CN116862995A - External camera parameter calibration device and method for large-spacing and public-view-field-free camera - Google Patents
External camera parameter calibration device and method for large-spacing and public-view-field-free camera Download PDFInfo
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Abstract
The invention discloses a camera external parameter calibration device and a camera external parameter calibration method for a large-distance and public-view-field-free camera, wherein the device comprises a translation track and an adjusting seat, and the adjusting seat can slide on the translation track and comprises a lifting rod, a rotating seat and a pitching table which are in connection; the adjusting seat is used for fixedly mounting a target or a plane plate; the translation track, the lifting rod, the rotating seat and the pitching platform are respectively used for adjusting the horizontal position, the vertical position, the rotating angle and the pitching angle of the target or the plane plate, and the pose change amounts of the rotation, the translation and the pitching angle can be respectively recorded. According to the method, the camera external parameter calibration device is combined with the target/plane plate, so that the target or the plane plate can move in a calibration space, and external parameter calibration is carried out on the two cameras. The method does not need to introduce large auxiliary equipment, is suitable for external parameter calibration between cameras with almost deviating lenses and large distance, reduces the requirement on the calibration environment, and has the advantages of simple design, easy construction, low cost and high calibration efficiency.
Description
Technical Field
The invention relates to the field of camera calibration, in particular to a camera external parameter calibration device and method for a large-spacing camera without a public view field.
Background
Currently, visual inspection has been widely used in the field of intelligent manufacturing, and because of the limited field of view of a single camera, multiple cameras are required to expand the field of view when measuring large-scale work (e.g., high-speed trains, automobiles, ships, aircraft, etc.). When a plurality of cameras exist, external parameters between the cameras need to be calibrated, and the calibration result of the external parameters of the cameras directly affects the accuracy of the visual detection result.
The existing camera external parameter calibration method generally searches or sets a mark point in a common view field of the cameras, and obtains a rotation translation matrix between the two cameras by taking the same mark point in the images as a constraint. However, this approach may fail when there is no common field of view between the cameras. To address this problem, existing solutions require the addition of additional auxiliary equipment:
as disclosed in patent document CN114373019a, a method for calibrating a camera without a common field of view by using an optimization method is disclosed, a third camera K having a common field of view with both left and right cameras is added as an intermediary, three-dimensional coordinates of each marker point in a camera K coordinate system in a common field of view I and a common field of view ii are obtained, when the camera lens to be calibrated is almost deviated, for example: in the wheel set detection system, as shown in fig. 1, a first camera and a second camera are respectively arranged on the inner sides of the tracks on the left side and the right side, the lens faces the outer sides of the tracks, the included angle of the optical axis is larger than 150 degrees, the distance between the two cameras exceeds 50cm, at the moment, the placement position of the third camera is far away, so that difficulty in selecting a mark point is increased, and the calibration precision is reduced.
In addition, as romin introduces a double theodolite to establish a space three-dimensional coordinate measurement system in the paper 'study and application of a multi-sensor machine vision measurement system', the three-dimensional coordinates of a control point on a light plane are directly measured, and the global calibration of the multi-camera vision measurement system is realized; in patent document CN112308926a, a photogrammetry system is introduced to assist in measuring the spatial coordinates of the encoding points, so as to obtain external parameters between cameras without a common field of view. The method needs to introduce high-precision measuring equipment, has high manufacturing cost, and is not suitable for introducing large auxiliary calibrating equipment when a camera is installed outdoors, such as a first camera and a second camera of a wheel set detection sensor are respectively installed on the inner sides of the train tracks on the left side and the right side.
Disclosure of Invention
In order to solve the technical problems, the invention provides the camera external parameter calibration device and the camera external parameter calibration method for the large-spacing and public-view-field-free camera, which realize that a target or a plane plate can move in a calibration space through the camera external parameter calibration device, can image in different camera view fields without introducing large auxiliary equipment, and can obtain an external parameter matrix between the cameras without the public view fields.
For this purpose, the technical scheme of the invention is as follows:
the camera external parameter calibration device for large-spacing and public-view-field-free cameras comprises two parts, wherein the positions of the two parts are fixed, the spacing is at least 50cm, the directions of lenses are opposite, and the included angle between optical axes is 120-180 degrees;
the camera external parameter calibration device comprises a translation track and an adjusting seat arranged on the translation track, wherein the adjusting seat can slide on the translation track and comprises a lifting rod, a rotating seat and a pitching table which are in a connection relationship; the adjusting seat is used for fixedly mounting a target or a plane plate;
the translation track, the lifting rod, the rotating seat and the pitching platform are respectively used for adjusting the horizontal position, the vertical position, the rotating angle and the pitching angle of the target or the plane plate, and can respectively record the pose variation of the rotating, the translation and the pitching angle.
