CN111028297B - 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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- G—PHYSICS
- 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 internal parameters and distortion of the camera by using a glass checkerboard calibration plate covering the full view field; projecting left and right view field projection images to a white area of a special calibration plate of a half-white half-checkerboard pattern respectively to calibrate internal parameters and distortion of the projector; vertically moving a special calibration plate to establish a three-dimensional reconstruction coordinate system; and calibrating camera external parameters and projector external parameters according to the three-dimensional reconstruction coordinate system. The calibration method designs a special calibration plate with a half white and half checkerboard, and constructs a three-dimensional reconstruction coordinate system to calibrate the projector, the camera and the surface structure light system by matching with the vertical lifting platform, the whole calibration scheme separates camera calibration, projector calibration and system external parameter calibration, 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.
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 other aspects. The surface structure light system consists of a projector and a camera, wherein the projector projects coding structure light to the surface of the measured object, the camera collects modulation patterns, the geometric information of the surface of the measured object is obtained through a decoding algorithm, and the common coding structure light comprises phase shift stripes, gray codes and the like. In order to obtain the actual three-dimensional information, the parameters of the camera and the projector and the external parameters of the camera and the projector relative to the three-dimensional reconstruction coordinate system are required to be calibrated.
The projector calibration method in the surface structure light system comprises two methods: firstly, projecting structured light such as phase shift stripes and the like to 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; the other is to project the characteristic point pattern to the calibration plate, calibrate the camera by using the actual characteristic point image on the calibration plate, calculate the space coordinates of the projection characteristic point by using the projection characteristic point image, obtain the characteristic point and the corresponding space coordinates of the projector image, and calibrate by using the traditional camera. The existing method for calibrating the external parameters of the system generally uses a certain plane of a calibration plate as a reference to establish a three-dimensional reconstruction coordinate system, and adopts 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 depends on a structured light algorithm and is influenced by algorithm precision, and the second method directly uses a conventional 2D calibration plate, so that the projected characteristic point pattern and the actual characteristic point pattern are overlapped and covered with each other to influence characteristic point extraction; the existing method for calibrating the external parameters of the system depends on the external parameter resolving precision in the calibrating process, and has poor position precision beyond the plane of the calibrating plate.
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 calibration method of the surface structured light system.
In order to solve the technical problems, the embodiment of the application discloses the following technical scheme:
in a first aspect, an embodiment of the present application discloses a calibration method of a surface structured light three-dimensional measurement system, where the method includes:
calibrating internal parameters and distortion of the camera by using a glass checkerboard calibration plate covering the full view field;
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 the projector;
vertically moving the special calibration plate to establish a three-dimensional reconstruction coordinate system;
and calibrating camera external parameters and projector external parameters according to the three-dimensional reconstruction coordinate system.
Optionally, calibrating camera internal parameters and distortion using a glass checkerboard calibration plate covering a full field of view, comprising:
placing the glass checkerboard calibration plates at different positions and different angles within the field of view and the depth of field;
collecting a plurality of target images;
and calculating to obtain a camera internal parameter matrix and a lens distortion coefficient matrix according to the target image.
Optionally, the special calibration plate white area for respectively projecting the left and right view field projection images to the half white half projection images, calibrating internal parameters and distortion of the projector, including:
respectively acquiring a projection checkerboard image and an actual checkerboard image corresponding to the left and right view field projection images;
calculating the 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;
calculating the space coordinates of the projected checkerboard corner points by utilizing the image coordinates of the projected checkerboard corner points on the special calibration plate;
calibrating projector internal parameters and lens distortion parameters according to the space coordinates and the corresponding coordinates of each angular point image in the left and right view field projection images.
