iphone - Using the Device motion instead of Accelerometer, Gyroscope and Magnetometer

Question

If I'm on iOS4, not using a specific handler, and needing the same update interval, what is the difference using the Device motion instead of specific Accelerometer, Gyroscope and Magnetometer updates ?

What happens if one of those 3 features is not available on the device if I use the Device motion ?

I mean, what will return deviceMotionAvailable if one of those feature is not available ?

Answer 1

In iOS 4 the magnetometer is not yet included in device motion API but handled by CLLocationManager (this changed in iOS 5). So if you have a gyro and an accelerometer, deviceMotioAvailable will return true independent of magnetometer. On the other hand if the gyro is missing you will always get false and you need to stay with accelerometerData.

Because Device Motion has one timestamp for both sensors, you will get reliable interpolated values for both sensors. Otherwise Device Motion wouldn't be able to do sensor fusion, the main advantage why this is the preferred way.

You can not rely on a fix frequency for CLLocationManager. didUpdateHeading is called whenever the system 'thinks' it should be. To get the different time coordinates between CLLocationManager and CMDeviceMotion normalised, you can have a look at NSTimeInterval to unix timestamp