crv2quat

Converts a Cartesian rotation vector,

\[\vec{\psi} = \psi\,\mathbf{\hat{n}}\]

into a “minimal rotation” quaternion, i.e. being the quaternion, \(\vec{\chi}\), defined as:

\[\vec{\chi}= \left[\cos\left(\frac{\psi}{2}\right),\, \sin\left(\frac{\psi}{2}\right)\mathbf{\hat{n}}\right]\]

the rotation axis, \(\mathbf{\hat{n}}\) is such that the rotation angle, \(\psi\), is in \([-\pi,\,\pi]\) or, equivalently, \(\chi_0\ge0\).

param psi:Cartesian Rotation Vector, CRV: \(\vec{\psi} = \psi\,\mathbf{\hat{n}}\). type psi:np.array returns:equivalent quaternion \(\vec{\chi}\) rtype:np.array