CN111815715A - Method and device for calibrating zoom pan-tilt camera and storage medium - Google Patents
Method and device for calibrating zoom pan-tilt camera and storage medium Download PDFInfo
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Abstract
The invention provides a method and a device for calibrating a zoom holder camera and a storage medium. The calibration method comprises the following steps: acquiring a first image at a first position and a second image at a second position under the same magnification, wherein the first image and the second image have coincident fields of view; extracting a plurality of first characteristic points of the first image and a plurality of second characteristic points of the second image, and matching the plurality of first characteristic points and the plurality of second characteristic points to obtain a plurality of groups of characteristic point pairs; and constructing multiple sets of quadratic equations with the focal length initial values as dependent variables according to the multiple sets of feature point pairs and the camera imaging model, and obtaining calibration parameters under the same multiplying power by solving the quadratic equations. The calibration method provided by the invention simplifies the solving process and improves the calibration efficiency and flexibility.
Description
Technical Field
The invention relates to the technical field of computer vision, in particular to a calibration method, calibration equipment and a storage device of a zoom pan-tilt camera.
Background
The Pan-Tilt-Zoom (PTZ) camera can automatically adjust and control focal length, attitude, aperture and the like, has the characteristics of flexibility, large field range, strong adaptability to illumination conditions and the like, and is widely applied to various fields such as video monitoring, electronic security, robot navigation, intelligent space and the like. In the prior art, calibration of the zoom holder camera often depends on reference objects such as a calibration plate and the like, and the calibration efficiency is low.
Therefore, in order to solve the above problems, it is necessary to provide a new calibration method, calibration apparatus, and storage medium for a zoom pan/tilt camera.
Disclosure of Invention
In order to achieve the above object, the present invention provides a calibration method for a zoom pan/tilt camera, the calibration method comprising: acquiring a first image at a first position and a second image at a second position under the same magnification, wherein the first image and the second image have coincident fields of view; extracting a plurality of first feature points of the first image and a plurality of second feature points of the second image, and matching the plurality of first feature points and the plurality of second feature points to obtain a plurality of groups of feature point pairs; and constructing a plurality of sets of quadratic equations with the focal length initial values as dependent variables according to the plurality of sets of feature point pairs and the camera imaging model, and obtaining the calibration parameters under the same multiplying power by solving the quadratic equations.
As a further improvement of the present invention, the constructing a quadratic equation with a focus initial value as a dependent variable according to the plurality of groups of feature point pairs and the camera imaging model to obtain calibration parameters based on the quadratic equation includes: screening a plurality of characteristic point pairs from the characteristic point pairs; constructing a plurality of quadratic equations corresponding to each characteristic point pair according to each characteristic point pair in a plurality of characteristic point pairs and the camera imaging model so as to obtain a plurality of initial focal length values corresponding to each characteristic point pair based on the plurality of quadratic equations; screening an optimal focal length value from the multiple initial focal length values according to the mapping error of the first characteristic point and the second characteristic point; and optimizing the optimal focal length value and the principal point parameter of the camera imaging model to obtain the calibrated focal length and the calibrated principal point parameter.
As a further improvement of the present invention, the screening out a plurality of characteristic point pairs from the plurality of groups of characteristic point pairs includes: and screening a plurality of characteristic point pairs from the plurality of groups of characteristic point pairs according to the regions of the plurality of groups of characteristic point pairs in the first image and the second image and the matching degree of the plurality of groups of characteristic point pairs.
As a further improvement of the present invention, the constructing, according to each feature point pair of a plurality of feature point pairs and the camera imaging model, a plurality of the quadratic equations corresponding to the each feature point pair to obtain a plurality of initial focal length values corresponding to the each feature point pair based on the plurality of the quadratic equations includes: calculating and obtaining a rotation parameter from the first position to the second position according to the first position and the second position; establishing a world coordinate system which is coincident with a first camera coordinate system of the first position, and establishing a relational expression about each characteristic point pair and the initial focal length value based on the camera imaging model and the rotation parameters; and converting the relational expression into the one-dimensional quadratic equation with the focal length initial value as a dependent variable.
