Automatic calibration apparatus for focus tracking curve, and method applicable to quick determination of optimal focal plane position of imaging camera in large-span scene

Abstract

The present application relates to the technical field of automatic focusing. Provided are an automatic calibration apparatus for a focus tracking curve, and a method applicable to quick determination of an optimal focal plane position of an imaging camera in a large-span scene. The automatic calibration apparatus comprises a calibration target, a fixing apparatus, a sliding rail, a supporting apparatus, a depth detection module, and an image capture and processing module, wherein the fixing apparatus is used for supporting the calibration target and enabling same to be rotatably arranged, the sliding rail is perpendicular to the calibration target and fixed to the fixing apparatus, the sliding rail extends in a horizontal direction, the supporting apparatus is slidably arranged on the sliding rail, the depth detection module is used for acquiring depth distribution data and transmitting the data to the image capture and processing module, and the image capture and processing module comprises a camera and a microcontroller for image processing and drive control. The automatic calibration apparatus provided in the present application can calibrate different fixed-focus cameras, so as to quickly and accurately obtain a focus tracking curve.

Description

An automatic calibration device for focus tracking curve and a method for quickly determining the optimal focal plane position of an imaging camera in a large-span scene

[0001] This application claims priority to a Chinese patent application filed with the Patent Office of China on January 2, 2024, with application number 202410001103.3 and invention name “Method for Rapidly Determining the Optimal Focal Plane Position for Imaging in Large-Span Scenes”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of automatic focusing technology, and in particular to an automatic calibration device for a focus tracking curve and a method for quickly determining the optimal focal plane position of an imaging camera in a large-span scene. Background Art

[0003] Autofocus technology uses sensors and algorithms to automatically adjust the lens focal length. It allows the camera to automatically focus on the subject during shooting, resulting in clear, sharp images. Therefore, determining the optimal focal plane position to achieve clear images is crucial for autofocus. Existing methods for determining the optimal focal plane position are primarily divided into active and passive focusing. Active focusing uses lasers, infrared sensors, or other methods to measure the distance between the objective lens and the target. The feedback drives a motor to focus based on the distance. Active focusing is unaffected by lighting conditions, is simple to operate, has a wide range of applications, and offers high clarity. Passive focusing uses an image sensor to image the object in the scene. A focus evaluation function and a focus strategy are used to determine the current focus state, thereby adjusting the lens focal length to achieve automatic focus on the object. This approach offers low cost, a stable focusing process, and high imaging efficiency. Global search algorithms and hill climbing algorithms are commonly used to achieve this. The global search method determines the optimal focus position based on the image clarity of the camera at each focus position. While highly accurate, this method suffers from low search efficiency. The hill climbing algorithm uses a fixed step size to search for the optimal focus position corresponding to maximum image clarity, offering the advantage of real-time performance. However, when the focal distance is far, the hill climbing algorithm is prone to fall into the false peak phenomenon, resulting in focusing errors.

[0004] However, when imaging surfaces within scenes with large depths, traditional active or passive focusing methods often suffer from insufficient depth of field or mismatched depth of field, resulting in poor image quality and slow performance. Wang et al. proposed a method for imaging within large depth intervals. This method achieves focused imaging based on the intermediate depth within the intervals within the scenes, and fuses multiple focused images to obtain images with a greater depth of field. Consequently, a solution is needed to quickly obtain the optimal focal plane position and sharp images within such scenes. Summary of the Invention

[0005] The purpose of this application is to solve the problem in the prior art of lacking a method for quickly obtaining the optimal focal plane position in a large-span scene and obtaining a clear image.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] A device for automatically calibrating a focus tracking curve comprises a calibration plate, a fixing device, a slide rail, a supporting device, a depth detection module, and an image acquisition and processing module, wherein the fixing device is used to support the calibration plate and rotate it, the slide rail is perpendicular to the calibration plate and fixed to the fixing device, the slide rail extends in a horizontal direction, the supporting device is slidably set on the slide rail, the supporting device is used to fix the depth detection module and the image acquisition and processing module, the depth detection module is used to obtain depth distribution data and transmit the data to the image acquisition and processing module, and the image acquisition and processing module includes a camera and a microcontroller for image processing and drive control.