The invention also discloses a method for calibrating the camera with large spacing and no public view field by using the camera external parameter calibration device, wherein the target is arranged on the adjusting seat, when in calibration, the target pose is adjusted, so that one camera can clearly acquire a target image, the pose of the adjusting seat is recorded as pose I, and the rotation translation relation between the camera and the current target coordinate system is calculated according to the coordinates of a plurality of mark points in the acquired target image under the camera coordinate system and under the target coordinate system;
moving an adjusting seat to adjust the target pose so that the other camera can clearly image, recording the pose of the adjusting seat as pose II, and calculating the rotation translation relation between the camera and the current target coordinate system according to the coordinates of a plurality of mark points in the target image acquired by the camera under the camera coordinate system and the target coordinate system;
based on the pose change quantity from the pose I to the pose II recorded by the camera external parameter calibration device, the rotation and translation relation between the two cameras is acquired and recorded as an external parameter matrix.
Further, the marking points at least comprise 6 marking points which are checkerboard corner points, concentric circles or circles;
the origin of the target coordinate system is arranged at the geometric center of the target or at the corner point of the target.
The invention also discloses another method for calibrating the cameras with large spacing and no public view field by using the camera external parameter calibration device, wherein a multi-line laser is fixed on one side of each camera in a matched manner, and the rotation and translation relationship between the camera and the matched multi-line laser is calibrated in advance; the method is characterized in that:
a plane plate is arranged on the adjusting seat; a global coordinate system is established in advance, and a plane equation of the plane plate under the global coordinate system at the initial pose is recorded as an initial plane equation;
the calibration method comprises the following steps:
s1, adjusting a plane plate to a camera view field, projecting a multi-line laser bar to the surface of the plane plate by a multi-line laser, adjusting the pose, and collecting clear laser bar images by a camera; selecting a plurality of three-dimensional points on different laser strips from the laser strip images to fit a space plane equation of the plane plate in a camera coordinate system, and marking the space plane equation as a plane equation A1;
recording the pose change quantity of the rotation, translation and pitching angles of the current pose of the adjusting seat relative to the initial pose, solving a space plane equation of a plane plate at the current pose in a global coordinate system according to the pose change quantity and the initial plane equation, and recording the space plane equation as a plane equation A2;
transforming the pose of the plane plate for a plurality of times, and obtaining a pair of plane equations A1 and A2 each time the pose is transformed;
a plurality of pairs of plane equations A1 and A2 are combined, and the rotation translation relation between a camera coordinate system and a global coordinate system is obtained;
s2, repeating the step S1 for the other camera to obtain a rotation translation relation between the coordinate system of the other camera and the global coordinate system;
s3, taking the global coordinate system as a medium, acquiring a rotation translation relation between the two cameras, and marking the rotation translation relation as an external parameter matrix.
Further, the calculation method of the initial plane equation includes the following two methods:
mode one: selecting at least 3 non-collinear characteristic points on a plane plate, wherein the characteristic points comprise corner points, edge points and holes; according to the processing size of the plane plate, three-dimensional coordinates of a plurality of feature points under a global coordinate system are obtained at the initial pose, and the obtained three-dimensional coordinate fitting space plane equation is used as an initial plane equation;
mode two: and at the initial pose, according to the processing size of the plane plate, acquiring a normal vector of the plane plate under a global coordinate system and a three-dimensional coordinate of a single feature point under the global coordinate system, and using a three-dimensional coordinate fitting space plane equation of the normal vector and the feature point as an initial plane equation.
Further, solving a space plane equation of the plane plate in the global coordinate system at the current pose, and recording the space plane equation as a plane equation A2; the method is as follows:
the equation coefficient of the initial plane equation is recorded as [ AB C D ];
the equation coefficient [ A ' B ' C ' D ' of plane equation A2 ']＝[A B C D]·[RT1] -1 ；
Wherein RT1 represents a rotation-translation relationship obtained according to the rotation, translation and pitching angle pose change amounts generated by the current pose of the adjusting seat relative to the initial pose, and the rotation-translation relationship is composed of a rotation angle adjustment change amount alpha, a pitching angle adjustment change amount beta, a translation change amount deltax along the horizontal direction and a translation change amount deltah along the vertical direction.
Preferably, the plane plate is a polygonal plane plate or a circular plane plate with holes on the surface;
preferably regular polygon planar panels, such as square planar panels, regular triangle planar panels, regular pentagons;
the surface of the plane plate is pure-color and unpatterned, and the difference between the color and the gray level of the color of the laser bar is more than 100.
