# Research on Real-Time Detection of Sprint Error Based on Visual Features and Internet of Things

Authors: Hengming Chen; Junyong Li
Journal: Security and Communication Networks
 (2021)

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## Abstract

The current sprint error detection methods do not consider the analysis of the visual characteristics of sprint error, which leads to low detection accuracy, long detection time, and poor detection stability. To overcome this defect, inspired by Internet of Things technology, a real-time sprint error detection method based on visual characteristics is proposed. Based on the basic principle of RFID action perception, the original phase data is preprocessed, the channel parameters are selected, and the tag layout is optimized to form the action-oriented feature. Based on the three-dimensional visual features, the three-dimensional coordinate points of the sports field are determined, and the movement features of the sprint are extracted and formally described. Based on the analysis of the visual characteristics of sprint errors, the block pheromones of single frame sprint motion edge contour are obtained for clustering, and the sprint errors’ feature information is obtained and filtered. Sift technology is used to obtain the boundary contour line and implement the corner characteristics. The Hessian matrix of contour wave domain edge detection is used to calculate the contour wave domain matrix of the image and draw the contour curve of the image of sprint error action to realize the detection of sprint error action. The experimental results show that the proposed method has good stability and can effectively improve the detection accuracy and shorten the detection time.


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## Body

## 1. Introduction

Sprint is one of the track and field events. Sprint is a high-difficulty movement completed under the condition of a large number of hypoxia in human organs and the visceral system [1]. Sprint provides energy by anaerobic metabolism, which is the acceleration movement after the start. It makes the human body quickly get rid of the static movement, produce the strongest explosive force, and enter the extreme sports state. With the continuous development of modern track and field sprint movement technology, there are more clear standard requirements for the technical movements of athletes in track and field sprint events. The correct sprint movement technology can reduce the energy consumption of athletes in the process of running. The wrong sprint technique will increase the external resistance, seriously hinder the running speed of athletes, and then affect the performance [2]. Under normal circumstances, the judgment of sprinters’ mistakes is mainly based on the use of eye observation by referees or experts. Due to the fast speed in the process of sprinting, or the large number of sprinters, the referees or experts cannot detect the mistakes, which seriously affects the quality of track and field sprinting [3]. In this state, how to effectively detect the wrong movement of the sprint has become the main problem to be solved in this field.The detection of sprinting errors has a direct impact on the quality of track and field sprint competition. Therefore, real-time detection of sprinting errors is of great significance. At present, a large number of scholars in related fields have carried out different degrees of research and achieved certain theoretical results. Reference [4] proposed a neural network-aided motion detection method based on an indoor optical camera communication link. The mobile phone front camera is used as the receiver, and the three-color LED array is used as the transmitter. Through the indoor optical camera communication link, the camera is used to observe the user's finger centroid motion, and the motion capture is applied to the neural network to realize the neural network-aided motion detection. In [5], a high-precision motion detection method based on a look-up table is proposed. The look-up table is composed of a predefined motion and a string representing the predefined motion. In [6], they propose a novel deep network termed mutual learning convolutional neural network (MLCNN) to transfer useful information between visible and thermal V-streams for VT Re-ID in 6G-enabled VIoT. The proposed MLCNN consists of the feature generation module and the mutual learning module. Reference [7] proposed a multistage context perception scheme to efficiently extract the contextual information corresponding to different-size receptive fields in the single image and construct a two-path information propagation to extract the interimage similarity and difference from the high-level image feature representations of the group images. However, these two methods do not improve image edge detection.The data in switch keying format is modulated on the LED array, and the motion is generated by the user's finger in the free-space link. The mobile phone front camera is used to capture the motion data, calculate the Levenshtein Distance and modify the Jaccard coefficient, and match it to the predefined motion in the look-up table, so as to accurately identify the motion type and realize the data transmission. However, the above method does not consider the visual characteristics of motion errors, which leads to the problems of low detection accuracy, poor stability, and long detection time.As a pioneering technology in the development of science and technology today, the Internet of Things (IoT) has attracted the attention of a wide range of scholars for its systematic, meticulous, and intelligent information processing technology. The Internet of Things refers to the connection of any object to the network through information sensing equipment according to an agreed agreement, and the object exchanges and communicates through information media to realize intelligent identification, positioning, tracking, supervision, and other functions. Because the IoT technology has strong scalability, thus we attempt to incorporate this advanced technology into the problem we are studying in order to reduce the sprint error.We carefully study the real-time detection of sprint error in this paper. In this study, error control and error processing should be fully considered in the equipment selection and technical processing of the work links such as automatic collection, transmission, and processing of monitoring data, so as to ensure that the overall accuracy of the system is improved. Security and communication networks in data should be given priority consideration.Specifically, a real-time detection method based on visual features is proposed. Based on the basic principle of RFID motion sensing, the original phase data is preprocessed. The reason for this is inspired by the IoT because, in the IoT, the deployment of smart sensors is a very important link. The coordinate points are determined by three-dimensional visual features, and the sprint action features are extracted and formally described. This paper analyzes the visual characteristics of sprint fault action and obtains the edge contour block pheromone for clustering. The method of edge detection in the Contourlet domain is used to detect the wrong movement in the sprint. It can effectively improve detection accuracy and shorten detection time.


## 2. Computer Vision and Internet of Things Technology

### 2.1. Characteristics of Computer Vision

The basic meaning of computer vision theory is to generate a multidimensional vector reflecting the essential characteristics of the recognized pattern according to the information of the input system [8]. The structure of the computer vision system is as Figure 1.Figure 1
Structure of computer vision system.According to Figure1, the computer belongs to the core part and needs to control the normal operation of each module. An image acquisition card is a kind of hardware device which can acquire digital video information and store and play it. A vision sensor is an instrument that uses optical elements and imaging devices to obtain the image information of the external environment to obtain enough original images to be processed by the machine vision system. The image processing system includes image processing hardware and image processing software. The main characteristics of computer vision are as follows:(1)
Vision can describe the image of the outside world, that is, the effective symbol to describe it(2)
Images are connected to the outside world. Vision can process a series of images to achieve an understanding of the outside world(3)
Pushing process is the main task of vision research, that is to understand what physical constraints and assumptions affect the processing and transformation(4)
Representation and processing are two of the most important concepts in visual theory. Representation is to express the object clearly. Understanding the characteristics of a thing can be achieved by establishing its representation or description


### 2.2. Computer Vision Features

The range of features used in object tracking in computer vision is very wide. Feature selection and extraction are carried out according to the characteristics of the matched object. In the field of image space extraction and representation, features can be divided into global features and local features. The following briefly introduces the common features of image matching in human motion tracking.(1)
Global feature: It is to extract the image features related to the whole image, which is applicable to a certain category of images. For the human body, the color of the clothes is not a very stable feature because of the great change in the color of the clothes. Global feature representation is a top-down method, which usually relies on human detection, tracking, and positioning to obtain the region of interest, and then encodes the region of interest as a whole, which contains a lot of information and has good discrimination(2)
Local features: Mainly originated from the biological vision system, it is natural based on local features, and some features of points or lines will be significantly stronger than the visual salient features of other image modes [9]. Local features can be further divided into interest points and dense local features. Many of the characteristics of local features are opposite to global features, which can be seen as a white down to up approach. In general, the discriminability of local features is not as good as global features under ideal imaging conditions, but it has good robustness against cluttered background interference and local occlusion


