Android: azimuth issue depending initial device tilt

Question

I'm currently programming an Android AR application and I have an issue with my Azimuth calculation depending of the initial device tilt.

I use the ROTATION_VECTOR sensor to get Azimuth, Altitude and Tilt.

When I launch my application and the phone is perpendicular with ground, I have the good azimuth from the North. When I launch the application and the phone is parallel to the ground, I have bad values. I have also strange values when I change device tilt.

This is my code :

public void onSensorChanged(SensorEvent event)
{
    if (event.sensor.getType() == sensor.TYPE_ROTATION_VECTOR)
    {
        SensorManager.getRotationMatrixFromVector(rotationVectorMatrix, event.values);
        SensorManager.remapCoordinateSystem(rotationVectorMatrix, SensorManager.AXIS_X, SensorManager.AXIS_Z, rotationMatrix);
        SensorManager.getOrientation(rotationMatrix, orientation);
        ...
    }
}

Answer 1

To get azimuth, you can use an accelerometer and magnetic field sensors. You can use following code to log azimuth value.

    public class MainActivity extends AppCompatActivity {

    private int mAzimuth = 0; // degree

    private SensorManager mSensorManager = null;

    private Sensor mAccelerometer;
    private Sensor mMagnetometer;

    boolean haveAccelerometer = false;
    boolean haveMagnetometer = false;

    @Override
    protected void onCreate( Bundle savedInstanceState ) {
        super.onCreate(savedInstanceState);

        mSensorManager = (SensorManager) getSystemService(Service.SENSOR_SERVICE);

        this.mAccelerometer = this.mSensorManager.getDefaultSensor( Sensor.TYPE_ACCELEROMETER );
        this.haveAccelerometer = this.mSensorManager.registerListener( mSensorEventListener, this.mAccelerometer, SensorManager.SENSOR_DELAY_GAME );

        this.mMagnetometer = this.mSensorManager.getDefaultSensor( Sensor.TYPE_MAGNETIC_FIELD );
        this.haveMagnetometer = this.mSensorManager.registerListener( mSensorEventListener, this.mMagnetometer, SensorManager.SENSOR_DELAY_GAME );

        if ( haveAccelerometer && haveMagnetometer ) {
            // ready to go
        } else {
            // unregister and stop
        }

    }

    private SensorEventListener mSensorEventListener = new SensorEventListener() {

        float[] gData = new float[3]; // accelerometer
        float[] mData = new float[3]; // magnetometer
        float[] rMat = new float[9];
        float[] iMat = new float[9];
        float[] orientation = new float[3];

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

        @Override
        public void onSensorChanged( SensorEvent event ) {
            float[] data;
            switch ( event.sensor.getType() ) {
                case Sensor.TYPE_ACCELEROMETER:
                    gData = event.values.clone();
                    break;
                case Sensor.TYPE_MAGNETIC_FIELD:
                    mData = event.values.clone();
                    break;
                default: return;
            }

            if ( SensorManager.getRotationMatrix( rMat, iMat, gData, mData ) ) {
                mAzimuth= (int) ( Math.toDegrees( SensorManager.getOrientation( rMat, orientation )[0] ) + 360 ) % 360;
                Log.d("AzimuthTag", "Azimuth:"+mAzimuth);
            }
        }
    };

}

Source