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Comment by Xcelerate | Hacker News Reader

I don't think the future is GPS at all. I remember reading a while back about a researcher who was working on developing tiny optical gyroscopes that were ridiculously precise, the idea being that you can calibrate their position once and after that all future locations are determined simply by integrating the acceleration of the gyroscope. It would work in places that GPS can't (like caves).

To me, that's really awesome. Personally, I think the coolest use would be in running watches to finally get a perfectly accurate pace instead of a slowly-updating estimate.

I'll see if I can find the link to the researcher's page.

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Dead reckoning is subject to cumulative errors, so that would have to be REALLY accurate.

To put it into perspective. Imagine a dead-reckoning system with 1ppm error (ridiculously low) and no drift (again ridiculous). Say you use this for in-car navigation. After driving around for 10k miles, the error is now 53 feet, which is too great for navigation.

There's more to navigation than city streets. That accuracy would be awesome for shipboard use.

Grandparent was talking specifically about replacing GPS; I pointed out one example where even an absurdly accurate DR system wouldn't be sufficient to completely replace GPS.

TIL "Dead Reckoning" is more than just a badass movie and band name. That's really neat!

This term comes from "ded" (short for "deduced") -- deduced because you are advancing your last fix based on course and speed.

That can synergize with GPS. Many OEM Nav systems in cars these days do something similar in tunnels, where GPS signals are unavailable.

But if gyroscopes became precise enough, I can't think of a reason for needing GPS anymore, can you?

So you can put the phone to sleep. Depending on the power usage of the gyroscope.

To keep track of your position using inertial measurement you need two types of sensor - gyroscopes, to work out which way you're pointing, and accelerometers, to work out how fast you're going.

An IMU in a smartphone would be subject to 10 m/s/s acceleration at all times under gravity, 50 m/s/s on a rollercoaster, and 100,000 m/s/s if you drop your phone on a hard surface.

Let's say we don't mind losing your location if you drop your phone, so we pick an accelerometer with a maximum range of 50 m/s/s.

Now, how accurately can we measure acceleration? The raw image setting on a fancy digital camera is 14 bits, which gives 16384 levels. CD audio is 16 bit, so it has 65,536 levels. Assume you can come up with a design that offers a 32 bit range, for a full 4 billion levels.

That means your measurements will be precise to 0.0000000116 m/s/s - pretty accurate, right?

The thing is, after 24 hours your phone will have an inaccurate estimate of its speed (0.0000000116 m/s/s * 24 hours = 0.001 m/s) and after 24 hours with that inaccurate speed estimate you'll have an inaccurate position estimate (0.001 m/s * 24 hours = 86.4 m) and the longer you leave it going, the bigger the error can get.

TLDR: You need super-precise sensors to do dead reckoning that stays accurate for long periods.

One of the secrets of useful dead reckoning systems is damping which is basically reducing your velocity toward zero (or some expected value) by a measurement slightly greater than your error. The result is if your cellphone sit's on a table you don't accumulate errors. Coupled with the occasional calibration and you end up with some surprisingly accurate systems.

Yes indeed! Of course, that doesn't reduce your position error, it only stops your position error growing while you're stationary. And you can't be stationary all the time (or if you can be, you don't need a navigation system at all!).

Inertial Navigation Systems like OxTS make [1] use GPS to get rid of this integration error that accumulates over time. For applications in vehicles you can also use the vehicle's speedometer, so you're measuring speed directly, which means fewer integration errors.

[1] http://www.oxts.com/default.asp?pageRef=69

http://news.ycombinator.com/item?id=4856914

I am somewhat doubtful about gyroscope replacing GPS. If it can actually happen, it will require, as noted by others, re-tuned/tweaked/calibrated/adjusted every day/week to void accumulated error/noise.

Keep in mind that as precise as gyroscope can get, they could be susceptible to shock (if you drop it on the ground).

But I am interested in seeing how it could develop into

IMUs [1] have been used in planes for a while now, I am not sure whether it is the future or the ancestor of GPS.

[1] http://en.wikipedia.org/wiki/Inertial_measurement_unit

Ancestor. GPS has displaced IMUs in aircraft as the primary navigation device.

And what happens once the phone's battery dies?

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