UNDERWATER NON-LINEAR CAMERA CALIBRATION: AN ACCURACY ANALYSIS

One of the most challenging problems associated with underwater 3D movement analysis is the accurate calibration of the cameras. Additional sources of errors are present in underwater acquisitions such as the nonlinear distortion caused by water interface, camera lenses (ex. wide angle) and housing’s glasses. Despite this, in the literature, systems based on a linear calibration model (DLT) were proposed (Yanai et al., 1996; Machtsiras & Sanders, 2009; Gourgoulis, et al. 2008). However, the results of underwater accuracy were not similar to those obtained out of the water. In Kwon, et al. 1999, the use of a modified DLT algorithm to model the distortion was proposed but the results of accuracy were not substantially improved, with Root Mean Square (RMS) values ranging from 5.6 to 7.2mm. Recently, alternative approaches were proposed to non-linear camera calibration and submillimeter accuracy was reached (Cerveri et al., 1998; Zhang, 2000; Pribanić, Sturm & Cifrek, 2008). However, these approaches were not applied underwater. In previous work, a new non-linear calibration method using a straight line plane object was proposed and tested out of the water (Silvatti et al., 2009 available in http://calib.googlecode.com). In this work, this novel method was tested in underwater conditions and its accuracy evaluated

ACCURACY OF SPORT ACTION CAMERAS FOR 3D UNDERWATER MOTION ANALYSIS

The purpose of this study was to evaluate the accuracy of sport action cameras for 3D underwater motion analysis. Two cameras (GoPro) were fixed in the swimming pool. The image resolution was set to 1920 x 1080, the view angle was set to 127o and the frame rate was 60 Hz. A Wi-Fi remote was used to start the cameras. A wand calibration method based on radial distortion model was used to calibrate the cameras. The accuracy was evaluated in eight trials of dynamic rigid bar tests (working volume 4?1?1.5m3). The results revealed mean absolute error ranging from 1.23 mm to 1.93 mm. These values of accuracy for underwater analysis can be considered acceptable for the majority of 3D underwater motion analyses, in particular for swimming biomechanics

Angle of attack of center of mass during the running of an entire 100m dash

The angle of attack is related to the body posture and changes during sprinting because of changes in the horizontal velocity. The aim of this study was to analyze the angle of attack of the center of mass and the horizontal velocity during a 100 m dash. Twelve video cameras were positioned along a running track to obtain the position of the center of mass. The horizontal velocity was derived from the position data. When the different sides were compared, the angles were lower on the right side than on the left side (P < 0.05), which tended to decrease with increasing horizontal velocity. The results show the variability of the angle of attack as associated to the horizontal velocity, and the differences considering laterality

KINETIC AND KINEMATIC FEATURES OF COUNTERMOVEMENT AND SAUTÉ JUMPS IN CLASSICAL BALLET DANCERS

The purpose of this study was to investigate how the external rotations of lower limbs influence the performance of ballet dancers in jumps. Four ballet dancers with high technical proficiency were recruited for a test, they performed three attempts the countermovement and sauté jump. Two force plates were used to determine ground reaction forces. Six cameras were used to collect the kinematic data. It was analyzed the peak of knee flexion, peak of ground force reaction and jump height. The performance in countermovement and sauté jump tests was compared through box plot analysis. In conclusion, even with a lower degree of knee flexion, dancers can produce higher jumps and more ground force reaction on countermovement jump. The results suggest that the attention focus when jumping is an important determinant of jump performance

3D KINEMATICAL ANALYSIS OF THE HAMMER THROW IN COMPETITIONS

This study analyzes 14 throws accomplished in Brazilian competitions and it compares with available international results in the literature. It calculates the angle, the velocity and the height of release of the hammer and the velocity curves in function of the time, starting from the 3D trajectory of the head of the hammer. The analyses relate the difference between Brazilian (averages of 55.38m male and 52.05m female) and international results (averages of 79.44m male and 70.60m female) and the release velocity (Brazilian averages of 24.59m/s male and 23.59m/s female, and international of 29.60m/s male and 28.89m/s female). The velocity curves in function of the time of the international releases show that the accelerations are higher and the deceleration lower during the turns, when compared with a Brazilian throw

