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FITS Binary Table Proposals
The FITS Working Group officially approved these 2 proposals in April 2005.
Proposal 1: Recommendation to Incorporate the "Variable-Length Array" Facility in Binary Tables into the FITS Standard
The "Variable-Length Array" FITS data format that is described in Appendix B.1 of the FITS Standard is now used by a number of major data analysis packages. Examples of current usage include the "Redistribution Matrix Files" (RMF), widely used in X-ray astronomy to store calibration information, and the pixel mask files used in the IRAF system. Many of the general software libraries for reading and writing FITS files that are documented on the FITS Support Office web site currently support this variable-length array format in FITS binary tables.Appendix B.1 is not an official part of the FITS Standard and is included in that document for informational purposes only. Because the implementations described above have now demonstrated the usefulness and importance of the Variable-Length Array Facility, it is recommended that Appendix B.1 be officially approved and incorporated into a new section number 8.3.5 of the FITS Standard, with the editorial changes shown in the draft PDF document. (Also available: a marked-up draft showing the changes from the current wording).
In addition, the following modifications to 3 sections of the FITS Standard are proposed to clarify the use of variable-length arrays:
- Section 8.3.2. TNULLn Keywords: Modify the 1st sentence from:
"The value field for this indexed keyword shall contain the integer that represents an undefined value for field n of data type B, I or J."
to
"The value field for this indexed keyword shall contain the integer that represents an undefined value for field n of data type B, I or J, or P array descriptor fields (section 8.3.5) that point to B, I, or J integer arrays."- Section 8.3.2, TDISPn Keywords: Replace the sentence,
"The meaning of this keyword is not defined for fields of type P in this standard but may be defined in conventions using such fields."
with,
"In the case of fields of type P, the TDISPn value applies to the data array pointed to by the array descriptor (section 8.3.5), not the values in the array descriptor itself."- Section 8.3.2, THEAP Keyword: Modify the 2nd sentence from
"The default value shall be the product of the values of NAXIS1 and NAXIS2."
to
"The default value, which is also the minimum allowed value, shall be the product of the values of NAXIS1 and NAXIS2."Finally, the current references to Appendix B.1 in the FITS Standard need to be replaced with references to the new section 8.3.5:
- Section 8.3.2, TSCALn Keywords: Replace the 3rd and 4th sentences,
"The interpretation for fields of type P is not defined. A proposed interpretation is described in Appendix B1."
with,
"The interpretation for fields of type P is defined in section 8.3.5."- Section 8.3.2, TZEROn Keywords: Replace the 3rd and 4th sentences,
"The interpretation for fields of type P is not defined. A proposed interpretation is described in Appendix B1."
with,
"The interpretation for fields of type P is defined in section 8.3.5."- Section 8.3.2, THEAP Keyword: replace the last sentence,
"A proposed application of this keyword is presented in Appendix B.1."
with,
"The use of this keyword is described in section 8.3.5."- Section 8.3.3.1, Array Descriptor: Replace the last 2 sentences,
"The meaning of these integers is not defined by this standard. The proposed application of this data type is described in Appendix B.1."
with,
"The meaning of these integers is defined in section 8.3.5."- Section 8.3.3.2, Bytes Following Main Table: Replace this entire section, which currently reads,
"The main data table shall be followed by zero or more bytes, as specified by the value of the PCOUNT keyword. The meaning of these bytes is not further defined by this standard. One proposed application is described in Appendix B.1."
with,
"The main data table shall be followed by an additional data area containing zero or more bytes, as specified by the value of the PCOUNT keyword. One use for this data area is described in section 8.3.5. This does not preclude other uses for these bytes."Proposal 2: Recommendation to Incorporate the "Multidimensional Array" Convention in Binary Tables into the FITS Standard
Appendix B.2 in the FITS Standard describes a "Multidimensional array" convention that uses the TDIMn keyword to define the dimensionality of arrays that are contained in binary table columns. Many FITS files now use this convention and contain the TDIMn keyword. Appendix B.2 is currently not an official part of the FITS Standard and is included in that document for informational purposes only. The widespread usage of the TDIMn keyword demonstrates the usefulness and importance of this convention, and thus it is recommended that the "Multidimensional array" convention described in Appendix B.2 be officially approved and incorporated into the definition of the TDIMn keyword in section 8.3.2 of FITS Standard with the editorial changes shown in the draft PDF document. (Also available: a marked-up draft showing the changes from the current wording).
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Last revised: Thursday, 13-Oct-2005 14:33:23 EDT
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