Standardising units and formats (and ref frames?) in transmission

[Petr Skoda]

Hi just a comment on Anita's nice analysis of user's wishes :

>> who want to search Galactic plane surveys in Galactic coordinates, since a 
>> simple box (from an image or catalogue) will give them what they want, but 
>> in RA and Dec it is horrid.

Its important that the client allows to enter the required coordinate 
system - it is even problem with RA in degrees required for SSA and 
Consearch POS argument - my colleagues like SPLAT as it allows to enter
the "native" representation of RA, DEC (e.g. for Vega RA
18:36:56.336
at the same time as VO required 279.23473500

The VOspec allows only degrees but if you enter the H:M:S representation
it makes strange numbers and performs the query of strange coordinates
(no complain).

Of course 90% of queries go first to the name resolver using name "Vega" 
but for some close binaries etc it is not trivial how to name it ....

I cannot now imagine how the proper TAP client will look like and how you 
enter the regions (rectangles in l,b) or more complicated (e.g. HST focal 
field) but again if the client will not allow easy input of multiple 
representations it may not be used by the community simply because of 
omission of this trivial issue (e.g Most of my colleagues using the web 
interfaces for surveys escape if it does not allow name resolution of RA, 
DEC input....

But this is on the client makers, the wire transmission is of course (and 
should be) transparent to end user....


>> Or, I want data with a certain spectral resolution which I specify in 
>> wavelength unts, but the data are in frequency units with a non-linear 
>> conversion - i.e., the spectal resolution at one end of the bandpass is 
>> different from that at the other, if the units are changed.

there is another catch here - the resolution in optical astronomy is 
mostly considered the unit-less (spec. resolution power lambda/dlambda)
whis is mostly constant over the long regions (e.g. echelle) but it is 
still rough estimate. But the registry services still require the units
but how to express it ?  in A/pixel ? If rebinned to 1D FITS (having 
CDELT1=constant - its easy) but how about the red and blue part of echelle 
spectra expressed in binary table ??)
How to convert this for characterisation ???

Petr Skoda

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*  Petr Skoda                         Phone : +420-323-649201, ext. 361 * 
*  Stellar Department                         +420-323-620361           *
*  Astronomical Institute AS CR       Fax   : +420-323-620250           *
*  251 65 Ondrejov                    e-mail: skoda at sunstel.asu.cas.cz  *
*  Czech Republic                                                       *
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