Newman Lau

MotionMaster: authoring and choreographing Kung-fu motions by sketch drawings

Sketch-drawings is an intuitive and comprehensive means of conveying movement ideas in character animation. We proposed a novel sketch-based approach to assisting the authoring and choreographing of Kungfu motions at the early stage of animation creation. Given two human figure sketches corresponding to the initial and closing posture of a Kungfu form, and the trajectory drawings on specific moving joints, MotionMaster can directly rapid-prototype the realistic 3D motion sequence by sketch-based motion retrieval and refinement based on a motion database. The animators can then preview and evaluate the recovered motion sequence from any viewing angles. After the 3D motion sequence has been associated with the 2D sketch drawing, the animator can also interactively and iteratively make changes on the 2D sketch drawing, and the system will automatically transfer the 2D changes to the 3D motion data of current interests. It greatly helps the animator focus on the movement idea development during the evolutionary process of building motion data for articulated characters.

Effects of body mass index and full body kinematics on tennis serve speed

Abstract Effective training to improve serve speed is important for competitive tennis players. The purposes of this study were to investigate the effects of anthropometric factors and whole body kinematics of elite players on ball speed and to propose possible training strategies for improving the quality of tennis serves. Body and racket kinematics of tennis serves of 12 male elite Hong Kong players were investigated. The tennis serve was divided into four phases: I) Back-Swing Phase, II) Lead-Leg-Drive Phase, III) Forward-Swing Phase, and IV) Follow-Through Phase. It was shown that racket-side knee range of motion during phases II and III (r=0.705; p<0.05), racket-side knee peak extension velocity during phase II (r=0.751; p<0.01), racket-side hip peak extension velocity during phase II (r=0.657; p<0.05), racket-side shoulder range of motion in the coronal plane during phase III (r=0.616; p<0.05), racket-side elbow peak extension velocity during phase III (r=0.708; p<0.01) and body mass index (r=0.577; p<0.05) were significantly correlated with ball speed. Body mass index and the identified kinematic parameters that were significantly correlated with ball speed could be used as training guidelines for coaches and players to improve serve speed. Players should pay particular attention in training to increasing the extension velocity and range of motion of the identified joints.

Mocap data editing via movement notations

In most motion editing approaches, the users often make changes on mocap data by specifying numerical parameters. However, it is not intuitive for a novice to edit motion sequences in motion planning tasks. In this paper, we present a method of notation-based motion editing, in which Labanotation, a well-developed notation language for human movements, is employed as the editing interface. It allows the user to specify the editing requirements via notation score, and the system will semi-automatically generate the desired motion data. The algorithmic steps of its pipeline and the core issues of converting Labanotation into motion sequences are discussed in detail. We show the results of our systems using martial arts motion as its testing data.

Motion segmentation method for hybrid characteristic on human motion

Motion segmentation and analysis are used to improve the process of classification of motion and information gathered on repetitive or periodic characteristic. The classification result is useful for ergonomic and postural safety analysis, since repetitive motion is known to be related to certain musculoskeletal disorders. Past studies mainly focused on motion segmentation on particular motion characteristic with certain prior knowledge on static or periodic property of motion, which narrowed methods applicability. This paper attempts to introduce a method to tackle human joint motion without having prior knowledge. The motion is segmented by a two-pass algorithm. Recursive least square (RLS) is firstly used to estimate possible segments on the input human-motion set. Further, period identification and extra segmentation process are applied to produce meaningful segments. Each of the result segments is modeled by a damped harmonic model, with frequency, amplitude and duration produced as parameters for ergonomic evaluation and other human factor studies such as task safety evaluation and sport analysis. Experiments show that the method can handle periodic, random and mixed characteristics on human motion, which can also be extended to the usage in repetitive motion in workflow and irregular periodic motion like sport movement.

Identifying Multifractality Structure on Postural Sway

From previous biomechanical researches, postural sway has been generally evaluated by descriptive statistics for the purpose of scientific and clinical purposes in analysing the variety of external perturbations and the corresponding responses by the human body. Although these approaches on analysing the responses enable the examinations on the characteristics and relationships between the input and output of different feedback systems, the stabilizing mechanism or the steady-state behaviour from the possible control schemes of the human body is not explicitly considered. In this research study, the multifractality structure on postural sway is identified by the numerical method on multifractal detrended fluctuation analysis. An experimental set of 11 healthy subjects were investigated by optical motion capture system from the retroreflective optical marker data attached on skin surface along the spinal curvature. It is observed that random walk characteristics, hence, correlations between present and history of data, are present in the time series. Multifractal detrended fluctuation analysis is further applied to get into the details about the correlation of data along the time series. The study reveals the degree of multifractality extracted from the data, and compares to shuffled data to ascertain the multifractality in spinal curvature movement is predominantly due to long-range correlations instead of probability distributions. The application of this computational technique attempts to describe the multiple strategies utilized by the motor control in response to static, yet swaying, human body posture.

