How to extract centreMassWorld data from realsense_ros_samples to implement into the arduino

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I will like to know by realsense_ros_person package which held inside of realsense_ros_samples. By reading through the readme file that posted in the github. i find out there is a published topic of person_tracking_output which contain the centreMassWorld coordinate and centreMassImage coordinate. The problem is i will like to know how i can extract the centreMassWorld coordinate from the person_tracking_output and implement it into the arduino code so that based on the value, the servo motor which connect to the arduino board can rotate based on it. Thanks