A comparison of calibration methods for stereo fluoroscopic imaging systems

We have conducted a research in order to clarify a movement of a top table tennis player using DLT method. We have tried to obtain basic data such as time intervals of various playing, times of shots, playing area, distance of movement and so on to plan a training program of a movement for table tennis.The objects of analysis were 5 games of YOO Nam Kyu, who was the SEOUL Olympic champion, in the 9th ASIAN Table Tennis Championships in Japan. The games were filmed at 60 frames/second with 6 VTR cameras which were installed at separate locations in the gymnasium. For the purpose of this analysis, the various time intervals are defined as follows: In-play Time was from the initial movement of the service to final contact with the ball during play. It is acknowledged that this definition differs slightly from the official ITTF regurations for “ball in play” time. Rally Time was from contact with the ball on service to final contact with the ball during play. Service Time was from the initial movement of the service to contact with the ball on service. Waiting Time was from one player's contact with the ball to the other player's contact.Two-dimensional coordinates on a TV monitor were computed with a VTR motion analyzer connected to a personal computer. These coordinates were then converted to real (X-Y-Z) coordinates using DLT method. The position of the player was estimated from the coordinates of the player's head (vertex), center of shoulders (acromions), center of hips (trochanterions) and center of ankles (malleolus fibulae points). Distance of movement and velocity of movement were computed for every body point in several directions; right to left and forward to backward (in relation to the table), and up to down. Distance of movement was a line that links the position of the player every 0.1 sec during Rally-time. Velocity of movement was calculated by dividing distance of movement by Rally-time for each rally.The results and findings are summarized as follows;1) Mean total In-play time was 144.63±27.69 sec (±SD). This represented about 20-30% of the games of which average was 611.75±33.50 sec long, meaning that about 70-80% of the games was excess time spent doing such things as picking up the ball or wiping off perspiration.2) Mean Service Time, Mean Rally Time, Mean In-play Time and Mean Waiting Time was 1.05±0.37 sec, 2.56±1.79 sec, 3.60±1.83 sec and 0.66±0.19 sec, respectively. This represented about 30% of In-play Time was Service Time and about 70% of it was Rally Time.3) Mean times of shots during 1 rally was 4.61±2.12. The distribution of times of shots during 1 rally showed that in the case of 74.6% of all rally, a player won or lost a point in 5 shots.4) The playing area for YOO was positioned at the side of his free hand in 4 games. In 1 game, it was positioned at the side of his racket hand. His main stroke of the game was different from previous 4 games.5) In each game, the distance of movement for YOO on a horizontal plane during Rally Time was between about 100m and 200m at the center of the ankles. And mean distance of movement for YOO on a horizontal plane during 1 rally was between about 3.5m and 4.0m at the center of the ankles. In the table tennis games, the player's repeated acceleration and deceleration in various directions was instantaneous.6) In each game, mean average velocity of movement for YOO on a horizontal plane during 1 rally was between 0.85m/sec and 1.08m/sec at the head, 0.90m/sec and 1.05m/sec at the center of the shoulders, 0.99m/sec and 1.18m/sec at the center of the hips and 1.36m/sec and 1.51m/sec at the center of the ankles.7) It seems that these new data and findings are very important to plan an efficient training program for table tennis coaches and players.

