Question for getting absolute acceleration.

[BravoJason]

I have a question for get absolute acceleration in KalmanLocationService class.

In onSensorChanged callback function:
android.opengl.Matrix.multiplyMV(absAcceleration, 0, rotationMatrixInv, 0, linearAcceleration, 0);
The question is that when the user hold the phone moving, I think apart we need to do rotate from the device coordinate to global coordinate and we also need to do projection in each global coordinate axis.

But for our code, I only see the rotation code and I didn't see the projection code.

Could you tell me is there any misunderstanding of the code?

[BravoJason]

You are right.

When we use the rotation matrix to rotate the vector, it will rotate the coordinate system.

It needn't to do projection.

[Lezh1k]

https://blog.maddevs.io/reduce-gps-data-error-on-android-with-kalman-filter-and-accelerometer-43594faed19c

Part with "Determining orientation of the phone in space" explains that.
Also greater explanation is here : https://www.youtube.com/watch?v=T9jXoG0QYIA&t=675s - ~11 min.