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Registered FITS Convention
The Substring Array Convention for Binary Tables
- Description: The substring array convention may be used to specify that a character array field (TFORMn = 'rA') consists of an array of either fixed-length or variable-length substrings within the field. This convention utilizes the option described in the FITS Standard to have additional characters following the datatype code character in the TFORMn value field. The full form for the value of TFORMn within this convention is
'rA:SSTRw/nnn'
and a simpler form that may be used for fixed-length substrings only is
'rAw'
where
- r is an integer giving the total length including any delimiters (in characters) of the field,
- A signifies that this is a character array field,
- : indicates that a convention indicator follows,
- SSTR indicates the use of this ``Substring Array'' convention,
- w is an integer $\leq$ {\tt r} giving the (maximum) number of characters in an individual substring (not including the delimiter), and
- /nnn if present, indicates that the substrings have variable-length and are delimited by an ASCII text character with decimal value nnn in the range 032 to 126 decimal, inclusive. This character is referred to as the delimiter character. The delimiter character for the last substring will be an ASCII NUL.
To illustrate this usage:
- '40A:SSTR8' signifies that the field is 40 characters wide and consists of an array of 5 8-character fixed-length substrings. This could also be expressed using the simpler form as '40A8'
- '100A:SSTR8/032' signifies that the field is 100 characters wide and consists of an array of variable-length substrings where each substring has a maximum length of 8 characters and, except for the last substring, is terminated by an ASCII SPACE (decimal 32) character.
- Submitted: 24-Mar-2009 by W. Pence, NASA/GSFC
- Registered: 22-Sept-2009
- Date and Place of First Usage: circa 1996
- Extent of Usage: The simpler 'rAw' form of this convention has been supported by the CFITSIO library since 1996 and has been used in some publicly distributed FITS files produced by various projects. The longer 'rA:SSTRw/nnn' form has rarely been used, and, as far as currently known, never for arrays of variable-length strings.
- Full Documentation: PDF format, Postscript format
- Comments and/or critiques:
- Sample FITS File: chandra_caldb.fits: a calibration index file generated by the Chandra mission. The 7th column in the table has TFORM7 = '630A70 '.
- Sample Header Listing: chandra_caldb.txt
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