Industrial CT system geometric parameter calibration method and device, electronic equipment and medium

Abstract

The invention relates to the technical field of computer vision, in particular to an industrial CT system geometric parameter calibration method and device, electronic equipment and a medium. Projection data of a to-be-measured object is obtained, and a world coordinate system, a camera coordinate system and an image coordinate system are established; and completing conversion from the world coordinate system to the camera coordinate system and conversion from the camera coordinate system to the image coordinate system, constructing a projection matrix according to the first conversion relation and the second conversion relation, and solving geometric parameters of the to-be-measured object based on the projection matrix and projection data. According to the method, the problems of large error, complicated operation and the like in traditional manual measurement and die body calibration are avoided, and the accuracy and the stability of industrial CT system geometric parameter calibration are improved.

Description

Technical Field

[0001] The present application relates to the field of computer vision technology, and in particular to a method, device, electronic equipment, and medium for calibrating geometric parameters of an industrial CT system. Background Art

[0002] Industrial CT (computed tomography) systems are widely used in fields such as nondestructive testing, reverse engineering, and materials science. Their imaging quality directly depends on the precise calibration of the system's geometric parameters. Traditional calibration of geometric parameters (such as the light pipe-to-detector distance (SDD) and the light pipe-to-rotation center distance (SID)) relies on manual measurement. This manual operation is prone to measurement errors, resulting in significant deviations between parameter values ​​and their true values. These errors can also directly distort projection data, affecting the clarity and resolution of the reconstructed image.

[0003] In addition, when using a phantom (such as a spherical array) to calibrate geometric parameters, it is usually necessary to capture projection images at a specific angle and calculate the SOD (source-to-object distance) and SDD (source-to-detector distance) by establishing a geometric equation for the field of view (FOV). This requires presetting a specific angle to capture images, which is complex and easily affected by angular errors. Solving equations based on limited angles may fall into local optimality, resulting in parameter deviations. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method, device, electronic equipment and medium for calibrating geometric parameters of an industrial CT system, thereby improving the accuracy of parameter calibration.

[0005] A first aspect of the present application provides a method for calibrating geometric parameters of an industrial CT system, the method comprising: Acquire projection data of the object to be measured; Establish the world coordinate system, camera coordinate system and image coordinate system; Converting the world coordinate system to the camera coordinate system, and converting the camera coordinate system to the image coordinate system; Constructing a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system; The geometric parameters of the object to be measured are solved based on the projection matrix and the projection data.

[0006] In an optional embodiment, the method further comprises: Identifying the position of the ball on the object to be measured based on each of N angle projection images based on Hough transform, wherein the projection data includes N angle projection images, and N is determined according to the acquisition angle interval and the acquisition angle; constructing the projection matrix based on ball position information of the ball position; Solve the projection matrix to obtain the geometric parameters.

[0007] In an optional implementation, solving the projection matrix to obtain the geometric parameters includes: Determine the geometric parameters corresponding to each angle according to the projection matrix of each acquisition angle, and obtain N groups of geometric parameters; The N groups of geometric parameters are averaged to obtain the final calibrated geometric parameters of the industrial CT system.

[0008] In an optional embodiment, before averaging the N groups of geometric parameters to obtain the final calibrated geometric parameters of the industrial CT system, the method further includes: Projecting the world coordinates of the object to be measured into the image coordinate system according to the projection matrix at the current angle to obtain predicted coordinates; Determining a distance between the predicted coordinates and the actual observed coordinates, and determining the distance as a reprojection error; comparing the reprojection error with a preset threshold; When the reprojection error is greater than the preset threshold, the geometric parameters corresponding to the current angle are eliminated.

[0009] In an optional embodiment, converting the world coordinate system to the camera coordinate system includes: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ; in, is the three-dimensional coordinate point in the camera coordinate system; is the three-dimensional coordinate point in the world coordinate system; R is a 3×3 rotation matrix, which represents the rotation relationship between coordinate systems; t is a 3×1 translation vector, which represents the translation relationship between coordinate systems.

[0010] In an optional embodiment, converting the camera coordinate system to the image coordinate system includes: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ; in, H is the combined transformation moment, which is used to transform the homogeneous coordinates in the camera coordinate system Convert to homogeneous pixel coordinates in the image coordinate system ; The combined transformation moment is determined by the following formula: ; in, dx and dy For the detector x and y Pixel equivalent in direction; is the offset of the origin of the image coordinate system in the pixel coordinate system; f is the focal length of the camera.

