Location Services: Part 1 (Location and Geocoding)

Overview of Location-Based Services Location-based services use real-time location data from a mobile device or smartphone to provide information, entertainment, or security. Location-Based services are available on most smartphones, and a majority of smartphone owners use location-based services. Many popular applications integrate location-based services. Examples include GasBuddy − TripAdvisor IMDb − Google Maps Starbucks − The Weather Channel Navigation − Facebook Places ©SoftMoore Consulting

Location Providers GPS is more accurate, but it only works outdoors it uses more battery power it doesn't return the location quickly Android’s Network Location Provider determines user location using cell towers and Wi-Fi signals. It is less accurate than GPS, but it works indoors and outdoors it uses less battery power it responds faster ©SoftMoore Consulting

Challenges in Determining User Location Multitude of location sources GPS, Cell-ID, and Wi-Fi can each provide a clue to users location. Determining which to use and trust is a matter of trade-offs in accuracy, speed, and battery-efficiency. User movement Because the user location changes, you should account for movement by re-estimating user location every so often. Varying accuracy Location estimates from each location source are not consistent in their accuracy. A location obtained 10 seconds ago from one source might be more accurate than the newest location from another or same source. ©SoftMoore Consulting

Location-Based Services in Android Android provides two location frameworks in package android.location in package com.google.android.gms.location (part of Google Play services) The framework provided by Google Play services is the preferred way to add location-based services to an application. simpler API − greater accuracy more power efficient − more versatile Note that some classes in package android.location are still used by the Google Play services API. ©SoftMoore Consulting

Download Google Repository (Android SDK Manager) ©SoftMoore Consulting

Set Up Google Play Services (https://developers. google Make sure that Google Repository is installed, as shown in the previous slide. Create an application using Android Studio. In Android Studio under “Gradle Scripts”, edit the build.gradle file for “Module: app” (not the build.gradle file for the project). Under dependencies (near the bottom), add the following line near the end: compile 'com.google.android.gms:play-services-location:10.2.0' Save the changes and click “Sync Project with Gradle Files” in the toolbar, or click on menu item Tools  Android  Sync Project with Gradle Files. ©SoftMoore Consulting

Set Up Google Play Services (continued) Add the following metadata to the application manifest. <application ... <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version"/> <activity </activity> </application> ©SoftMoore Consulting

Key Interfaces for Google Play Services (in package com. google Key Interfaces for Google Play Services (in package com.google.android.gms.common.api) GoogleApiClient main entry point for Google Play services integration uses the builder pattern to construct an instance selected methods include abstract void connect() abstract void disconnect() abstract void isConnected() GoogleApiClient.ConnectionCallbacks provides callbacks that are called when the client is connected or disconnected from the service abstract methods: void onConnected(Bundle connectionHint) void onConnectionSuspended(int cause) ©SoftMoore Consulting

Key Interfaces for Google Play Services (continued) GoogleApiClient.OnConnectionFailedListener provides callbacks for scenarios that result in a failed attempt to connect the client to the service abstract method: void onConnectionFailed(ConnectionResult result) ©SoftMoore Consulting

Requesting User Permissions In order to receive location updates, user permission must be declared in the Android manifest. ACCESS_COARSE_LOCATION to access locations provided by cell tower/Wi-Fi triangulation ACCESS_FINE_LOCATION to access locations provided by GPS Both permissions are classified as dangerous and therefore applications must check at runtime whether or not they have been granted. The ACCESS_FINE_LOCATION permission includes permission for both location providers. ©SoftMoore Consulting

Requesting User Permissions (continued) Example <manifest ... >   <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>     ... </manifest> ©SoftMoore Consulting

Steps in Connecting to Google Play Services Request permission in the manifest and at runtime. Import classes/interfaces. Declare that the activity implements callback interfaces. Declare/build GoogleApiClient object. Implement callback interfaces. Implement methods onStart(), onStop(), and possibly other lifecycle methods such as onPause() and onResume() to gracefully handle connections to Google Play Services ©SoftMoore Consulting

