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Di Marco R.,University of Rome La Sapienza | Di Marco R.,University of Sheffield | Rossi S.,University of Tuscia | Bachetti B.,University of Rome La Sapienza | And 3 more authors.
2015 IEEE International Symposium on Medical Measurements and Applications, MeMeA 2015 - Proceedings

Optoelectronic systems are largely employed for human movement analysis, where marker trajectories are used to estimate the articular joint kinematics. From a literature analysis it emerged that the error associated to the joint kinematics can be reduced performing the data collection in the center of the system calibration volume. According to human movement analysis literature, the foot-ankle complex appears to be the anatomical joint most affected by instrument inaccuracy, as it moves in the lower bound of the calibration volume during the gait cycle. A multi-segment marker-based model of the lower limb-including the pelvis, thigh, tibia, hindfoot, forefoot and hallux-was investigated in this paper. One healthy subject was asked to walk on the central and on two boundary areas of the capture volume calibrated for the experiments. The calibration procedure was focused on the exploitation of the effects on the joint angles of: (i) calibration volumes (i.e. the global one and two of its sub-volumes) and (ii) number of frames acquired for the calibration procedure (refinement frames). In order to quantify the precision of estimating the joint kinematics when changing the calibration procedure, the RMSE among different refinement frames using both the global volume and the two sub-volumes was computed as an index of the joint angles variation estimated on the sagittal plane. Two two-way ANOVAs were performed to evaluate whether the calibration volumes or the walking areas affect the kinematics. The statistical analysis highlighted a good robustness of the reconstruction algorithm implemented by the optoelectronic system manufacturer. Few variables showed significant differences for the RMSEs, with p-values lower than 0.05. No clear dependence on the body segments here analyzed emerged from the analysis. The coefficient of Multiple Correlations was computed in order to enlighten the similarities among the joint angles time patterns. We conclude that reconstructed trajectories can be affected by the same magnitude errors, regardless to the calibrated volume or the considered walking area. This finding allows conducting the gait analysis without paying attention when calibrating the system and without having to impose excessive restrictions to the tested subjects, allowing to keep their movement as natural as possible. © 2015 IEEE. Source

Di Marco R.,University of Rome La Sapienza | Di Marco R.,University of Sheffield | Rossi S.,University of Tuscia | Castelli E.,Laboratory of Movement Analysis and Robotics MARlab | And 4 more authors.
Measurement: Journal of the International Measurement Confederation

This paper proposes a methodology for evaluating the effect of different stereophotogrammetric system calibration procedures on the calculation of marker-based kinematics information. The methodology, based on calibrating the system using data recorded from capture volumes of different sizes and in trials of different durations, was applied to two different systems. The calibration data were used to reconstruct the static and dynamic position and orientation in space of a rigid wand carrying markers in known positions. The inaccuracies in the reconstruction of distances and angles from the wand markers were independent on the calibration data, with average errors lower than 1.7. mm and 0.7°, respectively. Similar results were obtained from human gait data, with the highest variations observed in the transverse plane kinematics and in the foot segment, suggesting that successful calibration procedures of different durations and performed in different volumes did not affect the metrological performance of the investigated systems. © 2016 The Authors. Source

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