface::_updateGeocentricPosition( double lat_geoc, double lon,
+					     double alt )
+{
+    double lat_geod, tmp_alt, sl_radius1, sl_radius2, tmp_lat_geoc;
+
+    // cout << "starting sea level rad = " << get_Sea_level_radius() << endl;
+
+    sgGeocToGeod( lat_geoc, ( get_Sea_level_radius() + alt ) * SG_FEET_TO_METER,
+		  &lat_geod, &tmp_alt, &sl_radius1 );
+    sgGeodToGeoc( lat_geod, alt * SG_FEET_TO_METER, &sl_radius2, &tmp_lat_geoc );
+
+    SG_LOG( SG_FLIGHT, SG_DEBUG, "lon = " << lon 
+	    << " lat_geod = " << lat_geod
+	    << " lat_geoc = " << lat_geoc
+	    << " alt = " << alt 
+	    << " tmp_alt = " << tmp_alt * SG_METER_TO_FEET
+	    << " sl_radius1 = " << sl_radius1 * SG_METER_TO_FEET
+	    << " sl_radius2 = " << sl_radius2 * SG_METER_TO_FEET
+	    << " Equator = " << SG_EQUATORIAL_RADIUS_FT );
+
+    _set_Geocentric_Position( lat_geoc, lon, 
+			      sl_radius2 * SG_METER_TO_FEET + alt );
+	
+    _set_Geodetic_Position( lat_geod, lon, alt );
+
+    _set_Sea_level_radius( sl_radius2 * SG_METER_TO_FEET );
+    _update_ground_elev_at_pos();
+
+    _set_sin_lat_geocentric( lat_geoc );
+    _set_cos_lat_geocentric( lat_geoc );
+
+    _set_sin_cos_longitude( lon );
+
+    _set_sin_cos_latitude( lat_geod );
+}
+
+void FGInterface::_update_ground_elev_at_pos( void ) {
+    double lat = get_Latitude();
+    double lon = get_Longitude();
+    double alt_m = get_Altitude()*SG_FEET_TO_METER;
+    double groundlevel_m = get_groundlevel_m(lat, lon, alt_m);
+    _set_Runway_altitude( groundlevel_m * SG_METER_TO_FEET );
 }
 
 // Extrapolate fdm based on time_offset (in usec)
@@ -67,7 +577,7 @@ void FGInterface::extrapolate( int time_offset ) {
     // -dw- metrowerks complains about ambiguous access, not critical
     // to keep this ;)
 #ifndef __MWERKS__
-    cout << "extrapolating FDM by dt = " << dt << endl;
+    SG_LOG(SG_FLIGHT, SG_INFO, "extrapolating FDM by dt = " << dt);
 #endif
 
     double lat = geodetic_position_v[0] + geocentric_rates_v[0] * dt;
@@ -89,32 +599,364 @@ void FGInterface::extrapolate( int time_offset ) {
     geocentric_position_v[2] = radius;
 }
 
+// Positions
+void FGInterface::set_Latitude(double lat) {
+    geodetic_position_v[0] = lat;
+}
 
-// Set the altitude (force)
-void fgFDMForceAltitude(int model, double alt_meters) {
-    double sea_level_radius_meters;
-    double lat_geoc;
+void FGInterface::set_Longitude(double lon) {
+    geodetic_position_v[1] = lon;
+}
 
-    // Set the FG variables first
-    fgGeodToGeoc( base_fdm_state.get_Latitude(), alt_meters, 
-		  &sea_level_radius_meters, &lat_geoc);
+void FGInterface::set_Altitude(double alt) {
+    geodetic_position_v[2] = alt;
+}
 
-    base_fdm_state.set_Altitude( alt_meters * METER_TO_FEET );
-    base_fdm_state.set_Radius_to_vehicle( base_fdm_state.get_Altitude() + 
-					  (sea_level_radius_meters * 
-					   METER_TO_FEET) );
+void FGInterface::set_AltitudeAGL(double altagl) {
+    altitude_agl=altagl;
+}
 