As a further improvement of the present invention, the constructing a relation for the each feature point pair and the initial focal length value based on the camera imaging model and the rotation parameter comprises: converting the image point coordinates of the first feature point into first coordinates under the first camera coordinate system based on the camera imaging model, and normalizing the first coordinates to obtain a first parameter related to the initial value of the focal length; converting the first parameter into a second coordinate under a second camera coordinate system at the second position according to the rotation parameter, and normalizing the second coordinate to obtain a second parameter related to the initial value of the focal length; and deriving the relation based on the first parameter and the second parameter.
As a further improvement of the present invention, the screening of a preferred focal length value from a plurality of initial focal length values according to a mapping error between the first characteristic point and the second characteristic point includes: calculating corresponding first feature points matched with the second feature points according to the camera imaging model and the second feature points; and screening out a preferred focal length value from the plurality of initial focal length values based on the corresponding first characteristic points and the difference value of the first characteristic points.
As a further improvement of the present invention, the optimizing the preferred focal length value and the principal point parameter of the camera imaging model to obtain the calibrated focal length and the calibrated principal point parameter includes: and carrying out nonlinear optimization on the optimal focal length value and the principal point parameter based on an LM nonlinear optimization algorithm to obtain the calibrated focal length and the calibrated principal point parameter.
As a further improvement of the present invention, the extracting a plurality of first feature points of the first image and a plurality of second feature points of the second image, and matching the plurality of first feature points and the plurality of second feature points to obtain a plurality of sets of feature point pairs includes: and extracting and matching the plurality of first characteristic points and the plurality of second characteristic points based on SURF or ORB characteristic extraction and matching algorithm to obtain a plurality of groups of characteristic point pairs.
The present invention also provides a zoom pan/tilt camera device, comprising: a processor, a memory, and a communication circuit, the processor coupled to the memory and the communication circuit, respectively; the processor, the memory and the communication circuit can realize the calibration method when in operation.
The invention also provides a storage device, which stores program instructions capable of being executed by a processor, wherein the program instructions are used for realizing the calibration method.
Compared with the prior art, the invention has the beneficial effects that:
according to the calibration method of the zoom holder video camera, provided by the invention, a quadratic equation which corresponds to the characteristic points and takes the initial focal length value as a dependent variable can be constructed by utilizing a plurality of groups of characteristic points and a camera imaging model, the initial focal length value can be directly calculated by solving the quadratic equation, a homography matrix does not need to be calculated, the solving process is simplified, and the calibration efficiency and flexibility are improved; in addition, the calibration method of the zoom pan-tilt camera provided by the invention realizes the on-line automatic calibration of the calibration parameters of the zoom pan-tilt camera, and the calibration process does not depend on reference objects such as a calibration plate, thereby further simplifying the calibration process and improving the calibration efficiency; meanwhile, the zooming pan-tilt camera is suitable for parameter calibration under the condition of continuous change of focal length.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts. Wherein:
FIG. 1 is a schematic overall flow chart of a calibration method of a zoom pan/tilt camera according to the present invention;
FIG. 2 is a schematic flow chart illustrating an embodiment of the step S13 in FIG. 1 according to the present invention;
FIG. 3 is a schematic flow chart illustrating a calibration method of a zoom holder camera according to an embodiment of the present invention;
FIG. 4 is a schematic structural diagram of an embodiment of a zoom pan/tilt/zoom camera apparatus according to the present invention;
FIG. 5 is a schematic structural diagram of a memory device according to an embodiment of the invention.
Detailed Description
The following describes in detail the embodiments of the present application with reference to the drawings attached hereto.
In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular system structures, interfaces, techniques, etc. in order to provide a thorough understanding of the present application.
