This page is a little more information dense, but it's what I learned quaternions from (after bashing my head against it for a couple of weeks) and it's good as

This page is a little more information dense, but it's what I learned quaternions from (after bashing my head against it for a couple of weeks) and it's good as a refresher because it is so dense. http://www.tutis.ca/Rotate/7quaternions.htm http://www.tutis.ca/Rotate/7quaternions.htm One thing I didn't see in the OP's linked article is how to transform a quaternion into a different coordinate system defined by another quaternion. For example, suppose you have a spaceship in a game at an arbitrary orientation defined by Q1 which is a rotation away from a conventional "unrotated" orientation, and you want to input say 5 degrees of yaw to the right. Well, you just construct a quaternion Q2 that is 5 degrees yaw to the right from this conventional unrotated orientation, and you can use quaternion conjugation to transform Q2 into the orientation of Q1 where it can then be applied to the spaceship's orientation. OP's link mentioned quaternion conjugation, but didn't really mention what it was good for. It is described in section IV of the 7quaternions link.