-    // additional work needed for some flight models
-    if ( model == FGInterface::FG_LARCSIM ) {
-	ls_ForceAltitude( base_fdm_state.get_Altitude() );
-    }
+// Velocities
+void FGInterface::set_V_calibrated_kts(double vc) {
+    v_calibrated_kts = vc;
+}
+
+void FGInterface::set_Mach_number(double mach) {
+    mach_number = mach;
+}
+
+void FGInterface::set_Velocities_Local( double north, 
+					double east, 
+					double down ){
+    v_local_v[0] = north;
+    v_local_v[1] = east;
+    v_local_v[2] = down;
+}
+
+void FGInterface::set_Velocities_Wind_Body( double u, 
+					    double v, 
+					    double w){
+    v_wind_body_v[0] = u;
+    v_wind_body_v[1] = v;
+    v_wind_body_v[2] = w;
+}
+
+// Euler angles 
+void FGInterface::set_Euler_Angles( double phi, 
+				    double theta, 
+				    double psi ) {
+    euler_angles_v[0] = phi;
+    euler_angles_v[1] = theta;
+    euler_angles_v[2] = psi;                                            
+}  
+
+// Flight Path
+void FGInterface::set_Climb_Rate( double roc) {
+    climb_rate = roc;
+}
+
+void FGInterface::set_Gamma_vert_rad( double gamma) {
+    gamma_vert_rad = gamma;
+}
+
+void FGInterface::set_Static_pressure(double p) { static_pressure = p; }
+void FGInterface::set_Static_temperature(double T) { static_temperature = T; }
+void FGInterface::set_Density(double rho) { density = rho; }
+
+void FGInterface::set_Velocities_Local_Airmass (double wnorth, 
+						double weast, 
+						double wdown ) {
+    v_local_airmass_v[0] = wnorth;
+    v_local_airmass_v[1] = weast;
+    v_local_airmass_v[2] = wdown;
+}
+
+
+void FGInterface::_busdump(void) {
+
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_pilot_rp_body_v[3]: " << d_pilot_rp_body_v[0] << ", " << d_pilot_rp_body_v[1] << ", " << d_pilot_rp_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_cg_rp_body_v[3]: " << d_cg_rp_body_v[0] << ", " << d_cg_rp_body_v[1] << ", " << d_cg_rp_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"f_body_total_v[3]: " << f_body_total_v[0] << ", " << f_body_total_v[1] << ", " << f_body_total_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"f_local_total_v[3]: " << f_local_total_v[0] << ", " << f_local_total_v[1] << ", " << f_local_total_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"f_aero_v[3]: " << f_aero_v[0] << ", " << f_aero_v[1] << ", " << f_aero_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"f_engine_v[3]: " << f_engine_v[0] << ", " << f_engine_v[1] << ", " << f_engine_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"f_gear_v[3]: " << f_gear_v[0] << ", " << f_gear_v[1] << ", " << f_gear_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"m_total_rp_v[3]: " << m_total_rp_v[0] << ", " << m_total_rp_v[1] << ", " << m_total_rp_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"m_total_cg_v[3]: " << m_total_cg_v[0] << ", " << m_total_cg_v[1] << ", " << m_total_cg_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"m_aero_v[3]: " << m_aero_v[0] << ", " << m_aero_v[1] << ", " << m_aero_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"m_engine_v[3]: " << m_engine_v[0] << ", " << m_engine_v[1] << ", " << m_engine_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"m_gear_v[3]: " << m_gear_v[0] << ", " << m_gear_v[1] << ", " << m_gear_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_dot_local_v[3]: " << v_dot_local_v[0] << ", " << v_dot_local_v[1] << ", " << v_dot_local_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_dot_body_v[3]: " << v_dot_body_v[0] << ", " << v_dot_body_v[1] << ", " << v_dot_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"a_cg_body_v[3]: " << a_cg_body_v[0] << ", " << a_cg_body_v[1] << ", " << a_cg_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"a_pilot_body_v[3]: " << a_pilot_body_v[0] << ", " << a_pilot_body_v[1] << ", " << a_pilot_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"n_cg_body_v[3]: " << n_cg_body_v[0] << ", " << n_cg_body_v[1] << ", " << n_cg_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"n_pilot_body_v[3]: " << n_pilot_body_v[0] << ", " << n_pilot_body_v[1] << ", " << n_pilot_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"omega_dot_body_v[3]: " << omega_dot_body_v[0] << ", " << omega_dot_body_v[1] << ", " << omega_dot_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_local_v[3]: " << v_local_v[0] << ", " << v_local_v[1] << ", " << v_local_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_local_rel_ground_v[3]: " << v_local_rel_ground_v[0] << ", " << v_local_rel_ground_v[1] << ", " << v_local_rel_ground_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_local_airmass_v[3]: " << v_local_airmass_v[0] << ", " << v_local_airmass_v[1] << ", " << v_local_airmass_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_local_rel_airmass_v[3]: " << v_local_rel_airmass_v[0] << ", " << v_local_rel_airmass_v[1] << ", " << v_local_rel_airmass_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_local_gust_v[3]: " << v_local_gust_v[0] << ", " << v_local_gust_v[1] << ", " << v_local_gust_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_wind_body_v[3]: " << v_wind_body_v[0] << ", " << v_wind_body_v[1] << ", " << v_wind_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"omega_body_v[3]: " << omega_body_v[0] << ", " << omega_body_v[1] << ", " << omega_body_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"omega_local_v[3]: " << omega_local_v[0] << ", " << omega_local_v[1] << ", " << omega_local_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"omega_total_v[3]: " << omega_total_v[0] << ", " << omega_total_v[1] << ", " << omega_total_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"euler_rates_v[3]: " << euler_rates_v[0] << ", " << euler_rates_v[1] << ", " << euler_rates_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"geocentric_rates_v[3]: " << geocentric_rates_v[0] << ", " << geocentric_rates_v[1] << ", " << geocentric_rates_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"geocentric_position_v[3]: " << geocentric_position_v[0] << ", " << geocentric_position_v[1] << ", " << geocentric_position_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"geodetic_position_v[3]: " << geodetic_position_v[0] << ", " << geodetic_position_v[1] << ", " << geodetic_position_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"euler_angles_v[3]: " << euler_angles_v[0] << ", " << euler_angles_v[1] << ", " << euler_angles_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_cg_rwy_local_v[3]: " << d_cg_rwy_local_v[0] << ", " << d_cg_rwy_local_v[1] << ", " << d_cg_rwy_local_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_cg_rwy_rwy_v[3]: " << d_cg_rwy_rwy_v[0] << ", " << d_cg_rwy_rwy_v[1] << ", " << d_cg_rwy_rwy_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_pilot_rwy_local_v[3]: " << d_pilot_rwy_local_v[0] << ", " << d_pilot_rwy_local_v[1] << ", " << d_pilot_rwy_local_v[2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"d_pilot_rwy_rwy_v[3]: " << d_pilot_rwy_rwy_v[0] << ", " << d_pilot_rwy_rwy_v[1] << ", " << d_pilot_rwy_rwy_v[2]);
+
+    SG_LOG(SG_FLIGHT,SG_INFO,"t_local_to_body_m[0][3]: " << t_local_to_body_m[0][0] << ", " << t_local_to_body_m[0][1] << ", " << t_local_to_body_m[0][2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"t_local_to_body_m[1][3]: " << t_local_to_body_m[1][0] << ", " << t_local_to_body_m[1][1] << ", " << t_local_to_body_m[1][2]);
+    SG_LOG(SG_FLIGHT,SG_INFO,"t_local_to_body_m[2][3]: " << t_local_to_body_m[2][0] << ", " << t_local_to_body_m[2][1] << ", " << t_local_to_body_m[2][2]);
+
+    SG_LOG(SG_FLIGHT,SG_INFO,"mass: " << mass );
+    SG_LOG(SG_FLIGHT,SG_INFO,"i_xx: " << i_xx );
+    SG_LOG(SG_FLIGHT,SG_INFO,"i_yy: " << i_yy );
+    SG_LOG(SG_FLIGHT,SG_INFO,"i_zz: " << i_zz );
+    SG_LOG(SG_FLIGHT,SG_INFO,"i_xz: " << i_xz );
