CN111028297A - Calibration method of surface structured light three-dimensional measurement system - Google Patents
Calibration method of surface structured light three-dimensional measurement system Download PDFInfo
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- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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Abstract
The application discloses a calibration method of a surface structured light three-dimensional measurement system, which comprises the following steps: calibrating the internal parameter and distortion of the camera by using a glass checkerboard calibration plate covering the full field of view; projecting left and right field projection images to a white area of a special calibration plate with a half-white half checkerboard pattern respectively, and calibrating internal parameters and distortion of the projector; vertically moving the special calibration plate, and establishing a three-dimensional reconstruction coordinate system; and calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system. According to the calibration method, the special calibration plate with half white and half checkerboard is designed, the three-dimensional reconstruction coordinate system is constructed in cooperation with the vertical lifting platform to calibrate the projector, the camera and the surface structured light system, the camera calibration, the projector calibration and the system external parameter calibration are separated by the overall calibration scheme, the structural light algorithm is not relied on, various error coupling interferences in the calibration process are avoided, and therefore the calibration precision is greatly improved.
Description
Technical Field
The application relates to the technical field of machine vision measurement, in particular to a calibration method of a surface structured light three-dimensional measurement system.
Background
The surface structured light three-dimensional measurement system plays an important role in industrial automation, including three-dimensional measurement, positioning, detection and the like. The surface structure light system consists of a projector and a camera, wherein the projector projects coding structure light to the surface of a measured object, the camera collects modulation patterns, geometric information of the surface of the measured object is obtained through a decoding algorithm, and the commonly used coding structure light comprises phase shift stripes, Gray codes and the like. In order to obtain actual three-dimensional information, parameters of the camera and the projector and system external parameters of the camera and the projector relative to a three-dimensional reconstruction coordinate system need to be obtained through calibration.
The projector calibration method in the surface structured light system comprises two methods: projecting structured light such as phase shift stripes and the like onto a calibration plate, determining projector image coordinates corresponding to camera image coordinates through algorithms such as phase shift and the like, resampling a camera target image to obtain a projector target image, and calibrating by using a traditional camera calibration method; and the other method is to project a characteristic point pattern to a calibration plate, calibrate the camera by using the actual characteristic point image on the calibration plate, calculate the spatial coordinates of the projected characteristic points by using the projected characteristic point image to obtain the characteristic points and the corresponding spatial coordinates of the projector image, and calibrate by using the traditional camera. The existing method for calibrating the external parameters of the system generally establishes a three-dimensional reconstruction coordinate system by taking a certain calibration plate plane as a reference, and takes the external parameters at the position in the calibration process as the external parameters of the system.
However, the first method in the projector calibration method relies on a structured light algorithm and is influenced by the algorithm precision, and if the second method directly uses a conventional 2D calibration plate, the projected characteristic point pattern and the actual characteristic point pattern are overlapped to influence the characteristic point extraction; the existing method for calibrating the external parameters of the system depends on the external parameter calculation precision in the calibration process, and the position precision outside the plane of the calibration plate is poor.
Disclosure of Invention
The application provides a calibration method of a surface structured light three-dimensional measurement system, which aims to solve the problem of poor precision of the conventional surface structured light system calibration method.
In order to solve the technical problem, the embodiment of the application discloses the following technical scheme:
in a first aspect, an embodiment of the present application discloses a calibration method for a surface structured light three-dimensional measurement system, where the method includes:
calibrating the internal parameter and distortion of the camera by using a glass checkerboard calibration plate covering the full field of view;
projecting left and right view field projection images to a white area of a special calibration plate of a half-white half-projection image respectively, and calibrating internal parameters and distortion of a projector;
vertically moving the special calibration plate to establish a three-dimensional reconstruction coordinate system;
and calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system.
Optionally, calibrating the camera internal parameter and distortion by using a glass checkerboard calibration plate covering the full field of view, comprising:
placing a glass chessboard pattern calibration plate at different positions and different angles within the range of the field of view and the depth of field;
collecting a plurality of target images;
and calculating to obtain a camera internal reference matrix and a lens distortion coefficient matrix according to the target image.
