Thanks (again) Ludwig. I've installed the satellite app and will try it out.
I realise that GPS accuracy is not always great in built-up areas. However, that doesn't explain why often the Maps application seems to have good GPS accuracy, but the LocationListener in this application doesn't - at the same moment in time! Maybe I do just need to use Skyhook in order to get a reliable GPS fix. Anna On 11 Feb, 18:26, Ludwig <[email protected]> wrote: > It is notoriously difficult for GPS chips to get a good fix in built-up > areas. 'Seeing the sky' is a bit loose a formulation: ideally a unit has to > be able to see five or more satellites and for accuracy purposes they must > not be all exactly overhead. Furthermore buildings bounce back the signals > adding to confusion. On a clear mountain top is best, maybe the top of > Canary Wharf tower. > That's why there have been different approaches to improve GPS accuracy, > e.g. triangulation from cell-towers. Skyhook Wireless claim to have a > library that improves accuracy, apparently newer versions of AndNav use it. > Other applications assume that you are always on a road and will place you > on the nearest one. > > I just published a little application that gives you a view of the satellite > constellation used to derive your location. You can get it > here:http://andappstore.com/AndroidPhoneApplications/apps/38257 > <http://andappstore.com/AndroidPhoneApplications/apps/38257>That > does not itself improve accuracy, but at least you can get an idea why your > accuracy is shite.. > > Ludwig > > 2009/2/11 Anna PS <[email protected]> > > > > > Hi, > > > I'm writing a mapping application. In simple terms, it sends some info > > about the user's current location to a server when the user clicks on > > a button. > > > I need the location to be absolutely correct, and when I first started > > to implement LocationListener, I found that it often wasn't. So I've > > used location.getAccuracy() to check the GPS accuracy, and warn the > > user - without submitting the data - if the location isn't accurate > > enough. > > > The code is below. > > > I've been trying the app outside and find that the accuracy is often > > 32m, 64m or even higher, even after 20 or 30 seconds. This is in > > central London, in full view of the sky, on a clear day! I need it to > > be below 10m. > > > At the same time, if I open the Maps application while standing in the > > same spot, it shows my GPS location as a blue spot on the map - > > suggesting the listener in Maps has perfect accuracy. > > > So what is the problem? Have I implemented the listener/check in the > > wrong way (which feels like the likely explanation), or is it that GPS > > in Android isn't good enough to write mapping applications? Does > > anyone else have experience of this? > > > Best, > > Anna > > > -------------------------------------------------- > > > //cut-down version of code > > > public class GPSTest extends Activity { > > > /** Called when the activity is first created. */ > > private static final String LOG_TAG = "GPSTest"; > > > private Double latitude = 0.0; > > private Double longitude = 0.0; > > private String latString = ""; > > private String longString = ""; > > > //Location items > > LocationManager locationmanager; > > LocationListener listener; > > Location location; > > private float gpsAccuracy; > > private long locationTime; > > private long currentTime; > > private long timeDifference; > > > //Textview and button > > private TextView tvErrorMessage; > > private View submitButton; > > > private String responseString; > > > private ProgressDialog pd; > > final Handler mHandler = new Handler(); > > final Runnable mUpdateResults = new Runnable() { > > public void run() { > > pd.dismiss(); > > updateResultsInUi(); > > } > > }; > > > private static int globalStatus = 0; > > private static final int GPS_NOT_FOUND = 1; > > private static final int GPS_OK = 2; > > > �...@override > > public void onCreate(Bundle savedInstanceState) { > > super.onCreate(savedInstanceState); > > Log.d(LOG_TAG, "onCreate"); > > setContentView(R.layout.main); > > > // Set up the button listeners > > findViews(); > > setListeners(); > > > // Register with GPS, throw an error if there's a failure > > if (!testProviders()) { > > tvErrorMessage > > .setText("Can't get location - check > > that GPS is turned on in > > Settings"); > > } > > } > > > �...@override > > public void onRestart() { > > super.onRestart(); > > Log.d(LOG_TAG, "onRestart"); > > // Register with GPS, throw an error if there's a failure > > if (!testProviders()) { > > tvErrorMessage > > .setText("Can't get location - check > > that GPS is turned on in > > Settings"); > > } > > } > > > // > > ********************************************************************** > > // findViews/setListeners: set up the button listeners > > // > > ********************************************************************** > > > private void findViews() { > > Log.d(LOG_TAG, "findViews"); > > submitButton = (Button) findViewById(R.id.submit_button); > > tvErrorMessage = (TextView) findViewById(R.id.tv_error); > > > } > > > private void setListeners() { > > Log.d(LOG_TAG, "setListeners"); > > submitButton.setOnClickListener(new OnClickListener() { > > public void onClick(View v) { > > uploadToServer(); > > } > > } > > }); > > } > > > // > > ********************************************************************** > > // testProviders: Register for location updates, warn if not found > > // > > ********************************************************************** > > public boolean testProviders() { > > Log.d(LOG_TAG, "testProviders"); > > String location_context = Context.LOCATION_SERVICE; > > locationmanager = (LocationManager) getSystemService > > (location_context); > > listener = new LocationListener() { > > public void onLocationChanged(Location location) { > > } > > > public void onProviderDisabled(String provider) { > > } > > > public void onProviderEnabled(String provider) { > > } > > > public void onStatusChanged(String provider, int > > status, > > Bundle extras) { > > } > > }; > > > locationmanager.requestLocationUpdates("gps", 0, 0, > > listener); > > > location = locationmanager.getLastKnownLocation("gps"); > > > if (location != null) { > > latitude = location.getLatitude(); > > longitude = location.getLongitude(); > > latString = latitude.toString(); > > longString = longitude.toString(); > > Log.d(LOG_TAG, "Location found: latitude" + > > latString > > + " and longitude " + longString); > > return true; > > > } else { > > Log.d(LOG_TAG, "Location not found"); > > return false; > > } > > > } > > > // > > ********************************************************************** > > // uploadToServer: uploads details, handled via a background thread > > // Also checks the age and accuracy of the GPS data first > > // > > ********************************************************************** > > private void uploadToServer() { > > Log.d(LOG_TAG, "uploadToServer"); > > pd = ProgressDialog > > .show( > > this, > > "Uploading, please wait...", > > "Uploading GPS location. > > This can take several seconds. Please > > be patient!", > > true, false); > > Thread t = new Thread() { > > public void run() { > > doUploadinBackground(); > > mHandler.post(mUpdateResults); > > } > > }; > > t.start(); > > } > > > private boolean doUploadinBackground() { > > Log.d(LOG_TAG, "doUploadinBackground"); > > DefaultHttpClient httpclient = new DefaultHttpClient(); > > HttpPost httppost = new HttpPost(<##uri##>); > > > // get GPS info - make sure it's sufficiently accurate > > if (location != null) { > > // Check that the location is up-to-date and > > reasonably accurate > > locationTime = location.getTime(); > > currentTime = System.currentTimeMillis(); > > timeDifference = (currentTime - locationTime) / > > 1000; > > > gpsAccuracy = location.getAccuracy(); > > int count = 0; > > > // Wait for accurate GPS data, up to a maximum of 5 > > seconds before > > // throwing an error > > while (((timeDifference > 30) || (gpsAccuracy > > > 10.0)) > > && (count < 10)) { > > location = > > locationmanager.getLastKnownLocation("gps"); > > locationTime = location.getTime(); > > ... > > read more » --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. 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