Cards and metacards
Keywords: class-herschel-fits

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Cards and metacards

In this document, we refer to 2 concepts in the FITS context:

- header cards. In the FITS standard, an header card has the form:

        CALVERS = 'HIFI_CAL_22_0'      / HIFI calibration version

  with an 8-characters key, a value, and a comment. In this document, we abusively refer to e.g. ``the card `CALVERS`'' as ``the value in the card which key is `CALVERS`''.

- header metacards. Not in the FITS standard, we refer as metacards when encoutering in the FITS header a pair of lines (contiguous or not, ordered or not) with the form:

      META_10 =    62.39999999999999 / [s]
      HIERARCH  key.META_10='integrationTime'

  i.e. a standard card and a `HIERARCH` (free-form) line. We can see that these 2 lines provide an indirection through a `META_XX` key (`XX` being a non-ambiguous number). In this case, we abusively refer to e.g. ``the metacard `integrationTime`'' as ``the value in the card which key (`META_10`) has the value `integrationTime` in the associated `HIERARCH` line''. Thanks to the metacards, case-sensitive keywords not limited to 8 characters can be used. There is also no need to refer to the exact `META_XX` name in the subsequent specifications, i.e. `XX` can vary from one file to another.

Next: Acknowledgements Up: Technical details Previous: FITS level Contents