android remove gravity from accelerometer readings

I am developing an application for Android where I need to remove gravity from accelerometer readings. I have read multiple discussions on this problem, I have also found an algorithm here, but I didn't really understand it.

I want to filter gravity from each axis, not from开发者_C百科 the total acceleration.

Could you please help me out? My code should be something like:

public void onSensorChanged(SensorEvent sensorEvent) {
    float vals[] = sensorEvent.values;
    float accelerationX = filterGravity(vals[0]);
    float accelerationY = filterGravity(vals[1]);
    float accelerationZ = filterGravity(vals[2]);
}

What code should I place in the filterGravity() method?

For a basic solution you would need a low pass filter other approaches like a Kalman filter are pretty tough regarding the maths behind. A simple example for Android is one click away from your link at http://developer.android.com/reference/android/hardware/SensorEvent.html#values.

Simply spoken a low pass filter builds a weighted average from all your history values. If you have for example a filtering factor of 0.1 it means that 10% of your current value is added to the previous mean value: newMeanValue = 10% of currentValue + 90% of oldMeanValue. That means even if there is an abrupt peak it will only push your mean value slowly because of the 10%.

Linear acceleration is what you need. Check Sensor.TYPE_LINEAR_ACCELERATION here.

If you do not have a phone with TYPE_LINEAR_ACCELERATION, you are stuck with TYPE_ACCELERATION, which cannot separate gravity (tilt) from linear acceleration.

One option is to apply the low-pass filter. Another approach is using sensor fusion if the gyroscope is available. Both approaches have their advantages and disadvantages.

I have lots of working examples in the open source project Acceleration Explorer.

Not too sure what you are trying to acomplish but if you are look for the magnitude (which will give a result between 0 and 1) then all you do is divide the result by 10

public void onSensorChanged(SensorEvent sensorEvent) {
float vals[] = sensorEvent.values;
float accelerationX = (vals[0]/10);
float accelerationY = (vals[1]/10);
float accelerationZ = (vals[2]/10);

}

In a game environment when the sensor is at full tilt your object will be at its maximum speed