Cinematography is an integral element in the interdisciplinary biomechanics research conducted in the Department of Kinesiology at the University of California, Los Angeles. For either an isolated recording of a movement phenomenon or as a recording component which is synchronized with additional transducers and recording equipment, high speed motion picture film has been effectively incorporated into resr'arch projects ranging from two and three dimensional analyses of human movements, locomotor mechanics of cursorial mammals and primates, to the structural responses and dynamic geometries of skeletal muscles, tendons, and ligaments. The basic equipment used in these studies includes three, 16 mm high speed, pin-registered cameras which have the capacity for electronic phase-locking. Crystal oscillators provide the generator pulses to synchronize the timing lights of the cameras and the analog-to-digital recording equipment. A rear-projection system with a sonic digitizer permits quantification of film coordinates which are stored on computer disks. The capacity for synchronizing the high speed films with additional recording equipment provides an effective means of obtaining not only position-time data from film, but also electromyographic, force platform, tendon force transducer, and strain gauge recordings from tissues or moving organisms. During the past few years, biomechanics research which comprised human studies has used both planar and three-dimensional cinematographic techniques. The studies included planar analyses which range from the gait characteristics of lower extremity child amputees to the running kinematics and kinetics of highly skilled sprinters and long-distance runners. The dynamics of race cycling and kinetics of gymnastic maneuvers were studied with cinematography and either a multi-dimensional force platform or a bicycle pedal with strain gauges to determine the time histories of the applied forces. The three-dimensional technique implemented at UCLA is the Direct Linear Transformation (DLT) method. DLT was developed from a close-range stereo-photogrammetry method to a technique flexible and accurate for 16 mm film applications in biomechanics. The DLT method has been used to document the three-dimensional kinematics of the ball, hand, forearm, and upper arm segments of pitchers during high velocity baseball throwing. The animal research which has incorporated cinematography has focused on both normal locomotor kinematics and kinetics, as well as spinalized locomotion, to assess neural control mechanisms which regulate gait. In addition, a new technique has been developed which allows the recording of in vivo tendon forces in an animal during unrestrained locomotion; via cinematography, movements of the limbs can be correlated with both myoelectric activity and tendon forces to analyze dynamics of muscle contractions during walking, running, and jumping. An additional area in which cinematography has proven useful is in the measurement of the architectural and structural deformations and strains which occur in skeletal muscles, tendons, and ligaments. These experiments have been done both in situ and in vitro, and have included both normal functional ranges of the tissues and incidences of mechanical failure or ruptures. The use of photographic techniques in these experiments is advantageous because the tissue changes can be documented without attaching mechanical apparatus to the tissue which can introduce artifacts. Although high speed cinematography does not solve all the data collection and recording needs in an integrated approach to biomechanics, it nevertheless forms an important constituent in a comprehensive research program. The positive attributes of high speed film records outweigh the laborious and tedious data reduction techniques which are frequently necessary to achieve high quality data.

The integration of computer vision algorithms and photogrammetric methods leads to procedures that increasingly automate the image-based 3D modeling process. The main objective of photogrammetry is to obtain a three-dimensional model using terrestrial or aerial images. Calibration of the camera and detection of the orientation parameters are important for obtaining accurate and reliable 3D models. For this purpose, many methods have been developed in the literature. However, since each method has different mathematical background, calibration results may be different. In this study, the effect of camera interior orientation parameters obtained from different methods on the accuracy of three-dimensional model will be examined. In this context, a test area consisting of 21 points was used. The test network was coordinated in a local coordinate system using geodetic methods. Some points of the test area were selected as the check point and accuracy analysis was performed. Direct Linear Transformation (DLT) method, MATLAB, Agisoft Lens, Photomodeler, 3D Flow Zephyr software were analysed. The lowest error value of 7.7 cm was achieved by modelling with Agisoft Lens.

High-speed dual fluoroscopy is a noninvasive imaging technology for three-dimensional skeletal kinematics analysis that finds numerous biomechanical applications. Accurate reconstruction of bone translations and rotations from dual-fluoroscopic data requires accurate calibration of the imaging geometry and the many imaging distortions that corrupt the data. Direct linear transformation methods are commonly applied for performing calibration using a two-step process that suffers from a number of potential shortcomings including that each X-ray source and corresponding camera must be calibrated separately. Consequently, the true imaging set-up and the constraints it presents are not incorporated during calibration. A method to overcome such drawbacks is the single-step self-calibrating bundle adjustment method. This procedure, based on the collinearity principle augmented with imaging distortion models and geometric constraints, has been developed and is reported herein. Its efficacy is shown with a carefully controlled experiment comprising 300 image pairs with 48 507 image points. Application of all geometric constraints and a 31 parameter distortion model resulted in up to 91% improvement in terms of precision (model fit) and up to 71% improvement in terms of 3-D point reconstruction accuracy (0.3-0.4 mm). The accuracy of distance reconstruction was improved from 0.3±2.0 mm to 0.2 ±1.1 mm and angle reconstruction accuracy was improved from -0.03±0.55(°) to 0.01±0.06(°). Such positioning accuracy will allow for the accurate quantification of in vivo arthrokinematics crucial for skeletal biomechanics investigations.

