Will iPhone location accuracy go beyond the call of duty?

If I set my CLLocationManager's desired accuracy to be kCLLocationAccuracyKilometer (accurate within a kilometer) will the iPhone deliver a better position eventually, when it gets it ? Or will it s开发者_StackOverflow社区top at my desired accuracy. I can't find this in the documentation.

The idea is that I need a fast fix for the location, but then I would like to go more accurate. Will I have to code this myself, or is it done for me automatically ?

I don't know if the following is 100% correct, but I am pretty sure it works like this: the accuracy filters are primarily designed to save energy. So if you specify that kCLLocationAccuracyKilometer is enough for you and the OS is pretty certain that it can locate you accurately within 1 km using triangulation only, it won't even power up the battery-draining GPS unit. So regarding your first question, the location manager will stop as soon as it reaches your desired accuracy.

Regarding the second question: I don't think the accuracy filter has any influence on the time you receive your first location update. The OS often caches your last known location and will deliver that one almost instantly even if you have specified a very high accuracy. Subsequent location updates will get more and more precise.

You should be able to easily test for yourself if this is indeed the real behavior.

Set the best accuracy you need (but not more, because location services consume too much power). LocationManager will call didUpdateToLocation of your CLLocationManagerDelegate every time accuracy is improved. Stop updating location as soon as you can to prevent battery exhausting.

No, it will stop at the specified accuracy. If you request only kCLLocationAccuracyKilometer then the GPS receiver won't be powered on and it will get no better than WiFi or Cell tower triangulation. [The only exception would be if another app in the background (like TomTom nav) already has the GPS on for high accuracy fixes, then you might get the high (<300m) accuracy fixes too).

If you want better you have to request it and you might as well request it immediately, you'll get the fast fix (1000m accuracy) fix right away and in a minute or two you'll get the high accuracy GPS fix (well, it can take 30 seconds up to 10 min depending on several things). No special coding is required, just specify the accuracy you eventually want.