WD-AccessData-1.0-20140312

[Robert J. Hanisch]

I've read all of the email, Petr.  And you are totally missing my point.
And the point that Mark Allen made.

Bandpass names are important, but not for the core SIAP protocol.  They
are important for user interfaces.  And that is a totally different issue
that what goes on the wire for a SIAP query.

Bob

On 3/20/14 7:14 PM, "Petr Skoda" <skoda at sunstel.asu.cas.cz> wrote:

>
>> I just have to add my 2-cents worth and say that I think this is wrong.
>> The protocol should be as simple as possible, and adding bandpass names
>>is
>> not.
>
>I think you did not see the previous discussion - WHY the bandpass names
>IS important:
>
>1) It is the primary information written in FITS header - the provider of
>the original data (e.g. camera acquisition system) always uses some
>simplified names, lists ....
>
>2) The names of particular filters MAY NOT be mapped precisely to the
>filter names - it is spcific to every project and there is not unique
>solution how to map it - but of course the filter profile service
>used in VOSA etc. tries to identify the most commonly used.
>
>3) The scientist know MUCH BETTER what kind of filter the particular
>survey (say resource) uses then the VO data provider can describe in
>metadata (and if he wants to be precise it requires a lot arguing with
>the 
>expert in e.g. photometry - moreover some filters have discontinuity
>(they 
>absorb) in certain regions so the only physical identification of it is
>the plot of transmissivity.
>
>4) It may be even worse - the instruments with many filters may such that
>are not described well by simple names. it may be e.g. Hbeta filter
>centered on some wavelength coresponding to the given redshift of this
>line. Some documentation of filters mentions only central wavelength not
>min and max range - Some state central wavelength and FWHM or half-width
>...
>
>
>So it is almost impossible for the (usually informatician with basic
>astronomical background) VO data publisher to find the exact mapping
>required here.
>And how will you distinguish two different images the filters of which
>have the similar wavelegth range or central wavelength - e.g. Johnson V
>and Stromgren y .....?
>
>BTW - the polarisation states are as well completely wrong and they should
>d not be listed as Q,U,V,I as none of this value is obtained separately
>and you cannot use it for query - but you may want to extract them in
>Accessdata - see the presntation of F. Paletou in Heidelberg.
>
>But it is more practical to refer to obseravtion with certain orientation
>of filter (half-wave plate) as e.g. U and to the one without polariser as
>I....
>
>>
>> If you want a user interface or toolkit that layers bandpass-based
>>queries
>> on top of the basic protocol, that is fine.  User sees bandpass name =
>>V,
>> protocol sees a wavelength range.  But everything you add onto the
>> protocol is another feature the data provider has to implement.
>He has to implement much more complicated translation to wavelength
>ranges 
>(very artificial and imprecise ) just to satisfy the characterization.
>But here it may be considered as the rough orientation value and it is
>legitimate use it in (very rough) discovery query to get at least
>something.
>But if the scientist need EXACTLY what he wants, there is no way how to
>do 
>it in a unique way.
>
>