scippneutron.conversion.beamline.beam_aligned_unit_vectors#

scippneutron.conversion.beamline.beam_aligned_unit_vectors(incident_beam, gravity)[source]#

Return unit vectors for a coordinate system aligned with the incident beam.

The unit vectors are

\begin{aligned} {\hat{e}}_{y} & = - g / | g | \\ z_{proj} & = b_{1} - (b_{1} \cdot {\hat{e}}_{y}) {\hat{e}}_{y} \\ {\hat{e}}_{z} & = z_{proj} / | z_{proj} | \\ {\hat{e}}_{x} & = {\hat{e}}_{y} \times {\hat{e}}_{z} \end{aligned}

where $b_{1}$ is the incident_beam and $g$ is the gravity vector. See the module-level docs of scippneutron.conversion.beamline for details.

Parameters:

incident_beam (Variable) – Beam from source to sample. Expects dtype=vector3.
gravity (Variable) – Gravity vector. Expects dtype=vector3.

Returns:

BeamAlignedUnitVectors – A dict containing the unit vectors with keys 'ex', 'ey', and 'ez'

Raises:

ValueError – If the incident beam is parallel to gravity. The rotation of the x-z plane is ill-define din this case.