Optionally, the method of calibrating the internal parameters and distortion of the projector includes the steps of projecting left and right field projection images to the white area of a special calibration plate of a half-white half-projection image, respectively, and calibrating the internal parameters and distortion of the projector:
respectively collecting projection checkerboard images and actual checkerboard images corresponding to the left and right field projection images;
calculating external parameters of the position of the special calibration plate by using calibrated internal parameters and distortion of the camera and actual checkerboard image coordinates;
calculating the space coordinates of the projection checkerboard angular points by using the image coordinates of the projection checkerboard angular points on the special calibration plate;
and calibrating internal parameters of the projector and distortion parameters of the lens according to the space coordinates and the coordinates of each corner point image in the corresponding left and right view field projection images.
Optionally, the acquiring the projection checkerboard image and the actual checkerboard image corresponding to the left and right field projection images respectively includes:
the projector projects a left view projection image to a white area of the dedicated calibration plate;
the camera respectively collects projection checkerboard images and actual checkerboard images corresponding to the left view field projection images;
horizontally rotating the special calibration plate;
the projector projects the right view projection image to a white area of the dedicated calibration plate;
and the camera respectively acquires a projection checkerboard image and an actual checkerboard image corresponding to the plurality of groups of right view field projection images.
Optionally, the calculating the external parameter of the position of the special calibration board by using the calibrated internal parameter and distortion of the camera and the actual checkerboard image coordinate includes:
establishing a space coordinate system;
obtaining the space coordinates of each angular point according to the actual checkerboard size;
extracting coordinates of corner points of the actual checkerboard images from the actual checkerboard images corresponding to the left and right field-of-view projection images respectively;
and calculating a rotation matrix and a translation matrix from each position space coordinate system to the camera coordinate system according to the calibrated internal parameter and distortion of the camera.
Optionally, calculating the spatial coordinates of the corner points of the projection checkerboard by using the image coordinates of the corner points of the projection checkerboard on the special calibration board, includes:
distortion correction is carried out on the projection checkerboard images corresponding to the left and right field projection images respectively;
extracting the coordinates of the angular points of the undistorted projection checkerboard image;
and calculating to obtain the space coordinates of the corresponding projection checkerboard corner points according to the camera internal parameters, distortion, the rotation matrix and the translation matrix of each position and the corner point coordinates of the undistorted projection checkerboard image.
Optionally, the vertically moving the dedicated calibration plate to establish a three-dimensional reconstruction coordinate system includes:
fixing the special calibration plate on a vertical lifting platform, and establishing a three-dimensional reconstruction coordinate system;
moving the dedicated calibration plate at fixed intervals;
and obtaining the space coordinates of each corner point of the actual checkerboard according to the size of the checkerboard on the special calibration board and the fixed interval.
Optionally, calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system includes:
respectively collecting projection checkerboard images and actual checkerboard images corresponding to a plurality of groups of left view field projection images at fixed intervals;
calibrating external parameters of the camera according to the space coordinates of each corner point of the actual checkerboard and the image coordinates of each corner point of the actual checkerboard;
and calibrating external parameters of the projector according to the image coordinates of each corner point in the left view field projection image and the space coordinates of the corner points of the projection checkerboard.
Optionally, calibrating external parameters of the camera according to the spatial coordinates of each corner point of the actual checkerboard and the image coordinates of each corner point of the actual checkerboard, including:
distortion correction is carried out on the actual checkerboard image according to the calibrated camera internal parameters and distortion;
extracting image coordinates of each corner point in the undistorted actual checkerboard image;
and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the camera coordinate system according to the image coordinates of each corner point in the undistorted actual checkerboard image and the space coordinates of each corner point of the actual checkerboard.
