Unbelievably inaccurate GPS points. What is the reason?

Question

I have developed an application for Android, for storing user\'s GPS location.

One of my customers gave me his device and I noticed that sometimes the accuracy of t

Answer 1

If you don't trust Google's Fused API, or any other algorithm, and you have some knowledge about NMEA formatted, raw GPS data, then I recommend you take a deep dive into the raw GPS data, and see what is actually going on.

You can get NMEA_0183 GPS messages from the GPS chipset, and analyze satellite constellation, SNR, DOP, lat, lon, etc.

LocationManager LM = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        ((LocationManager)getSystemService(Context.LOCATION_SERVICE)).requestLocationUpdates(LocationManager.GPS_PROVIDER,0,0,new LocationListener(){
            @Override
            public void onLocationChanged(Location loc) {}
            @Override
            public void onProviderDisabled(String provider) {}
            @Override
            public void onProviderEnabled(String provider) {}
            @Override
            public void onStatusChanged(String provider, int status,Bundle extras) {} });

        //for API23 and below
        LM.addNmeaListener(new GpsStatus.NmeaListener() {
        public void onNmeaReceived(long timestamp, String nmea) {
            Log.d(TAG, nmea+"\n");
        }});

       //for API24 and above
       LM.addNmeaListener(new OnNmeaMessageListener() {
        public void onNmeaMessage(String nmea, long timestamp) {
            Log.d(TAG, nmea+"\n");
        }});

Here are some useful NMEA sentences:

GGA - Global Positioning System Fix Data

GSA - GPS DOP and active satellites

GSV - Satellites in view

ZDA - Time & Date - UTC, day, month, year and local time zone