A calibration method and system for multi-camera imaging of large targets

Abstract

The present invention provides a calibration method and system for multi-camera imaging of large targets, comprising the following steps: S1: Configure a calibration block, a main camera, and several pairs of secondary cameras; the calibration block is provided with a main calibration area and a secondary calibration area; S2: Utilize the main calibration area of the calibration block to calibrate the zero plane of the main camera and obtain the calibration parameters of the main camera; S3: Taking the main camera as a reference camera, calibrate each secondary camera respectively to obtain the calibration parameters of each secondary camera; complete the static calibration of the main camera and each secondary camera; S4: After the static calibration is completed, drive the main camera and each secondary camera to move in the Y-axis direction to complete the dynamic calibration of the main camera and each secondary camera.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-camera joint imaging calibration equipment, and particularly to a calibration method and system for large-target multi-camera imaging. Background Art

[0002] With the development of technology, the demand for measurement and defect detection in all walks of life is increasing continuously. And in some specific industries, the size of the target object is very large, which makes it very difficult to detect the target object with a single camera. Therefore, multiple cameras are required to jointly image, and finally the image point cloud is processed to obtain the size of the target object, as well as the size and position of the defects. For the existing calibration methods for such large target objects, some use 2D cameras, usually using 2D calibration cards. The cameras are calibrated pairwise. The internal parameters of each camera are obtained through the traditional Zhang Zhengyou calibration method, and the external parameters of the cameras are obtained through the overlapping method to complete the calibration process, and finally complete the measurement of the large target object. There are also those that use 3D cameras to calibrate through polygonal prisms or cylinders combined with 2D patterns to complete the calibration imaging of the cameras. However, neither the 2D calibration card nor the polygonal prism or cylinder can effectively control the accuracy of the imaging system, and the measurement accuracy is always not ideal.

[0003] Therefore, it is very necessary to design a calibration method and system for large-target multi-camera imaging to complete the calibration work at one time and improve the work efficiency of calibration. Summary of the Invention

[0004] In view of this, the present invention proposes a calibration method and system for multi-camera imaging that can complete the calibration of multiple cameras for the same large target at one time.

[0005] The technical solution of the present invention is realized as follows:

[0006] On the one hand, the present invention provides a calibration method for large-target multi-camera imaging, including the following steps:

[0007] S1: Configure a calibration block, a main camera, and several pairs of secondary cameras; the calibration block is provided with a main calibration area and a secondary calibration area;

[0008] S2: Use the main calibration area of the calibration block to correct the zero plane of the main camera to obtain the calibration parameters of the main camera;

[0009] S3: Taking the main camera as the reference camera, correct each secondary camera respectively to obtain the calibration parameters of each secondary camera; complete the static calibration of the main camera and each secondary camera;

[0010] S4: After the static calibration is completed, drive the main camera and each secondary camera to move in the Y-axis direction to complete the dynamic calibration of the main camera and each secondary camera.

[0011] Based on the above technical solutions, preferably, the calibration block described in step S1 includes a base, a first calibration unit, a second calibration unit, and a third calibration unit; the base is arranged vertically, and the first calibration unit, the second calibration unit, and the third calibration unit are sequentially arranged at one end of the base away from the ground and are all rotatably connected to the base, and the first calibration unit, the second calibration unit, and the third calibration unit are relatively fixedly arranged; at least one side surface of the first calibration unit is provided with a first coding structure and / or a second coding structure protruding outward; the side surface of the second calibration unit is provided with a third coding structure or a fourth coding structure protruding outward; each side surface of the third calibration unit is provided with a plurality of fifth coding structures protruding outward; each side surface of the second calibration unit and the third coding structure or the fourth coding structure are used as the main calibration area of the calibration block; the side surface of the first calibration unit and its first coding structure and / or second coding structure, and the side surface of the third calibration unit and a plurality of fifth coding structures are all used as the secondary calibration area of the calibration block.

[0012] Preferably, the contours of the first calibration unit, the second calibration unit, and the third calibration unit are all regular pentagons; the shapes of the first coding structure, the second coding structure, the third coding structure, the fourth coding structure, and the fifth coding structure are all different; the main camera and the secondary cameras are respectively arranged on the extension lines of the connections between the vertices of the regular pentagon of the second calibration unit and the longitudinal central axis and are arranged facing a vertex, and the first secondary camera and the fourth secondary camera are respectively on the left side of the main camera, and the second secondary camera and the third secondary camera are respectively on the right side of the main camera.

[0013] Further preferably, the contour of the first coding structure is a triangular prism; the second coding structure is an isosceles trapezoid body; the third coding structure is a hexagonal frustum; the fourth coding structure is a non-isosceles trapezoid body; the fifth coding structure is a cuboid.

[0014] Further preferably, the step of using the main calibration area of the calibration block to calibrate the zero plane of the main camera and obtain the calibration parameters of the main camera in step S2 includes the following steps:

[0015] S21: Define the vertex facing the side surface where the third coding structure of the second calibration unit is located as the main reference point P2, and the adjacent vertices of the fourth coding structures on the two side surfaces of the second calibration unit adjacent to the vertex P2 as P1 and P3; take the vertical direction as the Y axis, the X axis points to the center of the second calibration unit, and the Z axis is respectively orthogonal to the Y axis and the X axis; the plane where the straight line where the vertices P1, P2, and P3 are located is the zero plane of the main camera to be calibrated, that is, the XOZ plane, and the main camera collects the contour lines of the side surface edges of the side surface of the second calibration unit or the fourth coding structure at the vertices P1, P2, and P3.

[0016] S22: Obtain the calibration parameters of the zero plane, determine the intercept position of the zero plane of the main camera, and adjust the main camera so that the contour lines of the side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 collected by the main camera coincide with the intercept line of the zero plane of the main camera; Calculate the slope of the straight line where the vertices P1, P2, and P3 are located, and the tilt angle A can be obtained, that is, the rotation angle of the main camera around the Y axis. Rotate the contour lines of the side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 by the angle A; Then calculate the position offset of the vertex P2 from the center point (0, 0) to obtain the offset amounts [x, z] in the X-axis direction and the Z-axis direction. Offset this contour line as a whole by the distance [x, z], and then the three parameters [Xref, 0, Zref, 0, Bref, 0] can be obtained.

