A 3D camera extrinsic parameter calibration method, device, system and medium

Abstract

The application discloses a 3D camera external parameter calibration method, device, system and medium, the method obtains the point cloud image information of a standard ball photographed by a 3D camera, fits the standard ball to obtain the three-dimensional coordinates of the ball center of a space ball model and the diameter; the three-dimensional coordinates of the ball center of the standard ball and the diameter are measured by a measuring device; after the data are one-to-one corresponding, matrix conversion is carried out, and the external parameter of the 3D camera relative to the measuring device is obtained. It can meet the demand of external parameter calibration of devices or sensors such as a three-coordinate measuring machine which cannot obtain images.

Description

Technical Field

[0001] This invention belongs to the field of extrinsic parameter calibration technology, and specifically relates to a 3D camera extrinsic parameter calibration method, device, system and medium. Background Technology

[0002] Compared to conventional cameras, 3D cameras can acquire 3D point clouds of object surfaces, providing a more intuitive representation of the object's 3D shape. They are widely used in tasks such as object pose estimation and 3D detection in fields like autonomous driving, industrial robotics, and VR. The extrinsic parameters of a 3D camera are coordinate transformation matrices representing the relative position and orientation of the 3D camera with respect to other devices or sensors. This can be represented by a 3×3 rotation matrix R and a 3D translation vector S. Calibrating the extrinsic parameters of a 3D camera involves calculating the transformation relationship between the 3D coordinates of the point cloud captured by the 3D camera in the camera coordinate system and the coordinate systems of other devices or sensors. This is essentially the process of calculating the aforementioned rotation matrix and translation vector, a prerequisite for the 3D camera to work collaboratively with other devices or sensors.

[0003] Current 3D camera extrinsic parameter calibration often uses the Zhang Zhengyou calibration method, which uses a checkerboard calibration board as an intermediate coordinate system between the camera coordinate system and the world coordinate system, and performs calibration based on pairwise coordinate transformations. While the transformation from the 3D camera coordinate system to the calibration board coordinate system is relatively easy to solve, for devices or sensors such as coordinate measuring machines (CMMs) that cannot directly acquire images, it is impossible to calculate their coordinate transformations to the calibration board coordinate system. Therefore, it is not easy to solve the 3D camera extrinsic parameter calibration problem in the coordinate systems of these devices or sensors using traditional methods. Summary of the Invention

[0004] To address the difficulty in converting the coordinate system of a device or sensor to that of a calibration board when calibrating the extrinsic parameters of a 3D camera for devices or sensors that cannot acquire images, such as coordinate measuring machines, in existing methods, this invention provides a 3D camera extrinsic parameter calibration method, device, system, and medium.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The first aspect of this invention discloses a method for calibrating the extrinsic parameters of a 3D camera, comprising the following steps:

[0007] Acquire point cloud image information captured by a 3D camera, wherein the point cloud image information includes at least three standard spheres and the centers of all standard spheres lie on at least two three-dimensional straight lines;

[0008] In the point cloud image information, spatial sphere models of all standard spheres are sequentially fitted and extracted, and the three-dimensional coordinates and diameter of the center of each spatial sphere model are calculated.

[0009] Obtain the three-dimensional coordinates and diameter of the center of the standard sphere corresponding to each standard in the image information, as measured by the measuring device;

[0010] The correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere is determined based on the diameter of the space sphere model and the diameter of the standard sphere.

[0011] Based on the correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere, the transformation matrix between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere is calculated to obtain the extrinsic parameters of the 3D camera relative to the measuring device.

[0012] In one possible design, the step of sequentially fitting and extracting spatial sphere models of all standard spheres from the point cloud image information and calculating the three-dimensional coordinates of the center and diameter of each spatial sphere model includes:

[0013] A. Fit and extract a spatial sphere model of a standard sphere from the point cloud image information;

[0014] B. Based on the points in the spatial sphere model, calculate the three-dimensional coordinates of the center of the spatial sphere model and its diameter;

[0015] C. Remove the point cloud data used in step A to fit the spatial sphere model from the point cloud image information;

[0016] D. Repeat steps A, B, and C until the three-dimensional coordinates and diameters of N spatial sphere models are obtained, where N is the number of standard spheres in the image information.

