Gyro CMAttitude pitch, roll and yaw angle problems - iphone

Question

I have a problem getting pitch, roll and yaw angles from CMAttitude class.
First, I did a normal Gyro using 'CMMotionManager' class and atributes x,y,z and worked fine.
Then, I tried to use CMAttitude for "absolute angles", but I doesn't work because It seems that is not updating data. Angles are always 0 (but the isn't errors or warnings)
I have searched a lot in stackoverflow, and used some solutions I find, but I have the same problem.
Here's my code:
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
motionManager = [[CMMotionManager alloc] init];
CMDeviceMotion *deviceMotion = motionManager.deviceMotion;
CMAttitude *attitude = deviceMotion.attitude;
referenceAttitude = attitude;
[motionManager startGyroUpdates];
timer = [NSTimer scheduledTimerWithTimeInterval:1/30.0
target:self
selector:#selector(doGyroUpdate)
userInfo:nil
repeats:YES];
}
-(void)doGyroUpdate {
//cambia el frame de referencia
[motionManager.deviceMotion.attitude multiplyByInverseOfAttitude: referenceAttitude];
double rRotation = motionManager.deviceMotion.attitude.roll*180/M_PI;
double pRotation = motionManager.deviceMotion.attitude.pitch*180/M_PI;
double yRotation = motionManager.deviceMotion.attitude.yaw*180/M_PI;
NSString *myString = [NSString stringWithFormat:#"%f",rRotation];
self.angYaw.text = myString;
myString = [NSString stringWithFormat:#"%f",pRotation];
self.angPitch.text = myString;
myString = [NSString stringWithFormat:#"%f",yRotation];
self.angRoll.text = myString;
}
Thanks a lot! :D

Answer 1

motionManager has 4 modes: Accelerometer, Gyroscope, Magnetometer and Device motion.
Depending on which one you need, you need to start appropriate mode: startAccelerometerUpdates, startGyroUpdates, startMagnetometerUpdates or startDeviceMotionUpdates.
You are starting startGyroUpdates but reading deviceMotion property. In your case only gyroData will be available.
do this instead and you will be getting the deviceMotion data:
[motionManager startDeviceMotionUpdates];