The terms "system" and "network" are often used interchangeably herein. The term "and/or" herein is merely an association describing an associated object, meaning that three relationships may exist, e.g., a and/or B, may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship. Further, the term "plurality" herein means two or more than two.
The zooming pan-tilt camera comprises a ball machine, a gun with a pan-tilt and the like, and the equipment can adjust a monitoring area through the rotation of the pan-tilt, and has the characteristic of flexible use. Specifically, the pan-tilt can move up and down and left and right, a camera is carried on the pan-tilt, multi-angle monitoring of the camera can be achieved, and the pan-tilt can be divided into a horizontal pan-tilt and an omnidirectional pan-tilt according to different rotating angles.
In an actual application scene, in order to obtain local detail information of the scene, the zoom holder camera also needs to adjust the magnification of the camera, that is, the focal length of the camera, and the corresponding image principal point can change along with the zoom, and the focal length and the principal point parameters are often indispensable in gun-ball linkage, ball machine positioning and three-dimensional reconstruction, so that the calibration of the camera parameters is a very critical link, and the accuracy of the calibration result and the stability of the algorithm directly influence the accuracy of the result generated by the camera work.
Based on the above, the invention provides a calibration method of a zoom pan-tilt camera, which can realize the online high-efficiency and high-precision calibration of parameters, wherein the calibration method adopts the zoom pan-tilt camera to obtain a first image at a first position and a second image at a second position under the same magnification, and the first image and the second image have coincident view fields; extracting a plurality of first characteristic points of the first image and a plurality of second characteristic points of the second image, and matching the plurality of first characteristic points and the plurality of second characteristic points to obtain a plurality of groups of characteristic point pairs; and constructing a plurality of sets of quadratic equations with the focal length initial values as dependent variables according to the plurality of sets of feature point pairs and the camera imaging model, and obtaining the calibration parameters under the same multiplying power based on the quadratic equations.
Therefore, in the invention, the focal length initial value can be directly calculated by solving the one-dimensional quadratic equation without calculating a homography matrix, thereby simplifying the solving process and improving the efficiency and the flexibility of calibration; compared with the traditional offline calibration method which needs to use a three-dimensional or planar calibration object in the prior art, namely a method for calibrating the internal and external parameters of the camera by acquiring the image data of the calibration object offline and combining the image data with an imaging model, such as a two-step calibration method of Tsai, a planar calibration method of Zhang Zhengyou and the like, the calibration method provided by the invention realizes the online automatic calibration of the calibration parameters of the zoom holder camera, the calibration process does not depend on reference objects such as a calibration plate and the like, the calibration flow is further simplified, and the calibration efficiency is improved; meanwhile, the zooming pan-tilt camera is suitable for parameter calibration under the condition of continuous change of focal length.
With reference to fig. 1, the following further describes a calibration method of a zoom holder camera provided by the present invention, where the calibration method specifically includes:
s11: a first image at a first position and a second image at a second position at the same magnification are acquired, and the first image and the second image have coincident fields of view.
Specifically, in one embodiment, the zoom camera first captures a first image at a first position, and then captures a second image at a second position by rotating the pan-tilt without changing the magnification, wherein the first image and the second image have a coincident field of view. In another embodiment, the zoom camera may capture the second image at the second position, and then capture the first image at the first position by rotating the pan-tilt without changing the magnification, wherein the first image and the second image have a coincident field of view. In other words, the order of capturing the first image and the second image is not limited in the present invention, and it is only necessary to ensure that the first image and the second image have a coincident view field, regardless of whether capturing the first image first and then capturing the second image, or capturing the second image first and then capturing the first image.
S12: and extracting a plurality of first characteristic points of the first image and a plurality of second characteristic points of the second image, and matching the plurality of first characteristic points and the plurality of second characteristic points to obtain a plurality of groups of characteristic point pairs.
