getJSON แต่ข้อมูลไม่ออกมาเลย เขียนโค๊ดผิดตรงใหนเหรอคะ

function addMark(markID) {
		var str = './serverside/point_avr_get.php?qtype=mark&mark_id=' + markID + '&' + jQuery.now();	
		$.getJSON( str, function(rec) {
			$.each(rec.mark, function(j, item) {
				var newpoint = new OpenLayers.Geometry.Point(item.lon, item.lat);
				var newPoint = [];
					
					g_line_oldpoint[markID] = newpoint;	
					m_lon = item.lon;
					m_lat = item.lat;
									});
				var lonlat_get = new OpenLayers.LonLat(m_lon , m_lat);
				var pic_get = 'images/talk.png';
				var sz = new OpenLayers.Size(34, 25);
				var offset = new OpenLayers.Pixel(-(size.w/2), -size.h);
				var icon_get = new OpenLayers.Icon(pic_get, sz, null, offset);
				m_marker_get[markID] = new OpenLayers.Marker(lonlat_get, icon_get);
				m_markers.addMarker(g_marker_get[markID]);	
			
		
		});

<?
	include("gbvar.php");
?>
<?
	$g_qtype = $_GET['qtype'];
	$g_carid = $_GET['car_id'];
	$mark = $_GET['mark'];
	$mark_id = $_GET['mark_id'];
	$con = mysql_connect($db_host, $db_user, $db_pass) or die('Could not connect: ' . mysql_error());
	mysql_select_db($db_name, $con) or die('Could not select database');
	if ( $g_qtype == "realtime" ) $query = "SELECT * FROM cars WHERE id = '$g_carid'";
	else if ( $g_qtype == "log" ) {
		$g_dtstart = $_GET['dt_start'];
		$g_dtend = $_GET['dt_end'];
		$g_dtstart = str_replace('%20', ' ', $g_dtstart);
		$g_dtend = str_replace('%20', ' ', $g_dtend);
		$query = "SELECT gps_lon, gps_lat, car_picture FROM point_log WHERE ( dt_post BETWEEN '$g_dtstart' AND '$g_dtend' ) AND ( car_id = '$g_carid' )";
	}
	else if($g_qtype=="mark")
	{
		$query="select * from mark where mark_id='$mark_id'";
		}
	$result = mysql_query($query) or die('Query failedqqqqq: ' . mysql_error());

	$arr = array();
	if ( mysql_num_rows($result) != 0 ) {
		while($row=mysql_fetch_assoc($result)) {	
			$arr[] = $row;
		}
		header('Content-type: application/json');
		if ( $g_qtype == "realtime" ) echo json_encode(array('cars'=>$arr));	
		else if ( $g_qtype == "log" ) echo json_encode(array('point_log'=>$arr));
		else if ( $g_qtype == "mark" ) echo json_encode(array('mark'=>$arr));
	}
	mysql_free_result($result);
	mysql_close($con);
?>