Per LCR-581:

To be added to LSE-30 (OSS):

Beam Projector Coordinate Relationship

Specification: Coordinate system transformations shall be measured
and/or computed relating the collimated beam projector position and
telescope pupil position to the illumination position on the telescope
optical elements and focal plane, and a software interface shall be
developed to represent these relationships, including their possible
evolution in time.

Justification:

This is necessary to facilitate the data acquisition and reduction. The
user shall be able to specify an LSST pupil and focal plane position for
a given spot, then have the CBP and telescope offset accordingly.
Similarily, the spot positions should be predictable based on the CBP
and telescope position.

This requirement will need to be flowed down appropriately to the Data
Management and Observatory Control System requirements documents. It is
assumed that Data Management will develop a Python interface that
represents the relationships, and that the Observatory Control System
will use those in the construction of the control system functions
relating to the collimated beam projector.

Note the requirements on DM above. These should be reflected in LDM-151.