|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
[fitsbits] INHERIT and Hierarchical Grouping
On Tue 2007-04-17T15:25:24 -0400, William Pence hath writ:
the Hierarchical Grouping convention (now also open for public comment) provides a more general mechanism for specifying the relationship between multiple HDUs that may be in different files Does anyone have any comments about the Hierarchical Grouping convention itself? Are there any deficiencies or limitations in this convention that have not been considered? Are there alternative ways of accomplishing the same thing that might be simpler or offer more features than this convention? My initial impression was that the Hierarchical Grouping Convention (HGC) was initially a way of handling interconversions between FITS files and HDF files. That made it seem like "feature envy", and also like a solution in search of a problem. I think that in general the FITS community has not tried hard enough to acknowledge the cases where interoperability is hindered because one team chose one way of representing complex data structures. In most cases everyone else simply uses exactly the same data reduction system for those sorts of FITS files. The problems are solved because everything that has to know how somehow just knows how. Doug Mink's WCSTools code for FITS has all sorts of heuristics about how it tries to make sense of the zoo of different coordinate conventions which evolved before the WCS papers were approved and adopted. Bill Joye's DS9 viewer has a raft of GUI buttons to push so that the user can select which set of heuristics should be used when trying to decide how to present the data in a multi-HDU FITS file. HGC adopted a mentality that no existing HDU would have to be modified. That means that no single-HDU-minded application has any way of knowing that a given HDU belongs to a group. In some cases that's okay because the individual HDUs have significant meaning even when they stand alone. But in other cases the individual HDUs are small parts of a normalized data scheme where the picture only makes sense when all parts are considered. Those cases more nearly resemble the sorts of activity that goes on inside relational databases. What HGC does not provide merely within its descriptive document is a strongly motivating example of such things or MUST/SHOULD/MAY advisories which would guide the implementation of some sort of integrity checking mechanism. My impression is that I would want to have Bill Pence's questions answered by someone who has a deep knowledge of the sorts of problems that arise with highly structured data and the sorts of mechanisms that are used in relational databases. -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99845 University of California Voice: +1 831 459 3046 Lng -122.06025 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[fitsbits] INHERIT and Hierarchical Grouping | Doug Tody | FITS | 0 | April 17th 07 09:20 PM |
[fitsbits] INHERIT and Hierarchical Grouping | William Pence | FITS | 0 | April 17th 07 08:25 PM |
[fitsbits] Start of the ''Hierarchical Grouping' Public CommentPeriod | William Pence | FITS | 0 | April 9th 07 08:17 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Rob Seaman | FITS | 0 | April 6th 07 08:28 PM |
[fitsbits] Start of the 'INHERIT' Public Comment Period | Robert Hanisch | FITS | 0 | April 6th 07 06:20 PM |