[0017] S23: The camera moves along the Y axis, obtain the point cloud data set scanned by the main camera, remove the influence of stray points. The side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 intersect to obtain the straight lines line1, line2, and line3. Interpolating and fitting line1, line2, and line3 can obtain a fitting plane. In order to correct the fitting plane to the zero plane, first, project line2 onto the YOZ plane, calculate the slope of the projected straight line to obtain the angle between the straight line and the Y axis, and then the rotation angle of the fitting plane in the YOZ plane can be obtained; Then project line2 onto the XOY plane, calculate the slope of the projected straight line to obtain the angle between the straight line and the Y axis, and then the angle between the fitting plane and the XOY plane can be obtained, thereby obtaining the other two angular deflection data of the calibration parameters of the main camera; Use the lower edge coordinate of the third calibration unit of the calibration block as the Y-axis 0 point, and use the lower edge coordinates of the three-layer main reference points as the offset of the Y-axis data to obtain the six calibration parameters [Xref, Yref, Zref, Aref, Bref, Cref] of the main camera.

[0018] More preferably, in step S3, taking the main camera as the reference camera, calibrate each sub-camera respectively to obtain the calibration parameters of each sub-camera; Completing the static calibration of the main camera and each sub-camera includes the following steps:

[0019] S31: According to the contour information of the image, confirm the overlapping area of the main camera and the first sub-camera. Extract the data of the corresponding overlapping area line segment in the main camera for fitting to obtain the inclination angle B1 of the fitted straight line. Then, extract the line segment of the corresponding overlapping area in the first sub-camera for fitting to obtain the inclination angle B2 of the fitted straight line. Calculate the angle between the inclination angles B1 and B2, so as to obtain the rotation angle of the overlapping segment of the first sub-camera and the main camera, which is the calibration angle Bcalib1 in the Y-axis direction of the first sub-camera. Extract a common corner point from the overlapping area line segment, calculate the mapping of the corner point on the first sub-camera to this corner point on the main camera, and the offsets in the X and Z directions [Xcalib1, Zcalib1] can be obtained. Thus, the static calibration parameters of the first sub-camera [Xcalib1, 0, Zcalib1, 0, Bcalib1, 0] are obtained;

[0020] S32: Operate the main camera and the second sub-camera simultaneously. Referring to the content of step S31, obtain the rotation angle of the overlapping segment of the second sub-camera and the main camera, which is the calibration angle Bcalib2 in the Y-axis direction of the second sub-camera. Extract a common corner point from the overlapping area line segment, calculate the mapping of the corner point on the second sub-camera to this corner point on the main camera, and the offsets in the X and Z directions [Xcalib2, Zcalib2] can be obtained. Thus, the static calibration parameters of the second sub-camera [Xcalib2, 0, Zcalib2, 0, Bcalib2, 0] are obtained;

[0021] S33: Rotate the second calibration unit 72° along the vertical direction to verify the calibration accuracy of the main camera, the first sub-camera and the second sub-camera. If the coincidence degree of the contour data is within the repeat accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repeat accuracy range of the dynamic data acquisition range of each camera, recalibration is required, and steps S31, S32 and S33 are repeated;

[0022] S34: After the first sub-camera and the second sub-camera are calibrated correctly, write the static calibration parameters into the first sub-camera and the second sub-camera for the static calibration corresponding to the first sub-camera and the second sub-camera;

[0023] S35: After the posture calibration of the main camera, the first auxiliary camera and the second auxiliary camera is completed, the calibration block is rotated again, the third encoding structure of the second calibration unit and its side surface are aligned with the main camera, the first auxiliary camera is used as the reference camera to calibrate the fourth auxiliary camera, and the second auxiliary camera is used as the reference to calibrate the third auxiliary camera. The calibration method is the same as step S31, and the static calibration parameters [Xcalib3,0, Zcalib3,0, Bcalib3,0] of the third auxiliary camera and the static calibration parameters [Xcalib4,0, Zcalib4,0, Bcalib4,0] of the fourth auxiliary camera can be obtained; at this point, the preliminary static calibration of all cameras is completed;

[0024] Further preferably, after the preliminary static calibration of all cameras in step S3 is completed, a static calibration verification step S36 is also included, and the specific content is:

[0025] S36: After the preliminary static calibration of the main camera and each auxiliary camera is completed, the main camera and each auxiliary camera are adjusted to the vertices of the regular pentagon facing the first calibration unit and fixed, and the static calibration accuracy of the main camera and each auxiliary camera is verified as a whole to ensure that the center point position of the calibration block cannot change due to the movement of the main camera and each auxiliary camera in the Y direction; the main camera and each auxiliary camera are framed as a whole. If the time acquisition accuracy of the calibration result is within the repetitive accuracy range of the corresponding camera acquisition data, the calibration result is considered to be accurate and the static calibration is completed; if the deviation exceeds this range, first determine the degree to which the data deviation range exceeds the repetitive accuracy of the camera acquisition data. If the deviation from the repetitive accuracy of the camera acquisition data is limited, fine-tune it in the first calibration unit; if the deviation result is too large, it is necessary to return to the second calibration unit for recalibration, that is, repeat steps S31-S35 until the correction accuracy of the contour meets the requirements.

