Yeah something else I need to do. lazy question, if I have an IMU that is swaying around as I try to move in a linear direction (e.g. Forward) is that something this kind of filtering would be used for? Regarding displacement estimation.

Edit: I get fusion is regarding multiple sensors

Normally, there are several types of sensors available, but most use 9DOF packages (3-axis gyroscope, accelerometer, and magnetometer)

gyroscope: fast over-sampled low-pass filter, but slowly drifts compounding heading errors

accelerometer: relatively stable, but dead-reckoning errors compound quickly

magnetometer: best stability, but low-sample rate and vulnerable to metal/magnets fooling/blinding the sensors

The fusion algorithms usually weights which data is consistent with the motion path, and attenuates the estimated pose errors.

Notably, not all sensors are equal quality, but there are probably better options now. =3