Specifically, since the plurality of first feature points and the plurality of second feature points have a one-to-one matching relationship, the first feature points and the second feature points that are matched with each other are a set of feature point pairs, and thus, the plurality of first feature points and the plurality of second feature points are matched to obtain a plurality of sets of feature point pairs. In an embodiment, the present invention extracts and matches the plurality of first feature points and the plurality of second feature points based on SURF (speedup Robust Features) or orb (organized FAST and organized brief) feature extraction and matching algorithm, so as to obtain a plurality of sets of feature point pairs. Of course, in other embodiments of the present invention, other feature extraction and matching algorithms, such as SIFT, may be used, as long as the first feature point and the second feature point are obtainedThe matching is carried out to obtain the effect of the characteristic point pairs, thus realizing the purpose of the invention. For the convenience of the following description, the first feature points are denoted as
Where i is 1 … n, and a plurality of second characteristic points are recorded as
Where i is 1 … n.
S13: and constructing multiple sets of quadratic equations with the focal length initial values as dependent variables according to the multiple sets of feature point pairs and the camera imaging model, and obtaining calibration parameters under the same multiplying power by solving the quadratic equations.
According to a group of characteristic point pairs and a camera imaging model, a quadratic equation with the focal length initial value as a dependent variable can be constructed, the initial value of the focal length can be obtained by solving the quadratic equation, a homography matrix does not need to be calculated, the calculation process is simpler, and the calibration efficiency is improved. Therefore, according to the multiple groups of characteristic point pairs and the camera imaging model, a plurality of unary quadratic equations with the focal length initial values as dependent variables can be constructed, and the multiple focal length initial values can be obtained by solving the multiple unary quadratic equations.
With reference to fig. 2, in an embodiment, the step S13 specifically includes:
s131: and screening a plurality of characteristic point pairs from the plurality of groups of characteristic point pairs.
Considering that in the step S12, the extraction and matching of the first feature point and the second feature point are susceptible to mismatching and lens distortion, and the focal length error calculated by only one feature point pair is large, the present invention screens out a plurality of feature point pairs from the plurality of feature point pairs according to the regions of the plurality of feature point pairs in the first image and the second image and the matching degree of the plurality of feature point pairs, thereby reducing the influence of mismatching and lens distortion.
In an embodiment, a plurality of feature point pairs may be screened out by setting a preset coordinate range threshold and a preset matching degree threshold. The method comprises the steps that a preset coordinate range threshold value is set, so that a plurality of characteristic points are guaranteed to be taken from the middle part of an image, and further the influence of lens distortion is reduced; through setting a preset matching degree threshold value, a plurality of characteristic point pairs are guaranteed to have higher matching degree, and then the influence of mismatching is reduced. Of course, in other embodiments of the present invention, other methods besides setting the threshold may be used for screening, and the purpose of the present invention can be achieved as long as the effect of reducing the influence of the specific point on the mismatch and the lens distortion is achieved.
S132: and constructing a plurality of unary quadratic equations corresponding to each characteristic point pair according to each characteristic point pair of the characteristic point pairs and the camera imaging model so as to obtain a plurality of initial focal length values corresponding to each characteristic point pair based on the unary quadratic equations.
Specifically, according to a first position and a second position, rotation parameters from the first position to the second position are calculated and obtained; establishing a world coordinate system which is coincident with a first camera coordinate system of a first position, and establishing a relational expression about each characteristic point pair and the initial focal length value based on the camera imaging model and the rotation parameters; and converting the relation into a one-dimensional quadratic equation with the initial focal length value as a dependent variable.
The method specifically comprises the following steps of constructing a relation of each feature point pair and an initial focal length value based on a camera imaging model and a rotation parameter: firstly, converting the image point coordinates of a first characteristic point into first coordinates under a first camera coordinate system based on a camera imaging model, and normalizing the first coordinates to obtain a first parameter related to an initial value of a focal length; then, according to the rotation parameter, converting the first parameter into a second coordinate in a second camera coordinate system at a second position, and normalizing the second coordinate to obtain a second parameter related to the initial value of the focal length; and deriving and obtaining the relation based on the first parameter and the second parameter.