Optionally, calibrating external parameters of the projector according to image coordinates of each corner point in the left view field projection image and space coordinates of corner points of the projection checkerboard, including:
distortion correction is carried out on the projection checkerboard image according to the calibrated camera internal parameter and distortion;
extracting image coordinates of each corner point in the undistorted projection checkerboard image;
calculating to obtain the space coordinates of the corner points of the projection checkerboard according to the camera internal parameters, distortion, rotation matrix, translation matrix and the image coordinates of each corner point in the undistorted projection checkerboard image;
calculating coordinates of each corner point of the undistorted left view field projection image according to the calibrated internal parameters and distortion of the projector;
and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the projector coordinate system according to the coordinates of each corner point of the undistorted left view field projection image and the space coordinates of the corner points of the projection checkerboard.
Compared with the prior art, the beneficial effect of this application is:
the calibration method of the surface structured light three-dimensional measurement system provided by the embodiment of the application comprises the following steps: calibrating the internal parameter and distortion of the camera by using a glass checkerboard calibration plate covering the full field of view; projecting left and right field projection images to a white area of a special calibration plate with a half-white half checkerboard pattern respectively, and calibrating internal parameters and distortion of the projector; vertically moving the special calibration plate, and establishing a three-dimensional reconstruction coordinate system; and calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system. According to the calibration method, the special calibration plate with half white and half checkerboard is designed, the three-dimensional reconstruction coordinate system is constructed in cooperation with the vertical lifting platform to calibrate the projector, the camera and the surface structured light system, the camera calibration, the projector calibration and the system external parameter calibration are separated by the overall calibration scheme, the structural light algorithm is not relied on, various error coupling interferences in the calibration process can be avoided, and therefore the calibration precision can be greatly improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
fig. 2 is a schematic view of a calibration plate dedicated to the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 3 is a schematic diagram of left and right view field projection images in the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 4 is a detailed flowchart of S200 in the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 5 is a detailed flowchart of S201 in the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 6 is a detailed flowchart of S202 in the calibration method of the area structured light three-dimensional measurement system according to the embodiment of the present application;
FIG. 7 is a diagram of a structured light system imaging relationship provided in an embodiment of the present application;
fig. 8 is a detailed flowchart of S203 in the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application;
FIG. 9 is a schematic diagram of a vertical translation specialized calibration plate provided in accordance with an embodiment of the present application;
fig. 10 is a detailed flowchart of S400 in the calibration method of the area structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 11 is a detailed flowchart of S402 in the calibration method of the area structured light three-dimensional measurement system according to the embodiment of the present application;
fig. 12 is a detailed flowchart of S403 in the calibration method of the area structured light three-dimensional measurement system according to the embodiment of the present application.
Detailed Description
In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, a flowchart of a calibration method of a surface structured light three-dimensional measurement system provided in the embodiment of the present application is shown.
As shown in fig. 1, a calibration method of a surface structured light three-dimensional measurement system provided in the embodiment of the present application includes:
s100: the camera internal parameters and distortion are calibrated using a glass checkerboard calibration plate covering the full field of view.
According to the Zhangyingyou scaling principle, a glass checkerboard scaling plate is used for scaling internal parameters and lens distortion parameters of the camera. Specifically, calibration plates are placed at different angles at different positions within the market and the depth of field, 20-30 target images are collected, and an openCV (open CV library calibration function) is used for calculating to obtain a camera internal reference matrix ACAnd the distortion coefficient matrix D of the camera lensC。
The openCV is calibrated by using a checkerboard, and in order to find the checkerboard template, a function cv2. findchessboardregisters () in the openCV can be used, and if the template is detected by the function, the function returns a corresponding corner point; after finding the corner point, the function cv2.corner sub pix () can be used to obtain more accurate pixel coordinates of the corner point, and the function cv2.draw chessboardcorrers () can be used to draw the corner point on the image for display; the three-dimensional points used for calibration and the two-dimensional point pairs on the image corresponding to the three-dimensional points are obtained through the steps, calibration is carried out by using a function cv2.draw chessboardcorrers (), and the function returns a calibration result, an internal parameter matrix of the camera and a distortion coefficient.
