Question

I am using MyLocationOverlay to display the current location. However, it takes a while for the location to get updated. I wanted to implement something like the “follow me” feature on iPhone wherein the location of the user is also moving as the user moves. How can I make the marker of MyLocationOverlay to perform live update on its location?

Please note that I override the draw() and drawMyLocation() because I need to draw a custom marker.

My current code looks like this: (The problem with my code is that the marker does not move along with the user. Since it takes a while before onLocationChanged is called, the marker will just suddenly jump from one place to another.)

@Override
public synchronized void onLocationChanged(Location location)
{
    if (location != null && mapController != null)
    {
        //Recenter map based on current location
        mapController.animateTo(new GeoPoint((int) (location.getLatitude() * 1e6), (int) (location.getLongitude() * 1e6)));
    }
    super.onLocationChanged(location);
}

Answer 1

You can give location manager minimal interval to wait between calling that method, but it’s not exactly going to mind that interval 100% of the time (see description of LocationManager.requestLocationUpdates()). Might be shorter, might be longer – because, e.g. it can be cloudy and gps chip won’t be able to get location updates as regularly as you’d want it to.

There’s no proper way to overcome this – location services will always have imperfections. Every location-aware app I used “hung” the marker from time to time because gps chip lost fix for a moment.

The only thing you can do to smooth this a bit is to remember the speed of movement and should gps lose fix give the map marker fake updates based on the assumption that the user is moving in the same direction with the same speed they were when gps had a fix. But it only makes sense to do that for like 2-5 skipped real updates (just to smooth the cases when fix is lost for several seconds).

UPD For that, you can implement kind of proxy location listener, which will update your marker strictly minding the intervals you specify, e.g. every 200 ms, and do so based on it’s stored location. And the stored location can be asynchronously updated by the real location listener. Location objects have time of the fix that provided data (see getTime() method), you can use that to determine whether you should still “predict” next marker movement or the location is old enough to give up and notify user that gps has no clue where they are 🙂