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1

Real-time camera pose estimation based on volleyball court view

Szelag K., Kurowski P., Bolewicki P., Sitnik R.

Opto-Electronics Review

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2019

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Vol. 27, No. 2

202--212

EN

The use of technology in sports has increased in recent years. One of the most influential of these technologies is referee support systems. Team sports such as volleyball require accurate and robust tracking systems that do not affect either the players or the court. This paper introduces the application of intrinsic and extrinsic camera calibration in a 12-camera volleyball referee system. Intrinsic parameters are calculated by using the classic pinhole model and Zhang’s method. To perform extrinsic calibration in real time, the volleyball court is treated as a global calibration artifact. Calibration keypoints are defined as court-line intersections. In addition, a new keypoint detection algorithm is proposed. It enables achievement of an accurate camera pose in regard to the court. With all 12 cameras calibrated in a common coordinate system, a dynamic camera stereo pair creation is possible. Therefore, with known ball 2D image coordinates, the 3D real ball coordinates can be reconstructed and the ball trajectory can be estimated. The performance of the proposed method is tested on a synthetic data set, including 3Ds Max rendering and real data scenarios. The mean camera pose error calculated for data biased with keypoint detection errors is approximately equal to 0.013% of the measurement volume. For the real data experiment with a human hand phantom, it is possible to determine the presence of the human phantom on the basis of the ball reflection attitude.

2

Power–velocity relationship and muscular strength in female volleyball players during preparatory period and competition season

Buśko Krzysztof

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 2

31--36

EN

The aim of the study was to investigate changes of power–velocity relationship and muscular strength of female volleyball players during preparatory period and competition season. Methods: The study was conducted on eleven female volleyball players: age 21.6 ± 1.7 years, body height 177.9 ± 4.7 cm, body mass 71.3 ± 6.6 kg. Power–velocity relationship was determined by means of five maximal 10-second cycloergometer efforts with external loads equal to: 2.5, 5, 7.5, 10 and 12.5% of body weight (BW). The joint torque of flexors and extensors of an elbow, shoulder, hip, knee and trunk was measured using a torque meter. The measurement were taken before (I) and after (II) the preparatory period, after the first (III) and second (IV) competitive season. Results: The power with a load equal to 2.5, 5.0, 7.5, 10.0% BW increased significantly after first and second competitive season. The sums of joint torque for the lower and upper limb changed insignificantly. In the case of the right upper limb, sum of the joint torques was significantly reduced by 9.5% between measurement I and IV. Sum of the left upper limb was significantly decreased by 9.8% between measurement I and II. Sum of the joint torque of the trunk was significantly increased between measurements I and II, III and IV by 12.9%, 12.3% and 11.2%, respectively. Conclusion: Obtained results may suggest that selection of the training loads was adequate for training power output and muscle strength of lower limbs but too little emphasis was placed on development of strength in the muscles of the upper limbs.

3

Accurate ball tracking in volleyball actions to support referees

Kurowski P., Szelag K., Zaluski W., Sitnik R.

Opto-Electronics Review

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2018

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Vol. 26, No. 4

296--306

EN

This paper proposes a method for offline accurate ball tracking for short volleyball actions in sport halls. Our aim is to detect block touches on the ball and to determinate accurate trajectory and impact positions of the ball to support referees. The proposed method is divided into two stages, namely training and ball tracking, and is based on background subtraction. Application of the Gaussian mixture model has been used to estimate a background, and a high-speed camera with a capture rate of 180 frames per second and a resolution of 1920 × 1080 are used for motion capture. In sport halls significant differences in light intensity occur between each sequence frame. To minimize the influence of these light changes, an additional model is created and template matching is used for accurate determination of ball positions when the ball contour in the foreground image is distorted. We show that this algorithm is more accurate than other methods used in similar systems. Our light intensity change model eliminates almost all pixels added to images of moving objects owing to sudden changes in intensity. The average accuracy achieved in the validation process is of 0.57 pixel. Our algorithm accurately determined 99.8% of all ball positions from 2000 test frames, with 25.4 ms being the average time for a single frame analysis. The algorithm presented in this paper is the first stage of referee support using a system of many cameras and 3D trajectories.

4

Izokinetyczna ocena ekscentrycznej siły mięśni grupy tylnej i przedniej uda siatkarzy

Kabaciński J., Murawa M., Żyła T., Gorwa J., Dworak L. B.

Aktualne Problemy Biomechaniki

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2017

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z. 12

35--40

PL

W pracy określono wartości wybranych wskaźników ekscentrycznej siły mięśni uda siatkarzy w warunkach izokinetycznych. Ocenie poddano stosunek momentu siły hamstrings do quadriceps (H/Q) oraz bilateralny deficyt maksymalnego momentu siły mięśni (BD) dla prędkości kątowych 30°/s, 60°/s i 90°/s. Wartości maksymalnego H/Q zawierały się od 69.0% (90°/s) do 81.3% (30°/s), natomiast średniego H/Q od 68.6% (90°/s) do 78.7% (30°/s). Ponadto, stwierdzono nieistotny BD (poniżej 7%) dla obu zespołów mięśniowych.