+    SG_LOG(SG_FLIGHT,SG_INFO,"nlf: " << nlf );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_rel_wind: " << v_rel_wind );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_true_kts: " << v_true_kts );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_rel_ground: " << v_rel_ground );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_inertial: " << v_inertial );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_ground_speed: " << v_ground_speed );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_equiv: " << v_equiv );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_equiv_kts: " << v_equiv_kts );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_calibrated: " << v_calibrated );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_calibrated_kts: " << v_calibrated_kts );
+    SG_LOG(SG_FLIGHT,SG_INFO,"gravity: " << gravity );
+    SG_LOG(SG_FLIGHT,SG_INFO,"centrifugal_relief: " << centrifugal_relief );
+    SG_LOG(SG_FLIGHT,SG_INFO,"alpha: " << alpha );
+    SG_LOG(SG_FLIGHT,SG_INFO,"beta: " << beta );
+    SG_LOG(SG_FLIGHT,SG_INFO,"alpha_dot: " << alpha_dot );
+    SG_LOG(SG_FLIGHT,SG_INFO,"beta_dot: " << beta_dot );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_alpha: " << cos_alpha );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_alpha: " << sin_alpha );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_beta: " << cos_beta );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_beta: " << sin_beta );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_phi: " << cos_phi );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_phi: " << sin_phi );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_theta: " << cos_theta );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_theta: " << sin_theta );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_psi: " << cos_psi );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_psi: " << sin_psi );
+    SG_LOG(SG_FLIGHT,SG_INFO,"gamma_vert_rad: " << gamma_vert_rad );
+    SG_LOG(SG_FLIGHT,SG_INFO,"gamma_horiz_rad: " << gamma_horiz_rad );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sigma: " << sigma );
+    SG_LOG(SG_FLIGHT,SG_INFO,"density: " << density );
+    SG_LOG(SG_FLIGHT,SG_INFO,"v_sound: " << v_sound );
+    SG_LOG(SG_FLIGHT,SG_INFO,"mach_number: " << mach_number );
+    SG_LOG(SG_FLIGHT,SG_INFO,"static_pressure: " << static_pressure );
+    SG_LOG(SG_FLIGHT,SG_INFO,"total_pressure: " << total_pressure );
+    SG_LOG(SG_FLIGHT,SG_INFO,"impact_pressure: " << impact_pressure );
+    SG_LOG(SG_FLIGHT,SG_INFO,"dynamic_pressure: " << dynamic_pressure );
+    SG_LOG(SG_FLIGHT,SG_INFO,"static_temperature: " << static_temperature );
+    SG_LOG(SG_FLIGHT,SG_INFO,"total_temperature: " << total_temperature );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sea_level_radius: " << sea_level_radius );
+    SG_LOG(SG_FLIGHT,SG_INFO,"earth_position_angle: " << earth_position_angle );
+    SG_LOG(SG_FLIGHT,SG_INFO,"runway_altitude: " << runway_altitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"runway_latitude: " << runway_latitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"runway_longitude: " << runway_longitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"runway_heading: " << runway_heading );
+    SG_LOG(SG_FLIGHT,SG_INFO,"radius_to_rwy: " << radius_to_rwy );
+    SG_LOG(SG_FLIGHT,SG_INFO,"climb_rate: " << climb_rate );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_lat_geocentric: " << sin_lat_geocentric );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_lat_geocentric: " << cos_lat_geocentric );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_longitude: " << sin_longitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_longitude: " << cos_longitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"sin_latitude: " << sin_latitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"cos_latitude: " << cos_latitude );
+    SG_LOG(SG_FLIGHT,SG_INFO,"altitude_agl: " << altitude_agl );
 }
 
