diff --git a/configure.ac b/configure.ac
index 6e021f9ef..c89d87aa2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -193,7 +193,8 @@ network_LIBS="$LIBS"
 LIBS=""
 
 dnl check for some default libraries
-AC_SEARCH_LIBS(cos, [fastm m])
+AC_SEARCH_LIBS(sqrt, [am ffm fm fastm m])
+AC_SEARCH_LIBS(ceil, m)
 AC_SEARCH_LIBS(dlclose, dl)
 
 base_LIBS="$LIBS"
diff --git a/src/FDM/MagicCarpet.cxx b/src/FDM/MagicCarpet.cxx
index 0402c28a5..2dc4008fd 100644
--- a/src/FDM/MagicCarpet.cxx
+++ b/src/FDM/MagicCarpet.cxx
@@ -111,6 +111,7 @@ void FGMagicCarpet::update( double dt ) {
 			     sl_radius + get_Altitude() + climb );
     // cout << "sea level radius (ft) = " << sl_radius << endl;
     // cout << "(setto) sea level radius (ft) = " << get_Sea_level_radius() << endl;
+    _update_ground_elev_at_pos();
     _set_Sea_level_radius( sl_radius * SG_METER_TO_FEET);
     _set_Altitude( get_Altitude() + climb );
 }
diff --git a/src/FDM/SP/ACMS.cxx b/src/FDM/SP/ACMS.cxx
index c5b7eefdd..5b75f8520 100644
--- a/src/FDM/SP/ACMS.cxx
+++ b/src/FDM/SP/ACMS.cxx
@@ -103,6 +103,7 @@ void FGACMS::update( double dt ) {
     _set_Euler_Rates(0,0,0);
 
     _set_Geocentric_Position( lat_geoc, get_Longitude(), sl_radius);
+    _update_ground_elev_at_pos();
     _set_Sea_level_radius( sl_radius * SG_METER_TO_FEET);
 
 }
diff --git a/src/FDM/UFO.cxx b/src/FDM/UFO.cxx
index e8df63e42..357c26258 100644
--- a/src/FDM/UFO.cxx
+++ b/src/FDM/UFO.cxx
@@ -191,6 +191,7 @@ void FGUFO::update( double dt ) {
 			     sl_radius + get_Altitude() + climb );
     // cout << "sea level radius (ft) = " << sl_radius << endl;
     // cout << "(setto) sea level radius (ft) = " << get_Sea_level_radius() << endl;
+    _update_ground_elev_at_pos();
     _set_Sea_level_radius( sl_radius * SG_METER_TO_FEET);
     _set_Altitude( get_Altitude() + climb );
 }
diff --git a/src/FDM/YASim/YASim.cxx b/src/FDM/YASim/YASim.cxx
index 742101917..d374a3e5e 100644
--- a/src/FDM/YASim/YASim.cxx
+++ b/src/FDM/YASim/YASim.cxx
@@ -366,6 +366,7 @@ void YASim::copyFromYASim()
     double lat, lon, alt;
     sgCartToGeod(s->pos, &lat, &lon, &alt);
     _set_Geodetic_Position(lat, lon, alt*M2FT);
+    _update_ground_elev_at_pos();
 
     // UNUSED
     //_set_Geocentric_Position(Glue::geod2geocLat(lat), lon, alt*M2FT);
diff --git a/src/FDM/flight.cxx b/src/FDM/flight.cxx
index 9bda7929a..43b5aa03b 100644
--- a/src/FDM/flight.cxx
+++ b/src/FDM/flight.cxx
@@ -515,9 +515,7 @@ 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 );
-    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 );
+    _update_ground_elev_at_pos();
 
     _set_sin_lat_geocentric( lat_geoc );
     _set_cos_lat_geocentric( lat_geoc );
@@ -554,9 +552,7 @@ 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 );
-    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 );
+    _update_ground_elev_at_pos();
 
     _set_sin_lat_geocentric( lat_geoc );
     _set_cos_lat_geocentric( lat_geoc );
@@ -566,6 +562,13 @@ void FGInterface::_updateGeocentricPosition( double lat_geoc, double 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)
 void FGInterface::extrapolate( int time_offset ) {
diff --git a/src/FDM/flight.hxx b/src/FDM/flight.hxx
index 5b01cff0a..dd32bde2c 100644
--- a/src/FDM/flight.hxx
+++ b/src/FDM/flight.hxx
@@ -238,6 +238,7 @@ public:
     void _busdump(void);
     void _updateGeodeticPosition( double lat, double lon, double alt );
     void _updateGeocentricPosition( double lat_geoc, double lon, double alt );
+    void _update_ground_elev_at_pos( void );
     void _updateWeather( void );
 
     inline void _set_Inertias( double m, double xx, double yy, 
diff --git a/src/Main/renderer.cxx b/src/Main/renderer.cxx
index 06ef1bcd9..b5566b0c2 100644
--- a/src/Main/renderer.cxx
+++ b/src/Main/renderer.cxx
@@ -494,11 +494,10 @@ FGRenderer::update( bool refresh_camera_settings ) {
     glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ) ;
     glHint( GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST ) ;
 
-    double agl =
-        current_aircraft.fdm_state->get_Altitude() * SG_FEET_TO_METER
-        - cur_fdm_state->get_Runway_altitude_m();
+    double agl = current__view->getAltitudeASL_ft()*SG_FEET_TO_METER
+      - current__view->getSGLocation()->get_cur_elev_m();
 
-    if ( agl > 50.0 ) {
+    if ( agl > 10.0 ) {
         scene_nearplane = 10.0f;
         scene_farplane = 120000.0f;
     } else {