1. Location Services: Part 1 (Location and Geocoding)

2. 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
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3. 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
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4. 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.
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5. 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.
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6. Download Google Repository (Android SDK Manager)
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7. 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.
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8. Set Up Google Play Services (continued)
Add the following metadata to the application manifest.
<application
...
<meta-data
android:name="com.google.android.gms.version"
<activity
</activity>
</application>
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9. 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)
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10. 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)
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11. 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.
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12. Requesting User Permissions (continued)
Example
<manifest ... >   <uses-permission
android:name="android.permission.ACCESS_FINE_LOCATION"/>     ... </manifest>
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13. 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
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14. 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 protected void onCreate(Bundle savedInstanceState) buildGoogleApiClient(); checkAccessLocationPermission(); }
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15. Example: Connecting to Google Play Services (continued)
protected synchronized void buildGoogleApiClient() { googleApiClient = new GoogleApiClient.Builder(this) .addConnectionCallbacks(this) .addOnConnectionFailedListener(this) .addApi(LocationServices.API) .build(); public void onConnected(Bundle connectionHint) Log.i(LOG_TAG, "googleApiClient is connected ");
add location
services API
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16. 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());
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17. 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(); ...
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18. 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.
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19. 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 or higher
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20. 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
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21. 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
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22. 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.
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23. 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.
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24. 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.
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25. 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
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26. 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);
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27. 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.
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28. 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.
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29. 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); }
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30. Example: Translating a Location to an Address (continued)
catch (IOException ex) { Log.e(LOG_TAG, ex.getMessage()); } return address;
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31. 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
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32. Example: Obtaining the Last Known Location
public class MainActivity extends AppCompatActivity implements ConnectionCallbacks, OnConnectionFailedListener { ... private TextView latTextView; private TextView longTextView; private TextView addrTextView; }
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33. 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(); }
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34. 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); }
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35. 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");
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36. Example: Obtaining the Last Known Location (continued)
else { String addressNotAvailable = getString(R.string.address_not_available); addressLines.append(addressNotAvailable); } addrTextView.setText(addressLines.toString());
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37. Obtaining the Last Known Location
Last location
Address of this location
(obtained using geocoding)
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38. 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.
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39. 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
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40. 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); }
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41. Example: Receiving Location Updates
public class MainActivity extends AppCompatActivity implements ConnectionCallbacks, OnConnectionFailedListener, LocationListener { protected GoogleApiClient googleApiClient; protected LocationRequest locationRequest; protected Location location; public void onCreate(Bundle savedInstanceState) buildGoogleApiClient(); createLocationRequest(); }
initialize to last
location as described
earlier in this section
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42. 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);
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43. 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
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44. Example: Using LocationListener (continued)
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45. 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)
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46. Setting a Mock Location on an Emulator Using the Emulator’s Extended Controls
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47. 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
KML Tutorial
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48. Relevant Links Making Your App Location-Aware
Set Up Google Play Services
Getting the Last Known Location
Receiving Location Updates
Displaying a Location Address
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