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On representing rotations by Rodrigues parameters in non‐orthonormal reference systems
Author(s) -
Morawiec A.
Publication year - 2016
Publication title -
acta crystallographica section a
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.742
H-Index - 83
ISSN - 2053-2733
DOI - 10.1107/s2053273316009426
Subject(s) - orthonormal basis , cartesian coordinate system , covariance and contravariance of vectors , orthonormality , rotation matrix , euler angles , lattice (music) , unit vector , mathematics , invariant (physics) , pure mathematics , coordinate system , mathematical analysis , geometry , physics , mathematical physics , quantum mechanics , acoustics
A Rodrigues vector is a triplet of real numbers used for parameterizing rotations or orientations in three‐dimensional space. Because of its properties ( e.g. simplicity of fundamental regions for misorientations) this parameterization is frequently applied in analysis of orientation maps of polycrystalline materials. By conventional definition, the Rodrigues parameters are specified in orthonormal coordinate systems, whereas the bases of crystal lattices are generally non‐orthogonal. Therefore, the definition of Rodrigues parameters is extended so they can be directly linked to non‐Cartesian bases of a crystal. The new parameters are co‐ or contravariant components of vectors specified with respect to the same basis as atomic positions in a unit cell. The generalized formalism allows for redundant crystallographic axes. The formulas for rotation composition and the relationship to the rotation matrix are similar to those used in the Cartesian case, but they have a wider range of applicability: calculations can be performed with an arbitrary metric tensor of the crystal lattice. The parameterization in oblique coordinate frames of lattices is convenient for crystallographic applications because the generalized parameters are directly related to indices of rotation‐invariant lattice directions and rotation‐invariant lattice planes.