Internet of Things Sensors - Part 1 Location Services

Transcription

1 Internet of Things Sensors - Part 1 Location Services Aveek Dutta Assistant Professor Department of Computer Engineering University at Albany SUNY adutta@albany.edu

2 Introduction ANDROIDS ARE ALIVE - Locate, See, Listen, Understand and Mobile Sensors are the bridge between the cyber and the physical world Our goal is to understand the nuts and bolts of these sensors and create impactful solutions

3 Sensors Sensor type in mobile devices Location sensors: Determine a device s location using a variety of sensors including GPS Physical sensors: Detect device-specific properties such as orientation, acceleration, and rotation and environmental properties such as light, magnetic field, and barometric pressure NFC scanner: Detects near field communication (NFC) tags and sharing Camera: Collects visual images Microphone: Records audio and speech recognition External sensors: Any sensor connected using the Android Open Accessory (AOA) mechanism.

4 Part 1: Location Services Methods to determine location Outdoor, Indoor, other (RFID - Active, Passive) Determine location in Android Tracking device movement in Android Proximity alert, Geocoding

5 Methods Used To Determine Location In Android, components which support this functionality are called location providers, and each has its set of strengths and weaknesses. Location acquisition methods: GPS Provider - mostly outdoors Network Provider Embedded in protocol - e.g. - Cellular communications Acquired from Wi-Fi access points Other isolated systems - RFID tags, ibeacon, et

6 GPS Provider The Global Positioning System (GPS) uses a system of 27 satellites to determine a receiver s (like your phone) current location (X,Y,Z) and Time (UTC) Need information from at least 4 satellites (Line of Sight) The receiver in the phone is useless without the rest of the system More information - Detailed tutorial on GPS

7 GPS - How it works Each GPS satellite transmits its current position (ephemeris data) and almanac. A GPS receiver determines its distance from multiple satellites. highly synchronized clocks required for accurate location. GPS receiver uses triangulation to obtain current location. Concise book with Matlab based SDR code Improvements - Assisted GPS (A-GPS) and Simultaneous GPS (S-GPS) A-GPS uses mobile network to obtain almanac and other info (can be disabled in Android) Older CDMA based cellular systems has S-GPS

8 GPS - Limitations Needs a LOS to the constellation Does not work indoors, tunnels, subterranean (tactical environment) May take time to solve, accuracy and power trade-off: A factor for IoT devices Multipath (dense urban areas), Dilution of Precision will affect accuracy Multipath Reflection cause decoding errors GDOP - Geometric Dilution of Precision source: and

9 Location - Wi- Fi based Provide location information - Cell towers, Wi-Fi APs Location is really a point in a reference frame Wi-Fi radio often consumes less power than the GPS Based on the signal strength, the device then makes a query to the Google location service (not Android location service) MOOC on Google Location Service

10 Location - Cellular based Unique ID of the towers and signal strength (= distance) are used to triangulate the position of the receiver Go to for tower information Less accurate in absence of explicit timing information

11 Other (mostly indoors) RFID based positioning Active, Passive, Smart dust Useful reading [Link] Indoor positioning (mapping) RF fingerprinting (Wifarer, PhD Thesis) Bluetooth Low Energy (ibeacon, Estimote) More advanced - Array processing (AoA estimation) Hybrid methods provide the best result

12 Indoor Positioning Many Applications Indoor Navigation (Accuware) Targeted marketing (Skyhook) Assistive technology Augmented reality What about orientation (compass) Gaze tracking (pupil-labs) Source: _Fig15ShopperBehavior-Simplified.jpg

13 Know Your Tools

14 Android This course may not make you an APP development ninja Understand Algorithm and Implementation trade-off Optimum implementation takes time and practice The APP is just the front-end / UI, back-end matters equally Getting Started Tutorial on Android Studio Sensors overview Codes from the reference book. GIT repository Coursera: Video lectures on Android programming from University of Maryland More programming course material - University of Alabama WWW - make sure to filter the noise, learn but don t copy

15 Determining a Device s Current Location The majority of the classes are in android.location package For a basic app, you will need to use five members Classes: LocationManager LocationProvider Location Criteria Interfaces: LocationListener

16 Classes and Interfaces The LocationManager allows an app to tell Android to receive updated location In addition, provides current state such as available location providers, GPS status, etc Provide cached location of the device. LocationProvider is an abstraction for the different sources of location Location class encapsulates the actual location data to an app Once an app receives a Location object, it starts the application-specific processing LocationListener contains a group of callback methods that are called in reaction to changes in a device s current location or changes in location service Criteria class is used to query for providers with certain characteristics.

