Let me just quickly declassify this for you. Here is the relevant VOR/VTOL MFD code:
void Orthodome (double lng1, double lat1, double lng2, double lat2,
double &dist, double &dir)
{
double A = lng2-lng1;
double dlng = fabs(A);
double dlat = fabs(lat2-lat1);
if (dlat < 1e-14) {
dist =...