[0017] In one possible design, the correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere is determined by using an index sorting method for the diameter of the space sphere model and the diameter of the standard sphere.

[0018] In one possible design, the correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere is determined by indexing the diameters of the space sphere model and the standard sphere, including:

[0019] The three-dimensional coordinate indexes of the center of the space sphere model and the center of the standard sphere are determined based on the diameter of the space sphere model and the diameter of the standard sphere, respectively.

[0020] The correspondence between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere is established based on the three-dimensional coordinate index of the center of the spatial sphere model and the three-dimensional coordinate index of the center of the standard sphere.

[0021] In one possible design, the step of calculating the transformation matrix of the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere based on the correspondence between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere, and obtaining the extrinsic parameters of the 3D camera relative to the measuring device, includes: calculating the average value of the three-dimensional coordinates of the centers of all spatial sphere models and the average value of the three-dimensional coordinates of the centers of all standard spheres column by column, to obtain the coordinates of the center point of the spatial sphere model and the center point of the standard sphere;

[0022] Calculate the difference between the three-dimensional coordinates of the center of each spatial sphere model and the coordinates of the center point of the spatial sphere model, and the difference between the three-dimensional coordinates of the center of each standard sphere and the coordinates of the center point of the standard sphere. Perform matrix multiplication on the two differences to obtain a matrix.

[0023] Perform singular value decomposition on the matrix to obtain the transpose of the left singular matrix and the right singular matrix;

[0024] Calculate the rotation matrix based on the transpose of the left and right singular matrices;

[0025] Calculate the translation vector based on the rotation matrix, the center point of the spatial sphere model, and the center point of the standard sphere.

[0026] The second aspect of the present invention discloses a 3D camera extrinsic parameter calibration device, comprising a memory and a controller connected in sequence. The memory stores a computer program, and the controller is used to read the computer program and execute a 3D camera extrinsic parameter calibration method as described in the first aspect and any of its possibilities.

[0027] A third aspect of this invention discloses a 3D camera extrinsic parameter calibration system, comprising:

[0028] There are at least three standard spheres, and all the standard spheres lie on at least two three-dimensional straight lines;

[0029] A 3D camera, the 3D camera being used to capture point cloud image information of the calibration sphere;

[0030] A measuring device for measuring the three-dimensional coordinates of the center and the diameter of the standard sphere;

[0031] A 3D camera extrinsic parameter calibration device as described in the second aspect, wherein the 3D camera extrinsic parameter calibration device is signal-connected to the 3D camera and the measuring device.

[0032] In one possible design, the standard ball is connected to the base via a connector.

[0033] In one possible design, the measuring device is a device or sensor that cannot acquire images.

[0034] The fourth aspect of the present invention discloses a computer-readable storage medium storing instructions that, when executed on a computer, perform a 3D camera extrinsic parameter calibration method as described in the first aspect and any of its possibilities.

[0035] Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

[0036] This solution fits a standard sphere from the image information captured by a 3D camera into a spatial sphere model. By performing a transformation matrix on the three-dimensional coordinates of the center of the spatial sphere model and the center of the standard sphere measured by the measuring device, the extrinsic parameters of the 3D camera relative to the measuring device are obtained, thus meeting the extrinsic parameter calibration requirements of the 3D camera in the coordinate system of devices or sensors that cannot acquire images, such as coordinate measuring machines. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of the external parameter calibration method of the present invention;

[0039] Figure 2 This is a schematic diagram of the calibration device. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0041] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0043] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] The first aspect of this invention discloses a 3D camera extrinsic parameter calibration method, which facilitates high-efficiency and high-precision extrinsic parameter calibration of 3D cameras when calibrated in coordinate systems of devices or sensors that cannot acquire images, such as coordinate measuring machines. This method can be, but is not limited to, executed by a single 3D camera extrinsic parameter calibration device. This device can be software or a combination of software and hardware, and can be integrated into smart devices such as mobile terminals, tablets, computers, and servers. Specifically, the 3D camera extrinsic parameter calibration method includes steps S01 to S05. It should be noted that steps S01 to S05 are not restrictive in terms of their order; they are merely for identification purposes, and the order of the steps is primarily determined by the sequence of signals described.

