CN117252930A - Method and system for calibrating internal and external parameters of multi-camera monitoring system of large exhibition hall - Google Patents

Method and system for calibrating internal and external parameters of multi-camera monitoring system of large exhibition hall Download PDF

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CN117252930A
CN117252930A CN202311222096.1A CN202311222096A CN117252930A CN 117252930 A CN117252930 A CN 117252930A CN 202311222096 A CN202311222096 A CN 202311222096A CN 117252930 A CN117252930 A CN 117252930A
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camera
calibration
pose
dimensional
coordinate system
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龙宇轩
徐晓刚
王军
马寅星
李玲
何鹏飞
谢正超
唐乾坤
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Zhejiang Lab
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Zhejiang Lab
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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
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/30—Subject of image; Context of image processing
    • G06T2207/30204—Marker
    • G06T2207/30208—Marker matrix

Abstract

The invention discloses a method and a system for calibrating internal and external parameters of a multi-camera monitoring system of a large exhibition hall, comprising the following steps: acquiring multi-camera video data as calibration data; preprocessing the calibration data; monocular camera calibration is carried out to obtain an initial value of the camera internal parameter; performing preliminary estimation on camera external parameters by using a chain method to obtain the pose of each camera relative to a world coordinate system as a camera external parameter initial value; performing preliminary estimation on the positions and the postures of the calibration plates to obtain initial values of the positions and the postures of the calibration plates under each specific posture; constructing a gross weight projection error as an objective function and introducing a regular term based on distortion parameters; and minimizing an objective function with a regular term by using the camera internal parameter initial value, the camera external parameter initial value and the positioning plate pose initial value to solve the global optimization problem, so as to obtain the optimal camera internal and external parameters. The invention can reduce labor cost and risk, improve the accuracy of the camera internal and external parameter calibration, and is suitable for the application scene of the multi-camera system internal and external parameter calibration in high altitude suspension or in open space.

Description

Method and system for calibrating internal and external parameters of multi-camera monitoring system of large exhibition hall
Technical Field
The invention belongs to the technical field of machine vision, and particularly relates to an internal and external parameter calibration method and system for a multi-camera monitoring system of a large exhibition hall.
Background
In large-scale exhibition halls, three-dimensional positioning of people or objects relative to the ground is usually realized through a monitoring camera system, and internal and external parameters of the camera system are required to be accurately calibrated for obtaining accurate three-dimensional positioning. The internal parameters include parameters such as principal point, focal length, and distortion; external parameters include the pose of the camera, such as translation and rotation relative to the world coordinate system. The main features of large-scale hall monitoring camera systems are that the cameras are often suspended at high altitudes where normal persons cannot reach, and that the monitoring cameras often have significant wide-angle distortion.
In order to accurately acquire the internal parameters (including distortion parameters) of each camera, conventional calibration methods require acquisition of close calibration data for the camera system, generally requiring the calibration plate to occupy at least one third of the image. This means that the long ladder and even the aerial ladder need to be sequentially climbed to approach each monitoring camera, and the cameras are re-picked or the calibration plate is moved for a plurality of times so as to acquire internal reference calibration data. If attempts are made to avoid this inconvenience, i.e. to collect calibration data directly on the ground, this will lead to inaccurate reference estimates; the reason for this is that the calibration plate on the ground is far from the camera, the duty ratio of the calibration plate in the image is small, and the whole of the lens cannot be accumulated even if it moves around on the ground, which means defective calibration data.
Chinese patent application publication No. CN108717714a discloses a multi-camera calibration method, calibration system, storage medium, and electronic device, which requires that the shot data need to cover the full field of view of the camera, and then optimize the internal and external parameters of the multi-camera system by minimizing the total weight projection error. However, for a multi-camera system arranged in a high-altitude suspension way in a large-scale exhibition hall, the problem that the occupation ratio of a calibration plate in a shot image is too small and the visual field cannot be completely covered can occur.
In addition, cameras in the exhibition hall are distributed in the exhibition hall in a scattered manner, the area of the exhibition hall can reach thousands of meters, and the common view of adjacent cameras is limited, so that the external parameter calibration between every two cameras brings about larger accumulated errors. Moreover, the multi-camera system is often not perfectly synchronized, and in order for adjacent cameras to capture a calibration object in the same posture, the calibration object (such as a calibration plate) needs to be in an absolute static state. To avoid the problem, a conventional method is to arrange a calibration target or a large calibration plate on the floor of an exhibition hall in a large area, thereby obtaining the external parameters (i.e., the pose with respect to the world coordinate system) of each camera independently.
The conventional method has no innovation requirement on the algorithm, but has the following problems: a large amount of labor cost is consumed, time is wasted, and the labor cost is proportional to the number of cameras; the use of heavy equipment may be required, resulting in accidental damage to the exhibition hall site; moving the calibration plate aloft can bring potential risks to data acquisition personnel. Therefore, a new calibration method for a large-scale exhibition hall multi-camera system is urgently needed, labor cost and risk are reduced, heavy equipment is avoided, and meanwhile, the internal parameters and the external parameters of the exhibition hall camera system are accurately estimated.
Disclosure of Invention
In view of the above, the present invention aims to provide a method and a system for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall, which uses a movable calibration plate and introduces a regular term based on distortion parameters to carry out global optimization algorithm innovation, and can obtain accurate internal parameters and external parameters of the camera only by simple and labor-saving calibration data acquisition and processing, thus being suitable for calibrating the internal and external parameters of the multi-camera system in high-altitude suspension or in open space.
