Android getOrientation Azimuth gets polluted when phone is tilted

Question

I\'m having a really annoying problem with a AR view acting like a compass. So when I hold the phone in portrait (so that the screen is pointing to my face), then I call the

Answer 1

For complete code see https://github.com/hoananguyen/dsensor
Keep a history and average out, I do not know the correct interpretation of pitch and roll so the following code is for azimuth only.

Class members

private List<float[]> mRotHist = new ArrayList<float[]>();
private int mRotHistIndex;
// Change the value so that the azimuth is stable and fit your requirement
private int mHistoryMaxLength = 40;
float[] mGravity;
float[] mMagnetic;
float[] mRotationMatrix = new float[9];
// the direction of the back camera, only valid if the device is tilted up by
// at least 25 degrees.
private float mFacing = Float.NAN;

public static final float TWENTY_FIVE_DEGREE_IN_RADIAN = 0.436332313f;
public static final float ONE_FIFTY_FIVE_DEGREE_IN_RADIAN = 2.7052603f;

onSensorChanged

@Override
public void onSensorChanged(SensorEvent event)
{
     if (event.sensor.getType() == Sensor.TYPE_GRAVITY)
     {
         mGravity = event.values.clone();
     }
     else
     {
        mMagnetic = event.values.clone();
     }

     if (mGravity != null && mMagnetic != null)
     {
          if (SensorManager.getRotationMatrix(mRotationMatrix, null, mGravity, mMagnetic))
          {
              // inclination is the degree of tilt by the device independent of orientation (portrait or landscape)
              // if less than 25 or more than 155 degrees the device is considered lying flat
              float inclination = (float) Math.acos(mRotationMatrix[8]);
              if (inclination < TWENTY_FIVE_DEGREE_IN_RADIAN 
                      || inclination > ONE_FIFTY_FIVE_DEGREE_IN_RADIAN)
              {
                  // mFacing is undefined, so we need to clear the history
                  clearRotHist();
                  mFacing = Float.NaN;
              }
              else
              {
                  setRotHist();
                  // mFacing = azimuth is in radian
                  mFacing = findFacing(); 
              }
          }
     }
}

private void clearRotHist()
{
    if (DEBUG) {Log.d(TAG, "clearRotHist()");}
    mRotHist.clear();
    mRotHistIndex = 0;
}

private void setRotHist()
{
    if (DEBUG) {Log.d(TAG, "setRotHist()");}
    float[] hist = mRotationMatrix.clone();
    if (mRotHist.size() == mHistoryMaxLength)
    {
        mRotHist.remove(mRotHistIndex);
    }   
    mRotHist.add(mRotHistIndex++, hist);
    mRotHistIndex %= mHistoryMaxLength;
}

private float findFacing()
{
    if (DEBUG) {Log.d(TAG, "findFacing()");}
    float[] averageRotHist = average(mRotHist);
    return (float) Math.atan2(-averageRotHist[2], -averageRotHist[5]);
}

public float[] average(List<float[]> values)
{
    float[] result = new float[9];
    for (float[] value : values)
    {
        for (int i = 0; i < 9; i++)
        {
            result[i] += value[i];
        }
    }

    for (int i = 0; i < 9; i++)
    {
        result[i] = result[i] / values.size();
    }

    return result;
}