### 2.3. The Internet of Things

Internet of Things refers to the ubiquitous end devices (Devices) and facilities (Facilities), including sensors with “intrinsic intelligence,” mobile terminals, industrial systems, numerical control systems, and home smart facilities, video surveillance systems, and “enabled,” such as RFID-attached assets (Assets), individuals and vehicles carrying wireless terminals, and “smart objects or animals” or “smart dust” (Mote), through various wireless and/or wired long-distance and/or short-distance communication networks to achieve interconnection (M2M), application integration (Grand Integration), and cloud computing-based SaaS operations, etc. In the environment of Intranet, Extranet, and/or Internet, appropriate information security assurance mechanism is adopted to provide safe, controllable, and even personalized real-time online monitoring, positioning and tracing, alarm linkage, dispatching and commanding, management and service functions such as plan management, remote control, security protection, remote maintenance, online upgrades, statistical reports, decision support, leadership desktop (Cockpit Dashboard), to achieve “efficient, energy-saving, safe, and safe” for “everything,” and the integration of “management, control, and operation” of “environmental protection”.


### 2.4. RFID Motion Sensing Technology

#### 2.4.1. Basic Principle of RFID Motion Perception

There are two kinds of motion-sensing methods used in the RFID motion detection system: one is based on the change of tag antenna impedance, and the other is based on the change of signal propagation path. The basic principles of these two ways are different. The following is a detailed analysis of the differences through the elaboration of the backscatter communication principle and the RFID signal propagation model:(1)
The action sensing method based on the change of tag antenna impedance: the current in the reader antenna radiates the electromagnetic wave signal to the air through the antenna to form the changing electromagnetic field, and the tag senses the changing magnetic field through its own antenna coil to generate the induced current. The induced current on the tag antenna and the current of the reader antenna can also form electromagnetic waves. The radiated electromagnetic waves return to the reader antenna and then generate the signal that can be detected by the reader, namely, the backscatter signal [10].The backscatter signal radiated by the tag is generated by the induced current that changes with time on the tag antenna. Therefore, the change of the current on the tag antenna will cause the backscatter signal to change accordingly. This effect can be used for human motion detection. Assuming that the tag antenna is a dipole antenna, the currentI induced on the tag antenna can be expressed as(1)I=−EincZC+ZAγcos2γL/4.In formula (1), ZC and ZA represent the corresponding impedances of the tag chip and the tag antenna, Einc is the incident electric field of the tag antenna, L is the length of the tag antenna, and γ is the free-space phase constant.When the incident electric field of the tag antenna is constant, the induced current will change with the impedance of the tag chip or tag antenna. Unlike the tag chip, the impedance of the tag antenna can be easily changed by touching the tag. In fact, the human body can be equivalent to a circuit with a certain impedance. When a person touches a tag, the equivalent impedance of the tag antenna becomes the sum of the original impedance and the human body impedance, which makes the induced current change accordingly. Finally, this change will be reflected in the signal received by the RFID reader.(2)
Action perception method based on changes in signal propagation path: RFID readers send radio frequency signals into the air through an antenna, and the radio frequency signals are in the process of propagation. Due to the influence of the surrounding environment, reflection, scattering, and diffraction will occur, thereby forming multiple propagation paths. Therefore, the signalSt received by the signal receiving end of the RFID reader/writer is superimposed by the signals returned by the N paths:(2)St=∑i=1NAite−jφit=Sdirt+Sstat+Sdynt.In formula (2), Ait is the complex number of the i path signal attenuation and initial phase shift, φit represents the phase shift over time, Sdirt represents the direct path signal returned directly after label processing, and Sstat represents the path through surrounding objects The reflected static multipath signal Sdynt represents the dynamic multipath signal reflected by surrounding objects. The static multipath signal is formed by the reflection of static objects, while the dynamic multipath signal is formed by the reflection of moving objects.In the process of human action, the propagation path of the RFID signal will change accordingly, so that the final backscatter signal presents different characteristics with the change of action. Through the observation and analysis of these characteristics, the corresponding action can be identified.


#### 2.4.2. RFID Action Sensing Channel Parameters

The change of the impedance of the tag antenna and the change of the signal propagation path will cause the corresponding change of the signal received by the RFID reader and writer. This change is used by the RFID action detection system to represent specific actions [11]. The common underlying channel parameters are analyzed and explained in detail as follows:(1)
Signal strength: When the tag gets energy from the electromagnetic wave emitted by the reader, part of the energy is returned to the reader through the backscattered signal. The signal strength is the measurement of the backscattering signal energy of each tag received by the reader. For a given system composed of readers, antennas, and tags, the signal strengthRSSI under ideal conditions is mainly determined by the distance d from the tag to the reader’s antenna:(3)RSSI=10logPr=10logGtλ2σ4π3d4+10logPt.In formula (3), Pr represents the energy sum of the backscattered signal, Pt represents the reader’s transmit power, Gt represents the reader’s antenna gain, λ represents the carrier wavelength, and σ represents the cross-sectional area of the tag radar. In the actual environment, many factors will affect the value of the signal strength RSSI, leading to different prediction results.(2)
Phase: The reader can return the phase difference between the transmitted signal and the backscattered signal of the tag, which provides an additional choice for the description of the tag state in the RF environment. For a given system composed of readers, antennas, and tags, ideally, the phaseθ is determined by the distance d from the tag to the reader’s antenna, and the phase value will repeat at every half wavelength:(4)θ=2πλ2d+θT+θR+θTagmod2π.In formula (4), θT represents the transmitter circuit of the reader, θR represents the receiver circuit of the reader, and θTag represents the reflection characteristic of the tag, which will cause additional phase shift. In the actual environment, the phase value will be affected by many other noises, such as multipath effects and other noise sources in the environment.(3)
Doppler shift: The Doppler shift reported by the reader is the frequency offset caused by the relative motion between the tag and the reader. This feature helps to distinguish moving tags from stationary tags, and in some cases, it can even determine the direction of tag motion. Assuming that the moving speedv of the labeled object is much less than the speed of light, the Doppler frequency shift of the carrier signal of the reader with wavelength λ is(5)fm=2vλcosα.In formula (5), α is the angle between the direction of movement of the object and the antenna of the reader. Assuming that ΔT represents the duration of a data packet, the phase change Δθ introduced by the Doppler shift of fm Hertz during this time period can be expressed as(6)Δθ=2π2fmΔT.From this, the calculation formula of Doppler frequency shift can be derived:(7)fm=Δθ4πΔT.The Doppler shift reported by the reader is affected by many factors, including the signal-to-noise ratio of the received signal, the multipath signal in the process of signal propagation, and the mode of the reader inventory.(4)
Tag reading rate: The tag reading rate is defined as the number of times each tag is read by the reader/writer per second [12]. The reader will not report this information to the upper application, but when the label is read each time, the reader will return the packet containing the time stamp to the upper application, and the upper application can obtain the label reading rate through calculation.To sum up, human action may cause different channel parameters to change, and the characteristics of each parameter are different. Therefore, the action detection system needs to select appropriate channel parameters as the signal input of action detection according to the designed action.


