[coords] Question - Time domain coordinates and frames

[CresitelloDittmar, Mark]

On Fri, Apr 13, 2018 at 8:52 PM, CresitelloDittmar, Mark <
mdittmar at cfa.harvard.edu> wrote:

> I'd just like to point out that in that diagram, ALL of the coordinates
> refer to a TimeFrame... and therefore, have a timescale and refpos
> available.
> In the examples I included, they all refer to the SAME timeframe, but this
> is not required (though perhaps discouraged). However, there is no need for
> the MJD to 'ignore' an offset that applies only to the TimeOffset type.
>
> You hit on the difference, and the core of the question which started this
> thread.
> This arrangement says that the Frame applies to an instant, not to a
> relative time.  So each of the coordinate types (JD, MJD, ISO, TimeOffset)
> define a particular instant
> by providing both the zero point (TimeInstant) + offset from there.
>

That is, a TimeOffset provides both which == an Instant, while the others
ARE an Instant either by definition or by an absolute zero point (MJD).
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ivoa.net/pipermail/dm/attachments/20180413/2b6ce3aa/attachment.html>