How Tesla’s Model S Tracks Your Location In a Tunnel Without GPS

It's called "dead reckoning."

Oct 15 2015, 1:30pm

GPS doesn't work if you're in a tunnel, but the Tesla Model S has come up with a solution.

As YouTuber Bjørn Nyland progresses along a tunnel, the car's display shows him moving parallel to the road, but not actually on it—but it still displays his position relative to how far along he is on his journey. Once Nyland exits the tunnel, the arrow indicating his position snaps back into place with the return of GPS.

As Nyland explains, the car's software uses a technique to figure out where you are (the technical name for this is "dead reckoning"). It takes your previously known position and guesses your current spot using your wheel rotation and the angle of your steering wheel.

Nyland also notes that in many cases, the Tesla's system of calculation is more accurate than Google's map. One tunnel he drives through is depicted on the map as a straight line, but the arrow follows the actual curves and bends of the tunnel.

When he finally comes out of the tunnel, the Tesla's calculation was only off by about 10 meters. Is there anything these cars can't do?