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
in a first aspect, the method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall provided by the embodiment of the invention comprises the following steps:
acquiring multi-camera video data as calibration data, and preprocessing the calibration data to respectively obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates;
monocular camera calibration is carried out on each camera by using the two-dimensional-three-dimensional point pair set to obtain an initial value of the internal parameters of the camera, the pose of each camera relative to the calibration plate and the pose of the initial camera relative to the world coordinate system;
performing camera external parameter preliminary estimation based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate by using a chained method to obtain the pose of each camera relative to the world coordinate system as a camera external parameter initial value;
performing initial estimation on the positions and postures of the calibration plates according to the camera external parameter initial values and the positions and postures of each camera relative to the calibration plates to obtain initial values of the positions and postures of the calibration plates under each specific posture;
constructing a gross weight projection error based on the point-to-set as an objective function, and introducing a regular term based on distortion parameters to the objective function;
and using the camera internal parameter initial value, the camera external parameter initial value and the positioning plate pose initial value as initial values for solving the global optimization problem, and minimizing an objective function with a regular term to solve the global optimization problem so as to obtain the optimal camera internal and external parameters.
Specifically, the acquiring the multi-camera video data as calibration data includes:
preparing a calibration plate capable of moving on the ground and a plurality of fixed calibration points in advance, and defining a world coordinate system G;
selecting any one of the cameras as an initial camera C 1 At the initial camera C 1 Arranging calibration points on the ground in the visual field, and acquiring video data as first calibration data;
moving the calibration plate, moving a circle in the exhibition hall and changing the gesture of the calibration plate to cover the visual field of each camera at all times to acquire video data as second calibration data;
and (3) moving the calibration plate, moving a circle in the exhibition hall, changing the posture of the calibration plate from time to time, and collecting calibration data in the common field of view of two adjacent cameras, so as to form a communicated and closed-loop camera relation diagram, and obtaining video data as third calibration data.
Specifically, the preprocessing the calibration data to obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates respectively includes:
recording three-dimensional coordinates of the calibration point in a world coordinate system, marking two-dimensional coordinates corresponding to the three-dimensional coordinates of the calibration point in an image of the first calibration data, and recording all two-dimensional-three-dimensional point data as a point pair set omega G ；
Image sampling is carried out on all videos of the second calibration data and the third calibration data, two-dimensional angular point coordinates of the calibration plate are extracted from images containing the calibration plate, the two-dimensional angular point coordinates and corresponding three-dimensional angular point coordinates in a coordinate system of the calibration plate are stored, and all two-dimensional-three-dimensional point data are recorded as a point pair set omega;
selecting images from at least two cameras and simultaneously containing the calibration plate in the same static state for the third calibration data, extracting two-dimensional angular point coordinates of the calibration plate and corresponding three-dimensional coordinates in a coordinate system of the calibration plate from the images, and recording all two-dimensional-three-dimensional point data as a point pair set omega S Wherein
The set of point pairs omega G Point pair set Ω and Point pair set Ω S Together forming a set of two-dimensional-three-dimensional point pairs of step 2.
Specifically, the method for obtaining the pose of each camera relative to the world coordinate system as the initial value of the camera external parameter by using the chained method to perform the preliminary estimation of the camera external parameter based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate comprises the following steps:
corresponds to the point pair set omega S The pose of the calibration plate present in the camera is initialized by the camera C 1 And adjacent camera C 2 Simultaneous capturing according to the initial camera C 1 Pose relative to world coordinate system and initial camera C 1 And camera C 2 Positioning relative to the calibration plate, respectivelyPose, obtain camera C 2 Pose relative to world coordinate system; by adopting the same method, the pose of the known camera relative to the world coordinate system and the pose of the known camera and the pose of the unknown camera relative to the calibration plate are sequentially used for the adjacent cameras by using a chain method, the pose of the unknown camera relative to the world coordinate system is obtained, and finally, the pose of each camera relative to the world coordinate system is obtained to be used as a camera external parameter initial value.
Specifically, the constructing the gross weight projection error based on the point-to-set serves as an objective function, and a regular term based on distortion parameters is introduced to the objective function, and the method comprises the following steps:
any point pair (X, X) E omega G ∪Ω S Wherein x is the nth camera C n Two-dimensional angular point coordinates of the captured image on a calibration plate coordinate system correspond to the calibration plate B of the mth gesture m A three-dimensional angular point coordinate X on a calibration plate coordinate system; the loss function is thus constructed as a reprojection error:wherein pi is n Is camera C n Is>For camera pose, i.e. world coordinate system G to camera C n Transformation matrix of coordinate system, < >>The position of the calibration plate is the calibration plate B m Transformation matrix from coordinate system to world coordinate system G 2 Is the square of the L2 norm; will all belong to omega G ∪Ω S Summing the constructed re-projection errors to obtain a total weight projection error function E; constructing a distortion parameter matrix K, enabling each row of the distortion parameter matrix K to correspond to the distortion parameters of the appointed camera, and introducing a regularization term g (K) based on the distortion parameters in the camera internal parameters to obtain an objective function with the regularization term as E+λg (K), wherein λ is a weight coefficient.
