[fitsbits] Start of the CONTINUE keyword Public Comment Period

[Rob Seaman]

Hi Bill,

> I've revised the documentation about this convention to try to  
> address all the comments that have been received so far.  Please  
> see the new PDF (or postscript) documentation file available from  
> the FITS Registry at
> http://fits.gsfc.nasa.gov/fits_registry.html.

Certainly an improvement.  If we can agree that a broader discussion  
of implementing long string support within the standard will follow,  
I withdraw any objections from this end to the convention being  
registered.

> I don't really see any technical problem with writing the CHECKSUM  
> keyword as a continuation over 2 (or more) keywords.  The algorithm  
> for initializing the header and calculating the CHECKSUM keyword  
> value(s) would need to be modified slightly, but it would still  
> follow the same basic procedure.

Indeed, the FITS checksum encoding could accommodate such a  
complication, but both writers (or generalized keyword editors) and  
readers would have to know about the 32-bit alignment requirements  
for CHECKSUM keywords.  To modify my previous example a bit, this  
keyword:

	CHECKSUM= 'nADTnADQnADQnADQ'    /  ASCII 1's complement checksum

is not the same as this expression of overtly the same value:

	CHECKSUM= 'nADTnADQn&      '    /  ASCII 1's complement checksum
	CONTINUE  'ADQnADQ'

The 32-bit integer alignment is different, breaking the 1's  
complement legerdemain.  Other keywords won't have this peculiar  
requirement, but additional semantic or logistical complications can  
be anticipated.

- Rob

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