[0008] In an exemplary embodiment, the calibration plate includes a large calibration plate and a small calibration plate; wherein the small calibration plate is fixed on the large calibration plate, and the small calibration plate is perpendicular to the direction of the camera visual axis, and the sample set is laid on the small calibration plate.

[0009] In an exemplary embodiment, the fixing device includes a base and a bracket located on the base, the bracket is fixed at both ends of the large calibration plate in the length direction, and a rotating device is provided on the side of the two brackets facing away from the large calibration plate, and the rotating device is used to control the rotation of the large calibration plate.

[0010] In an exemplary embodiment, one end of the slide rail is fixed to the base, and the other end extends outward in a horizontal direction. A slider and a stepper motor are provided on the slide rail. The stepper motor is used to drive the slider to slide on the slide rail. The supporting device is fixed on the slider. A rope encoder is also provided on the slide rail. The main body of the rope encoder is located at the connection between the slide rail and the base, and one end of the rope of the rope encoder is fixed on the slider.

[0011] In an exemplary embodiment, the supporting device includes a supporting frame, a control box and a camera fixing device, wherein a microcontroller is placed in the control box, the supporting frame is extended upward in a vertical direction, the control box and the camera fixing device are both fixed on the supporting frame, the camera fixing device includes a camera housing and a cross rod frame, the cross rod frame is used to connect the camera housing and the supporting frame, the camera is set in the camera housing, and a depth sensor is also set on the camera housing.

[0012] In an exemplary embodiment, the slider remains parallel to the camera's visual axis when moving horizontally; the camera's visual axis and a large vertically placed calibration plate maintain a mutually perpendicular relationship, and the intersection of the straight line where the camera's visual axis is located and the plane where the calibration plate is located is located at the geometric center of the calibration plate; the rope of the rope encoder remains horizontal to the camera's visual axis.

[0013] The present application also provides a method for quickly determining the optimal focal plane position of an imaging camera in a large-span scene, which includes the following contents: S1: using an automatic calibration device for implementing the focus tracking curve to obtain a focus tracking curve of the distance-optimal focal plane position mapping relationship; S2: providing an extreme value search algorithm based on an improved hill climbing algorithm to obtain the optimal focal plane position.

[0014] In an exemplary embodiment, the extreme value search algorithm uses an improved hill climbing search method to determine six image recording points, and applies a curve fitting method to these recording points, and uses the peak point obtained by fitting the curve as the optimal focal plane position.

[0015] In an exemplary embodiment, the specific steps of the extreme value search algorithm are as follows:

[0016] Step S1: Given the initial focus position P0, control the camera to drive the focus value to search along the direction of increasing image clarity with a constant step size ΔVF, using the Laplace focus evaluation function value La Pi To characterize the image clarity at the corresponding position.

[0017] Step S2: Continuous imaging, and judging the interval where the true peak is located by the focus evaluation function value La: If La P3 <La P2 <La P1 (Judgment condition (1)), that is, the focus evaluation function value continuously decreases, then the corresponding focal plane position is recorded as P1 (the corresponding focus evaluation function value La Pi ), the focal plane positions corresponding to the two consecutive decreases in image clarity are P2 and P3.

[0018] Step S3: If La P2 <La P1 And La P3 >La P2 , that is, a local peak appears, then La P2 The focal plane position demarcation point is set, and the step size ΔVF is changed. Steps (1 to 2) are repeated for the left and right partitions to search for the focal plane position until the judgment condition (1) is met.

[0019] Step S4: Search in the opposite direction at the focal plane position (P3-P2) / 2 with a constant step length ΔVF, repeating steps 1 to 2. P6 <LaP5 <La P4 When , the corresponding focal plane position is recorded as P4. At this time, the focal plane positions where the clarity drops twice in succession are P5 and P6 respectively.

[0020] Step S5: During the hill climbing search process, record the six focus evaluation function values ​​(La Pi , i = 1, 2, 3 ... 6) and the corresponding focal plane positions (P1 to P6), and curve fitting is performed using the discrete focus evaluation function value and the focal plane position parameters to obtain the optimal focal plane position.

