A method for estimating the speed of a moving target

Abstract

The present invention discloses a method for estimating the speed of a moving target. The built-in parameters of the camera can be easily obtained and only the information of two points is required to determine them, which greatly simplifies the process of obtaining the built-in parameters. In the case of a certain inclination angle, the monocular camera can still perform ranging, and the ranging scenario of the monocular camera is extended to most monitoring places. At the same time, in the case of a certain inclination angle, the monocular camera can still estimate the speed of an object, and the speed measurement scenario of the monocular camera is extended to most monitoring places.

Description

Technical Field

[0001] The present invention relates to the technical field of speed calculation, and in particular to a method for estimating the speed of a moving target based on a monitoring camera. Background Art

[0002] Object speed measurement technology can be divided into many types according to the hardware it relies on. Common types include radar speed measurement, coil speed measurement, sonic speed measurement, laser speed measurement, and video speed measurement. Video speed measurement is to analyze the object in the continuously shot pictures to obtain the real-time speed of the object. Video speed measurement technology includes two main parts: distance measurement and speed calculation. According to different distance measurement principles, video speed measurement technology can be further divided into many types.

[0003] Currently, most cameras used in distance measurement applications are binocular cameras, which can measure the depth and distance of objects through the BM algorithm or SGBM algorithm. In special application scenarios, such as autonomous driving of vehicles, the position and angle of the monocular camera will be specially set to calculate the distance to the vehicle in front through simple geometric principles.

[0004] In other simple applications of monocular camera speed measurement, a grid is drawn on the camera screen in advance. The pixel distance between the grids corresponds to the actual distance, and the actual speed is calculated by counting the number of grids crossed by the object within a certain period of time.

[0005] For monocular cameras, the most common method is to use simple geometric principles to measure distance and realize real-time speed calculation. The process mainly includes four steps: camera parameter acquisition, target recognition, horizontal distance measurement and real-time speed calculation. Figure 6 , Figure 7 , as follows:

[0006] (1) Camera parameter acquisition:

[0007] Here, the object / person height h 0 , the distance d from the object / person to the camera 0 、The pixel height w of the object / person in the picture after the camera images 0 All are known. According to the properties of similar triangles, the focal length f of the camera can be obtained as follows:

[0008]

[0009] Among them, α is the actual height of the image corresponding to the unit pixel. Further, the following formula can be obtained:

[0010]

[0011] (2) Target Identification:

[0012] For the identification of specific objects / people, we can use classic target detection algorithms such as Yolov5 to detect and obtain the pixel position (x l,t ,y l,t ,x r,t ,y r,t ), where (x l,t ,y l,t ) is the coordinate of the upper left corner of the detection box, (x r,t ,y r,t ) is the coordinate of the lower right corner of the detection box.

[0013] (3) Horizontal distance measurement:

[0014] According to the second step target detection result (x l,t ,y l,t ,x r,t ,y r,t ), we can get the pixel height w of the person in the camera image r ,as follows:

[0015] w r =y r,t -y l,t

[0016] Using the properties of similar triangles, we can get the actual distance d from the object / person to the camera at time t: t as follows:

[0017]

[0018] (4) Real-time speed calculation:

[0019] According to the calculation formula in the third step, the actual distance d from the object / person to the camera at time t can be obtained: t and the actual distance d from the object / person to the camera at time t+1 t+1 The expressions are as follows:

[0020]

[0021] and

[0022]

[0023] Assuming that the time interval between time t and time t+1 is T, the average speed S of the object / person in this time interval is:

[0024]

[0025] As long as the time interval is small enough, the average speed can be regarded as the real-time speed.

[0026] It can be seen that when a monocular camera is currently used for speed measurement, the speed calculation of the object / personnel depends on the realization of distance measurement. The distance measurement is calculated by the similar right triangle properties between the person and the camera, and the camera and the internal image. When the camera angle is not horizontal, a right triangle cannot be formed between the person and the camera, and the distance cannot be obtained by the properties of similar triangles. In addition, cameras with inclinations are widely used in various monitoring occasions, and the current method of speed measurement using a monocular camera will fail when facing a camera with a certain inclination. Therefore, the current method of speed measurement using a monocular camera can only be applied to special scenarios and cannot be widely used.

[0027] Therefore, how to provide a speed estimation method suitable for use in speed measurement scenarios with a monocular camera with an inclination is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the invention

[0028] In view of the above problems, the present invention provides a moving object speed estimation method for overcoming the above problems or at least partially solving the above problems.

