创建一个XML文档，以便使用PHP、MySQL&；谷歌地图

我正在使用以下内容创建一个带有PHP、MySQL和amp；谷歌地图：https://developers.google.com/maps/articles/phpsqlsearch_v3

到目前为止，我的代码如下：

<?php
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
error_reporting(-1);

require("dbinfo.php");
// Get parameters from URL
$center_lat = $_GET["lat"];
$center_lng = $_GET["lng"];
$radius = $_GET["radius"];
// Start XML file, create parent node
$dom = new DOMDocument("1.0");
$node = $dom->createElement("markers");
$parnode = $dom->appendChild($node);
// Opens a connection to a mySQL server
$connection=mysqli_connect($hostname, $username, $password);
if (!$connection) {
  die("Not connected : " . mysqli_error());
}

// Set the active mySQL database
$db_selected = mysqli_select_db($database, $connection);
if (!$db_selected) {
  die ("Can not use db : " . mysqli_error());
}
// Search the rows in the locations table
$query = sprintf("SELECT id, ( 3959 * acos( cos( radians('%s') ) * cos( radians( lat ) ) * cos( radians( lng ) - radians('%s') ) + sin( radians('%s') ) * sin( radians( lat ) ) ) ) AS distance FROM locations HAVING distance < '%s' ORDER BY distance LIMIT 0 , 20",
  mysqli_real_escape_string($center_lat),
  mysqli_real_escape_string($center_lng),
  mysqli_real_escape_string($center_lat),
  mysqli_real_escape_string($radius));
$result = mysqli_query($query);
$result = mysqli_query($query);
if (!$result) {
  die("Invalid query: " . mysqli_error());
}
header("Content-type: text/xml");
// Iterate through the rows, adding XML nodes for each
while ($row = @mysqli_fetch_assoc($result)){
  $node = $dom->createElement("location");
  $newnode = $parnode->appendChild($node);
  $newnode->setAttribute("name", $row['name']);
  $newnode->setAttribute("address", $row['address']);
  $newnode->setAttribute("lat", $row['lat']);
  $newnode->setAttribute("lng", $row['lng']);
  $newnode->setAttribute("distance", $row['distance']);
}
echo $dom->saveXML();
?>

当我运行这个时，我得到以下错误：

    Notice: Undefined index: lat in /customers/b/7/e/tournamentfinder.co.uk/httpd.www/test/genxml.php on line 11
 Notice: Undefined index: lng in /customers/b/7/e/tournamentfinder.co.uk/httpd.www/test/genxml.php on line 12
 Notice: Undefined index: radius in /customers/b/7/e/tournamentfinder.co.uk/httpd.www/test/genxml.php on line 13
 Warning: mysqli_select_db() expects parameter 1 to be mysqli, string given in /customers/b/7/e/tournamentfinder.co.uk/httpd.www/test/genxml.php on line 28
 Warning: mysqli_error() expects exactly 1 parameter, 0 given in /customers/b/7/e/tournamentfinder.co.uk/httpd.www/test/genxml.php on line 30 Can not use db :

有人能帮助我理解这一点吗？或者为我指明正确的方向吗？感谢您的帮助！

感谢