WD-AccessData-1.0-20140312

[Robert J. Hanisch]

I would also add to the mix the fact that bandpass names in optical/IR
astronomy and bandpass names in radio astronomy overlap.  So a search for
L-band, say, could be either the IR band or the radio band.  J, K, and V
are other obvious problems.

Bob

On 3/20/14 9:08 PM, "Petr Skoda" <skoda at sunstel.asu.cas.cz> wrote:

>On Fri, 21 Mar 2014, Mark Allen wrote:
>
>> An important part of the effort to make multi-dimensional data
>> accessible and useable within the VO is the engagement with projects
>> that produce (or will produce) data cubes. To name some of these
>> projects that participated in the focus sessions and following
>> discussions:
>>
>> ALMA
>> LOFAR
>> ASKAP
>> (SKA)
>> JVLA
>> CGPS (survey)
>> CALIFA
>> MUSE
>> (ESO IFUs)
>> (JWST IFUs)
>>
>> Data from some of these have been shown in demonstrations and are being
>> used to guide developments within VO projects. These are real data
>> cubes. Further examples welcome.
>
>OK - I was little bit concerned whether the real format of the above
>projects was seen to judge the suitability of proposed trio (SIAP2
>accessdata datalink) of standards (with the current parameter
>restrictions).
>
>As I said in the special session it was shown more of the nice images and
>wishes than real data. And the only real data were presented on ALMA by
>JVO visage - but (I have seen it at Hawaii as well) at least still there
>the "energy" axis was represented by the individual channel ID - not real
>"energy" span in barycentric wavelength in m.
>
>And to be honest the IFUs so far in VO (I mean the Euro3D and he tools of
>Igor and Ivan) were rather presented as individual spectra referenced by
>fiber id (or slit ID)
>
>So it seems to be rather sparse cube in some axes in comparison to e.g.
>more densely covered "energy" axis.
>
>In fact the CALIFA as well is more dense in "energy" axis then in spatial
>axes. But I can say (after downloading) that the reduced product is realy
>the datacube with NAXIS3
>
>So I apologize for a little simplified view.
>
>
>> The current efforts on the standards are to satisfy minimal
>>requirements 
>> on discovery and access. Of course, doing science with data cubes
>> requires much more, and we will need to consider the roles of services,
>> user interfaces and tools. I think that some of your comments are
>>mixing 
>> these things together, in particular for BAND.
>
>My objection comes not because of datacubes (of e.g. IFU) but as it is
>(SIAP2) declared as image access protocol or in some sense image
>extraction (accessdata) protocol.
>
>The BANDNAME is crucial for science discovery in multicolour photometry
>surveys as well as the fiberID is crucial for multiobject spectra (look
>in 
>SDSS - the plate-fiber pair is crucial primary metadata - not the
>position 
>which is derived.
>
>If you want the insist on simple numerical energy band as primary
>information do not name it "Image protocol" but SDAP - simple datacube
>access protocol - and then everyone would know he should not expect the
>server of images (in different filters) here.
>
>  The standard needs to be
>> uniform and simple, but tools or services could offer any number of
>>ways 
>> for an astronomer to specify a wavelength/frequency/energy range. For
>> example, I think that a user interface could use a look-up of the SVO
>> filter service to do for BAND what the NED/CDS sesame name resolver
>>does 
>> for coordinates, presenting a way for the astronomer to deal with
>>filter 
>> names, but using the standard that speaks only in metres (or Hz).
>
>As I said - it is not uniquely mappable and will require much more effort
>to investigate the data before publishing. Moreover it will not allow you
>to select exactly what you want and know.
>
>The examaple with Sesame is perfect example how the generalized view
>without deeper investigation makes you troubles to achieve scientific
>goals.
>
>With some little simplification suppose the case you want to search for
>spectrum of double star. You have (at least) two spectra on one chip.
>Both 
>may be extracted and put is separate 1D spectra. But the RA DEC in FITS
>header belongs to only one position, the DATE-OBS is the same.
>
>Obiously you know during the reduction which spectrum belongs to what
>star and you name the OBJECT accordingly.
>
>For SSA you are obliged to use POS query - but it returns spectra of both
>stars obviously even with very small SIZE circle.
>When you have 100+ spectra of both stars how do you isolate only the one
>of the (e.g.) secondary component which has Balmer line emission and is
>the only interesting ?
>This is our case with HR1847A and B
>
>Fortunately in SSA there is the TARGETNAME parameter (optional) so I can
>query by TARGETNAME and ignore the POS. And although there may be some
>ambiguity in names (different spaces etc ...) I say in SSA
>TARGETNAME=HR1847B and I will fulfill my science goal.
>Of course if I do not know the TARGETNAME immediately - so first I
>perform 
>discovery query in large circles probably using SESAME names etc ....
>But once I know it I can precisely get what I want.
>
>I agree the protocol should be simple but IMHO if it is orthogonally
>designed it should allow me to isolate by proper combination of
>parameters 
>the individual entities (e.g. spectra, images). In case of SSA I have the
>combination of POS, SIZE (still yeilding the ambiguity) + TARGETNAME.
>In case of SIAP2 I need the BAND (with wider range) + BANDNAME (or better
>BANDID) to get exactly THAT image.
>
>Does anybody already see how it is important?
>
>In terms of "ontology" or semantics:
>The object of my investigation is some entity described by extremely
>large 
>number of different atributes characterizing one or another property.
>I will assign to it a label. So when I want to select it I will use the
>label.
>
>If it is possible I can map one label to another in a unique -
>bijective way. So I can use this new label  to point
>to it as well. If this label is Halpha or 6562.8e-10m (in air) its fine
>(but I must use some tollerance).
>
>But if I want to map symbol to interval - it is not bijective anymore. As
>in wider interval may be more narrower subintervals (narrow-band
>photometry images). Stating the wider interval (490e-9/700e-9m) will
>return me ALL the subband images and I cannot imagine how to select only
>Johnson V filter image.
>
>If there are thousands of images I am deemed to die after manual
>selection or get very angry on whole stupid VO garbage ;-)
>
>
>