Example: Connecting to Google Play Services import com.google.android.gms.common.ConnectionResult; import com.google.android.gms.common.api.GoogleApiClient; import com.google. ... GoogleApiClient.ConnectionCallbacks; import com.google. ... GoogleApiClient.OnConnectionFailedListener; ... public class MainActivity extends AppCompatActivity implements ConnectionCallbacks, OnConnectionFailedListener { private GoogleApiClient googleApiClient; @Override protected void onCreate(Bundle savedInstanceState) buildGoogleApiClient(); checkAccessLocationPermission(); } (continued on next page) ©SoftMoore Consulting

Example: Connecting to Google Play Services (continued) protected synchronized void buildGoogleApiClient() { googleApiClient = new GoogleApiClient.Builder(this) .addConnectionCallbacks(this) .addOnConnectionFailedListener(this) .addApi(LocationServices.API) .build(); } @Override public void onConnected(Bundle connectionHint) Log.i(LOG_TAG, "googleApiClient is connected "); add location services API (continued on next page) ©SoftMoore Consulting

Example: Connecting to Google Play Services (continued) @Override public void onConnectionSuspended(int cause) { // The connection to Google Play services was lost. // Attempt to re-establish the connection. Log.i(LOG_TAG, "Connection suspended"); googleApiClient.connect(); } public void onConnectionFailed(ConnectionResult result) // Refer to the javadoc for ConnectionResult // for possible error codes. Log.i(LOG_TAG, "Connection failed: error code = " + result.getErrorCode()); (continued on next page) ©SoftMoore Consulting

Example: Connecting to Google Play Services (continued) @Override protected void onStart() { super.onStart(); googleApiClient.connect(); } protected void onStop() super.onStop(); if (googleApiClient.isConnected()) googleApiClient.disconnect(); ... (continued on next page) ©SoftMoore Consulting

Example: Connecting to Google Play Services (continued) // in method checkAccessLocationPermission() if (permissionCheck == PackageManager.PERMISSION_GRANTED) { isPermissionGranted = true; googleApiClient.connect(); } // in method onRequestPermissionsResult() if (requestCode == REQUEST_ACCESS_LOCATION) if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) ... Call googleApiClient.connect() if permission is granted. ©SoftMoore Consulting

Testing Google Play Services To test an application using the Google Play services SDK, you must use either A compatible Android device that runs Android 2.3 or higher and includes Google Play Store An Android emulator (virtual device) that runs the Google APIs platform based on Android 4.2.2 or higher ©SoftMoore Consulting

Key Location Classes and Interfaces In package android.location Class Location represents a geographic location sensed at a particular time Class Address represents an address as a set of strings describing a location. Class Geocoder translates between locations and addresses ©SoftMoore Consulting

Key Location Classes and Interfaces (continued) In package com.google.android.gms.location Class LocationServices main entry point for location services integration Interface FusedLocationProviderApi main entry point for interacting with the fused location provider Interface LocationListener receives notifications when the location has changed Class LocationRequest contains quality-of-service parameters for requests to the FusedLocationProviderApi ©SoftMoore Consulting

Class Location A location consists of a latitude a longitude a UTC timestamp A location can optionally contain information on altitude, speed, and bearing. Information specific to a particular provider or class of providers may be communicated to the application using method getExtras(), which returns a Bundle of key/value pairs. Each provider will only provide those entries for which information is available. ©SoftMoore Consulting

Selected Methods in Class Location (package android.location.Location) double getLatitude() Returns the latitude of this fix. double getLongitude() Returns the longitude of this fix. long getTime() Returns the UTC time of this fix in milliseconds since January 1, 1970. float bearingTo(Location dest) Returns the approximate bearing in degrees East of true North. float distanceTo(Location dest) Returns the approximate distance in meters between this location and the given location. ©SoftMoore Consulting

Selected Methods in Class Location (continued) double getAltitude() Returns the altitude if available, in meters. float getBearing() Get the bearing, in degrees. float getSpeed() Get the speed if it is available, in meters/second over ground. Bundle getExtras() Returns additional provider-specific information about the location fix as a Bundle. ©SoftMoore Consulting

