Predicting pointing errors from the track model

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Predicting pointing errors from the track model

The following notes accompany the program tracking.for in the [inclinometry.progs] directory on the summit. This program is designed to calculate the pointing errors in the absence of a track model.

Please read slowly . . .

MTUN025 (MTIN062) describes how the observed errors reflect the amounts by which the telescope must be moved from its commanded position to get `on-source' - ie

  daz +ve means that the telescope has been moved CW to reach source,
  del +ve ....................................... up ................

Based on the table in MTUN005 and the senses in MTUN025 sect 3., an activated track model with entries (F1,F2,F3) produces changes to the azimuth and elevation of the telescope of

roll(F2)*sin(el) - yaw(F1)*cos(el)
pitch(F3)

(on the sky), respectively. See the detailed consideration of the contribution of roll to these errors, for instance. Hence the pointing errors (daz,del) will be (or will change by) the negative of these, i.e. to

daz = - roll(F2)*sin(el) + yaw(F1)*cos(el)
del = - pitch(F3)

Pointing taken *without* the track model active will therefore show errors of

daz = roll(F2)*sin(el) - yaw(F1)*cos(el)
del = pitch(F3)

(Note added 980329)
It is clear however, that the sense of the model1 changes to az,el (and hence to (-daz,-del)) have not been correctly stated in MTUN025, and that, empirically, the effect of model1 (F1,F2,F3) being active is to make

daz = - roll(F2)*sin(el) + yaw(F1)*cos(el)
del = pitch(F3)

and that the negative of these

daz = roll(F2)*sin(el) - yaw(F1)*cos(el)
del = -pitch(F3)

are predicted for data taken without model1, which is what we want from this particular utility.

Iain Coulson
05 Nov 2004

Contact: Iain Coulson. Updated: Sat Nov 6 18:00:33 HST 2004

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