S200: and respectively projecting the left and right view field projection images to the white area of the special calibration plate of the half-white half-projection image, and calibrating the internal parameter and distortion of the projector.
The application designs a half white half check's special calibration board, as shown in fig. 2, this special calibration board left half is white, and the right half is black and white projection image, and the check size is 2mm, and pattern size 42mm 50mm, the equal symmetry about the pattern about the top and bottom uses the high definition photographic paper of IOS2333 standard resolution test card to print, pastes on the plastic-aluminum board smoothly.
The projection image design is shown in fig. 3, the left half of the left view field projection image pattern L is a black and white projection image, the right half of the right view field projection image pattern R is a black and white projection image, and the length-to-width ratio of the checkerboard dimension is 2:1 so as to adapt to stretching and scaling of different proportions in the transverse and longitudinal directions when the projector is obliquely projected.
The specific method for calibrating the internal reference and distortion of the projector by using the special calibration plate is shown in fig. 4:
s201: and respectively acquiring projection checkerboard images and actual checkerboard images corresponding to the left and right field-of-view projection images.
The method for acquiring the calibration image is specifically shown in fig. 5:
s2011: the projector projects the left field of view projection image onto the white area of the dedicated calibration plate.
S2012: the camera respectively collects projection checkerboard images and actual checkerboard images corresponding to the plurality of groups of left view field projection images.
S2013: and a special calibration plate for horizontal rotation.
S2014: the projector projects the right field of view projection image onto the white area of the dedicated calibration plate.
S2015: the camera respectively collects projection checkerboard images and actual checkerboard images corresponding to the plurality of groups of right view field projection images.
The projector projects the left view field Pattern to the white area on the left side of the special calibration board, the left view field Pattern and the right view field Pattern are not overlapped with each other, the camera acquires the image Img of the projected checkerboardPL CStopping projection, and collecting the actual checkerboard image Img on the same calibration plate by using a cameraCL CAnd obtaining a group of calibration graphs. Acquiring 10-15 groups of calibration graphs Img at different positionsPL CAnd ImgCL C. Then, rotating the special calibration board to enable the actual chessboard to be positioned at the left side, projecting the right view field projection image Pattern onto a white area at the right side of the special calibration board by the projector, and collecting 10-15 groups of corresponding calibration images ImgPR CAnd ImgCR C。
S202: and resolving external parameters of the position of the special calibration plate by using the calibrated internal parameters and distortion of the camera and the actual checkerboard image coordinates.
The specific method for calculating the external reference of the position of the special calibration plate is shown in fig. 6:
s2021: and establishing a space coordinate system.
S2022: and obtaining the space coordinates of each corner point according to the actual checkerboard size.
S2023: and respectively extracting the coordinates of the corner points of the actual checkerboard image from the actual checkerboard images corresponding to the left and right field-of-view projection images.
S2024: and calculating to obtain a rotation matrix and a translation matrix from each position space coordinate system to the camera coordinate system according to the calibrated camera internal parameter and distortion.
The imaging model of the structured light system is built according to the imaging relationship of the structured light system, which is shown in FIG. 7, OW-XWYWZWAs a space coordinate system, OP-XPYWZPAs a projector coordinate system, OP-UPVPFor projector image plane coordinate system, OC-XCYCZCAs camera coordinate system, OC-UCVCIs a camera image plane coordinate system. The projector will make a point P on the two-dimensional imagePProjected to a three-dimensional space point P, the camera images the three-dimensional space point P to a point P on a two-dimensional image planeCAccording to the working mechanism and the imaging relation of the projector, the projector can be equivalent to a reverse camera. Distortion of projector and camera lens by using common lens distortion model and distortion coefficient DP[k1 P，k2 P，p1 P，p2 P，k3 P]And DC[k1 C，k2 C，p1 C，p2 C，k3 C]And showing that the conversion between the actual image point and the undistorted image point is realized.