[0011] In an optional embodiment, constructing a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system includes: Determine the first conversion relationship: ; Determine the second conversion relationship: ; The projection matrix is ​​obtained by combining the first conversion relationship and the second conversion relationship: ; Wherein, P is the projection matrix; K is the camera intrinsic parameter matrix, .

[0012] A second aspect of the present application provides a geometric parameter calibration device for an industrial CT system, the device comprising: An acquisition module, used for acquiring projection data of the object to be measured; Establish a module for establishing the world coordinate system, camera coordinate system and image coordinate system; a conversion module, configured to convert the world coordinate system into the camera coordinate system, and convert the camera coordinate system into the image coordinate system; A construction module, configured to construct a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system; A solution module is used to solve the geometric parameters of the object to be measured based on the projection matrix and the projection data.

[0013] A third aspect of the present application provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the industrial CT system geometric parameter calibration method when executing the computer program.

[0014] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the above-mentioned industrial CT system geometric parameter calibration method are implemented.

[0015] In summary, the industrial CT system geometric parameter calibration method, device, electronic device and medium provided in the present application establish a world coordinate system, a camera coordinate system and an image coordinate system by acquiring projection data, and converting the world coordinate system to the camera coordinate system, and converting the camera coordinate system to the image coordinate system. Through these two conversion relationships, a connection can be established from the position of the object to be measured in the world coordinate system to its projection position in the image coordinate system, that is, the projection matrix, which can map the three-dimensional coordinates of the object to be measured in the world coordinate system to the two-dimensional coordinates in the image coordinate system, thereby establishing a mathematical relationship between the projection data and the geometric parameters. The geometric parameters can be solved through the projection data and the projection matrix, thereby improving the accuracy and stability of the geometric parameter calibration of the industrial CT system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of a method for calibrating geometric parameters of an industrial CT system shown in an embodiment of the present application; Figure 2 is a schematic diagram of a phantom in a projection data acquisition method shown in an embodiment of the present application; Figure 3 This is a schematic diagram of establishing a world coordinate system according to an embodiment of the present application; Figure 4 This is a functional module diagram of a geometric parameter calibration device for an industrial CT system shown in an embodiment of the present application; Figure 5 This is a schematic structural diagram of an electronic device shown in an embodiment of the present application; DETAILED DESCRIPTION The present invention will be further described below with reference to the accompanying drawings and examples.

[0017] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the fact that a better connection structure can be formed by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interactively without conflicting with each other.

[0018] Reference Figure 1 , which is a flow chart of a method for calibrating geometric parameters of an industrial CT system according to an embodiment of the present application, and the method for calibrating geometric parameters of an industrial CT system includes the following steps.

[0019] S11, obtaining projection data of the object to be measured.

[0020] In order to facilitate understanding of the inventive concept of this application, the object to be measured in the following embodiments is described by taking a mold with spirally arranged steel balls as an example.

[0021] In some embodiments, reference is made to Figure 2 The object to be measured, i.e., a mold with spirally arranged steel balls, can be placed on the scanning platform. The scanning ring rotates the detector at evenly spaced angles. The detector scans data at arbitrary evenly spaced intervals to obtain multiple sets of projection data. These sets of projection data are collected by rotating the detector at preset angle intervals (e.g., 1° or 0.5°). These multiple sets of projection data serve as input for subsequent geometric parameter calculations. The scanning range is not required to be 360°.

[0022] If the scanning ring collects 180° at intervals of 1°, 180 projection images are collected as projection data; if the scanning ring collects 270° at intervals of 0.5°, 540 projection images are collected as projection data.

[0023] By acquiring projection data, which is the two-dimensional image information obtained after the object to be measured is scanned by X-rays in the industrial CT system, it reflects the projection conditions of the object to be measured at different angles.

[0024] S12, establishing a world coordinate system, a camera coordinate system, and an image coordinate system.

[0025] In some embodiments, the electronic device can construct a world coordinate system, a camera coordinate system, and an image coordinate system. ) can be used as a reference to describe the spatial relationship between the detector and the object to be measured, and the position of the world coordinate system can be freely determined according to actual conditions. Figure 3 The origin of the world coordinate system is the phantom origin of the object to be measured. The steel balls are arranged spirally along its Z axis. The phantom origin is also the center point of the phantom imaging range.

