Characterization of gait is largely used for research on locomotion or for clinical improvement and follow up. There exists two main technologies for measurement of the kinematics of walking: IMU systems and optical tracking. Inertial measurement units are getting more and more popular because of their integrability, cost and lack of spatial limitations. Despite these advantages, optical motion tracking solutions offer a higher precision which is for various applications such as kinetics analysis. In that sense, the present study proposes a solution for the extension of one lower limbs’ optical measurement system toward open space applications. The tracking solution has the specificity of using only one “camera” placed behind the subject. Thus, by fastening the “camera” to a robotic vehicle, the markers on the subject’s body can be kept in the measuring range while the subjects is free from space limitations. The wheeled robotic platform can manage smooth motions while sustaining a precise pursuit of the measured subject. Investigations will be made to compare the mobile with the static measurement on treadmill.