[0021] In an exemplary embodiment, the experimental steps for constructing a focus tracking curve by the automatic calibration device are as follows:

[0022] Step S1: setting a depth range, and then dividing the depth range into a set of depth intervals according to a large depth of field interval division imaging method.

[0023] Step S2: Place a small calibration plate within the divided depth of field interval.

[0024] Step S3: The microprocessor drives the stepper motor to adjust the camera to a specified distance according to the depth of field range. The microprocessor controls the camera to focus and image, evaluates the image clarity of the image captured by the camera, and obtains the optimal focal plane position corresponding to the distance.

[0025] Step S4: Repeat steps S2 and S3 for the remaining depth of field interval sets.

[0026] Step S5: Change the depth range. The depth range must overlap with the previous depth range by at least 50%, and the depth range must be the same length as the previous depth range. Repeat steps S2 to S4.

[0027] Step S6: obtaining multiple sets of distances and corresponding optimal focal plane positions, and the microprocessor performs curve fitting using the distances and optimal focal plane positions as coordinate points to obtain a focus tracking curve of the distance-optimal focal plane position mapping relationship.

[0028] Compared with the prior art, this application has the following beneficial effects:

[0029] 1) The extreme value search algorithm proposed in this application can avoid the problem of falling into local peaks in the hill climbing algorithm. At the same time, it has fast focusing speed and high focusing accuracy, and can provide a reliable method support for camera calibration to obtain the focus tracking curve of the distance-optimal focal plane position mapping relationship.

[0030] 2) This application is applicable to a variety of fixed-focus cameras with integrated ranging functions. Cameras can be selected according to needs. It has great universality and a wide range of applications.

[0031] 3) The automatic calibration device proposed in this application can calibrate different fixed-focus cameras and quickly and accurately obtain focus tracking curves. After the depth sensor acquires depth data, the focus tracking curve can be used to quickly determine the optimal focal plane position within a large scene. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] FIG1 is a schematic diagram of the overall structure of an automatic calibration device for a focus tracking curve in one embodiment of the present application;

[0034] FIG2 is a schematic structural diagram of a camera housing on an automatic calibration device for a focus tracking curve in one embodiment of the present application;

[0035] FIG3 is a flow chart of an extreme value search algorithm in one embodiment of the present application.

[0036] Figure numerals: 1. Large calibration plate; 2. Servo; 3. Small calibration plate; 4. Bracket; 5. Base; 6. Cable encoder; 7. Linear slide; 8. Camera housing; 9. Cross rod bracket; 10. Support frame; 11. Control box; 12. Slider; 13. Stepper motor; 14. Coupling; 15. Camera; 16. Depth sensor. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0039] A method for quickly determining the optimal focal plane position of an imaging camera in a large-span scene is disclosed. The method uses a focus tracking method that combines active and passive focusing based on a range-finding camera. Furthermore, by constructing a focus tracking curve, the optimal focal plane position in the large-span scene is determined to ensure that a clear imaging effect can be quickly obtained in the scene.

[0040] Specifically, in one embodiment, the method includes the following:

[0041] (1) Obtain the focus tracking curve of the distance-optimal focal plane position mapping relationship.

[0042] Specifically, in one embodiment, a mapping relationship between distance and optimal focal plane position, ie, a focus tracking curve, is established through the ranging function of the camera itself.

[0043] By establishing a mapping relationship of the focus tracking curve, the position of the optimal focal plane in a large-span scene can be quickly determined, thereby improving the clarity and quality of imaging.

[0044] In order to focus the tracking curve, in one embodiment, an automatic calibration device for the focus tracking curve is provided.

[0045] Please refer to Figures 1 and 2. The automatic calibration device includes a rotating device, a fixing device, a calibration plate, a motion module, a supporting device, a depth detection module, and an image acquisition and processing module.

[0046] The calibration plate includes a large calibration plate 1 and a small calibration plate 3. The small calibration plate 3 is fixed on the large calibration plate 1 and is perpendicular to the visual axis of the camera 15. The small calibration plate 3 is covered with a sample set. In one embodiment, the sample set uses 1951USAF (1951 United States Air Force resolution test chart) to characterize the camera imaging clarity. The calibration plate is used to construct different depth of field ranges.

