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package Astro::FITS::HdrTrans::GEMINI;

=head1 NAME

Astro::FITS::HdrTrans::GEMINI - Base class for translation of Gemini instruments

=head1 SYNOPSIS

  use Astro::FITS::HdrTrans::GEMINI;

=head1 DESCRIPTION

This class provides a generic set of translations that are common to
instrumentation from the Gemini Observatory. It should not be used
directly for translation of instrument FITS headers.

=cut

use 5.006;
use warnings;
use strict;
use Carp;

# Inherit from the Base translation class and not HdrTrans itself
# (which is just a class-less wrapper).

use base qw/ Astro::FITS::HdrTrans::FITS /;

use Scalar::Util qw/ looks_like_number /;
use Astro::FITS::HdrTrans::FITS;

our $VERSION = "1.66";

# in each class we have three sets of data.
#   - constant mappings
#   - unit mappings
#   - complex mappings

# for a constant mapping, there is no FITS header, just a generic
# header that is constant
my %CONST_MAP = (
                );

# unit mapping implies that the value propogates directly
# to the output with only a keyword name change

my %UNIT_MAP = (
                AIRMASS_END         => "AMEND",
                AIRMASS_START       => "AMSTART",
                DEC_BASE            => "CRVAL2",
                EXPOSURE_TIME       => "EXPTIME",
                EQUINOX             => "EQUINOX",
                INSTRUMENT          => "INSTRUME",
                NUMBER_OF_EXPOSURES => "NSUBEXP",
                NUMBER_OF_EXPOSURES => "COADDS",
                OBJECT              => "OBJECT",
                X_REFERENCE_PIXEL   => "CRPIX1",
                Y_REFERENCE_PIXEL   => "CRPIX2"
               );

# Create the translation methods
__PACKAGE__->_generate_lookup_methods( \%CONST_MAP, \%UNIT_MAP );

=head1 COMPLEX CONVERSIONS

These methods are more complicated than a simple mapping. We have to
provide both from- and to-FITS conversions All these routines are
methods and the to_ routines all take a reference to a hash and return
the translated value (a many-to-one mapping) The from_ methods take a
reference to a generic hash and return a translated hash (sometimes
these are many-to-many)

=over 4

=cut

# Note use list context as there are multiple CD matrices in
# the header.  We want scalar context.
sub to_DEC_SCALE {
  my $self = shift;
  my $FITS_headers = shift;
  my $cd11 = $FITS_headers->{"CD1_1"};
  my $cd12 = $FITS_headers->{"CD1_2"};
  my $cd21 = $FITS_headers->{"CD2_1"};
  my $cd22 = $FITS_headers->{"CD2_2"};
  my $sgn;
  if ( ( $cd11 * $cd22 - $cd12 * $cd21 ) < 0 ) {
    $sgn = -1;
  } else {