CAMERA CALIBRATION FOR UNDERWATER APPLICATIONS: EFFECTS OF OBJECT POSITION ON THE 3D ACCURACY

The purpose of this study was to investigate the effects of object position in the working volume on the accuracy of 3D reconstruction, using four different camera calibration approaches: 1) the classical DLT, 2) the nonlinear DLT, 3) the 2D plate and 4) the wand calibration. The DVideo kinematic analysis system was used for underwater data acquisition. The system consisted of two gen-locked Basler cameras (100 Hz) enclosed in housings. A dynamic rigid bar test (acquisition volume - 4.5?1?1.5 m3) was used to obtain the accuracy of the 3D reconstruction. Larger errors were found using the classical and nonlinear DLT methods. Furthermore, these approaches were affected by the rigid body position in the working volume. In conclusion, 2D plate and wand calibration methods provided more accurate results and were not affected by object position in the volume

SEPARATE TRUNK VOLUMES AND RIBS MOTION CORRELATIONS IN SWIMMERS

The purpose of this study was that to analyze the separate trunk volumes and ribs motion correlations aiming to verify swimmers present better motor coordination or control during breathing. The trunk was represented by 53 markers, attached to the ribs, vertebrae, thorax and abdomen of 13 male swimmers and 10 non-athletes. From the 3D coordinates of the markers, obtained by a kinematical analysis system equipped with 6 digital video cameras (60Hz), in function of time, the rotation angles of the 2nd to the 10th ribs around the quasi-transversal axis and the volumes of 4 separate compartments of the trunk were calculated (superior thorax, inferior thorax, superior abdomen and inferior abdomen). Correlating the curves of ribs rotation angles with the curves of the separate volumes, swimmers presented higher values during vital capacity manoeuvers when the correlation involved the inferior thorax and the superior and inferior abdomen. These results showed a better coordination between the trunk volumes and the ribs motion in the swimmers during vital capacity manoeuvers, suggesting that swimming practice leads to the formation of an optimized breathing pattern when larger efforts are required from the respiratory system

SEPARATE TRUNK VOLUMES AND RIBS MOTION CORRELATIONS IN SWIMMERS

The purpose of this study was that to analyze the separate trunk volumes and ribs motion correlations aiming to verify swimmers present better motor coordination or control during breathing. The trunk was represented by 53 markers, attached to the ribs, vertebrae, thorax and abdomen of 13 male swimmers and 10 non-athletes. From the 3D coordinates of the markers, obtained by a kinematical analysis system equipped with 6 digital video cameras (60Hz), in function of time, the rotation angles of the 2nd to the 10th ribs around the quasi-transversal axis and the volumes of 4 separate compartments of the trunk were calculated (superior thorax, inferior thorax, superior abdomen and inferior abdomen). Correlating the curves of ribs rotation angles with the curves of the separate volumes, swimmers presented higher values during vital capacity manoeuvers when the correlation involved the inferior thorax and the superior and inferior abdomen. These results showed a better coordination between the trunk volumes and the ribs motion in the swimmers during vital capacity manoeuvers, suggesting that swimming practice leads to the formation of an optimized breathing pattern when larger efforts are required from the respiratory system

INFLUENCE OF YEARS OF SWIM TRAINING ON SEPARATE THORACOABDOMINAL VOLUMES DURING BREATHING

The purpose of this study was to verify the influence of the years of swim training on the separate thoracoabdominal volume variation during breathing using a kinematic analysis. Fifteen male swimmers were analyzed during tidal volume and vital capacity maneuvers. From the 3D coordinates of 30 markers fixed at the trunk the volumes of 4 separate compartments of the trunk (superior thorax, inferior thorax, superior abdomen and inferior abdomen) were calculated in function of time. During tidal volume, the coefficient of variation of the volumes of the superior and inferior abdomen increased with the years of swim training (

A 3D KINEMATICAL ANALYSIS OF LONG JUMP IN THE “GOLD MEETING RIO OF ATHLETICS 2007”

This study was based on the 3D kinematical analysis of long jump in an official competition of the International Association of Athletics Federation. A six camera kinematical analysis system was used to reconstruct the 3D coordinates of eighteen points, modeling the athlete’s body with the follow segments: head, trunk, arms, forearms, thighs, calves and feet. Several performance variables concerning the center of mass trajectories and velocities were used to characterize and compare the individual jumps. Descriptive statistics was used to compare the results obtained with those found in the literature