CN108662987B - Calibration method of 2D camera type laser measuring head - Google Patents
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- CN108662987B CN108662987B CN201810366473.1A CN201810366473A CN108662987B CN 108662987 B CN108662987 B CN 108662987B CN 201810366473 A CN201810366473 A CN 201810366473A CN 108662987 B CN108662987 B CN 108662987B
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- G01—MEASURING; TESTING
- 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
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
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Abstract
The invention discloses a calibration method of a 2D camera shooting type laser measuring head, wherein the measuring head comprises a packaging shell, a line laser and a CCD camera; the line laser is used for emitting a laser plane, the laser plane is projected to an object to be detected, a laser line for representing a profile is generated on the surface of the object to be detected, and the calibration plate is intersected with the laser plane emitted by the line laser; the CCD camera is used for shooting an image of the calibration plate; the calibration method comprises the steps of extracting laser light bars projected onto a calibration plate by a line laser through a difference method, extracting a central line, restoring the central line to a camera coordinate system, fitting a plurality of central lines in a space, calculating a space equation of a laser plane under the camera coordinate system, and further calculating a space position relation of the laser plane and the camera coordinate system; the invention can be used for accurately calibrating the internal parameters and the laser plane position of the laser measuring head; other auxiliary equipment is not needed in the calibration process, and the operation is simple.
Description
Technical Field
The invention relates to the field of profile measurement, in particular to a calibration method of a 2D camera shooting type laser measuring head.
Background
The appearance profile of an object contains a plurality of external basic information, such as: integrity, aesthetics, and the like. Measuring an object profile is a common method for obtaining profile dimensions. There are various methods for measuring the profile, such as: three-coordinate measuring instruments, machine vision measurements, and the like. In machine vision profilometry, the light-cutting method is a commonly used profilometry method. The light cutting method comprises the steps of projecting laser lines to the surface of an object to be detected, shooting outline information of the light-carrying bars, and obtaining an appearance outline through image processing. And measuring the profile by adopting a light cutting method, and calibrating the spatial position of the laser plane by adopting a mode that a calibration plate is close to the laser plane. Because it is difficult to ensure the laser plane and the calibration plate plane to be absolutely coincident, the calibration result is difficult to achieve higher precision.
Disclosure of Invention
The invention aims to provide a calibration method of a 2D camera type laser measuring head, which is suitable for calibrating the internal reference and laser plane positions of most camera type laser measuring heads and improves the calibration precision.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the utility model provides a calibration method of 2D formula of making a video recording laser measuring head, 2D formula of making a video recording laser measuring head is used for obtaining the 2D profile inspection data of the object that awaits measuring, its characterized in that: the 2D camera shooting type laser measuring head comprises a packaging shell, a line laser and a CCD camera, wherein the line laser and the CCD camera are arranged in the packaging shell; the line laser is used for emitting a laser plane, the laser plane is projected to an object to be detected, a laser line for representing a profile is generated on the surface of the object to be detected, and the calibration plate is intersected with the laser plane emitted by the line laser; the CCD camera is used for shooting an image of the calibration plate; the calibration method comprises the steps of extracting laser light bars projected onto a calibration plate by a line laser through a difference method, extracting a central line, restoring the central line to a camera coordinate system, fitting a plurality of central lines in a space, calculating a space equation of a laser plane under the camera coordinate system, and further calculating a space position relation of the laser plane and the camera coordinate system, wherein the calibration of a measuring head is divided into two parts: calibrating internal parameters of the camera and calibrating the position of the laser plane.
As a preferred mode, shooting calibration background images and calibration target images at a plurality of different angles in the whole calibration process; and the calibration background image and the calibration target image form a calibration image group.
As an optimal mode, the camera internal parameter calibration and the laser plane position calibration are separately calibrated, the camera internal parameter is calibrated firstly, and then the laser plane position is calibrated.
Preferably, the laser plane is perpendicular to the package housing axis.
