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Comment by tekno45 | Hacker News Reader

doesn't that still allow GPS communication?

It certainly does. Pure inertial guidance with smartphone sensors is garbage. I must say I'm a bit startled by how many people evidently think that GPS is an internet service...

Cell phones use A-GPS which relies on cellular data service. It allows for faster position fixes using base station signals. Of course a cell phone with a view of the sky can still get a position fix entirely from satellites, it just takes a little longer.

I've used GPS navigation extensively on my phone with no internet service; I drove clear across Canada with my simcard pulled, it works fine.

If I had to guess, these conflations of cell service with GPS are a product of misleading UX created by Google. OSMAnd makes the nature of GPS clear, displaying a count of satellites it's managed to hear. Enough satellites to get a location good enough for car navigation almost always takes less than a minute.

There are some other aspects of locations that use downloaded data, like building heights, wifi base station locations, etc.

Yes, it does but knowing where you are isn't the problem for these systems it seems. Also, you can get very far with inertial tracking: https://en.wikipedia.org/wiki/Inertial_navigation_system

Couple that with point clouds of the sea floor, manual input from humans, etc, you can do quite well.

Knowing where you are is very much the problem. If you are 100 meters east of where you think you are, the sea mount you think you are 100 meters west of is a big problem. Inertial navigation systems tell you your position relative to your last "known" location, but if that last point was inaccurate, or if too much error has accumulated since the last point, you can be significantly off from where you think you are.

Couple this with the lack of good maps of certain sections of the sea floor, and human error, and a collision every couple of years becomes probable.

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