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Comment by dingaling | Hacker News Reader

An in-car unit is permanently powered and can maintain a warm-fix for much faster positioning than a cold-fix from my phone, which takes about five minutes with a good view.

Plus the advantages of a large, external antenna. Instead of holding my phone out of the sunroof...

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What phone do you have that could possibly require 5 mins and an arm out the sunroof just for a GPS fix?

Many phones with data service switched off, which might be the case when driving abroad.

Data service has nothing to do with a GPS fix. Nothing at all. No data is used. GPS does not require any internet connection at all.

You are technically true but if you don't have internet connection to get the almanac (future position of satellites) you have to wait 12.5 minutes to download it very slowly from the GPS itself. That's what parent was saying. It works but the time-to-fix is very high.

AGPS uses data service to get the almanac.

Thank you. I learned something from this. How often does that almanac need to be updated, however?

Time to fix can be worse if you've moved since your last fix, or if you're moving quickly. If you don't have a network connection to download the almanac info, it takes 12.5 minutes to receive in its entirety.

These things are also true of Android Auto. It uses the GPS equipment in your car. I leave a dedicated phone in my car's glove box and it always has a strong location.

Android Auto also has access to the car's wheel speed and steering angle sensors so it can use dead reckoning when underground. GPS units can't do that.

> Android Auto also has access to the car's wheel speed and steering angle sensors

Hah, that's pretty interesting. To make a flippant joke, imagine if Facebook had this info, "Hey $AUTO_INSURER, 30% of people who visit your portal and log into it (we have this info because you added a 'Like our page on Facebook' iframe in the page) are bad drivers, you want to know who they are? Pay us and we'll tell you!".

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