The Fused Location Provider The location APIs in Google Play services contains a fused location provider The fused location provider manages the underlying location technology and provides a simple API that allows you to specify requirements at a high level, like high accuracy or low power optimizes the device’s use of battery power ©SoftMoore Consulting

Obtaining the Last Known Location Class LocationServices contains a static reference to a FusedLocationProviderApi object named LocationServices.FusedLocationApi Using this object, call getLastLocation(GoogleApiClient client) to obtain the best and most recent location currently available. Example (e.g., in a button’s onClick() method) FusedLocationProviderApi locationProvider = LocationServices.FusedLocationApi; Location lastLocation = locationProvider.getLastLocation(googleApiClient); ©SoftMoore Consulting

Geocoding Geocoding is the process of transforming a street address or other description of a location into a (latitude, longitude) coordinate. Reverse geocoding is the process of transforming a (latitude, longitude) coordinate into a (partial) address. ©SoftMoore Consulting

Class Geocoder Class Geocoder (in package android.location) handles geocoding and reverse geocoding. The Geocoder class requires a backend service that is not included in the core android framework. may not work on the emulator The Geocoder query methods will return an empty list if there no backend service in the platform. Use the isPresent() method to determine whether a Geocoder implementation exists. ©SoftMoore Consulting

Example: Translating a Location to an Address (Reverse Geocoding) private Address getAddress(Location location) { Address address = null; try Geocoder geocoder = new Geocoder(this); double latitude = location.getLatitude(); double longitude = location.getLongitude(); int maxResults = 1; List<Address> addresses = geocoder.getFromLocation (latitude, longitude, maxResults); if (addresses.size() > 0) address = addresses.get(0); } (continued on next page) ©SoftMoore Consulting

Example: Translating a Location to an Address (continued) catch (IOException ex) { Log.e(LOG_TAG, ex.getMessage()); } return address; ©SoftMoore Consulting

Translating an Address to a Location (Geocoding) Create a string with the address String addressStr = "171 Moultrie Street, Charleston, SC, 29409"; Create a Geocoder instance Geocoder geocoder = new Geocoder(this); Call the Geocoder method getFromLocationName() List<Address> addresses = geocoder.getFromLocationName(addressStr, 1); Retrieve the latitude and longitude from the first address Address address = addresses.get(0); // call address.getLatitude() and // address.getLongitude() as needed ©SoftMoore Consulting

Example: Obtaining the Last Known Location public class MainActivity extends AppCompatActivity implements ConnectionCallbacks, OnConnectionFailedListener { ... private TextView latTextView; private TextView longTextView; private TextView addrTextView; } (continued on next page) ©SoftMoore Consulting

Example: Obtaining the Last Known Location @Override protected void onCreate(Bundle savedInstanceState) { ... latTextView = (TextView) findViewById(R.id.latitude_text); longTextView = (TextView) findViewById(R.id.longitude_text); addrTextView = (TextView) findViewById(R.id.address_text); final Button getLocationButton = (Button) findViewById(R.id.getLocationButton); getLocationButton.setOnClickListener(new View.OnClickListener() ... // details on next page }); buildGoogleApiClient(); checkAccessLocationPermission(); } (continued on next page) ©SoftMoore Consulting

Example: Obtaining the Last Known Location (continued) // in the button's onClick() listener Address address = null; try { FusedLocationProviderApi locationProvider = LocationServices.FusedLocationApi; lastLocation = locationProvider.getLastLocation(googleApiClient); if (lastLocation != null) String latStr = Double.toString(lastLocation.getLatitude()); String longStr = Double.toString(lastLocation.getLongitude()); latTextView.setText(latStr); longTextView.setText(longStr); address = getAddress(lastLocation); } (continued on next page) ©SoftMoore Consulting

Example: Obtaining the Last Known Location (continued) } catch (SecurityException ex) { String errorMsg = getString(R.string.no_permission); Log.e(LOG_TAG, errorMsg, ex); StringBuilder addressLines = new StringBuilder(); if (address != null) int maxIndex = address.getMaxAddressLineIndex(); for (int i = 0; i <= maxIndex; ++i) addressLines.append(address.getAddressLine(i)) .append("\n"); (continued on next page) ©SoftMoore Consulting

