Two possible sources of inaccuracy for stereophotogrammetric systems

Stereophotogrammetric systems are often used to analyze the human body kinematics, both in in-vitro [1] and in-vivo applications [2]. Understanding the factors governing their final accuracy is thus fundamental to the final reliability of measurements. This work focuses on two possible sources of inaccuracy that may potentially affect a stereophotogrammetric system and that were observed with a VICON setup: 1) a drift in time of the global reference system; 2) a reconstruction error associated with camera occlusions. The first error makes acquisition taken at different time inconsistent and may highly affect long experimental sessions. The second error generates significant marker jumps when one or more cameras are occluded, even with a large camera set. To the authors’ knowledge, these errors were not reported in the literature yet, although they may potentially affect standard applications of stereophotogrammetric systems.