+// 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.)
+
+static bool penaltyForNav(FGNavRecord* aNav, const SGGeod &aGeod)
+{
+ switch (aNav->type()) {
+ case FGPositioned::ILS:
+ case FGPositioned::LOC:
+ case FGPositioned::GS:
+// FIXME
+// case FGPositioned::DME: we can't get the heading for a DME transmitter, oops
+ break;
+ default:
+ return false;
+ }
+
+ double hdg_deg = 0.0;
+ if (aNav->type() == FGPositioned::GS) {
+ int tmp = (int)(aNav->get_multiuse() / 1000.0);
+ hdg_deg = aNav->get_multiuse() - (tmp * 1000);
+ } else {
+ hdg_deg = aNav->get_multiuse();
+ }
+
+ double az1, az2, s;
+ SGGeodesy::inverse(aGeod, aNav->geod(), az1, az2, s);
+ az1 = az1 - hdg_deg;
+ SG_NORMALIZE_RANGE(az1, -180.0, 180.0);
+ return fabs(az1) > 90.0;
+}
+
+// Given a point and a list of stations, return the closest one to the
+// specified point.
+FGNavRecord *FGNavList::findNavFromList( const SGGeod &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;
+ SGVec3d aircraftCart = SGVec3d::fromGeod(aircraft);
+
+ 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->cart(), aircraftCart);
+ if ( d2 < min_dist && penaltyForNav(station, aircraft))
+ {
+ double dist = sqrt(d2);
+ d2 = (dist + 5000) * (dist + 5000);
+ }
+
+ if ( d2 < min_dist ) {
+ min_dist = d2;
+ nav = station;
+ }