Action Sport Cameras As An Instrument To Perform A 3d Underwater Motion Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Action sport cameras (ASC) are currently adopted mainly for entertainment purposes but their uninterrupted technical improvements, in correspondence of cost decreases, are going to disclose them for three-dimensional (3D) motion analysis in sport gesture study and athletic performance evaluation quantitatively. Extending this technology to sport analysis however still requires a methodologic step-forward to making ASC a metric system, encompassing ad-hoc camera setup, image processing, feature tracking, calibration and 3D reconstruction. Despite traditional laboratory analysis, such requirements become an issue when coping with both indoor and outdoor motion acquisitions of athletes. In swimming analysis for example, the camera setup and the calibration protocol are particularly demanding since land and underwater cameras are mandatory. In particular, the underwater camera calibration can be an issue affecting the reconstruction accuracy. In this paper, the aim is to evaluate the feasibility of ASC for 3D underwater analysis by focusing on camera setup and data acquisition protocols. Two GoPro Hero3+ Black (frequency: 60Hz; image resolutions: 1280x720/1920x1080 pixels) were located underwater into a swimming pool, surveying a working volume of about 6m(3). A two-step custom calibration procedure, consisting in the acquisition of one static triad and one moving wand, carrying nine and one spherical passive markers, respectively, was implemented. After assessing camera parameters, a rigid bar, carrying two markers at known distance, was acquired in several positions within the working volume. The average error upon the reconstructed inter-marker distances was less than 2.5mm (1280x720) and 1.5mm (1920x1080). The results of this study demonstrate that the calibration of underwater ASC is feasible enabling quantitative kinematic measurements with accuracy comparable to traditional motion capture systems.118Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Sao Paulo Research Foundation) [00/1293-1, 2006/02403-1, 2009/09359-6]Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (National Counsel of Technological and Scientific Development) [473729/2008-3, 304975/2009-5, 478120/2011-7, 234088/2014-1, 481391/2013-4]Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (Brazilian Federal Agency for Support and Evaluation of Graduation Education) [2011/10-7, 08/2014]Fundacao de Amparo a Pesquisa de Minas Gerais (Minas Gerais Research Foundation) [PEE-00596-14]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

THE INFLUENCE OF TWO VARIABLES OF THE NONLINEAR CAMERA CALIBRATION ON THE 3D UNDERWATER ACCURACY

The purpose of this study was to control two variables of the nonlinear camera calibration to evaluate if they affect the 3D undewater accuracy. Two cameras (GoPro, 60 Hz) were fixed in the swimming pool. In order to evaluate the influence of a distance constrain (1 and 2 markers) and the movement of the wand calibration, we performed three different movements: M1 (zig zag), M2 (circular) and M3 (up and down). In each condition the 3D accuracy were assessed in seven trials of a dynamic rigid bar test (ANOVA,

3D RECONSTRUCTION ACCURACY OF TWO MOVING MOTION ANALYSIS SYSTEMS: PRELIMINARY RESULTS

The purpose of this study was to compare the 3D reconstruction accuracy, through a rigid bar test, provided by two moving systems, optoelectronic cameras (MOCAP) and action sport cameras (ASC). The cameras were fixed in the same rolling rigid structure (4.4 × 4.0 × 2.5 m) and the data were acquired simultaneously by the two motion analysis systems. Algorithms were previously developed to perform the roto-translation of the global coordinate system from reference points arranged on the floor, while the cameras and the structure were moving (40 m, antero-posterior direction). The mean inter-markers distance was 598.93 mm and 585.27 mm, and the standard deviation was 6.20 mm and 2.23 mm, by ASC and MOCAP. Despite the ASC had a performance almost 3 times worse than the MOCAP, the ASC is a more portable system and less expensive

In-air versus underwater comparison of 3D reconstruction accuracy using action sport cameras

Action sport cameras (ASC) have achieved a large consensus for recreational purposes due to ongoing cost decrease, image resolution and frame rate increase, along with plug-and-play usability. Consequently, they have been recently considered for sport gesture studies and quantitative athletic performance evaluation. In this paper, we evaluated the potential of two ASCs (GoPro Hero3+) for in-air (laboratory) and underwater (swimming pool) three-dimensional (3D) motion analysis as a function of different camera setups involving the acquisition frequency, image resolution and field of view. This is motivated by the fact that in swimming, movement cycles are characterized by underwater and in-air phases what imposes the technical challenge of having a split volume configuration: an underwater measurement volume observed by underwater cameras and an in-air measurement volume observed by in-air cameras. The reconstruction of whole swimming cycles requires thus merging of simultaneous measurements acquired in both volumes. Characterizing and optimizing the instrumental errors of such a configuration makes mandatory the assessment of the instrumental errors of both volumes. In order to calibrate the camera stereo pair, black spherical markers placed on two calibration tools, used both in-air and underwater, and a two-step nonlinear optimization were exploited. The 3D reconstruction accuracy of testing markers and the repeatability of the estimated camera parameters accounted for system performance. For both environments, statistical tests were focused on the comparison of the different camera configurations. Then, each camera configuration was compared across the two environments. In all assessed resolutions, and in both environments, the reconstruction error (true distance between the two testing markers) was less than 3mm and the error related to the working volume diagonal was in the range of 1:2000 (3×1.3×1.5m(3)) to 1:7000 (4.5×2.2×1.5m(3)) in agreement with the literature. Statistically, the 3D accuracy obtained in the in-air environment was poorer (p<10(-5)) than the one in the underwater environment, across all the tested camera configurations. Related to the repeatability of the camera parameters, we found a very low variability in both environments (1.7% and 2.9%, in-air and underwater). This result encourage the use of ASC technology to perform quantitative reconstruction both in-air and underwater environments

