what's wrong to my code..where my return value found undefind...

var so;
var imgid_callback1;
const DIV_ID = 'locationsample';


function setup(){
  try {
    so = device.getServiceObject("Service.Location", "ILocation");

  }
  catch (e) {
      alert('<setup> ' +e);
  }
}


function getLocation(imgId) {


  var updateoptions = new Object();
  // Setting PartialUpdates to 'FALSE' ensures that user get atleast
  // BasicLocationInformation (Longitude, Lattitude, and Altitude.)
  updateoptions.PartialUpdates = false;

  var criteria = new Object();
  criteria.LocationInformationClass = "BasicLocationInformation";
  criteria.Updateoptions = updateoptions;

  try {
    var result = so.ILocation.GetLocation(criteria);
    if(!checkError("ILocation::getLocation",result,DIV_ID,imgId)) {
      document.getElementById(DIV_ID).innerHTML = showObject(result.ReturnValue);
    }
  }
  catch (e) {

    alert ("getLocation: " + e);
  }
}

function getLocationAsync(imgId) {
  var updateoptions = new Object();
  updateoptions.PartialUpdates = false;
 var criteria = new Object();
  criteria.LocationInformationClass = "BasicLocationInformation";
  criteria.Updateoptions = updateoptions;

imgid_callback1 = imgId;

  try {
    var result = so.ILocation.GetLocation(criteria, callback1);
    if(!checkError("ILocation::getLocationAsync",result,DIV_ID,imgId)) {
      showIMG(imgId,"");
    }
  }
  catch (e) {

    alert ("getLocationAsync: " + e);
  }
}


function callback1(transId, eventCode, result){
var latitude = result.ReturnValue.Latitude;     //<-----Error: Undefined Value
var longitude = result.ReturnValue.Longitude;

var req = null;
try {
req = new XMLHttpRequest();

if (typeof req.overrideMimeType != "undefined") {
req.overrideMimeType("text/xml");
}
req.onreadystatechange = function() {
if (req.readyState == 4) {
if (req.status == 200) {
}
} else {
alert("Error");
}
}



req.open("POST","http://localhost:8080/GPS/location",true);
req.setRequestHeader("longitude",+longitude);
req.setRequestHeader("latitude",+latitude);

req.send();
} catch (ex) {
alert(ex);
}
}