Maria Skublewska-Paszkowska

MOTION CAPTURE AS A MODERN TECHNOLOGY FOR ANALYSING ERGOMETER ROWING

The paper presents a purpose-built laboratory stand consisting of a Vicon motion capture system with reference video cameras, wireless EMG system, Concept 2 Indoor Rower ergometer, wireless heart rate monitor and the Nexus software. A pilot study of people who exercise on the ergometer helped to create a proper configuration of all the components of the laboratory. Moreover, a procedure for carrying out research was developed, which consists of several steps divided into 4 stages: preparation of the motion acquisition system; preparation of the participant; familiarising participants with the technique of rowing, recording their movements and acquiring other measurement signals. Preliminary analysis of the results obtained from heterogeneous signals from various devices showed that all the components of the research stand are mutually compatible and the received signals do not interfere with one another.

Comparison of Hierarchical Cluster Analysis Methods Applied to Image Segmentation by Watershed Merging

Watershed transformation is an image segmentation method. Its main advantage is that it extracts almost all edges present in the image. The edges are always continuous, which is the method’s main advantage. Unfortunately it detects all edges - even if they are very weak. This causes more classes being segmented than there are objects present in the image. This phenomenon is called oversegmentation.

Analysis of rowing based on handle trajectory

The paper presents an analysis of a rowing technique and the participants fatigue based on the handles trajectory. The rowing was recorded with the use of Vicon motion capture. Seven non-rowers were participants in the research. 42 strokes were analysed in three phases of rowing. Two theses: (i) “handle trajectory indicates the fatigue while rowing” and (ii) “the rowing technique may be assessed by analysing the handle trajectory” were proven. The presented research concerns the following aspects: (i) handle trajectory analysis in a designated range (specified by two markers positions attached to the ergometer), (ii) duration analysis of the incorrect rowing technique (in time domain), (iii) tilt analysis based on the angle of the handles position relative to the floor (determined using two markers attached to the handle) and (iv) handles velocity analysis (determined using one marker attached to the handle). The participants fatigue is indicated by two analysed factors: stroke time and the handles velocity. The research concerns three stages of rowing selected in a way that the different fatigue phases were expected to be visible. The average stroke time increases in the following stages: by 0.13 second and by 0.6 second respectively. While rowing, the handles velocity is decreased. The rowing technique is described by parameters such as: the proper handles position within set boundaries, the surface area encompassed by the handles trajectory outside the designated range, time of the incorrect rowing technique and the handles tilt. The surface area clearly shows that in the final stages the movements are more incorrect than initially. The mean values of the tilt indicate that due to the fatigue the technique worsens in the middle and the final rowing stages. It is observed the participants tilt the handle to the right while rowing. It clearly indicates irregular forces acting on the handle. There is a difference in muscle strength of both arms in the participants of this research.

The Influence of Picture Quality Scale Measure on Choosing the Wavelet Transform during Image Compression

One important issue of the image compression is the quality of the resultant image. The Picture Quality Scale Measure (PQS) was used to improve this quality. This perceptual measure evaluates the visual distortions in color compressed image on the basis of the original and the resultant ones. This measure uses also a group of observers who are needed to evaluate the distortions. The implementation of PQS measure together with neural network enabled the independence of human observers. It was also possible to use this measure to influence the quality during the process of image compression. Each level of the wavelet transform was compressed with one wavelet function which caused the least visual distortions which were computed by Picture Quality Scale. The image was compressed with different transforms. The choice of a particular transform was taken on the ground of the PQS value. There were five different wavelet transforms to choose: Haar, Daubechies degree 4, Daubechies degree 6, Daubechies degree 8 and 5/3 transform. The image was coded with Embedded Zerotree Wavelet Coding (EZW).

Motion Repeatability of Tennis Forehand Preparation Phase Without the Ball Using Three Dimensional Data

The forehand is one of the key shot in tennis. Its reparability is a very important aspect of gaining points. The first purpose of this paper is to create the algorithms for calculating the motion parameters for the preparation phase of the forehand, such as: the position of the head of the tennis racket relative to the player’s body, the elbow angle (i.e. whether the arm is bent or straight) and the placement of the player’s feet towards the front of the pelvis. The second aim of the study is to calculate the repeatability of the selected motion parameters (both for the body and the racket) of the preparation phase of the tennis forehand using coefficient of variation. The shots were performed in the motion capture laboratory using the Plug-in Gait biomechanical model. The described parameters are computed from three dimensional data, stored in C3D file.

