I saw it in the BNO08X Datasheet : The rotation vector provides an orientation output that is expressed as a quaternion referenced to magnetic north and gravity.BNO08X Datasheet

In magnetic north and gravity, which is the X-axis and which is the Y-axis? Do the coordinate systems they construct conform to the right-hand rule? Does the quaternion output by IMU represent the orientation (rotation) in this coordinate system?When located in the sewer, is the Rotation Vector data output by this IMU reliable and will the accuracy decrease?

thanks

Hi,
the BNO08X gives you orientation relative to magnetic north and gravity by default:

  • X points toward magnetic north, Y points east, Z points down (aligned with gravity) and the quaternion follows the right-hand rule.

In places like sewers, the magnetometer can be affected by interference (metal pipes, etc.), so yaw (heading) may become less accurate. Pitch and roll usually stay reliable since they mostly depend on accelerometer and gyro data.

Best,
Lovro

    lovro

    The first question: If the IMU rotation vector is converted into a Rotation Matrix (R), is this Rotation Matrix the attitude of the IMU accelerometer coordinate system in the magnetic North Pole and the gravitational coordinate system?

    In the second question: Before using this IMU to output the rotation vector, is it necessary to calibrate the IMU?

    The third question: I hope to obtain the gravitational direction of the drone when working in the sewer. Can I directly obtain the gravitational vector from the IMU?

    The fourth question: What is the Accuracy (rad) output by running the demo program？

    ~/depthai-python/examples$ python3 imu_rotation_vector.py
    Rotation vector timestamp: 0.000 ms
    Quaternion: i: 0.089355 j: 0.355103 k: 0.034058 real: 0.929932
    Accuracy (rad): 3.141602
    Rotation vector timestamp: 3.601 ms
    Quaternion: i: 0.088928 j: 0.354004 k: 0.036560 real: 0.930298
    Accuracy (rad): 3.141602
    Rotation vector timestamp: 6.231 ms
    Quaternion: i: 0.094604 j: 0.344543 k: 0.040955 real: 0.933105
    Accuracy (rad): 3.141602

    thanks