#### 2.4.3. Original Phase Preprocessing Based on RFID Group Tags

Based on the basic principle of RFID motion sensing, the original phase data is preprocessed. A passive remote controller based on RFID motion detection technology is designed to provide users with a natural and intuitive interactive control interface through the identification of key action and direction action [13]. Contact finger interaction and hand-held arm interaction are regarded as the basic direction of action design. According to the stability of parameters and the sensitivity of parameters to the distance between tag and reader antenna in different environments, channel parameters are selected. By optimizing the layout of tags, the geometric association between tags is enhanced, and the action-oriented feature is formed, so as to avoid the demand of the system for sample collection. The original phase preprocessing based on RFID group tags is as in Figure 2.Figure 2
Original phase preprocessing based on RFID group tags.According to Figure2, the RFID reader and the passive remote controller are responsible for collecting the original phase data, processing and analyzing the original data, and sending the user action to the application program after identifying the user action, so as to realize the action control of the application.


## 2.1. Characteristics of Computer Vision

The basic meaning of computer vision theory is to generate a multidimensional vector reflecting the essential characteristics of the recognized pattern according to the information of the input system [8]. The structure of the computer vision system is as Figure 1.Figure 1
Structure of computer vision system.According to Figure1, the computer belongs to the core part and needs to control the normal operation of each module. An image acquisition card is a kind of hardware device which can acquire digital video information and store and play it. A vision sensor is an instrument that uses optical elements and imaging devices to obtain the image information of the external environment to obtain enough original images to be processed by the machine vision system. The image processing system includes image processing hardware and image processing software. The main characteristics of computer vision are as follows:(1)
Vision can describe the image of the outside world, that is, the effective symbol to describe it(2)
Images are connected to the outside world. Vision can process a series of images to achieve an understanding of the outside world(3)
Pushing process is the main task of vision research, that is to understand what physical constraints and assumptions affect the processing and transformation(4)
Representation and processing are two of the most important concepts in visual theory. Representation is to express the object clearly. Understanding the characteristics of a thing can be achieved by establishing its representation or description


## 2.2. Computer Vision Features

The range of features used in object tracking in computer vision is very wide. Feature selection and extraction are carried out according to the characteristics of the matched object. In the field of image space extraction and representation, features can be divided into global features and local features. The following briefly introduces the common features of image matching in human motion tracking.(1)
Global feature: It is to extract the image features related to the whole image, which is applicable to a certain category of images. For the human body, the color of the clothes is not a very stable feature because of the great change in the color of the clothes. Global feature representation is a top-down method, which usually relies on human detection, tracking, and positioning to obtain the region of interest, and then encodes the region of interest as a whole, which contains a lot of information and has good discrimination(2)
Local features: Mainly originated from the biological vision system, it is natural based on local features, and some features of points or lines will be significantly stronger than the visual salient features of other image modes [9]. Local features can be further divided into interest points and dense local features. Many of the characteristics of local features are opposite to global features, which can be seen as a white down to up approach. In general, the discriminability of local features is not as good as global features under ideal imaging conditions, but it has good robustness against cluttered background interference and local occlusion


## 2.3. The Internet of Things

Internet of Things refers to the ubiquitous end devices (Devices) and facilities (Facilities), including sensors with “intrinsic intelligence,” mobile terminals, industrial systems, numerical control systems, and home smart facilities, video surveillance systems, and “enabled,” such as RFID-attached assets (Assets), individuals and vehicles carrying wireless terminals, and “smart objects or animals” or “smart dust” (Mote), through various wireless and/or wired long-distance and/or short-distance communication networks to achieve interconnection (M2M), application integration (Grand Integration), and cloud computing-based SaaS operations, etc. In the environment of Intranet, Extranet, and/or Internet, appropriate information security assurance mechanism is adopted to provide safe, controllable, and even personalized real-time online monitoring, positioning and tracing, alarm linkage, dispatching and commanding, management and service functions such as plan management, remote control, security protection, remote maintenance, online upgrades, statistical reports, decision support, leadership desktop (Cockpit Dashboard), to achieve “efficient, energy-saving, safe, and safe” for “everything,” and the integration of “management, control, and operation” of “environmental protection”.


## 2.4. RFID Motion Sensing Technology

### 2.4.1. Basic Principle of RFID Motion Perception

There are two kinds of motion-sensing methods used in the RFID motion detection system: one is based on the change of tag antenna impedance, and the other is based on the change of signal propagation path. The basic principles of these two ways are different. The following is a detailed analysis of the differences through the elaboration of the backscatter communication principle and the RFID signal propagation model:(1)
The action sensing method based on the change of tag antenna impedance: the current in the reader antenna radiates the electromagnetic wave signal to the air through the antenna to form the changing electromagnetic field, and the tag senses the changing magnetic field through its own antenna coil to generate the induced current. The induced current on the tag antenna and the current of the reader antenna can also form electromagnetic waves. The radiated electromagnetic waves return to the reader antenna and then generate the signal that can be detected by the reader, namely, the backscatter signal [10].The backscatter signal radiated by the tag is generated by the induced current that changes with time on the tag antenna. Therefore, the change of the current on the tag antenna will cause the backscatter signal to change accordingly. This effect can be used for human motion detection. Assuming that the tag antenna is a dipole antenna, the currentI induced on the tag antenna can be expressed as(1)I=−EincZC+ZAγcos2γL/4.In formula (1), ZC and ZA represent the corresponding impedances of the tag chip and the tag antenna, Einc is the incident electric field of the tag antenna, L is the length of the tag antenna, and γ is the free-space phase constant.When the incident electric field of the tag antenna is constant, the induced current will change with the impedance of the tag chip or tag antenna. Unlike the tag chip, the impedance of the tag antenna can be easily changed by touching the tag. In fact, the human body can be equivalent to a circuit with a certain impedance. When a person touches a tag, the equivalent impedance of the tag antenna becomes the sum of the original impedance and the human body impedance, which makes the induced current change accordingly. Finally, this change will be reflected in the signal received by the RFID reader.(2)
Action perception method based on changes in signal propagation path: RFID readers send radio frequency signals into the air through an antenna, and the radio frequency signals are in the process of propagation. Due to the influence of the surrounding environment, reflection, scattering, and diffraction will occur, thereby forming multiple propagation paths. Therefore, the signalSt received by the signal receiving end of the RFID reader/writer is superimposed by the signals returned by the N paths:(2)St=∑i=1NAite−jφit=Sdirt+Sstat+Sdynt.In formula (2), Ait is the complex number of the i path signal attenuation and initial phase shift, φit represents the phase shift over time, Sdirt represents the direct path signal returned directly after label processing, and Sstat represents the path through surrounding objects The reflected static multipath signal Sdynt represents the dynamic multipath signal reflected by surrounding objects. The static multipath signal is formed by the reflection of static objects, while the dynamic multipath signal is formed by the reflection of moving objects.In the process of human action, the propagation path of the RFID signal will change accordingly, so that the final backscatter signal presents different characteristics with the change of action. Through the observation and analysis of these characteristics, the corresponding action can be identified.


