A focal length calibration method and system for large-scale binocular vision measurement cameras

Abstract

The present application discloses a focal length calibration method and system for a large-scale binocular vision measurement camera, and relates to the field of binocular vision detection. The method includes using Zhang's calibration method to calibrate the left and right cameras in the binocular vision measurement camera respectively; making a length stick with both ends of the target being a sector; placing the length stick at a preset position, and obtaining the length stick image taken by the left and right cameras; respectively establishing the spatial point coordinate expressions of the sector corner points at both ends of the length stick containing the effective focal length of the camera, and using the spatial point coordinate expressions to determine the corner point distance expressions of the sectors at both ends of the length stick; setting the corner point distance expression equal to the actual distance between the sector corner points at both ends of the length stick, and obtaining the camera focal length inverse calculation expression; according to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, using the camera focal length inverse calculation expression, the effective focal length of the left and right cameras is obtained. The present application can simplify the camera focal length calibration process and improve the universality of visual measurement.

Description

Technical Field

[0001] The present application relates to the field of binocular vision detection, and in particular to a method and system for calibrating the focal length of a large-scale binocular vision measurement camera. Background Art

[0002] The main principle of binocular vision measurement is to obtain image information from the camera and obtain the geometric information of three-dimensional objects in the real world through corresponding image processing methods. The relationship between the coordinates of the points on the three-dimensional object in the image and the three-dimensional coordinates of the surface of the three-dimensional object in the real world is determined by the imaging geometry model of the camera. The parameters of this geometry model are the parameters of the camera. It mainly includes the internal and external parameters of the camera and the distortion parameters. The process of solving these parameters is camera calibration.

[0003] Camera calibration is a bridge between the coordinates of a point in the real world and the pixel coordinates of a point in a computer vision image. Camera calibration is a very critical link in computer vision measurement technology. The accuracy of the calibration result and the stability of the algorithm directly affect the final computer vision measurement results. The camera intrinsic parameters are parameters related to the camera's own characteristics, such as the camera's focal length, pixel size, etc.; the camera extrinsic parameters are parameters in the world coordinate system, such as the camera's position, rotation direction, etc. The camera intrinsic parameters and camera distortion parameters are determined by the camera lens, and the camera extrinsic parameters are determined by the positional relationship between the camera's camera station and the object being measured.

[0004] Since the calibration method of small-scale visual measurement camera is relatively mature and easy to operate, the parameters of small-scale visual measurement camera calibration are often selected in the actual large-scale measurement process. The pixel size and camera distortion parameters in the camera internal parameters are caused by the camera's own assembly and manufacturing errors. They are inherent parameters and will not change much in the large-scale visual measurement process. However, the effective focal length of the camera may change significantly, causing a large error in the measurement. Therefore, the effective focal length of the camera needs to be calibrated again in the large-scale visual measurement process.

[0005] Traditional camera effective focal length calibration requires the use of precise three-dimensional coordinate measurement systems such as total stations to set a large number of control points on the surface of the structure being measured for camera calibration. The calibration process is cumbersome. At the same time, instruments such as total stations are inconvenient to carry and expensive, which has a great impact on the universality of visual measurement. Summary of the invention

[0006] The purpose of this application is to provide a large-scale binocular vision measurement camera focal length calibration method and system, which can simplify the camera focal length calibration process and improve the universality of visual measurement.

[0007] To achieve the above objectives, this application provides the following solutions.

