Subject: 8 character limit

From: pence at tetra.gsfc.nasa.gov (William Pence)
Date: Wed, 27 Oct 93 12:32:17 EDT

Phil Hodge wrote:

> One disadvantage of a character-string
> keyword rather than a HISTORY record is that a FITS reader does not have
> to read more than the first eight characters of a character string, and
> this is likely to be insufficient for many programs.

From the practical point of view, I can see little excuse for FITS readers
not to support the maximum 68-character long string values.   There are 
important cases where a FITS reader would get into serious trouble if
it only read the first 8 characters.  For example,

TFORM1  = '1PE(10000)'
TDIM2   = '(1024,1024)'

The only place in the FITS Standard where I could find any mention of an
8-character limit was in section 5.3.2.1 in the discussion of Fixed Format
Character Strings where it recommends:

"Reading the data values in a FITS file should not require decoding any
more than the first eight characters of a character string value of a
keyword".

I don't understand what this means exactly, but given the above
examples where it is important to read more than 8 characters, this
recommendation seems to be out of date, and should perhaps be deleted
or at least clarified in future versions of the Standard.