### 2.4.2. RFID Action Sensing Channel Parameters

The change of the impedance of the tag antenna and the change of the signal propagation path will cause the corresponding change of the signal received by the RFID reader and writer. This change is used by the RFID action detection system to represent specific actions [11]. The common underlying channel parameters are analyzed and explained in detail as follows:(1)
Signal strength: When the tag gets energy from the electromagnetic wave emitted by the reader, part of the energy is returned to the reader through the backscattered signal. The signal strength is the measurement of the backscattering signal energy of each tag received by the reader. For a given system composed of readers, antennas, and tags, the signal strengthRSSI under ideal conditions is mainly determined by the distance d from the tag to the reader’s antenna:(3)RSSI=10logPr=10logGtλ2σ4π3d4+10logPt.In formula (3), Pr represents the energy sum of the backscattered signal, Pt represents the reader’s transmit power, Gt represents the reader’s antenna gain, λ represents the carrier wavelength, and σ represents the cross-sectional area of the tag radar. In the actual environment, many factors will affect the value of the signal strength RSSI, leading to different prediction results.(2)
Phase: The reader can return the phase difference between the transmitted signal and the backscattered signal of the tag, which provides an additional choice for the description of the tag state in the RF environment. For a given system composed of readers, antennas, and tags, ideally, the phaseθ is determined by the distance d from the tag to the reader’s antenna, and the phase value will repeat at every half wavelength:(4)θ=2πλ2d+θT+θR+θTagmod2π.In formula (4), θT represents the transmitter circuit of the reader, θR represents the receiver circuit of the reader, and θTag represents the reflection characteristic of the tag, which will cause additional phase shift. In the actual environment, the phase value will be affected by many other noises, such as multipath effects and other noise sources in the environment.(3)
Doppler shift: The Doppler shift reported by the reader is the frequency offset caused by the relative motion between the tag and the reader. This feature helps to distinguish moving tags from stationary tags, and in some cases, it can even determine the direction of tag motion. Assuming that the moving speedv of the labeled object is much less than the speed of light, the Doppler frequency shift of the carrier signal of the reader with wavelength λ is(5)fm=2vλcosα.In formula (5), α is the angle between the direction of movement of the object and the antenna of the reader. Assuming that ΔT represents the duration of a data packet, the phase change Δθ introduced by the Doppler shift of fm Hertz during this time period can be expressed as(6)Δθ=2π2fmΔT.From this, the calculation formula of Doppler frequency shift can be derived:(7)fm=Δθ4πΔT.The Doppler shift reported by the reader is affected by many factors, including the signal-to-noise ratio of the received signal, the multipath signal in the process of signal propagation, and the mode of the reader inventory.(4)
Tag reading rate: The tag reading rate is defined as the number of times each tag is read by the reader/writer per second [12]. The reader will not report this information to the upper application, but when the label is read each time, the reader will return the packet containing the time stamp to the upper application, and the upper application can obtain the label reading rate through calculation.To sum up, human action may cause different channel parameters to change, and the characteristics of each parameter are different. Therefore, the action detection system needs to select appropriate channel parameters as the signal input of action detection according to the designed action.


### 2.4.3. Original Phase Preprocessing Based on RFID Group Tags

Based on the basic principle of RFID motion sensing, the original phase data is preprocessed. A passive remote controller based on RFID motion detection technology is designed to provide users with a natural and intuitive interactive control interface through the identification of key action and direction action [13]. Contact finger interaction and hand-held arm interaction are regarded as the basic direction of action design. According to the stability of parameters and the sensitivity of parameters to the distance between tag and reader antenna in different environments, channel parameters are selected. By optimizing the layout of tags, the geometric association between tags is enhanced, and the action-oriented feature is formed, so as to avoid the demand of the system for sample collection. The original phase preprocessing based on RFID group tags is as in Figure 2.Figure 2
Original phase preprocessing based on RFID group tags.According to Figure2, the RFID reader and the passive remote controller are responsible for collecting the original phase data, processing and analyzing the original data, and sending the user action to the application program after identifying the user action, so as to realize the action control of the application.


## 2.4.1. Basic Principle of RFID Motion Perception

There are two kinds of motion-sensing methods used in the RFID motion detection system: one is based on the change of tag antenna impedance, and the other is based on the change of signal propagation path. The basic principles of these two ways are different. The following is a detailed analysis of the differences through the elaboration of the backscatter communication principle and the RFID signal propagation model:(1)
The action sensing method based on the change of tag antenna impedance: the current in the reader antenna radiates the electromagnetic wave signal to the air through the antenna to form the changing electromagnetic field, and the tag senses the changing magnetic field through its own antenna coil to generate the induced current. The induced current on the tag antenna and the current of the reader antenna can also form electromagnetic waves. The radiated electromagnetic waves return to the reader antenna and then generate the signal that can be detected by the reader, namely, the backscatter signal [10].The backscatter signal radiated by the tag is generated by the induced current that changes with time on the tag antenna. Therefore, the change of the current on the tag antenna will cause the backscatter signal to change accordingly. This effect can be used for human motion detection. Assuming that the tag antenna is a dipole antenna, the currentI induced on the tag antenna can be expressed as(1)I=−EincZC+ZAγcos2γL/4.In formula (1), ZC and ZA represent the corresponding impedances of the tag chip and the tag antenna, Einc is the incident electric field of the tag antenna, L is the length of the tag antenna, and γ is the free-space phase constant.When the incident electric field of the tag antenna is constant, the induced current will change with the impedance of the tag chip or tag antenna. Unlike the tag chip, the impedance of the tag antenna can be easily changed by touching the tag. In fact, the human body can be equivalent to a circuit with a certain impedance. When a person touches a tag, the equivalent impedance of the tag antenna becomes the sum of the original impedance and the human body impedance, which makes the induced current change accordingly. Finally, this change will be reflected in the signal received by the RFID reader.(2)
Action perception method based on changes in signal propagation path: RFID readers send radio frequency signals into the air through an antenna, and the radio frequency signals are in the process of propagation. Due to the influence of the surrounding environment, reflection, scattering, and diffraction will occur, thereby forming multiple propagation paths. Therefore, the signalSt received by the signal receiving end of the RFID reader/writer is superimposed by the signals returned by the N paths:(2)St=∑i=1NAite−jφit=Sdirt+Sstat+Sdynt.In formula (2), Ait is the complex number of the i path signal attenuation and initial phase shift, φit represents the phase shift over time, Sdirt represents the direct path signal returned directly after label processing, and Sstat represents the path through surrounding objects The reflected static multipath signal Sdynt represents the dynamic multipath signal reflected by surrounding objects. The static multipath signal is formed by the reflection of static objects, while the dynamic multipath signal is formed by the reflection of moving objects.In the process of human action, the propagation path of the RFID signal will change accordingly, so that the final backscatter signal presents different characteristics with the change of action. Through the observation and analysis of these characteristics, the corresponding action can be identified.


