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=over 4

=item DPI - Pi

=item D2PI - 2 * Pi

=item D1B2PI - 1 / (2 * Pi)

=item D4PI - 4 * Pi

=item D1B4PI - 1 / (4 * Pi)

=item DPISQ - Pi ** 2 (Pi squared)

=item DSQRPI - sqrt(Pi)

=item DPIBY2 - Pi / 2: 90 degrees in radians

=item DD2R - Pi / 180: degrees to radians

=item DR2D - 180/Pi:  radians to degrees

=item DAS2R - pi/(180*3600): arcseconds to radians

=item DR2AS - 180*3600/pi: radians to arcseconds

=item DH2R - pi/12: hours to radians

=item DR2H - 12/pi: radians to hours

=item DS2R - pi / (12*3600): seconds of time to radians

=item DR2S - 12*3600/pi: radians to seconds of time

=item D15B2P - 15/(2*pi): hours to degrees * radians to turns

=back

=cut

# Could implement these directly via the include file in the XS layer.
# Since these cant change - implement them explicitly.

# Pi
use constant DPI => 3.1415926535897932384626433832795028841971693993751;

# 2pi
use constant D2PI => 6.2831853071795864769252867665590057683943387987502;

# 1/(2pi)
use constant D1B2PI => 0.15915494309189533576888376337251436203445964574046;

# 4pi
use constant D4PI => 12.566370614359172953850573533118011536788677597500;

# 1/(4pi)
use constant D1B4PI => 0.079577471545947667884441881686257181017229822870228;

# pi^2
use constant DPISQ => 9.8696044010893586188344909998761511353136994072408;

# sqrt(pi)
use constant DSQRPI => 1.7724538509055160272981674833411451827975494561224;

# pi/2:  90 degrees in radians
use constant DPIBY2 => 1.5707963267948966192313216916397514420985846996876;

# pi/180:  degrees to radians
use constant DD2R => 0.017453292519943295769236907684886127134428718885417;

# 180/pi:  radians to degrees
use constant DR2D => 57.295779513082320876798154814105170332405472466564;

# pi/(180*3600):  arcseconds to radians
use constant DAS2R => 4.8481368110953599358991410235794797595635330237270e-6;

# 180*3600/pi :  radians to arcseconds
use constant DR2AS => 2.0626480624709635515647335733077861319665970087963e5;

# pi/12:  hours to radians
use constant DH2R => 0.26179938779914943653855361527329190701643078328126;

# 12/pi:  radians to hours
use constant DR2H => 3.8197186342054880584532103209403446888270314977709;

# pi/(12*3600):  seconds of time to radians
use constant DS2R => 7.2722052166430399038487115353692196393452995355905e-5;

# 12*3600/pi:  radians to seconds of time
use constant DR2S => 1.3750987083139757010431557155385240879777313391975e4;

# 15/(2pi):  hours to degrees x radians to turns
use constant D15B2P => 2.3873241463784300365332564505877154305168946861068;


=head2 Extra functions

These are exportable using the 'funcs' tag or used directly
through the Astro::PAL namespace.

They directly match the Astro::SLA equivalents.

=over 4

=item B<lstnow_tel>

Return current LST (in radians) and MJD for a given telescope.
The telescope identifiers should match those present in palObs.
The supplied telescope name is converted to upper case.

   ($lst, $mjd) = lstnow_tel($tel);

Aborts if telescope name is unknown.

=cut

sub lstnow_tel {

  croak 'Usage: lstnow_tel($tel)' unless scalar(@_) == 1;

  my $tel = shift;

  # Upper case the telescope
  $tel = uc($tel);

  # Find the longitude of this telescope
  my ($ident, $name, $w, $p, $h) = palObs( $tel );

  # Check telescope name
  croak "Telescope name $tel unrecognised by palObs()"
    unless defined $ident;

  # Convert longitude to west negative
  $w *= -1.0;

  # Run lstnow
  lstnow($w);