Dosen Pengampu: Hendry Gunawan S.Kom, MM

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MOBILE COMPUTING

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Android and Location

• _{Inputs to location for Android device}

include:

– _GPS

– _{cell-ID (cell tower)} – _{Wi-Fi networks}

• _{Network Location Provider combines cell-ID}

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Global Positioning System

• _GPS

• _{US System that provides}

position, navigation, and timing

• _{Space Segment, Control}

Segment, User Segment

• _{US Air Force develops, maintains,}

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GPS Space Segment

• _{24 core satellites}

• _{medium earth orbit, 20k km}

above the earth

• _{6 orbital planes with 4}

satellites each

• _{generally 4 satellites in line}

of sight at any spot on the earth

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GPS Space Segment

• _{satellites circle the} earth twice a day

• _{upgraded over time} with diferent

generations of satellites

• _{Current generation of} satellites being

developed by

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GPS Control Segment

• _{Ground facilities that}

– _{monitor transmissions, perform analysis,}

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GPS User Segment

• _{Onboard clocks with accuracy of 1}

nanosecond (1 billionth of a second)

• _{Satellites transmit one-way}

• _{receiver calculates position and}

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GPS User Segment

• accuracy normally within 5 - 10 meters

• _{precision requires accuracy of clocks and timing}

signal on the order of 20 nanoseconds

• the Special and General theories of Relativity must be taken into account to achieve the

desired accuracy

• Special relativity predicts clocks on satellites go slower, on the order of 10 microseconds per day

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GPS Accuracy

• _{Selective Availability: intentional}

degradation of signals for civilian use

– _ended

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GPS Accuracy

• _{civilian GPS: aka SPS (Standard Positioning}

Service)

• _{military GPS: aka PPS 9 (Precise Positioning}

Service)

• _{military broadcasts on two frequencies, civilian}

only one

• _{"This means military users can perform}

ionospheric correction, a technique that reduces radio degradation caused by the Earth's

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Android and Location

• _{Currently 3 methods of obtaining}

location

– _GPS

– NETWORK

• _{combines cell tower triangulation and}

wireless networks

– _PASSIVE

• _{not a real provider, just piggy back of other}

applications

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GPS

• _{most accurate but,}

• _{only works OUTDOORS} • _{quickly consumes}

battery power

• _{delay in acquiring}

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Network

• _{Combines cell}

tower triangulation and in range

wireless networks

• _{If no cellular}

capability or plan

on device (tablets?) then just wireless

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Wireless Network and Location

• _{Use to use StreetView}

cars

• _{Now, use the devices}

themselves to map locations to wi-f

spots

• _{Apple and Microsoft}

do the same thing

• _{default on dev}

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Finding Location

• _{Add appropriate permission to}

AndroidManifest.xml

• _{Get instance of}_{LocationManager}_using

getSystemService method using

LOCATION_SERVICE

• _{Choose location provider (from all providers or}

using _{getBestProvider} method)

• _{Implement a}_{LocationListener}_class

• _Call_{requestLocationUpdates}_{method with}

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Quickly Finding Location

• _{If you want a simple fx (location) get}

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AndroidManifest.xml

• _{User Permission in manifest}

• _{Options: ACCESS_FINE_LOCATION or}

ACCESS_COARSE_LOCATION

• _{ACCESS_COARSE_LOCATION for use}

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Uses Features

• _{In addition to request permissions the}

AndroidManifest.xml fle can list features the app uses.

• _{Google Play uses these tags to flter}

applications for users

• _{examples of features: bluetooth,}

camera, location, network, microphone, nfc (near feld

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Location Manager

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Simple Location Program

• _{Just to demonstrate capabilities} • _{After setting up listener show all}

providers

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Properties of Location Providers

• _name • _enabled • _accuracy • _power requirements

• _{monetary cost} • _{requires cell}

• _{requires network}

•

requires

satellite

•

supports

altitude

•

supports

bearing

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Bearing

• _direction

• _{360 degrees}

• _{degrees east of north} • _{0 = north}

• _{90 = east}

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Program Output

• _{network (wif and}

cell tower id)

• _gps

• _passive

– _{use location}

updates

requested by

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dev Phones (no cell service)

name Network Passive GPS

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LocationListener

• _{Implement class that implements}

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Obtaining Locations

• _{Register the LocationListener to receive}

location updates

• _{locationManager.requestLocationUpdates(L}

ocationManager.NETWORK_PROVIDER, 15000, 10, locationListener);

– _{provider: name of provider to register with} – _{minTime: the minimum time interval for}

notifcations, in milliseconds. only a hint to conserve power, and actual time between

location updates may be greater or lesser than this value.

