"Stefan" wrote in message
...

Just a few examples: It could be QNH everywhere (requires defined QNH
regions).


If it's QNH everywhere there's no transition altitude.



It could be GPS altitude (would even simplify things a lot, but requires
all aircraft to be expensively equipped). Heck, it could even be radar
altitude everywhere, of course compensated for ground elevation. As I
said, whether it would make sense or even be practical is a different
question, but there are a lot of solutions which are thinkable.


How does one set the barometric pressure for GPS altitude or radar altitude?