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[fitsbits] MIME for compressed FITS?
On Tue 2007-05-22T15:21:13 -0700, Rob Seaman hath writ:
An application/FITS can be any conforming FITS object such as MEF - but few clients will know what to do with it. This was the problem that finally overcame the energy barrier to promp the creation of the FITS MIME document. Bill Joye was trying to figure out how ds9 could tell just what it was supposed to do with a purportedly FITS file that it obtained by any means, but in particular he was hoping that MIME types might provide a solution. By the end of the FITS MIME effort it became clear that the solution of this problem is not possible within the Internet mechanisms but is internal to FITS. What is a FITS tile compressed SIF file? It remains an application/ FITS, but can it be promoted (if that is the right word) to image/ FITS with a different content encoding? (It remains a coherent representation of a single image.) Steve appears to assert "no" and that the vast internet community will have no truck with the (even vaster in physical domain) astronomical community. Given the last year's tweak in the tile compression mechanisms a FITS tile compressed SIF file (which must consist of a PHDU plus an extension HDU that is a table and is thus application/fits) can now be isomorphic with a classical FITS file with a single PHDU (which can be image/fits). content-(en)coding is not directly relevant to this. The alternative is to turn application/FITS into something useful, I suppose. That's it. FITS needs mechanisms for saying This file (and/or HDU) makes use of the following list of features and conventions. With that in place a FITS application might ascertain whether it has any interest or ability to make sense of the content which has been stuffed into the zoo of extension HDUs. Do we need to consider another round of MIME murmurings? Failing that, is MIME really of any value to FITS? MIME is essential to those VO exchanges of data which rely on HTTP as a transfer mechanism. This sort of problem is not specific to the FITS community. At the time of the FITS MIME effort, however, not even the internet community had a standardized mechanism for describing the transmission of a file of given MIME media type and compression via the mechanisms described for SMTP. The specification for HTTP has the concept of content-(en)coding, but the specification for sending MIME media types in e-mail messages did not. Anyhow, Bill Joye would love to see this problem addressed. As things stand ds9 basically has to be told which set of heuristics to use when it is given a FITS file, and the interpretation of all other complex data stored in FITS is equally reliant on implicit agreements between the creator and consumer. The IAUFWG effort to make a list of recognized FITS conventions is one step toward the solution. -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855 University of California Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m |
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