[0008] In a first aspect, the present application provides a large-scale binocular vision measurement camera focal length calibration method, comprising: using Zhang's calibration method to calibrate the left and right cameras in the binocular vision measurement camera respectively, and obtaining the internal and external parameters of the left and right cameras; the visual measurement scale range of the binocular vision measurement camera is greater than a preset value; making a length stick with both end targets being fan-shaped; placing the length stick at a preset position, and using the binocular vision measurement camera to shoot the length stick to obtain the length stick image shot by the left and right cameras; respectively extracting the three-dimensional coordinates of the corner point positions of the sectors at both ends of the length stick in the length stick images shot by the left and right cameras; respectively establishing spatial point coordinate expressions of the corner points of the sectors at both ends of the length stick, and using the spatial point coordinate expressions to determine the corner point distance expressions of the sectors at both ends of the length stick; the spatial point coordinate expressions contain the effective focal length of the camera; setting the corner point distance expression equal to the actual distance between the corner points of the sectors at both ends of the length stick, and obtaining the camera focal length inverse calculation expression; according to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, using the camera focal length inverse calculation expression, the effective focal length of the left and right cameras is obtained.

[0009] In the second aspect, the present application provides a large-scale binocular vision measurement camera focal length calibration system, which is used to execute the above-mentioned large-scale binocular vision measurement camera focal length calibration method, and the large-scale binocular vision measurement camera focal length calibration system includes: a binocular vision measurement camera, a length rod and a computer; the targets at both ends of the length rod are both fan-shaped; the binocular vision measurement camera is connected to the computer; the computer uses Zhang's calibration method to calibrate the left and right cameras in the binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras; the binocular vision measurement camera is used to shoot the length rod at a preset position to obtain the length rod images shot by the left and right cameras; the computer is used to obtain the effective focal length of the left and right cameras according to the internal and external parameters of the left and right cameras and the length rod images shot by the left and right cameras.

[0010] According to the specific embodiments provided in this application, this application discloses the following technical effects.

[0011] The present application provides a large-scale binocular vision measurement camera focal length calibration method and system, which manufactures a length rod with fan-shaped targets at both ends. The length rod is used as a calibration object of known length. Based on the fact that the distance between the targets of the length rod in the measured space is equal to the actual length of the length rod, the effective focal length of the camera can be inversely calculated. This overcomes the defects of the traditional camera effective focal length calibration, which requires the use of a precise three-dimensional coordinate measurement system such as a total station to set a large number of control points on the surface of the measured structure for camera calibration, and the cumbersome calibration process, and simplifies the camera focal length calibration process; and does not require the assistance of other spatial coordinate measuring instruments (such as total stations, laser trackers, etc.), thereby increasing the universality of binocular vision three-dimensional space point coordinate measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 The present invention is a flowchart of a method for calibrating the focal length of a large-scale binocular vision measurement camera in one embodiment of the present application.

[0014] Figure 2 A schematic diagram of the shape of a length rod provided in another embodiment of the present application.

[0015] Figure 3 for Figure 2 A partial enlarged schematic diagram of the target surface I of the medium-length rod.

[0016] Figure 4 A schematic diagram of binocular vision measurement focal length calibration provided in another embodiment of the present application.

[0017] Figure 5 A schematic diagram of binocular stereoscopic vision point coordinate measurement provided by another embodiment of the present application.

[0018] Figure 6 A schematic diagram of a simplified process of calibrating a focal length of a large-scale binocular vision measurement camera provided in another embodiment of the present application. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0021] Since the effective focal length of the camera changes with the image depth during large-scale visual measurement, it is necessary to recalibrate the effective focal length of the camera. Figure 1 As shown, the present application provides a large-scale binocular vision measurement camera focal length calibration method, including the following steps 101 to 107.

[0022] Step 101: using Zhang's calibration method to calibrate the left and right cameras in a binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras; the visual measurement scale range of the binocular vision measurement camera is greater than a preset value.

[0023] Step 102: Make a long rod with fan-shaped targets at both ends.

[0024] Step 103: placing a length stick at a preset position, and using the binocular vision measurement camera to photograph the length stick, to obtain images of the length stick photographed by the left and right cameras.

[0025] Step 104: extracting the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick images taken by the left and right cameras respectively.

[0026] Step 105: Establish spatial point coordinate expressions of the corner points of the sectors at both ends of the length rod respectively, and use the spatial point coordinate expressions to determine the corner point distance expressions of the sectors at both ends of the length rod. The spatial point coordinate expressions include the effective focal length of the camera.

