Re: Some FITS tables suggestions

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2 total messages Started by Thierry Forveille Wed, 07 Oct 1992 15:03

#31

Author: Thierry Forveille
Date: Wed, 07 Oct 1992 15:03

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Lucio Chiappetti (LUCIO@IFCTR.MI.CNR.IT) writes

> YES, conventions are needed to avoid those incompatibilities, which can
> be very annoying.
> And I would say those conventions are needed beyond the area of databases,
> but, for instance, in the area of keywords describing the content of a
> photon list.
> At the moment I am using provisional, local conventions for the designation
> of columns for a photon list : for instance I call THETA and PHI the angular
> cooordinates of a photon (from the optical axis), X and Y the coordinates in
> micron on the focal plane, and XPOSITN YPOSITN the coordinates in detector
> pixels ...or I call ENERGY true energy in keV, but PHA energy in channels,
> and I ignore whether they are consistent e.g. with EXSAS or PROS - which
> I am told are not compatible among them)

I certainly agree that conventions for keywords names should be agreed upon 
in the various subfields of astronomy, but they should at least be compatible
with the existing standard. Specifically, A VALID FITS FILE MUST USE SI
UNITS. This tends to be repeatedly forgotten, even though it was already 
explicitly specified in the original FITS paper.
X and Y should therefore be stored in metres, not microns, ENERGY in Joules
not kev (or cm**-1, or Kelvin, or GHz),  and so on...
Also, there are some well established conventions to store projected angular
coordinates (RA---GLS or GLAT-ATF or...) though I am not sure they are part
of the standard yet.


	Thierry Forveille
	Observatoire de Grenoble
	forveill@gag.observ-gr.fr

Re: Some FITS tables suggestions

#35

Author: Barry Schlesinger
Date: Thu, 08 Oct 1992 20:32

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In article <199210071503.AA12607@chenas.inria.fr>, forveill@gag.observ-gr.fr (Thierry Forveille) writes...
>Lucio Chiappetti (LUCIO@IFCTR.MI.CNR.IT) writes
> 
>> YES, conventions are needed to avoid those incompatibilities, which can
>> be very annoying.
>> And I would say those conventions are needed beyond the area of databases,
>> but, for instance, in the area of keywords describing the content of a
>> photon list.
>> At the moment I am using provisional, local conventions for the designation
>> of columns for a photon list : for instance I call THETA and PHI the angular
>> cooordinates of a photon (from the optical axis), X and Y the coordinates in
>> micron on the focal plane, and XPOSITN YPOSITN the coordinates in detector
>> pixels ...or I call ENERGY true energy in keV, but PHA energy in channels,
>> and I ignore whether they are consistent e.g. with EXSAS or PROS - which
>> I am told are not compatible among them)
> 

Development of area-specific standard keywords and table headers would 
certainly make the task of human interpreters of FITS files easier.  
The different research groups working in the same area should compare 
their proposed names and try to agree on common conventions.

>I certainly agree that conventions for keywords names should be agreed upon 
>in the various subfields of astronomy, but they should at least be compatible
>with the existing standard. Specifically, A VALID FITS FILE MUST USE SI
>UNITS. This tends to be repeatedly forgotten, even though it was already 
>explicitly specified in the original FITS paper.
>X and Y should therefore be stored in metres, not microns, ENERGY in Joules
>not kev (or cm**-1, or Kelvin, or GHz),  and so on...

FITS paper I provides some recommended units.  The use of SI units is 
not required.   The NOST Draft FITS Standard recommends use of the
units in the IAU Style Manual.  In the community review process, this
recommendation has proved acceptable.  The IAU Style Manual adds a
number of units common in astronomy to the SI list. 

>Also, there are some well established conventions to store projected angular
>coordinates (RA---GLS or GLAT-ATF or...) though I am not sure they are part
>of the standard yet.
> 

These conventions are contained in documents proposing conventions for 
world coordinates.  Community consensus on conventions has not yet 
been achieved, although there does appear to be community consensus 
that progress on standardizing world coordinate conventions is needed.

				Barry Schlesinger
				NOST FITS Support Office

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