17 Android Manifest App declares its intentions to use location services in the Android manifest The two permissions that deal with live location data: android.permission.access_fine_location android.permission.access_coarse_location Trade-off: Accuracy, Time-to-fix and battery Location providers: GPS, Network, Passive (saves battery) Either specify with LocationManager or pass attributes in the Criteria object

18 Implementing LocationListener Must contain an implementation of the following methods: abstract void onlocationchanged(location location) abstract void onproviderdisabled(string provider) Provide a way for an app to be notified when the user disables location provider abstract void onproviderenabled(string provider) Called when a new location is ready for consumption by an app Provide a way for an app to be notified when the user enables location provider abstract void onstatuschanged(string provider, int status, Bundle extras) When a provider either goes offline or comes back online

19 Requesting Location Updates The app is now ready to ask Android to provide it with location when available. Apps can only request to be notified when updated location is available Call the LocationManager.requestSingleLocati on() method inside onresume() Optimize battery drain LocationManager.requestLocationUp dates(provider, 0, 0, pendingintent)

20 Tracking Device Movement

21 Tracking Useful for navigation. Any other application? To perform background tasks: Services and Broadcast receivers Similar to location services but viewing of movement is new feature

22 Functional View Continuous tracking more active hardware, which affect battery life. Mainly three Android application components: Display both the current location and previous locations A BroadcastReceiver that receives location data in the background and stores in a database Another BroadcastReceiver that receives location updates only when the app is in the foreground Figure 3-2 in the Book

23 Viewing the tracking data TrackLocationActivity will display a Google map with the tracked points The app will also update the screen as new points are received It uses the following classes from the Google Maps library: MapView OverlayItem ItemizedOverlay MapActivity The application manifest needs to contain the following code: <uses-library android:name="com.google.android.maps" />.

24 MapView The MapView is the view that displays the map The layout for the activity includes a <com.google.android.maps.mapview> element with an android:apikey attribute (see Listing 3-7) The API key attribute is necessary to use the map view. The key is generated from the certificate that is used to sign the APK for your app which is located at l (see Listing 3-7)

25 OverlayItem OverlayItem is an object that is drawn on the map It is a container for the location data latitude, longitude and accuracy The class PointOverlayItem extends OverlayItem and can be used in the app as a container for location info that is received from the Android location service.

26 ItemizedOverlay and MapActivity ItemizedOverlay holds the list of overlay items, and how to draw those Because ItemizedOverlay is abstract, the example app creates the class TrackLocationOverlay that extends ItemizedOverlay. TrackLocationOverlay maintains a list of PointOverlayItems that will be plotted in the map by the draw() method To use the Google Maps external library, TrackLocationActivity will need to extend MapActivity. Two important methods: isroutedisplayed() and islocationdisplayed() Used by the Google Maps library for accounting purposes and need to accurately reflect if the activity is currently displaying route and location information

27 Proximity and Geocoding

28 Proximity Alert Trigger events based on proximity to certain POI Could be a more active system based on local sensing (not a location based proximity alert) Uses GPS (energy management, sleep cycle) Off-road nav, backcountry hiking, waypoints (Alpine Quest)

29 Geofencing Sets up a virtual barrier Acquisition or Dissemination of information is limited to geographical boundaries Geo-restriction or Geo-blocking (GeoIP Database)

30 Proximity Alerts - App Structure The application must perform three main tasks To allow the user to define the target location to be used by LocationManager To make a call to the LocationManager to set the proximity alert To respond to the proximity alert in order to set the Notification To accomplish the first task, the app must translate a location entered by the user into a form that can be used by the LocationManager. The complexity here is that the LocationManager needs latitude and longitude coordinates to set a proximity alert, whereas humans tend to refer to locations by name. To help bridge this gap, Android supports geocoding. Geofencing documentation [Link]

31 Geocoding Geocoding is converting a location name to its Lat-Lon Android provides native support to geocode and reverse geocode The app contains the activity GeocodeActivity Collects target location information from the user and geocoding the location for use by the LocationManager GeocodeActivity allows the user to enter free-form text List of possible matches is generated by passing string to the Geocoder class.

32 Geocoder Class android.location.geocoder: The Geocoder class is responsible for both geocoding and reverse geocoding A call to Geocoder is made when the user clicks the Lookup Location button. The manifest for GeocodeActivity specifies that the method onlookuplocationclick() will be run when the button is clicked. The implementation for onlookuplocationclick() is shown in Listing 4-1.

33 Proximity Alerts - Geocoding - Limitations LocationManager.requestLocationUpdate() include values that control the frequency of location updates and desired location providers. Requesting frequent location updates, especially with the GPS consumes power. The default proximity implementation does not require a call to LocationManager.requestLocationUpdates(), hence no control over update frequency This may not be proximity alerts with a long expiration Android s proximity alert implementation uses the GPS provider, an app needs to include this android.permission.access_fine_location in its manifest Though this is not inherently a problem, it does not give the app developer much flexibility. With regards to permissions in Android, the general rule of thumb is to limit the list of required permissions as much as possible.

34 Summary Basics of outdoor and indoor positioning Accessing location, tracking in Android and design trade-off Discussed some of the foundation classes, and examined the implementation of a simple app Utilize proximity alerts and geocoding as a tool for various applications Consider negative effects on battery life along with the simple API

35 Resources Example Proximity Alert Application in Google Play Store for reference. Example Wake Up GPS App in Google Play Store with enhanced features. Network Cell Info App which tracks your movement based on Network Signal. ($$$)