Specifically, the construction method of the regular term g (K) of the distortion parameter comprises the following steps:
constructing an undirected graph taking the cameras as nodes, and connecting the nodes of the undirected graph between cameras with the same model; from the undirected graph, an adjacency matrix W can be obtained, and then a Laplace matrix L is directly calculated; the last true regularization term g (K) =trace (K T LK), where trace (·) is the trace of the matrix, K T Is the transpose of the distortion parameter matrix K.
Specifically, the minimizing the objective function with the regularization term to solve the global optimization problem to obtain the optimal internal and external parameters of the camera includes:
and constructing a nonlinear global optimization problem min (E+lambdag (K)) with a regular term, and solving the nonlinear global optimization problem min by using a Levenberg-Marquardt algorithm, wherein a weight coefficient lambda >0, so as to obtain the optimal camera internal and external parameters.
In a second aspect, in order to achieve the above object, an embodiment of the present invention further provides an internal and external parameter calibration system for a multi-camera monitoring system in a large-scale exhibition hall, including: the camera comprises a data acquisition and preprocessing module, a monocular camera calibration module, a camera external parameter preliminary estimation module, a calibration plate pose preliminary estimation module and a camera external parameter optimization module;
the data acquisition and preprocessing module is used for acquiring multi-camera video data as calibration data, preprocessing the calibration data to respectively obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates;
the monocular camera calibration module is used for carrying out monocular camera calibration on each camera by using the two-dimensional-three-dimensional point pair set to obtain an initial value of a camera internal parameter, the pose of each camera relative to the calibration plate and the pose of the initial camera relative to a world coordinate system;
the camera external parameter preliminary estimation module is used for carrying out camera external parameter preliminary estimation based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate by using a chain method to obtain the pose of each camera relative to the world coordinate system as a camera external parameter initial value;
the calibration board pose preliminary estimation module is used for carrying out preliminary estimation on the calibration board poses according to the camera external parameter initial values and the poses of each camera relative to the calibration board to obtain the calibration board pose initial values under each specific pose;
the camera internal and external parameter optimization module is used for constructing total weight projection errors based on point-to-set as an objective function, introducing a regular term based on distortion parameters to the objective function, and using a camera internal parameter initial value, a camera external parameter initial value and a positioning plate pose initial value as initial values for solving a global optimization problem, and minimizing the objective function with the regular term to solve the global optimization problem so as to obtain the optimal camera internal and external parameters.
In order to achieve the above object, the embodiment of the present invention further provides an external parameter calibration device for a multi-camera monitoring system of a large-scale exhibition hall, which includes a memory and a processor, wherein the memory is used for storing a computer program, and the processor is used for implementing the external parameter calibration method for the multi-camera monitoring system of the large-scale exhibition hall provided by the embodiment of the present invention in the first aspect when executing the computer program.
In a fourth aspect, in order to achieve the above object, an embodiment of the present invention further provides a computer-readable storage medium, where a computer program is stored on the storage medium, and when the computer program is used in a computer, the method for calibrating an internal parameter and an external parameter of a multi-camera monitoring system in a large-scale exhibition hall according to the first aspect of the present invention is implemented.
Compared with the prior art, the invention has the beneficial effects that at least the following steps are included:
(1) The method has the advantages that the data acquisition mode of camera calibration is simple and labor-saving, all calibration data acquisition of the multi-camera monitoring system in the exhibition hall can be completed only by moving the calibration plate on the ground and arranging a plurality of calibration points, the plate is not required to be lifted manually, the trouble of acquiring data in high air and other matters are avoided, the initial parameters of the camera are not required to be given in advance, the method is simple and labor-saving, and the labor cost and risk are reduced.
(2) According to the method, on the basis of the global optimization problem, the regular term based on the distortion parameters is introduced, the problem of inaccurate internal parameter estimation caused by the fact that the calibration plate is far away from the camera is solved, the robustness and accuracy of the internal parameter estimation are effectively improved, and the accuracy of the external parameter estimation is indirectly improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of a method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall, which is provided by the embodiment of the invention;
FIG. 2 is an image with a calibration plate acquired by a camera according to an embodiment of the present invention, and corresponds to the calibration plate in the same posture as that of FIG. 3;
FIG. 3 is an image with a calibration plate acquired by another camera according to an embodiment of the present invention, corresponding to the calibration plate in the same posture as that of FIG. 2;
FIG. 4 is an image acquired by a camera of an embodiment of the present invention, including a plurality of calibration points on the ground;
FIG. 5 is a schematic view of a camera system in a world coordinate system and a calibration plate position at a certain pose, wherein the coordinate axis units are meters, provided by an embodiment of the present invention;
fig. 6 is a schematic structural diagram of an internal and external parameter calibration system of a multi-camera monitoring system for a large-scale exhibition hall according to an embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description is presented by way of example only and is not intended to limit the scope of the invention.
The invention is characterized in that: aiming at the problems that in the prior art, when the camera system internal and external parameter calibration method is applied to a scene of a large exhibition hall, the labor cost and the risk are high, the use of heavy machinery possibly causes site damage and the calibration precision is to be improved, the embodiment of the invention provides the large exhibition hall multi-camera monitoring system internal and external parameter calibration method and system, and the accuracy of the large exhibition hall camera internal and external parameter calibration is improved by innovating a movable calibration plate and a global optimization algorithm.
First, define ζ G→C The transformation matrix of the coordinate system G to the coordinate system C is as follows: where R is a 3×3 rotation matrix and t is a 3×1 translation vector.