Optionally, collecting the projection checkerboard image and the actual checkerboard image corresponding to the left and right view field projection images respectively, including:
the projector projects a left view field projection image to a white area of the special calibration plate;
the camera respectively collects a plurality of groups of projection checkerboard images and actual checkerboard images corresponding to the left view field projection images;
horizontally rotating the special calibration plate;
the projector projects a right view field projection image to a white area of the special calibration plate;
and the camera respectively acquires a plurality of groups of projection checkerboard images and actual checkerboard images corresponding to the right view field projection images.
Optionally, calculating the external parameter of the position of the special calibration plate by using the calibrated internal parameter and distortion of the camera and the actual checkerboard image coordinates, including:
establishing a space coordinate system;
obtaining the space coordinates of each angular point according to the actual checkerboard size;
respectively extracting the angular point coordinates of the actual checkerboard image from the actual checkerboard image corresponding to the left and right view field projection images;
and (5) calculating a rotation matrix and a translation matrix of each position space coordinate system to a camera coordinate system according to the calibrated camera internal parameters and distortion.
Optionally, calculating the spatial coordinates of the projected checkerboard corner by using the image coordinates of the projected checkerboard corner on the special calibration plate includes:
respectively carrying out distortion correction on projection checkerboard images corresponding to the left and right view field projection images;
extracting angular point coordinates 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 coordinates of the undistorted projection checkerboard image.
Optionally, moving the special calibration plate vertically to establish a three-dimensional reconstruction coordinate system includes:
fixing the special calibration plate on a vertical lifting table to establish a three-dimensional reconstruction coordinate system;
moving the dedicated calibration plate at fixed intervals;
and obtaining the space coordinates of each angular 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 with fixed intervals;
calibrating camera external parameters according to the space coordinates of each angular point of the actual checkerboard and the image coordinates of each angular point of the actual checkerboard;
calibrating projector external parameters according to image coordinates of all angular points in the left view field projection image and space coordinates of the projection checkerboard angular points.
Optionally, calibrating the camera external parameters according to the spatial coordinates of each angular point of the actual checkerboard and the image coordinates of each angular point of the actual checkerboard, including:
correcting the distortion of the actual checkerboard image according to the calibrated camera internal parameters and the distortion;
extracting image coordinates of each corner 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 angular point in the undistorted actual checkerboard image and the spatial coordinates of each angular point of the actual checkerboard.
Optionally, calibrating the projector external parameters according to the image coordinates of each angular point in the left view field projection image and the space coordinates of the projection checkerboard angular points includes:
correcting the distortion of the projected checkerboard image according to the calibrated camera internal parameters and the distortion;
extracting image coordinates of each corner in the undistorted projection checkerboard image;
calculating to obtain the space coordinates of the projected checkerboard corner points according to the camera internal parameters, distortion, rotation matrix, translation matrix and the image coordinates of each corner point in the undistorted projected checkerboard image;
calculating coordinates of each corner point of the undistorted left view field projection image according to the internal parameters and the distortion of the calibrated 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 angular point of the undistorted left view projection image and the space coordinates of the angular points of the projection checkerboard.
Compared with the prior art, the beneficial effects of this application are:
the calibration method of the surface structured light three-dimensional measurement system provided by the embodiment of the application comprises the following steps: calibrating internal parameters and distortion of the camera by using a glass checkerboard calibration plate covering the full view field; projecting left and right view field projection images to a white area of a special calibration plate of a half-white half-checkerboard pattern respectively to calibrate internal parameters and distortion of the projector; vertically moving a special calibration plate to establish a three-dimensional reconstruction coordinate system; and calibrating camera external parameters and projector external parameters according to the three-dimensional reconstruction coordinate system. The calibration method designs a special calibration plate with a half white and half checkerboard, and constructs a three-dimensional reconstruction coordinate system to calibrate the projector, the camera and the surface structure light system by matching with the vertical lifting platform, the whole calibration scheme separates camera calibration, projector calibration and system external parameter calibration, and the calibration method does not depend on a structured light algorithm, so that various error coupling interferences in the calibration process can be avoided, and 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 illustrate the technical solutions of the present application, the drawings that are needed in the embodiments will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a flow chart 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 diagram of a special calibration plate in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 3 is a schematic diagram of left and right view field projection images in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 4 is a detailed flowchart of S200 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 5 is a detailed flowchart of S201 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 6 is a detailed flowchart of S202 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 7 is a diagram of imaging relationships of a structured light system according to an embodiment of the present application;
FIG. 8 is a detailed flowchart of S203 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 9 is a schematic diagram of a vertical movement dedicated calibration plate provided in an embodiment of the present application;
FIG. 10 is a detailed flowchart of S400 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
FIG. 11 is a detailed flowchart of S402 in a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application;
fig. 12 is a detailed flowchart of S403 in the calibration method of the surface structured light three-dimensional measurement system according to the embodiment of the present application.