[0026] Camera coordinate system ( ) The coordinate origin is the position of the detector's ray source, that is, the position where the light tube emits rays. The XY plane is parallel to the detector plane, and the Z axis is perpendicular to the detector plane.

[0027] Image coordinate system ( u , v ) includes the image physical coordinate system and the image pixel coordinate system. The ratio between the image physical coordinate system and the image pixel coordinate system is positively correlated with the detector pixel size. Here, the actual size of an object in the image = detector pixel size * the number of pixels occupied by the object.

[0028] S13, converting the world coordinate system into the camera coordinate system, and converting the camera coordinate system into the image coordinate system.

[0029] Since the position of the oblique line source is different from the position of the world coordinate origin and there is an angle deviation, the electronic device converts the world coordinate system into the camera coordinate system based on the rigid body transformation. That is, the relationship between the world coordinate system and the camera coordinate system is actually a rigid body rotation + translation transformation.

[0030] Specifically, the electronic device converts the world coordinate system into the camera coordinate system through rigid body transformation, where the rigid body transformation formula is expressed as follows: ; in, 、 、 represents the position of the camera coordinate system, 、 、 Represents the position of the world coordinate system, R represents the rotation matrix, and t represents the translation matrix.

[0031] To facilitate calculation and transformation, the above transformation relationship can be expressed in homogeneous coordinate form: ; in, is a 3 × 1 zero vector. The three-dimensional coordinate point in the world coordinate system is transformed to the camera coordinate system by multiplying it with the extrinsic parameter matrix (that is, the rotation matrix R and the translation matrix t).

[0032] At the same time, electronic devices are based on the camera focal length f and origin offset Build the combined transformation matrix H , by combining the transformation matrices H Convert the camera coordinate system to the image coordinate system. The combined transformation matrix H As shown below: ; in, dx and dy Indicates that the detector is x and y Pixel equivalent in direction, and Respectively represent the coordinates of the camera center in the pixel coordinate system.

[0033] By combining the transformation matrices H Project the three-dimensional coordinate point in the camera coordinate system to the two-dimensional pixel coordinate point in the image coordinate system .

[0034] Among them, the combined transformation matrix H Used to convert the homogeneous coordinates in the camera coordinate system Convert to homogeneous pixel coordinates in the image coordinate system , that is, .

[0035] When calculating specifically, first use the focal length of the camera f Project the point in the camera coordinate system to the normalized image plane, and then combine it with the detector pixel size dx and dy and origin offset and , get the final pixel coordinates, that is, the two-dimensional pixel coordinate points in the image coordinate system .

[0036] By establishing a world coordinate system, a camera coordinate system, and an image coordinate system, and converting the world coordinate system to the camera coordinate system, and vice versa, a connection can be established from the position of the object to be measured in the world coordinate system to its projected position in the image coordinate system.

[0037] S14: construct a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system.

[0038] Determine the three-dimensional coordinate point in the world coordinate system , the camera's rotation matrix R, the translation vector t, the camera's focal length f (i.e., SDD), the detector's pixel equivalents dx and dy in the horizontal and vertical directions, and the offset of the image coordinate system's origin in the pixel coordinate system , electronic devices can build a projection matrix based on this Determine the first transformation relationship (world coordinate system to camera coordinate system): ; Determine the second transformation relationship (camera coordinate system to image coordinate system): ; After merging, the matrix form of the second transformation relationship, that is, the projection matrix, is: ; Wherein, P is the projection matrix, which is used to describe the complete projection process from the world coordinate system to the image coordinate system; K is the camera intrinsic parameter matrix, .

[0039] S15, solving geometric parameters of the object to be measured based on the projection matrix and the projection data.

[0040] After obtaining the projection matrix, the electronic device can use the least squares method to solve the geometric parameters based on the collected projection data according to the projection matrix equation, including the distance SID from the light pipe to the rotation center, the distance SDD from the light pipe to the detector, the detector offset and the detector rotation angle.