[0027] Step 106: Let the corner point distance expression be equal to the actual distance between the fan-shaped corner points at both ends of the length rod to obtain the inverse expression of the camera focal length.

[0028] Step 107: According to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, the effective focal lengths of the left and right cameras are obtained by using the camera focal length inverse calculation expression.

[0029] The implementation of the above steps 101 to 107 overcomes the defects of the traditional camera effective focal length calibration, which requires the use of a precise three-dimensional coordinate measurement system such as a total station to set a large number of control points on the surface of the measured structure for camera calibration, and the cumbersome calibration process, thereby simplifying the camera focal length calibration process; and does not require the assistance of other spatial coordinate measuring instruments (such as a total station, a laser tracker, etc.), thereby increasing the universality of binocular vision three-dimensional space point coordinate measurement.

[0030] The method of the present application is suitable for the focal length calibration and calibration of large-scale binocular vision measurement cameras.

[0031] In another exemplary embodiment of the present application, the spatial posture of the camera is first obtained by Zhang's calibration method, and the above step 101 is replaced by the following steps 201 to 203.

[0032] Step 201: Set up a binocular vision measurement camera.

[0033] Step 202: calibrate the region of interest in the left and right images captured by the binocular vision measurement camera.

[0034] Step 203: Using Zhang's calibration method in the calibrated region of interest, the internal and external parameters of the binocular vision measurement camera are calibrated using a plane checkerboard plate to obtain the internal and external parameters of the left and right cameras in the binocular vision measurement camera.

[0035] The detailed implementation process of step 201 to step 203 is as follows: set up the binocular vision measurement system, select a fixed-focus lens with a focal length suitable for close-range conditions for the binocular vision measurement camera, set up the binocular vision measurement camera towards the object to be measured under close-range conditions, connect the binocular vision measurement system, and start the binocular vision measurement system. In order to avoid the problem of too large a field of view and too small a calibration plate, the region of interest (ROI) is calibrated according to the position of the measured point in the left and right images, so that the calibration plate occupies more than 2 / 3 of the calibrated ROI. Through Zhang's calibration method, the binocular vision measurement camera is calibrated at close range using a plane checkerboard plate to obtain the internal and external parameters of the left and right cameras in the binocular vision measurement camera at this time, and the distortion parameters, rotation matrix, and translation matrix of the left and right cameras are recorded.

[0036] In another exemplary embodiment of the present application, in order to select a suitable fixed-focus lens, after the above step 101, the method may further include the following steps 301 and 302.

[0037] Step 301: According to the lateral size of the imaging target surface of the camera, the object distance and the field width, according to the formula and , calculate the initial value of the camera lens focal length; where, and are the initial values ​​of the focal lengths of the left and right cameras, and are the object distances of the left and right cameras respectively (unit: mm), and are the field of view widths of the left and right cameras respectively (unit: mm), and They are the lateral dimensions (unit: mm) of the imaging target surfaces (such as CCD or CMOS sensors) of the left camera and the right camera respectively.

[0038] Step 302: The binocular vision measurement camera selects a fixed-focus lens that matches the initial focal length of the camera lens.

[0039] In another exemplary embodiment of the present application, in step 102, a length rod with both ends of the target being a fan is produced, and the shape of the length rod is as follows: Figure 2 In order to improve the dimensional accuracy of the length rod, the length rod is Figure 3 The target surface is shown in the partial enlarged view. The actual distance between the fan-shaped corner points at both ends of the length rod is known and is set to ,like Figure 4shown. Figure 4 P1 and P2 are the fan-shaped corner points at both ends of the length rod, and O1 and O2 are the optical centers of the left and right cameras.

[0040] In another exemplary embodiment of the present application, in step 103, the preset position of the length rod is any position in the measured space, and the length rod is placed so that the target surface of the length rod faces the direction of the camera.