Dynamic characteristic analysis of spinal motor control between 11- and 15-year-old children

Spinal motor control can provide substantial insight for the causes of spinal musculoskeletal disorders. Its dynamic characteristics however, have not been fully investigated. The objective of this study is to explore the dynamic characteristics of spinal motor control via the fractional Brownian motion mathematical technique. Spinal curvatures and repositioning errors of different spinal regions in 64 children age 11- or 15-years old during upright stance were measured and compared for the effects of age and gender. With the application of the fractional Brownian motion analytical technique to the changes of spinal curvatures, distinct persistent movement behaviors could be determined, which could be interpreted physiologically as open-loop behaviors. Moreover, it was found that the spinal motor control of 15-year-old children was better than that of 11-year-old children with smaller repositioning error and less curvature variability as well as shorter response time and smaller curvature deformation.

Revealing control mechanism from multifractal analysis on physiological signals

Multifractal theory has been widely used in various fields of research study. In this paper, methods were proposed to extract the multifractal descriptors of physiological signals from kinematic measurement of cervical spine region during postural sway when static sitting at upright position. The analysis is based on the multifractal detrended fluctuation analysis. The proposed multifractal parameters can be well described by variation space among the experimental subject group through acquisition of trials. Various analytical aspects of experiments have been conducted to verify the robustness and confidence of the proposed motor control mechanism. The exhibition of multifractality structure is hypothesized in describing various discharge of neural activity on motor control in order to balance the static posture through body sway. Variation on the long-range correlated structure can be found among subject groups. This is suggested as the reflection on coordinated behavior in the presence of external variation or pathological conditions. Both impersistent and persistent structures are observed in the multifractal spectrums from experiment. This reveals the relationship to the local and global neural interconnectivity, in which time scales can reflect local and progressively longer neighborhoods of neural interaction, within and outside the given spinal region. Results demonstrate that control mechanism can be revealed and knowledge discovered by means of the multifractal analysis and the extracted descriptors.

Fractal Analysis Design for Distinguishing Subject Characteristics on Motor Control of Neck Pain Patients

Literature reflects that there is considerable amount of research has been conducted concerning motor control and postural control of human body. Research findings also reveal the importance of stability and variability of movement in relation to spine, in particular. However, the evaluation method on stability and variability of spinal movement is limited on the linear methods in revealing the significance of movement. The knowledge on the nonlinearity and the dynamic features of spinal movement is still inadequate in describing the motor control and musculoskeletal characteristics.

Kinematic Study of Serve Velocity of Hong Kong Elite Tennis Players

Effective training for improving serve velocity is important for elite tennis players. The objective of this study is to investigate the relationship between whole body kinematics and ball velocity of tennis serve of Hong Kong Elite Tennis players. Twelve Hong Kong Tennis Team male players were recruited. Body kinematics of the players during tennis serves were monitored by a motion analysis system (Vicon MX, Oxford Metric, Oxford, UK) and correlated with the ball velocity. Compared to the Olympic 2000 tennis players, the front knee peak extension velocity, pelvic peak axial rotation velocity, trunk peak right rotation velocity, shoulder peak internal rotation velocity, elbow peak extension velocity and wrist peak flexion velocity of the Olympic players were 5, 2.1, 4.1, 2.9, 2.8 and 2.9 times, respectively, faster than those of the Hong Kong Elite Players. The mean serve velocity of Olympic players (182.9+/-14.0 km/h) was significantly faster than that of the Hong Kong Elite players (145.4+/-19.9 km/h; range: 119-180). The velocity of tennis serve of Hong Kong Elite players was within the range of the lower-level tournament western play-ers. The slower ball velocity of Hong Kong Elite players might be due to the differences in kinematic profile during serve. It was also found that the right shoulder peak internal rotation velocity, right rear knee range of motion, right rear hip peak extension velocity, right shoulder rotation range of motion and body weight were significantly correlated with the ball veloc-ity. Stepwise linear regression analysis showed that the right shoulder peak internal rotation velocity and body weight were significant predictors for ball velocity which contributed 3.8%, 85% respectively to the total variability (r2 = 0.878, p<0.05). The body kinematics and body weight were shown to have significant effects on ball velocity of tennis serve.

3 Motion Synthesis with Adaptation and Path Fitting

In this paper, we present an algorithm for motion synthesis. This algorithm is developed as a part of a large crowd simulation project which simulates the motion of the people by using a large database of motion captured data. Most of the crowd simulations divide the simulation process into two phases, the first phase is path generation, and the second phase is matching the motion clip to the generated path. The second phase is the goal of this paper. There are two problems we need to solve for the second phase. The first problem is that the generated motion should be attached to the path, and the speed of the generated motion must be matched with the path. The second problem is that the crowd simulation simulates different size of people, that is, the skeleton is scaled.