turtlebot irobot-create imu transformation and calibration [closed]

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Hi

I am adding an IMU to the irobotcreate base. If the IMU is not positioned on the base_link frame (body frame of robot) do you have to provide some kind of transform showing where the imu is relative to the base_link?

Also is the base_link frame physically located on the centre of the wheel axis of the create base?

Because i need to provide a transform from the base_link to the laser frame, but i measure this without knowing where the base_link frame is on the create base. The base_link frame is published by the create_drivers.