Shoemake's Animating rotation paper

Shomake shows how to use quaternions to interpolate between one or more
rotations. For a sequence of rotations, he shows how to construct a 
spline on the 4-D unit sphere to smoothly transition from one rotation 
to another.

His problem is one of interpolating between multiple arbitrary 
orientations. He solves it using a combination of quaternions for 
rotations and Bezier curves to combine rotations.

Key ideas: Rotations of objects are better represented by Quaternions 
than by Euler angles. Rotations can be combined using splines in 
quaternion space.

Contributions: Introduced quaternions to the graphics community.