Handling data cubes in VO

[Arnold Rots]

It occurred to me that the STC schema actually provides a ready
serialization for a more sophisticated dataset query.
It is the SearchLocation element.  An example is attached (using an
older version of the schema, but it does illustrate things).

The STC SearchLocation allows expressing a query in any or all axes -
time, position, velocity, spectral, redshift/Doppler - both in the
volume that is to be occupied and in the desirable properties of the
data that are requested, in terms of accuracy and resolution:

The AstroCoordSystem defines the coordinate systems but can be just
referenced in a single line to one that exists in a library of
standard coordinate systems.
The AstroCoordArea defines the coordinate volume that the query
requests to be filled, while the AstroCoords components, as far as
present, represent desirable values for errors, resolution, pixelsize,
and field-of-view (if the whole area cannot be filled at once).

Cheers,

  - 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 head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
--------------------------------------------------------------------------


<?xml version="1.0" encoding="UTF-8"?>
<SearchLocation xmlns="http://www.ivoa.net/xml/STC/stc-v1.20.xsd"
xmlns:crd="http://www.ivoa.net/xml/STC/STCcoords/v1.20"
xmlns:reg="http://www.ivoa.net/xml/STC/STCregion/v1.20"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.ivoa.net/xml/STC/stc-v1.20.xsd
stc-v1.20.xsd"> 
  <AstroCoordSystem ID="ICRS-TT-BARY">
    <TimeFrame>
      <Name>Time</Name>
      <TimeScale>TT</TimeScale>
      <BARYCENTER/>
    </TimeFrame>
    <SpaceFrame>
      <Name>Equatorial</Name>
      <ICRS/>
      <BARYCENTER/>
      <SPHERICAL coord_naxes="2"/>
    </SpaceFrame>
    <SpectralFrame>
      <Name>Wavelength</Name>
      <BARYCENTER/>
    </SpectralFrame>
  </AstroCoordSystem>
  <crd:AstroCoords coord_system_id="ICRS-TT-BARY">
    <crd:Position2D unit="deg">
      <crd:Name>RA,Dec</crd:Name>
      <crd:Resolution2>
        0.0001 0.0001
      </crd:Resolution2>
      <crd:Resolution2>
        0.0003 0.0003
      </crd:Resolution2>
      <crd:Size2>
        0.5 0.5
      </crd:Size2>
      <crd:Size2>
        0.67 0.67
      </crd:Size2>
      <crd:PixSize2>
        0.00005 0.00005
      </crd:PixSize2>
      <crd:PixSize2>
        0.00015 0.00015
      </crd:PixSize2>
    </crd:Position2D>
    <crd:Spectral unit="Angstrom">
      <crd:Name>Lambda</crd:Name>
      <crd:Resolution>300</crd:Resolution>
      <crd:Resolution>600</crd:Resolution>
    </crd:Spectral>
  </crd:AstroCoords>
  <AstroCoordArea ID="M81" coord_system_id="ICRS-TT-BARY">
    <TimeInterval>
      <StartTime>
        <crd:Timescale>TT</crd:Timescale>
        <crd:ISOTime>1900-01-01T00:00:00</crd:ISOTime>
      </StartTime>
    </TimeInterval>
    <Region>
      <reg:Circle unit="deg">
        <reg:Center>148.9 69.1</reg:Center>
        <reg:Radius>2</reg:Radius>
      </reg:Circle>
    </Region>
    <SpectralInterval unit="Angstrom">
      <LoLimit>4000</LoLimit>
      <HiLimit>7000</HiLimit>
    </SpectralInterval>
  </AstroCoordArea>
</SearchLocation>