libera_utils.kernel_maker.mechanism_quaternions

libera_utils.kernel_maker.mechanism_quaternions(angles: float | floating | ndarray | Series, axis: ndarray) → ndarray

SPICE scalar-first quaternions for rotation by each angle about axis.

q = [cos(theta/2), sin(theta/2) * axis] represents R(axis, theta), the mechanism frame’s rotation relative to its parent. Returns an (N, 4) array ordered (c, x, y, z).

Notes

The Az/El CK configs must declare FLIP SPICE QUATERNIONS (not plain SPICE QUATERNIONS) for these to load correctly. With FLIP, MSOPCK yields pxform(mechanism, parent) = R(axis, +angle); plain SPICE QUATERNIONS stores the transpose (the inverse rotation), which shows up as a large pointing error. This pairing of the scalar-first half-angle form with the FLIP declaration was pinned empirically against a controlled single-axis rotation, so the two must stay in sync.