+bool
+FGInterface::prepare_ground_cache_m(double ref_time, const double pt[3],
+                                    double rad)
+{
+  return ground_cache.prepare_ground_cache(ref_time, pt, rad);
+}
 
-// Set the local ground elevation
-void fgFDMSetGroundElevation(int model, double ground_meters) {
-    base_fdm_state.set_Runway_altitude( ground_meters * METER_TO_FEET );
-    cur_fdm_state->set_Runway_altitude( ground_meters * METER_TO_FEET );
+bool FGInterface::prepare_ground_cache_ft(double ref_time, const double pt[3],
+                                          double rad)
+{
+  // Convert units and do the real work.
+  sgdVec3 pt_ft;
+  sgdScaleVec3( pt_ft, pt, SG_FEET_TO_METER );
+  return ground_cache.prepare_ground_cache(ref_time, pt_ft, rad*SG_FEET_TO_METER);
 }
 
+bool
+FGInterface::is_valid_m(double *ref_time, double pt[3], double *rad)
+{
+  return ground_cache.is_valid(ref_time, pt, rad);
+}
+
+bool FGInterface::is_valid_ft(double *ref_time, double pt[3], double *rad)
+{
+  // Convert units and do the real work.
+  bool found_ground = ground_cache.is_valid(ref_time, pt, rad);
+  sgdScaleVec3(pt, SG_METER_TO_FEET);
+  *rad *= SG_METER_TO_FEET;
+  return found_ground;
+}
+
+double
+FGInterface::get_cat_m(double t, const double pt[3],
+                       double end[2][3], double vel[2][3])
+{
+  return ground_cache.get_cat(t, pt, end, vel);
+}
+
+double
+FGInterface::get_cat_ft(double t, const double pt[3],
+                        double end[2][3], double vel[2][3])
+{
+  // Convert units and do the real work.
+  sgdVec3 pt_m;
+  sgdScaleVec3( pt_m, pt, SG_FEET_TO_METER );
+  double dist = ground_cache.get_cat(t, pt_m, end, vel);
+  for (int k=0; k<2; ++k) {
+    sgdScaleVec3( end[k], SG_METER_TO_FEET );
+    sgdScaleVec3( vel[k], SG_METER_TO_FEET );
+  }
+  return dist*SG_METER_TO_FEET;
+}
+
+bool
+FGInterface::get_agl_m(double t, const double pt[3],
+                       double contact[3], double normal[3], double vel[3],
+                       int *type, double *loadCapacity,
+                       double *frictionFactor, double *agl)
+{
+  return ground_cache.get_agl(t, pt, 2.0, contact, normal, vel, type,
+                              loadCapacity, frictionFactor, agl);
+}
+
+bool
+FGInterface::get_agl_ft(double t, const double pt[3],
+                        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, 2.0, 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;
+}
+
+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])
+{
+  return ground_cache.caught_wire(t, pt);
+}
+
+bool
+FGInterface::caught_wire_ft(double t, const double pt[4][3])
+{
+  // Convert units and do the real work.
+  double pt_m[4][3];
+  for (int i=0; i<4; ++i)
+    sgdScaleVec3(pt_m[i], pt[i], SG_FEET_TO_METER);
+    
+  return ground_cache.caught_wire(t, pt_m);
+}
+  
+bool
+FGInterface::get_wire_ends_m(double t, double end[2][3], double vel[2][3])
+{
+  return ground_cache.get_wire_ends(t, end, vel);
+}
+
+bool
+FGInterface::get_wire_ends_ft(double t, double end[2][3], double vel[2][3])
+{
+  // Convert units and do the real work.
+  bool ret = ground_cache.get_wire_ends(t, end, vel);
+  for (int k=0; k<2; ++k) {
+    sgdScaleVec3( end[k], SG_METER_TO_FEET );
+    sgdScaleVec3( vel[k], SG_METER_TO_FEET );
+  }
+  return ret;
+}
+
+void
+FGInterface::release_wire(void)
+{
+  ground_cache.release_wire();
+}
+
+void fgToggleFDMdataLogging(void) {
+  cur_fdm_state->ToggleDataLogging();
+}