Detailed Description
In order to better understand the technical solutions in the present application, the following description will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, shall fall within the scope of the present application.
Referring to fig. 1, a flowchart of a calibration method of a surface structured light three-dimensional measurement system according to an embodiment of the present application is provided.
As shown in fig. 1, the calibration method of the surface structured light three-dimensional measurement system provided in the embodiment of the application includes:
s100: the camera internal parameters and distortions were calibrated using a glass checkerboard calibration plate covering the full field of view.
According to Zhang Zhengyou calibration method principle, a glass checkerboard calibration plate is used for calibrating camera internal parameters and lens distortion parameters. Specifically, calibration plates are placed at different angles at different positions in the market and depth of field range, 20-30 target images are collected, and an openCV library calibration function is used for calculation to obtainCamera internal reference matrix A C And camera lens distortion coefficient matrix D C 。
The openCV is calibrated using checkerboard, in order to find a checkerboard template, a function cv2.findchessbardconners () in the openCV can be used, which returns the corresponding corner points if a template is detected; after the corner is found, a more accurate corner pixel coordinate can be obtained by using a function cv2.corersubpix (), and the corner can be drawn on an image to be displayed by using a function cv2.drawChessBoard corners (); the three-dimensional point for calibration and the two-dimensional point pair on the image corresponding to the three-dimensional point are obtained through the steps, and the calibration is carried out by using a function cv2.drawChessBoard Corders (), and the function returns a calibration result, an internal parameter matrix of the camera and distortion coefficients.
S200: and respectively projecting left and right view field projection images to a white area of a special calibration plate of a half white half projection image to calibrate internal parameters and distortion of the projector.
The application designs a special calibration plate with half white and half checkerboard, as shown in fig. 2, the left half of the special calibration plate is white, the right half of the special calibration plate is a black-and-white projection image, the size of the checkerboard is 2mm x 2mm, the size of the pattern is 42mm x 50mm, the patterns are all symmetrical up and down and left and right, and high-definition photographic paper using an IOS2333 standard resolution test card is printed and flatly adhered to an aluminum plastic plate.
The projected image design is shown in fig. 3, the left half of the left view projection pattern L is a black and white projected image, the right half of the right view projection pattern R is a black and white projected image, and the aspect ratio of the checkerboard size is 2:1 so as to adapt to different proportions of stretching and scaling in the transverse and longitudinal directions when the projector is obliquely projected.
The specific method for calibrating the internal parameters and distortion of the projector by adopting the special calibration plate is shown in fig. 4:
s201: and respectively acquiring a projection checkerboard image and an actual checkerboard image corresponding to the left and right view field 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 a plurality of groups of left view field projection images.
S2013: and (3) horizontally rotating a special calibration plate.
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 L to the white area on the left side of the special calibration plate, the left view field Pattern L and the right side actual checkerboard image on the special calibration plate are not overlapped with each other, and the camera acquires the image Img of the projected checkerboard PL C Stopping projection, and collecting actual checkerboard image Img on the same calibration plate by using a camera CL C A set of calibration maps is obtained. Collecting 10-15 groups of calibration images Img at different positions PL C And Img CL C . Then, the special calibration plate is rotated to enable the actual checkerboard to be positioned on the left side, the projector projects a right view field projection image Pattern R to a white area on the right side of the special calibration plate, and 10-15 groups of corresponding calibration images Img are collected PR C And Img CR C 。
S202: and calculating the 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 position external parameters 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 angular point according to the actual checkerboard size.