[0041] In another exemplary embodiment of the present application, in order to extract the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick image taken by the left and right cameras, the image edge detection method is used to obtain the three-dimensional coordinates of the corner points of the length stick, and step 104 can be replaced by the following steps 401 to 402.

[0042] Step 401: using an edge detection algorithm to detect two fan-shaped edge lines in the target surface on both sides of the length stick in the length stick images taken by the left and right cameras.

[0043] Step 402: Identify the intersection of the two edge lines as the corner point of the length stick fan, and determine the intersection coordinates as the three-dimensional coordinates of the corner point positions of the fan at both ends of the length stick in the length stick images captured by the left and right cameras.

[0044] In another exemplary embodiment of the present application, from the geometric relationship between the left and right cameras and the corner points, it can be known that the spatial point coordinate expressions of the fan-shaped corner points at both ends of the length rod are as follows.

[0045] .

[0046] .

[0047] in, is the three-dimensional coordinate of the fan-shaped corner point at one end of the length rod, is the three-dimensional coordinate of the fan-shaped corner point at the other end of the length rod, B is the baseline distance between the left and right cameras, and The left and right camera optical axes are Axis angle, and The left and right camera optical axes are Axis angle, is the coordinate of the left camera on the Y axis, is the coordinate of the right camera on the Y axis, and are the effective focal lengths of the left and right cameras, respectively.

[0048] Exemplarily, a spatial point coordinate expression including the focal length of the camera can be obtained according to the accuracy analysis model of the binocular vision measurement system, and the spatial point coordinate expression is expressed by a collinear equation.

[0049] To simplify the analysis, assume that the two cameras are placed horizontally. The optical axes of the left and right cameras in the above formula are The axis angle is , the left and right camera optical axes and The axis angle is ,like Figure 5 shown. Figure 5 P(x,y,z) is the position coordinate of the measured point. is the position coordinate of the left camera Coordinates on the axis.

[0050] In another exemplary embodiment of the present application, according to the distance formula between two points, the expression for the distance between the corner points of the sectors at both ends of the length rod is as follows.

[0051] .

[0052] in, It is the actual distance between the fan-shaped corner points at both ends of the length rod.

[0053] In another exemplary embodiment of the present application, the effective focal length of the dual cameras can be calculated by reverse calculation based on the binocular vision three-dimensional space point measurement that the distance between the corner points of the sectors at both ends of the length rod in the measured space is equal to the actual distance of the length rod target. The specific implementation process of the above step 107 to obtain the effective focal length of the left and right cameras is as follows.

[0054] Step 501: Taking the position of any one of the left and right cameras as the origin of the world coordinate system, according to the internal and external parameters of the left and right cameras and based on the parallax triangle principle, obtain the coordinates of the position of the other camera in the left and right cameras and the coordinates of the optical center points of the left and right cameras.

[0055] Step 502: Based on the coordinates of the optical center points of the left and right cameras, use the formula , calculate the baseline distance between the left and right cameras; where, is the coordinate of the optical center of any camera in the left and right cameras, is the coordinate of the optical center of the other camera in the left and right cameras.

[0056] Step 503: According to the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick image taken by the other camera of the left and right cameras and the baseline distance of the left and right cameras, the effective focal length of the other camera of the left and right cameras is obtained by using the camera focal length inverse calculation expression.

[0057] For example, when any one of the left and right cameras is the left camera and the other camera is the right camera, in the process of obtaining the effective focal length of the right camera, the position coordinates of the left camera are (0, 0, 0) and the position coordinates of the right camera are ( XR , Y R , Z R ), the spatial point coordinate expressions of the fan-shaped corner points at both ends of the length rod are as follows.

[0058] and .