[0041] In an optional embodiment, the method further comprises: Identifying the position of the ball on the object to be measured based on each of N angle projection images based on Hough transform, wherein the projection data includes N angle projection images, and N is determined according to the acquisition angle interval and the acquisition angle; constructing the projection matrix based on ball position information of the ball position; Solve the projection matrix to obtain the geometric parameters.

[0042] In some embodiments, the electronic device performs a circle finding operation. Specifically, based on the Hough transform algorithm, the positions of the balls (e.g., 12 balls) on the object to be measured are identified in the collected projection data (i.e., N angle projection images), and the coordinates of each ball in the image coordinate system are obtained. and the coordinates in the world coordinate system The scanning process is dynamic, and no dynamic threshold is used to segment the image. Instead, the Hough transform is directly applied to perform circle finding.

[0043] Next, the solution and parameter separation operations are performed. Specifically, for each angle projection image collected at each angle, the position information of the ball is used to construct an overdetermined set of equations containing geometric parameters, and the solution is used to obtain a 3×4 projection matrix. In other words, for each ball, the following projection equation can be established: ; Among them, P is a 3×4 projection matrix, is the scale factor.

[0044] Assuming there are 12 balls, we can solve 12 equations simultaneously. Since each equation has two independent constraints ( and ), so at least 6 points (12 equations) are required to uniquely determine the 11 degrees of freedom of P (the rank of P is 11). By expanding the equation into a system of linear equations, P can be solved by the least squares method or other numerical methods. Specifically, P can be expanded into a vector , then construct the linear equation system Ap=b, where A is the matrix constructed from the spherical coordinates and b is the vector constructed from the image coordinates. Next, use singular value decomposition (SVD) or other numerical methods to solve for p, thus obtaining the projection matrix P.

[0045] Among them, the projection matrix P can be decomposed into: ; By using RQ decomposition (or a variant of QR decomposition) to decompose the first 3 columns of P into KR, where K is an upper triangular matrix and R is an orthogonal matrix. The translation vector t can be extracted from the 4th column of P as follows: Then, the electronic device can extract the focal length f (also known as SDD), the principal point coordinates and other internal parameters from K, and extract the detector rotation angle (Euler angle or quaternion) and translation (SID is usually reflected in the z component of t, i.e. =SID).

[0046] Furthermore, the electronic device can also perform re-projection error analysis and screening operations. Specifically, for each angle projection image, the projection matrix P at the current angle is used to calculate the re-projection error. , project the world coordinates of the object to be measured into the image coordinate system, that is, multiply the world coordinates by the calculated projection matrix to obtain the predicted position pre of the world coordinates in the image coordinate system, and then calculate the Euclidean distance between the actual observation point pob in the image coordinates and the predicted position pre, and the Euclidean distance is called the reprojection error. If the reprojection error is greater than a preset threshold (for example, 5), it is determined that there is an error in the projection image of this angle, and the geometric parameters corresponding to this angle are eliminated and do not participate in the calculation of the final geometric parameters.

[0047] Finally, the electronic equipment can calculate the geometric parameter results. Specifically, if the scanning ring collects 180° at intervals of 1°, a total of 180 angle projection images are obtained. For each angle projection, the above-mentioned ball finding, solution and parameter separation, reprojection error analysis and screening operations are repeated. If the 180 sets of geometric parameters solved are all less than or equal to the preset threshold, 180 sets of geometric parameters are finally obtained. The average value of these 180 sets of geometric parameters is taken as the final calibrated geometric parameters of the industrial CT system, where SID is reflected in the t matrix of the projection matrix. If there are M groups of geometric parameters greater than the preset threshold, 180-M groups of geometric parameters are finally obtained.

[0048] Reference Figure 4 , which is a functional module diagram of the geometric parameter calibration device of the industrial CT system shown in an embodiment of the present application.

[0049] In some embodiments, the industrial CT system geometric parameter calibration device 40 may include multiple functional modules composed of computer program segments. The computer program of each program segment of the industrial CT system geometric parameter calibration device 40 may be stored in the memory of an electronic device and executed by at least one processor to perform (see Figure 1(Description) The function of calibrating the geometric parameters of an industrial CT system. It can be divided into multiple functional modules based on the functions it performs. These functional modules may include: an acquisition module 401, a creation module 402, a conversion module 403, a construction module 404, a solution module 405, and a screening module 406. A module, as referred to herein, refers to a series of computer program segments that can be executed by at least one processor and perform a fixed function, and is stored in a memory. In this embodiment, the functions of each module will be described in detail in subsequent embodiments.