In one embodiment, in the first position, PT values (P represents horizontal azimuth, T represents vertical azimuth, and P and T are collectively referred to as azimuth of the camera and are represented by PT values) of the zoom pan-tilt camera are denoted as P0 and T0; in the second position, PT values of the zoom pan-tilt camera are denoted as P1, T1. In the process that the zooming pan-tilt camera is located from the first position to the second position, the variation of the pitch angle is recorded as delta P, and the corresponding rotation matrix is recorded as R _ pitch; the variation of the Yaw angle is recorded as delta T, and the corresponding rotation matrix is recorded as R _ Yaw; the rotation vector from the first position to the second position is denoted as R, i.e. the rotation parameter is R, so the following relationship exists between the above parameters:
ΔP＝P0-P1，ΔT＝T0-T1
R＝R_Pitch*R_Yaw
further, with the first position as a reference, the world coordinate system is established at a position coinciding with the first camera coordinate system of the first position. And constructing a quadratic equation according to the same object points corresponding to the camera imaging model, namely the matching points, so as to obtain the initial focal length value by solving the quadratic equation.
By a pair of characteristic points
For example, take the principal point of the camera as the image center point (u)0v0) And the focal length is denoted as f. Firstly, converting the image point coordinates of the first characteristic point into a first camera coordinate system, and normalizing to obtain a first parameter related to the initial value of the focal length:
then, the first parameter is converted into a second coordinate in a second camera coordinate system of the second position by the rotation parameter R:
normalizing the second coordinate to obtain a second parameter related to the initial value of the focal length:
deriving the following relation based on the first parameter and the second parameter:
because the focal length can not be a negative value, the initial value of the focal length can be obtained by simply screening the approximate range information of the focal length. In an embodiment, the initial focal length values calculated according to the above contents are three sets of data with larger difference, wherein the first set of data is a negative value, the second set of data is very small, and the third set of data is located within the range of 2000-.
Thus, according to a characteristic point pair, an initial focus value can be obtained by the derivation. Based on the multiple groups of characteristic point pairs provided by the invention, a plurality of initial focal length values can be obtained through derivation.
S133: and screening out a preferred focal length value from the plurality of initial focal length values according to the mapping error of the first characteristic point and the second characteristic point.
Specifically, the S133 step includes: calculating a corresponding first feature point matched with the second feature point according to the camera imaging model and the second feature point; and screening an optimal focal length value from the plurality of initial focal length values based on the difference value of the corresponding first characteristic point and the first characteristic point obtained by the characteristic extraction and matching algorithm. The difference value corresponding to the first feature point and the first feature point is the mapping error. Therefore, the optimal focal length value with smaller mapping error is screened out according to the size of the mapping error, so that the influence of the mapping error on the calibration parameters is reduced.
S134: and optimizing the optimal focal length value and the principal point parameter of the camera imaging model to obtain a calibration focal length and a calibration principal point parameter.
In order to further improve the calibration precision, an LM nonlinear optimization algorithm is adopted to carry out nonlinear optimization on the optimized focal length value and the principal point parameter so as to obtain the calibration focal length and the calibration principal point parameter under the same multiplying power. And repeating the steps for calibration parameters under other multiplying powers. Therefore, compared with the existing calibration method suitable for the condition of fixed focal length, the zoom holder camera disclosed by the invention realizes the effect of parameter calibration suitable for the condition of continuous change of focal length.
With reference to fig. 3, a specific embodiment of the calibration method for a zoom pan/tilt camera provided by the present invention has the following main workflow: when the calibration is started, the zooming pan-tilt camera captures a first image at a first position; then, rotating the tripod head, and capturing a second image at a second position by the zooming tripod head camera; then, extracting and matching feature points of the first image and the second image, and screening out a plurality of feature point pairs by setting a preset coordinate range threshold and a preset matching degree threshold; calculating to obtain a plurality of initial focal length values, and screening out an optimal focal length value according to the mapping error; and finally, carrying out nonlinear optimization on the optimal focal length value and the principal point parameter to obtain a calibration parameter, and finishing calibration.