S2023: and respectively extracting the angular point coordinates of the actual checkerboard image from the actual checkerboard image corresponding to the left and right view field 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 parameters and distortion.
Building structured light systems according to structured light system imaging relationshipsThe imaging relation of the imaging model and the structured light system is shown in figure 7, O W -X W Y W Z W Is a space coordinate system, O P -X P Y W Z P For projector coordinate system, O P -U P V P For projector image plane coordinate system, O C -X C Y C Z C For camera coordinate system, O C -U C V C Is a camera image plane coordinate system. The projector will point P on the two-dimensional image P Projected to a three-dimensional space point P, and a camera images the three-dimensional space point P to a two-dimensional image plane at the point P C The projector can be equivalent to a reverse camera according to the working mechanism and imaging relation of the projector. Projector and camera lens distortion, adopting general lens distortion model, and using distortion coefficient D P [k 1 P ，k 2 P ，p 1 P ，p 2 P ，k 3 P ]And D C [k 1 C ，k 2 C ，p 1 C ，p 2 C ，k 3 C ]Representing that a conversion of an actual image point to an undistorted image point is achieved.
Undistorted image point coordinates of camera image and spatial coordinate relationship:
wherein A is C Is an internal reference matrix and comprises a focal length f x C 、f y C And principal point u 0 C 、v 0 C ，M C Is an extrinsic matrix, comprising a rotation matrix R from a space coordinate system to a camera coordinate system C And a translation matrix T C 。
A space coordinate system O is established by taking the upper left first corner of the actual checkerboard at each position as an origin wi -X wi Y wi Z wi ，X wi With axis vertically downwards, Y wi The axis being horizontal to the right, Z wi The shaft is perpendicular to the special calibration plate according to the actual chessThe space coordinates of each angular point are obtained by the size of the tray lattice, and the Z coordinate is 0. From the calibration map Img CL C And Img CR C Extracting the angular point coordinates (u) of the actual checkerboard image ci C ，v ci C ) According to calibrated camera internal reference A C And distortion coefficient D C Calculating to obtain a rotation matrix R from each position space coordinate system to a camera coordinate system i C And a translation matrix T i C 。
S203: and calculating the space coordinates of the projected checkerboard corner by utilizing the image coordinates of the projected checkerboard corner on the special calibration plate.
The specific method for calculating the space coordinates of the projected checkerboard corner is shown in fig. 8:
s2031: and respectively carrying out distortion correction on the projection checkerboard images corresponding to the left and right view field projection images.
S2032: and extracting angular point coordinates 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 matrixes, translation matrixes of all positions and the corner coordinates of the undistorted projection checkerboard image.
For projection checkerboard image Img PL C And Img PR C Performing distortion correction, extracting corner coordinates (u) of undistorted projected checkerboard image pi C ，v pi C ). The projection checkerboard and the actual checkerboard are coplanar on the special calibration plate, so that the space coordinate Z of the corner points of the projection checkerboard wi P =0. According to camera internal reference A C Distortion coefficient D C Rotation matrix R for each position i C And a translation matrix T i C By projecting checkerboard image corner coordinates (u pi C ，v pi C ) Calculating to obtain corresponding space coordinate X wi P And Y wi P 。
S204: calibrating projector internal parameters and lens distortion parameters according to the space coordinates and the coordinates of each angular point image in the corresponding left and right view field projection images.
