[fitsbits] Packed binary values

Mike Nolan a écrit :
We're trying to data formats a new spectral instrument. It will produce
binary tables in a vaguely SDFITS-like format, with a table column
that contains a data array. The array will have multiple axes: time,
frequency, polarization, etc., usually with only the frequency axis
being nondegenerate, with table rows generated (say) once per second.
At moderate data rates, the header information changes slowly compared
to the spectral dump rate, and the time axis may become nondegenerate
within a record. However, at the highest data rates packed binary data
(say 2 bits per sample) will have to be stored, and we're trying to figure
out how to best describe those in a way consistent with "principle of
least astonishment". Do others have experience or suggestions with this?

If you need that functionality, and as long as you can live
with integer number of bits per sample, I'd say that using
BITPIX=2, 3, 4 is probably the least disruptive path. It certainly
isn't standard (at least for now ;-)), but well written readers
will hopefully have graceful failures on that construct, and the
intent should be reasonably clear to all (modulo the signed/unsigned
ambiguity). Setting SIMPLE = F would perhaps be a good idea,
though ;-).

If you'd also need to store 1.5 bit per sample (3 level sampling) and
the like, then I'd have no useful suggestion...