Preferably, the method further comprises the steps of:
(1) fixing the position of the 2D camera type laser measuring head, placing the calibration plate in a visual field range which can be clearly shot by the CCD camera, and fixing the calibration plate;
(2) turning on the line laser, and collecting the image of the calibration plate at the moment as a calibration target image;
(3) closing the line laser, and collecting the image of the calibration plate at the moment as a calibration background image;
(4) the calibration background image and the calibration target image form an image group, when the image group at one angle is collected, the position of the calibration plate is changed, and the image group at the next angle is shot;
(5) calibrating all calibration background images, and calculating an internal parameter matrix of the CCD camera;
(6) the calibrated target image and the calibrated background image are differentiated, the laser light stripe central line is extracted, and the characteristic intersection point A of the light stripe central line and the rectangle outside the checkerboard characteristic points is calculatediAnd Bi；
(7) Restoring the characteristic intersection points to a camera coordinate system, fitting the characteristic intersection points of a plurality of angles, and calculating a space equation of a laser plane; and according to a space plane equation, calculating the correlation between the plane and the coordinate system, and solving a transformation matrix H.
As a preferred mode, calibrating a plurality of calibration background images at different angles, and acquiring an internal parameter matrix M of the camera by adopting a Zhang-Yongyou calibration method.
Preferably, the step (6) further comprises: the calibration target image and the calibration background image are subjected to subtraction, and an image only containing laser light bars is obtained; carrying out distortion correction on the extracted laser light bar image; the corrected laser light stripe image is divided by threshold value, the central line of the light stripe is extracted, and the characteristic intersection point A of the central line of the light stripe and the rectangle outside the sub-pixel corner point is calculatediAnd Bi(ii) a Calculating the coordinate A of the feature intersection point in the camera coordinate system through matrix operationciAnd Bci(ii) a Wherein the characteristic intersection point Ai、BiFeature intersection point A to the camera coordinate systemci、BciThe relation of (A) is as follows:
wherein s is a proportionality coefficient, and M is an internal reference matrix.
Preferably, the step (7) further comprises: fitting a plurality of feature intersection points as a plane, wherein the plane is the space position of the laser plane under the camera coordinate system; according to a rotation vector method, a rotation matrix R from a laser plane to a camera coordinate system can be calculated; and the translation matrix from the laser plane to the camera coordinate system is T, and the value is the coordinate of any point on the laser plane.
Preferably, when the position matrix is obtained in step (7), the transformation relation from the laser plane to the image coordinate system is as follows by accurately calibrating the internal parameters of the camera and the position of the laser plane:
wherein, the H matrix is a transformation matrix from the laser plane to the image plane, s is a proportionality coefficient, M is an internal reference matrix, R is a reference matrixijIs an element of the matrix R, TijIs an element of the matrix T.
As an optimal mode, after the calibration of the internal parameters of the camera and the calibration of the laser plane position are completed, under the condition that the relative positions of the camera and the line laser are not changed, the external environment is changed, and only the internal parameters need to be calibrated again.
Compared with the prior art, the invention has the beneficial effects that: 1: the invention can be used for accurately calibrating the internal parameters and the laser plane position of the laser measuring head; 2: the high-precision laser plane space position is obtained by fitting the laser light bars of a plurality of calibration planes; 3: if the positions of the camera and the line laser are not changed, the laser plane position is calibrated without calibration; 4: other auxiliary equipment is not needed in the calibration process, and the operation is simple.
Drawings
FIG. 1 is a schematic diagram of obtaining a calibration target image;
FIG. 2 is a flow chart of calibration image acquisition;
FIG. 3 is a schematic diagram of a calibrated target image feature intersection point;
FIG. 4 is a calibration calculation flow chart;
1 is a packaging shell; 2 is a line laser; 3 is a CCD camera; 4 is a laser plane; 5 is a calibration plate and 6 is a package housing axis.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
A2D camera shooting type laser measuring head calibration method, the 2D camera shooting type laser measuring head is used for obtaining 2D outline detection data of an object to be measured, as shown in figure 1, the 2D camera shooting type laser measuring head includes a packaging shell 1, a line laser 2 and a CCD camera 3, wherein the line laser 2 and the CCD camera are fixedly packaged in the shell 1; the laser plane 4 is vertical to the axis 6 of the packaging shell so as to measure the profile, the line laser 2 is used for emitting the laser plane 4, the laser plane 4 is projected to an object to be measured, a laser line for representing the profile is generated on the surface of the object to be measured, and the calibration plate 5 is intersected with the laser plane 4 emitted by the line laser 2; the CCD camera 3 is used for shooting an image of the calibration plate 5; before detection, the 2D camera type laser measuring head needs to be calibrated; the calibration method comprises the steps of extracting laser light bars projected onto a calibration plate by a line laser through a difference method, extracting a central line, restoring the central line to a camera coordinate system, fitting a plurality of central lines in a space, calculating a space equation of a laser plane under the camera coordinate system, and further calculating a space position relation of the laser plane and the camera coordinate system, wherein the calibration of a measuring head is divided into two parts: calibrating internal parameters of the camera and calibrating the position of the laser plane.