[0047] Step S01: Obtain point cloud image information captured by a 3D camera. The point cloud image information includes at least three standard spheres and the centers of all standard spheres are located on at least two three-dimensional straight lines.

[0048] The standard sphere here is an auxiliary device. To facilitate the placement of the standard sphere, it can be supported by the base 1 and the connecting part 2, with the connecting part 2 connecting the base 1 and the standard sphere 3. The standard sphere, base 1, and connecting part 2 together constitute the calibration device. The calibration device includes at least three standard spheres, and the centers of all standard spheres lie on at least two three-dimensional straight lines; that is, the centers of all standard spheres cannot lie on only one three-dimensional straight line. When performing extrinsic parameter calibration, at least three standard spheres of the calibration device must be placed within the field of view of the 3D camera, and these at least three standard spheres must lie on at least two three-dimensional straight lines.

[0049] The base of the calibration device provides a carrier and support for all components. The standard sphere is the core component of the calibration device, providing the diameter and center coordinates for the entire system. All parts should be made of rigid materials, and the material and color of the standard sphere should ensure that its surface can be captured and measured by the 3D camera and the equipment or sensor to be calibrated.

[0050] The calibration device includes at least three standard spheres. Of course, to improve calibration accuracy, the number of standard spheres can be appropriately increased, and the standard spheres should be appropriately distributed along as many three-dimensional straight lines as possible. In a specific setup, such as... Figure 2 The calibration device shown illustrates a schematic diagram using 12 white standard spheres that do not readily reflect light. The spheres are arranged in an array of 4 rows and 3 columns, with each row gradually decreasing in height from one end to the other. The largest standard sphere has a diameter of Φ63mm, and the diameters of adjacent standard spheres differ by 3mm. During installation, the calibration device should be positioned such that each standard sphere is within the camera's field of view.

[0051] Step S02: Sequentially fit and extract spatial sphere models of all standard spheres from the point cloud image information and calculate the three-dimensional coordinates and diameter of the center of each spatial sphere model.

[0052] Specifically, this step can be implemented through steps S021 to S024.

[0053] Step S021: The Random Sample Consensus (RANSAC) algorithm can be used to first fit and extract a spatial sphere model of a standard sphere from the point cloud image information.

[0054] Step S022: Based on the space sphere model, the three-dimensional coordinates and diameter of the center of the space sphere model can be calculated using the least squares method.

[0055]

[0056] Where, x i y i , z i To extract the 3D coordinates of the i-th point in the point cloud of the sphere, d is the diameter of the spatial sphere model.

[0057] This yields the three-dimensional coordinates and diameter of the first spatial sphere model. To facilitate the establishment of the correspondence between the two-dimensional array and the diameter, a two-dimensional array can be used for storage, or a table can be used for storage. Preferably, this solution uses a two-dimensional array to illustrate specific implementation methods. The three-dimensional coordinates and diameter can then be stored row-wise in a two-dimensional array [x,y,z,d].

[0058] Step S023: At this time, delete the point cloud of the spatial sphere model obtained by fitting above from the point cloud image information, and update to obtain a new captured point cloud.

[0059] Step S024: Repeat steps S021 to S023 until a two-dimensional array of size N×4 containing the three-dimensional coordinates and diameters of N spatial sphere models is obtained, where N is the number of standard spheres in the image information.

[0060] Step S03: Obtain the three-dimensional coordinates and diameter of the center of each standard sphere measured by the measuring device.

[0061] The measuring device in this step can be not only an existing device or sensor that can acquire images, but also a device or sensor that cannot acquire images, such as a coordinate measuring machine. Of course, to simplify the calibration method, other existing methods can also be used to calibrate the external parameters for devices or sensors that can acquire images.

