634	CHAPTER 18: Where Am I? Finding Your Way with Core Location

The technologies that Core Location depends on are hidden from your application. We don’t tell Core Location whether to use GPS, triangulation, or WPS. We just tell it how accurate we would like it to be, and it will decide from the technologies available to it which is best for fulfilling your request.

The Location Manager

The Core Location API is actually fairly easy to use. The main class we’ll work with is CLLocationManager, usually referred to as the location manager. To interact with Core Location, you need to create an instance of the location manager, like this:

CLLocationManager *locationManager = [[CLLocationManager alloc] init];

This creates an instance of the location manager, but it doesn’t actually start polling for your location. You must create an object that conforms to the CLLocationManagerDelegate protocol and assign it as the location manager’s delegate. The location manager will call delegate methods when location information becomes available or changes. The process of determining location may take some time—even a few seconds.

Setting the Desired Accuracy

After you set the delegate, you also want to set the requested accuracy. As we mentioned, don’t specify a degree of accuracy any greater than you absolutely need. If you’re writing an application that just needs to know which state or country the phone is in, don’t specify a high level of precision. Remember that the more accuracy you demand of Core Location, the more juice you’re likely to use. Also, keep in mind that there is no guarantee that you will get the level of accuracy you have requested.

Here’s an example of setting the delegate and requesting a specific level of accuracy:

locationManager.delegate = self; locationManager.desiredAccuracy = kCLLocationAccuracyBest;

The accuracy is set using a CLLocationAccuracy value, a type that’s defined as a double. The value is in meters, so if you specify a desiredAccuracy of 10, you’re telling Core Location that you want it to try to determine the current location within 10 meters, if possible. Specifying kCLLocationAccuracyBest, as we did previously, or specifying kCLLocationAccuracyBestForNavigation (where it uses other sensor data as well) tells Core Location to use the most accurate method that’s currently available. In addition, you can also use kCLLocationAccuracyNearestTenMeters, kCLLocationAccuracyHundredMeters, kCLLocationAccuracyKilometer, and kCLLocationAccuracyThreeKilometers.

Setting the Distance Filter

By default, the location manager will notify the delegate of any detected change in the device’s location. By specifying a distance filter, you are telling the location manager

www.it-ebooks.info