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Comment by wongarsu | Hacker News Reader

>Self-driving cars, for example, must have infinitesimally precise location data to avoid accidents.

With GPS having at best three metres accuracy? It's nice that they keep their data up to date, but I'm not so sure self-driving cars have anything to do with it.

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  With GPS having at best three metres accuracy?

Regular unaugmented GPS actually has something like 10m-3m of error. GNSS augmentation, like WAAS, gets you down to 1m. RTK GNSS gets you down to 1cm, but you need a stationary base station, and accuracy gets worse the farther away from the station you are. A REACH RTK pair costs $570: https://emlid.com/shop/reach-rtk-kit/

You can get down to 1mm of error with good antennas and long-term averaging-- no good for moving objects. This is how we measure continental drift.

If a self driving car can't deal with a 1.5 meter misalignement by relying on other sensors (camera, radar, laser), then there are way more serious issues...

Even with a +/-3 meter accuracy, a systematic 1.5 meter shift still makes a difference.

The mapping data used by some autonomous vehicles is indeed very precise--though I'm not sure I'd call it "infinitesimally precise." However, as you say, normal GPS by itself isn't accurate enough to align those maps with the physical world. It has to be augmented with sensors.

It's obviously desirable not to have a systematic error in how GPS lat/long corresponds to maps but it's within the error of GPS.

That doesn't make any sense to me either. To avoid accidents - do they mean so the car doesn't drive off the road when making a turn? Surely the car uses visual feedback as well.

Differential GPS can hit ~10cm level accuracy.

Those are also $3k ~ $5k and have to be configured to use a GPS base station. A professor once let us borrowed his. It had a full backpack and was supposedly accurate to 3cm using the airport as our base station.

DGPS is much cheaper than it used to be as it is a feature of most GPS chipsets, though its poorly documented how you enable it. You also need to provide a serial data link between the two GPS units (for most applications this is over RF).

Also, from my understanding, you only know the relative position of the two stations accurately, not the absolute world location.

Yes but I'm not sure why that's relevant to most autonomous vehicles or typical commercial/consumer GPS use.

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