Kim, Shin - A General Construction Scheme for Unit Quaternion Curves with
Simple High Order Derivatives

Kim and Shin's paper introduces a new form of unit quaternion curves in
SO(3) that share the same differential properties as spline curves and
explains a method of deriving these curves from a weighted sum of basis
functions represented in 3-space.  The purpose of their work is to improve
upon previous work done with quaternion curves, including finding a better
solution to the torque minimization problem (i.e. "finding a torque optimal
rotational path which connects the start and target orientations").  The
methods they use are extensions of previously defined quaternion curve
structures by representing quaternion curves in a new 'cumulative form' that
has several advantages over other quaternion curve representations.  I found
this paper difficult to understand without having any prior knowledge of
quaternion curves.