iPhone GPS CLLocation lock?

How do I go about in an iPhone app, getting the user to click a button to find their location, with the CLLocation automatically locking or stopping when a good enough results is found after a few seconds?

Is there a function or an algorithm?

ie: if it finds a lo开发者_运维技巧cation with accuracy of 5m, stop, or stop after 15 seconds of trying.

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The LocateMe sample application is a good starting point.