Shooting calibration background images and calibration target images at a plurality of different angles in the whole calibration process; and the calibration background image and the calibration target image form a calibration image group.
The camera internal parameter calibration and the laser plane position calibration are separately calibrated, the camera internal parameter is calibrated firstly, and then the laser plane position is calibrated.
As shown in fig. 2, in the calibration method of the 2D camera type laser measuring head, the image acquisition step is as follows:
(1) fixing the position of the 2D camera type laser measuring head, placing the calibration plate 5 in the visual field range which can be clearly shot by the CCD camera 3, and fixing the calibration plate 5;
(2) turning on the line laser 2, and collecting the image of the calibration plate at the moment as a calibration target image;
(3) closing the line laser 2, and collecting the image of the calibration plate at the moment as a calibration background image;
(4) the calibration background image and the calibration target image form an image group, when the image group at one angle is collected, the position of the calibration plate is changed, and the image group at the next angle is shot;
as shown in fig. 4, in the calibration method of the 2D camera type laser measuring head, the calibration algorithm includes the steps of:
(1) calibrating all calibration background images, and calculating an internal parameter matrix of the CCD camera;
(2) the calibrated target image and the calibrated background image are differentiated, the laser light stripe central line is extracted, and the characteristic intersection point A of the light stripe central line and the rectangle outside the checkerboard characteristic points is calculatediAnd Bi；
(3) Restoring the characteristic intersection points to a camera coordinate system, fitting the characteristic intersection points of a plurality of angles, and calculating a space equation of a laser plane; and according to a space plane equation, calculating the correlation between the plane and the coordinate system, and solving a transformation matrix H.
And calibrating a plurality of calibration background images at different angles, and acquiring an internal parameter matrix M of the camera by adopting a Zhang-Yongyou calibration method.
As shown in fig. 3, the step (2) of the calibration algorithm further includes: the calibration target image and the calibration background image are subjected to subtraction, and an image only containing laser light bars is obtained; carrying out distortion correction on the extracted laser light bar image; the corrected laser light stripe image is divided by threshold value, the central line of the light stripe is extracted, and the characteristic intersection point A of the central line of the light stripe and the rectangle outside the sub-pixel corner point is calculatediAnd Bi(ii) a Calculating the coordinate A of the feature intersection point in the camera coordinate system through matrix operationciAnd Bci(ii) a Wherein the characteristic intersection point Ai、BiFeature intersection point A to the camera coordinate systemci、BciThe relation of (A) is as follows:
wherein s is a proportionality coefficient, and M is an internal reference matrix.
The step (3) of the calibration algorithm further comprises the following steps: fitting a plurality of feature intersection points as a plane, wherein the plane is the space position of the laser plane under the camera coordinate system; according to a rotation vector method, a rotation matrix R from a laser plane to a camera coordinate system can be calculated; and the translation matrix from the laser plane to the camera coordinate system is T, and the value is the coordinate of any point on the laser plane.
When the position matrix is obtained in the calibration algorithm step (3), the internal parameters of the camera and the position of the laser plane are accurately calibrated, and the transformation relation from the laser plane to the image coordinate system is as follows:
wherein, the H matrix is a transformation matrix from the laser plane to the image plane, s is a proportionality coefficient, M is an internal reference matrix, R is a reference matrixijIs an element of the matrix R, TijIs an element of the matrix T.
