Jakub Smolka

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.

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).

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.

The rigid body gap filling algorithm

Using an optical passive motion capture system, researchers encounter problems involving marker occlusion. A marker can be covered during motion. This loss of information may cause various problems. For example, the output values of a biomechanical model (such as forces, moments etc.) cannot be computed or are incomplete in recording fragments in which markers are occluded. This paper presents a new, universal gap-filling algorithm for gaps in the trajectories of markers that belong to object segments which may be modelled (by approximation) as rigid bodies. It can fill in gaps in the trajectory of a marker which can be located at the beginning, at the end or in the middle of a recording. In order to assess the algorithm a series of automatic tests were conducted. A set of gapless files with real motion capture data post-processed by an expert was prepared. Then gaps of varying properties were artificially created in the test files. The gaps were filled using the proposed solution. The obtained results were compared to the original files prepared by the expert. The test dataset contains files with three types of movements representing different motion dynamics. The quality of the presented method was assessed for three body segments (head, torso and pelvic) and for three relative generated gap lengths (10%, 20% and 30%). 840 tests with artificially created missing markers were performed. Errors were highest for the torso segment and lowest for the head segment.

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.

What factors can affect lumbopelvic flexion-extension motion in the sagittal plane?: A literature review

Clinicians use forward bending and backward return in routine clinical examinations for evaluating spine mobility. The magnitude and timing of lumbar spine and pelvic contributions have been described in the literature as lumbopelvic rhythm. There is still limited knowledge about the factors which can determinate lumbar and hip mobility and coordination in the sagittal plane. The aim of this study is to demonstrate those factors contributing to the lumbopelvic rhythm and to explain the differences observed between subjects. The studies included in the review present possible explanations of observed lumbar-pelvic motion and/or coordination. They measure movement of the lumbar spine, the pelvis and/or the hip in the sagittal plane. The search was conducted in August 2017. Two databases (PubMed and Web of Science) were searched. The search identified 126 potentially relevant articles (53 in PubMed, 73 in Web of Science). Initial screening based on titles and abstracts retrieved 35 articles. The second stage of selection involved reading the full texts of articles. Twenty-four papers were selected in this stage. After careful bibliographic study, seven papers were added for this review, resulting in a total of 31. This literature review demonstrates those factors contributing to lumbopelvic motion. Age and gender, hamstring muscle tightness, feet position, muscle fatigue, movement speed and external loading as well phase of motion can affect various aspects of lumbopelvic rhythm.