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<?php

function distanceLatLng($a, $b)
{
    list($lat1, $lon1) = $a;
    list($lat2, $lon2) = $b;

	$theta = $lon1 - $lon2;
	$dist  = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
	$dist  = acos($dist);
	$dist  = rad2deg($dist);

    $meters = ($dist * 60 * 2 * 1000) * 1.2; // 20% de curva

    return $meters;
}