title: Quantitative underwater 3D motion analysis using submerged video cameras: accuracy analysis and trajectory reconstruction.
abstract: In this study we aim at investigating the applicability of underwater 3D motion capture based on submerged video cameras in terms of 3D accuracy analysis and trajectory reconstruction. Static points with classical direct linear transform (DLT) solution, a moving wand with bundle adjustment and a moving 2D plate with Zhang's method were considered for camera calibration. As an example of the final application, we reconstructed the hand motion trajectories in different swimming styles and qualitatively compared this with Maglischo's model. Four highly trained male swimmers performed butterfly, breaststroke and freestyle tasks. The middle fingertip trajectories of both hands in the underwater phase were considered. The accuracy (mean absolute error) of the two calibration approaches (wand: 0.96 mm - 2D plate: 0.73 mm) was comparable to out of water results and highly superior to the classical DLT results (9.74 mm). Among all the swimmers, the hands' trajectories of the expert swimmer in the style were almost symmetric and in good agreement with Maglischo's model. The kinematic results highlight symmetry or asymmetry between the two hand sides, intra- and inter-subject variability in terms of the motion patterns and agreement or disagreement with the model. The two outcomes, calibration results and trajectory reconstruction, both move towards the quantitative 3D underwater motion analysis.
authors.affiliation: a Faculty of Physical Education, University of Campinas , Campinas , Brazil.
authors.forename: Amanda P
authors.initials: AP
authors.lastname: Silvatti
authors.forename: Pietro
authors.initials: P
authors.lastname: Cerveri
authors.forename: Thiago
authors.initials: T
authors.lastname: Telles
authors.forename: Fábio A S
authors.initials: FA
authors.lastname: Dias
authors.forename: Guido
authors.initials: G
authors.lastname: Baroni
authors.forename: Ricardo M L
authors.initials: RM
authors.lastname: Barros
mesh_terms: D001696:Biomechanical Phenomena; D002138:Calibration; D003196:Computer Graphics; D003626:Data Display; D006225:Hand / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008962:Models, Theoretical; D009038:Motion; D009068:Movement / Q000502:physiology*; D011187:Posture / Q000502:physiology; D013550:Swimming / Q000193:education / Q000502:physiology*; D014741:Video Recording / Q000379:methods*