[coords] Question - Time domain coordinates and frames

[CresitelloDittmar, Mark]

Thanks Arnold..
I agree with how you described just about everything in terms of the
current types.
The one part that causes me confusion is below..

So.. timeOrigin
  1) should be provided in the Frame ONLY if the referring coordinate is a
TimeOffset.
  2) is expressed as a non-TimeOffset TimeStamp
  3) 'referenced to the same TimeFrame' (as the original TimeOffset?)  <<<
this I don't understand
       If the TimeOffset.frame contains a timeOrigin expressed as a MJD
       and that MJD refers to the same frame, that would be an MJD
referring to
       a frame with a timeOrigin, which opposes #1.
       If, the MJD refers to a different frame (with no timeOrigin), then
you have a short train of types/frames.

You are asserting that if I have 2 TimeOffset-s with different offsets,
they are in different frames.
   T1{ time=t1, frame=TimeFrame1{ timescale='TT', refPosition="TOPOCENTER",
timeOrigin=MJD{ date=50814.0, frame=TimeFrame1} } }
   T2{ time=t2, frame=TimeFrame2{ timescale='TT', refPosition="TOPOCENTER",
timeOrigin=MJD{ date=51179.0, frame=TimeFrame2} } }

or maybe
  TimeFrame0{ timescale="TT", refPosition="TOPOCENTER"}
   T1{ time=t1, frame=TimeFrame1{ timescale='TT', refPosition="TOPOCENTER",
timeOrigin=MJD{ date=50814.0, frame=TimeFrame0} } }
   T2{ time=t2, frame=TimeFrame2{ timescale='TT', refPosition="TOPOCENTER",
timeOrigin=MJD{ date=51179.0, frame=TimeFrame0} } }

but they are NOT in the same frame, with different offsets..
  TimeFrame0{ timescale="TT", refPosition="TOPOCENTER"}
   T1{ time=t1, frame=TimeFrame0, timeO=MJD{ date=50814.0,
frame=TimeFrame0} }
   T2{ time=t2, frame=TimeFrame0, timeO=MJD{ date=51179.0,
frame=TimeFrame0} }

Mark


On Thu, Apr 12, 2018 at 2:49 PM, Arnold Rots <arots at cfa.harvard.edu> wrote:

>
> The time stamp can be specified as:
> JD (no units required)
> MJD (no units required)
> ISO-8601 (no units required)
> TimeOffset (units required, as well as a value for timeOrigin in the frame)
>
> The timeOrigin should expressed as a TimeStamp (JD, MJD, or ISOTime, but
> NOT TimeOffset),
> referenced to the same TimeFrame.
>
> So, yes, this is recursive, but there are strict constraints on the
> timeOrigin which should prevent runaway looping.
>
>
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