JCMT Pointing - model parameters

1. the amount by which the main azimuth axis points north of the vertical (which is the equivalent of the TPOINT parameter AN)
2. the amount by which the main azimuth drive is east of the vertical (AW)
3. the amount by which the elevation axis and azimuth axis deviate from perpendicularity - specifically the amount by which the right-hand end of the elevation axis points above the horizontal (NPAE)
4. the amount by which the telescope beam and the elevation axis deviate from perpendicularity - specifically the amount by which the beam points right of the perpendicular to the elevation axis (the amount by which it points up or down is taken up in parameter 6) (CA)
5. the azimuth encoder zero-point - the encoder reading at true azimuth = 0 degrees (north) (IA)
6. the elevation encoder zero-point - the encoder reading at true horizontal (IE)
7. the flexure in the secondary mirror structure - the amount by which the secondary mirror droops below the geometric axis of the primary when the elevation = 0 degrees. (TF)

There are sign convention differences between the old FIT9 and the new TPOINT models.

The impact of errors in these 7 parameters affect the pointing in systematic ways shown graphically here.

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