NAME

       GIS::Distance::Formula - Formula base class.

DESCRIPTION

       This is the parent class for all GIS::Distance formula classes such as those listed at
       "FORMULAS" in GIS::Distance.

       To author your own formula class:

           package My::Formula;

           use parent 'GIS::Distance::Formula';

           sub _distance {
               my ($lat1, $lon1, $lat2, $lon2) = @_;

               # ...

               return $kilometers;
           }

           1;

       Then use it:

           my $gis = GIS::Distance->new('My::Formula');
           my $km = $gis->distance( @coords );

       The global $GIS::Distance::Formula::SELF is available when your "_distance()" subroutine
       is called if, and only if, the entry point was "distance" in GIS::Distance and NOT
       "distance_metal" in GIS::Distance or otherwise.

       Much of the interface described in GIS::Distance is actually implemented by this module.

SUPPORT

       See "SUPPORT" in GIS::Distance.

AUTHORS

       See "AUTHORS" in GIS::Distance.

LICENSE

       See "LICENSE" in GIS::Distance.