+// Given a point and a list of stations, return the closest one to the
+// specified point.
+FGNavRecord *FGNavList::findNavFromList( const SGVec3d &aircraft,
+ const nav_list_type &stations )
+{
+ FGNavRecord *nav = NULL;
+ double d2; // in meters squared
+ double min_dist
+ = FG_NAV_MAX_RANGE*SG_NM_TO_METER*FG_NAV_MAX_RANGE*SG_NM_TO_METER;
+
+ nav_list_const_iterator it;
+ nav_list_const_iterator end = stations.end();
+ // find the closest station within a sensible range (FG_NAV_MAX_RANGE)
+ for ( it = stations.begin(); it != end; ++it ) {
+ FGNavRecord *station = *it;
+ // cout << "testing " << current->get_ident() << endl;
+ d2 = distSqr(station->get_cart(), aircraft);
+
+ // cout << " dist = " << sqrt(d)
+ // << " range = " << current->get_range() * SG_NM_TO_METER
+ // << endl;
+
+ // LOC, ILS, GS, and DME antenna's could potentially be
+ // installed at the opposite end of the runway. So it's not
+ // enough to simply find the closest antenna with the right
+ // frequency. We need the closest antenna with the right
+ // frequency that is most oriented towards us. (We penalize
+ // stations that are facing away from us by adding 5000 meters
+ // which is further than matching stations would ever be
+ // placed from each other. (Do the expensive check only for
+ // directional atennas and only when there is a chance it is
+ // the closest station.)
+ int type = station->get_type();
+ if ( d2 < min_dist &&
+ (type == 4 || type == 5 || type == 6 || type == 12 || type == 13) )
+ {
+ double hdg_deg = 0.0;
+ if ( type == 4 || type == 5 ){
+ hdg_deg = station->get_multiuse();
+
+ } else if ( type == 6 ) {
+ int tmp = (int)(station->get_multiuse() / 1000.0);
+ hdg_deg = station->get_multiuse() - (tmp * 1000);
+
+ } else if ( type == 12 || type == 13 ) {
+ // oops, Robin's data format doesn't give us the
+ // needed information to compute a heading for a DME
+ // transmitter. FIXME Robin!
+ }
+
+ double az1 = 0.0, az2 = 0.0, s = 0.0;
+ SGGeod geod = SGGeod::fromCart(aircraft);
+ geo_inverse_wgs_84( geod, station->get_pos(), &az1, &az2, &s);
+ az1 = az1 - station->get_multiuse();
+ if ( az1 > 180.0) az1 -= 360.0;
+ if ( az1 < -180.0) az1 += 360.0;
+ // penalize opposite facing stations by adding 5000 meters
+ // (squared) which is further than matching stations would
+ // ever be placed from each other.
+ if ( fabs(az1) > 90.0 ) {
+ double dist = sqrt(d2);
+ d2 = (dist + 5000) * (dist + 5000);
+ }
+ }
+
+ if ( d2 < min_dist ) {
+ min_dist = d2;
+ nav = station;
+ }
+ }
+
+ return nav;