[0050] The acquisition module 401 is used to acquire projection data of the object to be measured.

[0051] The establishment module 402 is used to establish a world coordinate system, a camera coordinate system and an image coordinate system.

[0052] The conversion module 403 is configured to convert the world coordinate system into the camera coordinate system, and convert the camera coordinate system into the image coordinate system.

[0053] The construction module 404 is configured to construct a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system.

[0054] The solving module 405 is configured to solve the geometric parameters of the object to be measured based on the projection matrix and the projection data.

[0055] The solution module 405 is further used to: identify the position of the ball on the object to be measured based on each of N angle projection images in the Hough transform, where the projection data includes N angle projection images, and N is determined according to the acquisition angle interval and the acquisition angle; construct the projection matrix based on the ball position information of the ball position; and solve the projection matrix to obtain the geometric parameters.

[0056] The solution module 405 is further specifically configured to: determine the geometric parameters corresponding to each acquisition angle according to the projection matrix of each acquisition angle to obtain N groups of geometric parameters; and average the N groups of geometric parameters to obtain the final calibrated geometric parameters of the industrial CT system.

[0057] The screening module 406 is used to: project the world coordinates of the object to be measured into the image coordinate system according to the projection matrix of the current angle to obtain predicted coordinates; determine the distance between the predicted coordinates and the actual observed coordinates, and determine the distance as the reprojection error; compare the reprojection error with a preset threshold; when the reprojection error is greater than the preset threshold, eliminate the geometric parameters corresponding to the current angle.

[0058] The conversion module 403 is further specifically configured to: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ; in, is the three-dimensional coordinate point in the camera coordinate system; is the three-dimensional coordinate point in the world coordinate system; R is a 3×3 rotation matrix, which represents the rotation relationship between coordinate systems; t is a 3×1 translation vector, which represents the translation relationship between coordinate systems.

[0059] The conversion module 403 is further specifically configured to: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ; in, H is the combined transformation moment, which is used to transform the homogeneous coordinates in the camera coordinate system Convert to homogeneous pixel coordinates in the image coordinate system ; The combined transformation moment is determined by the following formula: ; in, dx and dy For the detector x and y Pixel equivalent in direction; is the offset of the origin of the image coordinate system in the pixel coordinate system; f is the focal length of the camera.

[0060] The construction module 404 is further specifically configured to: Determine the first conversion relationship: ; Determine the second conversion relationship: ; The projection matrix is ​​obtained by combining the first conversion relationship and the second conversion relationship: ; Wherein, P is the projection matrix; K is the camera intrinsic parameter matrix, .

[0061] It should be understood that the various variations and specific embodiments of the industrial CT system geometric parameter calibration method provided in the above embodiments are also applicable to the industrial CT system geometric parameter calibration device of this embodiment. Through the above detailed description of the industrial CT system geometric parameter calibration method, those skilled in the art can clearly understand the implementation method of the industrial CT system geometric parameter calibration device in this embodiment. For the sake of brevity of the specification, it will not be described in detail here.

[0062] See Figure 5 FIG. 1 is a schematic diagram of the structure of an electronic device according to an embodiment of the present application. In a preferred embodiment of the present application, the electronic device 5 includes a memory 51 , at least one processor 52 and at least one communication bus 53 .

[0063] Those skilled in the art should understand that Figure 5 The structure of the electronic device shown does not constitute a limitation of the embodiments of the present application, and can be either a bus structure or a star structure. The electronic device 5 can also include more or less other hardware or software than shown in the figure, or a different component arrangement.

[0064] In some embodiments, the electronic device 5 is a device capable of automatically performing numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application-specific integrated circuits, programmable gate arrays, digital processors, and embedded devices. The electronic device 5 may also include user devices, which include but are not limited to any electronic product capable of human-computer interaction with a user via a keyboard, mouse, remote control, touchpad, or voice-controlled device, such as a personal computer, tablet computer, smartphone, digital camera, etc.

[0065] In the above embodiments provided in the present application, it should be understood that the disclosed methods, devices, computer-readable storage media, and electronic devices can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the modules is merely a logical function division. In actual implementation, there may be other division methods, such as multiple components or modules can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or components or modules, which can be electrical, mechanical or other forms.