[0062] Specifically, taking a coordinate measuring machine (CMM) as an example, the three-dimensional coordinates and diameter of the center of each standard sphere are measured using the image information from the CMM, resulting in a two-dimensional array of size N×4 containing the three-dimensional coordinates and diameter of the standard sphere's center. For instance, if the calibration device contains 5 spheres, but only 3 standard spheres are within the field of view of the 3D camera during calibration, then it is sufficient to use the CMM to measure the standard spheres within the 3D camera's field of view.

[0063] Step S04: Determine the correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere based on the diameter of the space sphere model and the diameter of the standard sphere.

[0064] This step can be achieved by using an index sorting method based on the diameters of the space sphere model and the standard sphere, or by other methods, to determine the correspondence between the three-dimensional coordinates of the center of the space sphere model and the three-dimensional coordinates of the center of the standard sphere. Specifically, the index sorting can be either ascending or descending.

[0065] The index-based sorting method is as follows: First, determine the three-dimensional coordinate indices of the center of the space sphere model and the standard sphere based on their respective diameters. Then, establish the correspondence between the three-dimensional coordinates of the center of the space sphere model and the standard sphere based on these indices. Specifically, this generates two-dimensional arrays of size N×3 corresponding to the space sphere and the standard sphere, each containing only the three-dimensional coordinate values ​​of the center of the sphere.

[0066] For example, taking the diameter of a spatial sphere model as an example, let the diameters of all standard spheres form an arithmetic sequence, with the smallest diameter being a positive integer 'a' and the common difference of the arithmetic sequence being a positive integer 'b'. For the index of the two-dimensional array sorted by diameter, index j = (da) / b, where [] is the floor function; then, the corresponding coordinates [x, y, z] are used as the element with row index j in the two-dimensional array C. At this point, the two-dimensional array corresponding to the spatial sphere is only related to the three-dimensional coordinates of the sphere's center. Through the correspondence of indices, the correspondence between the three-dimensional coordinates of the spatial sphere model's center and the three-dimensional coordinates of the standard sphere's center can be determined.

[0067] by Figure 2 Taking the calibration device in the model as an example, this step ultimately forms 12 two-dimensional arrays corresponding to the 3D camera and 12 two-dimensional arrays corresponding to the coordinate measuring machine.

[0068] Step S05: Based on the correspondence between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere, calculate the transformation matrix between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere to obtain the extrinsic parameters of the 3D camera relative to the measuring device. Specifically, this step can be implemented using steps S051 to S055.

[0069] Step S051: Calculate the average of the three-dimensional coordinates of the centers of all spatial sphere models and the average of the three-dimensional coordinates of the centers of all standard spheres, respectively, to obtain the center point centroid of the spatial sphere model. C and the center point of the standard ball (centroid) M .

[0070] Step S052: Calculate the difference between the three-dimensional coordinates of the center of all spatial sphere models and the coordinates of the center point of the spatial sphere model, and the difference between the three-dimensional coordinates of the center of all standard spheres and the coordinates of the center point of the standard sphere. Perform matrix multiplication on the two differences to obtain a matrix H.

[0071] For example, such as Figure 2 The calibration device shown connects N two-dimensional arrays corresponding to the space spheres with Centroid. CPerform difference calculations to obtain matrix C; and then combine the N two-dimensional arrays corresponding to the standard spheres with centroid. M Perform the difference calculation to obtain matrix M. Then perform matrix multiplication on matrix C and matrix M to form a 12*12 matrix H.

[0072] H = C T *M

[0073] Step S053: Perform singular value decomposition on the matrix to obtain the left singular matrix U and the transpose of the right singular matrix V.

[0074] H=U*∑*V T

[0075] Step S054: Calculate the rotation matrix R based on the left singular matrix U and the transpose V of the right singular matrix.

[0076] R = V * U T , where the superscript T represents the transpose of the matrix.

[0077] Step S055: Calculate the translation vector S based on the rotation matrix, the center point of the space sphere model, and the center point of the standard sphere.

[0078] S = -centroid C *R T +centroid M .

