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lib/Astro/Coord/ECI/TLE.pm  view on Meta::CPAN

    $tle->before_reblessing ();
    bless $tle, $class;
    $tle->after_reblessing (@args);
    return $tle;
}

=item $kilometers = $tle->semimajor();

This method calculates the semimajor axis of the orbit, using Kepler's
Third Law (Isaac Newton's version) in the form

 T ** 2 / a ** 3 = 4 * pi ** 2 / mu

where

 T is the orbital period,
 a is the semimajor axis of the orbit,
 pi is the circle ratio (3.14159 ...), and
 mu is the Earth's gravitational constant,
    3.986005e5 km ** 3 / sec ** 2

The calculation is carried out using the period implied by the current
model.

=cut

{
    my $mu = 3.986005e5;	# km ** 3 / sec ** 2 -- for Earth.
    sub semimajor {
	my $self = shift;
	return $self->{&TLE_INIT}{TLE_semimajor} ||= do {
	    my $to2pi = $self->period / SGP_TWOPI;
	    exp (log ($to2pi * $to2pi * $mu) / 3);
	};
    }
}

=item $kilometers = $tle->semiminor();

This method calculates the semiminor axis of the orbit, using the
semimajor axis and the eccentricity, by the equation

 b = a * sqrt(1 - e)

where a is the semimajor axis and e is the eccentricity.

=cut

sub semiminor {
    my $self = shift;
    return $self->{&TLE_INIT}{TLE_semiminor} ||= do {
	my $e = $self->get('eccentricity');
	$self->semimajor() * sqrt(1 - $e * $e);
    };
}

=item $tle->set (attribute => value ...)

This method sets the values of the various attributes. The changing of
attributes actually used by the orbital models will cause the models to
be reinitialized. This happens transparently, and is no big deal. For
a description of the attributes, see L</Attributes>.

Because this is a subclass of L<Astro::Coord::ECI|Astro::Coord::ECI>,
any attributes of that class can also be set.

=cut

sub set {
    my ($self, @args) = @_;
    @args % 2 and croak "The set method takes an even number of arguments.";
    my ($clear, $extant);
    if (ref $self) {
	$extant = \%attrib;
    } else {
	$self = $extant = \%static;
    }
    while (@args) {
	my $name = shift @args;
	my $val = shift @args;
	exists $extant->{$name} or do {
	    $self->SUPER::set ($name, $val);
	    next;
	};
	defined $attrib{$name} or croak "Attribute $name is read-only.";
	if ( CODE_REF eq ref $attrib{$name} ) {
	    $attrib{$name}->($self, $name, $val) and $clear = 1;
	} else {
	    $self->{$name} = $val;
	    $clear ||= $attrib{$name};
	}
    }
    $clear and delete $self->{&TLE_INIT};
    return $self;
}

=item Astro::Coord::ECI::TLE->status (command => arguments ...)

This method maintains the internal status table, which is used by the
parse() method to determine which subclass (if any) to bless the
created object into. The first argument determines what is done to the
status table; subsequent arguments depend on the first argument. Valid
commands and arguments are:

status (add => $id, $type => $status, $name, $comment) adds an item to
the status table or modifies an existing item. The $id is the NORAD ID
of the body.

No types are supported out of the box, but if you have installed
L<Astro::Coord::ECI::TLE::Iridium|Astro::Coord::ECI::TLE::Iridium> that
or C<'iridium'> will work.

The $status is 0, 1, 2, or 3 representing in-service, spare, failed, or
decayed respectively.  The strings '+' or '' will be interpreted as 0,
'S', 's', or '?' as 1, 'D' as 3, and any other non-numeric string as 2.
The  $name and $comment arguments default to empty.

status ('clear') clears the status table.

status (clear => 'type') clears all entries of the given type in the
status table. For supported types, see the discussion of 'add',