[0026] Further preferably, after the static calibration in step S4 is completed, the main camera and each auxiliary camera are driven to move in the Y-axis direction to complete the dynamic calibration of the main camera and each auxiliary camera, which includes the following steps:

[0027] S41: driving the camera to move in the Y-axis direction for dynamic calibration; first, using the main camera and the first auxiliary camera to perform motion scanning, obtain point cloud data, and obtain an overlapping area image of the main camera and the first auxiliary camera, where the overlapping area is two adjacent planes;

[0028] S42: Calculate the included angle and rotation angle between two adjacent planes in the overlapping area; if the area images obtained by the main camera and the first sub-camera completely coincide, then the first intersection line line1 in the clockwise direction in the image obtained by the main camera coincides with the third intersection line Lleft3 in the clockwise direction in the image of the first sub-camera. Project the first intersection line Lleft1 in the image obtained by the first sub-camera from the vertical direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line, that is, obtain the included angle between the projection line and the Y-axis, so as to obtain the rotation angle Acalib1 of the fitting plane plane1 in the YOZ plane; then project the first intersection line Lleft1 from the horizontal direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line, that is, obtain the included angle between the line and the Y-axis, that is, obtain the included angle Ccalib1 between the fitting plane plane1 and the XOZ plane; take the edge coordinates of the lower end face of the third calibration unit of the calibration block as the zero point of the Y-axis, and take the regular pentagon vertices of the lower edges of the third calibration unit, the second calibration unit, and the first calibration unit corresponding to the main reference point as the offset Ycalib1 of the Y-axis quantity. Then, combined with the static calibration parameters of the first sub-camera, obtain all six camera parameters [Xcalib1, Ycalib1, Zcalib1, Acalib1, Bcalib1, Ccalib1] of the first sub-camera.

[0029] S43: Use the same content as in step S42 to perform dynamic calibration on the main camera and the second sub-camera, and combined with the current calibration parameters of the second sub-camera, obtain all six camera parameters [Xcalib2, Ycalib2, Zcalib2, Acalib2, Bcalib2, Ccalib2] of the second sub-camera;

[0030] S44: Rotate the calibration block as a whole by 72° around the Y-axis to verify the calibration accuracy of the main camera, the first sub-camera, and the second sub-camera. If the coincidence degree of the contour data of the main camera, the first sub-camera, and the second sub-camera is within the repetition accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repetition accuracy range of the dynamic data acquisition range of each camera, it is necessary to re-perform calibration, and repeat steps S42 and S43;

[0031] S45: After the main camera, the first sub-camera, and the second sub-camera are correctly calibrated, rotate the calibration block again, align the third coding structure of the second calibration unit and its side surface with the main camera, use the first sub-camera as the reference camera to calibrate the fourth sub-camera, and use the second sub-camera as the reference to calibrate the third sub-camera. The method is the same as step S42; thus, the calibration parameters [Xcalib3, Ycalib3, Zcalib3, Acalib3, Bcalib3, Ccalib3] of the third sub-camera and the static calibration parameters [Xcalib4, Ycalib4, Zcalib4, Acalib4, Bcalib4, Ccalib4] of the fourth sub-camera can be obtained; at this point, the preliminary dynamic calibration of all cameras is completed.

[0032] S46: After the cameras are calibrated using the current calibration parameters, rescan the calibration block, verify the imaging accuracy in the X and Z directions through the first calibration unit, and verify the imaging accuracy in the Y direction by analyzing the second calibration unit. If the results are within the acquisition data accuracy range of the cameras, the camera calibration ends; if there are deviations, analyze and fine-tune the data. If the error is too large, repeat the entire process until the calibration accuracy is met.

[0033] On the other hand, the present invention also provides a calibration system for large-target multi-camera imaging, including a calibration block, a main camera, a first sub-camera, a second sub-camera, a third sub-camera, and a fourth sub-camera; the contour of the calibration block is a regular pentagon, and the side surfaces at different positions of the calibration block are provided with first, second, third, fourth, and fifth coding structures that protrude outward; the first, second, third, fourth, and fifth coding structures are all different; it is characterized in that: the main camera, the first sub-camera, the second sub-camera, the third sub-camera, and the fourth sub-camera are internally installed with the above-mentioned calibration method for large-target multi-camera imaging.

[0034] The calibration method and system for large-target multi-camera imaging provided by the present invention have the following beneficial effects compared with the prior art:

[0035] By means of the special-shaped three-layer calibration block structure in this solution, each layer of the calibration block structure has a specific coding structure. Due to the difference in this coding structure, the coding of a specific layer has directionality, which can save the calibration time, improve the calibration efficiency, improve the imaging quality, and is especially suitable for large targets that require multiple cameras to work together to capture the shape. Brief Description of the Drawings

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 Flow chart of a calibration method and system for large target multi-camera imaging according to the present invention;

[0038] Figure 2 Schematic diagram of the arrangement positions of the calibration block and each camera in a calibration method and system for large target multi-camera imaging according to the present invention;

[0039] Figure 3 Perspective view of the calibration block in a calibration method and system for large target multi-camera imaging according to the present invention;

[0040] Figure 4 Exploded perspective view of the calibration block in a calibration method and system for large target multi-camera imaging according to the present invention;

[0041] Figure 5 Bottom view of the first calibration unit in a calibration method and system for large target multi-camera imaging according to the present invention;

[0042] Figure 6 Bottom view of the second calibration unit in a calibration method and system for large target multi-camera imaging according to the present invention;

[0043] Figure 7 Bottom view of the third calibration unit in a calibration method and system for large target multi-camera imaging according to the present invention;

[0044] Figure 8 Schematic diagram of the calibration contour of the main camera in a calibration method and system for large target multi-camera imaging according to the present invention;

[0045] Figure 9 Scanned point cloud map of the main camera in a calibration method and system for large target multi-camera imaging according to the present invention;

[0046] Figure 10 Image of the main camera, the first sub-camera, and the second sub-camera in a calibration method and system for large target multi-camera imaging according to the present invention after static correction is completed;

[0047] Figure 11 Image of the overlapping area of the main camera and the first sub-camera during dynamic calibration in a calibration method and system for large target multi-camera imaging according to the present invention.

[0048] Reference numerals: 1, first calibration unit; 100, first coding structure; 200, second coding structure; 2, second calibration unit; 300, third coding structure; 400, fourth coding structure; 3, third calibration unit; 500, fifth coding structure. Detailed implementation manners

[0049] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0050] As Figure 1 shown, on the one hand, the present invention provides a calibration method for large target multi-camera imaging, including the following steps:

[0051] S1: Configure a calibration block, a main camera, and several pairs of secondary cameras; the calibration block is provided with a main calibration area and a secondary calibration area.

