Does Tesla set time from the mobile network, or from GPS?
Since the cars essentially have internet access, it probably first pings one of the usual NTP servers by whatever internet connection is available (LTE or Wifi). Since LTE is a little slow to wake up its internet connection, if there isn't wifi or LTE, it might start with the tower timestamp picked up during registration. If it uses GPS clock at all, it's probably the last resort since it's not always "visible", like if you park in a garage.
It's cellular. When crossing time zones, it does not change time immediately, so it's not in the map. Cellular is the only network that effectively knows where you are kind of at. And each site broadcasts the time for that site, which is why it isn't an immediate change as you cross the time zone. You've got to switch to a cellular site in the next time zone before the time changes.
It probably is obtained from the cellular network, but GPS lets the car know precisely where it's located, so the only other info required would be time-zone boundaries.
GPS is fixed UTC time, but the way it works is kind of interesting and does not even require an onboard clock on the receiver at all. It computes where you are by computing your distance from each satellite in view by the clock drift from each one, combined with a known orbital track, via a lot of heavy trigonometry. It’s basically 4 dimensional (3 coordinates in space plus speed and time) triangulation.
Sure, but it also gives your precise position. Given your position and a time zone map, it would be easy to use only GPS to obtain local time.
I hear that's how it works in some kinds of aircraft, but I guess the commodity chipsets and software for cars and phones hasn't caught up yet.
Aircraft are using UTC, not local time. That gets rid of confusion when crossing multiple time zones.
Sure, but I'm but that takes quite a bit of work to do. Not only do you have to worry about the boundaries of the time zones, you have to worry about whether the area that you are in is observing Saving Time and then what day they switch to Saving Time.
