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[fitsbits] Interpretation of repeat count in binary tables
Is the repeat count in TFORM descriptors provided purely for efficiency reasons, or does it have some implications for the logical structure of the data? Specifically, suppose we have NAXIS1 = 12288 / width of table in bytes NAXIS2 = 12288 / number of rows in table .... TFIELDS = 3 TFORM1 = '1024E' TFORM2 = '1024E' TFORM3 = '1024E' Should the three columns each be interpreted as a 1024 x 12288 element 2-D array, or as a 12582912-element 1-D array? The first implies that if TFORMn = 'rTa', the default value of TDIMn = '(r)'. The second implies that if TDIMn is not explicitly specified then the repeat count is just provided for (rather spurious) efficiency reasons. Some FITS writers certainly use it as such. This question arises out of pure ignorance, but I have failed to find an answer in either the original binary table paper (Cotton et al 1995) or the current (2.0) or draft (3.0) FITS standards. In fact, none of these documents give any hint as to what the repeat count is for (unless TDIMn is explicitly present, or it is a character field). regards, Paddy ================================================== ==== Dr J. P. Leahy, Jodrell Bank Centre for Astrophysics, Current address: Osservatorio Astronomico di Trieste INAF, Via GB Tiepolo 11, 34143 Trieste, Italy Tel.+39 040 3199160 Fax +39 040 309418 |
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