[fitsbits] start of Public Comment Period on the INHERIT convention

[William Thompson]

One can argue about which is better, binary tables or IMAGE extensions, but the 
fact of the matter is that data providers do not necessarily follow your 
preferences.  I know of a lot of groups who have great resistance to using 
binary tables.  We shouldn't reject something simply because we think it should 
be done with binary tables instead.

Bill Thompson

On 07/01/15 08:46, Tom McGlynn (NASA/GSFC Code 660.1) wrote:
> Peter Weilbacher wrote:
>> On Wed, 1 Jul 2015, THIERRY FORVEILLE wrote:
>>
>>> "Frank Valdes" <valdes at noao.edu> writes
>>> ----- Original Message -----
>>>> P.S. I really don't like the suggestion that multiple "images", say
>>>> traditional CCD images, which are related should be "packed in a single
>>>> binary table".
>>>>
>>> The flip side is that doing that covers the need which you describe, and is
>>> already fully part of the standard.
>>>
>>> There is a non-trivial cost (in additional code in FITS readers that needs
>>> writing and, more importantly, maintaining) to multiple solution to the same
>>> problem, which I see as enough of a reason to say no to INHERIT.
>> On the other hand, reading and writing bintable data is less efficient
>> than writing image data. So when /using/ it, it creates extra overhead.
>> So depending on the use-case, writing MEF instead of bintables does make
>> a lot of sense, and that would benefit from INHERIT. (But since for
>> those purposes, INHERIT can be implicitly be assumed for the case at
>> hand, so that's a similarly weak argument for INHERIT as yours is
>> against. ;-))
>>
>>     Peter.
> Since the binary encoding is the same for the actual image data, the only
> difference here is in the header information,.  For very large images it won't
> matter much because the image data will dominate. For small images it won't
> matter much because the overhead of locating and opening the files will
> dominate.  However even then I think it's easy to construct use cases where
> using either binary tables or images (possibly with inherit )is more
> efficient.   I.e., if I have 100 images that I need to store, then I can do that
> in only 2 HDUs using a single binary table, while it might take 100 HDUs
> (including 100 headers) as images. On the other hand a single image requires the
> extra primary header HDU when encoded in a binary table.
>
>
> Note that binary tables can handle both a set of homogeneous images (as separate
> rows) and  heterogeneous images (as separate columns). In the former case the
> Green Bank convention (which I don't think should be in the standard for reasons
> discussed elsewhere) can play a role very similar to the inherit convention.
> For large images, the advent of tiled images may make using binary tables the
> preferred choice in the common cases where the user is interested in only a
> subset of the image.
>
>
>      Regards,
>      Tom McGlynn
>
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-- 
William Thompson
NASA Goddard Space Flight Center
Code 671
Greenbelt, MD  20771
USA

301-286-2040
William.T.Thompson at nasa.gov