[0029] The present invention provides the following scheme:

[0030] A moving target speed estimation method, comprising:

[0031] Get the image of the target area captured by the camera;

[0032] Determine the pixel coordinates of the midpoint of the picture and the pixel coordinates of the edge point of the picture, wherein the midpoint of the picture is the intersection of the horizontal midline and the vertical midline of the picture, and the edge point of the picture is the intersection of the vertical midline and the bottom edge line of the picture;

[0033] Get the height h from the camera to the ground 1 , the horizontal distance d from the edge of the picture to the camera 1 , the horizontal distance d from the midpoint of the picture to the edge point of the picture 2 , the pixel distance from the edge point of the picture to the midpoint of the picture is w;

[0034] Using the h 1 , the 1 , the 2 And the straight-line distance d from the midpoint of the picture to the camera is obtained by calculating w c , the focal length f of the camera and the actual height α of the imaging corresponding to the unit pixel of the camera;

[0035] Detecting a moving target in a first target image using a target detection network to obtain a first target detection frame; the first target image is an image of the target area at the tth moment acquired by the camera;

[0036] Get the pixel coordinates of the first target point and the pixel distance w from the first target point to the midpoint of the picture 1 , the first target point is the midpoint of the bottom edge of the first target detection frame;

[0037] Using the pixel coordinates of the first target point, the f, the α, the w 1 、 1 , the 1 , the 2 Calculate the actual horizontal distance d from the object / person to the camera at time t result,t ;

[0038] Detecting the moving target in the second target image using the target detection network to obtain a second target detection frame; the second target image is an image of the target area at the t+1th moment acquired by the camera;

[0039] Get the pixel coordinates of the second target point and the pixel distance w from the second target point to the midpoint of the picture 2 , the second target point is the midpoint of the bottom edge of the second target detection frame;

[0040] Using the pixel coordinates of the second target point, the f, the α, the w 2 、 1 , the 1 , the 2 Calculate the actual horizontal distance d from the object / person to the camera at time t+1 result,t+1 ;

[0041] Using the d result,t And the result,t+1 The speed of the moving target is obtained by calculating the time interval between the tth moment and the t+1th moment.

[0042] Preferably: the h is obtained by direct measurement 1 , the 1 , the 2 ; said d c Obtained by the following formula:

[0043]

[0044] Preferably: the f is calculated by the following formula:

[0045]

[0046] The relationship between f and α is expressed by the following formula:

[0047]

[0048] Where, d h For the edge points of the picture, make a perpendicular c The line segment of the edge, the d e is the straight-line distance d from the edge of the image to the camera e .

[0049] Preferably: the d h Obtained by the following formula:

[0050]

[0051] The d e Obtained by the following formula:

[0052]

[0053] Preferably: 1 Obtained by the following formula:

[0054] w 1 =y c -y t

[0055] Where: y c is the pixel y-axis coordinate of the midpoint of the image, t is the y-axis coordinate of the lower right corner of the first target detection box.

[0056] Preferably: the d result,t Obtained by the following formula:

[0057] d result,t =d 1 +d 2 -d horizental

[0058] Where: d horizental is the horizontal distance between the first target point and the midpoint of the picture.

[0059] Preferably: the d horizental Obtained by the following formula:

[0060]

[0061]

[0062] Where: strightis the straight-line distance between the first target point and the camera, and d target To make a perpendicular line from the first target point to d c The length of the line segment on the edge.

[0063] Preferably: the average speed s within the time interval is calculated as the speed of the moving object.

[0064] Preferably, the average speed s is obtained by the following formula:

[0065]

[0066] Where T is the time interval between time t and time t+1.

[0067] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0068] The embodiment of the present application provides a method for estimating the speed of a moving target. The method is convenient for obtaining the built-in parameters of the camera, and only requires information from two points to determine, which greatly simplifies the process of obtaining the built-in parameters. In the case of a certain inclination angle, the monocular camera can still perform ranging, and the ranging scene of the monocular camera is extended to most monitoring places. At the same time, in the case of a certain inclination angle, the monocular camera can still estimate the speed of the object, and the speed measurement scene of the monocular camera is extended to most monitoring places.

