It isn't hard, it's just that with a bit of road in between you and the sky the signal is lost. Airplane use barometric pressure for altitude is in part backwar

It isn't hard, it's just that with a bit of road in between you and the sky the signal is lost. Airplane use barometric pressure for altitude is in part backwards compatibility. https://en.wikipedia.org/wiki/Flight_level https://en.wikipedia.org/wiki/Flight_level