a little help for a little counter

[nintesa]

Hello from Italy!

I'm trying to create a little script (php/mysql/javascript) to record
visits of some of my sites. I have sites www.a.com, www.b.com ecc... and
I have my counter script on www.phptrack.net.

I compare the results of my counter with shinystat: visits (I would
better call it "pages viewed") is perfectly ok!! but I have a too big
number of visitors. I think there shoul be a problem with sessions...
could someone help me?

The js file is:

var screen_x=window .screen.width;
var screen_y=window .screen.height;
var cur_location = escape(window.l ocation.toStrin g());
var referer = escape(document .referrer);
document.write( '<img
src="http://phptrack.net/phptrack.php?si te_id='+phptrac k_site_id+'&s_x ='+screen_x+'&s _y='+screen_y+' &cur_loc='+cur_ location+'&refe rer='+referer+' "
width="0" height="0" border="0"/>');

and the php script is:

<?

session_start() ;

require('compon ents/phptrack/configure.php') ;
require('includ es/classes/db.php');
$db = new db(DB_HOST,DB_N AME,DB_USER,DB_ PASSWORD);


$site_id=(int)$ _GET['site_id'];

//$_SESSION[$site_id.'_visi tor_id']
//This because a visitor can visit both www.a.com and www.b.com in the
//same session!!


if (!($_SESSION[$site_id.'_visi tor_id']>0)) {
$sql_data = new sql_data;
$sql_data->add('previous_ visitor_id',0);
$sql_data->add('site_id', $site_id);
$sql_data->add('ip',$_SER VER['REMOTE_ADDR']);
$sql_data->add('language' ,$_SERVER['HTTP_ACCEPT_LA NGUAGE']);
$sql_data->add('browser', $_SERVER['HTTP_USER_AGEN T']);
$sql_data->add('screen_x' ,(int)$_GET['s_x']);
$sql_data->add('screen_y' ,(int)$_GET['s_y']);
$sql_data->perform('raw_v isitors');
$_SESSION[$site_id.'_visi tor_id']=$db->insert_id();
}


$sql_data = new sql_data;
$sql_data->add('site_id', $site_id);
$sql_data->add('visitor_i d',$_SESSION[$site_id.'_visi tor_id']);
$sql_data->add('time','no w()');
$sql_data->add('location' ,$_GET['cur_loc']);
$sql_data->add('referer', $_GET['referer']);
$sql_data->perform('raw_v isits');
?>

Thanks...