After the calibration of the internal parameters of the camera and the calibration of the laser plane position are completed, under the condition that the relative positions of the camera and the line laser are unchanged, the external environment is changed, and only the internal parameters need to be calibrated again.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (5)
1. The utility model provides a calibration method of 2D formula of making a video recording laser measuring head, 2D formula of making a video recording laser measuring head is used for obtaining the 2D profile inspection data of the object that awaits measuring, its characterized in that: the 2D camera shooting type laser measuring head comprises a packaging shell (1), a line laser (2) and a CCD camera (3) which are arranged inside the packaging shell (1); the line laser (2) is used for emitting a laser plane (4), the laser plane (4) is projected to an object to be measured, a laser line for representing a profile is generated on the surface of the object to be measured, and the calibration plate (5) is intersected with the laser plane (4) emitted by the line laser (2); the CCD camera (3) is used for shooting an image of the calibration plate (5); the calibration method comprises the steps of extracting laser light bars projected onto a calibration plate by a line laser through a difference method, extracting a central line, restoring the central line to a camera coordinate system, fitting a plurality of central lines in a space, calculating a space equation of a laser plane under the camera coordinate system, and further calculating a space position relation of the laser plane and the camera coordinate system, wherein the calibration of a measuring head is divided into two parts: calibrating internal parameters of a camera and calibrating the position of a laser plane;
shooting calibration background images and calibration target images at a plurality of different angles in the whole calibration process; the calibration background image and the calibration target image form a calibration image group; calibrating the internal parameters of the camera and the laser plane position separately, and then calibrating the laser plane position; the laser plane (4) is vertical to the axis (6) of the packaging shell;
the calibration method comprises the following steps:
(1) fixing the position of the 2D camera type laser measuring head, placing the calibration plate (5) in a visual field range which can be clearly shot by the CCD camera (3), and fixing the calibration plate (5);
(2) turning on the line laser (2), and collecting the image of the calibration plate at the moment as a calibration target image;
(3) closing the line laser (2), and collecting the image of the calibration plate at the moment as a calibration background image;
(4) the calibration background image and the calibration target image form an image group, when the image group at one angle is collected, the position of the calibration plate is changed, and the image group at the next angle is shot;
(5) calibrating all calibration background images, and calculating an internal parameter matrix of the CCD camera;
(6) the calibrated target image and the calibrated background image are differentiated, the laser light stripe central line is extracted, and the characteristic intersection point A of the light stripe central line and the rectangle outside the checkerboard characteristic points is calculatediAnd Bi；
(7) Restoring the characteristic intersection points to a camera coordinate system, fitting the characteristic intersection points of a plurality of angles, and calculating a space equation of a laser plane; according to a space equation, calculating the correlation between the plane and the coordinate system, and solving a transformation matrix H;
and calibrating a plurality of calibration background images at different angles, and acquiring an internal parameter matrix M of the camera by adopting a Zhang-Yongyou calibration method.
2. The method for calibrating a 2D camera-shooting type laser measuring head according to claim 1, wherein: the step (6) is further as follows: the calibration target image and the calibration background image are subjected to subtraction, and an image only containing laser light bars is obtained; carrying out distortion correction on the extracted laser light bar image; the corrected laser light stripe image is divided by threshold value, the central line of the light stripe is extracted, and the characteristic intersection point A of the central line of the light stripe and the rectangle outside the sub-pixel corner point is calculatediAnd Bi(ii) a Calculating the coordinate A of the feature intersection point in the camera coordinate system through matrix operationciAnd Bci(ii) a Wherein the characteristic intersection point Ai、BiFeature intersection point A to the camera coordinate systemci、BciThe relation of (A) is as follows:
wherein s is a proportionality coefficient, and M is an internal reference matrix.
3. The method for calibrating a 2D camera-shooting type laser measuring head according to claim 1, wherein: the step (7) is further as follows: fitting a plurality of feature intersection points as a plane, wherein the plane is the space position of the laser plane under the camera coordinate system; according to a rotation vector method, a rotation matrix R from a laser plane to a camera coordinate system can be calculated; and the translation matrix from the laser plane to the camera coordinate system is T, and the value is the coordinate of any point on the laser plane.
4. The method for calibrating a 2D camera-shooting type laser measuring head according to claim 1, wherein: when the position matrix is obtained in the step (7), the internal parameters of the camera and the position of the laser plane are accurately calibrated, and the transformation relation from the laser plane to the image coordinate system is as follows:
wherein, the H matrix is a transformation matrix from the laser plane to the image plane, s is a proportionality coefficient, M is an internal reference matrix, R is a reference matrixijIs an element of the matrix R, TijIs an element of the matrix T.
5. The method for calibrating a 2D camera-shooting type laser measuring head according to claim 1, wherein: after the calibration of the internal parameters of the camera and the calibration of the laser plane position are completed, under the condition that the relative positions of the camera and the line laser are unchanged, the external environment is changed, and only the internal parameters need to be calibrated again.
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| CN110470239B (en) * | 2019-08-07 | 2021-05-18 | 上海交通大学 | Laser profile sensor calibration system and method based on intersection point |
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| CN111750804B (en) * | 2020-06-19 | 2022-10-11 | 浙江华睿科技股份有限公司 | Object measuring method and device |
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| CN113096183B (en) * | 2021-03-18 | 2023-05-16 | 武汉科技大学 | Barrier detection and measurement method based on laser radar and monocular camera |
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