## 2.4.2. RFID Action Sensing Channel Parameters

The change of the impedance of the tag antenna and the change of the signal propagation path will cause the corresponding change of the signal received by the RFID reader and writer. This change is used by the RFID action detection system to represent specific actions [11]. The common underlying channel parameters are analyzed and explained in detail as follows:(1)
Signal strength: When the tag gets energy from the electromagnetic wave emitted by the reader, part of the energy is returned to the reader through the backscattered signal. The signal strength is the measurement of the backscattering signal energy of each tag received by the reader. For a given system composed of readers, antennas, and tags, the signal strengthRSSI under ideal conditions is mainly determined by the distance d from the tag to the reader’s antenna:(3)RSSI=10logPr=10logGtλ2σ4π3d4+10logPt.In formula (3), Pr represents the energy sum of the backscattered signal, Pt represents the reader’s transmit power, Gt represents the reader’s antenna gain, λ represents the carrier wavelength, and σ represents the cross-sectional area of the tag radar. In the actual environment, many factors will affect the value of the signal strength RSSI, leading to different prediction results.(2)
Phase: The reader can return the phase difference between the transmitted signal and the backscattered signal of the tag, which provides an additional choice for the description of the tag state in the RF environment. For a given system composed of readers, antennas, and tags, ideally, the phaseθ is determined by the distance d from the tag to the reader’s antenna, and the phase value will repeat at every half wavelength:(4)θ=2πλ2d+θT+θR+θTagmod2π.In formula (4), θT represents the transmitter circuit of the reader, θR represents the receiver circuit of the reader, and θTag represents the reflection characteristic of the tag, which will cause additional phase shift. In the actual environment, the phase value will be affected by many other noises, such as multipath effects and other noise sources in the environment.(3)
Doppler shift: The Doppler shift reported by the reader is the frequency offset caused by the relative motion between the tag and the reader. This feature helps to distinguish moving tags from stationary tags, and in some cases, it can even determine the direction of tag motion. Assuming that the moving speedv of the labeled object is much less than the speed of light, the Doppler frequency shift of the carrier signal of the reader with wavelength λ is(5)fm=2vλcosα.In formula (5), α is the angle between the direction of movement of the object and the antenna of the reader. Assuming that ΔT represents the duration of a data packet, the phase change Δθ introduced by the Doppler shift of fm Hertz during this time period can be expressed as(6)Δθ=2π2fmΔT.From this, the calculation formula of Doppler frequency shift can be derived:(7)fm=Δθ4πΔT.The Doppler shift reported by the reader is affected by many factors, including the signal-to-noise ratio of the received signal, the multipath signal in the process of signal propagation, and the mode of the reader inventory.(4)
Tag reading rate: The tag reading rate is defined as the number of times each tag is read by the reader/writer per second [12]. The reader will not report this information to the upper application, but when the label is read each time, the reader will return the packet containing the time stamp to the upper application, and the upper application can obtain the label reading rate through calculation.To sum up, human action may cause different channel parameters to change, and the characteristics of each parameter are different. Therefore, the action detection system needs to select appropriate channel parameters as the signal input of action detection according to the designed action.


## 2.4.3. Original Phase Preprocessing Based on RFID Group Tags

Based on the basic principle of RFID motion sensing, the original phase data is preprocessed. A passive remote controller based on RFID motion detection technology is designed to provide users with a natural and intuitive interactive control interface through the identification of key action and direction action [13]. Contact finger interaction and hand-held arm interaction are regarded as the basic direction of action design. According to the stability of parameters and the sensitivity of parameters to the distance between tag and reader antenna in different environments, channel parameters are selected. By optimizing the layout of tags, the geometric association between tags is enhanced, and the action-oriented feature is formed, so as to avoid the demand of the system for sample collection. The original phase preprocessing based on RFID group tags is as in Figure 2.Figure 2
Original phase preprocessing based on RFID group tags.According to Figure2, the RFID reader and the passive remote controller are responsible for collecting the original phase data, processing and analyzing the original data, and sending the user action to the application program after identifying the user action, so as to realize the action control of the application.


## 3. Feature Extraction of Sprint Errors

In the process of establishing the three-dimensional visual inspection model of sprinting error movement, the coordinate points of the three-dimensional coordinate system of the sports field are determined, the movement characteristics of sprinters in the three-dimensional coordinate system of the sports field are extracted, and the sprinting error movement rules in the coordinate system are formally described. This paper analyzes the visual characteristics of sprint error movement, obtains the block pheromone of the edge contour of single frame sprint movement for clustering, obtains the sprint error characteristic information of the human visual image, and filters the characteristic information to segment the visual characteristics of sprint error movement.


### 3.1. Determining the Three-Dimensional Coordinates of Sports Venues

In the process of three-dimensional visual detection modeling of sprinters' fault action, it is necessary to extract the characteristics of sprinters' actions based on three-dimensional coordinates. Firstly, the three-dimensional coordinate system of the sports field is established, and then the sprinters' fault action is formally described.Assuming that the venues for sports singles and dual exercises are 5 m long and 10 m wide, respectively, the starting angle of the sports field is set as the center point, the length is thex axis, the width is the y axis, and the height is expressed as the z axis; then, x0=10m, y0=10m; according to the height of the athlete's action, given the condition of z0=5m, the scale is 1m, and the three-dimensional coordinate system of the sports field is established as Figure 3.Figure 3
Three-dimensional coordinate system of the sports ground.


### 3.2. Marking of Key Joint Parts of Athletes

In order to formally describe the rules of sprinter's fault action, when describing the characteristics of sprinters, according to the requirements of sports action standards, it is necessary to use three-dimensional coordinate points to mark the joints and parts of the body, such as shoulders, fingers, toes, and feet, so as to obtain the athletes' action. The main markings are as follows:(1)
The coordinate point of the shoulder: Mark the left shoulder of the athlete asl and the right shoulder as r, then xljb,yljb,zljb represents the coordinate point of the left shoulder, and xrjb,yrjb,zrjb represents the coordinate point of the right shoulder.(2)
Finger coordinate point: Define the finger joint as a plane, wherexsz,ysz,zsz represents any point in the plane, xlsz,ylsz,zlsz represents the coordinate point of the left finger, and xrsz,yrsz,zrsz represents the coordinate point of the right finger.(3)
Toe coordinate point:xljj,yljj,zljj represents the coordinate point of the athlete’s left toe, and xrjj,yrjj,zrjj represents the coordinate point of the athlete’s right toe.(4)
Instep coordinate point: Take a coordinate point on the athlete’s instep, wherexljm,yljm,zljm represents the coordinate point of the left foot and xrjm,yrjm,zrjm represents the coordinate point of the right foot. According to the above description, use formula (8) to extract the motion characteristics of sprinters based on three-dimensional coordinates:(8)T1=xrjj,yrjj,zrjjxsz,ysz,zszxrsz,yrsz,zrszxrsz,yrsz,zrszxrjb,yrjb,zrjb.If we formally describe the wrong action of sprinting, the correctness of the technical action of sprinting can not only affect the current stage of sports but also affect the pre- and poststages of sports [14]. Formula (9) is used to formally describe the sprinting errors from multiple angles such as changes in the speed of a sprinter's movement, body position, action route, and trajectory of the body’s center of gravity:(9)SΔ=t1−p12T1K1+t2−p2K2+tm−pmKm.In formula (9), t1−p1,t2−p2,andtm−pm represent the sprint errors that may or have occurred at various stages, and K1,K2,andKm represent the angle formed by the joints and parts of the sprinter's body in the sprint movement.


