Not getting direction from sensors in landscape mode or after flipping orientation

Question

I'm trying to get the direction of the camera in Android. I have code that's working perfectly in portrait (I test it by slowly turning in a circle and looking at updates 1s apart), but it isn't working at all in landscape- The numbers seem to change randomly. It also gets totally out of whack after switching from portrait to landscape. Here's my code

public void onSensorChanged(SensorEvent event) {

    switch (event.sensor.getType()) {
    case Sensor.TYPE_ACCELEROMETER:
        accelerometerValues = event.values.clone();

        break;
    case Sensor.TYPE_MAGNETIC_FIELD:
        geomagneticMatrix = event.values.clone();
        break;
    default:
        break;
    }   

    if (geomagneticMatrix != null && accelerometerValues != null) {

        float[] R = new float[16];
        float[] I = new float[16];
        float[] outR = new float[16];

        //Get the rotation matrix, then remap it from camera surface to world coordinates
        SensorManager.getRotationMatrix(R, I, accelerometerValues, geomagneticMatrix);
        SensorManager.remapCoordinateSystem(R, SensorManager.AXIS_X, SensorManager.AXIS_Z, outR);
        float values[] = new float[4];
        SensorManager.getOrientation(outR,values);
        float direction = normalizeDegrees((float) Math.toDegrees(values[0]));
        float pitch = normalizeDegrees((float) Math.toDegrees(values[1]));
        float roll = normalizeDegrees((float) Math.toDegrees(values[2]));

        if((int)direction != (int)lastDirection){
            lastDirection = direction;
            for(CompassListener listener: listeners){
                listener.onDirectionChanged(lastDirection, pitch, roll);
            }
        }
    }
}

Any ideas what I'm doing wrong? I freely admit I don't 100% understand this. I also don't know why Google deprecated the orientation sensor- it seems like a common enough desire.

Answer 1

I seemed to have solved it, or at least improved it to the point where I know what was the problem. I put in a filter such that instead of delivering a single sensor reading, I'm remembering the last reading and applying a delta to it. Each new sensor point is allowed to add a maximum of 5 degrees. This completely filters out the weird hops, and forces it to converge to a value. I sill see an occasional odd jump, but I figure what I need is a more sophisticated filter. New code:

public void onSensorChanged(SensorEvent event) {
    if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE)
        return;

    switch (event.sensor.getType()) {
    case Sensor.TYPE_ACCELEROMETER:
        accelerometerValues = event.values.clone();

        break;
    case Sensor.TYPE_MAGNETIC_FIELD:
        geomagneticMatrix = event.values.clone();
        break;
    }   

    if (geomagneticMatrix != null && accelerometerValues != null) {

        float[] R = new float[16];
        float[] I = new float[16];
        float[] outR = new float[16];

        //Get the rotation matrix, then remap it from camera surface to world coordinates
        SensorManager.getRotationMatrix(R, I, accelerometerValues, geomagneticMatrix);
        SensorManager.remapCoordinateSystem(R, SensorManager.AXIS_X, SensorManager.AXIS_Z, outR);
        float values[] = new float[4];
        SensorManager.getOrientation(outR,values);

        int direction = filterChange(normalizeDegrees(Math.toDegrees(values[0])));
        int pitch = normalizeDegrees(Math.toDegrees(values[1]));
        int roll = normalizeDegrees(Math.toDegrees(values[2]));
        if((int)direction != (int)lastDirection){
            lastDirection = (int)direction;
            lastPitch = (int)pitch;
            lastRoll = (int)roll;
            for(CompassListener listener: listeners){
                listener.onDirectionChanged(lastDirection, pitch, roll);
            }
        }
    }
}

//Normalize a degree from 0 to 360 instead of -180 to 180
private int normalizeDegrees(double rads){
    return (int)((rads+360)%360);
}

//We want to ignore large bumps in individual readings.  So we're going to cap the number of degrees we can change per report
private int filterChange(int newDir){
    int change = newDir - lastDirection;
    int circularChange = newDir-(lastDirection+360);
    int smallestChange;
    if(Math.abs(change) < Math.abs(circularChange)){
        smallestChange = change;
    }
    else{
        smallestChange = circularChange;
    }
    smallestChange = Math.max(Math.min(change,5),-5);
    return lastDirection+smallestChange;
}

Answer 2

Did you consider, that when you change from portrait to landscape, accelerometer axes change ? Like Y-axis becomes Z-axis and so on. This might be one source of strange behavior.