Wow, another groundhog day, where jroa takes round in circles until we all get bored and go home.
My dedicated GPS unit works anywhere, from remote Scottish mountains to the middle of the ocean.
I've used it quite a few times on flights when I've been over the atlantic ocean at 30,000ft - it accurately tells me my location and altitude. It does not have a barometric sensor (which obviously wouldn't work in pressurized cabin anyway).
It would be impossible for a ground based system to do this. My challenge is: prove me wrong.