client/server distance

function vincenty_distance($fromCoord, $toCoord) {
        /* Vincenty formula for great-circle distance, in kilometers */
        $earthRadius = 6371;
        $fromLat = deg2rad($fromCoord["latitude"]);
        $fromLon = deg2rad($fromCoord["longitude"]);
        $toLat = deg2rad($toCoord["latitude"]);
        $toLon = deg2rad($toCoord["longitude"]);
        $deltaLon = $toLon - $fromLon;
        $a = pow(cos($toLat) * sin($deltaLon), 2) + pow(cos($fromLat) * sin($toLat) - sin($fromLat) * cos($toLat) * cos($deltaLon), 2);
        $b = sin($fromLat) * sin($toLat) + cos($fromLat) * cos($toLat) * cos($deltaLon);
        $angle = atan2(sqrt($a), $b);
        return $angle * $earthRadius;
}

if ($_SERVER["HTTP_X_FORWARDED_FOR"] == null) {
        $clientAddr = $_SERVER["REMOTE_ADDR"];
}
else {
        $clientAddr = $_SERVER["HTTP_X_FORWARDED_FOR"];
}

$serverCoord = geoip_record_by_name($serverAddr);
$clientCoord = geoip_record_by_name($clientAddr);
$client_distance = round(vincenty_distance($serverCoord, $clientCoord));