[0052] As Figures 2 - 7 shown, the calibration block mentioned here includes a base, a first calibration unit 1, a second calibration unit 2, and a third calibration unit 3; the base is arranged in the vertical direction, and the first calibration unit 1, the second calibration unit 2, and the third calibration unit 3 are sequentially arranged at one end of the base away from the ground and are all rotatably connected to the base. The first calibration unit 1, the second calibration unit 2, and the third calibration unit 3 are relatively fixedly arranged, that is, they rotate synchronously relative to the base; at least one side surface of the first calibration unit is provided with a first coding structure 100 and / or a second coding structure 200 protruding outward; the side surface of the second calibration unit 2 is provided with a third coding structure 300 or a fourth coding structure 400 protruding outward; each side surface of the third calibration unit 3 is provided with a plurality of fifth coding structures 500 protruding outward; the side surfaces of the second calibration unit 2 and its third coding structure 300 or fourth coding structure 400 serve as the main calibration area of the calibration block; the side surface of the first calibration unit 1 and its first coding structure 100 and / or second coding structure 200, and the side surface of the third calibration unit 3 and a plurality of fifth coding structures 500 all serve as the secondary calibration area of the calibration block. For large targets, multiple cameras often need to be set up.

[0053] As Figure 2 and Figure 3As shown in the figure, there are five cameras corresponding to this solution. In order to better identify each coding structure, the contours of the first calibration unit 1, the second calibration unit 2, and the third calibration unit 3 are all regular pentagons; the shapes of the first coding structure 100, the second coding structure 200, the third coding structure 300, the fourth coding structure 400, and the fifth coding structure 500 are different. Specifically, the first coding structure 100 is a regular triangular prism, the second coding structure 200 is an isosceles trapezoid, and the vertical thicknesses of the first coding structure 100 and the second coding structure are equivalent to the thickness of the first calibration unit 1. The third coding structure 300 is a hexagonal frustum structure; the fourth coding structure is a non-isosceles trapezoid; the fifth coding structure is a cuboid, and the thickness in the vertical direction is less than the thickness of the third calibration unit 3. Such a setting makes the coding structures at different positions easy to identify. Taking the first calibration unit 1 as an example, there are coding structures on its four side surfaces. Skipping the blank side surface and defining the four side surfaces in the counterclockwise direction, there are two first coding structures 100, one first coding structure 100 and one second coding structure 200, and two second coding structures 200 on the four side surfaces respectively. Let the combined meaning of the first coding structure be 0 and the combined meaning of the second coding structure 200 be 1, then the four side surfaces arranged counterclockwise are the four combinations of 00, 01, 10, and 11 in sequence.

[0054] The main camera and the sub-cameras are respectively arranged on the extension lines of the connections between the vertices of the regular pentagon of the second calibration unit and the longitudinal central axis, and are arranged facing a vertex, as Figure 2 shown. The first sub-camera and the fourth sub-camera are respectively on the left side of the main camera, and the second sub-camera and the third sub-camera are respectively on the right side of the main camera. The distance between adjacent vertices of the second calibration unit is 72°.

[0055] Further preferably, the contour of the first coding structure is a triangular prism; the second coding structure is an isosceles trapezoid; the third coding structure is a hexagonal frustum; the fourth coding structure is a non-isosceles trapezoid; the fifth coding structure is a cuboid.

[0056] S2: Using the main calibration area of the calibration block, calibrate the zero plane of the main camera to obtain the calibration parameters of the main camera.

[0057] This step specifically includes the following contents:

[0058] S21: Define the vertex facing the side surface where the third coding structure of the second calibration unit is located as the main reference point P2, and the adjacent vertices of the fourth coding structure on the side surfaces of the two second calibration units adjacent to the vertex P2 as P1 and P3; set the vertical direction as the Y-axis, the X-axis points to the center of the second calibration unit, and the Z-axis is respectively orthogonal to the Y-axis and the X-axis; the plane where the straight line where the vertices P1, P2, and P3 are located is the zero plane of the main camera to be calibrated, i.e., the XOZ plane. The main camera collects the contour lines of the side surfaces of the second calibration unit 2 or the side surface edges of the fourth coding structure 400 at the vertices P1, P2, and P3; the straight line where the vertices P1, P2, and P3 are located is as shown by the dotted line in Figure 6 . According to the design, the contour line includes six broken lines, as shown in Figure 8 . Looking from left to right, the line segment 1 intersects with the line segment 2 at the point P1, the line segment 3 and the line segment 4 intersect at the point P2, and the line segment 5 and the line segment 6 intersect at the point P3. According to the design, these three intersection points P1, P2, and P3 should be on the straight line Z = 0, and the point P2 is located at the center point (0, 0) of the XOZ plane.

[0059] S22: Obtain the calibration parameters of the zero plane, determine the intercept position of the zero plane of the main camera, and adjust the main camera so that the contour lines of the side surfaces of the second calibration unit 2 or the side surface edges of the fourth coding structure 400 collected by the main camera at the vertices P1, P2, and P3 coincide with the intercept line of the zero plane of the main camera; calculate the slope of the straight line where the vertices P1, P2, and P3 are located, and the tilt angle A can be obtained, that is, the rotation angle of the main camera around the Y-axis, and rotate the contour lines of the side surfaces of the second calibration unit 2 or the side surface edges of the fourth coding structure 400 at the vertices P1, P2, and P3 by the angle A; then calculate the position offset between the vertex P2 and the center point (0, 0) to obtain the offset amounts [x, z] in the X-axis direction and the Z-axis direction, and offset the whole contour line by the distance [x, z], then the three parameters [Xref, 0, Zref, 0, Bref, 0] can be obtained. Use this contour line to further obtain the zero plane.

