Direction of Attitude Quaternion

[manumerous]

Out of the log file I get a quaternion q = [q0, q1, q2, q3]. If I convert this quaternion to a rotation matrix do i get the rotation from the body to the world frame or vise versa?

Is there some documentation about that somewhere? I Somehow didn't find any.

[Jaeyoung-Lim]

@manumerous I believe it is following the mavlink spec: https://mavlink.io/en/messages/common.html#MAV_FRAME

Also this might help? https://docs.px4.io/master/en/ros/external_position_estimation.html

[manumerous]

Okay thanks. I found multiple mavlink message types containing quaternions. Unfortunately no of them explains anything about what kind of quaternion it is, exept that it is related to the aeronautical frame.

I would expect that the quaternion related the NED world frame (MAV_FRAME_LOCAL_NED i guess?) to the body frame (MAV_FRAME_BODY_FRD). Am I right here? Did I miss something in the specs?

[Jaeyoung-Lim]

Probably with MAV_FRAME_BODY_NED? but you can verify this by looking at the data. You can look at the direction of acceleration which should be aligned with the z axis most of the time

[manumerous]

Wouldn't the quat be equivalent between MAV_FRAME_BODY_NED and MAV_FRAME_LOCAL_NED? As far as I understood they only differ in translation and not orientation.

Not sure how I can determine the direction of the quad from the acceleration in z direction. Would you maybe have time for a quick sync this afternoon?

[Jaeyoung-Lim]

Sure, I am available before 3

the two framea are not equivalent

The local origin is set when you arm and the ned actually points to north east down while body is attached to the fmu

[manumerous]

Solving this issue was outsourced to:

https://github.com/PX4/PX4-Autopilot/issues/17347