The relationship between the undistorted image point coordinates of the camera image and the space coordinates is as follows:
wherein A isCIs an internal reference matrix including a focal length fx C、fy CAnd principal point u0 C、v0 C，MCIs a reference matrix comprising a spatial coordinate system to camera coordinate system rotation matrix RCAnd translation matrix TC。
Establishing a space coordinate system O by taking the first corner point at the upper left of the actual checkerboard at each position as an originwi-XwiYwiZwi，XwiWith the axis directed vertically downwards, YwiAxis horizontal to right, ZwiThe axis is vertical to the special calibration board, the space coordinate of each angular point is obtained according to the actual checkerboard size, and the Z coordinate is 0. From the calibration chart ImgCL CAnd ImgCR CExtracting the coordinates (u) of the corner points of the actual checkerboard imageci C，vci C) According to the calibrated camera internal parameter ACAnd distortion coefficient DCAnd calculating to obtain a rotation matrix R from each position space coordinate system to the camera coordinate systemi CAnd translation matrix Ti C。
S203: and calculating the space coordinates of the corner points of the projection checkerboard by using the image coordinates of the corner points of the projection checkerboard on the special calibration plate.
The specific method for calculating the spatial coordinates of the corner points of the projection checkerboard is shown in fig. 8:
s2031: and respectively carrying out distortion correction on projection checkerboard images corresponding to the left and right field projection images.
S2032: and extracting the coordinates of the corner points of the undistorted projection checkerboard image.
S2033: and calculating to obtain the space coordinates of the corresponding projection checkerboard corner points according to the camera internal parameters, distortion, rotation matrix and translation matrix of each position and the corner point coordinates of the undistorted projection checkerboard image.
For projection checkerboard image ImgPL CAnd ImgPR CCarrying out distortion correction to extract an undistorted projection checkerboard patternCoordinates of corner points of the image (u)pi C，vpi C). The projection checkerboard and the actual checkerboard on the special calibration board are coplanar, so the space coordinate Z of the corner point of the projection checkerboardwi P0. According to the camera internal parameter ACDistortion coefficient DCAnd a rotation matrix R for each positioni CAnd translation matrix Ti CBy projecting the coordinates of the corner points of the checkerboard image (u)pi C，vpi C) Calculating to obtain corresponding space coordinate Xwi PAnd Ywi P。
S204: and calibrating internal parameters of the projector and distortion parameters of the lens according to the space coordinates and coordinates of each corner point image in the corresponding left and right field projection images.
In the imaging model of the structured light system, the relationship between the undistorted pixel coordinate and the space coordinate of the projector image is as follows:
wherein A isPIs an internal reference matrix including a focal length fx P、fy PAnd principal point u0 P、v0 P，MPIs a reference matrix comprising a spatial coordinate system to camera coordinate system rotation matrix RPAnd translation matrix TP。
The spatial coordinates (X) of the corner points in the projection checkerboard on the known special calibration boardwi P，Ywi P，Zwi P) Calibrating a reference matrix A of the projector by using a camera calibration methodPAnd lens distortion coefficient matrix DP。
S300: and vertically moving the special calibration plate to establish a three-dimensional reconstruction coordinate system.
The special calibration plate is fixed on the vertical elevating table so that the special calibration plate moves at regular intervals in the system direction, as shown in fig. 9. Establishing a three-dimensional reconstruction coordinate system O by taking the first corner point at the upper left of the actual chessboard of the initial position calibration plate as an originalR-XRYRZR，XRWith axis parallel to the checkerboard pattern down, YRThe axis is parallel to the right of the checkerboard pattern, ZRThe axis is perpendicular to the dedicated calibration plate pointing system. And moving a special calibration plate to obtain a series of actual checkerboard angular points of the known solid. Knowing that the size of the checkerboard is s × s and the movement interval is Δ d, the coordinates of the corner point in the i row and j column of the nth position are:
XR C＝i×s,YR C＝j×s,ZR C＝n×Δd
s400: and calibrating external parameters of the external parameter projector of the camera according to the three-dimensional reconstruction coordinate system.
