How do I get the correct bearing (magnetic orientation) regardless of screen orientation?

Question

I want to get the current magnetic orientation regardless of the current screen orientation (landscape or portrait).

I found this example, but it's not orientation independant, right? And this didn't help me either. I did also read http://android-developers.blogspot.de/2010/09/one-screen-turn-deserves-another.html.

This is my current approach with the deprecated way I don't want to use (short):

mSensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);

private SensorEventListener sensorEventListener = new SensorEventListener() {

    public void onSensorChanged(SensorEvent event) {

        /* Get measured value */
        float current_measured_bearing = (float) event.values[0];

        /* Compensate device orientation */
        switch (((WindowManager) getSystemService(WINDOW_SERVICE))
                .getDefaultDisplay().getRotation()) {
        case Surface.ROTATION_90:
            current_measured_bearing = current_measured_bearing + 90f;
            break;
        case Surface.ROTATION_180:
            current_measured_bearing = current_measured_bearing - 180f;
            break;
        case Surface.ROTATION_270:
            current_measured_bearing = current_measured_bearing - 90f;
            break;
        }

But the last part is definitely wrong! How do I use the newer method getRotationMatrix() correctly in this case? (Orientation independent) Or do I simply have to use other values of the event.values[] array based on the Rotation Matrix? Or will I need to 'remap the coordinates'? So is that the correct way of achieving this?

I'm developing for devices with 360° screen rotation and on API Level 11+.

I know that those questions are asked very often but I could simply not transfer their answers to my question.

Superscription

I had the same problem posted here: #11773423 but the answer didn't work for me. Perhaps you have more luck. – Alehouse

Do you still need it? Because maybe we 'have to use other values of the event.values[] array?' based on the screen rotation? – Superscription

No, I cancelled the project (some AR stuff) as it turned out that the rotation sensors of most Android devices are not exact enough for what I had in mind. – Alehouse

Answer 1

OK I finally managed to get the code working!

First, I register a Sensor.TYPE_MAGNETIC_FIELD and Sensor.TYPE_GRAVITY: (like Hoan Nguyen said!)

/**
 * Initialize the Sensors (Gravity and magnetic field, required as a compass
 * sensor)
 */
private void initSensors() {

    LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
    SensorManager sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
    Sensor mSensorGravity = sensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY);
    Sensor mSensorMagneticField = sensorManager
            .getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);

    /* Initialize the gravity sensor */
    if (mSensorGravity != null) {
        Log.i(TAG, "Gravity sensor available. (TYPE_GRAVITY)");
        sensorManager.registerListener(mSensorEventListener,
                mSensorGravity, SensorManager.SENSOR_DELAY_GAME);
    } else {
        Log.i(TAG, "Gravity sensor unavailable. (TYPE_GRAVITY)");
    }

    /* Initialize the magnetic field sensor */
    if (mSensorMagneticField != null) {
        Log.i(TAG, "Magnetic field sensor available. (TYPE_MAGNETIC_FIELD)");
        sensorManager.registerListener(mSensorEventListener,
                mSensorMagneticField, SensorManager.SENSOR_DELAY_GAME);
    } else {
        Log.i(TAG,
                "Magnetic field sensor unavailable. (TYPE_MAGNETIC_FIELD)");
    }
}

And I use that SensorEventListner for the computation:

private SensorEventListener mSensorEventListener = new SensorEventListener() {

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

    @Override
    public void onSensorChanged(SensorEvent event) {

        if (event.sensor.getType() == Sensor.TYPE_GRAVITY) {

            mGravity = event.values.clone();

        } else if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {

            mMagnetic = event.values.clone();

        }

        if (mGravity != null && mMagnetic != null) {

            /* Create rotation Matrix */
            float[] rotationMatrix = new float[9];
            if (SensorManager.getRotationMatrix(rotationMatrix, null,
                    mGravity, mMagnetic)) {

                /* Compensate device orientation */
                // http://android-developers.blogspot.de/2010/09/one-screen-turn-deserves-another.html
                float[] remappedRotationMatrix = new float[9];
                switch (getWindowManager().getDefaultDisplay()
                        .getRotation()) {
                case Surface.ROTATION_0:
                    SensorManager.remapCoordinateSystem(rotationMatrix,
                            SensorManager.AXIS_X, SensorManager.AXIS_Y,
                            remappedRotationMatrix);
                    break;
                case Surface.ROTATION_90:
                    SensorManager.remapCoordinateSystem(rotationMatrix,
                            SensorManager.AXIS_Y,
                            SensorManager.AXIS_MINUS_X,
                            remappedRotationMatrix);
                    break;
                case Surface.ROTATION_180:
                    SensorManager.remapCoordinateSystem(rotationMatrix,
                            SensorManager.AXIS_MINUS_X,
                            SensorManager.AXIS_MINUS_Y,
                            remappedRotationMatrix);
                    break;
                case Surface.ROTATION_270:
                    SensorManager.remapCoordinateSystem(rotationMatrix,
                            SensorManager.AXIS_MINUS_Y,
                            SensorManager.AXIS_X, remappedRotationMatrix);
                    break;
                }