Action Sport Cameras as an Instrument to Perform a 3D Underwater Motion Analysis

Action sport cameras (ASC) are currently adopted mainly for entertainment purposes but their uninterrupted technical improvements, in correspondence of cost decreases, are going to disclose them for three-dimensional (3D) motion analysis in sport gesture study and athletic performance evaluation quantitatively. Extending this technology to sport analysis however still requires a methodologic step-forward to making ASC a metric system, encompassing ad-hoc camera setup, image processing, feature tracking, calibration and 3D reconstruction. Despite traditional laboratory analysis, such requirements become an issue when coping with both indoor and outdoor motion acquisitions of athletes. In swimming analysis for example, the camera setup and the calibration protocol are particularly demanding since land and underwater cameras are mandatory. In particular, the underwater camera calibration can be an issue affecting the reconstruction accuracy. In this paper, the aim is to evaluate the feasibility of ASC for 3D underwater analysis by focusing on camera setup and data acquisition protocols. Two GoPro Hero3+ Black (frequency: 60Hz; image resolutions: 1280×720/1920×1080 pixels) were located underwater into a swimming pool, surveying a working volume of about 6m3. A two-step custom calibration procedure, consisting in the acquisition of one static triad and one moving wand, carrying nine and one spherical passive markers, respectively, was implemented. After assessing camera parameters, a rigid bar, carrying two markers at known distance, was acquired in several positions within the working volume. The average error upon the reconstructed inter-marker distances was less than 2.5mm (1280×720) and 1.5mm (1920×1080). The results of this study demonstrate that the calibration of underwater ASC is feasible enabling quantitative kinematic measurements with accuracy comparable to traditional motion capture systems

Action sport cameras as an instrument to perform a 3D underwater motion analysis

Action sport cameras (ASC) are currently adopted mainly for entertainment purposes but their uninterrupted technical improvements, in correspondence of cost decreases, are going to disclose them for three-dimensional (3D) motion analysis in sport gesture study and athletic performance evaluation quantitatively. Extending this technology to sport analysis however still requires a methodologic step-forward to making ASC a metric system, encompassing ad-hoc camera setup, image processing, feature tracking, calibration and 3D reconstruction. Despite traditional laboratory analysis, such requirements become an issue when coping with both indoor and outdoor motion acquisitions of athletes. In swimming analysis for example, the camera setup and the calibration protocol are particularly demanding since land and underwater cameras are mandatory. In particular, the underwater camera calibration can be an issue affecting the reconstruction accuracy. In this paper, the aim is to evaluate the feasibility of ASC for 3D underwater analysis by focusing on camera setup and data acquisition protocols. Two GoPro Hero3+ Black (frequency: 60Hz; image resolutions: 1280×720/1920×1080 pixels) were located underwater into a swimming pool, surveying a working volume of about 6m3. A two-step custom calibration procedure, consisting in the acquisition of one static triad and one moving wand, carrying nine and one spherical passive markers, respectively, was implemented. After assessing camera parameters, a rigid bar, carrying two markers at known distance, was acquired in several positions within the working volume. The average error upon the reconstructed inter-marker distances was less than 2.5mm (1280×720) and 1.5mm (1920×1080). The results of this study demonstrate that the calibration of underwater ASC is feasible enabling quantitative kinematic measurements with accuracy comparable to traditional motion capture systems.118CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP473729/2008-3; 304975/2009-5; 478120/2011-7; 234088/2014-1; 481391/2013-400/1293-1; 2006/02403-1; 2009/09359-

The histograms of the residual error distribution (cumulated over the five trials) for HIGHRES (1920–1080) and LOWRES (1280–720).

<p>The average values were 1.28 and 2.41mm, respectively.</p

Minimum, mean and maximum inter-marker distance, averaged across 5 trials and the corresponding mean absolute error (<i>d</i>_<i>n</i>: 250mm).

<p>M1-1 (one marker with zig-zig movement); M2-1 (one marker with circular movement); M3-1 (one marker with up-down); M1-2 (two markers with zig-zig movement); M2-2 (two markers with circular movement). The post-hoc comparison results were reported (*<i>p</i><0.05).</p

Three different calibration wand movements to evaluate the calibration dependability.

<p>Three different calibration wand movements to evaluate the calibration dependability.</p

Schematic workflow of the two-stage camera calibration for a generic number of cameras.

<p>Schematic workflow of the two-stage camera calibration for a generic number of cameras.</p