[Comm2011] Log 2011-08-01; astrometry/rotator

[John P. McFarland]

Hi Koen,

Good to hear that at least part of the mystery is solved.  Once the fixes 
come in, let's hope there are no more surprises.  In addition to the rotator 
issue, I was wondering if the rotation asymmetry found by Armin may play any 
further role.  I have assumed that the offset of ~2000 pixels in both X and 
Y is currently compensated for by the pointing model, but I don't know if 
there is anything more to do about it from your point of view.  Please let 
me know what your ideas are concerning this.  Thanks!

Cheers,


-=John


On Tue, 2 Aug 2011, Konrad Kuijken wrote:

> The snow melted away, the wind dropped, the temperature went up to a 
> toasty 10 degrees, and we have been open since about 10pm.  Main priority 
> was to get the automatic acquisition of guide stars to work.
>
> In the process of that we may have found why the astrometric solutions 
> just would not converge. There appears to be a 1-deg backlash in the 
> instrument rotator of the vst, which means that depending on the direction 
> of motion the sky orientation can differ by a degree. No wonder it was 
> turning out to be difficult to predict where the guide stars would fall! 
> Half the time the solution was good, half the time the errors in the 
> predicted positions were over 100 pixels.
>
> An unpleasant surprise, but progress nonetheless. Pietro and Javier are 
> working on a solution... let's see.
>
> K
>
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