Taking an arbitrary point X in three-dimensional space as an example, if the point is defined in a coordinate system C, it isDefined in the coordinate system G as +.>ζ G→C A corresponding coordinate transformation can be constructed:
in the camera calibration problem of the embodiment of the invention, G is a world coordinate system, C is a camera, B is a calibration plate, and ζ is G→C The pose of the camera C, i.e., the transformation matrix of the world coordinate system G to the camera C coordinate system.
For any camera C n Defining its internal reference matrix asWherein (f) x ,f y ) Is focal length (c) x ,c y ) Is like a principal point. Defining the distortion parameter of the camera as (k) 1 ,k 2 ,k 3 ). The three-to-two-dimensional camera projection function is defined as:
π n ([x y z] T )＝[u v] T
wherein pi n For the projection function of the nth camera, x, y and z are values of three direction coordinate axes in the three-dimensional coordinate, u and v are values of two direction coordinate axes in the two-dimensional coordinate, and T is a transpose.
Specifically, if only radial distortion is considered, pi n The following coordinate calculation is included:
r＝x ′2 +y ′2
r ′ ＝1+k 1 r+k 2 r 2 +k 3 r 3
u＝f x r ′ x ′ +c x ，v＝f y r ′ y ′ +c y
the specific steps of the following embodiment include a data acquisition method and a calibration algorithm flow.
Fig. 1 is a flow chart of a method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to an embodiment of the invention. As shown in fig. 1, an embodiment provides a method for calibrating internal and external parameters of a multi-camera monitoring system of a large-scale exhibition hall, which comprises the following steps:
s1, preparing a calibration plate capable of moving on the ground and a plurality of fixed calibration points in advance, and defining a world coordinate system G.
In the embodiment, as shown in fig. 2 and 3, in order to prepare a calibration plate capable of moving on the ground, a standard checkerboard is printed on a plastic plate and attached to a bracket type whiteboard with a pulley, and the size of each checkerboard of the calibration plate is 14cm×14cm, so that the size of each checkerboard is ensured to enable the angular point coordinates of the checkerboard to be detected in an image. More than 3 calibration points are prepared in advance, and the calibration points should be large enough so that two-dimensional positions can be recognized in the camera image. A world coordinate system is defined, and a zero position and a direction of a coordinate axis are selected on the ground.
S2, selecting any camera as an initial camera C 1 At the initial camera C 1 And arranging calibration points on the ground in the visual field, and acquiring video data as first calibration data.
In an embodiment, in order to build the camera system on the world coordinate system, one camera is selected from the camera system as the initial camera C 1 At least 3 calibration points are arranged on the ground in the visible range, all the calibration points are ensured not to be on the same straight line, and the acquired video data containing the calibration points is taken as first calibration data as shown in fig. 4.
S3, moving the calibration plate for a circle in the exhibition hall, and changing the posture of the calibration plate to cover the visual field of each camera from time to time, so as to acquire video data as second calibration data.
In an embodiment, the calibration plate is moved to walk around in the exhibition hall and change the posture of the calibration plate from time to time, and the visual range of each camera is covered, as shown in fig. 5, which is a schematic diagram of the camera system in the world coordinate system and the position of the calibration plate in a certain posture, wherein the coordinate axis units are meters. Finally, the monitoring video of the camera system with the calibration plates with different postures is obtained and is specially used for camera internal parameter calibration and is recorded as second calibration data. When the posture of the calibration plate is changed, the white plate is pushed or the overturning angle of the white plate is changed.
S4, moving the calibration plate for a circle in the exhibition hall, changing the posture of the calibration plate from time to time, and collecting calibration data in the common field of view of two adjacent cameras, so that a communicated closed-loop camera relation diagram is formed, and video data is obtained as third calibration data.
In the embodiment, considering the problem that the camera system cannot achieve perfect time synchronization, the calibration plate is enlarged in the common visual range of each pair of adjacent cameras and stays for a plurality of seconds, and in the video data acquisition process, the monitoring of the camera in the exhibition hall is required to be observed so as to ensure that the adjacent cameras can simultaneously see the large calibration plate in the same static state. And (3) moving the calibration plate between each pair of adjacent cameras for multiple times, and changing the gesture of the calibration plate, so as to form a communicated and closed-loop camera relation diagram. And finally, acquiring a monitoring video of the camera system and recording the monitoring video as third calibration data. It is noted that the camera relationship forming the closed loop can effectively overcome error accumulation.
S5, preprocessing the first calibration data to obtain a two-dimensional-three-dimensional point pair set omega of the calibration points G 。
In an embodiment, three-dimensional coordinates of a calibration point in a world coordinate system are recorded, two-dimensional coordinates corresponding to the three-dimensional coordinates of the calibration point are marked in an image of first calibration data, and all two-dimensional-three-dimensional point data are recorded as a point pair set omega G 。
S6, preprocessing the second calibration data and the third calibration data to obtain a two-dimensional-three-dimensional point pair set omega of the corner points of the calibration plate.
In the embodiment, the video of the second calibration data and the third calibration data is subjected to image sampling, only the image containing the calibration plate is reserved, and the corner detection result of the calibration plate is conveniently checked. And extracting two-dimensional angular point coordinates of the calibration plate from the image containing the calibration plate, storing the two-dimensional angular point coordinates and corresponding three-dimensional angular point coordinates in a coordinate system of the calibration plate, and recording all two-dimensional-three-dimensional point data as a point pair set omega.