[0069] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0071] Figure 1 1 is a schematic diagram of obtaining the relevant parameters (α, f) of a tilt camera provided by an embodiment of the present invention;

[0072] Figure 2 is a schematic diagram of solving the target point (midpoint at the bottom of the detection frame) provided by an embodiment of the present invention;

[0073] Figure 3 is a triangular schematic diagram of a calculation process provided by an embodiment of the present invention;

[0074] Figure 4 is a schematic diagram of selecting a midpoint and an edge point of a picture provided by an embodiment of the present invention;

[0075] Figure 5 is a schematic diagram of the bottom midpoint of the detection frame provided by an embodiment of the present invention;

[0076] Figure 6 It is a schematic diagram of obtaining camera parameters (α, f) in the prior art;

[0077] Figure 7 It is a schematic diagram of horizontal distance measurement in the prior art. DETAILED DESCRIPTION

[0078] The technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0079] See also Figure 1 , is a moving target speed estimation method provided by an embodiment of the present invention, such as Figure 1 As shown, the method may include:

[0080] Get the image of the target area captured by the camera;

[0081] Determine the pixel coordinates of the midpoint of the picture and the pixel coordinates of the edge point of the picture, wherein the midpoint of the picture is the intersection of the horizontal midline and the vertical midline of the picture, and the edge point of the picture is the intersection of the vertical midline and the bottom edge line of the picture;

[0082] Get the height h from the camera to the ground 1 , the horizontal distance d from the edge of the picture to the camera 1 , the horizontal distance d from the midpoint of the picture to the edge point of the picture 2 , the pixel distance from the edge point of the picture to the midpoint of the picture is w; specifically, the h is obtained by direct measurement method 1 , the 1 , the 2 ; said d c Obtained by the following formula:

[0083]

[0084] Using the h 1 , the 1 , the 2 And the straight-line distance d from the midpoint of the picture to the camera is obtained by calculating w c, the focal length f of the camera and the actual height α of the imaging corresponding to the unit pixel of the camera; specifically, f is calculated by the following formula:

[0085]

[0086] The relationship between f and α is expressed by the following formula:

[0087]

[0088] Where, d h For the edge points of the picture, make a perpendicular c The line segment of the edge, the d e is the straight-line distance d from the edge of the image to the camera e .

[0089] The d h Obtained by the following formula:

[0090]

[0091] The d e Obtained by the following formula:

[0092]

[0093] Detecting a moving target in a first target image using a target detection network to obtain a first target detection frame; the first target image is an image of the target area at the tth moment acquired by the camera;

[0094] Get the pixel coordinates of the first target point and the pixel distance w from the first target point to the midpoint of the picture 1 , the first target point is the midpoint of the bottom edge of the first target detection frame; specifically, the w 1 Obtained by the following formula:

[0095] w 1 =y c -y t

[0096] Where: y c is the pixel y-axis coordinate of the midpoint of the image, t is the y-axis coordinate of the lower right corner of the first target detection box.

[0097] Using the pixel coordinates of the first target point, the f, the α, the w 1 、 1 , the 1 , the 2 Calculate the actual horizontal distance d from the object / person to the camera at time t result,tSpecifically, the d result,t Obtained by the following formula:

[0098] d result,t =d 1 +d 2 -d horizental

[0099] Where: d horizental is the horizontal distance between the first target point and the midpoint of the picture.

[0100] The d horizental Obtained by the following formula:

[0101]

[0102]

[0103] Where: stright is the straight-line distance between the first target point and the camera, and d target To make a perpendicular line from the first target point to d c The length of the line segment on the edge.

[0104] Detecting the moving target in the second target image using the target detection network to obtain a second target detection frame; the second target image is an image of the target area at the t+1th moment acquired by the camera;

[0105] Get the pixel coordinates of the second target point and the pixel distance w from the second target point to the midpoint of the picture 2 , the second target point is the midpoint of the bottom edge of the second target detection frame;

[0106] Using the pixel coordinates of the second target point, the f, the α, the w 2 、 1 , the 1 , the 2 Calculate the actual horizontal distance d from the object / person to the camera at time t+1 result,t+1 ;

[0107] Using the d result,t And the result,t+1 The speed of the moving target is obtained by calculating the time interval between the tth moment and the t+1th moment.

[0108] Furthermore, the average speed s within the time interval is calculated as the speed of the moving target.

[0109] The average speed s is obtained by the following formula:

[0110]

[0111] Where T is the time interval between time t and time t+1.

[0112] The moving target speed estimation method provided in the embodiment of the present application can use the relevant properties of similar triangles and right triangles to obtain the relevant parameters of the tilted monocular camera. At the same time, the relevant properties of similar triangles and right triangles are used to obtain the distance measurement of the tilted monocular camera to a specific point in the picture. In addition, the bottom midpoint of the object detection frame can be used as the detection target point, the distance is measured for this point, the speed is calculated, and the speed of this point is used as the object speed. This method can use a monocular camera to measure the distance to a specific moving target (moving object or person) with a certain inclination angle; the monocular camera can be used to perform real-time speed detection on a specific moving target.

[0113] The method provided in the embodiments of the present application is described in detail below.

