Harauz, G. Representation of rotations by unit quaternions Ultramicroscopy, 1990, 33, 209-213
A closed form solution by Horn of an absolute orientation problem in photogrammetry and robotics entails the equivalent expression of rotation matrices by unit quaternions [B.K.P. Horn, J. Opt. Soc. Am. 4 (1987) 629]. Such representation by quaternions offers practical advantages in electron microscopy of macromolecular structures, where rotation angles must also be determined by optimisation techniques.
Angular representation, Euler angles, Rotation matrix