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Comment by jfoutz | Hacker News Reader

when MacBooks got the inertial sensor for parking the hard disk, I hacked up a script to estimate velocity and precision. It was bad. It was fun to have friends drive around, and see how well it did.

It was great for screwing around. But yeah, getting real precision would be a massive undertaking.

__edit__ now that I think about it, they could get massive improvements by counting how many times the wheel rotated. The tire would change size as it wore down, but that would have been a really helpful datapoint.

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    I hacked up a script to estimate velocity and precision

Hahahaha that rules!

    they could get massive improvements by counting how 
    many times the wheel rotated. The tire would change 
    size as it wore down

I think the change in size due to rubber wear would be quite dwarfed by the change in size due to tire pressure changes and tire temperature changes (or somebody just replacing the tires with a slightly different model with different dimensions) Also what happens when you're doing sick drifting and the rotation of your wheels becomes entirely decoupled from your car's motion vector????

still, that totally makes sense. tire rotation is another datapoint (or, four datapoints) and a smart enough system could integrate that.

you could also recalibrate the tire data following a complete stop, when the car starts moving again, kind of a zero velocity update thing if I am understanding the wikipedia article on INS in a halfway competent way

The navigation app that I use (NAVITIME) supports connecting to one of those generic Chinese Bluetooth ODB2 dongles and then when you are in a tunnel it will use the car’s speedometer to figure out how far into the tunnel you are

That's awesome!

I'm wondering, though, how necessary it is? Have you found it to be an upgrade over standard GPS?

I don't drive through a lot of tunnels, but I've never noticed my various GPS apps and devices struggling with them over the years. I always assumed they just more or less accomplished the same thing via accelerometer and/or extrapolating your last known heading+velocity when entering the tunnel and/or some handy heuristics (the software assumes the driver is following the path of the tunnel and not boring his own path through the tunnel wall)

If NAVITIME is superior I will totally check that out just for the geekery of it, been meaning to get one of those ODB2 dongles just for the heck of it

Wheel slippage is probably far more significant.

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