Further, the multi-line laser projects at least two laser bars;
the origin of the global coordinate system is set at a spatial point where no position change occurs.
Further, in step S1, the pose of the plane plate is changed at least three times, and each time the pose is changed, a pair of plane equations A1 and a plane equation A2 are obtained.
Further, the translation track is fixedly arranged in the calibration field; the lifting rod is vertically arranged on the translation track and can slide left and right on the translation track;
the rotating seat is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the rotating seat; the pitching platform is arranged on the rotating seat, and the rotating seat is used for rotating the installation angle of the pitching platform; the pitching platform is used for installing the target/plane plate and adjusting the pitching angle of the target/plane plate;
or the pitching platform is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the pitching platform; the rotating seat is arranged on a pitching table, and the pitching table is used for adjusting the pitching angle of the rotating seat; the rotating seat is used for installing the target/plane plate and adjusting the installation angle of the target/plane plate.
The invention has the following beneficial effects:
(1) large auxiliary equipment with high manufacturing cost is not required to be introduced, and the equipment cost is reduced;
the camera external parameter calibration device realizes that the target or the plane plate can move in the calibration space, can image in different camera fields of view, and obtains an external parameter matrix between cameras without public fields of view by knowing the conversion relations under different poses.
(2) The requirements on the calibration environment are reduced, the camera external parameter calibration device can be carried out outdoors, the design is simple, the construction is easy, and the calibration efficiency is high.
(3) The camera lens is almost deviated, and the external parameter calibration between two cameras with large spacing is realized; for example, the wheel set detection system shown in fig. 1 is provided with two sensors (including cameras) at the left and right side rails respectively, forming a plurality of pairs of camera groups without a common field of view, and two camera lenses without a common field of view are nearly deviated.
Drawings
FIG. 1 is a schematic diagram of a wheel set detection system in the prior art;
FIG. 2 is a schematic diagram of the external camera parameter calibration device in embodiment 1;
FIG. 3 is a schematic diagram of the process of calibrating two cameras in example 1;
FIG. 4 is a schematic diagram of the calibration process of the four cameras in embodiment 1;
FIG. 5 is a schematic diagram of the process of calibrating two cameras in example 2;
fig. 6 is a schematic diagram of the calibration process of the four cameras in embodiment 2.
Detailed Description
The technical scheme of the present invention is described in detail below with reference to the accompanying drawings and examples.
Example 1
The camera external parameter calibration device for the large-spacing camera without the public view field comprises two parts, wherein the positions of the two parts are fixed, the spacing is at least 50cm, the directions of lenses are opposite, and the included angle between optical axes is 120-180 degrees;
as shown in fig. 2, the camera external parameter calibration device comprises a translation track 1 and an adjusting seat mounted on the translation track, wherein the adjusting seat can slide on the translation track and comprises a lifting rod 2, a rotating seat 3 and a pitching table 4 which are connected; in this embodiment, the adjusting seat is used for fixedly mounting the target 5;
the translation track 1, the lifting rod 2, the rotating seat 3 and the pitching table 4 are respectively used for adjusting the horizontal position, the vertical position, the rotating angle and the pitching angle of a target or a plane plate, and can respectively record the pose change amounts of the rotation, the translation and the pitching angle.
In the specific implementation, the translation track can be selected from a seventh axis ground track of the high-precision linear transmission robot, a guide rail with an encoder, an electric cylinder, a linear displacement table and the like;
the lifting rod can be a linear displacement linear sliding table, a charged vertical displacement table, an electric cylinder and the like;
the rotating seat can be a high-precision vacuum rotating workbench, a rotating cradle head, an electric angular position table and the like;
the pitching table can be a high-precision electric angular table, a pitching deflection table and an optical experiment radian tilting displacement table;
in the embodiment, a target is adopted to calibrate external parameters between cameras without a common field of view, wherein a translation track is fixedly arranged in a calibration field (around two cameras); the lifting rod 2 is vertically arranged on the translation track 1 and can slide left and right on the translation track 1;
the rotating seat is arranged on the lifting rod 2, and the lifting rod 2 is used for adjusting the height of the rotating seat 3; the pitching platform 4 is arranged on a rotating seat, and the rotating seat is used for rotating the installation angle of the pitching platform; the pitching platform is used for installing the target 5 and adjusting the pitching angle of the target;
alternatively, the pitching table 4 is mounted on the lifter 2, and the lifter 2 is used for adjusting the height of the pitching table 4; the rotating seat 3 is arranged on a pitching table, and the pitching table is used for adjusting the pitching angle of the rotating seat; the swivel mount is used for installing target 5, adjusts the installation angle of target.