[0060] S23: As shown in Figure 9As shown in the figure, the main camera moves along the Y axis to obtain the point cloud data set scanned by the main camera. After removing the influence of stray points, the side surfaces of the second calibration unit 2 or the edges of the side surfaces of the fourth coding structure 400 at vertices P1, P2, and P3 intersect to obtain straight lines line1, line2, and line3. Interpolation fitting of line1, line2, and line3 can obtain a fitting plane. According to the design, this fitting plane will fall on the YOZ plane. In order to correct the fitting plane to the zero plane, first, project line2 onto the YOZ plane, calculate the slope of the projected straight line to obtain the angle between the straight line and the Y axis, and thus obtain the rotation angle of the fitting plane in the YOZ plane; then project line2 onto the XOY plane, calculate the slope of the projected straight line to obtain the angle between the straight line and the Y axis, and thus obtain the angle between the fitting plane and the XOY plane, thereby obtaining the other two angular deflection data of the main camera calibration parameters; taking the lower edge coordinate of the third calibration unit of the calibration block as the Y-axis 0 point, and taking the lower edge coordinates of the three-layer main reference points as the offset of the Y-axis data, the six calibration parameters [Xref, Yref, Zref, Aref, Bref, Cref] of the main camera are obtained.

[0061] S3: Taking the main camera as the reference camera, calibrate each sub-camera respectively to obtain the calibration parameters of each sub-camera; complete the static calibration of the main camera and each sub-camera.

[0062] Specifically, it includes the following content:

[0063] S31: After the main camera is calibrated, turn on the main camera and the first sub-camera to image simultaneously. According to the contour information of the image, confirm the overlapping area of the main camera and the first sub-camera, and calibrate the first sub-camera according to the common overlapping area. Specifically, first, take out the data of the corresponding overlapping area line segment in the main camera for fitting to obtain the inclination angle B1 of the fitting straight line, and then take out the line segment of the corresponding overlapping area in the first sub-camera for fitting to obtain the inclination angle B2 of the fitting straight line, calculate the angle between the inclination angles B1 and B2, and thus obtain the rotation angle of the overlapping segment of the first sub-camera and the main camera, which is the calibration angle Bcalib1 in the Y-axis direction of the first sub-camera; second, take out a common corner point in the overlapping area line segment, calculate the mapping of the corner point on the first sub-camera to this corner point on the main camera, and thus obtain the offset amounts [Xcalib1, Zcalib1] in the X and Z directions; thus far, the static calibration parameters [Xcalib1, 0, Zcalib1, 0, Bcalib1, 0] of the first sub-camera are obtained.

[0064] S32: Operate the main camera and the second sub-camera simultaneously. Refer to the content of step S31, that is, obtain the overlapping area common to the second sub-camera and the main camera. Using the overlapping line segments or the corner points of the line segments, further obtain the rotation angle of the overlapping segment of the second sub-camera and the main camera, which is the calibration angle Bcalib2 in the Y-axis direction of the second sub-camera. Take out a common corner point in the line segments of the overlapping area, calculate the mapping of the corner point on the second sub-camera to this corner point on the main camera, and then the offset amounts in the X and Z directions [Xcalib2, Zcalib2] can be obtained. Thus, the static calibration parameters of the second sub-camera [Xcalib2, 0, Zcalib2, 0, Bcalib2, 0] are obtained.

[0065] S33: Rotate the second calibration unit by 72° in the vertical direction to verify the calibration accuracy of the main camera, the first sub-camera, and the second sub-camera. If the coincidence degree of the contour data is within the repeat accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repeat accuracy range of the dynamic data acquisition range of each camera, recalibration is required, and steps S31, S32, and S33 are repeated. The repeat accuracy range mentioned here is defined as ±0.05 mm.

[0066] S34: After the first sub-camera and the second sub-camera are calibrated correctly, write the static calibration parameters into the first sub-camera and the second sub-camera, corresponding to the static calibration of the first sub-camera and the second sub-camera.

[0067] S35: After the attitude calibration of the main camera, the first sub-camera, and the second sub-camera is completed, rotate the calibration block again, align the third coding structure and its side surface of the second calibration unit with the main camera, use the first sub-camera as the reference camera to calibrate the fourth sub-camera, and use the second sub-camera as the reference to calibrate the third sub-camera. The calibration method is the same as that in step S31, and then the static calibration parameters of the third sub-camera [Xcalib3, 0, Zcalib3, 0, Bcalib3, 0] and the static calibration parameters of the fourth sub-camera [Xcalib4, 0, Zcalib4, 0, Bcalib4, 0] can be obtained. Thus, the preliminary static calibration of all cameras is completed.

[0068] S36: After the preliminary static calibration of the main camera and each sub-camera is completed, adjust the main camera and each sub-camera to face the vertices of the regular pentagon of the first calibration unit and fix them. Conduct an overall verification of the static calibration accuracy of the main camera and each sub-camera to ensure that the center point position of the calibration block does not change due to the movement of the main camera and each sub-camera in the Y direction. Conduct an overall viewfinder for the main camera and each sub-camera. If the time acquisition accuracy of the calibration result is within the repetition accuracy range of the data collected by the corresponding camera, and similarly, if the data deviation range here can be ±0.05 mm, it is considered that the calibration result is accurate and the static calibration ends. If the deviation exceeds this range, first judge the degree to which the data deviation range exceeds the repetition accuracy of the data collected by the camera. If the deviation from the repetition accuracy range of the data collected by the camera is limited, such as within the limited range of ±0.05 mm to ±0.10 mm, then make fine adjustments in the first calibration unit. If the deviation result is too large, such as exceeding ±0.10 mm, it is necessary to return to the second calibration unit for re-calibration, that is, repeat steps S31 - S35 until the calibration accuracy of the contour meets the requirements.

[0069] S37: After the static calibration parameters of the four sub-cameras are confirmed, write the static calibration parameters of the first sub-camera, the second sub-camera, the third sub-camera, and the fourth sub-camera into the camera register to complete the calibration under static adjustment.

[0070] S4: After the static calibration is completed, drive the main camera and each sub-camera to move in the Y-axis direction to complete the dynamic calibration of the main camera and each sub-camera.

