Android device orientation without geomagnetic

Question

I need to get device orientation. As I know usually used TYPE_ACCELEROMETER and TYPE_MAGNETIC_FIELD sensors. My problem is that SensorManager.getDefaultSensor returns me null for geomagnetic sensor. It returns null for TYPE_ORIENTATION sensor too.

manager = (SensorManager) getSystemService(SENSOR_SERVICE);
Sensor sensorAcc = manager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), //normal object
        sensorMagn = manager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD); //null
orientationListener = new OrientationSensorListener();
manager.registerListener(orientationListener, sensorAcc, 10);
manager.registerListener(orientationListener, sensorMagn, 10);

I need another ways to get device orientation.

Answer 1

Orientation can be decomposed in three Euler angle : Pitch, Roll and Azimuth.

With only accelerometer datas, you cannot compute your Azimuth, neither the sign of your pitch.

You can try something as this to know something about your pitch and roll :

    private final float[] mMagnet = new float[3];               // magnetic field vector
    private final float[] mAcceleration = new float[3];         // accelerometer vector
    private final float[] mAccMagOrientation = new float[3];    // orientation angles from mAcceleration and mMagnet
    private float[] mRotationMatrix = new float[9];             // accelerometer and magnetometer based rotation matrix

    public void onSensorChanged(SensorEvent event) {
    switch (event.sensor.getType()) {
        case Sensor.TYPE_ACCELEROMETER:
            System.arraycopy(event.values, 0, mAcceleration, 0, 3);   // save datas
            calculateAccMagOrientation();                       // then calculate new orientation
            break;
        case Sensor.TYPE_MAGNETIC_FIELD:
            System.arraycopy(event.values, 0, mMagnet, 0, 3);         // save datas
            break;
        default: break;
    }
}
public void calculateAccMagOrientation() {
    if (SensorManager.getRotationMatrix(mRotationMatrix, null, mAcceleration, mMagnet))
        SensorManager.getOrientation(mRotationMatrix, mAccMagOrientation);
    else { // Most chances are that there are no magnet datas
        double gx, gy, gz;
        gx = mAcceleration[0] / 9.81f;
        gy = mAcceleration[1] / 9.81f;
        gz = mAcceleration[2] / 9.81f;
        // http://theccontinuum.com/2012/09/24/arduino-imu-pitch-roll-from-accelerometer/
        float pitch = (float) -Math.atan(gy / Math.sqrt(gx * gx + gz * gz));
        float roll = (float) -Math.atan(gx / Math.sqrt(gy * gy + gz * gz));
        float azimuth = 0; // Impossible to guess

        mAccMagOrientation[0] = azimuth;
        mAccMagOrientation[1] = pitch;
        mAccMagOrientation[2] = roll;
        mRotationMatrix = getRotationMatrixFromOrientation(mAccMagOrientation);
    }
}
public static float[] getRotationMatrixFromOrientation(float[] o) {
    float[] xM = new float[9];
    float[] yM = new float[9];
    float[] zM = new float[9];

    float sinX = (float) Math.sin(o[1]);
    float cosX = (float) Math.cos(o[1]);
    float sinY = (float) Math.sin(o[2]);
    float cosY = (float) Math.cos(o[2]);
    float sinZ = (float) Math.sin(o[0]);
    float cosZ = (float) Math.cos(o[0]);

    // rotation about x-axis (pitch)
    xM[0] = 1.0f;xM[1] = 0.0f;xM[2] = 0.0f;
    xM[3] = 0.0f;xM[4] = cosX;xM[5] = sinX;
    xM[6] = 0.0f;xM[7] =-sinX;xM[8] = cosX;

    // rotation about y-axis (roll)
    yM[0] = cosY;yM[1] = 0.0f;yM[2] = sinY;
    yM[3] = 0.0f;yM[4] = 1.0f;yM[5] = 0.0f;
    yM[6] =-sinY;yM[7] = 0.0f;yM[8] = cosY;

    // rotation about z-axis (azimuth)
    zM[0] = cosZ;zM[1] = sinZ;zM[2] = 0.0f;
    zM[3] =-sinZ;zM[4] = cosZ;zM[5] = 0.0f;
    zM[6] = 0.0f;zM[7] = 0.0f;zM[8] = 1.0f;

    // rotation order is y, x, z (roll, pitch, azimuth)
    float[] resultMatrix = matrixMultiplication(xM, yM);
    resultMatrix = matrixMultiplication(zM, resultMatrix);
    return resultMatrix;
}
public static float[] matrixMultiplication(float[] A, float[] B) {
    float[] result = new float[9];

    result[0] = A[0] * B[0] + A[1] * B[3] + A[2] * B[6];
    result[1] = A[0] * B[1] + A[1] * B[4] + A[2] * B[7];
    result[2] = A[0] * B[2] + A[1] * B[5] + A[2] * B[8];

    result[3] = A[3] * B[0] + A[4] * B[3] + A[5] * B[6];
    result[4] = A[3] * B[1] + A[4] * B[4] + A[5] * B[7];
    result[5] = A[3] * B[2] + A[4] * B[5] + A[5] * B[8];

    result[6] = A[6] * B[0] + A[7] * B[3] + A[8] * B[6];
    result[7] = A[6] * B[1] + A[7] * B[4] + A[8] * B[7];
    result[8] = A[6] * B[2] + A[7] * B[5] + A[8] * B[8];

    return result;
}

Answer 2

To get the angle of rotation when the device is not flat, implements OrientationEventListener. onOrientationChanged will give the device orientation. See https://developer.android.com/reference/android/view/OrientationEventListener.html for detail.