How to remove Gravity factor from Accelerometer readings in Android 3-axis accelerometer.

Question

Hi, Can anyone help on removing the g factor from accelerometer readings. I am using SensorEventListener with onSensorChanged() method for getting Sensor.TYPE_ACCELEROMETER data. I need only pure acceleration values in all directions. So at any state if the device is stable (or in constant speed), it should give (0.0,0.0,0.0) roughly. Currently, depending on its pitch and roll, it gives me variable output depending on the g forces acting on each axis.

I hope there is some formula to remove this, as I also get orientation values (pitch and roll) from Sensor.TYPE_ORIENTATION listener. I had used some but didn't work.

Any help please ?

Answer 1

Differentiating with respect to time a function of time rids you of the constants.

So by taking the derivative of the accelerometer's signal you'll get the "Jerk", which you can then re-integrate in order to get the non-constant part of the acceleration you're looking for.

In Layman's terms, take a sample from the accelerometer every 1 second, and subtract it from the previous sample. If the answer is (very close to) zero, you're not accelerating relatively to earth. If the result is non-zero, integrate it (in this case, multiply by one second), you have your acceleration.

Two things, though : -Look out for noise in the signal, round off your input. -Don't expect hyper-accurate results from on-chip accelerometers. You can use them to detect shaking, changes in orientation, but not really for knowing how many G's you're experiencing while making sharp turns in your car.