4 ms·

How can you do inertial navigation for a car inside a tunnel? afaik the only info you have is the speed and distance covered, from the wheels, but that info can

How can you do inertial navigation for a car inside a tunnel? afaik the only info you have is the speed and distance covered, from the wheels, but that info can't be shared unless you hook up with the car through obd2 or maybe android auto, the phone itself can't do it, right?

gostsamo 5y ago
you have gyroscope and accelerometer data which can tell you distance and direction changes up to the sensitivity of the instruments.
- tekdude 5y ago
  Just to add to this, submarines and ICBMs navigate by inertial systems. The good ones (incredibly expensive) are extremely precise. The problem with INS though is that every minuscule error compounds over time... since there is no external reference. The longer you navigate by INS, the less certain you can be. With GPS, the system is constantly getting new reference signals from the satellites (which periodically get their own from ground stations).
BombNullIsland 5y ago
You can't, mems gyroscopes drift too quickly to be useful. Most tunnels where GPS "works" pass a repeated GPS signal through a leaky feeder, the receiver uses doppler to figure out your speed and guestimate distance. I guess because of the point source on the surface the phone must also think the tunnel is a vertical shaft as well. The new ones create take ephemeris and almanac data and create simulated time signals for the repeaters exact location. This is the same thing that military jammers do near important locations like embassies and bases to ensure that enemy missiles hit somewhere across the road.
aqfamnzc 5y ago
In addition to the other answers here, I'd imagine many stock navigation systems are hooked in to the car's CAN bus which would have speed and sometimes steering angle. Obviously getting that data to a phone is a different story.
- nitrogen 5y ago
  The car also most likely has a built-in compass.
contingencies 5y ago
Inertial navigation means calculating your next location based upon your speed and trajectory. Cars can calculate how fast they are going and when they turn from wheel size, revolutions and steering inputs, they don't necessarily need IMUs to imply this data. Sibling responses in this thread miss this point.

gostsamo 5y ago

you have gyroscope and accelerometer data which can tell you distance and direction changes up to the sensitivity of the instruments.

tekdude 5y ago
Just to add to this, submarines and ICBMs navigate by inertial systems. The good ones (incredibly expensive) are extremely precise. The problem with INS though is that every minuscule error compounds over time... since there is no external reference. The longer you navigate by INS, the less certain you can be. With GPS, the system is constantly getting new reference signals from the satellites (which periodically get their own from ground stations).

BombNullIsland 5y ago

You can't, mems gyroscopes drift too quickly to be useful. Most tunnels where GPS "works" pass a repeated GPS signal through a leaky feeder, the receiver uses doppler to figure out your speed and guestimate distance. I guess because of the point source on the surface the phone must also think the tunnel is a vertical shaft as well. The new ones create take ephemeris and almanac data and create simulated time signals for the repeaters exact location. This is the same thing that military jammers do near important locations like embassies and bases to ensure that enemy missiles hit somewhere across the road.

aqfamnzc 5y ago

In addition to the other answers here, I'd imagine many stock navigation systems are hooked in to the car's CAN bus which would have speed and sometimes steering angle. Obviously getting that data to a phone is a different story.

nitrogen 5y ago
The car also most likely has a built-in compass.

contingencies 5y ago

Inertial navigation means calculating your next location based upon your speed and trajectory. Cars can calculate how fast they are going and when they turn from wheel size, revolutions and steering inputs, they don't necessarily need IMUs to imply this data. Sibling responses in this thread miss this point.