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lib/Geo/Ellipsoids.pm  view on Meta::CPAN

=cut

sub n {
  my $self = shift;
  my $lat  = shift; #degrees
  die('Error: Latitude (degrees) required.') unless defined $lat;
  return $self->n_rad(rad_deg($lat));
}

=head2 n_rad

Method returns the value of n given latitude (radians).

  my $n_rad = $obj->n_rad($lat);

Reference: John P. Snyder, "Map Projections: A Working Manual", USGS, page 25, equation (4-20) http://pubs.er.usgs.gov/usgspubs/pp/pp1395

=cut

sub n_rad {
  my $self = shift;
  my $lat  = shift; #radians
  die('Error: Latitude (radians) required.') unless defined $lat;
  my $a    = $self->a;
  my $e2   = $self->e2;
  return $a / sqrt(1 - $e2 * sin($lat)**2);
}

=head2 rho

rho is the radius of curvature of the earth in the meridian plane.

  my $rho=$obj->rho($lat);

=cut

sub rho {
  my $self = shift;
  my $lat  = shift; #degrees
  die('Error: Latitude (degrees) required.') unless defined $lat;
  return $self->rho_rad(rad_deg($lat));
}

=head2 rho_rad

rho is the radius of curvature of the earth in the meridian plane. Sometimes denoted as R'.

  my $rho = $obj->rho_rad($lat);

Reference: John P. Snyder, "Map Projections: A Working Manual", USGS, page 24, equation (4-18) http://pubs.er.usgs.gov/usgspubs/pp/pp1395

=cut

sub rho_rad {
  my $self = shift;
  my $lat  = shift; #radians
  die('Error: Latitude (radians) required.') unless defined $lat;
  my $a    = $self->a;
  my $e2   = $self->e2;
  return $a * (1-$e2) / ( 1 - $e2 * sin($lat)**2 )**(3/2)
  #return $a * (1-$e2) / sqrt(1 - $e2 * sin($lat)**(3/2)); #Bad formula from somewhere
}

=head2 polar_circumference

Method returns the value of the semi-minor axis times 2*PI.

  my $polar_circumference=$obj->polar_circumference;

=cut

sub polar_circumference {
  my $self = shift;
  return 2 * PI() * $self->b();
}

=head2 equatorial_circumference

Method returns the value of the semi-major axis times 2*PI.

  my $equatorial_circumference=$obj->equatorial_circumference;

=cut

sub equatorial_circumference {
  my $self = shift;
  return 2 * PI() * $self->a();
}

sub _setref {
  my $self  = shift;
  my $param = shift;
  if ('HASH' eq ref($param)) {
    if (defined($param->{'a'})) {
      $self->{'a'}          = $param->{'a'};
      $self->{'shortname'}  = 'Custom' unless defined($self->shortname);
      if (defined $param->{'i'}) {
        $self->{'i'}        = $param->{'i'};
        undef($self->{'b'});
        undef($self->{'f'});
        $self->{'longname'} = 'Custom Ellipsoid {a=>'.$self->a.',i=>'.$self->i.'}'  unless defined($self->longname);
      } elsif (defined $param->{'b'}){
        $self->{'b'}        = $param->{'b'};
        undef($self->{'i'});
        undef($self->{'f'});
        $self->{'longname'} = 'Custom Ellipsoid {a=>'.$self->a.',b=>'.$self->b.'}'  unless defined($self->longname);
      } elsif (defined $param->{'f'}){
        $self->{'f'}        = $param->{'f'};
        undef($self->{'b'});
        undef($self->{'i'});
        $self->{'longname'} = 'Custom Ellipsoid {a=>'.$self->a.',f=>'.$self->f.'}'  unless defined($self->longname);
      } else {
        $self->{'b'}        = $param->{'a'};
        undef($self->{'f'});
        undef($self->{'i'});
        $self->{'longname'} = 'Custom Sphere {a=>'.$self->a.'}' unless defined($self->longname);
      }
    } else {
      die('Error: a must be defined');
    }
  } else {