Question

My Problem:
It takes two page loads from my mobile browser (testing with iphone) to get an accurate result. The first load will be half a mile or more off, and then the second load will be very close.

My question:
What needs to be done to get the accurate location on the first load?

Extra Info:

I’ve read through http://www.w3.org/TR/geolocation-API/ and am taking advantage of watchPosition with the enableHighAccuracy. Also I am using maximumAge:0 and timeout not set.

From http://www.w3.org/TR/geolocation-API/

If maximumAge is set to 0, the implementation must immediately attempt to acquire a new position object

the default value used for the timeout attribute is Infinity

My code is listed below

// Try HTML5 geolocation
    if(navigator.geolocation) {

    // updated this with watchPosition rather than getCurrentPosition
      navigator.geolocation.getCurrentPosition(function(position) {
        var pos = new google.maps.LatLng(position.coords.latitude,
                                         position.coords.longitude);

        var infowindow = new google.maps.InfoWindow({
          map: map,
          position: pos,
          content: 'Location found using HTML5.'
        });

        map.setCenter(pos);
      }, function() {
        handleNoGeolocation(true);
      },
    // enable high accuracy
    //  {maximumAge:100, timeout:5000, enableHighAccuracy: true}
            // 
                {maximumAge:0, enableHighAccuracy: true}
      );
    } else {
      // Browser doesn't support Geolocation
      handleNoGeolocation(false);
    }
  }

  function handleNoGeolocation(errorFlag) {
    if (errorFlag) {
      var content = 'Error: The Geolocation service failed.';
    } else {
      var content = 'Error: Your browser doesn\'t support geolocation.';
    }

Answer 1

I have the solution to getting the most accurate geolocation possible. You need to call clearWatch() after a given timeout. The timeout maybe time and or an event such as form click.

In my application I use a 5 second timeout and a click of a form element.

Here’s all the useful code snippets.

Set the onclick

<select onclick="aFormClick()" id="location"

Set the timeout in the function that is the parent of the watchPosition function

setTimeout("stopWatchPosition()",5000);

Create a function to listen for the form click

function aFormClick(){
stopWatchPosition();
}

Create the function for calling clearnWatch()

function stopWatchPosition(){
if (clearWatchCalled == 0){
    navigator.geolocation.clearWatch(watchID);
    clearWatchCalled++;
}
}

Make sure your watchPosition can be referenced by the ID

watchID = navigator.geolocation.watchPosition(function(position) {