                /* Calculate Orientation */
                float results[] = new float[3];
                SensorManager.getOrientation(remappedRotationMatrix,
                        results);

                /* Get measured value */
                float current_measured_bearing = (float) (results[0] * 180 / Math.PI);
                if (current_measured_bearing < 0) {
                    current_measured_bearing += 360;
                }

                /* Smooth values using a 'Low Pass Filter' */
                current_measured_bearing = current_measured_bearing
                        + SMOOTHING_FACTOR_COMPASS
                        * (current_measured_bearing - compass_last_measured_bearing);

                /* Update normal output */
                visual_compass_value.setText(String.valueOf(Math
                        .round(current_bearing))
                        + getString(R.string.degrees));

                /*
                 * Update variables for next use (Required for Low Pass
                 * Filter)
                 */
                compass_last_measured_bearing = current_measured_bearing;

            }
        }
    }
};

Superscription

What do you try to achieve here? Hold your device in portrait mode and then rotate the device by 15 degree the current_measured_bearing will be differed by 15 degree. Is this what you want? – Flex

Yes thats It, for example. – Superscription

hey what is the value for SMOOTHING_FACTOR_COMPASS?? – Clothes

Can you add all imports and consts? – Hookup

Answer 2

Sensor.TYPE_ORIENTATION is depreciated and only good if the device is flat. When using Sensor.TYPE_ORIENTATION, the bearing (azimuth) is the direction where the device Y-axis points. So if the device is held vertical, the direction where the Y-axis points using as the bearing does not make sense. It only make sense to calculate the direction where the back camera points. To find this direction you have to use Sensor.TYPE_MAGNETIC_FIELD and Sensor.TYPE_GRAVITY or Sensor.TYPE_ACCELEROMETER. If using Sensor.TYPE_ACCELEROMETER, you have to filter the accelerometer values.
Using these sensors, you call getRotationMatrix and then remapCoordinateSystem(inR, AXIS_X, AXIS_Z, outR) before calling getOrientation. To get a stable direction you should keep a history of the direction and then calculate the average. For an implementation using TYPE_GRAVITY check Android getOrientation Azimuth gets polluted when phone is tilted

Flex

Thank you for this solution. So now I'm going to write the code based on this. – Superscription

Answer 3

I think this code may help you:

    //get orientation
private int getScreenOrientation() {
    int rotation = getWindowManager().getDefaultDisplay().getRotation();
    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);
    int width = dm.widthPixels;
    int height = dm.heightPixels;
    int orientation;
    // if the device's natural orientation is portrait:
    if ((rotation == Surface.ROTATION_0
            || rotation == Surface.ROTATION_180) && height > width ||
        (rotation == Surface.ROTATION_90
            || rotation == Surface.ROTATION_270) && width > height) {
        switch(rotation) {
            case Surface.ROTATION_0:
                orientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
                break;
            case Surface.ROTATION_90:
                orientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
                break;
            case Surface.ROTATION_180:
                orientation =
                    ActivityInfo.SCREEN_ORIENTATION_REVERSE_PORTRAIT;
                break;
            case Surface.ROTATION_270:
                orientation =
                    ActivityInfo.SCREEN_ORIENTATION_REVERSE_LANDSCAPE;
                break;
            default:
                Log.e(TAG, "Unknown screen orientation. Defaulting to " +
                        "portrait.");
                orientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
                break;              
        }
    }
    // if the device's natural orientation is landscape or if the device
    // is square:
    else {
        switch(rotation) {
            case Surface.ROTATION_0:
                orientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
                break;
            case Surface.ROTATION_90:
                orientation = ActivityInfo.SCREEN_ORIENTATION_PORTRAIT;
                break;
            case Surface.ROTATION_180:
                orientation =
                    ActivityInfo.SCREEN_ORIENTATION_REVERSE_LANDSCAPE;
                break;
            case Surface.ROTATION_270:
                orientation =
                    ActivityInfo.SCREEN_ORIENTATION_REVERSE_PORTRAIT;
                break;
            default:
                Log.e(TAG, "Unknown screen orientation. Defaulting to " +
                        "landscape.");
                orientation = ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE;
                break;              
        }
    }

    return orientation;
}

Benuecongo

Thamk you for your code and sorry for such a late answer, but this only returnes the screen orientation as an int (in the ActivityInfo.SCREEN_ORIENTATION_XX-style). This is a very useful part of code, but do you also know how to use the rotation matrix? – Superscription

Can you help me out on this question please? – Burrstone