[0079] The resulting R is the rotation matrix from the 3D camera-captured point cloud to the device coordinate system, and S is the translation vector. (x) C ,y C ,z C Convert to a three-coordinate system point (x) M ,y M ,z M The formula for ) is:

[0080] [x M ,y M ,z M ] = [x C ,y C ,z C ]*R T +S.

[0081] A second aspect of this invention discloses a 3D camera extrinsic parameter calibration device, comprising a memory and a controller connected in sequence. The memory stores a computer program, and the controller is used to read the computer program and execute a 3D camera extrinsic parameter calibration method as described in the first aspect and any of its possibilities. Specifically, the memory may include, but is not limited to, random-access memory (RAM), read-only memory (ROM), flash memory, first-in-first-out (FIFO) memory, and / or first-in-last-out (FILO) memory, etc.; the controller may not be limited to using a microcontroller of the STM32F105 series. Furthermore, the computer device may also include, but is not limited to, a power supply unit, a display screen, and other necessary components.

[0082] The third aspect of the present invention discloses a 3D camera extrinsic calibration system, comprising at least three standard spheres, a measuring device, a 3D camera, and a 3D camera extrinsic calibration equipment.

[0083] At least three standard spheres are required, and all standard spheres must lie on at least two three-dimensional straight lines. To secure the standard spheres, they are connected to the base via connectors. The standard spheres, connectors, and base together constitute the calibration device, as shown below. Figure 2 As shown. There are at least three standard spheres 3. Of course, to improve calibration accuracy, the number of standard spheres can be appropriately increased. The standard spheres should be distributed appropriately on as many three-dimensional straight lines as possible. In use, the calibration device must have at least three standard spheres 3 within the field of view of the 3D camera, and the standard spheres within the field of view of the 3D camera must be on at least two three-dimensional straight lines.

[0084] A 3D camera is used to capture point cloud image information of the calibration sphere.

[0085] The measuring device is used to measure the three-dimensional coordinates of the center and the diameter of the standard sphere. It can be a device or sensor that cannot acquire images, or it can be a device or sensor that can acquire images. For example, it can be a coordinate measuring machine.

[0086] The 3D camera extrinsic calibration device is the 3D camera extrinsic calibration device described in the second aspect. The 3D camera extrinsic calibration device is signal-connected to the 3D camera and the measuring device. It achieves 3D camera extrinsic calibration by acquiring image information from the 3D camera and the three-dimensional coordinates and diameter of the center of a standard sphere measured by the measuring device, through the extrinsic calibration method in the first aspect.

[0087] The fourth aspect of the present invention discloses a computer-readable storage medium storing instructions that, when executed on a computer, perform a 3D camera extrinsic parameter calibration method as described in the first aspect and any of its possibilities.

[0088] The operating principles of the equipment, systems and media disclosed in aspects two to four of this solution are detailed in the method described in aspect one, and will not be repeated here.

[0089] By adopting the above four solutions, the pose of a 3D camera in the coordinate system of a coordinate measuring machine or other equipment or sensors can be quickly calibrated using only one 3D camera shot. This not only solves the problem of the lack of applicable methods for calibrating a 3D camera to a coordinate measuring machine, but also establishes the correspondence between two or more coordinate systems, improving the calibration speed of the 3D camera. Furthermore, it can improve the calibration accuracy by increasing the number of standard balls in the calibration device.