S7, further preprocessing the third calibration data to obtain a two-dimensional-three-dimensional point pair set omega of the multi-camera corresponding to the corner points of the calibration plate in the same static state S 。
In an embodiment, for a video of the third calibration data, images from at least two cameras and simultaneously including the calibration plate in the same stationary state are selected, two-dimensional corner coordinates of the calibration plate and corresponding three-dimensional corner coordinates in the calibration plate coordinate system are extracted from the images, and all the two-dimensional-three-dimensional point data are recorded as a point pair set Ω S WhereinMarking the detected two-dimensional angular points on the images in different colors according to the sequence, checking the angular point detection sequence of the calibration plates in the multi-purpose calibration data, namely, the calibration plates corresponding to the same gesture as shown in fig. 2 and 3, wherein the angular points detected at the moment are exactly opposite in sequence due to the opposite viewing angles of the two cameras, and if the angular points are exactly opposite in sequence, correcting the sequence so as to ensure that the angular points keep one on the same calibration plateSo that.
S8, using the point pair set omega G And omega, independently calibrating each camera by a monocular camera to obtain an initial value of the internal parameters of the camera, the pose of each camera relative to the calibration plate and the pose of the initial camera relative to a world coordinate system.
In an embodiment, point pair sets Ω and Ω are used G Monocular camera calibration is carried out on each camera, the obtained camera internal parameter initial values comprise distortion parameters, focal lengths and image principal points, and the pose zeta of each camera relative to the calibration plate B→C Initial camera C 1 Pose relative to world coordinate system is recorded as rigid transformation matrixIt should be noted that, since the calibration plate occupies much less than one third of the image, the monocular calibration is inaccurate, which means that the camera internal parameters estimated in this step need further optimization.
S9, using the point pair set omega S And carrying out preliminary estimation on camera external parameters based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate by adopting a chain method to obtain the pose of each camera relative to the world coordinate system as a camera external parameter initial value.
In an embodiment, corresponds to a set of point pairs Ω S The pose of the calibration plate present in the camera is initialized by the camera C 1 And adjacent camera C 2 Simultaneous capturing according to the initial camera C 1 Pose relative to world coordinate system GObtaining camera C 2 Pose +.>
Wherein,is camera C 2 Pose relative to the coordinate system of calibration plate B, < >>Is camera C 1 Pose relative to the calibration plate B coordinate system. Repeating the method can use->And obtaining the pose of other cameras relative to the world coordinate system G. And the pose of the known camera relative to the world coordinate system and the pose of the known camera and the pose of the unknown camera relative to the calibration plate are sequentially used for the adjacent cameras by using a chained method, the pose of the unknown camera relative to the world coordinate system is obtained, and finally, the pose of each camera relative to the world coordinate system is obtained and is used as a camera external parameter initial value. It should be noted that the use of the chained approach can result in accumulation of camera pose errors, requiring the use of closed loop optimization to remove the error accumulation.
S10, carrying out preliminary estimation on the positions and the postures of the calibration plates according to the camera external parameter initial values to obtain the initial values of the positions and the postures of the calibration plates under each specific posture.
In an embodiment, the initial pose estimation of the camera is utilized to calculate the initial pose value of the calibration plate under each specific pose. For example, for camera C obtained 2 Pose and camera C relative to calibration plate B coordinate system 2 Pose relative to world coordinate system GCan calculate the pose zeta of the corresponding calibration plate B B→G ：
Wherein ζ B→G The coordinate transformation matrix from the coordinate system of the calibration plate B to the world coordinate system G is the pose of the calibration plate.
S11, based on point pair set omega G And omega S Structure of the deviceGross weight projection error as an objective function.
In the embodiment, a point pair (X, X) E omega is arbitrarily taken G ∪Ω S Wherein x is the nth camera C n Two-dimensional angular point coordinates of the captured image on a calibration plate coordinate system correspond to the calibration plate B of the mth gesture m And (3) a three-dimensional angular point coordinate X on a calibration plate coordinate system. The loss function is thus constructed as a reprojection error:wherein pi is n Is camera C n Is>For camera pose, i.e. world coordinate system G to camera C n A transformation matrix of the coordinate system,the position of the calibration plate is the calibration plate B m Transformation matrix from coordinate system to world coordinate system G 2 The camera pose +.>And mark the board position appearance->Are independent variables of the error function, and the projection function pi n Including camera focal length, image principal point and distortion parameter independent variables.
All belong to the point pair set omega G ∪Ω S In the examples, a small number of monocular point pairs, i.e. belonging to omega but not belonging to omega, may also be added S Is included) the constructed re-projection errors are summed to obtain a total weight projection error function E. The gross weight projection error function E is taken as an objective function for global optimization of camera parameters.
S12, introducing a regular term based on distortion parameters to the objective function.
In order to solve the problem of unstable internal parameter estimation caused by small occupation of a calibration plate in an image, a few very reasonable priori knowledge with strong generalization needs to be introduced: cameras of the same model may have different focal lengths, but must have nearly identical lens aberrations.
In an embodiment, a distortion parameter matrix K is constructed so that each row corresponds to a distortion parameter of a specified camera, and a regularization term g (K) based on the distortion parameter in the camera internal parameters is introduced to obtain an objective function with the regularization term as e+λg (K), where λ is a weight coefficient.