### 3.3. Analysis of the Visual Characteristics of Sprint Mistakes

On the basis of the formal description of the above sprint movement, the visual characteristics of sprint errors are analyzed. Assuming that the width of the sprint motion image isW and the height is H, the background image B of the motion scene and the visual characteristic image I of the current sprint motion are divided into subblocks to obtain the block pheromone of the edge contour of a single frame of sprint motion:(10)minFx=f1x,f2x,…,fmxT,s.t.gi≤0,i=1,2,…,q,hj=0,j=1,2,…,p.In formula (10), gi is the moment of inertia of the human body around the vertical axis, hj is the moment of inertia in the horizontal direction, q is the length of the grid formed by the human body's trajectory, p is the width, and fmx is the pixel intensity of the edge corners.The above-mentioned segmentation information elements of the edge contour of a single frame sprint are clustered to obtain the information of the human visual image of sprint fault characteristics, filter the information, segment the curve of the visual features of the short-run errors, and obtain the three-dimensional viewpoint switching motion equation of the analysis of the short-run fault action features by using the following formula:(11)x˙=VcosθcosψV,y˙=Vsinθ,z˙=−VcosθsinψV,(12)θ˙=ωysinγ+ωzcosγ.In formula (11), x,y,andz are the positions of the centroid of the visual image of the sprint movement, and ψV is the switching deflection angle of the sprint movement area. To sum up, the analysis realizes the analysis of the visual characteristics of the error movement in sprint and provides the data basis for the next three-dimensional visual comparison. The analysis process of the visual characteristics of the error movement in the sprint is shown in Figure 4.Figure 4
Analysis process of visual characteristics of sprint error action.


## 3.1. Determining the Three-Dimensional Coordinates of Sports Venues

In the process of three-dimensional visual detection modeling of sprinters' fault action, it is necessary to extract the characteristics of sprinters' actions based on three-dimensional coordinates. Firstly, the three-dimensional coordinate system of the sports field is established, and then the sprinters' fault action is formally described.Assuming that the venues for sports singles and dual exercises are 5 m long and 10 m wide, respectively, the starting angle of the sports field is set as the center point, the length is thex axis, the width is the y axis, and the height is expressed as the z axis; then, x0=10m, y0=10m; according to the height of the athlete's action, given the condition of z0=5m, the scale is 1m, and the three-dimensional coordinate system of the sports field is established as Figure 3.Figure 3
Three-dimensional coordinate system of the sports ground.


## 3.2. Marking of Key Joint Parts of Athletes

In order to formally describe the rules of sprinter's fault action, when describing the characteristics of sprinters, according to the requirements of sports action standards, it is necessary to use three-dimensional coordinate points to mark the joints and parts of the body, such as shoulders, fingers, toes, and feet, so as to obtain the athletes' action. The main markings are as follows:(1)
The coordinate point of the shoulder: Mark the left shoulder of the athlete asl and the right shoulder as r, then xljb,yljb,zljb represents the coordinate point of the left shoulder, and xrjb,yrjb,zrjb represents the coordinate point of the right shoulder.(2)
Finger coordinate point: Define the finger joint as a plane, wherexsz,ysz,zsz represents any point in the plane, xlsz,ylsz,zlsz represents the coordinate point of the left finger, and xrsz,yrsz,zrsz represents the coordinate point of the right finger.(3)
Toe coordinate point:xljj,yljj,zljj represents the coordinate point of the athlete’s left toe, and xrjj,yrjj,zrjj represents the coordinate point of the athlete’s right toe.(4)
Instep coordinate point: Take a coordinate point on the athlete’s instep, wherexljm,yljm,zljm represents the coordinate point of the left foot and xrjm,yrjm,zrjm represents the coordinate point of the right foot. According to the above description, use formula (8) to extract the motion characteristics of sprinters based on three-dimensional coordinates:(8)T1=xrjj,yrjj,zrjjxsz,ysz,zszxrsz,yrsz,zrszxrsz,yrsz,zrszxrjb,yrjb,zrjb.If we formally describe the wrong action of sprinting, the correctness of the technical action of sprinting can not only affect the current stage of sports but also affect the pre- and poststages of sports [14]. Formula (9) is used to formally describe the sprinting errors from multiple angles such as changes in the speed of a sprinter's movement, body position, action route, and trajectory of the body’s center of gravity:(9)SΔ=t1−p12T1K1+t2−p2K2+tm−pmKm.In formula (9), t1−p1,t2−p2,andtm−pm represent the sprint errors that may or have occurred at various stages, and K1,K2,andKm represent the angle formed by the joints and parts of the sprinter's body in the sprint movement.


## 3.3. Analysis of the Visual Characteristics of Sprint Mistakes

On the basis of the formal description of the above sprint movement, the visual characteristics of sprint errors are analyzed. Assuming that the width of the sprint motion image isW and the height is H, the background image B of the motion scene and the visual characteristic image I of the current sprint motion are divided into subblocks to obtain the block pheromone of the edge contour of a single frame of sprint motion:(10)minFx=f1x,f2x,…,fmxT,s.t.gi≤0,i=1,2,…,q,hj=0,j=1,2,…,p.In formula (10), gi is the moment of inertia of the human body around the vertical axis, hj is the moment of inertia in the horizontal direction, q is the length of the grid formed by the human body's trajectory, p is the width, and fmx is the pixel intensity of the edge corners.The above-mentioned segmentation information elements of the edge contour of a single frame sprint are clustered to obtain the information of the human visual image of sprint fault characteristics, filter the information, segment the curve of the visual features of the short-run errors, and obtain the three-dimensional viewpoint switching motion equation of the analysis of the short-run fault action features by using the following formula:(11)x˙=VcosθcosψV,y˙=Vsinθ,z˙=−VcosθsinψV,(12)θ˙=ωysinγ+ωzcosγ.In formula (11), x,y,andz are the positions of the centroid of the visual image of the sprint movement, and ψV is the switching deflection angle of the sprint movement area. To sum up, the analysis realizes the analysis of the visual characteristics of the error movement in sprint and provides the data basis for the next three-dimensional visual comparison. The analysis process of the visual characteristics of the error movement in the sprint is shown in Figure 4.Figure 4
Analysis process of visual characteristics of sprint error action.


