Viability of 2D Swimming Kinematical Analysis Using a Single Moving Camera

Abstract

Despite its limitations, 2D kinematical analysis remains a simple and valid alternative for swimming analysis. This analysis is limited by the length of the field of view, and the reconstruction errors are proportional to the calibrated area. A possible solution for these problems is the usage of moving cameras that allow for tracking an object across a larger area without the concerns of the calibration area. The purpose of this study was to verify the viability of the utilization of moving cameras for underwater 2D kinematical analysis. Two calibration processes were evaluated: (i) obtaining the extrinsic parameters for every frame based on pool markers (M1) and; (ii) constraining the degrees of freedom of the camera’s movements and tracking translation based on the principal point (M2). M1 obtained better accuracy in reconstructing the coordinates of static markers (mean error: 12.1 against 14.2 mm from a static camera) and in the estimation of the rod length (−2.6 vs. 12.6 mm). M2 obtained better accuracy when evaluating the distance between the points (−0.3 mm) than that for position estimation (58.6 mm). The results indicate that moving cameras are a viable alternative for 2D underwater kinematic analysis, but M2 had limitations about real position extraction.

Keywords

• kinematic analysis
• camera calibration
• swimming