In the structured light system imaging model, the relationship between the undistorted pixel coordinates and the space coordinates of the projector image is as follows:
wherein A is P Is an internal reference matrix and comprises a focal length f x P 、f y P And principal point u 0 P 、v 0 P ，M P Is an extrinsic matrix, comprising a rotation matrix R from a space coordinate system to a camera coordinate system P And a translation matrix T P 。
The spatial coordinates of corner points in the projection checkerboard on special calibration plates are known (X wi P ，Y wi P ，Z wi P ) Calibrating the projector reference matrix A by using a camera calibration method P And a lens distortion coefficient matrix D P 。
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 lifting table so that the special calibration plate moves towards the system direction at fixed intervals, as shown in fig. 9. The first left corner of the actual checkerboard of the initial position calibration plate is used as the original to establish a three-dimensional reconstruction coordinate system O R -X R Y R Z R ，X R The axis being parallel to the checkerboard pattern downwards, Y R The axis being parallel to the checkerboard pattern to the right, Z R The axis is perpendicular to the dedicated calibration plate pointing towards the system. And (3) a series of actual checkerboard corner points with known stereo are obtained through the movement of the special calibration plate. Given that the checkerboard size is s×s and the movement interval is Δd, the coordinates of the corner points of the row j and the column i at the nth position are:
X R C ＝i×s,Y R C ＝j×s,Z R C ＝n×Δd
s400: and calibrating the camera external parameters and the projector external parameters according to the three-dimensional reconstruction coordinate system.
Constructing a three-dimensional target and a three-dimensional reconstruction coordinate system, and calibrating camera external parameters; and (3) reversely calculating three-dimensional reconstruction coordinates of the projection checkerboard image coordinates on the special calibration plate, and calibrating projector external parameters.
The specific method for calibrating the camera external parameters and the projector external parameters is shown in fig. 10:
s401, respectively acquiring projection checkerboard images and actual checkerboard images corresponding to a plurality of groups of left view field projection images with fixed distances.
The projector projects a left view field projection image PatternL to a white area on the left side of a special calibration plate, and the camera acquires a projection checkerboard image Img P C Stopping projection, and collecting an actual checkerboard image Img by a camera C C A set of calibration maps is obtained. And (5) vertically moving the special calibration plate, and acquiring 5 groups of calibration images at fixed intervals.
S402: and calibrating camera external parameters according to the space coordinates of each angular point of the actual checkerboard and the image coordinates of each angular point of the actual checkerboard.
As shown in fig. 11, a specific method for calibrating the external parameters of the camera is as follows:
s4021: and carrying out distortion correction on the actual checkerboard image according to the calibrated camera internal parameters and distortion.
S4022: and extracting the image coordinates of each corner 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 angular point in the undistorted actual checkerboard image and the spatial coordinates of each angular point of the actual checkerboard.
According to the calibrated camera internal parameters and distortion coefficients, calibrating a graph Img C C Performing distortion correction, extracting the angular point coordinates (u) c C* ，V c C* )). The spatial coordinates of each corner point of the actual checkerboard are known (X R C ，Y R C ，Z R C ) According to the camera model, a rotation matrix R from the three-dimensional reconstruction coordinate system to the camera coordinate system is calculated C And a translation matrix T C 。
S403: calibrating projector external parameters according to image coordinates of all angular points in the left view field projection image and space coordinates of all angular points of the projection checkerboard.
As shown in fig. 12, a specific method for calibrating the external parameters of the projector is as follows:
s4031: and correcting the distortion of the projected checkerboard image according to the calibrated camera internal parameters and the distortion.
S4032: and extracting image coordinates of each corner in the undistorted projection checkerboard image.
S4033: and calculating to obtain the space coordinates of the projected checkerboard corner points according to the image coordinates of each corner point in the camera internal parameters, distortion, rotation matrix, translation matrix and undistorted projected checkerboard image.
S4034: and calculating the coordinates of each corner point of the undistorted left view field projection image according to the internal parameters and the distortion of the calibrated 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 angular point of the undistorted left view projection image and the space coordinates of the angular points of the projection checkerboard.
