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burnsep
Jul 2, 2005


Sagebrush posted:

This isn't quite right. Cell phone GPS chips aren't any "weaker" than those in other receivers. There isn't even a "weaker" or "stronger" that makes sense, really -- it's a digital signal. Either you receive enough data that it works perfectly, or you get nothing usable. Without getting into too much detail, the first time you try to get a GPS fix your receiver (or phone) needs to know where the satellites currently are, so that it can triangulate your location. It does this by downloading orbital data directly from the satellites it can see. This data is coming from outer space over a narrow channel, so it takes a very long time to receive -- 12.5 minutes for the full message. All receivers without A-GPS take the same amount of time to get a fix because they need to download the almanac (as it's called) from the same source.

Basically, all that A-GPS does is send this data to you over your data connection instead of the GPS stream. The almanac is quite small, and can arrive in seconds over a 3G/4G data link -- and once your phone has it, it can compute a fix in seconds. A-GPS also allows your phone to receive corrections for things like ionospheric conditions (space weather), which might otherwise distort the signal and decrease accuracy; and it can allow your phone to combine data from multiple sources, such as known wi-fi networks and their relative signal strength at different positions, to increase accuracy even more.

Don't confuse this with the fake "GPS" that the wifi iPads and early iPhones have -- they don't actually have a GPS chip at all, and instead try to triangulate your location from the nearest wifi networks in Apple's database. The only reason this works is because all iPhones will occasionally send Apple their geographic location and a list of all the network SSIDs they can see (starbucks, AT&T, your personal network, etc), and their relative signal strengths. Wifi iPads then access this database, compare it to the networks they can see at that time, and try to estimate roughly where they are. Fascinating, huh?

Actually yes, thanks for that.

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burnsep
Jul 2, 2005


leidend posted:

I remember reading a magazine in the 90s that predicted we'd all be using projected HUDs on our front window by now.
I'm 100% sure that in the late 90's I saw a TV ad for a luxury sedan that had a heat vision HUD for night driving. In the ad, the driver narrowly avoids hitting a deer thanks to it. Thinking back on it, I must be mistaken, but the memory is very strong. Am I crazy?

burnsep
Jul 2, 2005


Captain Trips posted:

lol @ that last line. The idea of fitting six people into a Dodge Spirit is the ridiculous thing.

Were corporations people back then? Because I remember the Spirit and you could maybe fit 3 people and a stack of paperwork in there.

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