The specific calibration method is as follows:
a method for calibrating a large-spacing camera without a public view field by using a camera external parameter calibration device comprises the steps of installing targets on an adjusting seat, adjusting the target pose during calibration, enabling a camera to clearly acquire target images, recording the pose of the adjusting seat as pose I, and calculating the rotation translation relation RT between the camera and a current target coordinate system according to the coordinates of a plurality of mark points in the acquired target images under the camera coordinate system and under the target coordinate system, wherein the target is arranged on the adjusting seat A ；
Moving the adjusting seat to adjust the target pose so that the other camera can clearly image, recording the pose of the adjusting seat as pose II, and according to the sitting of a plurality of mark points in the target image acquired by the camera under the camera coordinate system and the target coordinate systemTarget, resolving the rotation translation relation RT between the camera and the current target coordinate system B ；
Based on the pose change quantity from the pose I to the pose II recorded by the camera external parameter calibration device, the rotation and translation relation between the two cameras is acquired and recorded as an external parameter matrix.
Specifically, a rotation translation relationship RT between the pose I and the pose II is obtained based on the pose change quantity from the pose I to the pose II recorded by the camera external parameter calibration device;
the rotation-translation relationship RT is composed of a rotation angle variation α, a pitch angle adjustment variation β, a variation Δx of translation in the horizontal direction, and a variation Δh of translation in the vertical direction.
For example, the camera external parameter calibration device rotates counterclockwise along the center axis of the pitching table, rotates counterclockwise along the center axis of the rotating seat by α, moves Δx in the horizontal direction, and moves Δh in the vertical direction
And taking RT as a medium, acquiring a rotation translation relation between the two cameras, and recording the rotation translation relation as an external reference matrix.
Namely: external matrix between camera one and camera two = RT A ×RT×RT B -1 。
Wherein due to RT A /RT B At least 6 constraint on the marker points is needed, for this purpose, the marker points in the target at least comprise 6, which are checkerboard corner points, concentric circles or circles; typically more than 10 marker points are provided.
The origin of the target coordinate system is arranged at the geometric center of the target or at the corner point of the target.
As an expanding application of the embodiment, the scheme of the embodiment is applied to calibrating four cameras synchronously, as shown in fig. 4, the four cameras form a plurality of pairs of camera sets without public view fields, the layout of the camera sets without public view fields is approximately rectangular, the translation tracks are arranged on symmetry axes of the rectangles, and each pair of camera sets without public view fields is calibrated by using targets.
The specific process is as follows:
the positions of the four cameras to be calibrated are fixed, the optical axes of the first camera, the second camera and the third camera and the fourth camera are almost deviated, the distance between any two cameras exceeds 50cm, and the four cameras to be calibrated have no public view field;
moving a target to a target pose A by using a camera external parameter calibration device, acquiring a target image by a camera I at the pose, and acquiring a rotation translation relation T between the camera I and a current target coordinate system Ato1 ；
Moving a target to a target pose B by using a camera external parameter calibration device, acquiring a target image by a camera II at the pose, and acquiring a rotation translation relation T between the camera II and a current target coordinate system Bto2 ；
Moving a target to a target pose C by using a camera external parameter calibration device, acquiring a target image by a camera three at the pose, and acquiring a rotation translation relation T between the camera three and a current target coordinate system Cto3 ；
Moving a target to a target pose D by using a camera external parameter calibration device, acquiring a target image by a camera four at the pose, and acquiring a rotation translation relation T between the camera four and a current target coordinate system Dto4 ；
The pose transformation matrix T generated by moving the target pose A to the target pose B, moving the target pose A to the target pose C and moving the target pose A to the target pose D is calculated respectively through data (comprising translation track 1 movement data, lifting rod 2 movement data, rotating seat 3 rotation angle and pitching table 4 rotation angle) recorded by a camera external parameter calibration device AtoB 、T AtoC 、T AtoD ；
The coordinate system rotation translation relations (external parameters) between the first camera and the second camera, the first camera and the third camera, and the first camera and the fourth camera are respectively:
T 21 ＝T 2toB T BtoA T Ato1 ＝T Bto2 -1 T AtoB -1 T Ato1
T 31 ＝T 3toC T CtoA T Ato1 ＝T Cto3 -1 T AtoC -1 T Ato1
T 41 ＝T 4toD T DtoA T Ato1 ＝T Dto4 -1 T AtoD -1 T Ato1
as a follow-up application, the information collected by the second camera, the third camera and the fourth camera is respectively converted into the coordinate system of the first camera through external parameters of the four cameras, so that the coordinate system of the collected information is unified.
