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package GIS::Distance::GreatCircle;
use 5.008001;
use strictures 2;
our $VERSION = '0.20';
use parent 'GIS::Distance::Formula';
use Math::Trig qw( deg2rad asin );
use GIS::Distance::Constants qw( :all );
use namespace::clean;
sub _distance {
my ($lat1, $lon1, $lat2, $lon2) = @_;
$lon1 = deg2rad($lon1);
$lat1 = deg2rad($lat1);
$lon2 = deg2rad($lon2);
$lat2 = deg2rad($lat2);
my $c = 2*asin( sqrt(
( sin(($lat1-$lat2)/2) )**2 +
cos($lat1) * cos($lat2) *
( sin(($lon1-$lon2)/2) )**2
) );
return $KILOMETER_RHO * $c;
}
1;
__END__
=encoding utf8
=head1 NAME
GIS::Distance::GreatCircle - Great circle distance calculations.
=head1 DESCRIPTION
A true Great Circle Distance calculation. This was created because the
L<GIS::Distance::MathTrig> formula uses L<Math::Trig>'s
C<great_circle_distance()> which doesn't actually appear to use the
actual Great Circle Distance formula (more likely Cosine).
A faster (XS) version of this formula is available as
L<GIS::Distance::Fast::GreatCircle>.
Normally this module is not used directly. Instead L<GIS::Distance>
is used which in turn interfaces with the various formula classes.
=head1 FORMULA
c = 2 * asin( sqrt(
( sin(( lat1 - lat2 )/2) )**2 +
cos( lat1 ) * cos( lat2 ) *
( sin(( lon1 - lon2 )/2) )**2
) )
=head1 SUPPORT
See L<GIS::Distance/SUPPORT>.
=head1 AUTHORS
See L<GIS::Distance/AUTHORS>.
=head1 LICENSE
See L<GIS::Distance/LICENSE>.
=cut
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