Constructing a three-dimensional target and a three-dimensional reconstruction coordinate system, and calibrating external parameters of the camera; and (4) reversely calculating the three-dimensional reconstruction coordinates by using the projection checkerboard image coordinates on the special calibration board, and calibrating the external parameters of the projector.
The specific method for calibrating the camera external parameter and the projector external parameter is shown in fig. 10:
s401, projection checkerboard images and actual checkerboard images corresponding to a plurality of groups of left view field projection images with fixed intervals are collected respectively.
The projector projects the left view field projection image Pattern onto the white area on the left side of the special calibration board, and the camera collects the projection checkerboard image ImgP CStopping projection, and collecting actual checkerboard image Img by cameraC CAnd obtaining a group of calibration graphs. The special calibration plate is vertically moved, and 5 groups of calibration graphs are collected at fixed intervals.
S402: and calibrating external parameters of the camera according to the space coordinates of each corner point of the actual chessboard and the image coordinates of each corner point of the actual chessboard.
As shown in fig. 11, the specific method for calibrating the external parameters of the camera includes:
s4021: and carrying out distortion correction on the actual checkerboard image according to the calibrated camera internal reference and distortion.
S4022: and extracting the image coordinates of each corner point in the undistorted actual checkerboard image.
S4023: and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the camera coordinate system according to the image coordinates of each corner point in the undistorted actual checkerboard image and the space coordinates of each corner point of the actual checkerboard.
According to the calibrated camera internal reference and distortion coefficient, the calibration graph Img is subjected toC CDistortion correction is carried out, and the coordinates (u) of the corner points of the undistorted actual checkerboard image are extractedc C*，Vc C*)). The spatial coordinates (X) of each corner point of the actual chessboard are knownR C，YR C，ZR C) According to the camera model, calculating to obtain a rotation matrix R from the three-dimensional reconstruction coordinate system to the camera coordinate systemCAnd translation matrix TC。
S403: and calibrating external parameters of the projector according to the image coordinates of each corner point in the left view field projection image and the space coordinates of each corner point of the projection checkerboard.
As shown in fig. 12, the specific method for calibrating external parameters of the projector includes:
s4031: and carrying out distortion correction on the projection checkerboard image according to the calibrated camera internal parameter and distortion.
S4032: and extracting the image coordinates of each corner point in the undistorted projection checkerboard image.
S4033: and calculating to obtain the space coordinates of the corner points of the projection checkerboard according to the camera internal parameters, distortion, rotation matrix, translation matrix and the image coordinates of each corner point in the undistorted projection checkerboard image.
S4034: and calculating coordinates of each corner point of the undistorted left view field projection image according to the calibrated internal parameters and distortion of the projector.
S4035: and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the projector coordinate system according to the coordinates of each corner point of the undistorted left view field projection image and the space coordinates of the corner points of the projection checkerboard.
According to the calibrated camera internal reference and distortion coefficient, the calibration graph Img is subjected toP CDistortion correction is carried out, and the image coordinates (u) of each corner point in the undistorted projection checkerboard image are extractedp C*，vp C*). Spatial coordinate Z of ith position projection checkerboard angular pointRi PI × Δ d, according to the camera parameters aC、DC、RCAnd TCBy projecting checkerboard image coordinates (u)p C*，vp C*) Calculating the corresponding space coordinate XR PAnd YR P。
The image coordinates (u) of each corner point in the left view field projection image Pattern are knownp P，vp P) Calculating the image coordinate (u) of the undistorted angular point according to the calibrated internal reference and distortion coefficient of the projectorp P*，vp P*). The space coordinates (X) of the corner points of the projection checkerboard in the three-dimensional reconstruction coordinate system are obtainedR P,YR P,ZR P) According to the projector model, calculating to obtain a rotation matrix R from the three-dimensional reconstruction coordinate system to the projector coordinate systemPAnd translation matrix TP。
In conclusion, a three-dimensional reconstruction coordinate system is established, and external parameters from the three-dimensional reconstruction coordinate system to a camera coordinate system are obtained through calibration: rotation matrix RCAnd translation matrix TCInner reference of video camera ACAnd distortion coefficient DC(ii) a And calibrating to obtain external parameters from the three-dimensional reconstruction coordinate system to the projector coordinate system: rotation matrix RPAnd translation matrix TPReference A in the projectorPAnd distortion coefficient DP. The position relation between a camera and a projector in the structured light system and respective internal parameters are calibrated, and the actual three-dimensional coordinates measured by the structured light system can be calculated.