[0071] Specifically, it includes the following steps:

[0072] S41: Drive the camera to move in the Y-axis direction for dynamic calibration. First, use the main camera and the first sub-camera for motion scanning to obtain point cloud data and obtain the overlapping area image of the main camera and the first sub-camera. The overlapping area is two adjacent planes.

[0073] S42: Calculate the included angle and rotation angle between two adjacent planes in the overlapping area; if the area images obtained by the main camera and the first auxiliary camera completely overlap, then the first intersection line line1 in the clockwise direction in the image obtained by the main camera coincides with the third intersection line Lleft3 in the clockwise direction in the image of the first auxiliary camera. Project the first intersection line Lleft1 in the image obtained by the first auxiliary camera from the vertical direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line, that is, obtain the included angle between the projection line and the Y-axis, so as to obtain the rotation angle Acalib1 of the fitting plane plane1 in the YOZ plane; then project the first intersection line Lleft1 from the horizontal direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line to obtain the included angle of the line with respect to the Y-axis, that is, obtain the included angle Ccalib1 between the fitting plane plane1 and the XOZ plane; taking the edge coordinates of the lower end surface of the third calibration unit of the calibration block as the zero point of the Y-axis, and taking the regular pentagon vertices of the lower edges of the third calibration unit, the second calibration unit, and the first calibration unit corresponding to the main reference point as the offset Ycalib1 of the Y-axis quantity. Then, combining the static calibration parameters of the first auxiliary camera, obtain all six camera parameters [Xcalib1, Ycalib1, Zcalib1, Acalib1, Bcalib1, Ccalib1] of the first auxiliary camera;

[0074] S43: Use the same content as in step S42 to perform dynamic calibration on the main camera and the second auxiliary camera, and combine the calibration parameters of the second auxiliary camera today to obtain all six camera parameters [Xcalib2, Ycalib2, Zcalib2, Acalib2, Bcalib2, Ccalib2] of the second auxiliary camera;

[0075] S44: Rotate the calibration block as a whole by 72° around the Y-axis to verify the calibration accuracy of the main camera, the first auxiliary camera, and the second auxiliary camera. If the coincidence degree of the contour data of the main camera, the first auxiliary camera, and the second auxiliary camera is within the repeatability accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repeatability accuracy range of the dynamic data acquisition range of each camera, it is necessary to re-perform calibration, and repeat steps S42 and S43;

[0076] S45: After the main camera, the first sub-camera, and the second sub-camera are correctly calibrated, rotate the calibration block again, align the third coding structure of the second calibration unit and its side surface with the main camera, use the first sub-camera as the reference camera to calibrate the fourth sub-camera, and use the second sub-camera as the reference to calibrate the third sub-camera. The method is the same as step S42; thus, the calibration parameters [Xcalib3, Ycalib3, Zcalib3, Acalib3, Bcalib3, Ccalib3] of the third sub-camera and the static calibration parameters [Xcalib4, Ycalib4, Zcalib4, Acalib4, Bcalib4, Ccalib4] of the fourth sub-camera can be obtained; at this point, the preliminary dynamic calibration of all cameras is completed.

[0077] S46: After the camera is calibrated using the current calibration parameters, rescan the calibration block, verify the imaging accuracy in the X and Z directions through the first calibration unit, and verify the imaging accuracy in the Y direction by analyzing the second calibration unit. If the result is within the acquisition data accuracy range of the camera, the camera calibration ends; if there is a deviation, analyze and fine-tune the data. If the error is too large, repeat the entire process until the calibration accuracy is met.

[0078] On the other hand, the present invention also provides a calibration system for large-target multi-camera imaging, including a calibration block, a main camera, a first sub-camera, a second sub-camera, a third sub-camera, and a fourth sub-camera; the contour of the calibration block is a regular pentagon, and the side surfaces at different positions of the calibration block are provided with first, second, third, fourth, and fifth coding structures that protrude outward; the first, second, third, fourth, and fifth coding structures are all different; it is characterized in that: the main camera, the first sub-camera, the second sub-camera, the third sub-camera, and the fourth sub-camera incorporate the above-mentioned calibration method for large-target multi-camera imaging.

[0079] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A calibration method for multi-camera imaging of large targets, characterized in that It includes the following steps: S1: Configure a calibration block, a main camera, and several pairs of secondary cameras; the calibration block is provided with a main calibration area and a secondary calibration area; S2: Use the main calibration area of the calibration block to calibrate the zero plane of the main camera and obtain the calibration parameters of the main camera; S3: Take the main camera as the reference camera and calibrate each secondary camera respectively to obtain the calibration parameters of each secondary camera; complete the static calibration of the main camera and each secondary camera; S4: After the static calibration is completed, drive the main camera and each secondary camera to move in the Y-axis direction to complete the dynamic calibration of the main camera and each secondary camera; The calibration block described in step S1 includes a base, a first calibration unit, a second calibration unit, and a third calibration unit; the base is arranged vertically, and the first calibration unit, the second calibration unit, and the third calibration unit are sequentially arranged at one end of the base away from the ground and are all rotatably connected to the base, and the first calibration unit, the second calibration unit, and the third calibration unit are relatively fixedly arranged; at least one side surface of the first calibration unit is provided with a first coding structure and / or a second coding structure protruding outward; the side surface of the second calibration unit is provided with a third coding structure or a fourth coding structure protruding outward; each side surface of the third calibration unit is provided with a plurality of fifth coding structures protruding outward; each side surface of the second calibration unit and the third coding structure or the fourth coding structure are used as the main calibration area of the calibration block; the side surface of the first calibration unit and its first coding structure and / or second coding structure, and the side surface of the third calibration unit and a plurality of fifth coding structures are all used as the secondary calibration area of the calibration block.