Example 2
In this embodiment, the structure of the camera external parameter calibration device is the same as that of embodiment 1, except that the adjusting seat is used for fixing the plane plate; namely: the translation track is fixedly arranged in the calibration field (around the two cameras); the lifting rod is vertically arranged on the translation track and can slide left and right on the translation track;
the rotating seat is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the rotating seat; the pitching platform is arranged on the rotating seat, and the rotating seat is used for rotating the installation angle of the pitching platform; the pitching platform is used for installing the plane plate and adjusting the pitching angle of the plane plate;
or the pitching platform is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the pitching platform; the rotating seat is arranged on the pitching platform, and the pitching platform is used for adjusting the pitching angle of the rotating seat; the rotating seat is used for installing the plane plate and adjusting the installation angle of the plane plate.
In the embodiment, a plane plate is adopted to calibrate external parameters between cameras without public view fields, wherein a multi-line laser is fixed on one side of each camera in a matched mode, and the rotation translation relation between the camera and the matched multi-line laser is calibrated in advance; the method is suitable for external parameter calibration between the multi-line structure optical sensors, wherein the inside of the multi-line structure optical sensor shell comprises a camera and a multi-line laser with fixed relative positions;
the specific calibration method is as follows:
a method for calibrating a camera with a large distance and no public view field by using a camera external parameter calibration device comprises the following steps:
a plane plate is arranged on the adjusting seat; a global coordinate system is established in advance, and a plane equation of the plane plate under the global coordinate system at the initial pose is recorded as an initial plane equation;
the calibration method comprises the following steps:
s1, adjusting a plane plate to a camera view field, as shown in FIG. 5, projecting a multi-line laser bar to the surface of the plane plate by a multi-line laser, adjusting the pose, and collecting a clear laser bar image by a camera; selecting a plurality of three-dimensional points on different laser strips from the laser strip images to fit a space plane equation of the plane plate in a camera coordinate system, and marking the space plane equation as a plane equation A1;
recording the pose change quantity of the rotation, translation and pitching angles of the current pose of the adjusting seat relative to the initial pose, solving a space plane equation of a plane plate at the current pose in a global coordinate system according to the pose change quantity and the initial plane equation, and recording the space plane equation as a plane equation A2;
the pose of the plane plate is transformed for a plurality of times, and a pair of plane equations A1 and A2 are obtained after each pose transformation;
a plurality of pairs of plane equations A1 and A2 are combined, and the rotation translation relation between a camera coordinate system and a global coordinate system is obtained;
since there are 6 degrees of freedom, 12 unknown parameters, and a pair of plane equations can provide 4 equations to solve the rotational-translational relationship between the camera coordinate system and the global coordinate system, a minimum of 3 pairs of plane equations are required to complete the solution. For this purpose, in step S1, the pose of the plane plate is changed at least three times, and a pair of plane equations A1 and a pair of plane equations A2 are obtained each time the pose is changed.
S2, repeating the step S1 for the other camera to obtain a rotation translation relation between the coordinate system of the other camera and the global coordinate system;
s3, taking the global coordinate system as a medium, acquiring a rotation translation relation between the two cameras, and marking the rotation translation relation as an external parameter matrix.
Wherein the plane plate is a polygonal plane plate or a circular plane plate with holes on the surface; preferably, the design is a regular polygon plane plate, such as a square plane plate, a regular triangle plane plate and a regular pentagon;
the surface of the plane plate is pure-color and unpatterned, and the gray level difference between the color of the plane plate and the color of the laser bar is more than 100.
The multi-line laser projects at least two laser bars;
the origin of the global coordinate system is set at a spatial point where no change in position occurs. For example at the geometric centre, at the edge position of the translation track;
specifically, the calculation method of the initial plane equation includes the following two methods:
mode one: selecting at least 3 non-collinear characteristic points on a plane plate, wherein the characteristic points comprise corner points, edge points and holes; according to the processing size of the plane plate, three-dimensional coordinates of a plurality of feature points under a global coordinate system are obtained at the initial pose, and the obtained three-dimensional coordinate fitting space plane equation is used as an initial plane equation;
for example: the square plane plate selects four corner points and obtains coordinates of the four corner points under a global coordinate system; and acquiring a space plane equation by using the non-collinear four-point coordinates.
