Which sensor for rotating android phone?

Question

Imagine you are pointing at the TV. You have your phone gripped in your hand. Now, rotate your wrist.

Which sensor would I need to manage to detect such a movement?

Gyroscope? Orientation? Accelerometer?

Answer 1

The sensors TYPE_MAGNETIC_FIELD and TYPE_ACCELEROMETER are fine to detect that (as TYPE_ORIENTATION is now deprecated).

You will need:

a few matrix:

private float[] mValuesMagnet      = new float[3];
private float[] mValuesAccel       = new float[3];
private float[] mValuesOrientation = new float[3];

private float[] mRotationMatrix    = new float[9];

a listener to catch the values the sensors send (this will be an argument of SensorManager.registerListener() that you will have to call to setup your sensors):

private final SensorEventListener mEventListener = new SensorEventListener() {
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }

    public void onSensorChanged(SensorEvent event) {
        // Handle the events for which we registered
        switch (event.sensor.getType()) {           
            case Sensor.TYPE_ACCELEROMETER: 
                System.arraycopy(event.values, 0, mValuesAccel, 0, 3); 
                break; 

            case Sensor.TYPE_MAGNETIC_FIELD: 
                System.arraycopy(event.values, 0, mValuesMagnet, 0, 3); 
                break; 
    }
};

And you'll need to compute the azimuth, pitch, and roll:

    SensorManager.getRotationMatrix(mRotationMatrix, null, mValuesAccel, mValuesMagnet);
    SensorManager.getOrientation(mRotationMatrix, mValuesOrientation);  

mValuesOrientation is then filled with:

• mValuesOrientation[0]: azimuth, rotation around the Z axis.
• mValuesOrientation[1]: pitch, rotation around the X axis.
• mValuesOrientation[2]: roll, rotation around the Y axis.

Check the documentation of getOrientation() to know how the axis are defined. You may need to use SensorManager.remapCoordinateSystem() to redefine these axis.