iLounge

1

So, the iPhone uses the surface-to-air recovery system that the CIA developed to get operatives out of hotspots, and that Morgan Freeman recommended Batman use to get Lau out of Hong Kong in The Dark Knight?

The iPhone really can do anything!!!

Posted by Tommy on July 8, 2009 at 6:09 AM (PST)

2

Unless I’ve entirely misunderstood what he’s saying, I find these claims really hard to believe. Having used a first generation iPhone for nearly two years (the one that depended entirely upon skyhook) and having just switched to a 3GS (with GPS), the accuracy has improved exponentially. How is it possible that my iPhone is still dependent on skyhook nearly 75% of the time, but it is now multiple times more accurate?

Posted by urbanslaughter on July 8, 2009 at 6:18 AM (PST)

3

“How is it possible that my iPhone is still dependent on skyhook nearly 75% of the time, but it is now multiple times more accurate?”

Likely, Skyhook locates your phone initially (large blue circle) while GPS kicks in later and improves the accuracy to the value to which you’re accustomed (blue circle shrinks).

Posted by David on July 8, 2009 at 6:46 AM (PST)

4

If I understand correctly, GPS gets its answer as the coordinates that best satisfy multiple equations in multiple unknowns, making an initial guess, testing it, repeatedly guessing until it finds a rough location solution, then refining that iteratively until it can’t get better; you see this as it hunts for satellites for a while, then locks in with poor resolution that slowly improves. The initial guess / lack of approximate answer is what takes older units so long; newer ones start from the last location before power-off, which makes sense and drops initial lock-on time by a factor of 3 or so (as long as power-off was recent). So my guess, extending from the post above, is the iPhone gets that initial solution very quickly from Wi-Fi (as though the first GPS guess were correct, and/or taken from last location before power-down), then refines it by GPS. The 75% sounds similar to the improvement between old & newer GPS methods.

Posted by David H on July 8, 2009 at 2:33 PM (PST)

5

I always turn WiFi off when I’m not using it, and even with WiFi off, a GPS fix on my iPhone 3G takes about 2 to 4 seconds. The number of times I’ve seen the accuracy circle be too large for GPS fix and too small for a cell tower fix (meaning its using Skyhook)? Probably 3 or 4 times. Out of hundreds of times I’ve used the iPhone to get location.

I think he’s just using statistics wrong. I’m sure if you take all the positioning queries all iPhones have ever had, there probably have been more using Skyhook than GPS, because for a while there was no iPhone hardware with GPS, plus a heck of a lot of those units are still in use today.

I really like how Skyhook works, both in phones and those SD cards for photo geotagging, but this guy is seriously deluded if he thinks its used more than GPS or is faster than A-GPS .

Posted by Muero on July 9, 2009 at 5:40 AM (PST)

6

I suspect that skyhook is used for anything where GPS accuracy is unnecessary.  Locations for twitter, yelp, weather, etc as well as any time an app asks for location but doesn’t have a view of the sky.

Posted by paanta on July 14, 2009 at 7:27 AM (PST)