According to the calibrated camera internal parameters and distortion coefficients, calibrating a graph Img P C Performing distortion correction, extracting image coordinates (u) of each corner in the undistorted projection checkerboard image p C* ，v p C* ). Space coordinate Z of corner point of i-th position projection checkerboard Ri P =i×Δd, according to camera parameter a C 、D C 、R C And T C By projecting checkerboard image coordinates (u p C* ，v p C* ) Calculate the corresponding space coordinate X R P And Y R P 。
The coordinates (u) of each corner image in the left view projection image PatternL are known p P ，v p P ) Calculating the image coordinates (u) of the undistorted corner point according to the calibrated projector internal parameters and distortion coefficients p P* ，v p P* ). The spatial coordinates (X) of the projection checkerboard corner points in the three-dimensional reconstruction coordinate system are calculated R P ,Y R P ,Z R P ) According to the projector model, calculating a rotation matrix R from the three-dimensional reconstruction coordinate system to the projector coordinate system P And a translation matrix T P 。
In sum, a three-dimensional reconstruction coordinate system is established, and external parameters from the three-dimensional reconstruction coordinate system to the camera coordinate system are obtained through calibration: rotation matrix R C And a translation matrix T C Camera internal reference A C And distortion coefficient D C The method comprises the steps of carrying out a first treatment on the surface of the The calibration obtains the external parameters from the three-dimensional reconstruction coordinate system to the projector coordinate system: rotation matrix R P And a translation matrix T P Projector internal reference A P And distortion coefficient D P . The position relation of the camera and the projector in the structured light system and the respective internal parameters are calibrated, and the position relation can be used for calculating the actual three-dimensional coordinates measured by the structured light system.
The calibration method of the surface structured light three-dimensional measurement system provided by the embodiment of the application firstly uses the glass checkerboard target with high precision covering the full view field to calibrate the internal parameters and distortion of the camera, and the obtained parameters are more stable in the whole view field. Secondly, a designed special calibration plate is used, and the mode of respectively collecting target mark images by projecting checkerboard patterns from left and right view fields is adopted to calculate camera external parameters corresponding to different calibration plate positions, so that projector internal parameters and distortion are calibrated. The projection pattern is simple, no special design style is required to be added, the projection image acquired by the camera and the actual image are not interfered with each other, and the feature points can be directly extracted by adopting a stable and mature angular point extraction algorithm; the left view field and the right view field are used for independently projecting and extracting characteristic points and are jointly used for calibrating the projector, so that a good calibrating effect can be achieved on the whole view field of the projector. The vertical moving guide rail is used for constructing a three-dimensional target, spatial characteristic points at different positions in the whole space are used for participating in calibration, and the external parameters of the structured light system are calibrated.
The calibration method provided by the application adopts the designed special calibration plate and is matched with the vertical lifting platform to construct a three-dimensional target, the projector, the camera and the surface structure light system are calibrated, the camera calibration, the projector calibration and the system external parameter calibration are separated by the whole calibration scheme, the method does not depend on a structured light algorithm, 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 of the invention 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 application 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 are not intended to limit the scope of the present application.
Claims (10)
1. A method for calibrating a surface structured light three-dimensional measurement system, the method comprising:
calibrating internal parameters and distortion of the camera by using a glass checkerboard calibration plate covering the full view field;
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 the projector;
vertically moving the special calibration plate to establish a three-dimensional reconstruction coordinate system;
and calibrating camera external parameters and projector external parameters according to the three-dimensional reconstruction coordinate system.
2. The method of calibrating according to claim 1, wherein calibrating camera internal parameters and distortion using a glass checkerboard calibration plate covering a full field of view comprises:
placing the glass checkerboard calibration plates at different positions and different angles within the field of view and the depth of field;
collecting a plurality of target images;
and calculating to obtain a camera internal parameter matrix and a lens distortion coefficient matrix according to the target image.
