robot location prediction step

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Hi,

In the robot_localisation package, when the use_control param is set to true then the values from the cmd_vel topic are used for the state prediction. But what if its set false. How does the prediction setup work?

I looked at one of the questions posed where it is explained how the prediction step works link.

The transition function for x is x_new = x_old + vx * t + 0.5 * a * t^2

Normally this would mean the vx and aare obtained from the previous state and when the use_control param is true, then these values are obtained from cmd_vel topic.

When I look at the documentation of robot_localisation package, it says

Note: The presence and inclusion of linear acceleration data from an IMU will currently “override” the predicted linear acceleration value.

Which I'm not able to understand as the values from the IMU are used for the correction step and not prediction.

I know I'm assuming something wrong here, but could someone please explain to me how it works?

Thanks Sriram