geo_distance.php

<?php

/*
 * Great-circle distance computational forumlas
 *
 * https://en.wikipedia.org/wiki/Great-circle_distance
 */

$earth_radius_km = 6371;

function haversineDistance($latitude1, $longitude1, $latitude2, $longitude2) {
    $lat1 = deg2rad($latitude1);
    $lng1 = deg2rad($longitude1);
    $lat2 = deg2rad($latitude2);
    $lng2 = deg2rad($longitude2);

    $d_lat = abs($lat1 - $lat2);
    $d_lng = abs($lng1 - $lng2);

    $a = pow(sin($d_lat / 2), 2) + cos($lat1) * cos($lat2)
        * pow(sin($d_lng / 2), 2);

    $d_sigma = 2 * asin(sqrt($a));

    global $earth_radius_km;
    return($earth_radius_km * $d_sigma);
}

function vincentyDistance($latitude1, $longitude1, $latitude2, $longitude2) {
    $lat1 = deg2rad($latitude1);
    $lng1 = deg2rad($longitude1);
    $lat2 = deg2rad($latitude2);
    $lng2 = deg2rad($longitude2);

    $d_lng = abs($lng1 - $lng2);

    // Numerator
    $a = pow(cos($lat2) * sin($d_lng), 2);

    $b = cos($lat1) * sin($lat2);
    $c = sin($lat1) * cos($lat2) * cos($d_lng);
    $d = pow($b - $c, 2);

    $e = sqrt($a + $d);

    // Denominator
    $f = sin($lat1) * sin($lat2);
    $g = cos($lat1) * cos($lat2) * cos($d_lng);

    $h = $f + $g;

    $d_sigma = atan2($e, $h);

    global $earth_radius_km;
    return($earth_radius_km * $d_sigma);
}

?>