In image-based measurements, quantitative image data must be mapped to three-dimensional object space. Analytical photogrammetric methods, which may be used to accomplish this task, are discussed from the viewpoint of experimental fluid dynamicists. The Direct Linear Transformation (DLT) for camera calibration, used in pressure sensitive paint, is summarized. An optimization method for camera calibration is developed that can be used to determine the camera calibration parameters, including those describing lens distortion, from a single image. Combined with the DLT method, this method allows a rapid and comprehensive in-situ camera calibration and therefore is particularly useful for quantitative flow visualization and other measurements such as model attitude and deformation in production wind tunnels. The paper also includes a brief description of typical photogrammetric applications to temperature- and pressure-sensitive paint measurements and model deformation measurements in wind tunnels.

This paper presents a simple analogy to track red green and blue (RGB) color markers in real time through charged coupled device (CCD) calibrated by using direct linear transformation (DLT) method. A graphical user interface (GUI) application is designed in Matlab 2015a, to display real time actual measurements to ease detection of objects for grabbing through a robot gripper and place it at desired location.

This study is to analyze the kinematic variables of inward <TEX>$1{\frac{1}{2}}$</TEX> somersault in platform diver. For the manner, 3 people form the national diving team in the year 2000were chosen as the subjects and two S-VHS video cameras set in 60frames/sec were used for recording their motions. Coordinated raw positions data through digitizing are smoothing by butter-worth's low-pass filterin method at a cut off frequency 6.0Hz. and the direct linear transformation(DLT) method was employed to obtain 3-D position coordinates. The conclusions were as follows. However, horizontal distance which is the change of the COG, form the point of the jump to the point of Event 3 where the player is out of the board range completely, Subject B showed 105.1cm and 71.1cm of the vertical distance which are shorter horizontal distance and higher vertical distance, thus, took a great advantage of the position to prepare for the entry. Therefore, if a player takes higher position by speeding up the vertical velocity at the moment of the jumping off the board, and stays in the air longer, the player can have more time to show his skill. Because of the use of the characteristics of the inward somersault, keeping the safe distance form the board is important but in order to higher the completeness, it is ideal to keep the horizontal distance little over 100cm. Also, the angles of shoulder and elbow from Event 1 to 4, depending on swing of the arms, motions in the air, getting ready for the entry, showed some difference individual by individual, according to the velocity of the thigh and shank showed much difference while getting ready and take-off, and it's because of the individual's different bending and straightening for horizontal and vertical distance.

This study was designed to examine the kinematic factors in the phase during the marche fente motion. For this study, the subjects were 5 elite male fencing players. The direct linear transformation (DLT) method was used in calculating 3-D coordinate of the digitized body parts. The cubic spline function was used for smoothing and the kinematic data for displacement, velocity, angle variables were calculated for Kwon3d ver 2.1. And the following conclusions were drawn; 1. It show that the marche phase appeared to longer time than the pante phase In the performance time. For the fast attack, it showed that the subjects should be moving in a short stride width. 2. For a fast and stable movement posture in the marche phase, the vertical change of COG must be maintain the same position as possible, but all subjects appeared to decrease the COG because of a excessive the knee flection. 3. In the COG velocity change, all the subjects showed to the same change in both the marche and the fente phase. However in the attack extremity velocity, it increased velocity in order of upper arm, fore arm, and hand in the marche phase, but it showed different velocity among each subjects at the moment of stabbing. So that in order to do effective stabbing, they have to extend their upper extremity max and do faster the distal segment than the proximal segment. 4. It showed to take a fast and stable movement, because some subjects showed the big anteroposterior angle of the trunk flexed max shoulder angle and elbow angle of their attack arm and the other upper extremity.

Three dimensional (3-D) high-speed photography was used to record the tennis service actions of eight elite tennis players. The direct linear transformation (DLT) method was used for 3-D space reconstruction from 2-D images recorded from laterally placed cameras operating at 200fps. Seven of the eight subjects initially positioned their center of gravity toward the front foot during the stance phase. When the elbow reached 90° in the backswing, the knees of the eight subjects were at or near their maximum attained flexion, and the upper arm was an extension of a line joining both shoulder joints. A mean maximum vertical shoulder velocity of 1.7ms−1 during the leg drive produced a force at the shoulder that was eccentric to the racket-limb, thus causing a downward rotation of this limb as measured by a mean velocity of the racket of −5.8ms−1 down the back. This leg drive increased the angular displacement of the loop and therefore provided a greater distance over which the racket could be accelerated for impact. All subjects swung the racket up to the ball, and all but one hit the ball with the racket angled slightly backward (M = 93.9°). An effective summation of body segments was apparent because resultant linear velocities showed an increase as the more distal segment endpoint approached impact, although all subjects decelerated the racket immediately prior to impact. Mean resultant ball velocities of 34.4ms−1 for the female subjects and 42.4ms−1 for the male subjects were achieved.

