Android rotation matrix sensor to get rotation angles failed

Question

I am currently working on the motion sensor about measure the orientation angle of my Android device. When it comes to implementation , the device turns to zero no matter how we turn or not. Are there any conditions to initialize the float array such the angle can be calculated ?

The below is my code

public class MainActivity extends Activity  implements SensorEventListener {

    private SensorManager sensorManager;

    TextView xCoor; // declare X axis object
    TextView yCoor; // declare Y axis object
    TextView zCoor; // declare Z axis object
    float[] mRotationMatrixFromVector =  new float[3];
    float[] mRotationMatrix =  new float[9];
    float[] orientationVals =  new float[3];

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        xCoor=(TextView)findViewById(R.id.xcoor); // create X axis object
        yCoor=(TextView)findViewById(R.id.ycoor); // create Y axis object
        zCoor=(TextView)findViewById(R.id.zcoor); // create Z axis object

        sensorManager=(SensorManager)getSystemService(SENSOR_SERVICE);
        // add listener. The listener will be HelloAndroid (this) class
        sensorManager.registerListener(this, 
                sensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR),
                SensorManager.SENSOR_DELAY_NORMAL);

    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // TODO Auto-generated method stub
        // check sensor type
        if(event.sensor.getType()==Sensor.TYPE_ROTATION_VECTOR){


            SensorManager.getRotationMatrixFromVector(mRotationMatrixFromVector, event.values);

            SensorManager.remapCoordinateSystem(mRotationMatrixFromVector,
                    SensorManager.AXIS_X, SensorManager.AXIS_Z,
                    mRotationMatrix);

            SensorManager.getOrientation(mRotationMatrix, orientationVals);

            // Optionally convert the result from radians to degrees
            orientationVals[0] = (float) Math.toDegrees(orientationVals[0]);
            orientationVals[1] = (float) Math.toDegrees(orientationVals[1]);
            orientationVals[2] = (float) Math.toDegrees(orientationVals[2]);


            xCoor.setText("X: "+ String.valueOf(orientationVals[0]));
            yCoor.setText("Y: "+ String.valueOf(orientationVals[1]));
            zCoor.setText("Z: "+ String.valueOf(orientationVals[2]));
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        // TODO Auto-generated method stub

    }
}

Answer 1

From docs: mRotationMatrixFromVector must have length 9 or 16.