Android Low pass filter and High pass filter

Question

I have a very basic question. What is Low Pass filter and High Pass filter in case of Android Accelerometer?

When I see the output from the Accelerometer Sensor, I

Answer 1

Low Pass Filter: passes low-frequency signals and reduces the amplitude of signals with frequencies higher than the threshold frequency

High Pass Filter: passes high-frequency signals and reduces the amplitude of signals with frequencies lower than the threshold frequency

If you look at the documentation, it says: "in order to measure the real acceleration of the device, the contribution of the force of gravity must be eliminated. This can be achieved by applying a high-pass filter. Conversely, a low-pass filter can be used to isolate the force of gravity."

You could check out this tutorial on low pass filtering: http://www.raweng.com/blog/2013/05/28/applying-low-pass-filter-to-android-sensors-readings/

Reading the docs at http://developer.android.com/reference/android/hardware/SensorEvent.html#values, you can see that you can access the a values on all x,y,z axis by doing:

values[0] - a on x axis
values[1] - a on y axis
values[2] - a on z axis