2. The calibration method for large target multi-camera imaging according to claim 1, wherein, The contours of the first calibration unit, the second calibration unit, and the third calibration unit are all regular pentagons; the shapes of the first coding structure, the second coding structure, the third coding structure, the fourth coding structure, and the fifth coding structure are all different; the main camera and the secondary cameras are respectively arranged on the extension line of the connection between the vertex of the regular pentagon of the second calibration unit and the longitudinal central axis and are arranged facing a vertex. On the left side of the main camera are the first secondary camera and the fourth secondary camera, and on the right side of the main camera are the second secondary camera and the third secondary camera.

3. The calibration method for multi-camera imaging of large targets according to claim 2, wherein, The contour of the first coding structure is a triangular prism; the second coding structure is an isosceles trapezoid body; the third coding structure is a hexagonal frustum; the fourth coding structure is a non-isosceles trapezoid body; the fifth coding structure is a cuboid.

4. A calibration method for large-target multi-camera imaging according to claim 2, characterized in that, The step of using the main calibration area of the calibration block to calibrate the zero plane of the main camera and obtain the calibration parameters of the main camera described in step S2 includes the following steps: S21: Define the vertex facing the side surface where the third coding structure of the second calibration unit is located as the main reference point P2, and the adjacent vertices of the fourth coding structures on the two side surfaces of the second calibration unit adjacent to the vertex P2 as P1 and P3; take the vertical direction as the Y-axis, the X-axis points to the center of the second calibration unit, and the Z-axis is respectively orthogonal to the Y-axis and the X-axis; the plane where the straight line where the vertices P1, P2, and P3 are located is the zero plane of the main camera to be calibrated, that is, the XOZ plane, and the main camera collects the contour lines of the side surfaces of the side surfaces or the fourth coding structures of the second calibration unit at the vertices P1, P2, and P3; S22: Obtain the calibration parameters of the zero plane, determine the intercept position of the zero plane of the main camera, and adjust the main camera so that the contour lines of the side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 collected by the main camera coincide with the intercept line of the zero plane of the main camera; calculate the slope of the line where the vertices P1, P2, and P3 are located, and the tilt angle A can be obtained, that is, the rotation angle of the main camera around the Y axis, and rotate the contour lines of the side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 by the angle A; then calculate the position offset of the vertex P2 from the center point (0, 0) to obtain the offset amounts [x, z] in the X-axis direction and the Z-axis direction, and offset this contour line as a whole by the distance [x, z], and then the three parameters [Xref, 0, Zref, 0, Bref, 0] can be obtained. S23: The camera moves along the Y axis, obtains the point cloud data set scanned by the main camera, removes the influence of stray points. The side surfaces of the second calibration unit or the side surface edges of the fourth coding structure at the vertices P1, P2, and P3 intersect to obtain the straight lines line1, line2, and line3. Interpolation fitting of line1, line2, and line3 can obtain a fitting plane. In order to correct the fitting plane to the zero plane, first, project line2 onto the YOZ plane, calculate the slope of the projected line to obtain the angle of the line with respect to the Y axis, and then the rotation angle of the fitting plane in the YOZ plane can be obtained; then project line2 onto the XOY plane, calculate the slope of the projected line to obtain the angle of the line with respect to the Y axis, and then the angle between the fitting plane and the XOY plane can be obtained, thereby obtaining the other two angular deflection data of the calibration parameters of the main camera; taking the lower edge coordinate of the third calibration unit of the calibration block as the Y-axis 0 point, and taking the lower edge coordinates of the three-layer main reference points as the offset amount of the Y-axis data, the six calibration parameters [Xref, Yref, Zref, Aref, Bref, Cref] of the main camera can be obtained.

5. A calibration method for multi-camera imaging of large targets according to claim 4, characterized in that, In step S3, taking the main camera as the reference camera, calibrate each sub-camera respectively to obtain the calibration parameters of each sub-camera; completing the static calibration of the main camera and each sub-camera includes the following steps: S31: According to the contour information of the image, confirm the overlapping area of the main camera and the first sub-camera, extract the data of the corresponding overlapping area line segment in the main camera for fitting to obtain the inclination angle B1 of the fitting line, then extract the line segment of the corresponding overlapping area in the first sub-camera for fitting to obtain the inclination angle B2 of the fitting line, calculate the angle between the inclination angles B1 and B2, and thus obtain the rotation angle of the overlapping segment of the first sub-camera and the main camera, which is the calibration angle Bcalib1 in the Y-axis direction of the first sub-camera; extract a common corner point in the overlapping area line segment, calculate the mapping of the corner point on the first sub-camera to this corner point on the main camera, and then the offset amounts [Xcalib1, Zcalib1] in the X direction and the Z direction can be obtained; thus, the static calibration parameters [Xcalib1, 0, Zcalib1, 0, Bcalib1, 0] of the first sub-camera are obtained. S32: Operate the main camera and the second secondary camera simultaneously. Referring to the content of step S31, the rotation angle of the overlapping segment between the second secondary camera and the main camera is the calibration angle Bcalib2 of the second secondary camera in the Y-axis direction; extract a common corner point from the overlapping area line segment, calculate the mapping from the corner point on the second secondary camera to this corner point on the main camera, and the offsets in the X and Z directions [Xcalib2, Zcalib2] can be obtained; thus, the static calibration parameters of the second secondary camera [Xcalib2, 0, Zcalib2, 0, Bcalib2, 0] are obtained. S33: Rotate the second calibration unit 72° along the vertical direction to verify the calibration accuracy of the main camera, the first secondary camera, and the second secondary camera. If the coincidence degree of the contour data is within the repeatability accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repeatability accuracy range of the dynamic data acquisition range of each camera, recalibration is required, and steps S31, S32, and S33 are repeated. S34: After the first secondary camera and the second secondary camera are calibrated correctly, write the static calibration parameters into the first secondary camera and the second secondary camera, corresponding to the static calibration of the first secondary camera and the second secondary camera. S35: After the attitude calibration of the main camera, the first secondary camera, and the second secondary camera is completed, rotate the calibration block again, align the third coding structure and its side surface of the second calibration unit with the main camera, calibrate the fourth secondary camera with the first secondary camera as the reference camera, and calibrate the third secondary camera with the second secondary camera as the reference. The calibration method is the same as that in step S31, and the static calibration parameters of the third secondary camera [Xcalib3, 0, Zcalib3, 0, Bcalib3, 0] and the static calibration parameters of the fourth secondary camera [Xcalib4, 0, Zcalib4, 0, Bcalib4, 0] can be obtained. At this point, the preliminary static calibration of all cameras is completed.