[0047] The fixing device includes a base 5 and a bracket 4 placed on the base 5, and the bracket 4 is used to fix and install the rotating device; the base 5 is placed horizontally, and the bracket 4 is vertically arranged on the base 5 and is located at both ends of the length direction of the large calibration plate 1.

[0048] The rotating device includes two steering gears 2 equipped with steering gear arms, and the two steering gears 2 are used to control the rotation of the large calibration plate 1. In one embodiment, the two steering gears 2 are located on a side of the bracket 4 away from the large calibration plate 1.

[0049] The motion module includes a linear motion device and a support device, wherein the linear motion device includes a linear guide (linear slide 7), a slider 12, a coupling 14, a stepper motor 13 and a rope encoder 6. The linear guide is fixed to a side of the base 5 and extends in a direction perpendicular to the large calibration plate 1. The slider 12 slides along the length of the linear slide 7 (slide). In one embodiment, the slider 12 remains parallel to the visual axis of the camera 15 when moving horizontally. The coupling 14 is located at the end of the slide away from the base 5. The coupling 14 is used to connect the linear guide and the stepper motor 13. The stepper motor 13 is used to control the precise sliding of the slider 12. The stretch encoder 6 is used to feedback the object distance to achieve closed-loop control of the linear motion device. The body of the rope encoder 6 is mounted on the base 5, and its rope is fixed to the slider 12.

[0050] The supporting device is arranged above the slider 12. In one embodiment, the supporting device includes a supporting frame 10, a control box 11 and a camera fixing device. The supporting frame 10 is vertically arranged above the slider 12. The control box 11 is sleeved on the supporting frame 10. A microcontroller is provided in the control box 11 for controlling each module of the automatic calibration device. The camera fixing device consists of a camera housing 8 and a cross rod frame 9, wherein the cross rod frame 9 is used to connect the camera housing 8 and the supporting frame 10, and realize the sliding of the camera housing 8 in the height direction of the supporting frame 10.

[0051] The depth detection module uses an ST micro-array depth sensor based on the time-of-flight (TOF) principle to obtain depth distribution data and transmit the obtained depth distribution data to the microprocessor. In one embodiment, the depth detection module includes a depth sensor 16, which is fixed to the camera housing 8.

[0052] The image acquisition and processing module includes a camera 15 and a microcontroller for image processing and drive control. The camera 15 is fixed within the camera housing 8 and is a fixed-focus camera, due to its wide field of view and high image quality. The camera 15 is used to acquire images and transmit the acquired information to the microcontroller. The microcontroller uses a Raspberry Pi 4B as an image acquisition processor to achieve image acquisition and clarity evaluation, while also adjusting the distance of the motion module and controlling the rotation device. Furthermore, the microcontroller is capable of image processing and is a high-performance processing module with a large memory capacity. In one embodiment, the visual axis of the camera 15 is perpendicular to the vertically positioned large calibration plate 1, and the intersection of the straight line on which the visual axis of the camera 15 lies and the plane on which the calibration plate lies is located at the geometric center of the large calibration plate 1. The visual axis of the camera 15 is arranged parallel to the cable of the cable encoder 6.

[0053] In one embodiment, in order to achieve control of the camera 15, the microcontroller quickly searches for the optimal focal plane position by controlling the adjustment of the voice coil motor of the camera 15, and when the microcontroller receives that the image taken by the camera 15 does not include all the small calibration plates 3 laid out within the depth range, the microcontroller will control the rotating device to change the inclination angle of the large calibration plate 1 so that the camera field of view can cover the entire depth range, and control the camera to take a new picture at this position.

[0054] (2) In order to further improve the speed and accuracy of the mapping relationship, an extreme value search algorithm based on an improved hill climbing algorithm is proposed. This algorithm can effectively improve the search efficiency and ensure that the optimal focal plane position can be found quickly and accurately in complex scenes.

[0055] In one embodiment, the extremum search algorithm uses an improved hill climbing search method to determine six image recording points, and then applies a curve fitting method to these recording points. The peak point obtained by fitting the curve is used as the optimal focal plane position. The specific steps are shown in the flowchart of Figure 3. The specific steps are as follows:

[0056] Step S1: Given the initial focus position P0, control the camera to drive the focus value to search along the direction of increasing image clarity with a constant step size ΔVF, using the Laplace focus evaluation function value La Pi To characterize the image clarity at the corresponding position.

