package GIS::Distance::Formula;

use Moose;
use Carp qw( croak );

=head1 ATTRIBUTES

=head2 kilometer_rho

Number of kilometers around the equator of the earth.
Defaults to 6371.64.

=cut

has 'kilometer_rho' => (
    is      => 'ro',
    isa     => 'Num',
    default => 6371.64,
);

=head2 deg_ratio

Number of units in a single decimal degree (lat or lon) at the equator.
The default, 0.0174532925199433, is derived from:

  $gis->distance( 10,0 => 11,0 )->km() / $gis->kilometer_rho()

=cut

has 'deg_ratio' => (
    is      => 'ro',
    isa     => 'Num',
    default => 0.0174532925199433,
);

=head1 METHODS

=head2 distance

This method is just a placeholder and throws an errors if called.  The
distance() method should be re-implemented by any class that extends
this class.

=cut

sub distance {
    my $class = __PACKAGE__;
    croak( qq{distance() can not be called on $class directly} );
}

1;