– _{minDistance: min distance interval for}

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requestLocationUpdates

• _{More on arguments}

• _{0 for minTime AND minDistance indicate} obtain updates as frequently as possible • _for_{background services}_recommended

minTime >= 300,000 ms to avoid

consuming too much power with the GPS or Wi-Fi receivers

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Location Data

• _{onLocationChange}

method in the

LocationListener receives Location objects

• _{toString shown}

• _{latitude, longitude,}

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Sample GPS Locations

• _{ET = Elapsed}

time: Time

passed since device start up

• _{Altitude in}

meters

• _{units for velocity:}

meters / sec

– _{1 m/s ~= 2.2}

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Location Strategies

• _{Location aware applications}

– _{compelling? better information to user?}

• _{GPS -> slow, only works outdoors,}

consumes lots of power, very accurate

• _{Network -> fast, works indoor and}

outdoor, uses less power, less accurate

• _{Issues: multiple sources (cell id with call}

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Getting a Fix

• _{Some applications (driving directions,}

sport tracking) require constant location data

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Periodic Location Updates

• _{Many location aware applications do not need a}

constant stream of location updates

• _{Obtaining location pattern:}

1. Start application.

2. Sometime later, start listening for updates from desired location providers.

3. Maintain a "current best estimate" of location by fltering out new, but less accurate fxes.

4. Stop listening for location updates.

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Getting Location

• _{Timeline for getting location based}

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Last Known Location

• _{Recall, application is part of a larger}

system

• _{other applications may have asked}

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Current Best Estimate

• _{The most recent location, may not be}

the most accurate

• _{Evaluating a location}

– _{how long has it been since the current}

best estimate?

– _{is the accuracy of the new location}

update better than the best estimate?

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LocationManager - Useful

Methods

• _{addProximityAlert(double latitude, double longitude,}

foat radius, long expiration, PendingIntent intent) – _{Sets a proximity alert for the location given by the position}

(latitude, longitude) and the given radius.

• _{List<String> getAllProviders()}

– _{Returns a list of the names of all known location providers.}

• _{Location getLastKnownLocation(String provider)}

– _{Returns a Location indicating the data from the last known}

location fx obtained from the given provider.

• _{Location class: foat distanceTo(Location dest)}

– _{Returns the approximate distance in meters}

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GeoCoding

• _{Geocoding is the process of converting addresses}

(like "1600 Amphitheatre Parkway, Mountain View, CA") into geographic coordinates (like latitude

37.423021 and longitude -122.083739), which you can use to place markers on a map, or position the map.

• _{Reverse geocoding is the process of converting}

geographic coordinates into a human-readable

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GeoCoding

• _{LocationManager and GooglePlayServices}

provide a Location object

• _{Contains latitude and longitude}

• _{Latitude, degrees north of south of}

equator North Pole = 90N or +90, equator = 0, South Pole = 90S or -90

• _{longitude, degrees east or west of prime}

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GeoCoding

• _{Various databases exists to give}

address(es) at a given lat and long

• _{Web Service?}

• _{GeoCoder class in Android provides:}

– _{geocoding: convert physical address to}

lat / long

– _{reverse geocoding: convert lat / long to}

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GeoCoding

• _{Accessing Google database of}

addresses

• _{Making network calls may block the}

Activity

• _{Key to not "BLOCK THE UI THREAD"} • _{Meaning, don't do expensive}

computations or possibly slow

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GeoCoding

• _{When address button clicked use a}

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Reverse GeoCoding

• _{Get lat and long from last known}

location of LocationTest app

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If Successful

• _{Geocoder returns a list of possible}

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Geofencing

• A geo-fence is a virtual perimeter for a real-world geographic area.

• Geo-fencing (geofencing) is a feature in a software program that uses the global positioning system (GPS) or radio frequency identifcation (RFID) to defne geographical boundaries.

• Geo-fencing allow an administrator to set up triggers so when a device enters (or exits) the boundaries defned by the administrator, an alert is issued.

• Many geo-fencing applications incorporate Google Earth, allowing administrators to defne boundaries on top of a satellite view of a specifc geographical area. Other applications defne boundaries by longitude and latitude or through user-created and Web-based maps.

• Geofence virtual barriers can be active or passive. Active geofences require an end user to opt-in to location services and a mobile app to be open. Passive geofences are always on; they rely on Wi-Fi and cellular data instead of GPS or RFID and work in the background.

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Geofencing

• _{Location Services also supports creating and}

monitoring geofences

• _{App can create a geo fence}

– _{latitude and longitude} – _radius

• _{Once a geofence is created app can ask}

Location Services for notifcations

– _{when device enters geofence} – _{when device leaves geofence}

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