[0114] The method provided in the embodiment of the present application calculates the specific built-in parameters of the monocular camera through the relevant information of two special points in the case of an inclination. The distance measurement of the object is converted into the distance measurement of the bottom midpoint of the object, and the distance estimation of the bottom midpoint is obtained by using the relevant properties of the triangle. The speed estimation of the object is converted into the speed estimation of the bottom midpoint of the object, and the speed estimation of the bottom midpoint is obtained by using the relevant properties of the triangle.

[0115] The specific implementation mainly includes four steps: camera parameter acquisition, object / personnel target recognition, straight-line distance and horizontal distance calculation, and real-time speed calculation.

[0116] (1) Camera parameter acquisition:

[0117] Get the camera image, select the midpoint of the center line of the image as the center point of the image, and select the bottom endpoint of the center line of the image as the edge point of the image, such as Figure 4 shown.

[0118] like Figure 1 As shown, by direct measurement, the height h from the camera to the ground can be obtained 1 , the horizontal distance d from the edge of the picture to the camera 1 , the horizontal distance d from the middle point of the picture to the edge point of the picture 2 . According to the Pythagorean theorem, we can know that the straight-line distance d from the edge of the image to the camera is e for

[0119]

[0120] And the straight-line distance d from the midpoint of the picture to the camera c for

[0121]

[0122] By making a perpendicular line to the edge of the picture c The line segment on the edge where the line segment is located can obtain the length d of the line segment h for:

[0123]

[0124] It is known that the pixel distance from the edge point to the midpoint of the picture is w. At this time, it can be observed that d e and d h The right triangle on the side where is similar to the right triangle on the side where w and f are located, then the focal length f of the camera satisfies:

[0125]

[0126] Among them, α is the actual height of the image corresponding to the unit pixel. Further, the following formula can be obtained:

[0127]

[0128] (2) Object / person target recognition:

[0129] For the identification of specific objects / people, we can use classic target detection algorithms such as Yolov5 to detect and obtain the pixel position (x l,t ,y l,t ,x r,t ,y r,t ), where (x l,t ,y l,t ) is the coordinate of the upper left corner of the detection box, (x r,t ,y r,t ) is the coordinate of the lower right corner of the detection box. Assume that the pixel coordinate of the midpoint of the image is (x c ,y c ).

[0130] Further, such as Figure 5 As shown in the figure, the bottom midpoint of the detection frame represents the object / person. For simplicity, we only consider the case where the bottom midpoint of the detection frame is below the midpoint of the image. For the case where the bottom midpoint is above the midpoint of the image, similar calculations can be performed. At the tth moment, the pixel coordinates (x t ,y t ) and is the vertical pixel distance w from the point to the midpoint of the picture at time t 1 They are

[0131]

[0132] w 1 =yc -y t

[0133] (3) Calculation of straight-line distance and horizontal distance:

[0134] Now calculate the linear distance and horizontal distance from the bottom midpoint of the detection frame of a specific object / person to the camera. Figure 2 As shown, we need to find the straight-line distance d between the target point (the midpoint of the bottom of the detection frame) and the camera. stright , and the horizontal distance d between the target point and the midpoint of the picture horizental .

[0135] To make the calculation clear, the main triangle relationships are extracted, such as Figure 3 As shown, make a perpendicular line from the target point to d c The length of the line segment is d target The overall calculation process is carried out in two steps:

[0136] Calculate the angle α 1 and α 2 According to the properties of a right triangle, the included angle can be obtained by the following formula:

[0137]

[0138] Among them, w 1 is the pixel distance from the first target point to the midpoint of the picture.

[0139] Calculate the length d stright d horizental and d target According to the relevant properties of similar triangles and right triangles, the following formulas are satisfied:

[0140]

[0141] Solving the above three formulas, we can get the length d stright d horizental and d target At this time, the horizontal distance d from the target point to the camera at time t is result,t for

[0142] d result,t =d 1 +d 2 -d horizental

[0143] It is understandable that the result,t+1 The calculation method of d result,t The calculation method is the same and will not be repeated here.

[0144] (4) Real-time speed calculation:

[0145] According to the calculation formula in the third step, the actual horizontal distance d from the object / person to the camera at time t can be obtained: result,t and the actual horizontal distance d from the object / person to the camera at time t+1 result,t+1 The expressions are as follows:

[0146] d result,t =d 1 +d 2 -d horizental,t

[0147] and

[0148] d result,t+1 =d 1 +d 2 -d horizental,t+1

[0149] Assuming that the time interval between time t and time t+1 is T, the average speed s of the object / person in this time interval is:

[0150]

[0151] As long as the time interval is small enough, the average speed can be regarded as the real-time speed.

