I have posted a question How can I get horizontal rotation angle whatever device orientation?

Please see the origin post to get the image of the direction of x, y and z axis.

  • pitch: a pitch is a rotation around x-axis
  • roll: a roll is a rotation around y-axis
  • yaw: a yaw is a rotation around z-axis

When mobile phone is portrait, like the image showing, x-axis is horizontal and y-axis is vertical. So I can get horizontal angle by using the roll. (I can get a quaternion anytime when mobile rotating, then I can convert the quaternion to euler angle.)

But when mobile phone is landscape, x-axis is vertical and y-axis is horizontal. The roll is no more horizontal angle. So I don't know how to get is. I have tried to exchange x and y in the quaternion but no worked.

How can I get the horizontal angle? Is there a unified formula to produce the quaternion or rotation matrix?


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