[0090] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A 3D camera extrinsic calibration method, characterized in that: The method comprises the following steps: acquiring point cloud image information captured by a 3D camera, the point cloud image information comprising at least three standard spheres and all the centers of the standard spheres being on at least two three-dimensional straight lines; fitting and extracting spatial sphere models of all the standard spheres in the point cloud image information in sequence and calculating three-dimensional coordinates and diameters of the centers of each spatial sphere model; acquiring three-dimensional coordinates and diameters of the centers of the standard spheres corresponding to each standard sphere in the image information measured by a measuring device; determining a corresponding relationship between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere according to the diameters of the spatial sphere model and the diameters of the standard sphere; The average of the three-dimensional coordinates of the centers of all the space sphere model spheres and the average of the three-dimensional coordinates of the centers of all the standard spheres are calculated respectively according to columns to obtain the center point coordinates centroid of the space sphere model C and the center point coordinates centroid of the standard sphere M ; respectively calculating differences between the three-dimensional coordinates of the center of all the spatial sphere models and the three-dimensional coordinates of the center of the spatial sphere model, differences between the three-dimensional coordinates of the center of all the standard spheres and the three-dimensional coordinates of the center of the standard sphere, and performing matrix multiplication on the two differences to obtain a matrix H, wherein, H = C T M, in the formula, C is a matrix obtained by calculating the differences between the three-dimensional coordinates of the center of all the spatial sphere models and the three-dimensional coordinates of the center of the spatial sphere model, M is a matrix obtained by calculating the differences between the three-dimensional coordinates of the center of all the standard spheres and the three-dimensional coordinates of the center of the standard sphere, and T represents transposition of a matrix; performing singular value decomposition on the matrix to obtain a left singular matrix and a transpose of a right singular matrix, wherein H = U *∑* V T , in the formula, U is a left singular matrix, and V is a transposition of a right singular matrix; calculating a rotation matrix R according to the left singular matrix and the transposition of the right singular matrix, wherein, R = V*U T ; A translation vector S is calculated from the rotation matrix, the center point of the space sphere model and the center point of the standard sphere, S = -centroid C *R T +centroid M . 2.The 3D camera extrinsic calibration method of claim 1, wherein: the fitting and extracting of the spatial sphere models of all the standard spheres in the point cloud image information and the calculation of the three-dimensional coordinates and diameters of the centers of each spatial sphere model comprise: A. fitting and extracting a spatial sphere model of one standard sphere in the point cloud image information; B. calculating the three-dimensional coordinates and diameters of the center of the spatial sphere model according to the points in the spatial sphere model; C. eliminating the point cloud used for fitting the spatial sphere model in step A from the point cloud image information; D. repeating steps A, B and C until the three-dimensional coordinates and diameters of N spatial sphere models are obtained, wherein N is the number of standard spheres in the image information.

3. The 3D camera extrinsic calibration method of claim 1, wherein: The corresponding relationship between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere is determined by using an index sorting method for the diameters of the spatial sphere model and the diameters of the standard sphere.

4. The 3D camera extrinsic calibration method of claim 1, wherein: The corresponding relationship between the three-dimensional coordinates of the center of the spatial sphere model and the three-dimensional coordinates of the center of the standard sphere is determined by using an index sorting method for the diameters of the spatial sphere model and the diameters of the standard sphere, comprising: respectively determining spatial sphere center three-dimensional coordinate indexes and standard sphere center three-dimensional coordinate indexes according to the diameters of the spatial sphere model and the diameters of the standard sphere; establishing a corresponding relationship between the spatial sphere center three-dimensional coordinates and the standard sphere center three-dimensional coordinates according to the spatial sphere center three-dimensional coordinate indexes and the standard sphere center three-dimensional coordinate indexes.

5. A 3D camera extrinsic parameter calibration device, comprising a memory and a controller connected in sequence, and the memory stores a computer program, characterized in that: The controller is configured to read the computer program and execute the 3D camera external parameter calibration method according to any one of claims 1-4. 6.A 3D camera extrinsic calibration system, characterized in that, comprise: at least three standard spheres, the standard spheres being at least three and all the standard spheres being on at least two three-dimensional straight lines; a 3D camera, the 3D camera being configured to capture point cloud image information of the standard spheres; a measuring device, the measuring device being configured to measure three-dimensional coordinates and diameters of the centers of the standard spheres; The 3D camera external parameter calibration device according to claim 5, wherein the 3D camera external parameter calibration device is signal connected with the 3D camera and the measuring device.

7. The 3D camera extrinsic calibration system of claim 6, wherein: The standard ball is connected to the base through the connecting piece. 8.The 3D camera extrinsic calibration system of claim 6, wherein: The measuring device is a device or sensor that cannot acquire images.

9. A computer-readable storage medium having stored thereon instructions, the computer-readable storage medium comprising: When the instructions are run on the computer, the 3D camera external parameter calibration method according to any one of claims 1-4 is executed.

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