[0059] In another exemplary embodiment of the present application, in order to improve the calibration accuracy of the effective focal length, multiple camera effective focal length calibration operations are performed, and the average value of the effective focal length is used as the two effective focal length values ​​of the final dual cameras (left and right cameras). After the above step 107, the method may also include: changing the preset position of the length stick for multiple times, and after each change of the preset position, returning to the step of "placing the length stick at the preset position, and using the binocular vision measurement camera to shoot the length stick, and obtaining the length stick image shot by the left and right cameras", to obtain multiple effective focal lengths of the left and right cameras, and taking the average value of the multiple effective focal lengths of the left and right cameras as the final effective focal length of the left and right cameras.

[0060] Taking the example of 3 preset positions of the length rod, the effective focal lengths of the left and right cameras are calculated respectively, and then the average of the effective focal lengths of the left and right cameras is calculated respectively. The final effective focal lengths of the left and right cameras are , It is expressed as follows.

[0061] .

[0062] .

[0063] in, and Indicates the effective focal length of the left and right cameras when the length bar is in the first preset position. and Indicates the effective focal length of the left and right cameras when the length bar is in the second preset position. and Indicates the effective focal length of the left and right cameras when the length stick is in the third preset position.

[0064] This method can effectively improve the calibration accuracy of the camera focal length. At the same time, it does not require the assistance of other spatial coordinate measuring instruments (such as total stations, laser trackers, etc.), which increases the universality of binocular vision three-dimensional space point coordinate measurement.

[0065] Figure 6The figure is a brief flow chart of a large-scale binocular vision measurement camera focal length calibration method. T1: Build a calibration platform and start the equipment. T2: Use Zhang's camera calibration method to calibrate the internal and external parameters of the camera. T3: Make a length stick, make targets on both sides of the length stick, and measure the actual distance. T4: Use binocular vision to detect the corner points of the targets on both sides of the length stick and calculate the distance between the two corner points. T5: Make the distance of the binocular vision detection target equal to the actual distance of the length stick, and calculate the effective focal length of the camera. T6: Repeat the calculation steps of the effective focal length, and calculate the average value of the effective focal length as the final effective focal length. Among them, the equipment mentioned in T1 is a binocular vision measurement system, and the distance of the binocular vision detection target in T5 refers to the distance between the two corner points.

[0066] The main principle of this application is to first obtain the spatial position and initial focal length of the camera through Zhang's calibration method, and express the spatial point coordinate expression by the collinear equation. The spatial point coordinate expression represents the distance between the corner points of the sectors at both ends of the length rod, and the spatial point coordinate expression is equal to the distance value of the corner points of the sectors at both ends of the length rod obtained by the laser rangefinder, and the effective focal length of the camera is calculated in reverse, which solves the problem of the effective focal length calibration of the camera by the traditional method.

[0067] This application can calibrate the camera focal length without contact, is simple to operate, easy to use, and more accurate than traditional camera calibration methods.

[0068] Based on the same inventive concept, the embodiment of the present application also provides a large-scale binocular vision measurement camera focal length calibration system for implementing the large-scale binocular vision measurement camera focal length calibration method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more large-scale binocular vision measurement camera focal length calibration system embodiments provided below can refer to the limitations of the large-scale binocular vision measurement camera focal length calibration method above, and will not be repeated here.

[0069] In an exemplary embodiment, a large-scale binocular vision measurement camera focal length calibration system is provided, including: a binocular vision measurement camera, a length stick, and a computer. The targets at both ends of the length stick are fan-shaped; the binocular vision measurement camera is connected to the computer; the computer uses Zhang's calibration method to calibrate the left and right cameras in the binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras; the binocular vision measurement camera is used to shoot the length stick at a preset position to obtain the length stick images shot by the left and right cameras; the computer is used to obtain the effective focal lengths of the left and right cameras according to the internal and external parameters of the left and right cameras and the length stick images shot by the left and right cameras.

[0070] As an optional implementation, the computer specifically includes: a calibration module, a corner point coordinate extraction module, a corner point distance determination module, an inverse calculation expression acquisition module and an effective focal length acquisition module.

[0071] The calibration module is used to calibrate the left and right cameras in the binocular vision measurement camera respectively by using Zhang's calibration method to obtain the internal and external parameters of the left and right cameras.

