/// usual earth centered wgs84 coordiante system. Units are meters.
/// On success, true is returned.
bool get_cart_ground_intersection(const SGVec3d& start, const SGVec3d& dir,
/// usual earth centered wgs84 coordiante system. Units are meters.
/// On success, true is returned.
bool get_cart_ground_intersection(const SGVec3d& start, const SGVec3d& dir,