How do you acquire wheel pose in /tf (e.g., robot_front_left_wheel)?

[HanzhiC]

Hi, I am considering using wheel odometry from our RB-Vogui.
It seems that the information from the wheel encoder is not published, and the wheel poses are provided in /tf as "robot_base_left_wheel", "robot_front_left_wheel", etc. I guess these poses are computed from the wheel encoders right?
So, could you tell me if the wheel pose is calculated from wheel encoder information only (without fusing information from other sensors)? If not, could you tell me how can I acquire raw wheel encoder information?
Thank you!