## 4. Real-Time Detection of Sprint Error

On the basis of the three-dimensional visual analysis of sprint fault action based on computer vision features and RFID group tags, through the feature analysis, it is necessary to carry out three-dimensional visual detection of sprint fault action. In order to increase the image reconstruction level of sprint movement, it is necessary to select the appropriate corner matching method to obtain the distribution parameters of each modeling point and to identify the wrong movement of sprint [15]. To this end, this paper proposes a three-dimensional vision detection method for sprint errors based on edge detection in the contour wave domain. The detailed implementation process is as follows.For a gray-scale sprint motion imageGX,Y, we extract a small subregion W∈G from the image, move the subregion image horizontally and vertically, and denote the displacement as ΔX and ΔY, respectively. We use formula (13) to calculate the subregion image in the square of the gray value change before and after translation:(13)GX,Y=b0,fX,Y<T,b1,fX,Y≥T.Using SIFT technology [16], the corner characteristics of the boundary contour line of the human body are acquired, formula (13) is substituted into the following formula, and formula (14) is used to calculate the gray value of all frame images at X,Y:(14)PX,Y=1,14BG−IG−YG×GX,Y>0,0,otherwise.Since motion detection is the key to realize the evaluation of sprint erroneous actions, the three-dimensional visual feature extraction algorithm of sprint erroneous actions is adopted, the contour wave domain edge detection algorithm is designed, and the Hessian matrix is used to calculate the image contour wave domain matrix as(15)D=Ix2IxIyIxIyIy2.In formula (15), Ix is the error feature of the sprint motion image, Iy is the vertical zoom amount in the motion, and IxIy is the correlation between the wrong action and the correct action. We carry out the first-order Taylor expansion on the formula (15) and use the formula (16) to obtain the feature quantity of edge detection in the contour wave domain:(16)ϕt=lgpt1−pt+Htpt+HL−1−Ht1−pt,(17)pt=∑i=0tpi.In formula (16), Ht and HL−1 are the edge partial derivatives of the contour wave domain of the image GX,Y in the horizontal and vertical directions, respectively. Substituting formulae (17) into (16), we get(18)Ht=−∑i=0tpilgpi.Therefore, the solution to the change of the region is converted to the two eigenvalues of the structure matrixMX,Y, that is, the two eigenvalues of the matrix MX,Y: λ1 and λ2. Regarding the local structure matrix M as an autocorrelation function, we judge whether the detection point X,Y is the corner point of the image according to the two eigenvalues in the local structure matrix M [17]. Assume that the probability density function of the NSQCT coefficient of the image is pmm, and the probability density function of the noise is pnn. Therefore, the relational expression of using formula (19) to obtain the human visual feature SIFT corner detection is(19)pmmpnn=αβα+β2=γγ+12.In formula (19), α represents the gray value of the human visual feature at X,Y, β represents the information entropy space, and γ+1 represents the modal tracking corner information of the human edge feature. Through the above processing, the SIFT corner detection algorithm is used to draw the contour curve of the sprint error action image, and the contour wave domain is smoothed to realize the sprint error action detection.


## 5. Experimental Analysis

### 5.1. Experimental Environment and Data

In order to verify the effectiveness of the real-time detection method for sprint errors based on visual features and the Internet of Things, the host used in this experiment is configured with Pentium(R)D CPU 2.80GH, 2.79 GHz, 2.00 GB memory, and a Laird S9028PCR with 9dBi gain UHF circularly polarized flat panel antenna and several Alien Az-9629 UHF RFID tags measuring 25.5  mm × 25.5  mm. The reader antenna is fixed on the top of the room by an aluminum alloy bracket and connected with the reader through the feeder, while the reader communicates with the notebook through the network cable. In the process of action, the user needs to hold a passive remote control to interact with the action recognition system. The simulation software is MATLAB 7.0. The three-dimensional dynamic mechanical model is used to build the kinematic model of human movement, and the three-dimensional feature parameter model is obtained. The spatial pose parameter setting of the sprint action feature kinematic model is shown in Table 1.Table 1
Spatial pose parameters of the kinematic model of sprint movement characteristics.
iqi/rαi/rαi′/mmdi/mmBM1q1−π/211−π/4,π/22q2−π/2−π/210−π/4,π/23q3−π/2π/201−28π/18,π/24q4−π/2000.79π/365q5π/2100.56/18In Table1, i represents the serial number of the parameter, qi and αi, respectively, represent the arc of the space position during sprinting, the unit is r, αi′ and di, respectively, represent the distance of the space position during sprinting, the unit is mm, and BM represents the constraint of sprint movement.According to the above-mentioned three-dimensional model parameter setting, the visual feature collection of the sprint motion image is performed, and the image stabilization sensitivity of the sprint motion visual feature collection and jitter is −130 Bm, the resolution is 0.5 m, and the pixel value is 540×400. The tones of the misoperation recognition of sprinting are quantified into 16 levels. Based on the step response, the disturbance signal of fault action is added. When the time is close to the 70s, the disturbance feature with an amplitude of 1 is added. The disturbance pulse is collected for 1s to describe the disturbance feature of the sprint image. After binarization and Susan wavelet operator processing in the rectangular region, the noise interference is eliminated by link domain analysis and median filtering. When Susan is less than the threshold, the point is judged as an edge point, and the image is filtered. Based on the above simulation environment and parameter setting, the original three-dimensional visual image of sprint posture is obtained as Figure5.Figure 5
Original sprint image.It can be seen from the analysis of Figure5 that the original sprint image contains some fault action features. In order to correct the sprint posture, it is necessary to recognize and extract the fault action features. In this paper, the three-dimensional visual detection method based on edge detection in the Contourlet domain is used to analyze the visual features of sprint error actions, and the edge detection algorithm is used to extract the edge contour features. The extraction results of sprint error actions are shown in Figure 6.Figure 6
Extraction results of short-run error action.It can be seen from the analysis of Figure6 that the real-time detection method based on visual features and the Internet of Things can effectively achieve the feature extraction and detection of sprint error movement and improve the judgment ability of sprint movement.


### 5.2. Comparison of Error Detection Accuracy in Sprint

In order to further test the performance of the proposed method, the methods in [4] and [5] are, respectively, used to compare the three-dimensional vision of sprint error action under contour wave domain edge detection, and the detection accuracy of sprint error action of different methods is obtained as shown in Figure 7.Figure 7
Comparison of detection accuracy of different methods of sprint error movement.It can be seen from the analysis of Figure7 that when the number of experiments is 30, the average detection accuracy of the method in [4] is 81%, the average detection accuracy of the method in [5] is 62%, and the average detection accuracy of the proposed method is as high as 93%. Therefore, compared with the methods in [4] and [6], the average detection accuracy of the proposed method is higher, which can effectively improve the detection accuracy of sprint error because the proposed method uses three-dimensional visual features to extract the movement characteristics of sprinters and formally describes the rules of sprinting mistakes, so as to improve the detection accuracy of sprinting mistakes.


### 5.3. Comparison of the Stability of the Error Movement Detection in Sprint

We further verify the detection stability of the real-time detection method of sprint error action based on visual features and Internet of Things, respectively, use the methods in [4] and [5] and the proposed method for comparison, and get the comparison results of the detection stability of different methods of sprint error action as shown in Figure 8.Figure 8
Comparison results of sprint error detection stability of different methods.The analysis of Figure8 shows that when the number of experiments is 30, the stability of the average sprint error detection of the method in [4] is 63%, the stability of the average sprint error detection of the method in [5] is 80%, and the stability of the average sprint error detection of the proposed method is as high as 97%. Therefore, compared with the methods in [4] and [6], the proposed method has better stability in the detection of running errors.