EN

In the study the values of selected indicators of thigh eccentric isokinetic strength in volleyball athletes at angular velocities 30°/s, 60°/s and 90°/s was determined. The evaluation included the hamstrings to quadriceps torque ratio (H/Q) and peak torque bilateral deficit (BD). The peak H/Q values ranged from 69.0% (90°/s) to 81.3% (30°/s), whereas average H/Q values ranged from 68.6% (90°/s) to 78.7% (30°/s). Moreover, no significant BD values (less than 7%) were found for both muscle groups.

5

Dynamic load indicators for take-off–landing sequence in blocks and attacks of elite female volleyball players

Kabaciński J., Dworak L. B., Murawa M., Rzepnicka A.

Acta of Bioengineering and Biomechanics

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2016

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Vol. 18, no. 1

41--46

EN

Purpose: Dynamic loads during landings determined by the ground reaction forces (GRFs) may elaborate internal loads and increase the risk of overload knee injuries as a result of performing volleyball jumps many times. The study dealt with a biomechanical assessment of dynamic load indicators in female volleyball players for the motion sequence of take-off–landing in blocks and attacks. Methods: Twelve professional female volleyball players participated in the study. Blocks and attacks were filmed by two cameras. GRFs vs. time graphs were recorded with the use of a force platform. Values of dynamic load indicators in terms of the relations of peak of vertical component of GRF, build-up index of this force (BIF), and power output (P) during landing to the vGRF, BIF and P during take-off (L/T) were calculated. Results: The statistically significant ( p < 0.05) highest values of L/T indicators were found for back row attack spikes: 2.4 (vGRF), 12.2 (BIF) and 3.1 (P). In the case of blocks, slide attack spikes and attack line spikes, results of these variables were in range: 1.8÷2.1, 5.9÷7.6 and 2.1÷2.9, respectively. Conclusions: The reduction of GRFs during landings contributes to decreasing the level of the load indicators L/T which should minimize the incidence of anterior cruciate ligament and patellar tendon injuries in female volleyball players.

6

Biomechaniczna ocena zdolności siłowych siatkarek

Michnik R., Jurkojć J., Czapla K.

Modelowanie Inżynierskie

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2012

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T. 13, nr 44

217-222

PL

W ramach pracy przedstawiono metodykę badań umożliwiającą wyznaczenie izokinetycznych charakterystyk zespołów mięśniowych stawu kolanowego, pozwalających na ocenę stopnia wytrenowania sportowców oraz weryfikację metod treningowych. W ramach badań dokonano pomiarów momentów sił mięśniowych w warunkach pracy izokinetycznej na stanowisku pomiarowym Biodex System Pro 4. Badania przeprowadzono na grupie zawodniczek drużyny AZS Politechnika Śląska.

EN

A research methodology enabling determination of isokinetic characteristics of knee flexors and extensors muscles is presented in the paper. The methodology can be used in estimation of volleyball players fitness and evaluation of training methods. Within the frame of conducted research measurements of muscle forces torques of knee flexors and extensors were carried out. All measurements were performed by means of the Biodex System Pro 4.The group of professional volleyball players from the AZS Silesian University of Technology team was examined.

7

Changes of the maximal muscle torque of male volleyball players during training

Buśko K., Staniak Z.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2006

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z. 26

47-50

EN

The aim of the study was to follow the changes of the maximal muscle torque of male volleyball players during training performed in the preparatory and starting period. Muscle torque measurements in static conditions were performed in preparatory (I, III) and starting (II, IV) periods for two years. The sum of muscle torque of the trunk and sum of muscle torque of lower extremities were decreases between I and II period, and increases between III and IV period. The sum of muscle torque of upper extremities were significantly increases between III and IV period. The significant differences between II and IV period were observed for upper extremities.

8

Analysis of kinematics in volleyball attack

Rak Z., Czapla K.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2006

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z. 31

135-140

EN

In the article there is description of correctly performed attack in volleyball. In the kinematical analysis a video of attack by 2nd league team member was recorded, the player's movement was mapped and kinematical parameters of this motion stated. Exemplary trajectories of movements of separate player's joints, their speed and acceleration are included.

9

Analiza ataku siatkarskiego w ujęciu przestrzennym

Makowski M., Rak Z.

Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska

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2006

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z. 30

169-174

PL

W artykule przedstawiono analizę kinematyczną ataku siatkarskiego. W celu wyznaczenia parametrów kinematycznych ruchu stawów siatkarza, przeprowadzono wideorejestrację przestrzenną z użyciem dwóch kamer. Uzyskane obrazy wideo poddano analizie w programie APAS. System ten, dzięki modułom o zróżnicowanym przeznaczeniu, pozwolił na odczyt położenia markerów, umieszczonych na ciele siatkarza, podczas trwania całego ruchu. Zamieszczono przykładowe przebiegi analizowanych parametrów.

EN

The article presents a kinematical analysis of a volleyball attack. Empirical research has been conducted using spatial video recording with the help of two videocameras. Obtained video images were analyzed in APAS program. That system, thanks to its multifunctional modules, served the purpose of recording the location of markers placed on the body of the examined person during the entire movement time. The results - exemplary proceedings of the analyzed parameters - are given.