Analysis of Selected Elements of a Rower’s Posture Using Motion Capture – a Case Study

The paper presents research on the motion capture of rowers practising on the Concept II Indoor Rower ergometer, using a motion capture device produced by the Vicon company, as well as a wireless heart rate monitor. The aim of the article is to analyse and assess the extent of variation of the angular position of the rower’s back at different phases of rowing and in different degrees of fatigue. The back’s position during rowing was recorded using three markers: one being a component of the Plug-in Gait model (T10) and two additional ones (marked as S1 and S2). The results obtained with the motion capture system allow to clearly identify the degree of training of the subjects studied, their fatigue and rowing technique on the basis of the analysis of changes in the inclination of the back in different positions of the successive phases of rowing.

A method for collision detection using mobile devices

From April 2018, all cars and light vans sold in the European Union are to have a built-in eCall system. Its task will be automatic detection of accidents and informing the emergency services. The system will be installed in new cars. The installation in older vehicles may be difficult or uneconomical. This article presents the concept of a system executing similar tasks using a mobile device. A smartphone can be used to automatically send information about the collision, but also enables automatic voice connection. This can make it possible/easier for victims to call for help. The proposed system can also perform the function of the “black box” recording information on a moving vehicle before the collision. In the proposed solution it is also possible to set up an emergency number. Instead of emergency services, relatives can be notified and, if necessary, they can notify rescuers. The article presents the results of measurements recorded using mobile device sensors which allows an algorithm to be developed that recognizes collisions and an experimental implementation of the proposed system. The collision detection method and its implementation presented in this paper use an improved motion type recognition method developed by the authors. The motion type recognition method is used to reduce the risk of a false collision detection. The method is also briefly discussed.

IMPROVED MOTION TYPE IDENTIFICATION METHOD USING MOBILE DEVICE SENSORS

This paper presents an application of built-in sensors of a mobile device – a more robust version of authors’ own motion type detection method introduced in previous work. Use of accelerometer and magnetometer for recording acceleration in the World’s coordinate system is explained. The original results and identification criteria are briefly described. New tests and their results are presented. An improved version of the motion type identification method is introduced.

ALGORITHMS FOR TENNIS RACKET ANALYSIS BASED ON MOTION DATA

Modern technologies, such as motion capture systems (both optical and markerless), are more and more frequently used for athlete performance analysis due to their great precision. Optical systems based on the retro-reflective markers allow for tracking motion of multiple objects of various types. These systems compute human kinetic and kinematic parameters based on biomechanical models. Tracking additional objects like a tennis racket is also a very important aspect for analysing the player’s technique and precision. The motion data gathered by motion capture systems may be used for analysing various aspects that may not be recognised by the human eye or a video camera. This paper presents algorithms for analysis of a tennis racket motion during two of the most important tennis strokes: forehand and backhand. An optical Vicon system was used for obtaining the motion data which was the input for the algorithms. They indicate: the velocity of a tennis racket’s head and the racket’s handle based on the trajectories of attached markers as well as the racket’s orientation. The algorithms were implemented and tested on the data obtained from a professional trainer who participated in the research and performed a series of ten strikes, separately for: 1) forehand without a ball, 2) backhand without a ball, 3) forehand with a ball and 4) backhand with a ball. The computed parameters are gathered in tables and visualised in a graph.

Watershed merging method for color images

Watershed transformation can be applied to color as well as to gray-scale images. A problem arises when dealing with color images. It is caused by the fact that pixels in such images are vectors that describe all color components whereas the watershed transformation requires a scalar height function as its input. There are multiple gradient magnitude definitions for color images that allow for the needed conversion. As in the case of gray-scale images, the image after watershed transformation is heavily over-segmented. One can blur the image before calculating the gradient magnitude, threshold the gradient image or merge the resulting watersheds. Unfortunately, the result is still over-segmented. A solution presented in this paper complements those mentioned above. It uses hierarchical cluster analysis methods for joining similar classes of the over-segmented image into a given number of clusters. After the image has been preprocessed and segmented, the over-segmentation is reduced by means of the cluster analysis. The attribute values for each watershed in each color component are calculated and clustering is performed. The resulting similarity hierarchy allows for the simple selection of the number of clusters in the final segmentation. Several clustering methods, including complete linkage and Wards methods with different sets of components, have been tested. Selected results are presented.