# [Volute] r5272 - trunk/projects/time-domain/timesysnote

Volute commit messages volutecommits at g-vo.org
Wed Dec 12 11:01:41 CET 2018

Author: msdemlei
Date: Wed Dec 12 11:01:41 2018
New Revision: 5272

Log:
timesysnote: editorial changes in preparation of 1.1 publication

Modified:
trunk/projects/time-domain/timesysnote/Makefile
trunk/projects/time-domain/timesysnote/timesysnote.tex

Modified: trunk/projects/time-domain/timesysnote/Makefile
==============================================================================
--- trunk/projects/time-domain/timesysnote/Makefile	Wed Dec 12 10:39:35 2018	(r5271)
+++ trunk/projects/time-domain/timesysnote/Makefile	Wed Dec 12 11:01:41 2018	(r5272)
@@ -7,7 +7,7 @@
DOCVERSION = 1.1

# Publication date, ISO format; update manually for "releases"
-DOCDATE = 2018-12-15
+DOCDATE = 2018-12-12

# What is it you're writing: NOTE, WD, PR, REC, PEN, or EN
DOCTYPE = NOTE

Modified: trunk/projects/time-domain/timesysnote/timesysnote.tex
==============================================================================
--- trunk/projects/time-domain/timesysnote/timesysnote.tex	Wed Dec 12 10:39:35 2018	(r5271)
+++ trunk/projects/time-domain/timesysnote/timesysnote.tex	Wed Dec 12 11:01:41 2018	(r5272)
@@ -141,68 +141,6 @@

\section{A TIMESYS Element}

-\begin{table}[th]
-\begin{widedescription}
-\item[TAI] (International Atomic Time) atomic time standard, ${\rm TT}- -\rm{TAI} = 32.184 {\rm s}$.
-\item[TT] (Terrestrial Time; IAU standard) time measured by a
-continuous clock on the surface of an ideal Earth. Defined via TCG as
-having been idential on 1977-01-01 and since running slower than it by
-an empirically determined factor $L_C$.  It is continuous with the
-ephemeris time ET widely used before 1984-01-01; in TIMESYS, the term TT
-should therefore be used for times in ET, too.
-\item[UT] Earth rotation time. We do not distinguish between UT0, UT1,
-and UT2; applications requiring this level of precision need additional
-metadata.  This should also be used to label GMT times in datasets covering
-dates before 1972-01-01.
-\item[UTC] (Universal Time, Coordinated) this is TAI, with leap seconds
-inserted occasionally in order to keep UTC within 0.9 s of UT1.
-\item[GPS] (Global Positioning System) runs (approximately) synchronously with
-TAI
-\item[TCG] (Geocentric Coordinate Time) time measured by a clock moving
-with the Earth's center but not subject to the gavitational potential of
-the Earth.
-\item[TCB] (Barycentric Coordinate Time) derived from TCG, but
-taking into account the relativistic effects of the gravitational potential at the barycenter as well as velocity time dilation
-variations due to the eccentricity of the Earth’s orbit.  See
-\citet{1999A&A...348..642I} for details.
-\item[TDB] (Barycentric Dynamical Time) runs slower than TCB at a constant rate
-so as to remain approximately in step with TT; runs therefore
-quasi-synchronously with TT, except for the relativistic effects
-introduced by variations in the Earth’s velocity relative to the
-barycenter.
-\item[UNKNOWN] This value indicates clients cannot transform the times
-reliably; this is to be used for simulated data, free-running clocks,
-or data for which information on the time scale has been lost.
-\end{widedescription}
-\caption{The initial list of defined time scales, evolved from the STC 1
-data model \citep{2007ivoa.spec.1030R}.  In a vocabulary, the
-descriptions should contain normative references.}
-\label{table:timescales}
-\end{table}
-
-
-\begin{table}[th]
-\begin{widedescription}
-\item[TOPOCENTER] The location of the instrument that made the observation
-\item[GEOCENTER] The center of the earth
-\item[BARYCENTER] The barycenter of the solar system
-\item[HELIOCENTER] The center of the sun
-\item[EMBARYCENTER] The barycenter of the Earth-Moon system
-\item[UNKNOWN] The times cannot be transformed to a different reference
-position reliably.  This is to be used for simulated data or for data
-for which the reference position has been lost.
-\end{widedescription}
-
-\caption{The initial list of defined reference positions, evolved from the STC 1
-data model \citep{2007ivoa.spec.1030R}.  In a vocabulary, the
-descriptions should contain normative references.}
-\label{table:refposes}
-\end{table}
-
-
To cover the use cases outlined above, we propose to introduce a new
VOTable element, TIMESYS.  It is allowed whereever COOSYS is and would
reside lexically behind COOSYS definitions if these are present.
@@ -240,19 +178,19 @@
given.\footnote{When using calendar epochs written in yr or Ba, note
that conventionally Julian years are tied to the TDB timescale and
Besselian years to ET (written here as TT)
-\citep{2015A&A...574A..36R}.}
+\citep{2015A+A...574A..36R}.}
Future
VOTable or VOUnits versions may define other such representations.
\item[\xmlel{timescale}]  This is the time scale used.  The IVOA defines
a set of interoperable time scales.  An initial list is given in
-Table~\ref{table:timescales}.  In the prototype, this list is hardcoded
+sect.~\ref{sect:timescales}.  In the prototype, this list is hardcoded
in the schema; we believe that the list should reside in an IVOA
vocabulary in implementation both in order to attach precise meanings
and in order to allow extensions to the list without having to change
the schema.
\item[\xmlel{refposition}] The reference position again is a simple string,
with the initial set of defined values given in
-Table~\ref{table:refposes}.  Again, while the prototype schema contains
+sect.~\ref{sect:refposes}.  Again, while the prototype schema contains
an enumeration of the allowed values, we believe these should eventually
reside in an IVOA vocabulary.
\end{bigdescription}
@@ -260,6 +198,74 @@
The attribute names correspond to attributes of the frame type in
current drafts of the STC2 data model.