[0152] In summary, the method for estimating the speed of a moving target provided by the present application is convenient for obtaining the built-in parameters of the camera, and only requires information from two points to determine, which greatly simplifies the process of obtaining the built-in parameters. In the case of a certain inclination angle, the monocular camera can still perform ranging, and the ranging scene of the monocular camera can be extended to most monitoring places. At the same time, in the case of a certain inclination angle, the monocular camera can still estimate the speed of the object, and the speed measurement scene of the monocular camera can be extended to most monitoring places.

[0153] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0154] It can be known from the description of the above implementation methods that those skilled in the art can clearly understand that the present application can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present application or certain parts of the embodiments.

[0155] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0156] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for estimating the speed of a moving target, characterized in that, it includes: Obtain the image of the target area collected by the camera; Determine the pixel coordinates of the midpoint of the image and the pixel coordinates of the edge point of the image. The midpoint of the image is the intersection of the horizontal midline and the vertical midline of the image, and the edge point of the image is the intersection of the vertical midline and the bottom edge line of the image; Obtain the height h from the camera to the ground 1 and the horizontal distance d from the edge point of the screen to the camera 1 and the horizontal distance d from the midpoint of the screen to the edge point of the screen 2 and the pixel distance from the edge point of the screen to the midpoint of the screen is w; Using the said h 1 、the said d 1 、the said d 2 and the said w, calculate to obtain the straight-line distance d from the point on the screen to the camera c 、the focal length f of the camera and the actual height α corresponding to the imaging of a single pixel of the camera; Use the target detection network to detect the moving target in the first target image to obtain the first target detection frame; The first target image is the image of the target area at the t-th moment obtained by the camera; Obtain the pixel coordinates of the first target point and the pixel distance w from the first target point to the midpoint of the screen 1 , where the first target point is the midpoint of the bottom edge of the first target detection box; Using the pixel coordinates of the first target point, the f, the α, the w 1 , the h 1 , the d 1 , the d 2 Calculate the actual horizontal distance d from the object / person to the camera at the t-th moment result,t ; Use the target detection network to detect the moving target in the second target image to obtain the second target detection frame; The second target image is the image of the target area at the (t + 1)-th moment obtained by the camera; Obtain the pixel coordinates of the second target point and the pixel distance w from the second target point to the midpoint of the screen 2 , where the second target point is the midpoint of the bottom edge of the second target detection frame; Using the pixel coordinates of the second target point, the f, the α, the w 2 , the h 1 , the d 1 , the d 2 Calculate the actual horizontal distance d from the object / person to the camera at the (t + 1)-th moment result,t+1 ; Using the said d result,t and the said d result,t+1 Combined with the time interval between the t-th moment and the (t + 1)-th moment, the speed of the moving target is calculated and obtained.

2. The method for estimating the speed of a moving target according to claim 1, characterized in that, The h is obtained by using the direct measurement method 1 and the d 1 and the d 2 ; the d c is obtained by the following formula:

3. The method for estimating the speed of a moving target according to claim 1, characterized in that, The f is calculated by the following formula: The relationship between the f and the α is expressed by the following formula: where d h is a line segment perpendicular to the side where the screen edge point is located, and the d c is the line segment where the screen edge point is located, and the d e is the straight-line distance d from the screen edge point to the camera e .

4. The method for estimating the speed of a moving target according to claim 3, characterized in that, Said d h is obtained by the following formula: Said d e Obtained by the following formula:

5. The method for estimating the speed of a moving target according to claim 1, characterized in that, The said w 1 is obtained by the following formula: w 1 = y c -y t Where: y c is the pixel y-axis coordinate of the point in the said screen, and the said y t is the y-axis coordinate of the lower right corner of the said first target detection box.

6. The method for estimating the speed of a moving target according to claim 1, characterized in that, Said d result,t is obtained by the following formula: d result,t = d 1 + d 2 - d horizental where: d horizental is the horizontal distance between the first target point and the midpoint of the screen.

7. The method for estimating the speed of a moving target according to claim 6, characterized in that, Said d horizental is obtained by the following formula: Where: the d stright is the straight-line distance between the first target point and the camera, and the d target is the length of the line segment perpendicular to the side where d c is located, drawn from the first target point.

8. The method for estimating the speed of a moving target according to claim 1, characterized in that, Calculate the average speed s within the time interval as the speed of the moving target.

9. The method for estimating the speed of a moving target according to claim 8, characterized in that, The average speed s is obtained by the following formula: In the formula, T is the time interval between the t-th moment and the (t + 1)-th moment.

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