relative fluxes

[Alberto Micol]

Douglas Tody wrote:
> Hi Guys -
>
> Having a multiplicity of formats would be a problem as well.  

Hi Doug,

This is exactly what we suffer from already now, given that the standard
allows for a "NATIVE" FITS format. The so much used ground-based
format (1D image) is passed on as "NATIVE" within the VO, and because
of that the VO (not the final users which are happy with it) does not know
how to treat it. It would be much simpler to recognise that such 
ground-based format
exists and that it is widely used, and hence allow proper VO description 
of it.
 
With a little addition to the IVOA standard we would suddenly open the doors
to many ground-based observatories!
> I would
> prefer to encourage client apps to update to the more powerful Spectrum
> DM and its formats now that we have this.  We can down-convert on a
> case by case basis to support legacy apps if necessary, but with the
> introduction of the VO why not try to move to another level.
>
In principle you are right, but the current status of things is that:
- we have (I think) many ground-based observatories that use the 1D 
image format
- we have only a bunch (up to 5 maybe?) of tools that support VO 
spectroscopy
visualisation/analysis

Hence, it is clear that changing a small number of spectroscopy 
application tools
is much easier than having to transform all the existing ground-based 
spectra.
Plus, some of those tools already support the 1D image format anyway.
> What major
> spectral archives do we have that would benefit from such support?
>
I can report that ESO stores spectra in 1D image format.

It would indeed be nice to know which other data providers use the 1D 
FITS IMAGE format
for their 1D spectra in their archives...

>     - Doug
>
Alberto

>
> On Fri, 26 Jun 2009, Petr Skoda wrote:
>
>>
>> Good hit !!
>>
>> I am glad that this question is coming again. I consider this the 
>> most critical issue for easy conversion of ground based optical 
>> archives.
>> The rejection of opening 1D FITS in VOSpec is one of the  obstacle 
>> for optical astronomers but no one wants to hear that !
>> In fact it prevented me to use ESA SSA server and only with 
>> collaboration with Phillipe Prugniel (who has on-the-fly 1D FITS  to 
>> BINTABLE convertor as part of Pleinpot pipeline) I could finally see 
>> my spectra in VOSPEC. (it took 2 years to notice this)
>>
>>> One example that comes to mind is that ground based spectra are very 
>>> often
>>> published using a 1D image FITS format, where the 1 axis is the 
>>> wavelength
>>> (using CDELT1, CRVAL1, CPIX1 to specify the wavelength wcs).
>>
>>> That format is NOT supported by the SSA, and that might cause indeed
>>> problems to the ground based data providers. Sure, they could translate
>>> FITS files on the fly, but we shall not forget that data providers 
>>> have many other
>>> things to do than try to twist their data into the VO.
>>
>> Another issue - there is no simple tool for the conversion of 1D FITS 
>> to BINTABLE so its now easy to make archive for VOSpec consumption.
>>
>> Just looking at any
>>> registry
>>> the number of space-based SSA services greatly outnumber the 
>>> ground-based ones
>>> At the level of about 90 vs 10 (or worse).
>>
>> And still some are giving strange outputs...
>>
>>
>>
>>
>> The one I stated is certainly not
>>> the only reason
>>> for this (calibrating a ground-based spectrum is much more 
>>> difficult), but the format problem
>>> exists (and I can tell, now that I work for a grond base archive!)
>>
>> YES !!!  Many smaller observatories would be eager to publish spectra 
>> in VO and they have already web based archives but the spectra should 
>> be used as they are.
>>
>> The 1D FITS is the format where all astronomers know how to get it 
>> (e.g. from IRAF or MIDAS) in worst case over ASCII tables - but its 
>> is what they are forced to do every day. But I have met only about 
>> 10% of stellar astronomers who know what is BINTABLE FITS.
>>
>> Petr
>>
>> ************************************************************************* 
>>
>> *  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                                                       *
>> ************************************************************************* 
>>