Mode two: and at the initial pose, according to the processing size of the plane plate, acquiring a normal vector of the plane plate under a global coordinate system and a three-dimensional coordinate of a single feature point under the global coordinate system, and using a three-dimensional coordinate fitting space plane equation of the normal vector and the feature point as an initial plane equation.
For example: the origin of the global coordinate system is arranged at the geometric center of the translation track, the plane plate is horizontally placed at the initial pose of the camera external parameter calibration device, the geometric center is right opposite to the origin of the global coordinate system, and the normal vector of the plane plate under the global coordinate system is (0, 1); and then selecting an angle or a hole on the plane plate as a characteristic point, calculating the three-dimensional coordinate of a single characteristic point under the global coordinate system, and solving a space plane equation by using a point method.
Further, solving a space plane equation of the plane plate in the global coordinate system at the current pose, and recording the space plane equation as a plane equation A2; the method is as follows:
the equation coefficient of the initial plane equation is recorded as [ AB C D ];
the initial plane equation is: ax+by+cz+d=0;
the equation coefficient [ A ' B ' C ' D ' of plane equation A2 ']＝[A B C D]·[RT1] -1 ；
The RT1 is a rotation and translation relation obtained according to the pose change quantity of rotation, translation and pitching angles of the current pose recorded by the adjusting seat relative to the initial pose, and the rotation and translation relation is composed of a rotation angle adjusting change quantity alpha, a pitching angle adjusting change quantity beta, a change quantity deltax of translation along the horizontal direction and a change quantity deltah of translation along the vertical direction.
For example, the camera external parameter calibration device rotates counterclockwise along the center axis of the pitching table, rotates counterclockwise along the center axis of the rotating seat by α, moves Δx in the horizontal direction, and moves Δh in the vertical direction
As an expanding application of the embodiment, the scheme of the embodiment is applied to a wheel set detection system, as shown in fig. 1, four detection sensors are distributed in a rectangular shape and are distributed on the inner side of a train track, cameras with fixed relative positions and multi-line lasers are arranged in each vision sensor, the four cameras form a plurality of pairs of camera sets without a public field of view, and a rotation translation relation (external reference matrix) between camera coordinate systems in the four sensors is calibrated.
As shown in fig. 6, the translation track is installed on a symmetry axis of the rectangle, and in a specific implementation, a clamping mechanism is arranged below the translation track and used for respectively clamping a left train track and a right train track, so that the camera external parameter calibration device is horizontally arranged on the two tracks of the train, and each pair of camera units without a public field of view is calibrated by using a plane plate.
The specific process is as follows:
the positions of the four cameras to be calibrated are fixed, the optical axes of the first camera, the second camera and the third camera and the fourth camera are almost deviated, the distance between any two cameras exceeds 50cm, and the four cameras to be calibrated have no public view field;
calibrating a first camera:
the plane plate is moved to a target pose A by using a camera external parameter calibration device, a laser projects multi-line laser stripes to the plane plate, and a camera acquires images; changing the pose for a plurality of times (at least three times) near the pose to form a target pose set A1, and obtaining a pair of plane equations A1 and a pair of plane equations A2 each time the pose is changed; simultaneous pairs of plane equations A1 and A2 are as follows:
solving a rotation translation relation T between a camera coordinate system and a global coordinate system wto1 The method comprises the steps of carrying out a first treatment on the surface of the Wherein the left side of the equation represents the equation coefficients of the plurality of plane equations A1, and the right side of the equation represents the equation coefficients of the plurality of plane equations A2; the equation coefficients of the plane equation A2 are calculated as follows:
the equation coefficient of the initial plane equation is recorded as [ AB C D ];
the equation coefficient [ A ' B ' C ' D ' of plane equation A2 ']＝[A B C D]·[RT1] -1 ；
The RT1 is a rotation and translation relation obtained according to the pose change quantity of rotation, translation and pitching angles of the current pose recorded by the adjusting seat relative to the initial pose, and the rotation and translation relation is composed of a rotation angle adjusting change quantity alpha, a pitching angle adjusting change quantity beta, a change quantity deltax of translation along the horizontal direction and a change quantity deltah of translation along the vertical direction.
In the above equation set, matrix T wto1 With 6 degrees of freedom and 12 unknown parameters, a pair of plane equation pairs can provide 4 equations, and when more than 3 pairs of plane equation pairs are acquired, the above overdetermined linear equation set can be solved.