[0072] The corner point coordinate extraction module is used to respectively extract the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick images taken by the left and right cameras.

[0073] The corner point distance determination module is used to establish the spatial point coordinate expressions of the fan-shaped corner points at both ends of the length rod, which contain the effective focal length of the camera, and use the spatial point coordinate expressions to determine the corner point distance expressions of the fan-shaped corner points at both ends of the length rod.

[0074] The inverse calculation expression obtaining module is used to make the corner point distance expression equal to the actual distance between the fan-shaped corner points at both ends of the length rod, and obtain the camera focal length inverse calculation expression.

[0075] The effective focal length acquisition module is used to obtain the effective focal lengths of the left and right cameras according to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner points, using the camera focal length inverse calculation expression.

[0076] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A large-scale binocular vision measurement camera focal length calibration method, characterized in that: include: The left and right cameras in the binocular vision measurement camera are calibrated respectively by using Zhang's calibration method to obtain the internal and external parameters of the left and right cameras; the visual measurement scale range of the binocular vision measurement camera is greater than a preset value; Make a long rod with both ends of the target being fan-shaped; Place a length stick at a preset position, and use the binocular vision measurement camera to shoot the length stick to obtain images of the length stick shot by the left and right cameras; The three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick images taken by the left and right cameras are respectively extracted; Establishing spatial point coordinate expressions of the corner points of the sectors at both ends of the length rod respectively, and using the spatial point coordinate expressions to determine the corner point distance expressions of the sectors at both ends of the length rod; the spatial point coordinate expressions include the effective focal length of the camera; Let the corner point distance expression be equal to the actual distance between the fan-shaped corner points at both ends of the length stick, and obtain the inverse expression of the camera focal length; According to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, the effective focal lengths of the left and right cameras are obtained by using the camera focal length inverse calculation expression; According to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, the effective focal lengths of the left and right cameras are obtained by using the camera focal length inverse calculation expression, which specifically includes: Taking the position of any one of the left and right cameras as the origin of the world coordinate system, according to the internal and external parameters of the left and right cameras and based on the parallax triangle principle, the coordinates of the position of the other camera in the left and right cameras and the coordinates of the optical center of the left and right cameras are obtained; According to the coordinates of the optical center of the left and right cameras, use the formula , calculate the baseline distance between the left and right cameras; where, is the coordinate of the optical center of any camera in the left and right cameras, is the coordinate of the optical center of the other camera in the left and right cameras, B is the baseline distance between the left and right cameras; According to the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick image taken by the other camera of the left and right cameras and the baseline distance of the left and right cameras, the effective focal length of the other camera of the left and right cameras is obtained by using the camera focal length inverse calculation expression; Extract the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick images taken by the left and right cameras, specifically including: The edge detection algorithm is used to detect two edge straight lines of the fan-shaped target surface on both sides of the length stick in the length stick images taken by the left and right cameras; The intersection of the two edge lines is identified as the corner point of the length stick fan, and the intersection coordinates are determined as the three-dimensional coordinates of the corner point positions of the fans at both ends of the length stick in the length stick images taken by the left and right cameras.

2. The large-scale binocular vision measurement camera focal length calibration method according to claim 1, characterized in that: The Zhang calibration method is used to calibrate the left and right cameras in the binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras, and then it also includes: According to the lateral size of the camera's imaging target surface, object distance and field of view width, according to the formula and , calculate the initial value of the camera lens focal length; where, and are the initial values ​​of the focal lengths of the left and right cameras, and are the object distances of the left and right cameras, respectively. and are the field of view widths of the left and right cameras, respectively. and are the lateral dimensions of the imaging target surfaces of the left camera and the right camera respectively; The binocular vision measurement camera uses a fixed-focus lens that meets the initial focal length value of the camera lens.

