Today's Agenda

• Administrivia
  • Final project spec
• Learning goals
  • Review of Sensors
  • Implement location
  • Time to work on Sensing activity (and turn in screenshot)

Sensing: Categories of Sensors - Review

• Motion Sensors
  • Measure acceleration forces and rotational forces along three axes
  • Includes accelerometers, gravity sensors, gyroscopes, and rotational vector sensor
  • Accelerometers and gyroscope are generally HW based, Gravity, linear acceleration, rotation vector, significant motion, step counter, and step detector may be HW or SW based
• Environmental Sensors
  • Measures relative ambient humidity, illuminance, ambient pressure, and ambient temperature
  • All four sensors are HW based
• Position Sensors
  • Determine the physical position of the device.
  • Includes orientation, magnetometers, and proximity sensors
  • Geomagnetic field sensor and proximity sensor are HW based

Do this now:

Clone the Sensing and Location Activity repo if you have not already.

Location

• Locations are generally reported as Latitude and Longitude coordinates.
  • Generally reported using “Global Position System” (GPS)
  • Can also use cell tower or WiFi localization.
• Three ways to do this
  • LocationManager
  • Fused Location Provider API
    • Need to set up Google Play Services on the device (including emulators)
    • Less power consumption
  • Google Awareness API
    • Requires Google credits ($$$)

Location: details

• Specify app permissions
  • Do we need to get the locations in the foreground or background?
  • Do we want a precise or approximate location?
• How do we want to get the data
  • At a particular time (once)
  • At regular intervals?
  • When a certain event occurs, like someone goes out of a boundary.

Reminder: Snapshots vs Fences

Listeners are used to receive sensor or location updates at different intervals

• This is like taking a snapshot of the sensor or location at a period of time.

Fences (or Geofences) are a way to create an area of interest around a specific location. Listener is called any time a condition is true.

Google Awareness API in Android

• A way to have your app react to the current situation
• Seven signals (time, location, places, activity (like walking), beacons, headphones, and weather)
• Allows for:
  • Ease of implementation
  • Better context data (raw signals are processed for quality)
  • Optimal system health (less impact on battery life)
• Includes two APIs
  • Fence API
  • Snapshot API

Snapshot with Google Awareness API

But if you do...

Fences with Google Awareness API

Notify you every time a condition is true

// Create the primitive fences.
AwarenessFence walkingFence = DetectedActivityFence.during(DetectedActivityFence.WALKING);

Use the FenceClient to register a a fence. Requires a FenceUpdateRequest, then use FenceClient.updateFences()

Need to call addFence() for each fence to add.

Location: Getting data with LocationManager

This part you do need to know....

Location: Getting data with LocationManager

The LocationManager is the "simplest" way to get the location.

Start by declaring permissions in AndroidManifest.xml

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

Location: Getting data with LocationManager

LocationManager - Main class to access location services

• Reference can be obtained by calling getSystemService() in in the onCreate() in your Activity
• Pick a location provider (like GPS_PROVIDER) or have the system pick based on criteria such as cost or accuracy.
• Check if the provider is available

LocationListener#onLocationChanged - to get notifications at regular intervals

LocationManager#getLastKnownLocation() - will get you a snapshot of the last known location

Location - an actual location

LocationManager example

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_COARSE);
criteria.setCostAllowed(false);
String provider = locationManager.getBestProvider(criteria, false);
Location location = null;
try {
    location = locationManager.getLastKnownLocation(provider);
    MyLocationListener mylistener = new MyLocationListener();
    if (location != null) {
        mylistener.onLocationChanged(location);
    } else { ... }
    // location updates: at least 1 meter and 500 milli seconds change
    locationManager.requestLocationUpdates(provider, 500, 1, mylistener);
} catch (SecurityException e) { ... }

Location: Getting data with Fused Location Provider

• Fused location provider is another mechanism to get locations
  • ✅ Faster
  • ✅ Provides more accurate locations
  • ❌ Requires Google Play Services installed on your device.
• Specify app permissions
  • Do we need to get the locations in the foreground or background?
  • Do we want a precise or approximate location?
• Create the location services client (a FusedLocationProviderClient) and set up a listener to get the location.

Location: Getting data with LocationManager

FusedLocationProviderClient - Location services client

• Reference can be obtained by calling LocationServices.getFusedLocationProviderClient() in in the onCreate() in your Activity

FusedLocationProviderClient#requestLocationUpdates - to get notifications at regular intervals

FusedLocationProviderClient#getLastKnownLocation() - will get you a snapshot of the last known location

• Need to have an OnSuccessListener callback set up.

Location - an actual location

Location: Getting data with FusedLocationProviderClient

First get the FusedLocationProviderClient

// Initialize Location Services Client for continuous location checking
FusedLocationProviderClient mFusedLocationClient =
    LocationServices.getFusedLocationProviderClient(this);
mLocationRequest = LocationRequest.create();
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
mLocationRequest.setInterval(DEFAULT_UPDATE_INTERVAL * 1000);
mLocationRequest.setInterval(FAST_UPDATE_INTERVAL * 1000);

This will request the location permissions, need to gracefully handle if the user says no

Location: Requestion updates from FusedLocationProviderClient

First create a callback to handle the updates:

private final LocationCallback mLocationCallback = new LocationCallback() {
  @Override
  public void onLocationResult(LocationResult locationResult) {
    List<Location> locationList = locationResult.getLocations();
    if (locationList.size() > 0) {
        // do something with the locations...
    }
  }
};

Location: Requestion updates from FusedLocationProviderClient

If the user approves location permissions, connect the callback.

mFusedLocationClient.requestLocationUpdates(mLocationRequest, mLocationCallback,
    Looper.myLooper());

Location: Stop tracking Location

Generally good principle to stop tracking if the app is paused (responding to onPause) or the user revokes permissions

if (mFusedLocationClient != null) {
  mFusedLocationClient.removeLocationUpdates(mLocationCallback);

Classroom activity

Adding a map using Mapbox

Mapbox is free to use if your app is under 25,000 monthly active users (no credit card needed to use the service)

To use it:

• Sign up for an account & verify your email
• Create a token for your app
• Follow the instructions for how to install
• The README.md in the Sensing and Location repository has information on how to get started.

Using a MapView interactor

Once you've added your MapView to the screen (either in an .xml file or programatically), you can interact with it using their mapbox-map API API.

Example 1 - setting the camera to a zoom level:

// Build a camera options object
CameraOptions co = new CameraOptions.Builder().zoom(mZoomLevel).build();
// Set the camera to use the CameraOptions object
mMapView.getMapboxMap().setCamera(co);

Using a MapView interactor

Once you've added your MapView to the screen (either in an .xml file or programatically), you can interact with it using their mapbox-map API API.

Example 2 - setting the camera to a specific position:

Point p = Point.fromLngLat(mCurrentLocation.getLongitude(),
                           mCurrentLocation.getLatitude());
// Build a camera options object to be at a particular Point
CameraOptions co = new CameraOptions.Builder().center(p).build();
// Set the camera to use the CameraOptions object
mMapView.getMapboxMap().setCamera(co);

End of Deck