Calibrating a second camera:
moving the plane plate to a target pose B by using a camera external parameter calibration device, projecting a multi-line laser bar to the plane plate by a laser, and acquiring an image by a camera II; changing the pose for a plurality of times (at least three times) near the pose to form a target pose set B1, and obtaining a pair of plane equations A1 and A2 each time the pose is changed; simultaneous multiple pairs of flatPlane equation A1 and plane equation A2, and calculate the rotation-translation relationship T between the camera two-coordinate system and the global coordinate system wto2 ；
Calibrating a camera III:
moving the plane plate to a target pose C by using a camera external parameter calibration device, projecting a multi-line laser bar on the three-way plane plate of the laser, and collecting images by using a camera III; changing the pose for a plurality of times (at least three times) near the pose to form a target pose set C1, and obtaining a pair of plane equations A1 and A2 each time the pose is changed; simultaneous multiple pairs of plane equations A1 and A2, and a rotational-translational relationship T between the three-coordinate system and the global coordinate system of the camera is obtained wto3 ；
Calibrating a camera IV:
moving the plane plate to a target pose D by using a camera external parameter calibration device, projecting multi-line laser strips to the plane plate by using a laser in four directions, and collecting images by using a camera; changing the pose for a plurality of times (at least three times) near the pose to form a target pose set D1, and obtaining a pair of plane equations A1 and A2 each time the pose is changed; simultaneous multiple pairs of plane equations A1 and A2, and a rotation-translation relationship T between the four-coordinate system and the global coordinate system of the camera is obtained wto4 ；
External parameters between cameras:
the coordinate system rotation translation relations (external parameters) between the first camera and the second camera, between the first camera and the third camera and between the first camera and the fourth camera are respectively T 21 、T 31 、T 41 ：
T 21 ＝T 2tow T wto1 ＝T 2tow -1 T wto1
T 31 ＝T 3tow T wto1 ＝T 3tow -1 T wto1
T 41 ＝T 4tow T wto1 ＝T 4tow -1 T wto1
As a follow-up application of the external parameter matrix, the information acquired by the second camera, the third camera and the fourth camera is respectively converted into the coordinate system of the first camera through external parameters of the four cameras, so that the coordinate system of the acquired information is unified.
For convenience in explanation and accurate definition in the appended claims, the terms "upper", "lower", "inner" and "outer" are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application to thereby enable others skilled in the art to make and utilize the invention in various exemplary embodiments and with various alternatives and modifications. It is intended that the scope of the invention be defined by the following claims and their equivalents.
Claims (10)
1. The camera external parameter calibration device for large-spacing and public-view-field-free cameras comprises two parts, wherein the positions of the two parts are fixed, the spacing is at least 50cm, the directions of lenses are opposite, and the included angle between optical axes is 120-180 degrees;
the method is characterized in that: the camera external parameter calibration device comprises a translation track and an adjusting seat arranged on the translation track, wherein the adjusting seat can slide on the translation track and comprises a lifting rod, a rotating seat and a pitching table which are in a connection relationship; the adjusting seat is used for fixedly mounting a target or a plane plate;
the translation track, the lifting rod, the rotating seat and the pitching platform are respectively used for adjusting the horizontal position, the vertical position, the rotating angle and the pitching angle of the target or the plane plate, and can respectively record the pose variation of the rotating, the translation and the pitching angle.
2. The method for calibrating the camera with large spacing and no public view field by using the camera external parameter calibration device according to claim 1, wherein the target is arranged on the adjustment seat, and the target pose is adjusted during calibration, so that one camera can clearly acquire a target image, the pose of the adjustment seat is recorded as pose I, and the rotation translation relation between the camera and the current target coordinate system is calculated according to the coordinates of a plurality of mark points in the acquired target image under the camera coordinate system and under the target coordinate system;
moving an adjusting seat to adjust the target pose so that the other camera can clearly image, recording the pose of the adjusting seat as pose II, and calculating the rotation translation relation between the camera and the current target coordinate system according to the coordinates of a plurality of mark points in the target image acquired by the camera under the camera coordinate system and the target coordinate system;
based on the pose change quantity from the pose I to the pose II recorded by the camera external parameter calibration device, the rotation and translation relation between the two cameras is acquired and recorded as an external parameter matrix.
3. The method of claim 2, wherein: the marking points at least comprise 6 marking points which are checkerboard angular points, concentric circles or circles;
the origin of the target coordinate system is arranged at the geometric center of the target or at the corner point of the target.