According to the calibration method of the surface structured light three-dimensional measurement system, the internal parameters and distortion of the camera are calibrated by using the high-precision glass checkerboard target covering the whole field of view, and the obtained parameters are more stable in the whole field of view. Secondly, a designed special calibration plate is used, the mode that left and right view field projection checkerboard patterns respectively collect target maps is adopted, and camera external parameters corresponding to different calibration plate positions are resolved, so that internal parameters and distortion of the projector are calibrated. The projection pattern is simple, no special design pattern is required to be added, the projection image collected by the camera does not interfere with the actual image, and the feature points can be directly extracted by adopting a stable and mature angular point extraction algorithm; the characteristic points are extracted by independent projection of the left and right view fields and are jointly used for projector calibration, so that the whole projector view field can be well calibrated. The method has the advantages that the vertical moving guide rail is used for constructing the three-dimensional target, the spatial characteristic points at different positions in the whole space are used for participating in calibration, and the external parameter of the structured light system is calibrated.
The calibration method provided by the application adopts the designed special calibration plate, and is matched with the vertical lifting platform to construct the three-dimensional target, and calibrate the projector, the camera and the surface structured light system, the camera calibration, the projector calibration and the system external reference calibration are separated by the integral calibration scheme, and the calibration method does not depend on a structured light algorithm, so that various error coupling interferences in the calibration process are avoided, and the calibration precision is greatly improved.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.
The above-described embodiments of the present application do not limit the scope of the present application.
Claims (10)
1. A calibration method of a surface structured light three-dimensional measurement system is characterized by comprising the following steps:
calibrating the internal parameter and distortion of the camera by using a glass checkerboard calibration plate covering the full field of view;
projecting left and right view field projection images to a white area of a special calibration plate of a half-white half-projection image respectively, and calibrating internal parameters and distortion of a projector;
vertically moving the special calibration plate to establish a three-dimensional reconstruction coordinate system;
and calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system.
2. The calibration method according to claim 1, wherein calibrating the camera internal reference and distortion using a checkerboard calibration plate covering the full field of view comprises:
placing a glass chessboard pattern calibration plate at different positions and different angles within the range of the field of view and the depth of field;
collecting a plurality of target images;
and calculating to obtain a camera internal reference matrix and a lens distortion coefficient matrix according to the target image.
3. The calibration method according to claim 1, wherein projecting the left and right field projection images to the white area of the dedicated calibration board of the half-white half projection image respectively, calibrating the internal parameters and distortion of the projector, comprises:
respectively collecting projection checkerboard images and actual checkerboard images corresponding to the left and right field projection images;
calculating external parameters of the position of the special calibration plate by using calibrated internal parameters and distortion of the camera and actual checkerboard image coordinates;
calculating the space coordinates of the projection checkerboard angular points by using the image coordinates of the projection checkerboard angular points on the special calibration plate;
and calibrating internal parameters of the projector and distortion parameters of the lens according to the space coordinates and coordinates of each corner point image in the corresponding left and right field projection images.