In summary, according to the calibration method of the zoom holder camera provided by the invention, a quadratic equation with a focus initial value as a dependent variable and corresponding to feature points can be constructed by using a plurality of groups of feature points and a camera imaging model, the initial focus value can be directly calculated by solving the quadratic equation without calculating a homography matrix, the solving process is simplified, and the calibration efficiency and flexibility are improved; in addition, the calibration method of the zoom pan-tilt camera provided by the invention realizes the on-line automatic calibration of the calibration parameters of the zoom pan-tilt camera, and the calibration process does not depend on reference objects such as a calibration plate, thereby further simplifying the calibration process and improving the calibration efficiency; meanwhile, the zooming pan-tilt camera is suitable for parameter calibration under the condition of continuous change of focal length.
The invention also provides calibration equipment which comprises an acquisition module, an extraction module and a construction module. Specifically, the acquisition module is used for acquiring a first image at a first position and a second image at a second position under the same magnification, and the first image and the second image have a coincident field of view; the extraction module is used for extracting a plurality of first characteristic points of the first image and a plurality of second characteristic points of the second image, and matching the plurality of first characteristic points and the plurality of second characteristic points to obtain a plurality of groups of characteristic point pairs; the construction module is used for constructing a plurality of sets of unary quadratic equations with the focal length initial values as dependent variables according to the plurality of sets of feature point pairs and the camera imaging model so as to obtain the calibration parameters under the same multiplying power by solving the unary quadratic equations.
Referring to fig. 4, the present invention further provides a zoom holder camera device, which includes a processor 41, a memory 42 and a communication circuit 43, wherein the processor 41 is coupled to the memory 42 and the communication circuit 43, respectively, and the calibration method in any of the above embodiments can be implemented when the processor 41, the memory 42 and the communication circuit 43 operate.
Specifically, the processor 41 is configured to control itself and the memory 42 to implement the steps in any of the calibration method embodiments described above. Processor 41 may also be referred to as a CPU (Central Processing Unit). The processor 41 may be an integrated circuit chip having signal processing capabilities. The Processor 41 may also be a general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. In addition, processor 41 may be implemented collectively by a plurality of integrated circuit chips.
Referring to fig. 5, the present invention further provides a storage device, where the storage device 60 stores a program instruction 600 capable of being executed by a processor, and the program instruction 600 is used to implement the calibration method in any of the above embodiments. That is, when the calibration method is implemented in software and sold or used as a standalone product, the calibration method may be stored in a storage device 60 readable by an electronic device, and the storage device 60 may be a usb disk, an optical disk, a server, or the like.
In the several embodiments provided in the present application, it should be understood that the disclosed method and apparatus may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, a division of a module or a unit is merely a logical division, and an actual implementation may have another division, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of devices or units through some interfaces, and may be in an electrical, mechanical or other form.
Units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, a network device, or the like) or a processor (processor) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above description is only for the purpose of illustrating embodiments of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings of the present application or are directly or indirectly applied to other related technical fields, are also included in the scope of the present application.
Claims (10)
1. A calibration method of a zoom pan-tilt camera is characterized by comprising the following steps:
acquiring a first image at a first position and a second image at a second position under the same magnification, wherein the first image and the second image have coincident fields of view;
extracting a plurality of first feature points of the first image and a plurality of second feature points of the second image, and matching the plurality of first feature points and the plurality of second feature points to obtain a plurality of groups of feature point pairs;
and constructing a plurality of sets of quadratic equations with the focal length initial values as dependent variables according to the plurality of sets of feature point pairs and the camera imaging model, and obtaining the calibration parameters under the same multiplying power by solving the quadratic equations.
