9-axis sensor fusion implementation DT0058& DT0060

[TIENHUA]

Hi Sir,

1. Regarding Initialization (Absolute Orientation)In my application, I need to obtain an absolute orientation (Roll, Pitch, and Yaw) relative to the Earth's frame. Is my understanding correct that the Initial Quaternion must be computed using both Accelerometer and Magnetometer data (as per DT0058 Step 4) to establish the starting reference?Since the gyroscope only measures angular rates, is it true that a 6-axis (Acc+Gyro) initialization alone cannot provide an absolute Yaw/Heading reference?
2. Regarding DT0060 Step 2 I would like to confirm the definitions and implementation of the mixing process:

Q1 Definition: Is Q1 the "dynamic quaternion" that is updated via gyroscope integration in Step 1?
Q2 Definition: Is Q2 the "reference quaternion" calculated from the accelerometer and magnetometer data, used to correct the drift of Q1?
Weighting Parameter (alpha): For a handheld device, what is the recommended range for the alpha parameter in the formula Q = Q1*alpha + Q2*(1-alpha) to achieve a good balance between responsiveness and drift rejection?

[Federica Bossi]

Hi @TIENHUA ,

Yes, to obtain an absolute orientation (Roll, Pitch, Yaw) in the Earth frame, the initial quaternion must be computed from accelerometer + magnetometer (as described in DT0058). A 6‑axis (Acc + Gyro) system cannot provide an absolute yaw/heading reference, because the gyroscope only measures angular rate and yaw would drift without the magnetic field (or another absolute reference).

Q1 is the dynamic quaternion produced by integrating gyroscope data (Step 1).

Q2 is the reference quaternion computed from accelerometer + magnetometer at each step, used to correct drift.