6. A calibration method for multi-camera imaging of large targets according to claim 5, characterized in that After the preliminary static calibration of all cameras in step S3 is completed, it also includes a verification step S36 for static calibration, and the specific content is as follows: S36: After the preliminary static calibration of the main camera and each secondary camera is completed, adjust the main camera and each secondary camera to face the vertices of the regular pentagon of the first calibration unit and fix them. Conduct an overall verification of the static calibration accuracy of the main camera and each secondary camera to ensure that the center point position of the calibration block does not change due to the movement of the main camera and each secondary camera in the Y direction; conduct an overall view of the main camera and each secondary camera. If the time acquisition accuracy of the calibration result is within the repeatability accuracy range of the data collected by the corresponding camera, the calibration result is considered accurate, and the static calibration ends; if the deviation exceeds this range, first judge the degree to which the data deviation range exceeds the repeatability accuracy of the data collected by the camera. If the deviation from the repeatability accuracy range of the data collected by the camera is limited, fine-tune it on the first calibration unit; if the deviation result is too large, it is necessary to return to the second calibration unit for recalibration, that is, repeat steps S31 - S35 until the calibration accuracy of the contour meets the requirements.

7. A calibration method for large-target multi-camera imaging according to claim 5, characterized in that After the static calibration described in step S4 is completed, drive the main camera and each sub-camera to move in the Y-axis direction to complete the dynamic calibration of the main camera and each sub-camera, which includes the following steps: S41: Drive the cameras to move in the Y-axis direction for dynamic calibration; First, use the main camera and the first sub-camera to perform motion scanning to obtain point cloud data, and obtain the overlapping area image of the main camera and the first sub-camera. The overlapping area is two adjacent planes; S42: Calculate the angle and rotation angle between two adjacent planes in the overlapping area; if the area images obtained by the main camera and the first sub-camera completely overlap, then the first intersection line line1 in the clockwise direction in the image obtained by the main camera coincides with the third intersection line Lleft3 in the clockwise direction of the first sub-camera. Project the first intersection line Lleft1 in the image obtained by the first sub-camera from the vertical direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line, that is, the angle between the projection line and the Y-axis, so as to obtain the rotation angle Acalib1 of the fitting plane plane1 in the YOZ plane; then project the first intersection line Lleft1 from the horizontal direction onto the leftmost fitting plane plane1 of the main camera, and find the slope of the projection line, that is, the angle between the line and the Y-axis, that is, the angle between the fitting plane plane1 and the XOZ plane Ccalib1; take the edge coordinates of the lower end surface of the third calibration unit of the calibration block as the zero point of the Y-axis, and take the vertices of the regular pentagon at the lower edges of the third calibration unit, the second calibration unit, and the first calibration unit corresponding to the main reference point as the offset Ycalib1 of the Y-axis quantity. Then, combined with the static calibration parameters of the first sub-camera, obtain all six camera parameters [Xcalib1, Ycalib1, Zcalib1, Acalib1, Bcalib1, Ccalib1] of the first sub-camera; S43: Adopt the same content as step S42 to perform dynamic calibration on the main camera and the second sub-camera, and combined with the current calibration parameters of the second sub-camera, obtain all six camera parameters [Xcalib2, Ycalib2, Zcalib2, Acalib2, Bcalib2, Ccalib2] of the second sub-camera; S44: Rotate the calibration block as a whole by 72° around the Y-axis to verify the calibration accuracy of the main camera, the first sub-camera, and the second sub-camera. If the coincidence degree of the contour data of the main camera, the first sub-camera, and the second sub-camera is within the repetition accuracy range of the dynamic data acquisition range of each camera, it is considered that the calibration is correct; if the deviation of the coincidence degree of the contour data exceeds the repetition accuracy range of the dynamic data acquisition range of each camera, it is necessary to re-perform the calibration, and repeat steps S42 and S43; S45: After the main camera, the first sub-camera, and the second sub-camera are calibrated correctly, rotate the calibration block again, align the third coding structure and its side surface of the second calibration unit with the main camera, use the first sub-camera as the reference camera to calibrate the fourth sub-camera, and use the second sub-camera as the reference to calibrate the third sub-camera. The method is the same as step S42; The calibration parameters [Xcalib3, Ycalib3, Zcalib3, Acalib3, Bcalib3, Ccalib3] of the third camera and the static calibration parameters [Xcalib4, Ycalib4, Zcalib4, Acalib4, Bcalib4, Ccalib4] of the fourth camera can be obtained; So far, the preliminary dynamic calibration of all cameras is completed; S46: After the camera completes calibration using the current calibration parameters, re-scan the calibration block, verify the imaging accuracy in the X and Z directions through the first calibration unit, and verify the imaging accuracy in the Y direction through the analysis of the second calibration unit. If the result is within the acquisition data accuracy range of the camera, the camera calibration ends; if there is a deviation, analyze and fine-tune the data. If the error is too large, repeat the entire process until the calibration accuracy is met.

8. A calibration system for multi-camera imaging of large targets, comprising a calibration block, a main camera, a first sub-camera, a second sub-camera, a third sub-camera and a fourth sub-camera; the contour of the calibration block is a regular pentagon, and first coding structures, second coding structures, third coding structures, fourth coding structures and fifth coding structures protruding outward are arranged on the side surfaces at different positions of the calibration block; the first coding structure, the second coding structure, the third coding structure, the fourth coding structure and the fifth coding structure are all different; characterized in that: The main camera, the first camera, the second camera, the third camera, and the fourth camera incorporate the calibration method for large-target multi-camera imaging as described in any one of claims 1-7.

Images