DistanceCalculator::calculate

public function calculate(Location $location1, Location $location2)
{
	if(
		empty($location1->getLatitude())
		|| empty($location1->getLongitude())
		|| empty($location2->getLatitude())
		|| empty($location2->getLongitude())
	)
	{
		return false;
	}

	$lat1 = $location1->getLatitude() / 180 * M_PI;
	$lat2 = $location2->getLatitude() / 180 * M_PI;
	$lon1 = $location1->getLongitude() / 180 * M_PI;
	$lon2 = $location2->getLongitude() / 180 * M_PI;

	return (float)acos(sin($lat1)*sin($lat2)
		+ cos($lat1)*cos($lat2)
		* cos($lon2-$lon1))
		* self::EARTH_RADIUS;
}