About the draft itself Re: WD-SIA-2.0

[Petr Skoda]

On Tue, 6 May 2014, Arnold Rots wrote:

> But the usage of wavelength in radio astronomy is never precise
> and is equivalent to the role band designations (L, C, U, K, ...) play.

exactly - the precise wavelength/energy range can be stated (with 
sufficient precision) only for spectra. But for IMAGE (SIA !)
it is always very difficult to state what energy/wavelength range is 
exactly covered - this goes to filters description and more subtle 
metadata. So the only relevant information you can get from image original 
metadata from data acquisition system is something like BANDNAME - the 
transformation to energy is done artificially during publishing phase when 
some VO publisher tries to understand those BANDNAME ids and translate 
them using some tables - a nice source of errors the scientist might be 
tracking a long time ....

But as it is (as was said some time ago) job for the client not SIA 
server, I am very wondering what the final solution will be and whether 
the scientists will accept the IVOA view of consistent data model ;-)

BTW - polarisation states are not strictly enumerated and never one image 
is only in given stokes value- there are cross-talks, partial 
pollarization etc ..... again depends on type and quality of 
filters and its definition .... so its similar to BANDNAME as well.




>
> I am old enough to remember that some optical astronomers
> supported the modernization of replacing wavelength by
> wavenumber - physically more meaningful (like frequency).

a lot of theoretical and model (even measured) spectra are still presented 
in wave numbers - for larger range it is more natural than logorithms etc 
....

*************************************************************************
*  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                                                       *
*************************************************************************