How to change the position of "base_link" frame?

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The robot frame is usually published by your robot driver which integrates wheel encoder values (or in addition with a gyro/imu) in order to broadcast the relative transformation between odom and base_link. The location of base_linkw.r.t. the robot body is driver specific here.

Options:

• You could change the driver code, but you would need to compile from source and update the package manually in the future.
• If the driver has the option to change the base_link name, rename base_link and add a static_transform_publisher to your robot launch file in order to create a new base_linkat the rotational center.
• Create a new link, e.g. nav_link at the rotational center with a static_transform_publisher in your robot launch file. Configure the navigation stack accordingly (the base frame can be set in the global and local costmap parameters). I haven't tried this option yet. Ideally, planners should adhere to the base frame specification in all internal transformations.

Some drivers are only publishing joint states and utilize a robot_state_publisher to provide the corresponding robot frames from a robot model description, usually a URDF file. Sometimes xacro is utilized to generate URDF files. In that case, you can adjust the robot model in one of the following ways:

• Move the current base_link frame to the rotational center and adjust all inherited transformations (children frames) as well.
• Choose a different name for the current base_link frame and add a new base_linkat the rotational center (e.g. as a child frame from the old one).
• Create a new link, e.g. nav_link at the rotational center. Refer to option 3. above for further comments.