Specify the measured collimation offset of the feed.

Arguments:

Double collim

The component of the collimation offset of the feed that is perpendicular to the elevation great circle on the sky. Positive values for this parameter indicate that the target encoder azimuth must be increased by the specified value to point the feed at the target topocentric azimuth.

Example:

The following example tells the control system that to point at a topocentric azimuth of az degrees, it must actually make the telescope azimuth encoder read az + -0.1109/cos(el) degrees.

  cal_collimation -0.1109

Context:

It would be difficult to precisely line up the optic axis of the receiver with the optic axis of the telescope. The misalignment can be split into two orthogonal components, one parallel to the direction of increasing elevation, and one perpendicular to this on the sky. The component in the direction of increasing elevation is corrected by the elevation offset and flexure terms of the pointing model. This leaves the misalignment perpendicular to the direction of increasing elevation, which can be specified by the command described above. In general this parameter is determined by fitting the pointing model to a large number of pointings on point sources evenly distributed around the sky.