Hi, all:

I wrote a post on interpolating quaternions with circular blending.

http://allenchou.net/game-math-series/

Circular blending is an interpolation technique that produces "quaternion curves" with C1 continuity, as opposed to the commonly used piece-wise slerp technique that has only C0 continuity.

Here's a video comparing the two techniques.

https://www.youtube.com/watch?v=rsx9BGZiX_E