Re: Handling data cubes in VO

From: Arnold Rots <arots-at-head.cfa.harvard.edu>
Date: Fri, 17 Feb 2006 12:46:02 -0500 (EST)


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 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/
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<?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> Received on 2006-02-17Z17:46:52