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Comment by actionfromafar | Hacker News Reader

The currents would accelerate the dead reckoning unit just like any other force, including from the impellers.

Not arguing that small autonomous systems could use something smaller and cheaper.

The dead reckoning itself doesn't detect the ocean currents; these are separate estimates that need to be integrated to determine actual position https://en.wikipedia.org/wiki/Submarine_navigation#Deep_wate...

Huh, I don't understand why. :-D Someone please explain. If I tugged the sub, wouldn't the IMU detect that? Why is a current doing the tugging any different.

now I'm guessing, but perhaps it's like if you walk up the aisle of a moving train, how fast are you travelling? And how fast does it feel like you're travelling?

Sure, I would get confused by that too, but I thought the point of the IMU is that it has its own frame of reference. Elsewhere in these comments was someone mentioning an IMU which could detect a building growing in size when warmer. The IMU doesn't "know" there's water outside or how the water is moving. It knows how much force it's been pushed around by.

Aha! IMU <> "dead reckoning"? In the wikipedia article they are listed separately. Dead reckoning is meaning tracking things like the revolutions of a propeller and a compass to compute position, whereas an IMU is three accelerometers, three gyros and three magnetometers? https://en.wikipedia.org/wiki/Inertial_measurement_unit

Haha oops. :-)

many INS packages also include a DVL (Doppler velocity log) which measures speed over ground if you’re in range of the bottom.

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