<?php
function encludean_method($lat1, $lon1, $lat2, $lon2)
{
	$R = 6372.8; // km

	$lat1 = deg2rad($lat1);
	$lat2 = deg2rad($lat2);
	$lon1 = deg2rad($lon1);
	$lon2 = deg2rad($lon2);

	$a = (cos($lat2) * cos($lon2)) - (cos($lat1) * cos($lon1));
	$b = (cos($lat2) * sin($lon2)) - (cos($lat1) * sin($lon1));
	$c = sin($lat2) - sin($lat1);
	$ch = sqrt(pow($a, 2.0) + pow($b, 2.0) + pow($c, 2.0));
	$phi = 2.0 * asin($ch / 2.0);

	return $R * $phi;
}

var_dump(encludean_method(36.12, -86.67, 33.94, -118.40));
var_dump(encludean_method(50.24, 28.68, 50.32, 29.05));
var_dump(encludean_method(1.5745, 103.6200, 1.5748, 103.6195));