Professional Android 4 Application Development

506 x CHAPTER 12 HARDWARE SENSORS
LISTING 12-9 (continued)
angle[2] += sensorEvent.values[2] * dT;
}
lastTime = sensorEvent.timestamp;
}
public void onAccuracyChanged(Sensor sensor, int accuracy) {}
};
SensorManager sm
= (SensorManager)getSystemService(Context.SENSOR_SERVICE);
int sensorType = Sensor.TYPE_GYROSCOPE;
sm.registerListener(myGyroListener,
sm.getDefaultSensor(sensorType),
SensorManager.SENSOR_DELAY_NORMAL);
code snippet PA4AD_Ch12_Sensors/src/MyActivity.java
It’s worth noting that orientation values derived solely from a gyroscope can become increasingly
inaccurate due to calibration errors and noise. To account for this effect, gyroscopes are often used
in combination with other sensors — particularly accelerometers — to provide smoother and more
accurate orientation results. A virtual gyroscope was introduced in Android 4.0 (API level 14) that
attempts to reduce this drift effect.
INTRODUCING THE ENVIRONMENTAL SENSORS
One of the most exciting areas of innovation in mobile hardware is the inclusion of an increasingly
rich array of sensors. In addition to the orientation and movement sensors described earlier in this
chapter, environmental Sensors are now becoming available in many Android devices.
Like orientation Sensors, the availability of specific environmental Sensors depends on the host
hardware. Where they are available, environmental Sensors can be used by your application to:
‰ Improve location detection by determining the current altitude
‰ Track movements based on changes in altitude
‰ Alter the screen brightness or functionality based on ambient light
‰ Make weather observations and forecasts
‰ Determine on which planetary body the device is currently located
Using the Barometer Sensor
A barometer is used to measure atmospheric pressure. The inclusion of this sensor in some Android
devices makes it possible for a user to determine his or her current altitude and, potentially, to
forecast weather changes.
To monitor changes in atmospheric pressure, register an implementation of SensorEventListener
with the Sensor Manager, using a Sensor object of type Sensor.TYPE_PRESSURE. The current