4. The calibration method according to claim 3, wherein the collecting of the projection checkerboard image and the actual checkerboard image corresponding to the left and right field projection images respectively comprises:
the projector projects a left view projection image to a white area of the dedicated calibration plate;
the camera respectively collects projection checkerboard images and actual checkerboard images corresponding to the left view field projection images;
horizontally rotating the special calibration plate;
the projector projects the right view projection image to a white area of the dedicated calibration plate;
and the camera respectively acquires a projection checkerboard image and an actual checkerboard image corresponding to the plurality of groups of right view field projection images.
5. The calibration method according to claim 3, wherein the step of calculating the external parameter of the position of the dedicated calibration plate by using the calibrated camera internal parameter, distortion and the actual checkerboard image coordinates comprises:
establishing a space coordinate system;
obtaining the space coordinates of each angular point according to the actual checkerboard size;
extracting coordinates of corner points of the actual checkerboard images from the actual checkerboard images corresponding to the left and right field-of-view projection images respectively;
and calculating a rotation matrix and a translation matrix from each position space coordinate system to the camera coordinate system according to the calibrated internal parameter and distortion of the camera.
6. The calibration method according to claim 5, wherein calculating the spatial coordinates of the projected checkerboard corner points using the image coordinates of the projected checkerboard corner points on the dedicated calibration board comprises:
distortion correction is carried out on the projection checkerboard images corresponding to the left and right field projection images respectively;
extracting the coordinates of the angular points of the undistorted projection checkerboard image;
and calculating to obtain the space coordinates of the corresponding projection checkerboard corner points according to the camera internal parameters, distortion, the rotation matrix and the translation matrix of each position and the corner point coordinates of the undistorted projection checkerboard image.
7. The calibration method according to claim 1, wherein vertically moving the dedicated calibration plate to establish a three-dimensional reconstruction coordinate system comprises:
fixing the special calibration plate on a vertical lifting platform, and establishing a three-dimensional reconstruction coordinate system;
moving the dedicated calibration plate at fixed intervals;
and obtaining the space coordinates of each corner point of the actual checkerboard according to the size of the checkerboard on the special calibration board and the fixed interval.
8. The calibration method according to claim 7, wherein calibrating the camera external parameter and the projector external parameter according to the three-dimensional reconstruction coordinate system comprises:
respectively collecting projection checkerboard images and actual checkerboard images corresponding to a plurality of groups of left view field projection images at fixed intervals;
calibrating external parameters of the camera according to the space coordinates of each corner point of the actual checkerboard and the image coordinates of each corner point of the actual checkerboard;
and calibrating external parameters of the projector according to the image coordinates of each corner point in the left view field projection image and the space coordinates of each corner point of the projection checkerboard.
9. The calibration method according to claim 8, wherein calibrating the external parameters of the camera according to the spatial coordinates of the corner points of the actual checkerboard and the image coordinates of the corner points of the actual checkerboard comprises:
distortion correction is carried out on the actual checkerboard image according to the calibrated camera internal parameters and distortion;
extracting image coordinates of each corner point in the undistorted actual checkerboard image;
and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the camera coordinate system according to the image coordinates of each corner point in the undistorted actual checkerboard image and the space coordinates of each corner point of the actual checkerboard.
10. The calibration method according to claim 9, wherein calibrating the external parameters of the projector according to the image coordinates of each corner point in the left-view projection image and the spatial coordinates of each corner point of the projection checkerboard comprises:
distortion correction is carried out on the projection checkerboard image according to the calibrated camera internal parameter and distortion;
extracting image coordinates of each corner point in the undistorted projection checkerboard image;
calculating to obtain the space coordinates of the corner points of the projection checkerboard according to the camera internal parameters, distortion, rotation matrix, translation matrix and the image coordinates of each corner point in the undistorted projection checkerboard image;
calculating coordinates of each corner point of the undistorted left view field projection image according to the calibrated internal parameters and distortion of the projector;
and calculating to obtain a rotation matrix and a translation matrix from the three-dimensional reconstruction coordinate system to the projector coordinate system according to the coordinates of each corner point of the undistorted left view field projection image and the space coordinates of the corner points of the projection checkerboard.
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