pytransform3d.rotations.compact_axis_angle

pytransform3d.rotations.compact_axis_angle(a)

Compute 3-dimensional axis-angle from a 4-dimensional one.

In a 3-dimensional axis-angle, the 4th dimension (the rotation) is represented by the norm of the rotation axis vector, which means we transform \(\left( \boldsymbol{\hat{e}}, \theta \right)\) to \(\theta \boldsymbol{\hat{e}}\).

We usually assume active rotations.

Parameters:

aarray-like, shape (4,)

Axis of rotation and rotation angle: (x, y, z, angle).

Returns:

aarray, shape (3,)

Axis of rotation and rotation angle: angle * (x, y, z) (compact representation).