[fitsbits] reopening of Public Comment Period on the Green Bank convention

[William Pence]

On 6/1/2016 11:14 AM, Demitri Muna wrote:

> There is a significant difference between documenting use of the FITS 
> format and incorporating it into the standard. As an example, I 
> recently came across UV data, which immediately crashed my FITS 
> viewer, and then this in the AIPS File Format Memo:
>>
>> In the UV-tables form, the visibility data are written as a FITS 
>> binary table, normally placed after the other table extensions. The 
>> primary HDU has an AIPS conventional form meant primarily to be so 
>> odd as to act as a reliable identifier. The primary HDU asserts that 
>> the primary data has two axes, the first of which has 777777701 
>> values while the second has zero values. This is sufficient to tell 
>> all FITS readers that the primary data set is not a random groups 
>> data set and otherwise contains no data.
>>
> This may be convention, but it's *lying*. I'm sure that there are 
> untold numbers of FITS files of UV data that use this convention. 
> Should it be part of the standard? Absolutely not.

It is legal for a FITS image to have one or more zero length axes as 
well as other non-zero length axes, so these UV visibility data do 
conform to the requirements of the FITS standard and are not lying.  One 
could say that these 2D images really are 777777701 pixels wide, but 
because they are 0 pixel high they are hard to see.  :-)

-Bill


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