[fitsbits] Associating a string with each plane in a cube {External}

[Dubois-Felsmann, Gregory P.]

Dear colleagues,

Before I consider inventing something from scratch, I'd like to ask:

Is there an existing convention that would allow associating a string with each plane in a FITS cube?  (This would have the semantics of a label to be displayed in a client.)  For us, this would be in the context of a FITS file where the cube was just one of a number of other extensions, including 2D images with dimensions different from the cube, and binary tables.

If I did invent something from scratch, I might look at piggybacking on the way a lookup-table WCS might work for the third axis of the cube:

A lookup-table following the standard for, say, CTYPE3='WAVE-TAB' would use an association between the cube extension and a binary-table extension (via the prescribed header-keyword references), and then the lookup table would be expressed as two columns of a one-row table, one column for the pixel coordinates (optionally) and one for the wavelength values as a single array-valued cell.  I could imagine adding another column to the table that had an "array of strings" type, and putting the plane labels there.  But of course there's nothing in the standard that would tell a client to actually look at such a thing.

So if there's prior art there, I'd very much like to hear about it.

If not, you may be seeing a "convention" document from me about this one of these days.

Many thanks,
Gregory

--
Gregory Dubois-Felsmann, Ph.D. | Senior Staff Scientist | Caltech/IPAC
Science Platform Scientist, Vera C. Rubin Observatory
Pipeline System Designer, NASA SPHEREx mission
Mail Code MR 100-22 | Pasadena, CA 91125-2200 | gpdf at ipac.caltech.edu