1. Proposed Changes to the FITS Data Format
and the FITS Standard Document
IAU FITS Working Group Technical Panel:
W. Pence, L. Chiappetti, C. Page, R. Shaw, and E. Stobie
Summary
Purpose of this Update
Major changes to update and clarify the FITS Standard definition document are now being considered by the IAU FITS Working Group. This poster lists the most significant of the more than 500 individual changes to the wording of this document that have been proposed. The proposed new document is now available for public comment from the FITS Support Office Web site at fits.gsfc.nasa.gov. Please review the proposed changes, and send any comments or suggestions to the FITSBITS list, or to one of the technical panel members listed above, by October 12th.
Add material approved by the IAU FWG subsequent to the last major update of the Standard in 1999 (e.g. MIME types).
Add material from the approved journal papers on World Coordinate Systems.
Add new requirements and recommendations as needed.
Clarify questions raised on FITSBITS in the past 8 years.
Adopt more precise language throughout.
Eliminate obsolete material.
Update references.
Reorganize sections into a more logical order.
Proposed Requirements Changes
Deprecate 'Special Records' at the end of a FITS file.
Character keyword values no longer need be padded to at least 8 characters long, as in TTYPE1 = 'TIME '.
Explicitly state that existing FITS files are exempt from subsequent new FITS requirements.
PCOUNT and GCOUNT keywords must immediately follow the last NAXISn keyword in all extensions.
EXTEND keyword is no longer required in the primary HDU of multiple HDU files.
EXTNAME, EXTVER, and EXTLEVEL keywords are no longer excluded from the primary HDU.
Embedded spaces in numeric ASCII table fields are not allowed.
Deprecate implicit decimal points in floating-point fields in ASCII tables.
Add the TDISPn keyword as a reserved keyword in ASCII tables, not just binary tables.
New Recommendations
New FITS extension types should only be created if existing types are inadequate.
The order of FITS keywords in a header should be preserved during data processing operations.
Keywords with a value should not be repeated within a header.
All table columns should have a name as given by the TTYPEn keyword.
Other Editorial Changes
New Introduction chapter gives a brief history of FITS and a revision history of the document.
Simplify and clarify the discussion of physical blocking and delete references to obsolete tape media.
Add clarification that keywords without an “= “ in bytes 9-10 should be interpreted like commentary keywords.
Clarify that there is no restriction on the magnitude or precision of keyword values or numeric values in ASCII tables (i.e., not limited to range of 32 or 64 bit reals).
New section describes recommended physical units strings, taken from WCS Paper I.
Expand the discussion on the use of BSCALE, BZERO, and BLANK keywords, especially with regard to unsigned integers. Similar text added for the TSCALn, TZEROn, and TNULLn keywords.
New chapter provides tutorial on the meaning and use of WCS keywords.
Delete several obsolete appendices to the document.
Add new appendix describing FITS MIME types (text copied from RFC 4047)
Numerous typographical changes to the text for added clarity and emphasis.
Remaining Steps in the Approval Process
The Public Comment Period on the proposed changes closes in October.
Tech Panel produces new draft in response to the public comments.
The 4 Regional FITS Committees formally review and comment on the revised draft.
If necessary, further revisions will be made to address the Regional FITS committee comments.
Formal vote by the IAU FWG to approve the final draft as the new FITS Standard.
If there are no controversial issues that could delay matters, this approval process could be completed by early 2008.
Come to the FITS BoF, 19:30 Monday, to discuss current FITS issues.