The construction method based on the regular term g (K) of the distortion parameter comprises the following steps: constructing an undirected graph taking the cameras as nodes, and connecting the nodes of the undirected graph between cameras with the same model; from the undirected graph, an adjacency matrix can be obtainedN is the total number of cameras, specifically, if N 1 Personal camera->And the nth 2 Personal camera->The model is the sameOtherwise, let->
The laplace matrix L is directly calculated from the adjacency matrix W:
L＝D-W
wherein D is a diagonal matrix, D i,i ＝∑ j W i,j Wherein W is i,j Is the element of the ith row and the jth column in W;
constructing a distortion parameter matrixWith each row corresponding to a distortion parameter (k) of a camera 1 ,k 2 ,k 3 ) The distortion parameter matrix K contains distortion parameters of all cameras, and as the distortion of the cameras with the same model is similar, a regular term for the distortion parameters is introduced:
g(K)＝trace(K T LK)
where trace (·) is the trace of the matrix, K T Is the transpose of the distortion parameter matrix K.
In an ideal case, if the camera systems shipped at the same time have no errors in production and manufacture, the cameras of the same model must have the same distortion parameters, i.e., g (K) =0. The regularization term is used to provide effective prior knowledge to overcome the problem of difficult calibration of camera internal parameters.
S13, minimizing an objective function with a regular term to solve the global optimization problem, and obtaining the optimal internal and external parameters of the camera.
In an embodiment, a nonlinear global optimization problem min (E+λg (K)) with a canonical term is constructed, where the weight coefficient λ>0, the parameters to be solved are all camera external parametersAnd internal parameters (including distortion parameter matrix K, focal length and image principal point of each camera) and all calibration plate pose +.>N is the total number of cameras, and M is the total number of the positions and the postures of the calibration plate.
Since the optimization problem is nonlinear least squares, it is solved using the Levenberg-Marquardt algorithm. All parameters are first combined into a one-dimensional array, wherein the transformation matrix, i.e. the pose, is split into a 3 x 3 rotation matrix and a 3 x 1 translation vector, wherein the rotation matrix can be represented by an axis angle, so that a transformation matrix can be represented by 6 parameters. The axis angle representation can be specifically referred to by the formula rodrich:
wherein,for the axis angle representation of the rotation matrix R, +.>Is a unit vector of the number of units,is->Is an antisymmetric matrix of I 3×3 Is a 3 x 3 identity matrix.
The specific solving steps are as follows:
s13.1, fixing all camera internal parameters as the internal parameters obtained in the step S8, only minimizing total weight projection errors, namely solving mines, and only performing iterative optimization on the camera external parameters and the positions of the calibration plates to obtain primarily optimized camera external parametersAnd mark the board position appearance->And when the minE is solved, using the camera external parameters obtained in the step S9 as initial values and using the calibration plate pose obtained in the step S10 as initial values.
S13.2, taking the camera external parameters and the calibration plate pose obtained in the S13.1 as initial values, taking the camera internal parameters obtained in the step S8 as initial values, solving an optimization problem min (E+λg (K)) containing a regularization term, optimizing all parameters including the camera internal parameters and the external parameters, and outputting more accurate camera internal and external parameters.
In an embodiment, a specific implementation method for solving by using the Levenberg-Marquardt algorithm may use the method optimize. Least_squares in the numerical calculation library scipy to solve the least squares problem, and define a residual function r, so thatThe input of the residual function is a one-dimensional array, which comprises camera internal and external parameters and calibration plate pose. For the residual function r, a numerical method may be used to find the jacobian matrix, i.e., the first derivative, for use in the iterative optimization in S13.2. Residual function used in S13.1 +.>Is part of r, i.e.)>Since the internal reference is not iteratively solved in S13.1, the column corresponding to the internal reference in the jacobian matrix is set to 0, and the other settings are the same as in S13.2.
In a comprehensive way, the movable calibration plate is adopted, the manufacturing cost of the movable calibration plate is very low, the movable calibration plate is convenient to move or change the posture of the movable calibration plate, the trouble of manually lifting the plate by two hands is omitted, the surface of the movable calibration plate cannot be bent, the movable calibration plate can be stationary, the labor cost and the risk are reduced, and the time and the labor are saved; and a regular term based on distortion parameters is introduced to carry out global optimization algorithm innovation, so that the global optimization problem is solved to obtain the optimal internal and external parameters of the camera, the robustness and the accuracy of internal and external parameter estimation are improved, and the accurate internal and external parameter calibration can be realized. The camera internal and external parameter calibration method provided by the invention is suitable for a multi-camera system suspended at high altitude or in an open space, and can be extended to solve the camera calibration problem in other similar large-scale scenes.
Based on the same inventive concept, the embodiment also provides an internal and external parameter calibration system 600 of the multi-camera monitoring system of the large-scale exhibition hall, as shown in fig. 6, comprising: the camera external parameter optimization module 650 comprises a data acquisition and preprocessing module 610, a monocular camera calibration module 620, a camera external parameter preliminary estimation module 630, a calibration plate pose preliminary estimation module 640 and a camera external parameter optimization module;
the data acquisition and preprocessing module 610 is configured to acquire multi-camera video data as calibration data, and preprocess the calibration data to obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates respectively;
the monocular camera calibration module 620 is configured to perform monocular camera calibration on each camera using the two-dimensional-three-dimensional point pair set to obtain an initial value of a camera internal parameter, a pose of each camera relative to the calibration board, and a pose of the initial camera relative to the world coordinate system;
the camera extrinsic initial estimation module 630 is configured to perform camera extrinsic initial estimation based on a pose of an initial camera relative to a world coordinate system and a pose of each camera relative to a calibration board by using a chained method, so as to obtain a pose of each camera relative to the world coordinate system as a camera extrinsic initial value;
the calibration board pose preliminary estimation module 640 is configured to perform preliminary estimation on the calibration board pose according to the camera external parameter initial values and the pose of each camera relative to the calibration board, so as to obtain a calibration board pose initial value under each specific pose;
the camera internal and external parameter optimization module 650 is configured to construct a total weight projection error based on the point-to-set as an objective function, introduce a regular term based on distortion parameters to the objective function, and use the camera internal parameter initial value, the camera external parameter initial value and the calibration plate pose initial value as initial values for solving the global optimization problem, minimize the objective function with the regular term to solve the global optimization problem, and obtain the optimal camera internal and external parameters.