3. The calibration method according to claim 1, wherein the calibrating the projector internal parameters and distortions by projecting the left and right field of view projection images onto the dedicated calibration plate white area of the half-white half-projection image, respectively, comprises:
respectively acquiring a projection checkerboard image and an actual checkerboard image corresponding to the left and right view field projection images;
calculating the 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;
calculating the space coordinates of the projected checkerboard corner points by utilizing the image coordinates of the projected checkerboard corner points on the special calibration plate;
calibrating projector internal parameters and lens distortion parameters according to the space coordinates and the coordinates of each angular point image in the corresponding left and right view field projection images.
4. A calibration method according to claim 3, wherein the respectively acquiring the projected checkerboard image and the actual checkerboard image corresponding to the left and right field of view projected image comprises:
the projector projects a left view field projection image to a white area of the special calibration plate;
the camera respectively collects a plurality of groups of projection checkerboard images and actual checkerboard images corresponding to the left view field projection images;
horizontally rotating the special calibration plate;
the projector projects a right view field projection image to a white area of the special calibration plate;
and the camera respectively acquires a plurality of groups of projection checkerboard images and actual checkerboard images corresponding to the right view field projection images.
5. A calibration method according to claim 3, wherein calculating the external parameters of the position of the dedicated calibration plate using the calibrated camera internal parameters, 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;
respectively extracting the angular point coordinates of the actual checkerboard image from the actual checkerboard image corresponding to the left and right view field projection images;
and (5) calculating a rotation matrix and a translation matrix of each position space coordinate system to a camera coordinate system according to the calibrated camera internal parameters and distortion.
6. The calibration method according to claim 5, wherein calculating spatial coordinates of projected checkerboard corner using image coordinates of projected checkerboard corner on the dedicated calibration plate comprises:
respectively carrying out distortion correction on projection checkerboard images corresponding to the left and right view field projection images;
extracting angular point coordinates 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 coordinates of the undistorted projection checkerboard image.
7. The method of calibrating according to claim 1, wherein vertically moving the dedicated calibration plate establishes a three-dimensional reconstruction coordinate system, comprising:
fixing the special calibration plate on a vertical lifting table to establish a three-dimensional reconstruction coordinate system;
moving the dedicated calibration plate at fixed intervals;
and obtaining the space coordinates of each angular point of the actual checkerboard according to the size of the checkerboard on the special calibration board and the fixed interval.
8. The method of calibrating according to claim 7, wherein calibrating camera and projector parameters 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 with fixed intervals;
calibrating camera external parameters according to the space coordinates of each angular point of the actual checkerboard and the image coordinates of each angular point of the actual checkerboard;
calibrating projector external parameters according to image coordinates of all angular points in the left view field projection image and space coordinates of all angular points of the projection checkerboard.
9. The method according to claim 8, wherein calibrating the camera outliers based on the spatial coordinates of each corner of the actual checkerboard and the image coordinates of each corner of the actual checkerboard comprises:
correcting the distortion of the actual checkerboard image according to the calibrated camera internal parameters and the distortion;
extracting image coordinates of each corner 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 angular point in the undistorted actual checkerboard image and the spatial coordinates of each angular point of the actual checkerboard.
10. The method of calibrating a projector according to claim 9, wherein calibrating the projector external parameters based on the image coordinates of each corner in the left field of view projection image and the spatial coordinates of each corner of the projection checkerboard comprises:
correcting the distortion of the projected checkerboard image according to the calibrated camera internal parameters and the distortion;
extracting image coordinates of each corner in the undistorted projection checkerboard image;
calculating to obtain the space coordinates of the projected checkerboard corner points according to the camera internal parameters, distortion, rotation matrix, translation matrix and the image coordinates of each corner point in the undistorted projected checkerboard image;
calculating coordinates of each corner point of the undistorted left view field projection image according to the internal parameters and the distortion of the calibrated 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 angular point of the undistorted left view projection image and the space coordinates of the angular points of the projection checkerboard.
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