Subject: On final text of BINTABLE proposal

From: [email-masked]
Date: Thu, 10 Mar 94 17:36:39 +0100

Garching, Mar. 10, 1994

Dear IAU-FWG members,
 I have the following comments on the BINTABLE proposal
(ref. Draft May 4, 1993, as available at fits.cv.nrao.edu
/fits/documents/proposals/: 145877 May 18 16:29 bintable2.ps):

 1) page 3, point 9, par. 2:
    'The number of bytes determined .. should equal NAXIS1 but
     NAXIS1 should be used as the definition of the actual length
     of the row.'

     This statement is vague. It only 'suggests' that the sum of
     TFORM's is equal to NAXIS1 and does not state the exact
     rule for decoding if they are not. There are two options:
      A) clearly to state that they must be equal! (It should be
         possible to write a program which does it correct). 
      B) maintain the option of having them different in which case
         a sentence must be added to specify the decoding rule e.g.
         the columns which storage exceed NAXIS1 are regarded as NULL
         columns.
     I would prefer option A.

 2) page 4, point 2:
     The sentence 'The default value for EXTVER should be 1' should
     be added in conformance with the general rules for extensions.

 3) page 5, point 12:
     With reference to the discussion of the usage of the keyword
     AUTHOR (i.e. only for the human author who compiled the data
     and not the program which wrote the file), a sentence of
     clarification should be added (or duplication from the ASCII
     table definition).

 4) page 5, point 1:
     The action or meaning of other characters that T,F and NUL
     should be defined. The three main options:
      A) abort decoding - non-conforming data set!
      B) treat value as invalid value,
      C) treat value as false
     I would prefer option B.

 I recommend that the above mentioned clarifications are implemented
in the final proposal if both authors and IAU-FWG members agree.

Best regards,

Preben Grosbol
Chairman, IAU FITS WG

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From: [email-masked] (Bill Cotton)
Date: Mon, 14 Mar 94 08:18:43 EST

I have the following responses to Preben's comments (10 Mar 94) on
the binary table draft:

1) Possible ambiguity between NAXIS1 and the sum of the TFORMs. 
   The reason this was originally left vague was that it allowed a way
to pad a row to a "magic" number of bytes in a simple way.  Since
there is a proper way to do this (given in Section 5, page 5) it's not
really necessary to allow NAXIS1 and the sum of the byte counts from
the TFORM to differ.  Thus, I would agree with Preben's option A and
suggest that the last sentence of point 9, page 3 read:

"The number of bytes determined from summing the TFORMnnn values must
equal NAXIS."

2) The default value of EXTVER should be 1.
   I agree.

3)  Usage of AUTHOR.
   I agree with Preben and suggest the following sentence be added to
point 12, page 5.

"This is the human or organization that collected the information
given in this table."

4) What do logical values other than "T", "F" or NULL mean?
   There shouldn't really be any values other than these three and if
there are then probably something went wrong in the FITS writer.  I
think any other values should be disallowed and that the following be
added to the end of point 1, page 5:

"Any other values are illegal."

(I would also agree to Preben's option A, consider other values
undefined or equivalent to NULL but I think option C, any other value
= false, is a bad idea.)

-Bill Cotton