don't mix geodetic and geocentric coordinates

diff --git a/src/Environment/ridge_lift.cxx b/src/Environment/ridge_lift.cxx
index 9e291d3a1741efcb0037f40ad62ad70b0b14cbbb..4a371a3ae9d79e3688488d2131327cfeb9ee7918 100644 (file)
--- a/src/Environment/ridge_lift.cxx
+++ b/src/Environment/ridge_lift.cxx
@@ -163,25 +163,24 @@ void FGRidgeLift::update(double dt) {
        timer -= dt;
        if (timer <= 0.0 ) {
 
-               // NOTE: this mixes geocentric and geodetic calculations which give mathematically incorrect results
-               //       probably this is acceptable for calculating the ridge lift, converting from 
-               //       geodetic to geocentric coordinates is somewhat expensive
-
                // probe0 is current position
                probe_lat_deg[0] = _user_latitude_node->getDoubleValue();
                probe_lon_deg[0] = _user_longitude_node->getDoubleValue();
                probe_elev_m[0]  = _ground_elev_node->getDoubleValue() * SG_FEET_TO_METER;
 
-               SGGeoc myPosition = SGGeoc::fromDegM( probe_lon_deg[0], probe_lat_deg[0], 20000.0 );
+               // position is geodetic, need geocentric for advanceRadM
+               SGGeod myGeodPos = SGGeod::fromDegM( probe_lon_deg[0], probe_lat_deg[0], 20000.0 );
+               SGGeoc myGeocPos = SGGeoc::fromGeod( myGeodPos );
                double ground_wind_from_rad = _surface_wind_from_deg_node->getDoubleValue() * SG_DEGREES_TO_RADIANS + SG_PI;
 
                // compute the remaining probes
-               for (int i = 1; i < sizeof(probe_lat_deg)/sizeof(probe_lat_deg[0]); i++) {
-                       SGGeoc probe = myPosition.advanceRadM( ground_wind_from_rad, dist_probe_m[i] );
-                       probe_lat_deg[i] = probe.getLatitudeDeg();
-                       probe_lon_deg[i] = probe.getLongitudeDeg();
-                       if (!globals->get_scenery()->get_elevation_m(
-                               SGGeod::fromDegM(probe_lon_deg[i],probe_lat_deg[i], 20000), probe_elev_m[i], NULL )) {
+               for (int i = 1; i < sizeof(probe_elev_m)/sizeof(probe_elev_m[0]); i++) {
+                       SGGeoc probe = myGeocPos.advanceRadM( ground_wind_from_rad, dist_probe_m[i] );
+                       // convert to geodetic position for ground level computation
+                       SGGeod probeGeod = SGGeod::fromGeoc( probe );
+                       probe_lat_deg[i] = probeGeod.getLatitudeDeg();
+                       probe_lon_deg[i] = probeGeod.getLongitudeDeg();
+                       if (!globals->get_scenery()->get_elevation_m( probeGeod, probe_elev_m[i], NULL )) {
                                // no ground found? use elevation of previous probe :-(
                                probe_elev_m[i] = probe_elev_m[i-1];
                        }