Example: Obtaining the Last Known Location (continued) else { String addressNotAvailable = getString(R.string.address_not_available); addressLines.append(addressNotAvailable); } addrTextView.setText(addressLines.toString()); ©SoftMoore Consulting

Obtaining the Last Known Location Last location Address of this location (obtained using geocoding) ©SoftMoore Consulting

Interface LocationListener Interface LocationListener is used for receiving notifications from the FusedLocationProvider when the location has changed. The interface specifies one abstract callback method that is called when the location changes. void onLocationChanged(Location location) Note that there are two Android interfaces named LocationListener, one in package android.location, and one that is part of Google Play Services in package com.google.android.gms.location. This section refers to the interface defined in Google Play Services. ©SoftMoore Consulting

Receiving Location Updates Connect to Google Play services as described earlier in this section. Set up a location request specifying quality-of-service parameters for the FusedLocationProviderApi. Examples include priority (accuracy versus power) desired interval for updates Implement the LocationListener callback. Request location updates usually part of the onConnected() method ©SoftMoore Consulting

Example: Set Up LocationRequest private static final int INTERVAL = 10000; // 10 seconds private static final int FASTEST_INTERVAL = 5000; // 5 seconds protected void createLocationRequest() { locationRequest = new LocationRequest(); // Set desired interval for location updates (inexact) locationRequest.setInterval(INTERVAL); // Explicitly set the fastest interval for location updates locationRequest.setFastestInterval(FASTEST_INTERVAL); // request the most accurate locations available locationRequest.setPriority( LocationRequest.PRIORITY_HIGH_ACCURACY); } ©SoftMoore Consulting

Example: Receiving Location Updates public class MainActivity extends AppCompatActivity implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener { protected GoogleApiClient googleApiClient; protected LocationRequest locationRequest; protected Location location; ... @Override public void onCreate(Bundle savedInstanceState) buildGoogleApiClient(); createLocationRequest(); } initialize to last location as described earlier in this section (continued on next page) ©SoftMoore Consulting

Example: Receiving Location Updates (continued) @Override public void onConnected(Bundle connectionHint) { ... // initialize location as described earlier updateUI(); startLocationUpdates(); } protected void startLocationUpdates() FusedLocationProviderApi locationProvider = LocationServices.FusedLocationApi; locationProvider.requestLocationUpdates(googleApiClient, locationRequest, this); (continued on next page) ©SoftMoore Consulting

Example: Receiving Location Updates (continued) @Override public void onLocationChanged(Location location) { this.location = location; updateUI(); } public void onResume() super.onResume(); if (googleApiClient.isConnected()) startLocationUpdates(); ... // other lifecycle methods LocationListener callback method ©SoftMoore Consulting

Example: Using LocationListener (continued) ©SoftMoore Consulting

Location Services on the Emulator A virtual device (emulator) does not have GPS or real location providers, so it uses a “mock” GPS provider that always returns the same position unless it is changed manually. The location on the emulator can be changed using the location tab for the emulator’s extended controls (click ... on the emulator control panel) ©SoftMoore Consulting

Setting a Mock Location on an Emulator Using the Emulator’s Extended Controls ©SoftMoore Consulting

Using the Emulator’s Extended Controls The Emulator Control panel can send simulated location data in three different ways: Manually send longitude/latitude coordinates to the device. Loading a GPX file describing a route for playback to the device. Loading a KML file describing individual place marks for sequenced playback to the device. See the following for details of GPX and KML files: GPX: The GPS Exchange Format http://www.topografix.com/gpx.asp KML Tutorial http://code.google.com/apis/kml/documentation/kml_tut.html ©SoftMoore Consulting

Relevant Links Making Your App Location-Aware https://developer.android.com/training/location/index.html Set Up Google Play Services https://developers.google.com/android/guides/setup Getting the Last Known Location https://developer.android.com/training/location/retrieve-current.html Receiving Location Updates https://developer.android.com/training/location/receive-location-updates.html Displaying a Location Address https://developer.android.com/training/location/display-address.html ©SoftMoore Consulting