This report describes the measuring system applying the direct linear transformation (DLT) method as one of the principal methods for three dimensional image analysis to measure the location of the contact line with running. Two cameras are provided on the roof of the train taking pictures continuously by which the distance between the train and the cable can be obtained after compared both picture. Pictures are superposed by the location data to identify the measuring point for easy reference.

While rugby is a collision sport, many anterior cruciate ligament (ACL) injuries of the knee involve noncontact changes of direction. This study investigates the risk factors of ACL injury in rugby players by establishing the relationship between noncontact directional change by the players and the consequent alteration of the player’s center of gravity (CG) and knee joint motion. Methods: Photographs were taken when players at a university rugby football club changed their direction of movement by 45° or 90° (n = 10). The player’s motions were assessed to determine 3- and 2-dimensional coordinate values of markers on the players by using the direct linear transformation method. The values were used to calculate knee joint flexion 40 ms after foot grounding, the CG position (height and rearward position), and the abduction angle of the knee joint. A paired t test was used for statistical analysis; a probability level of less than 5 % was considered significant. Results and Discussion: No significant differences were observed in the knee flexion angle between a 45° and a 90° change in direction. However, the CG position (height and rearward position) and the abduction angle of the knee joint increased as the magnitude of the change in direction increased (p < 0.01). Because increases in the rearward CG and abduction angle of the knee joint are considered risk factors for ACL injury, the risk of ACL injury is predicted to go up as the magnitude of the change in direction increases.

Automated Calibration of Robot Coordinates for Reconfigurable Assembly Systems

The aim of the study was to describe and compare kinematics in two types of execution of attack hit, the goofy approach and regular approach. The research group consisted of players from the Czech Republic’s top league (n = 12, age 28.0 ± 4.3 years, body height 196.6 ± 5.6 cm, body mass 89.7 ± 6.7 kg) divided into two groups according to the individual type of approach in the attack. Analysis of movement was performed by 3D kinematics video analysis, space coordinates were calculated by the DLT (Direct Linear Transformation) method together with interpretation software TEMA Bio 2.3 (Image Systems AB, Sweden). The players started their run-up from a distance of about 4 – 4.5 m from the net with similar maximal vertical velocity (2.91 – 2.96 m⋅s-1). The trajectory of players with goofy approach seemed to be convenient for the rotation of shoulders and hips in the moment of ball contact. Differences between both groups were observed. Players with a goofy approach had a longer flight phase compared to regularly approaching players.

In this paper, we describe a method for automatically tracking the location of a player on the pitch from the video image of a football game. In this method, the player location on the video image is determined by employing binary image transformation based on the color features of the player’s uniform and a centroid computation of the binary image. The image area for the position tracking and the color threshold value in the binarization are automatically adapted in the tracking process to accommodate the motion of the player as well as the lighting condition, which is dependent on the pitch location. The field coordinates of the player location are determined from the video coordinates by using the two dimensional DLT (Direct Linear Transformation) method. The automatic tracking method was evaluated for video data which were collected for a football game. The results indicated that the correctly detected rate of the tracking method was 99.93 %.

The purpose of this study was to attempt new starting motion and supply present starting motion in the 500M short track speed skating according to the center of gravity position. The center of gravity position ratio was divided starting motion into five(type A : front 80%-back 20%, type B front 70%-back 30%, type C : front 50%-back 50%, type D : front 30%-back 70%, type E : front 20%-back 80%). The three dimension motion analysis with DLT(direct linear transformation) method was executed using two video cameras. The following conclusion was that It was appear that reaction and execution time in starting motion was the most short in type B. It was characteristic that step of skaters was shorten and center of gravity position ratio was not effect to change of the step in each event. It was appear that the displacement of type D and type E were longer than that type A and type B during the starting motion. It was appear that skill types of center of gravity position ratio to the front were lower than that to the back and contract a posture. Observing the above, it was conclusion that skill type B of center of gravity position ratio to the tent was more effect than that to the back. But it is important that these skill type was most used to the competition and estimate the result.