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Location tracking on iOS devices without GPS (for example an iPod touch) sometimes works without any internet connection (it nearly always works with an interne
by ugh 16y ago
Location tracking on iOS devices without GPS (for example an iPod touch) sometimes works without any internet connection (it nearly always works with an internet connection – WLAN access points are used to determine the approximate location), especially in urban environments (with a lot of WLAN access points). I always figured that iOS devices download location info on all the surrounding WLAN access points (maybe even those not in range – it seemed like that in my tests) as soon as you use location services and are connected to the internet.
This database could have something to do with that.
- thought_alarm 16y agoYes, when you use the location services in, say, a new city then your device will download and cache the WiFi location data for a large radius around that initial lookup the next time it has an internet connection. It's pretty cool, actually. That database isn't infinitely large, as unused location information will be removed as new location data comes in.
- andrewgleave 16y agoI seem to remember this being talked about at one last year's WWWDC sessions.
- Maxious 16y agoI remember hearing this on reddit but the post is mirrored at http://www.volnation.com/forum/pub/127425-iphone-bug-2.html#post4924534 http://www.volnation.com/forum/pub/127425-iphone-bug-2.html#... 'Look at the video for session 115, "Using Core Location in iOS". Skip to around 13:45 for the discussion of "Course Cell Positioning" where they discuss the cache in detail.'
- wallnutboy 16y agoAndroid achieves this well, too. I guess Apple are just following Google's move (remember when Google recorded all the wireless access points with their streetview vans?)
- dedward 16y agoDoes the iPhone actually have real GPS, or is it just based on 3G towers?
- jessedhillon 16y agoIt has A-GPS, which is inferior in some ways to true GPS, but is much more accurate than triangulating from towers (which it will resort to under certain conditions.) http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_GPS http://en.wikipedia.org/wiki/List_of_devices_with_Assisted_G...
- tienshiao 16y agoThe iPhone (3G, 3GS, and 4) and the 3G iPads have fully functional GPS hardware, and also use A-GPS to acquire a position fix. If you've ever used a normal standalone GPS in one city and gotten on a plane and flown across the country and tried to use the GPS again, you'll know that it can take 5+ minutes to reacquire a fix that first time off the plane.
- ugh 16y agoAssisted GPS seems to be a very poor choice of name. I have repeatedly met people who wrongly believe that Assisted GPS is not actual GPS.
- jessedhillon 16y agoSome AGPS devices cannot determine their own position from a satellite signal, whereas others can as long as they have received an almanac from a server in the recent past. It depends what you mean by "actual GPS". Some implementations are completely incapable of acting in a standalone capacity.
- ugh 16y agoHere is what the Wikipedia article you linked to says: "Standalone" or "Autonomous" GPS operation use radio signals from satellites alone. A-GPS additionally uses … Wrong?