Sensors and location based services

SENSORS AND

LOCATION BASED SERVICES

ChinmayVS @ B.A.(U).G

14 JAN 2012

Sensors & location based services

• Compass- Bearing

• Gyroscope, Accelerometer- Detect motion.

• Barometer- Calculate Altitude.

• nGPShttp://goo.gl/RWEKL (Experimental.)

2SENSORS AND LOCATION BASED SERVICES

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cvs@BA(U)G$ who am i

• Android >2yrs. Remember anyone?

• - sensors development. 10million+ units sold.

• Presently working @

PathPartnerTech.com

“Sense-ors” on Android

1. ACCELEROMETER

2. GYROSCOPE

3. MAGNETIC_FIELD

4. LIGHT

5. PRESSURE

6. AMBIENT_TEMP

7. RELATIVE_HUMIDITY

8. PROXIMITY

9. LINEAR_ACCELERATION

10. GRAVITY

11. ROTATION_VECTOR

12. TEMPERATURE

13. ORIENTATION

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REAL

DEPRECEATED

A sensor (also called detector) is a device that measuresa physical quantity and converts it into a signal which can be read by

an observer or by an instrument.

VIRTUAL

“Sense-ors” on Android

1. ACCELEROMETER

2. GRAVITY

3. LINEAR_ACCELERATION

4. GYROSCOPE

5. MAGNETIC FIELD

6. ORIENTATION

7. PROXIMITY

8. ROTATION VECTOR

9. LIGHT

10. BAROMETER

11. AMBIENT TEMPERATURE

12. RELATIVE HUMIDITY

13. TEMPERATURE

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MOTION

A sensor (also called detector) is a device that measuresa physical quantity and converts it into a signal which can be read by

an observer or by an instrument.

POSITION

ENVIRONMENT

Sensors in Android applications

• Use-cases of sensors in apps:1. Active-Input

2. Passive-Input

3. Active-Passive

4. Auto-Rotate

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Application developer

Android window manager

Sensors in Android applications (1/4)

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• Active input

Sensors in Android applications (2/4)

• Passive input

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Sensors in Android applications (3/4)

• Active-passive

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Sensors in Android applications (4/4)

• Auto-rotate

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Compass : Bearing (Azimuth)

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90o

180o

Compass : Bearing

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• iPad as in-flight navigator. Android?

• Magnetic north != Geographic North

• WiFi / Network provider + Compass = GPS?

POSITION (LAT, LONG) + BEARING

Compass : Magnetic Declination

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Accelerometer, Gyroscope : Motion

• |Accelerometer| != 9.8 Motion

• Initial bearing + rotation of device,

POSITION (LAT, LONG) + BEARING + SPEED

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• Remember this ?“ WiFi / Network provider + Compass = GPS”

now how about,

“ WiFi / Network provider + Compass + Barometer ”

POSITION (LAT, LONG) + BEARING + SPEED + ALTITUDE > GPS

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Barometer : Altitude

nGPS : World Geomagnetic model

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Using Sensors in your app

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http://goo.gl/hWOQuSensorEvent

http://goo.gl/1DRUvSensorManager

http://goo.gl/AVBDV

http://goo.gl/eKq6a

Examples :

Sensor app-dev Tips and tricks

Sensor calibration. 1. one-turn deserves another (axes-calib) 2. zero-calib

Polling rate fastest/game/ui/normal?

Sensor fusion Hard-way

Easy-way (Invensense ) http://goo.gl/bHmDe

Lessons from WindowOrientationListener.javaAndroid/frameworks/base/core/java/android/view/WindowOrientationListener.java

When to register/unregister SensorEventListener

When to acquire/release Wakelocks

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WindowOrientationListener.java

Low-pass filter the tilt and orientation angles to avoid "twitchy" behaviour.

When the orientation angle reaches a certain threshold, transition

These thresholds have some hysteresis built-in to avoid oscillation.

Use the magnitude to judge the accuracy of the data. Under ideal conditions, the magnitude should equal to that of gravity.

When it differs significantly, we know the device is under external acceleration

Use the tilt angle to judge the accuracy of orientation data. When the tilt angle is high in magnitude, we distrust the orientation data.

When the device is flat, small physical motion = large changes in orientation angle.

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App-dev Tips and tricks

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register sensorEventListener

unregister sensorEventListener

acquire wakelock

release wakelock

Thank You!!

Questions?

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CONTACT ME

android-porting android-developers

android-kernel android-platform