### 5.4. Comparison of Detection Time of Sprint Error Movement

On this basis, the detection time of the real-time detection method of sprint error action based on visual features and the Internet of Things is verified. The methods in [4] and [5] and the proposed method are, respectively, used for comparison. The detection time of sprint error action of different methods is compared as shown in Table 2.Table 2
Comparison of detection time of different methods of sprint error movement.
Experiment times/time1015202530The proposed method5.348.189.9711.2312.09The method in [4]12.9813.8715.7617.0519.99The method in [5]14.7616.8018.6520.9623.57The method in [6]9.3610.3713.6814.2617.62The method in [7]6.548.9910.5712.5914.22According to the data in Table2, with the increase of the number of experiments, the detection time of different methods of sprint error action increases. When the number of experiments reaches 30, the detection time of the method in [4] is 19.99s, the detection time of the method in [5] is 23.57s, and the detection time of the proposed method is only 12.09s. Therefore, compared with the methods in [4] and [5], the detection time of the proposed method is shorter. Reference [6] also obtained relatively good results, but compared with this paper, it took a slightly longer time at Time 15 and Time 25.


## 5.1. Experimental Environment and Data

In order to verify the effectiveness of the real-time detection method for sprint errors based on visual features and the Internet of Things, the host used in this experiment is configured with Pentium(R)D CPU 2.80GH, 2.79 GHz, 2.00 GB memory, and a Laird S9028PCR with 9dBi gain UHF circularly polarized flat panel antenna and several Alien Az-9629 UHF RFID tags measuring 25.5  mm × 25.5  mm. The reader antenna is fixed on the top of the room by an aluminum alloy bracket and connected with the reader through the feeder, while the reader communicates with the notebook through the network cable. In the process of action, the user needs to hold a passive remote control to interact with the action recognition system. The simulation software is MATLAB 7.0. The three-dimensional dynamic mechanical model is used to build the kinematic model of human movement, and the three-dimensional feature parameter model is obtained. The spatial pose parameter setting of the sprint action feature kinematic model is shown in Table 1.Table 1
Spatial pose parameters of the kinematic model of sprint movement characteristics.
iqi/rαi/rαi′/mmdi/mmBM1q1−π/211−π/4,π/22q2−π/2−π/210−π/4,π/23q3−π/2π/201−28π/18,π/24q4−π/2000.79π/365q5π/2100.56/18In Table1, i represents the serial number of the parameter, qi and αi, respectively, represent the arc of the space position during sprinting, the unit is r, αi′ and di, respectively, represent the distance of the space position during sprinting, the unit is mm, and BM represents the constraint of sprint movement.According to the above-mentioned three-dimensional model parameter setting, the visual feature collection of the sprint motion image is performed, and the image stabilization sensitivity of the sprint motion visual feature collection and jitter is −130 Bm, the resolution is 0.5 m, and the pixel value is 540×400. The tones of the misoperation recognition of sprinting are quantified into 16 levels. Based on the step response, the disturbance signal of fault action is added. When the time is close to the 70s, the disturbance feature with an amplitude of 1 is added. The disturbance pulse is collected for 1s to describe the disturbance feature of the sprint image. After binarization and Susan wavelet operator processing in the rectangular region, the noise interference is eliminated by link domain analysis and median filtering. When Susan is less than the threshold, the point is judged as an edge point, and the image is filtered. Based on the above simulation environment and parameter setting, the original three-dimensional visual image of sprint posture is obtained as Figure5.Figure 5
Original sprint image.It can be seen from the analysis of Figure5 that the original sprint image contains some fault action features. In order to correct the sprint posture, it is necessary to recognize and extract the fault action features. In this paper, the three-dimensional visual detection method based on edge detection in the Contourlet domain is used to analyze the visual features of sprint error actions, and the edge detection algorithm is used to extract the edge contour features. The extraction results of sprint error actions are shown in Figure 6.Figure 6
Extraction results of short-run error action.It can be seen from the analysis of Figure6 that the real-time detection method based on visual features and the Internet of Things can effectively achieve the feature extraction and detection of sprint error movement and improve the judgment ability of sprint movement.


## 5.2. Comparison of Error Detection Accuracy in Sprint

In order to further test the performance of the proposed method, the methods in [4] and [5] are, respectively, used to compare the three-dimensional vision of sprint error action under contour wave domain edge detection, and the detection accuracy of sprint error action of different methods is obtained as shown in Figure 7.Figure 7
Comparison of detection accuracy of different methods of sprint error movement.It can be seen from the analysis of Figure7 that when the number of experiments is 30, the average detection accuracy of the method in [4] is 81%, the average detection accuracy of the method in [5] is 62%, and the average detection accuracy of the proposed method is as high as 93%. Therefore, compared with the methods in [4] and [6], the average detection accuracy of the proposed method is higher, which can effectively improve the detection accuracy of sprint error because the proposed method uses three-dimensional visual features to extract the movement characteristics of sprinters and formally describes the rules of sprinting mistakes, so as to improve the detection accuracy of sprinting mistakes.


## 5.3. Comparison of the Stability of the Error Movement Detection in Sprint

We further verify the detection stability of the real-time detection method of sprint error action based on visual features and Internet of Things, respectively, use the methods in [4] and [5] and the proposed method for comparison, and get the comparison results of the detection stability of different methods of sprint error action as shown in Figure 8.Figure 8
Comparison results of sprint error detection stability of different methods.The analysis of Figure8 shows that when the number of experiments is 30, the stability of the average sprint error detection of the method in [4] is 63%, the stability of the average sprint error detection of the method in [5] is 80%, and the stability of the average sprint error detection of the proposed method is as high as 97%. Therefore, compared with the methods in [4] and [6], the proposed method has better stability in the detection of running errors.


## 5.4. Comparison of Detection Time of Sprint Error Movement

On this basis, the detection time of the real-time detection method of sprint error action based on visual features and the Internet of Things is verified. The methods in [4] and [5] and the proposed method are, respectively, used for comparison. The detection time of sprint error action of different methods is compared as shown in Table 2.Table 2
Comparison of detection time of different methods of sprint error movement.
Experiment times/time1015202530The proposed method5.348.189.9711.2312.09The method in [4]12.9813.8715.7617.0519.99The method in [5]14.7616.8018.6520.9623.57The method in [6]9.3610.3713.6814.2617.62The method in [7]6.548.9910.5712.5914.22According to the data in Table2, with the increase of the number of experiments, the detection time of different methods of sprint error action increases. When the number of experiments reaches 30, the detection time of the method in [4] is 19.99s, the detection time of the method in [5] is 23.57s, and the detection time of the proposed method is only 12.09s. Therefore, compared with the methods in [4] and [5], the detection time of the proposed method is shorter. Reference [6] also obtained relatively good results, but compared with this paper, it took a slightly longer time at Time 15 and Time 25.


## 6. Conclusion

In this paper, inspired by IoT technology, the real-time detection method of sprint fault action based on visual features and the Internet of Things is proposed, which gives full play to the advantages of visual features and Internet of Things technology. The detection accuracy of sprint fault action is high, which can effectively shorten the detection time of sprint fault action, and has good detection stability. However, in the process of real-time detection of sprint fault action, this method does not consider dimension reduction to deal with the characteristics of sprint fault action, so as to reduce the amount of storage and computation. Therefore, in the next step of the research, we reduce the dimension of sprint fault action features and further improve the three-dimensional visual detection model to make the detection results more accurate.



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*Source: 2136776-2021-08-04.xml*