About the draft itself Re: WD-SIA-2.0

[Arnold Rots]

A few random comments.

François rightly raises the question what the coverage in the various
coordinates means.
As currently written it is very sloppy.

Also, the spectral units are enigmatic.
What does "units of the data" mean?
And what is "barycentric wavelength"? Conversion from frequency to
wavelength as applied at the gravitational potential at the barycenter?
Or does it mean to reduce the spectral coordinate to the barycenter only
dynamically? That's pretty inconvenient for people who are doing Galactic
work.

And since everybody expects me to say this: I bemoan the absence of the
redshift/Doppler coordinate.

Since polarization is an enumerated axis, I think POL=I,Q,U,V should be
perfectly acceptable, but POL=I/V is not.
Note that by explicitly endorsing Stokes parameters, other polarization
expressions (circular, linear, vector) are excluded.

  - Arnold

-------------------------------------------------------------------------------------------------------------
Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------------------------------------------



On Mon, Apr 14, 2014 at 11:51 AM, François Bonnarel <
francois.bonnarel at astro.unistra.fr> wrote:

> Hi all,
>     One more thing.
>  page 9 and 10, : 2.1.3 BAND
> The text states "The value is an open or closed numeric interval of the
> values in the native spectral axis coordinate system and units of data". at
> the beggining.
> At the end of the same paragraph it states "Energy values used in the BAND
> parameter are always assumed to barycentric wavelength and the units are
> always meters". One should make a choice.
> Other people have said that frequency units have the advantage of being
> stable.
>
> Best regards
> François
>
>
>
> Le 11/04/2014 18:55, François Bonnarel a écrit :
>
>  Le 25/11/2013 18:27, Patrick Dowler a écrit :
>>
>>>
>>> I have uploaded the current (incomplete) WD to the document repository:
>>>
>>> http://www.ivoa.net/documents/SIA/20131115/
>>>
>>> This is far fro m complete but I wanted to get an initial round of
>>> comments so we could stabilise something and get on to implementing it.
>>>
>>>
>>>  Hi all,
>>    I am coming back to the SIAV2 draft and proposes some changes or ask
>> some questions here.
>> 0 ) page 5. the last sentence in the introduction is incomplete . "For
>> access to datacubes SIA...."
>>
>> I ) 1.2.4 and 1.2.5 . (page 7) I would merge these two paragraphs and
>> write the 1.2.5 sentence ahead because the main motivation to have
>> AccessData resource with operations  is because  datacubes are too large.
>>
>> II ) 1.2.4 (page 7) and 2 intro (page 8). There is some confusion between
>> "Data Access" as in "Data access layer" which is general and "AccessData"
>> resource wich as far as i understand is there to "Access inside the data"
>> or "extract from the data". So "a low level data access service" should be
>> rephrased " a low  level AccessData service" (1.2.4) and "plan and execute
>> data access operations" should be "plan and execute AccessData operations"
>>
>> III ) I don't understand "alternate authentication schemes". Can you give
>> an example ?
>>
>>
>> IV ) POS, BAND and TIME
>>
>>       IN case of shapes and intervals what is the relationship between
>> this shape and the range of FOV of the dataset ?
>> BAND states clearly that "searching using an interval will find any data
>> with energy coverage that overlaps the specified interval". (page 10)
>> "THe TIME parameter defines the time interval to be extracted from the
>> data". Does that mean the same behavior?
>>
>> The POS behavior for ROI should be the same by default for consistency.
>> But it is not stated in the text.
>>
>> By the way   other behavior (find out datasets where coverage is totally
>> included in the ROI/ parameter ranges, or alternatly intersecting with
>> them) is also  interesting. Should we reintroduce the SIAV1 INTERSECT
>> parameter for that behavior description ? Or do we wait the next version of
>> SIAV2 ?
>>
>> V ) POL .  Pat has asked a question about the meaning of having several
>> POL parameters . OR or AND ? (page 12)
>>      I think AND will be also needed. Stokes parameter is an ordered list
>> according to FITS  standard = I,Q,U,V
>>     So consistenly with other parameters I/V or Q/V would mean the whole
>> range of Stokes paremeters from I to V or Q to V
>>
>> VI ) 2.2 metadata resource. "The output format is an XML document defined
>> by the ImageDM" . Will it be an XML document ? a VOTABLE one ? Or something
>> else ? Should SIAV2 version 1.1 have to say a world about the output format
>> ?
>>
>>
>>
>> cheers
>> François
>>
>
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