Based on the same inventive concept, the embodiment also provides an internal and external parameter calibration device of the multi-camera monitoring system of the large-scale exhibition hall, which comprises a memory and a processor, wherein the memory is used for storing a computer program, and the processor is used for realizing the internal and external parameter calibration method of the multi-camera monitoring system of the large-scale exhibition hall when executing the computer program.
Based on the same inventive concept, the embodiment also provides a computer-readable storage medium, wherein the storage medium is stored with a computer program, and when the computer program is used by a computer, the method for calibrating the internal parameters and the external parameters of the multi-camera monitoring system of the large-scale exhibition hall is realized.
It should be noted that, the internal and external parameter calibration system of the multi-camera monitoring system in a large-scale exhibition hall, the internal and external parameter calibration device of the multi-camera monitoring system in a large-scale exhibition hall and a computer readable storage medium provided in the foregoing embodiments all belong to the same concept as the internal and external parameter calibration method embodiment of the multi-camera monitoring system in a large-scale exhibition hall, and the specific implementation process is detailed in the internal and external parameter calibration method embodiment of the multi-camera monitoring system in a large-scale exhibition hall, which is not described herein again.
The foregoing detailed description of the preferred embodiments and advantages of the invention will be appreciated that the foregoing description is merely illustrative of the presently preferred embodiments of the invention, and that no changes, additions, substitutions and equivalents of those embodiments are intended to be included within the scope of the invention.

Claims (10)

1. The method for calibrating the internal and external parameters of the multi-camera monitoring system of the large exhibition hall is characterized by comprising the following steps of:
acquiring multi-camera video data as calibration data, and preprocessing the calibration data to respectively obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates;
monocular camera calibration is carried out on each camera by using the two-dimensional-three-dimensional point pair set to obtain an initial value of the internal parameters of the camera, the pose of each camera relative to the calibration plate and the pose of the initial camera relative to the world coordinate system;
performing camera external parameter preliminary estimation based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate by using a chained method to obtain the pose of each camera relative to the world coordinate system as a camera external parameter initial value;
performing initial estimation on the positions and postures of the calibration plates according to the camera external parameter initial values and the positions and postures of each camera relative to the calibration plates to obtain initial values of the positions and postures of the calibration plates under each specific posture;
constructing a gross weight projection error based on the point-to-set as an objective function, and introducing a regular term based on distortion parameters to the objective function;
and using the camera internal parameter initial value, the camera external parameter initial value and the positioning plate pose initial value as initial values for solving the global optimization problem, and minimizing an objective function with a regular term to solve the global optimization problem so as to obtain the optimal camera internal and external parameters.
2. The method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to claim 1, wherein the acquiring multi-camera video data as calibration data comprises:
preparing a calibration plate capable of moving on the ground and a plurality of fixed calibration points in advance, and defining a world coordinate system G;
selecting any one of the cameras as an initial camera C 1 At the initial camera C 1 Arranging calibration points on the ground in the visual field, and acquiring video data as first calibration data;
moving the calibration plate, moving a circle in the exhibition hall and changing the gesture of the calibration plate to cover the visual field of each camera at all times to acquire video data as second calibration data;
and (3) moving the calibration plate, moving a circle in the exhibition hall, changing the posture of the calibration plate from time to time, and collecting calibration data in the common field of view of two adjacent cameras, so as to form a communicated and closed-loop camera relation diagram, and obtaining video data as third calibration data.
3. The method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to claim 2, wherein the preprocessing of the calibration data to obtain two-dimensional and three-dimensional point pair sets corresponding to the coordinates of the calibration points and the coordinates of the calibration plates respectively comprises:
recording three-dimensional coordinates of the calibration point in a world coordinate system, marking two-dimensional coordinates corresponding to the three-dimensional coordinates of the calibration point in an image of the first calibration data, and recording all two-dimensional-three-dimensional point data as a point pair set omega G ；
Image sampling is carried out on all videos of the second calibration data and the third calibration data, two-dimensional angular point coordinates of the calibration plate are extracted from images containing the calibration plate, the two-dimensional angular point coordinates and corresponding three-dimensional angular point coordinates in a coordinate system of the calibration plate are stored, and all two-dimensional-three-dimensional point data are recorded as a point pair set omega;
selecting images from at least two cameras and simultaneously containing the calibration plate in the same static state for the third calibration data, extracting two-dimensional angular point coordinates of the calibration plate and corresponding three-dimensional coordinates in a coordinate system of the calibration plate from the images, and recording all two-dimensional-three-dimensional point data as a point pair set omega S Wherein
The set of point pairs omega G Point pair set Ω and Point pair set Ω S Together forming a set of two-dimensional-three-dimensional point pairs of step 2.
