qter2anax.m

Converts a quaternion representation of a rotation into angle-axis rotation parameters. The quaternion is first normalised to unit Euclidean length; the rotation angle is then 2*atan2(n,q.u), where n is the norm of the vector part, and the rotation axis is the vector part divided by n. When the vector part has zero norm, the rotation is the identity, and the function returns a zero angle about the [0 0 1] axis.

Syntax

    [rot_axis,rot_angle]=qter2anax(q)

Parameters

    q   -   quaternion, a structure with four fields
            q.u, q.i, q.j, q.k giving the four compo-
            nents of the quaternion

Outputs

    rot_axis  - cartesian direction vector as a row 
                with three real elements

    rot_angle - rotation angle in radians

Notes

See the notes on rotation conventions for the basic definitions of rotations in Spinach.

See also

euler2dcm.m, wigner.m, anax2qter.m, anax2dcm.m, axis_tsymm.m, dcm2euler.m, dcm2wigner.m, euler_sup.m, rotmat_align.m, rotor_stack.m, xyz2sph.m, Kernel_utilities

Version 2.13, authors: Ilya Kuprov