Comment by algaeontoast | Hacker News Reader

Comment by algaeontoast | Hacker News Reader

Wow this is totally cool, but also totally fucked.

Granted, anyone who's been unaware of the insane accuracy of inertial tracking (prevalent since the iPhone 4) is in for a rude awakening. In short, inertial tracking / positioning uses Apple's CoreMotion co-processor to figure out the relative direction and speed a device is traveling. This makes it possible to navigate for miles without cell service or GPS in maps (I've done this for over 30miles in google maps, while keeping the car icon on the road) and also works accurately enough to tell which floor or room of a building someone is in.

It's also been found that the co-processor can remain on for up to two days and stores info without needing the rest of the device to be on.

The inertial trackers in current-day phones do not have anything like that kind of stability. They accumulate errors at an accelerating rate (they are essentially doing a double-integration of the error).

Using just MEMs based accelerometers, your position error would be hundreds of feet within a minute or two. Gyro and compass can slow the error down a bit, but not enough to be within a road width over 30 miles.

I think it's more likely that GPS was working in the anecdote above. It would be hard to find a place that had 30 miles of road and couldn't get a GPS/GLONASS fix.

Where were you going that you didn't have GPS coverage for 30 miles?

GPS coverage works even without Network/WiFi coverage. I find it very, very unlikely inertial tracking using iPhone inertial sensors would be accurate up to 30 miles.

Could you provide a source please on the fact that iPhones use inertial navigation for predicting location (either public or private apis)

Sauce: https://www.idownloadblog.com/2014/03/05/iphone-5s-m7-tracki...

I was driving through rural Kentucky shortly after the 2017 eclipse.

It doesn't really matter how rural the area is - GPS works pretty well outside of the polar circles. AGPS does use data connection to accelerate first fix time, but will be accurate after that without data.

This link just says that the M7 is still active after main phone has shut down. Nothing about inertial navigation.

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