NAME

Time::GPS - Global Positioning System time

DESCRIPTION

The Global Positioning System (GPS) includes as an integral feature the
dissemination of a very precise time scale.  This time scale is produced
by atomic clocks on the satellites, and is steered to keep in step with
International Atomic Time (TAI).  The GPS time scale is thus indirectly
a realisation of Terrestrial Time (TT).  GPS time is one of the most
accurate and the most accessible realisations of TAI.

This module represents instants on the TAI time scale as a scalar
number of TAI seconds since an epoch.  This is an appropriate form
for all manner of calculations.  The epoch used is that of TAI, at
UT2 instant 1958-01-01T00:00:00.0 as calculated by the United States
Naval Observatory, even though GPS did not exist then.  This matches
the convention used by "Time::TAI" for instants on the TAI scale and by
"Time::TT" for instants on the TT scale.

There is also a conventional way to represent GPS time instants using
day-based notations associated with planetary rotation `time' scales.
The `day' of GPS is a nominal period of exactly 86400 GPS seconds,
which is slightly shorter than an actual Terran day.  The start of
the GPS time scale, at UTC instant 1980-01-06T00:00:00.0 (TAI instant
1980-01-06T00:00:19.0) is assigned the label 1980-01-06T00:00:00.0
(MJD 44244.0).  Because GPS time is not connected to Terran rotation,
and so has no inherent concept of a day, it is somewhat misleading to
use such day-based notations.  Conversion between this notation and the
linear count of seconds is supported by this module.  This notation does
not match the similar day-based notations used for TAI and TT.

INSTALLATION

	perl Build.PL
	./Build
	./Build test
	./Build install

AUTHOR

Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

Copyright (C) 2006, 2009, 2010 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
