PHP计算地图上两点间的距离

class GeoHelper
{
    /**
     * @param int $lat1
     * @param int $lon1
     * @param int $lat2
     * @param int $lon2
     * @param string $unit
     * @return
     */
    public static function distance($lat1, $lon1, $lat2, $lon2, $unit = "K")
    {
        $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);
        $miles = $dist * 60 * 1.1515;
        $unit = strtoupper($unit);

        if ($unit == "K") {
            return ($miles * 1.609344);
        } else
            if ($unit == "N") {
                return ($miles * 0.8684);
            } else { //mi
                return $miles;
            }
    }

    /**
     *
     * @param string $address
     * @param string $apikey
     * @return array [1]:lat [0]:lng
     */
    public static function getLatLng($address, $apikey)
    {
        $find = array("\\n", "\\r", " ");
        $replace = array("", "", "+");
        $address = str_replace($find, $replace, $address);
        $url = 'http://maps.google.com/maps/geo?q=' . $address . '&key=' . $apikey .
            '&sensor=false&output=xml&oe=utf8';
        $response = self::xml2array($url);
        $coordinates = $response['kml']['Response']['Placemark']['Point']['coordinates'];
        if (!empty($coordinates)) {
            $point_array = split(",", $coordinates);
            return $point_array;
        }
    }
}

图上, PHP