[fitsbits] Strange FITS File

[William Pence]

One of the scientists who worked on the ASCA X-ray satellite mission
recognized this file as being a calibration file generated for that mission
in 1994.  It is available from:

ftp://legacy.gsfc.nasa.gov/caldb/data/asca/gis/bcf/rti_gis_1024_040693.fits

That extra blank FITS block at the end of the file was not intentional and
was the result of a processing or software glitch.  More recent files of
that type don't have that extra block.  Fortuitously, this meets the
requirement of a FITS 'special record', but that was not the intention.

Has any observatory or mission ever intentionally created FITS files
containing special records?  I never really understood the purpose of
special records.  Would it be prudent to deprecate special records before
someone abuses this large loop-hole in the definition of what constitutes a
FITS file?

Bill Pence

Chris Lawton wrote:
> 
> I have a FITS file with an unexpected file size. The file has a Primary HDU
> with 5 Card Images and no data.  It also has a Binary Table with 1024 rows, 3
> fields in each row, and 2 bytes per field. So I calculate the file size to be:
> 
> Primary Data
>         5 Card Images               400 bytes  => 2880 bytes
>         No Data                       0 bytes
> Binary Table
>         45 Card Image:              3600 bytes => 5760 bytes
>         1024 Rows, 3 Fields, int16: 6144 bytes => 8640 bytes
> 
> Expected File Size = 17280 bytes
> 
> However, the actual file size is 20160 (2880 more than expected).
> 
> Is it common for fits files to be padded like this?
> 
> FV can read this file.  I've compared the card images read by my reader to the
> cared images read by FV - no difference.  The problem my reader has is after it
> reads the Primary HDU and then Binary Table (and reads the values correctly),
> it tries to read another extension because the file pointer is is not at the
> end of the file.  However, no extension exists, just padding.  I've been
> through the fits standard and can't find anything obvious that I've missed. Any
> thoughts?
> 
> I'd be happy to share the file.  I can't recall exactly where I got it, but it
> may have been a sample image with FitsView or another file reader (the file
> name is rti_gis_1024_040693.fits).
-- 
____________________________________________________________________
Dr. William Pence                          William.D.Pence @ nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
Greenbelt MD 20771                         +1-301-286-1684 (fax)