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Comment by sounddust | Hacker News Reader

As far as I can tell, the iPhone cannot determine one's location solely from the GPS antenna. If you travel to a place where you haven't been before, location services simply won't work until you obtain internet connectivity for a few seconds.

I don't know if this is because the iPhone's GPS functionality is crippled, or if it's a software limitation. I'd imagine that if you wanted to overcome this limitation, you'd need to jailbreak your phone and use 3rd party mapping software at a minimum.

*Note: once it has located you, it will generally track you correctly while you're moving, even if you leave the area where you had internet connectivity.

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Are you sure you've had 12 minutes with a clear view of the sky? Each GPS satellite carries the entire constellation's almanac. After downloading that (which is a 12.5 minute process), then you can download the ephemeris from each satellite, which takes 30 seconds. You need 4 satellites to get a location fix.

The almanac is valid for 180 days, so you only need to wait 12 minutes once. From then on, you only need the ephemeris from 4 visible satellites, which takes less than a minute to download.

It confuses me that the iPhone wouldn't be able to do this, because I can buy a $10 microchip that's the size of a dime that can do it. Give it electricity, wait 15 minutes, the location comes out the other side. I would be shocked if the iPhone were incapable of doing this.

> I can buy a $10 microchip that's the size of a dime that can do it. Give it electricity, wait 15 minutes, the location comes out the other side.

How do you know when the 15 minutes starts, though? Dedicated GPSs tell you things like how many satellites they have in view and how accurate their fix is, but dumbed-down devices like to pretend location is magic. I'd hope they'd at least provide the gritty details through CoreLocation so a user can buy an app if she wants to know which bench outside the train station to sit at sipping coffee while the phone orients itself.

You don't need to know "when it starts", it transmits in a loop, you need to collect ~12.5 minutes of that loop to get the entire almanac. (lousy software _might_ not understand unless it finds some particular preset mark in the loop, but it's not a GPS system architecture problem)

The user needs to know when the almanac is being received and when the whole thing is in when looking for a clear-view-of-sky spot to sit a while.

The best you can do with CoreLocation is set desiredAccuracy to kCLLocationAccuracyBest and wait for it to fall below 100 feet with no way to find out if it ever will.

Less than a minute is still a long time to wait for a position, and it requires visible satellites.

With the iPhone I get a decent location in seconds and a more accurate one in ten. Indoors.

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