[0066] The components described as separate parts may or may not be physically separate, and the components shown as components may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of these components may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0067] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each component may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.

[0068] If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0069] It should be noted that for the aforementioned method embodiments, for ease of description, they are all expressed as a series of action combinations. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, because according to the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0070] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0071] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for calibrating geometric parameters of an industrial CT system, characterized in that: The method comprises: Acquire projection data of the object to be measured; Establish the world coordinate system, camera coordinate system and image coordinate system; Converting the world coordinate system to the camera coordinate system, and converting the camera coordinate system to the image coordinate system; Constructing a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system; The geometric parameters of the object to be measured are solved based on the projection matrix and the projection data.

2. The method for calibrating geometric parameters of an industrial CT system according to claim 1, wherein: The method further comprises: Identifying the position of the ball on the object to be measured based on each of N angle projection images based on Hough transform, wherein the projection data includes N angle projection images, and N is determined according to the acquisition angle interval and the acquisition angle; constructing the projection matrix based on ball position information of the ball position; Solve the projection matrix to obtain the geometric parameters.

3. The method for calibrating geometric parameters of an industrial CT system according to claim 2, wherein: Solving the projection matrix to obtain the geometric parameters includes: Determine the geometric parameters corresponding to each angle according to the projection matrix of each acquisition angle, and obtain N groups of geometric parameters; The N groups of geometric parameters are averaged to obtain the final calibrated geometric parameters of the industrial CT system.

4. The method for calibrating geometric parameters of an industrial CT system according to claim 3, wherein: Before averaging the N groups of geometric parameters to obtain the final calibrated geometric parameters of the industrial CT system, the method further includes: Projecting the world coordinates of the object to be measured into the image coordinate system according to the projection matrix at the current angle to obtain predicted coordinates; Determining a distance between the predicted coordinates and the actual observed coordinates, and determining the distance as a reprojection error; comparing the reprojection error with a preset threshold; When the reprojection error is greater than the preset threshold, the geometric parameters corresponding to the current angle are eliminated.

5. The method for calibrating geometric parameters of an industrial CT system according to claim 1, wherein: The converting the world coordinate system to the camera coordinate system comprises: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ； in, is the three-dimensional coordinate point in the camera coordinate system; is the three-dimensional coordinate point in the world coordinate system; R is a 3×3 rotation matrix, which represents the rotation relationship between coordinate systems; t is a 3×1 translation vector, which represents the translation relationship between coordinate systems.

6. The method for calibrating geometric parameters of an industrial CT system according to claim 1, wherein: The converting the camera coordinate system to the image coordinate system comprises: The three-dimensional coordinate point of the world coordinate system is converted to the camera coordinate system using the following formula: ； in, H is the combined transformation moment, which is used to transform the homogeneous coordinates in the camera coordinate system Convert to homogeneous pixel coordinates in the image coordinate system ; The combined transformation moment is determined by the following formula: ； in, dx and dy For the detector x and y Pixel equivalent in direction; is the offset of the origin of the image coordinate system in the pixel coordinate system; f is the focal length of the camera.

7. The method for calibrating geometric parameters of an industrial CT system according to claim 1, wherein: The constructing of a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system includes: Determine the first conversion relationship: ； Determine the second conversion relationship: ； The projection matrix is ​​obtained by combining the first conversion relationship and the second conversion relationship: ； Wherein, P is the projection matrix; K is the camera intrinsic parameter matrix, .

8. A geometric parameter calibration device for an industrial CT system, characterized in that: The device comprises: An acquisition module, used for acquiring projection data of the object to be measured; Establish a module for establishing the world coordinate system, camera coordinate system and image coordinate system; a conversion module, configured to convert the world coordinate system into the camera coordinate system, and convert the camera coordinate system into the image coordinate system; A construction module, configured to construct a projection matrix according to a first transformation relationship from the world coordinate system to the camera coordinate system and a second transformation relationship from the camera coordinate system to the image coordinate system; A solution module is used to solve the geometric parameters of the object to be measured based on the projection matrix and the projection data.

9. An electronic device, characterized in that: The method comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for calibrating geometric parameters of an industrial CT system according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for calibrating geometric parameters of an industrial CT system according to any one of claims 1 to 7 are implemented.

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