4. The method for calibrating the external parameters of the multi-camera monitoring system of the large-scale exhibition hall according to claim 3, wherein the step of using the chain method to perform preliminary estimation of the external parameters of the camera based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate to obtain the pose of each camera relative to the world coordinate system as the initial value of the external parameters of the camera comprises the following steps:
corresponds to the point pair set omega S The pose of the calibration plate present in the camera is initialized by the camera C 1 And adjacent camera C 2 Simultaneous capturing according to the initial camera C 1 Pose relative to world coordinate system and initial camera C 1 And camera C 2 The camera C is obtained by respectively corresponding to the positions and the attitudes of the calibration plates 2 Pose relative to world coordinate system; by adopting the same method, the pose of the known camera relative to the world coordinate system and the pose of the known camera and the pose of the unknown camera relative to the calibration plate are sequentially used for the adjacent cameras by using a chain method, the pose of the unknown camera relative to the world coordinate system is obtained, and finally, the pose of each camera relative to the world coordinate system is obtained to be used as a camera external parameter initial value.
5. A method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to claim 3, wherein the method for constructing total weight projection errors based on point-to-set as an objective function, introducing regular terms based on distortion parameters to the objective function comprises:
any point pair (X, X) E omega G ∪Ω S Wherein x is the nth camera C n Two-dimensional angular point coordinates of the captured image on a calibration plate coordinate system correspond to the calibration plate B of the mth gesture m A three-dimensional angular point coordinate X on a calibration plate coordinate system; the loss function is thus constructed as a reprojection error:wherein pi is n Is camera C n Is>For camera pose, i.e. world coordinate system G to camera C n Transformation matrix of coordinate system, < >>The position of the calibration plate is the calibration plate B m Transformation matrix from coordinate system to world coordinate system G 2 Is the square of the L2 norm; will all belong to omega G ∪Ω S Summing the constructed re-projection errors to obtain a total weight projection error function E; constructing a distortion parameter matrix K, enabling each row of the distortion parameter matrix K to correspond to the distortion parameters of the appointed camera, and introducing a regularization term g (K) based on the distortion parameters in the camera internal parameters to obtain an objective function with the regularization term as E+λg (K), wherein λ is a weight coefficient.
6. The method for calibrating internal and external parameters of a multi-camera monitoring system of a large-scale exhibition hall according to claim 5, wherein the construction method comprises the following steps:
constructing an undirected graph taking the cameras as nodes, and connecting the nodes of the undirected graph between cameras with the same model; from the undirected graph, an adjacency matrix W can be obtained, and then a Laplace matrix L is directly calculated; the last true regularization term g (K) =trace (K T LK), where trace (·) is the trace of the matrix, K T Is the transpose of the distortion parameter matrix K.
7. The method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to claim 5 or 6, wherein the minimizing the objective function with the regularization term to solve the global optimization problem, to obtain the optimal internal and external parameters of the camera, comprises:
and constructing a nonlinear global optimization problem min (E+lambdag (K)) with a regular term, and solving the nonlinear global optimization problem min by using a Levenberg-Marquardt algorithm, wherein a weight coefficient lambda >0, so as to obtain the optimal camera internal and external parameters.
8. An inside and outside parameter calibration system of a large-scale exhibition hall multi-camera monitoring system is characterized by comprising: the camera comprises a data acquisition and preprocessing module, a monocular camera calibration module, a camera external parameter preliminary estimation module, a calibration plate pose preliminary estimation module and a camera external parameter optimization module;
the data acquisition and preprocessing module is used for acquiring multi-camera video data as calibration data, preprocessing the calibration data to respectively obtain two-dimensional-three-dimensional point pair sets corresponding to the calibration point coordinates and the calibration plate coordinates;
the monocular camera calibration module is used for carrying out monocular camera calibration on each camera by using the two-dimensional-three-dimensional point pair set to obtain an initial value of a camera internal parameter, the pose of each camera relative to the calibration plate and the pose of the initial camera relative to a world coordinate system;
the camera external parameter preliminary estimation module is used for carrying out camera external parameter preliminary estimation based on the pose of the initial camera relative to the world coordinate system and the pose of each camera relative to the calibration plate by using a chain method to obtain the pose of each camera relative to the world coordinate system as a camera external parameter initial value;
the calibration board pose preliminary estimation module is used for carrying out preliminary estimation on the calibration board poses according to the camera external parameter initial values and the poses of each camera relative to the calibration board to obtain the calibration board pose initial values under each specific pose;
the camera internal and external parameter optimization module is used for constructing total weight projection errors based on point-to-set as an objective function, introducing a regular term based on distortion parameters to the objective function, and using a camera internal parameter initial value, a camera external parameter initial value and a positioning plate pose initial value as initial values for solving a global optimization problem, and minimizing the objective function with the regular term to solve the global optimization problem so as to obtain the optimal camera internal and external parameters.
9. The device for calibrating the internal and external parameters of the large-scale exhibition hall multi-camera monitoring system comprises a memory and a processor, wherein the memory is used for storing a computer program, and the processor is used for realizing the method for calibrating the internal and external parameters of the large-scale exhibition hall multi-camera monitoring system according to any one of claims 1-7 when the computer program is executed.
10. A computer-readable storage medium, on which a computer program is stored, characterized in that the method for calibrating internal and external parameters of a multi-camera monitoring system in a large-scale exhibition hall according to any one of claims 1-7 is implemented when the computer program is used in a computer.
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