4. A method for calibrating a camera with a large distance and no public view field by using the camera external parameter calibration device as claimed in claim 1, wherein a multi-line laser is fixed on one side of the camera in a matched manner, and the rotation translation relation between the camera and the matched multi-line laser is calibrated in advance; the method is characterized in that:
a plane plate is arranged on the adjusting seat; a global coordinate system is established in advance, and a plane equation of the plane plate under the global coordinate system at the initial pose is recorded as an initial plane equation;
the calibration method comprises the following steps:
s1, adjusting a plane plate to a camera view field, projecting a multi-line laser bar to the surface of the plane plate by a multi-line laser, adjusting the pose, and collecting clear laser bar images by a camera; selecting a plurality of three-dimensional points on different laser strips from the laser strip images to fit a space plane equation of the plane plate in a camera coordinate system, and marking the space plane equation as a plane equation A1;
recording the pose change quantity of the rotation, translation and pitching angles of the current pose of the adjusting seat relative to the initial pose, solving a space plane equation of a plane plate at the current pose in a global coordinate system according to the pose change quantity and the initial plane equation, and recording the space plane equation as a plane equation A2;
transforming the pose of the plane plate for a plurality of times, and obtaining a pair of plane equations A1 and A2 each time the pose is transformed;
a plurality of pairs of plane equations A1 and A2 are combined, and the rotation translation relation between a camera coordinate system and a global coordinate system is obtained;
s2, repeating the step S1 for the other camera to obtain a rotation translation relation between the coordinate system of the other camera and the global coordinate system;
s3, taking the global coordinate system as a medium, acquiring a rotation translation relation between the two cameras, and marking the rotation translation relation as an external parameter matrix.
5. The method of claim 4, wherein: the calculation mode of the initial plane equation comprises the following two modes:
mode one: selecting at least 3 non-collinear characteristic points on a plane plate, wherein the characteristic points comprise corner points, edge points and holes; according to the processing size of the plane plate, three-dimensional coordinates of a plurality of feature points under a global coordinate system are obtained at the initial pose, and the obtained three-dimensional coordinate fitting space plane equation is used as an initial plane equation;
mode two: and at the initial pose, according to the processing size of the plane plate, acquiring a normal vector of the plane plate under a global coordinate system and a three-dimensional coordinate of a single feature point under the global coordinate system, and using a three-dimensional coordinate fitting space plane equation of the normal vector and the feature point as an initial plane equation.
6. The method of claim 4, wherein: solving a space plane equation of a plane plate in a global coordinate system at the current pose, and recording the space plane equation as a plane equation A2; the method is as follows:
the equation coefficient of the initial plane equation is recorded as [ A B C D ];
the equation coefficient [ A ' B ' C ' D ' of plane equation A2 ']＝[A B C D]·[RT1] -1 ；
Wherein RT1 represents a rotation-translation relationship obtained according to the rotation, translation and pitching angle pose change amounts generated by the current pose of the adjusting seat relative to the initial pose, and the rotation-translation relationship is composed of a rotation angle adjustment change amount alpha, a pitching angle adjustment change amount beta, a translation change amount deltax along the horizontal direction and a translation change amount deltah along the vertical direction.
7. The method of claim 4, wherein: the plane plate is a polygonal plane plate or a circular plane plate with holes on the surface;
preferably regular polygon planar panels, such as square planar panels, regular triangle planar panels, regular pentagons;
the surface of the plane plate is pure-color and unpatterned, and the difference between the color and the gray level of the color of the laser bar is more than 100.
8. The method of claim 4, wherein: the multi-line laser projects at least two laser bars;
the origin of the global coordinate system is set at a spatial point where no position change occurs.
9. The method of claim 4, wherein: in step S1, the pose of the plane plate is transformed at least three times, and a pair of plane equations A1 and a pair of plane equations A2 are obtained each time the pose is transformed.
10. The camera exogenous calibration device of claim 1, wherein: the translation track is fixedly arranged in the calibration field; the lifting rod is vertically arranged on the translation track and can slide left and right on the translation track;
the rotating seat is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the rotating seat; the pitching platform is arranged on the rotating seat, and the rotating seat is used for rotating the installation angle of the pitching platform; the pitching platform is used for installing the target/plane plate and adjusting the pitching angle of the target/plane plate;
or the pitching platform is arranged on the lifting rod, and the lifting rod is used for adjusting the height of the pitching platform;
the rotating seat is arranged on a pitching table, and the pitching table is used for adjusting the pitching angle of the rotating seat; the rotating seat is used for installing the target/plane plate and adjusting the installation angle of the target/plane plate.
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| CN117557659A (en) * | 2024-01-10 | 2024-02-13 | 吉林大学 | Opposite camera global calibration method and system based on one-dimensional target and turntable |
| CN117557659B (en) * | 2024-01-10 | 2024-03-19 | 吉林大学 | Opposite camera global calibration method and system based on one-dimensional target and turntable |
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