android device angle to vertical axis

I am developing an application where I would require to retrieve the angle between the device and the vertical axis (the axis pointing to the center of the Earth).

So far, all the documen开发者_高级运维tations and tutorials I found were not very conclusive.

Could you please explain me how can I do this or provide me with a link to a clear tutorial to help me find a solution to this problem?

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First, I created a SensorEventListener implementation

private SensorEventListener sensorEventListener = 
    new SensorEventListener() {

    /** The side that is currently up */
    //private Side currentSide = null;
    //private Side oldSide = null;
    private float azimuth;
    private float pitch;
    private float roll;

    public void onAccuracyChanged(Sensor sensor, int accuracy) {}

    public void onSensorChanged(SensorEvent event) {            
        azimuth = event.values[0];     // azimuth
        pitch = event.values[1];     // pitch
        roll = event.values[2];        // roll
        //code to deal with orientation changes;
        //pitch is the angle between the vertical axis and the device's y axis (the one from the center of the device to its top)
    } 
};

Then, I register this listener to an Orientation Sensor

SensorManager sensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
Sensor sensor;
List<Sensor> sensors = sensorManager.getSensorList(
        Sensor.TYPE_ORIENTATION);
if (sensors.size() > 0) {
    sensor = sensors.get(0);
    sensorManager.registerListener(
            sensorEventListener, sensor, 
            SensorManager.SENSOR_DELAY_NORMAL);
} else {
    //notify the user that there's no orientation sensor
}