Pointing Origins (POs) are positions defined in the focal plane of the telescope (in units of mm in the X, Y plane). The telescope software (i.e. MAGIQ) will place the target coordinates at this point in the focal plane. In addition, for appropriate tracking modes (i.e. vertical angle mode), this defines the point around which stars in the field will appear to rotate.
Most (all?) instruments have a REF pointing origin which places the target The REF* pointing origin is defined on each guider. It is special in that it ties guider pixel coordinates to the XIM, YIM focal plane coordinates. When acquiring targets, the OAs will “adjust pointing” on the REF* PO. Adjust pointing updates the zero point of the telescope pointing model, called the CA/CE (collimations Az/El). The REF* PO is defined in a clear, easy to see position in the focal plane, so that the OAs can see the target (if it is bright enough of course) and perform any fine centering that is needed.
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