This document discusses sensors and location-based services on Android devices. It describes several types of sensors including compass, gyroscope, accelerometer, barometer, and GPS. It provides examples of how these sensors can be used in applications for active input, passive input, active-passive functions, and auto-rotate capabilities. The document also offers tips for sensor calibration, polling rates, sensor fusion, and managing sensor event listeners and wake locks in apps.

1. SENSORS AND
LOCATION BASED SERVICES
ChinmayVS @ B.A.(U).G
14 JAN 2012

2. Sensors & location based services
• Compass
- Bearing
• Gyroscope, Accelerometer
- Detect motion.
• Barometer
- Calculate Altitude.
• nGPS
http://goo.gl/RWEKL (Experimental.)
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3. cvs@BA(U)G$ who am i
• Android >2yrs. Remember anyone?
• - sensors development. 10million+ units sold.
• Presently working @
PathPartnerTech.com
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4. “Sense-ors” on Android
A sensor (also called detector) is a device that measures
a physical quantity and converts it into a signal which can be read by
an observer or by an instrument.
1. ACCELEROMETER
2. GYROSCOPE
3. MAGNETIC_FIELD
REAL
4. LIGHT
5. PRESSURE
6. AMBIENT_TEMP
7. RELATIVE_HUMIDITY
8. PROXIMITY
VIRTUAL 9. LINEAR_ACCELERATION
10. GRAVITY
11. ROTATION_VECTOR
DEPRECEATED
12. TEMPERATURE
13. ORIENTATION
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5. “Sense-ors” on Android
A sensor (also called detector) is a device that measures
a physical quantity and converts it into a signal which can be read by
an observer or by an instrument.
1. ACCELEROMETER
2. GRAVITY
MOTION
3. LINEAR_ACCELERATION
4. GYROSCOPE
5. MAGNETIC FIELD
POSITION 6. ORIENTATION
7. PROXIMITY
8. ROTATION VECTOR
9. LIGHT
10. BAROMETER
ENVIRONMENT 11. AMBIENT TEMPERATURE
12. RELATIVE HUMIDITY
13. TEMPERATURE
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6. Sensors in Android applications
• Use-cases of sensors in apps:
1. Active-Input
2. Passive-Input Application developer
3. Active-Passive
4. Auto-Rotate Android window manager
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7. Sensors in Android applications (1/4)
• Active input
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8. Sensors in Android applications (2/4)
• Passive input
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9. Sensors in Android applications (3/4)
• Active-passive
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10. Sensors in Android applications (4/4)
• Auto-rotate
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11. Compass : Bearing (Azimuth)
90o
180o
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12. Compass : Bearing
• iPad as in-flight navigator. Android?
• Magnetic north != Geographic North
• WiFi / Network provider + Compass = GPS?
POSITION (LAT, LONG) + BEARING
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13. Compass : Magnetic Declination
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14. Accelerometer, Gyroscope : Motion
• |Accelerometer| != 9.8  Motion
• Initial bearing + rotation of device,
POSITION (LAT, LONG) + BEARING + SPEED
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15. Barometer : Altitude
• 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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16. nGPS : World Geomagnetic model
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17. Using Sensors in your app
SensorEvent http://goo.gl/hWOQu
SensorManager http://goo.gl/1DRUv
Examples :
http://goo.gl/AVBDV
http://goo.gl/eKq6a
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18. 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.java
Android/frameworks/base/core/java/android/view/WindowOrientationListener.java
 When to register/unregister SensorEventListener
 When to acquire/release Wakelocks
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19. 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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20. App-dev Tips and tricks
register
sensorEventListener
acquire wakelock
release wakelock
unregister
sensorEventListener
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21. Thank You!!
Questions?
android-porting android-developers
android-kernel android-platform
CONTACT ME
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