SENSING LOCATIONinDecode - 17th December 2015

LOCATION STRATEGIES ON MOBILE DEVICES

CHALLENGES IN DETERMINING LOCATION

• Obtaining user location from a mobile device can be complicated. There are several reasons why a location reading (regardless of the source) can contain errors and be inaccurate. Some sources of error in the user location include:

• 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 must account for movement by re-estimating user location every so often.

• Varying accuracy

• Location estimates coming 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.

http://developer.android.com/guide/topics/location/strategies.html

SHIELD THE DEVELOPER FROM THE COMPLEXITIES INVOLVED

IN SENSING LOCATION

ALLOW MULTIPLE APPS TO ACCESS LOCATION DATA

WITHOUT KILLING THE BATTERY

LOCATION MANAGER

METHODS OF SENSING LOCATION

RADIO WAVESHow long would it take for a RF signal to travel from the moon to Earth? (Distance is approximately 400,000km)

SPEED OF LIGHT 300,000KM/S

EVERY MILLISECOND 300KM

IS TRAVELLED

LOCATION: GPSHow many satellites does a GPS receiver need to see in

order to determine location in 3d space?

LOCATION: GPSHow accurate is GPS?

LOCATION: GPSSignal reflection

LOCATION: CELLULARFrequency reuse

LOCATION: CELLULARFrequency Reuse

IN DENSELY POPULATED URBAN ENVIRONMENTS WE NEED MORE SHORT RANGE

CELLS SO LOCATION ACCURACY INCREASES

WIFI POSITIONING

ACCURACY LINKED TO RANGE OF WIFI ACCESS

POINTSNOT SO GOOD IN THE

COUNTRYSIDE

ANDROID

LOCATION MANAGER

FLOW FOR OBTAINING USER LOCATION

• Here's the typical flow of procedures for obtaining the user location:

1. Start application.

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

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

4. Stop listening for location updates.

5. Take advantage of the last best location estimate.

FLOW FOR OBTAINING USER LOCATION

LAST KNOWN LOCATION

CONSIDERATIONS

• What is the use case you are trying to solve for?

• How accurate do you need the location data to be?

• How soon do you need the location data?

• How often do you need the location data?

REFERENCES

• http://developer.android.com/guide/topics/location/strategies.html

• http://developer.android.com/training/location/index.html