VOTable for Images

[Seaman, Robert Lewis - (rseaman)]

Could this work with tile compressed FITS images, which are indeed bintables?

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona
--

On 10/16/19, 4:27 PM, "apps-bounces at ivoa.net on behalf of Mark Taylor" <apps-bounces at ivoa.net on behalf of M.B.Taylor at bristol.ac.uk> wrote:

    Mark,
    
    I don't think this is going to work.  The <FITS> element in VOTable
    is only designed to point at a FITS Binary Table (BINTABLE extension),
    not a FITS image (primary HDU or IMAGE extension).  The reason that
    the extnum has to be >0 is that you can't put a BINTABLE in the primary
    HDU, only in one of the later extensions.  If a VOTable parser gets
    directed from the FITS element to an HDU that does not contain
    a BINTABLE, it's going to fail to understand it; that's certainly
    true of my parser, and I'd say it's the clear intention of the
    standard, e.g. (VOTable 1.3 section 2.3):
    
      Henceforth, we shall abbreviate "FITS Binary Table and its Conventions"
      simply by the word "FITS".
    
    If you wanted to insert the content of an image dataset into a VOTable
    document, you'd have to do something like use a cell of a table
    with multi-dimensional array type.
    
    Mark
    
    On Wed, 16 Oct 2019, CresitelloDittmar, Mark wrote:
    
    > All,
    > 
    > In my presentation at the interop (DM session), I mentioned that the
    > VOTable serializations of the 2D and 4D image fail validation.
    > 
    > I'm not terribly surprised (it is VO*Table* after all), but I have some
    > small hope of working up to some usage work on the Cube-Image in the near
    > future and am not sure what the strategy is for serializing/annotating
    > image datasets.
    > 
    > Looking for suggestions..
    > 
    > Basically, I'm currently using the same mode that I do with tabular
    > datasets.  Include the header metadata, describe the content, point to the
    > FITS file.
    > 
    >       <FIELD ID="_col-image" name="image" datatype="int"/>
    >       <DATA>
    >         <FITS extnum="0">
    >           <STREAM
    > href="file:///data/vao/staff/mcd/docs/models/dm/Cube/examples/src/chandra_2Dsky_image.fits"/>
    >         </FITS>
    >       </DATA>
    > 
    > 1) obviously, there is no field named "image" in the dataset, I could use
    > the block name, but it's still a hack
    > 2) extnum="0"
    > The VOTable spec is pretty clear that the extensions are "numbered from 1
    > up, the main header being numbered 0".
    > So, it's no surprise that I get the following validation error on this:
    > (using votlint in stilts_3.0-9)
    >    ERROR (l.293, c.26): cvc-minInclusive-valid: Value '0' is not
    > facet-valid with respect to minInclusive '1' for type 'positiveInteger'.
    >    ERROR (l.293, c.26): cvc-attribute.3: The value '0' of attribute
    > 'extnum' on element 'FITS' is not valid with respect to its type,
    > 'positiveInteger'.
    >    ERROR (l.294, c.112): Non-positive extension number extnum=0
    >    WARNING (l.294, c.112): Read error for external stream
    > uk.ac.starlink.table.TableFormatException: Can't read FITS header
    > 
    > And, if I point it at a non-table HDU in later extensions...
    >    WARNING (l.294, c.93): Read error for external stream
    > java.io.IOException: No table HDU at extension 2
    > 
    > I suppose I could do it with the <BINARY> node, but it'd be nice for the
    > redirect to work.
    > 
    > Mark
    > 
    
    --
    Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
    m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/