FITS headers

For historical reasons, IRCAM headers prior to ORAC were somewhat jumbled, disorganised, and some violated the FITS standard. The pipeline corrects, orders and structures the headers to help the human reader locate information quickly, and allow complete conversion to FITS.

For IRCAM, Michelle, and UFTI, even since ORAC came online, the raw headers do not provide a sky co-ordinate system. IRIS2 also has an incomplete sky co-ordinate system supplied in the raw headers. Using information in the raw headers, the pipeline creates a FITS world co-ordinate system using a tangent plane projection in the AIPS convention--this is quite adequate given the small fields of view--which it imports into the NDF's WCS component. Thus GAIA and KAPPA can display these co-ordinates on overlay grids and axes. For all these, such as KAPPA's display with axes, you may need to select the appropriate astrometric Frame like this.

 % wcsframe <your_NDF> frame=sky

where you substitute your NDF's name for <your_NDF>. The mosaics from the pipeline should already have the sky domain set. INGRID headers are also revised by the pipeline into an AIPS system.
[<instrument>/_CREATE_WCS_, <instrument>/_GET_PLATE_SCALE_]

Note that the reference pixel of the equatorial co-ordinates in the raw headers was until recently only known to a few arcseconds, but now should be of the order of 0.5 arcseconds. The pipeline sets empirical reference pixels now matched by the telescope control system; see primitive _CREATE_WCS_ for details. For critical work, you should tie in your frames with online catalogues, as available through GAIA.