2. The calibration method according to claim 1, wherein constructing a quadratic equation with the initial focal length value as a dependent variable according to the plurality of groups of pairs of feature points and the camera imaging model to obtain calibration parameters based on the quadratic equation comprises:
screening a plurality of characteristic point pairs from the characteristic point pairs;
constructing a plurality of quadratic equations corresponding to each characteristic point pair according to each characteristic point pair in a plurality of characteristic point pairs and the camera imaging model so as to obtain a plurality of initial focal length values corresponding to each characteristic point pair based on the plurality of quadratic equations;
screening an optimal focal length value from the multiple initial focal length values according to the mapping error of the first characteristic point and the second characteristic point;
and optimizing the optimal focal length value and the principal point parameter of the camera imaging model to obtain the calibrated focal length and the calibrated principal point parameter.
3. The calibration method according to claim 2, wherein the step of screening a plurality of characteristic point pairs from the plurality of groups of characteristic point pairs comprises:
and screening a plurality of characteristic point pairs from the plurality of groups of characteristic point pairs according to the regions of the plurality of groups of characteristic point pairs in the first image and the second image and the matching degree of the plurality of groups of characteristic point pairs.
4. The calibration method according to claim 2, wherein the constructing, according to each of the plurality of pairs of feature points and the camera imaging model, a plurality of the unary quadratic equations corresponding to the each pair of feature points to obtain a plurality of initial focal length values corresponding to the each pair of feature points based on the plurality of the unary quadratic equations comprises:
calculating and obtaining a rotation parameter from the first position to the second position according to the first position and the second position;
establishing a world coordinate system which is coincident with a first camera coordinate system of the first position, and establishing a relational expression about each characteristic point pair and the initial focal length value based on the camera imaging model and the rotation parameters;
and converting the relational expression into the one-dimensional quadratic equation with the focal length initial value as a dependent variable.
5. The calibration method according to claim 4, wherein the constructing a relation for each feature point pair and the initial focal length value based on the camera imaging model and the rotation parameter comprises:
converting the image point coordinates of the first feature point into first coordinates under the first camera coordinate system based on the camera imaging model, and normalizing the first coordinates to obtain a first parameter related to the initial value of the focal length;
converting the first parameter into a second coordinate under a second camera coordinate system at the second position according to the rotation parameter, and normalizing the second coordinate to obtain a second parameter related to the initial value of the focal length;
and deriving the relation based on the first parameter and the second parameter.
6. The calibration method according to claim 2, wherein the step of screening out a preferred focal length value from the plurality of initial focal length values according to the mapping error between the first feature point and the second feature point comprises:
calculating corresponding first feature points matched with the second feature points according to the camera imaging model and the second feature points;
and screening out a preferred focal length value from the plurality of initial focal length values based on the corresponding first characteristic points and the difference value of the first characteristic points.
7. The calibration method according to claim 2, wherein the optimizing the preferred focal length value and the principal point parameter of the camera imaging model to obtain the calibrated focal length and the calibrated principal point parameter comprises:
and carrying out nonlinear optimization on the optimal focal length value and the principal point parameter based on an LM nonlinear optimization algorithm to obtain the calibrated focal length and the calibrated principal point parameter.
8. The calibration method according to claim 1, wherein the extracting a plurality of first feature points of the first image and a plurality of second feature points of the second image, and matching the plurality of first feature points and the plurality of second feature points to obtain a plurality of groups of feature point pairs comprises:
and extracting and matching the plurality of first characteristic points and the plurality of second characteristic points based on SURF or ORB characteristic extraction and matching algorithm to obtain a plurality of groups of characteristic point pairs.
9. A zoom pan/tilt camera apparatus, comprising: a processor, a memory, and a communication circuit, the processor coupled to the memory and the communication circuit, respectively;
the processor, the memory and the communication circuit are operable to implement the calibration method of any of claims 1-8.
10. A memory device, characterized by program instructions stored therein which are executable by a processor for implementing a calibration method as claimed in any one of claims 1 to 8.
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