LocationAndMaps

LocationAndMaps - Location & Maps   Mobile...

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Unformatted text preview: Location & Maps   Mobile applications can benefit from being location ­aware, e.g.,   Routing from a current to a desired location   Searching for stores near a current location   Android allows applications to determine & manipulate location   Represents a position on the Earth   A Location instance consists of:   Latitude, longitude, a UTC timestamp   Optionally, altitude, speed, and bearing   Represent sources of location data   Actual data may come from   GPS satellites   Cell phone towers   Internet   Different LocationProviders will exhibit different tradeoffs between cost, accuracy, availability & timeliness   Passive   Returns locations generated by other providers   Requires android.permission.ACCESS_FINE_LOCATION   Network   Determines location based on cell tower and WiFi access points   Requires either ▪  android.permission.ACCESS_COARSE_LOCATION or android.permission.ACCESS_FINE_LOCATION   GPS   Determines location using satellites   Requires android.permission.ACCESS_FINE_LOCATION   System service for accessing location data   getSystemService(Context.LOCATION_SERVICE)   Enables   Determining the last known user location   Registering for location updates   Registering to receive Intents when the device nears a given location   Defines callback methods that are called when Location or LocationProvider status changes   void onLocationChanged(Location location)   void onProviderDisabled(String provider)   void onProviderEnabled(String provider)   void onStatusChanged(String provider, int status, Bundle extras) 1.  2.  3.  4.  Start listening for updates from location providers Maintain a "current best estimate" of location When estimate is “good enough”, stop listening for location updates Use best location estimate public class LocationGetLocationActivity extends Activity { … public void onCreate(Bundle savedInstanceState) { … final LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); bestReading = locationManager. getLastKnownLocation(LocationManager.GPS_PROVIDER); … locationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0,0, locationListener); … … final LocationListener locationListener = new LocationListener() { public synchronized void onLocationChanged(Location location) { if (location.getAccuracy() < bestReading.getAccuracy()) { bestReading = location; tv.setText(getDisplayString(location)); } … } …. Executors.newScheduledThreadPool(1).schedule( new Runnable() { public void run() { locationManager.removeUpdates(locationListener); } }, 10000, TimeUnit.MILLISECONDS); …   Several factors to consider   Measurement time   Accuracy   Provider type   Location measurement really drains the battery   To limit battery use   Return updates less frequently   Restrict the set of Location Providers ▪  Use least accurate (cheaper) provider necessary   Always check last known measurement   Turn off updates in onPause()       A visual representation of area Today’s examples use Google Maps library Not part of standard Android distribution   Install SDK add ­on   build against add ­on ("Google APIs (Google Inc.)"   Permissions   <uses ­library android:name="com.google.android.maps" />   <uses ­permission android:name="android.permission.INTERNET" />   MapActivity   MapView   GeoPoint   Overlay   ItemizedOverlay   Base class for Activities that display MapViews   Subclass creates MapView in onCreate()   Only one MapActivity is allowed per process   Extends ViewGroup   Displays a Map in one of several modes   Street View  ­ photographs   Satellite View – aerial   Traffic View – real time traffic superimposed   Supports panning and zooming   Support overlay views   Requires a Maps API key   See http://code.google.com/android/add ­ons/google ­apis/mapkey.html public class MapsEarthquakeMapActivity extends MapActivity { public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } protected boolean isRouteDisplayed() { return false; } } <RelativeLayout .."> <com.google.android.maps.MapView android:id="@+id/mapview" android:layout_width="fill_parent" android:layout_height="fill_parent" android:clickable="true" android:apiKey=”my Maps API key" /> </RelativeLayout>   Represents a location on Earth   latitude and longitude measured in microdegrees   1 microdegree == 1 millionth of a degree   Manages information drawn over a map   E.g., points of interest within a given city   MapView maintains a list of overlays   Retrieve via MapView.getOverlays() 21   Subclass of Overlay   Manages a list of OverlayItems   OverlayItems have a particular location   Draws a drawable at OverlayItem’s location   Keeps track of a focused item 22 public class MapsEarthquakeMapActivity extends MapActivity { List<Overlay> mapOverlays; Drawable mOverlayDrawable; EartQuakeDataOverlay itemizedOverlay; MapView mapView = null; public void onCreate(Bundle savedInstanceState) { … new HttpGetTask() .execute( "http://api.geonames.org/earthquakesJSON? north=44.1&south= ­9.9&east= ­22.4&west=55.2&username=demo” ); … mapView …. mapView.setBuiltInZoomControls(true); mapOverlays = mapView.getOverlays(); mOverlayDrawable = this.getResources() .getDrawable(R.drawable.pushpin_red); itemizedOverlay = new EartQuakeDataOverlay(mOverlayDrawable); } … // called when HttpGet().execute() finishes private void onFinishGetRequest(List<EarthQuakeRec> result) { for (EarthQuakeRec rec : result) { itemizedOverlay.addOverlay(new OverlayItem(rec.getGeoPoint(), String.valueOf(rec.getMagnitude()), "")); } mapOverlays.add(itemizedOverlay); MapController mc = mapView.getController(); mc.setCenter(new GeoPoint((int) (14.6041667 * 1E6), (int) (120.9822222 * 1E6))); } public class EartQuakeDataOverlay extends ItemizedOverlay<OverlayItem> { ArrayList<OverlayItem> mOverlays = new ArrayList<OverlayItem>(); protected EartQuakeDataOverlay(Drawable defaultMarker) { super(boundCenter(defaultMarker)); } public void addOverlay(OverlayItem overlay) { mOverlays.add(overlay); populate(); } protected OverlayItem createItem(int i) { return mOverlays.get(i); } public int size() { return mOverlays.size(); } }   LocationGetLocation   MapsMapActivity ...
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This note was uploaded on 01/13/2012 for the course CMSC 436 taught by Professor Porter during the Fall '11 term at Maryland.

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