[wfc] CHECKSUM Proposal

[William Pence]

Peter Teuben wrote:
> 
> Bob Seaman, Bill Pence and Arnold Rots have spiffed up the CHECKSUM proposal,
> and have submitted their new proposal for review. Please have a look at
>         http://heasarc.gsfc.nasa.gov/docs/heasarc/fits/checksum.html
> where you can find the proposal, including the old one, in HMTL and PS format.
> 
> As far as implementations, I believe CFITSIO is the only library that handles
> this proposal, unless somebody can confirm otherwise (the list of FITS I/O
> implementations is getting quite large now).

There have been several independent implementations of the CHECKSUM
procedure:

1.  There are two distinct operational implementations at NOAO, in addition
to Rob Seaman's original checksum tools that are still in use.

NOAO uses it on several "save the bits" servers in both hemispheres.
They have maybe three million images containing checksums.  There are
five STB systems at NOAO (including WIYN and NSO).  Keck and Lick
also use STB - probably one server each.  SOAR will use STB.

The IRAF foreign file encapsulation mechanism supports the checksum.
This is a building block of NOAO's pipeline processing design, which is
receiving renewed interest as they proceed with the NOAO Science Archive.

2.  The CHECKSUM algorithms are built into the CFITSIO library (supported by
the HEASARC).  Subroutines are provided in C and Fortran to a) compute and
write the CHECKSUM keyword in a file, b) update the CHECKSUM keyword if it
exists and is out of date, and c) verify whether the current CHECKSUM
keywords in a file are valid.  These routines provide the basis for the
'fchecksum' program that is distributed with the HEASARC ftools software
package.

3.  Arnold Rots wrote an implementation for use with the XTE X-ray satellite
data.  That code is now used for a few Chandra data products.

-Bill Pence
-- 
____________________________________________________________________
Dr. William Pence                          pence at tetra.gsfc.nasa.gov
NASA/GSFC Code 662         HEASARC         +1-301-286-4599 (voice)     
Greenbelt MD 20771                         +1-301-286-1684 (fax)