CoreMotion wont give me roll, pitch and yaw

Question

sBefore UIAccelerometer was deprecated from iOS I used the data from x, y and z from this class to calculate pitch, roll and yaw. I also had to do some filtering, but now I see that with the CoreMotion library I can get these data from the CMAttitude class and would really like to use these properties, but somehow I fail to do so.

Now, what I have done is to instantiate

CMMotionManager *motionManager;
CMDeviceMotion  *deviceMotion;
CMAttitude      *attitude;
...
deviceMotion    = motionManager.deviceMotion;
attitude        = deviceMotion.attitude;

motionManager.accelerometerUpdateInterval = 0.065; // 65ms
[motionManager startAccelerometerUpdates];

I am able to read x,y and z from motionManager.accelerometerData.acceleration.<x,y or z> but trying to read from attitude.<roll,pitch,yaw> gives me 0.

NSLog(@"Roll: %f", attitude.roll); // = 0

I read out the values in a method triggered by a continous timer each 100ms.

Any ideas on what I`m missing?

Answer 1

In order to use deviceMotion.attitude you have to call [motionManager startDeviceMotionUpdates].

startAccelerometerUpdates provides accelerometer data only like startGyroUpdates will give you gyroData. Note that device motion data is more than just accelerometer and gyro data as both of them will be combined (sensor fusion) to achieve more precision.