Changeset 1771 for trunk/doc/pslib/psLibADD.tex

Timestamp:

Sep 9, 2004, 2:40:42 PM (22 years ago)

Author:

Paul Price

Message:

Moved time tables into the SDRS, along with more thorough specification.

File:

• trunk/doc/pslib/psLibADD.tex (modified) (4 diffs)

trunk/doc/pslib/psLibADD.tex

@@ -1 @@
-%%% $Id: psLibADD.tex,v 1.45 2004-09-09 20:17:05 price Exp $
+%%% $Id: psLibADD.tex,v 1.46 2004-09-10 00:40:42 price Exp $
 \documentclass[panstarrs]{panstarrs}
 
@@ -880 +880 @@
 
 
-
 \paragraph{Universal Time (UT1)}
 \label{sec:ut1}
@@ -888 +887 @@
 from UT0 which does not involve corrections for polar motion.  UT1 may
 be calculated from UTC through a table lookup of the appropriate value
-of UTC - UT1 (\S\ref{sec:tables}).
+of UTC - UT1.
 
 \paragraph{Julian Day and Modified Julian Day}
@@ -982 +981 @@
 The polar coordinates, $x_p$ and $y_p$, required for \code{SLA_AOPPA}
 (and hence the \code{psGrommit}s), may be calculated through table
-lookups (\S\ref{sec:tables}).
-
-\paragraph{Table Lookups}
-\label{sec:tables}
-
-The offset of UTC from UT1, $\Delta$ UT1 = UTC - UT1, as well as the
-pole coordinates, $x_p$ and $y_p$, may be determined from table
-lookups.  Tables are available covering different time periods and
-with different time resolution:
-
-\begin{itemize}
-\item \code{ftp://maia.usno.navy.mil/ser7/ser7.dat}
-\item \code{ftp://maia.usno.navy.mil/ser7/finals.all} with explanatory
-  guide at \code{ftp://maia.usno.navy.mil/ser7/readme.finals} . See also
-  the web page \code{http://maia.usno.navy.mil/}.
-\item \code{http://hpiers.obspm.fr/eoppc/eop/eopc01/eopc01.1900-2004}
-  (contains estimates prior to 1972).
-\end{itemize}
-
-For the present time, it should be assumed that these tables reside on
-local disk in known locations (i.e., there is no need that they are
-downloaded from the internet and parsed by PSLib), containing the
-minimum required information in a format that may be read quickly by
-PSLib as required.
-
-The location of these files, their priority order, and the ``from''
-and ``to'' dates of applicability will be known beforehand.
-\tbd{Later, the location of these files, as well as the order of their
-specification, will be made configurable.}
-
-When a value is required, the table with the highest priority shall be
-checked to see if the date is within the range of applicability for
-the table.  If not, the table with the next highest priority shall be
-checked.  If a table is found that is applicable, then the appropriate
-value shall be derived from linear interpolation between the nearest
-entries in the table.  If no table is found that is applicable, and
-the required date is later than those in the table, a warning shall be
-generated, and a formula shall be applied (specifically, the formula
-contained in the Bulletin A,
-\code{ftp://maia.usno.navy.mil/ser7/ser7.dat}); the formula must be
-easily configurable (i.e., not requiring recompilation, as the formula
-will likely change with each Bulletin A).  For dates prior to those
-covered in the tables, the function shall generate a warning and
-assume that TDT is identical to UTC (which, from Reingold \&
-Dershowitz Figure 12.2 appears accurate to $\sim 10$ sec to about
-1700), and that the polar motion ($x_p,y_p$) are zero.
-Archeoastronomy is not a perceived PSLib application, so there is no
-need for high precision at such early dates.
-
-The tables shall be read in only when required by the user, and shall
-remain in memory until the termination of the program.  An additional
-function, \code{psTimeTableReset} should be provided in order to force
-the reloading of the time tables.
-
+lookups.
 
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