why did old (like 90s/2000s) GPS take up to 15 minutes to get a lock, in giant bulky units, but my running watch gets it in 15 seconds?
In: 3751
A pure GPS unit will still take a minute or two to get a location.
Phones and other consumer devices use what’s called AGPS, or assisted GPS. They use less precise but quicker means of geolocation to get a quick fix while working to narrow it down with more precise methods.
Your phone knows what cell tower you’re connected to and can estimate distance based on signal strength, so with a database of cell tower locations there’s a quick estimate. There are databases of public Wi-Fi networks and their locations if you’re in a built-up area. Your phone knows your approximate altitude so could compare against a topographical map. It’s got an accelerometer so it knows approximately how far it’s moved since the last time it checked its location.
All those can be used to narrow it down while waiting for a definitive fix from GPS.
You know when you open the maps app on your phone and your location is a circle the size of a small town, then it narrows down to a block, and then it keeps shrinking until it’s an accurate dot? That’s AGPS at work.
Latest Answers