Question

I want to use the accelerometer in android for my app.
In documentation its given as below:

   final float alpha = 0.8;

   // Isolate the force of gravity with the low-pass filter.

   gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];

But lowpass filter works as below:

    output = alpha*input + (1-alpha)*previousoutput;

My query is why we are taking gravity as input and sensor event as previous output?
It must be other way around.

Answer 1

Technically it uses linear mix of two inputs: mix(α,x,y) = α * x + (1-α) * y.

Now mix(α,x,y) is equivalent to mix(1-α,y,x).
So you can reverse signals as you wanted, make alpha = 0.2 and everything will work the same.