[Comm2011] Astrometry header items

[John P. McFarland]

Hi Ewout,

I found in the headers for all OBJECT-type observations that the standard 
astrometry keywords indicate a pixel-based system with RA and DEC keywords 
added.  The keywords present and their values are as follows:

RA/DEC = telescope CRVAL1/2 values
CTYPEn = PIXEL
CRVALn = 1.0
CDELTn = 1.0
CRPIXn = original values for each chip
CDm_n  = <missing>

The HeaderTranslatorOCAM adds to the headers of the RawScienceFrames the 
nominal values from the expected parameters:

CTYPEn = RA,DEC--TAN
CRVALn = telescope RA/DEC values from header
CRPIXn = original values for each chip
CDm_n  = from chip schematic diagram

These last ones should nominally be set properly at the telescope, 
particularly the CDm_n values as these indicate the possibly variable 
position of the rotator with respect to the sky.

Cheers,


-=John


On Wed, 13 Apr 2011, E. M. Helmich wrote:

> Hi Andrea,
>
> During OCAM1A Thomas Szeifert mentioned that he thought there was a document 
> describing which header items related to astrometry must be present. Did he 
> get back to you on this, and can you inform us which header items will be 
> present?
>
> Regards,
> Ewout
>
> -- 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
> Drs. Ewout Helmich
> Kapteyn Astronomical Institute,
> Astro-WISE/OmegaCEN
>
> Landleven 12
> P.O.Box 800
> 9700 AV Groningen
> The Netherlands
>
> email: helmich at astro.rug.nl
> tel: +31(0)503634548
>
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
>