html5 geolocation is not showing on mobile device #WiFi - html

Question

I have implemented Html5 geo-location.It works Good in system.
But when i used to run this on mobile device it's not working if my location service is turned off .
However my mobile devices is Connected through WiFi it is not showing location.It as to show something nearest point
function writeAddressName(latLng) {
var geocoder = new google.maps.Geocoder();
geocoder.geocode({
"location": latLng
},
function(results, status) {
if (status == google.maps.GeocoderStatus.OK)
document.getElementsByName("address").item(0).value = results[0].formatted_address;
else
document.getElementById("error").innerHTML += "Unable to retrieve your address" + "<br />";
});
}
function geolocationSuccess(position) {
var userLatLng = new google.maps.LatLng(position.coords.latitude, position.coords.longitude);
// Write the formatted address
writeAddressName(userLatLng);
var myOptions = {
zoom : 16,
center : userLatLng,
mapTypeId : google.maps.MapTypeId.ROADMAP
};
// Draw the map
var mapObject = new google.maps.Map(document.getElementById("map"), myOptions);
// Place the marker
new google.maps.Marker({
map: mapObject,
position: userLatLng
});
}
function geolocationError(positionError) {
document.getElementById("error").innerHTML += "Error: " + positionError.message + "<br />";
}
function geolocateUser() {
// If the browser supports the Geolocation API
if (navigator.geolocation)
{
var positionOptions = {
enableHighAccuracy: true,
timeout: 10 * 1000 // 10 seconds
};
navigator.geolocation.getCurrentPosition(geolocationSuccess, geolocationError, positionOptions);
}
else
document.getElementById("error").innerHTML += "Your browser doesn't support the Geolocation API";
}
window.onload = geolocateUser;