+\subsection{An Initial List of Timescales}
+\label{sect:timescales}
+
+The following list of timescales, evolved from the STC 1
+data model \citep{2007ivoa.spec.1030R}, reflects the terms enumerated
+for the \xmlel{timescale} attribute.  It is expected that the actual
+VOTable 1.4 schema will reference a vocabulary (tentatively expected to
+reside at \url{http://ivoa.net/rdf/timescale}), and we will try to
+provide normative references where possible.
+
+\begin{bigdescription}
+\item[TAI] (International Atomic Time) atomic time standard, ${\rm TT}- +\rm{TAI} = 32.184 {\rm s}$.
+\item[TT] (Terrestrial Time; IAU standard) time measured by a
+continuous clock on the surface of an ideal Earth. Defined via TCG as
+having been idential on 1977-01-01 and since running slower than it by
+an empirically determined factor $L_C$.  It is continuous with the
+ephemeris time ET widely used before 1984-01-01; in TIMESYS, the term TT
+should therefore be used for times in ET, too.
+\item[UT] Earth rotation time. We do not distinguish between UT0, UT1,
+and UT2; applications requiring this level of precision need additional
+metadata.  This should also be used to label GMT times in datasets covering
+dates between 1925-01-01 and 1972-01-01. GMT in astronomical use before
+1925 had a 12 hour offset and would require a new term.
+\item[UTC] (Universal Time, Coordinated) this is TAI, with leap seconds
+inserted occasionally in order to keep UTC within 0.9 s of UT1 (a
+different convention was in use before 1972-01-01).
+\item[GPS] (Global Positioning System) runs (approximately) synchronously with
+TAI
+\item[TCG] (Geocentric Coordinate Time) time measured by a clock moving
+with the Earth's center but not subject to the gavitational potential of
+the Earth.
+\item[TCB] (Barycentric Coordinate Time) derived from TCG, but
+taking into account the relativistic effects of the gravitational potential at the barycenter as well as velocity time dilation
+variations due to the eccentricity of the Earth’s orbit.  See
+\citet{1999A+A...348..642I} for details.
+\item[TDB] (Barycentric Dynamical Time) runs slower than TCB at a constant rate
+so as to remain approximately in step with TT; runs therefore
+quasi-synchronously with TT, except for the relativistic effects
+introduced by variations in the Earth’s velocity relative to the
+barycenter.
+\item[UNKNOWN] This value indicates clients cannot transform the times
+reliably; this is to be used for simulated data, free-running clocks,
+or data for which information on the time scale has been lost.
+\end{bigdescription}
+
+\subsection{An Initial List of Reference Positions}
+\label{sect:refposes}
+
+The following list of reference positions, evolved from the STC 1
+data model \citep{2007ivoa.spec.1030R}, reflects the terms enumerated
+for the \xmlel{refposition} attribute.  It is expected that the actual
+VOTable 1.4 schema will reference a vocabulary (tentatively expected to
+reside at \url{http://ivoa.net/rdf/refposition}), and we will try to
+provide normative references where possible.
+
+\begin{bigdescription}
+\item[TOPOCENTER] The location of the instrument that made the observation
+\item[GEOCENTER] The center of the earth
+\item[BARYCENTER] The barycenter of the solar system
+\item[HELIOCENTER] The center of the sun
+\item[EMBARYCENTER] The barycenter of the Earth-Moon system
+\item[UNKNOWN] The times cannot be transformed to a different reference
+position reliably.  This is to be used for simulated data or for data
+for which the reference position has been lost.
+\end{bigdescription}
+
+
\section{Examples}

At this point, the time series available from the ivoa.obscore table on
@@ -321,7 +327,7 @@
in the finished specification.

At this point, there is support on the server side for the proposal
-in the DaCHS suite \citep{2014A&C.....7...27D} as
+in the DaCHS suite \citep{2014A+C.....7...27D} as
of the 1.2.1 beta.  On the client side, the maintainers of the Aladin
\citep{soft:Aladin} and SPLAT Virtual Observatory clients
have signaled they are considering an
@@ -333,7 +339,11 @@
\subsection{Changes from version 1.0}

\begin{itemize}
+\item Now allowing magic strings \verb|MJD-origin| and \verb|JD-origin|
+in the \xmlel{timeorigin} attribute.
\item Fixed \verb|_MJD| example (which was plain broken in 1.0).
+\item Replacing UT1 timescale with UT (reviewers remarked that actual UT1
+should be extremely rare in practice).
\item Improved descriptions of a few time scales based on reviewer
feedback.
\end{itemize}