With regards to the objective parameters, a practical scenario was designed to consider the effect of distance in the tracking performance. A 6 × 6 grid with 25 cm × 25 cm squares was designed and printed on a plastic sheet that was fixed to the floor, covering an area of 1.5 m2. The right ankle joint (tibiotalar) of an experimenter was fixed in all the intersection points of the grid (49 in total) using a cast. The position of the joint was estimated by the different tracking systems during 5 s.
With regards to the subjective parameters, three different configurations of a virtual reality-based system with a stepping exercise3 (see Balance) using the three different tracking systems were installed in the physical therapy area of a neurorehabilitation unit in a large metropolitan hospital. The experiences with the three tracking systems of healthy individuals, individuals with stroke, and therapists were collected through two ad-hoc questionnaires.
The optical tracking system provided the best accuracy while the electromagnetic device provided the most inaccurate results. However, this tracking solution provided the best jitter values, in contrast to the skeleton tracking, which had the worst results. Healthy individuals and professionals preferred the skeleton tracking solution rather than the optical and electromagnetic solution (in that order). Individuals with stroke chose the optical solution over the other options. Our results show that subjective perceptions and preferences are far from being constant among different populations, thus suggesting that these considerations, together with the performance parameters, should be also taken into account when designing a rehabilitation system.