Currently I am investigating compass mechanism on Android and I would recommend to start with low-pass filter in your case. What you need to do - is to apply low-pass filter to both ACCELEROMETER and MAGNETIC_FIELD sensors data. Here is how I implemented that:
private float[] accel;
private float[] geomagnetic;
float R[] = new float[9];
float I[] = new float[9];
float orientation[] = new float[3];
@Override
public void onSensorChanged(SensorEvent event)
{
synchronized (this)
{
float azimuth = -1f;
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
accel = lowPass( event.values.clone(), accel );
if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
geomagnetic = lowPass(event.values.clone(), geomagnetic);
if (accel != null && geomagnetic != null)
{
boolean success = SensorManager.getRotationMatrix(R, I,
accel, geomagnetic);
SensorManager.remapCoordinateSystem(R,
SensorManager.AXIS_X, SensorManager.AXIS_Z, R);
if (success)
{
SensorManager.getOrientation(R, orientation);
azimuth = orientation[0]; // orientation contains:
// azimuth, pitch
// and roll
float newHeading = azimuth * 360 / (2 * 3.14159f);
//do what you need to do with new heading
}
}
}
}
/*
* time smoothing constant for low-pass filter 0 ≤ alpha ≤ 1 ; a smaller
* value basically means more smoothing See:
* http://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization
*/
static final float ALPHA = 0.15f;
/**
* @see http
* ://en.wikipedia.org/wiki/Low-pass_filter#Algorithmic_implementation
* @see http
* ://developer.android.com/reference/android/hardware/SensorEvent.html
* #values
*/
protected float[] lowPass(float[] input, float[] output)
{
if (output == null)
return input;
for (int i = 0; i < input.length; i++)
{
output[i] = output[i] + ALPHA * (input[i] - output[i]);
}
return output;
}