# The coordinate system of linear acceleration

Hi everyone,

I bought the MMC sensor, and I download the data from the Metabase APP. I have a question about the linear acceleration output.

When the sensor roll down on a slope, the linear acceleration output is related to the coordinate system fixed with the sensor or the original stationary reference system? I can not find the explanation on the tutorial. Looking forward to your reply, thanks a lot.

## Comments

https://mbientlab.com/tutorials/Orientation.html?highlight=orientation

I'm not sure exactly what you are asking. Just move the board yourself in each direction and see which axis responds according.

Hi Eric,

Thanks for your reply. I have checked the tutorial, it only mentioned the orientation of each axis.

Sorry I did not make the question clear. A picture to describe the reference frame and the body frame is shown below. The sensor is moving forward from t=0 to t=∆t. If I want to get the velocity, I need to integrate the linear acceleration. As you can see from the picture, the sensor is rolling forward, so the sensor axis has been rotated during the movement. In fact, the linear velocity should be related to the reference frame which is always kept stationary in the starting point. That's why I want to know the linear acceleration output is measured with respect to the body frame or the reference frame.

Thanks again for your patience to answer the question.

In your picture, linear acceleration should be non-zero at some point because there is translational motion.

Post the data you measured from your experiment? Does it match what you expected? If not, what is the expected output?