[coords] Question - Time domain coordinates and frames

[CresitelloDittmar, Mark]

All,

So, (again depending on what constitutes a Frame change in the time
domain).  If we change the model a bit (see attached image).  We can remove
the recursive problem, accommodate the annotation of particular 'real'
values in data, and allow for the variations on JD/MJD that Paul alluded
to.  It is NOT as rigid in the ISOTime.  With this model, origin changes in
Frame would be more on the Calendar level.. and I agree with Markus that we
could make a statement that we are supporting Gregorian, other systems can
follow.

The change basically puts the Frame relation to a specific moment in time,
that being represented by an absolute TimeInstant:(JD/MJD/ISO) or a
relative TimeOffset.  The TimeOffset, provides the zero point as
TimeInstant + value for time since then.

I'm also including some example serializations to show the mapping.  These
use the current vo-dml/mapping syntax.
The "_alt" versions use this diagram, the others are from the current model.

Mark



On Fri, Apr 13, 2018 at 9:04 AM, CresitelloDittmar, Mark <
mdittmar at cfa.harvard.edu> wrote:

> One more point on this:
>
> On Thu, Apr 12, 2018 at 5:18 PM, Arnold Rots <arots at cfa.harvard.edu>
> wrote:
>
>> No, the timeOrigin is only REQUIRED in a TimeFrame if it is referenced by
>> a TimeOffset.
>> So, *both the TimeOffset and the timeOrigin can (and should!) refer to
>> the same TimeFrame*.
>> (they should, because specifying the origin in a different TimeFrame is
>> asking for trouble)
>>
>>
> What I'm taking away from this is:
>   + TimeOffset and TimeOrigin are in the same Frame..
>   + the TimeOffset has/requires a timeOrigin
>   + the TimeOrigin should ignore the timeOrigin
>
> From this, I would have to conclude that the timeOrigin is a property of
> the TimeOffset, not the Frame.
>
>
>> It does mean that TimeOffsets that use different timeOrigins need to
>> reference different TimeFrames.
>> That is not a problem, since most TimeOffset-based time series will use
>> the same timeOrigin.
>>
>
> The question is more if they are *considered *to be in the same frame.
> If I have 2 TimeOffsets,  T1 and T2, both in "TDB", "BARYCENTER"... are
> they in the same frame?  even if they have different offsets?
>
> Mark
>
>
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