CMMotionManager: Device Calibration does not work on a real device

Question

I've a strange behavior with CMMotionManager. I try to calibrate the position of my device to enable my App to support multiple device orientations.

When I debug my App on a real device (not in Simulator), everything is working fine. When I run the same App without debugging, the calibration does not work.

Here's my code:

static CMMotionManager* _motionManager;
static CMAttitude* _referenceAttitude;

// Returns a vector with the current orientation values
// At the first call a reference orientation is saved to ensure the motion detection works for multiple device positions
+(GLKVector3)getMotionVectorWithLowPass{
    // Motion
    CMAttitude *attitude = self.getMotionManager.deviceMotion.attitude;
    if (_referenceAttitude==nil) {
        // Cache Start Orientation
        _referenceAttitude = [_motionManager.deviceMotion.attitude copy];
    } else {
        // Use start orientation to calibrate
        [attitude multiplyByInverseOfAttitude:_referenceAttitude];
        NSLog(@"roll: %f", attitude.roll);
    }
    return [self lowPassWithVector: GLKVector3Make(attitude.pitch,attitude.roll,attitude.yaw)];
}

+(CMMotionManager*)getMotionManager {
    if (_motionManager==nil) {
        _motionManager=[[CMMotionManager alloc]init];
        _motionManager.deviceMotionUpdateInterval=0.25;
        [_motionManager startDeviceMotionUpdates];
    }
    return _motionManager;
}

score 0 · Accepted Answer · answered Apr 27 '14 at 12:52

I've found a solution. The issue was caused due the different timing behavior between debug and non debug mode. CMMotionManager needs a little time for initializing, before it returns correct values. The solution was to postpone the calibration for 0.25 seconds.

This code works:

+(GLKVector3)getMotionVectorWithLowPass{
    // Motion
    CMAttitude *attitude = self.getMotionManager.deviceMotion.attitude;
    if (_referenceAttitude==nil) {
        // Cache Start Orientation
        // NEW:
        [self performSelector:@selector(calibrate) withObject:nil afterDelay:0.25];

    } else {
        // Use start orientation to calibrate
        [attitude multiplyByInverseOfAttitude:_referenceAttitude];
        NSLog(@"roll: %f", attitude.roll);
    }
    return [self lowPassWithVector: GLKVector3Make(attitude.pitch,attitude.roll,attitude.yaw)];
}

// NEW:
+(void)calibrate  
      _referenceAttitude = [self.getMotionManager.deviceMotion.attitude copy]
}

CMMotionManager: Device Calibration does not work on a real device

1 Answers1