The Napkin Representation

[Alasdair Allan]

All,

Okay, returning to the napkin representation of VOTimeSeries thrown  
together at the HTU meeting in Tucson, it looks something like this...

<TimeSeries type="...">
   <Meta>
      <Param name="..." value="..." ucd="..." units="..." />
      <Param name="..." value="..." ucd="..." units="..." />
      <Group name="...">
         <Param name="..." value="..." ucd="..." units="..." />
         <Param name="..." value="..." ucd="..." units="..." />
      </Group>
   </Meta>
   <Data>
      <Row number="1">
         <Time>
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Time>
         <Flux type="...">
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Flux>
      </Row>
      <Row number="2">
         <Time>
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Time>
         <Flux type="...">
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Flux>
      </Row>
        .
        .
        .
   </Data>
</TimeSeries>

where a row may (optionally) also contain

      <Row number="1">
         <Time>
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Time>
         <Flux type="...">
            <Value> ... </Value>
            <Uncertainty> ... </Uncertainty >
         </Flux>
         <Position units="...">
            <RA> ... </RA>
             <Dec> ... </Dec>
             <Uncertainty> ... </Uncertainty >
         </Position>
      </Row>

an RA and Dec, or again optionally, replacing the entire thing with  
an STC description of the position and time if it is complicated  
enough to warrant that, e.g.

   <Row number="1">
     <ObsDataLocation xmlns="..." xmlns:xlink="..."   
xsi:schemaLocation="...">
       <ObservatoryLocation id="..." xlink:type="simple"  
xlink:href="..."/>
       <ObservationLocation>
         <AstroCoordSystem id="...">
           <CoordFrame id="...">
             <Name>...</Name><CARTESIAN coord_naxes="1"/>
           </CoordFrame>
           <TimeFrame>
             <TimeScale>...</TimeScale><TOPOCENTER/>
           </TimeFrame>
           <SpaceFrame>
             <ICRS/><TOPOCENTER/><SPHERICAL coord_naxes="2"/>
           </SpaceFrame>
         </AstroCoordSystem>
         <AstroCoords coord_system_id="...">
           <ScalarCoordinate unit="..." frame_id="...">
             <Value>...</Value>
           </ScalarCoordinate>
           <Time>
             <TimeInstant><ISOTime>...</ISOTime></TimeInstant>
           </Time>
           <Position2D unit="...">
             <Value2><C1>...</C1><C2>-...</C2></Value2>
           </Position2D>
         </AstroCoords>
         <AstroCoords coord_system_id="...">
           <ScalarCoordinate unit="mag" frame_id="...">
             <Value>...</Value>
           </ScalarCoordinate>
           <Time>
             <TimeInstant><ISOTime>...</ISOTime></TimeInstant>
           </Time>
           <Position2D unit="deg">
             <Value2><C1>...</C1><C2>...</C2></Value2>
           </Position2D>
         </AstroCoords>
       </ObservationLocation>
     </ObsDataLocation>
   </Row>

Bearing in mind that there has to be to a way to represent simply a  
(perhaps very long) list of "time, flux" pairs without using STC or  
other complicated bits and pieces or widespread adoption will be  
difficult. That, and in a lot of cases the STC element inside the  
VOEvent message would just have
to be (mostly) repeated for every row as the RA&Dec wouldn't be  
changing. Which is certainly very wasteful way of doing things...

We decided that for the non-STC represetnation we'd restirct  
ourselves to TDB (i.e. BJD), UTC and MJD and frame number only for  
the time stamps, although you would also be able to specify a  
<TimeSeries type="delta_t"> with an additional mandatory <Param> line  
inside the <Meta> block specifying the start of the series, e.g.

<Param name="first" value="..." ucd="..." units="..." >

similar to that necessary for the <TimeSeries type="frame_number"> case.

Attached is an almost readable version of the original napkin for  
posterity (and comparison).

Cheers,
Al.
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