title: Understanding quaternions and axis angle representations
body: <p>I have a sensor that gives me a quaternion. I convert the quaternion to an axis-angle representation using <a href="http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToAngle/" rel="nofollow">http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToAngle/</a>. When I hold the sensor on a flat surface and rotate the sensor pressed against the flat surface, I would have expected the axis to be the same and the angle to vary from 0-360 degrees - but this does not happen (the axis varies significantly). Any ideas why? Maybe I don't understand the axis-angle representation?</p>