A Computational Analysis of Line-Oriented Screw Transformations in Robotics

This paper contains a computational analysis and comparison of various representations of a general rigid body spatial screw displacement. Point transformations and line transformations are treated separately. In the context of point transformations, only a brief summary of the known techniques (i.e., homogeneous transforms and quaternion/vector pairs) and their computational behavior is given. Among line transformations, which comprise the primary focus of this paper, four mathematical formalisms for effecting a general spatial screw displacement are presented and analyzed in terms of computational efficiency in performing (a) general screw displacements of lines, and (b) compositions of screw displacement operators. Both sequential and parallel algorithms are given for each operation. The four formalisms considered are: (1) dual orthogonal 3 x 3 matrix, (2) dual unit quaternion, (3) dual special unitary 2 x 2 matrix, and (4) dual Pauli spin matrices. The conclusion reached is that quaternion/vector pairs are the most economical of the point transformation operators, whereas dual unit quaternions represent the most compact and most efficient line transformation formalism.