3. The large-scale binocular vision measurement camera focal length calibration method according to claim 1, characterized in that: The spatial point coordinate expressions of the fan-shaped corner points at both ends of the length rod are: ； ； in, is the three-dimensional coordinate of the fan-shaped corner point at one end of the length rod, is the three-dimensional coordinate of the fan-shaped corner point at the other end of the length rod, B is the baseline distance between the left and right cameras, and The left and right camera optical axes are Axis angle, and The left and right camera optical axes are Axis angle, is the coordinate of the left camera on the Y axis, is the coordinate of the right camera on the Y axis, and are the effective focal lengths of the left and right cameras, respectively.

4. The large-scale binocular vision measurement camera focal length calibration method according to claim 3, characterized in that: The expression for the distance between the corner points of the sectors at both ends of the length bar is: ； in, It is the actual distance between the fan-shaped corner points at both ends of the length rod.

5. The large-scale binocular vision measurement camera focal length calibration method according to claim 1, characterized in that: According to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner point positions, the effective focal lengths of the left and right cameras are obtained by using the camera focal length inverse calculation expression, and then the following is also included: The preset position of the length stick is changed multiple times, and after each change of the preset position, the method returns to the step of "placing the length stick at the preset position, and using the binocular vision measurement camera to shoot the length stick, and obtaining the length stick images shot by the left and right cameras", to obtain multiple effective focal lengths of the left and right cameras, and the average value of the multiple effective focal lengths of the left and right cameras is used as the final effective focal length of the left and right cameras.

6. The large-scale binocular vision measurement camera focal length calibration method according to claim 1, characterized in that: The Zhang calibration method is used to calibrate the left and right cameras in the binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras, including: Set up binocular vision measurement camera; Mark the region of interest in the left and right images taken by the binocular vision measurement camera; In the calibrated area of ​​interest, Zhang's calibration method is used to calibrate the internal and external parameters of the binocular vision measurement camera using a plane checkerboard plate to obtain the internal and external parameters of the left and right cameras in the binocular vision measurement camera.

7. A large-scale binocular vision measurement camera focal length calibration system, characterized in that: The large-scale binocular vision measurement camera focal length calibration system is used to perform the large-scale binocular vision measurement camera focal length calibration method according to any one of claims 1 to 6, and the large-scale binocular vision measurement camera focal length calibration system comprises: a binocular vision measurement camera, a length rod and a computer; The targets at both ends of the length rod are both fan-shaped; The binocular vision measurement camera is connected to the computer; The computer uses Zhang's calibration method to calibrate the left and right cameras in the binocular vision measurement camera respectively to obtain the internal and external parameters of the left and right cameras; The binocular vision measurement camera is used to photograph the length stick at a preset position to obtain the length stick images photographed by the left and right cameras; The computer is used to obtain the effective focal lengths of the left and right cameras according to the internal and external parameters of the left and right cameras and the length bar images taken by the left and right cameras.

8. The large-scale binocular vision measurement camera focal length calibration system according to claim 7, characterized in that: The computer specifically includes: A calibration module is used to calibrate the left and right cameras in the binocular vision measurement camera respectively by using Zhang's calibration method to obtain the internal and external parameters of the left and right cameras; A corner point coordinate extraction module is used to extract the three-dimensional coordinates of the corner points of the sectors at both ends of the length stick in the length stick images taken by the left and right cameras respectively; A corner point distance determination module is used to establish spatial point coordinate expressions of the corner points of the sectors at both ends of the length rod, and determine the corner point distance expressions of the sectors at both ends of the length rod using the spatial point coordinate expressions; the spatial point coordinate expressions include the effective focal length of the camera; The inverse calculation expression obtaining module is used to make the corner point distance expression equal to the actual distance between the fan-shaped corner points at both ends of the length rod, and obtain the camera focal length inverse calculation expression; The effective focal length acquisition module is used to obtain the effective focal lengths of the left and right cameras according to the internal and external parameters of the left and right cameras and the three-dimensional coordinates of the corner points, using the camera focal length inverse calculation expression.

Images