Is there a formula to convert a quaternion to an angle?
Looking to do something on the iPhone using the Core Motion API and the gyro so that based on data I receive from it (in the form of quaternions) I can project a UIView on the screen.
Thanks
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3Does this do it? It's math, not code, but you can probably make the leap from one to the other. http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles – FrustratedWithFormsDesigner Sep 29 '10 at 20:28
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Yes, see Quaternions and spatial rotation. The unit quaternion (w, x, y, z) represents a rotation about the axis (x, y, z) of an angle of 2*cos-1(w).
Note that this is only true of unit quaternions. Non-unit quaternions do not represent rotations.
Adam Rosenfield
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Is this going to give me both the horizontal and vertical angles? Again, I'm working with an iPhone 4 and try to project a UIView on to the screen based on how the phone is being held. thanks – wgpubs Sep 29 '10 at 21:17
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Also note, that you need to use the *absolute value* of w to get the minimal angle. – quasi Jun 27 '22 at 13:30