[0057] Step S2: Continuous imaging, and judging the interval where the true peak is located by the focus evaluation function value La: If La P3 <La P2 <La P1 (Judgment condition (1)), that is, the focus evaluation function value continuously decreases, then the corresponding focal plane position is recorded as P1 (the corresponding focus evaluation function value LaPi ), the focal plane positions corresponding to the two consecutive decreases in image clarity are P2 and P3.

[0058] Step S3: If La P2 <La P1 And La P3 >La P2 , that is, a local peak appears, then La P2 The focal plane position demarcation point is set, and the step size ΔVF is changed. Steps (1 to 2) are repeated for the left and right partitions to search for the focal plane position until the judgment condition (1) is met.

[0059] Step S4: Search in the opposite direction at the focal plane position (P3-P2) / 2 with a constant step length ΔVF, repeating steps 1 to 2. P6 <La P5 <La P4 When , the corresponding focal plane position is recorded as P4. At this time, the focal plane positions where the clarity drops twice in succession are P5 and P6 respectively.

[0060] Step S5: During the hill climbing search process, record the six focus evaluation function values ​​(La Pi , i = 1, 2, 3 ... 6) and the corresponding focal plane positions (P1 to P6), and curve fitting is performed using the discrete focus evaluation function value and the focal plane position parameters to obtain the optimal focal plane position.

[0061] At the same time, in order to fully reflect the clarity level of the best focus position, the Laplace operator that characterizes the edge and detail features of the image is used as the evaluation standard for the image clarity of each focus position. The focus evaluation function is:

[0062] Among them, g(x,y) represents the grayscale value at (x,y), g(x,y+1) represents the grayscale value at (x,y+1), g(x,y-1) represents the grayscale value at (x,y-1), g(x-1,y) represents the grayscale value at (x-1,y), g(x+1,y) represents the grayscale value at (x+1,y), M represents the position point in the horizontal direction of the image, N represents the position point in the vertical direction of the image, and the La value is the evaluation result of the current image focusing effect.

[0063] In one embodiment, the experimental steps for constructing a focus tracking curve by the automatic calibration device are as follows:

[0064] S1: setting a depth range, and then dividing the depth range into a set of depth intervals according to a large depth of field interval imaging method.

[0065] S2: Place a small calibration plate within the divided depth of field range.

[0066] S3: The microprocessor drives the stepper motor to adjust the camera to the specified distance according to the depth of field range. The microprocessor controls the camera to focus the image and evaluates the image clarity of the image collected by the camera, and obtains the optimal focal plane position corresponding to the distance.

[0067] S4: Repeat S2-S3 for the remaining depth of field interval sets.

[0068] S5: Change the depth range. The depth range must overlap with the previous depth range by at least 50%, and the depth range must be the same length as the previous depth range. Repeat S2-S4 above.

[0069] S6: obtaining multiple sets of distances and corresponding optimal focal plane positions, and the microprocessor performing curve fitting using the distances and optimal focal plane positions as coordinate points to obtain a focus tracking curve of the distance-optimal focal plane position mapping relationship.

[0070] In one exemplary embodiment, a method for rapidly determining the optimal focal plane position of an imaging camera within a wide-span scene includes: using the aforementioned automatic calibration device for focus tracking curves and employing an extremum search algorithm based on an improved hill climbing algorithm to obtain a focus tracking curve representing a distance-optimal focal plane position mapping relationship; and determining the optimal focal plane position within the focus tracking curve representing a distance-optimal focal plane position mapping relationship based on depth distribution data acquired by a depth detection module within the automatic calibration device. Depth can be understood as distance within the focus tracking curve.

[0071] The extreme value search algorithm based on the improved hill climbing algorithm can be specifically applied to "obtaining the optimal focal plane position corresponding to the distance" in S3 of the experimental step of constructing the focus tracking curve by the automatic calibration device.

[0072] After being calibrated by the calibration device, a rangefinder camera can quickly and accurately determine the optimal focal plane position by detecting scene depth information in a wide-span scene using a curve mapping relationship, providing an effective solution for the further development of imaging technology.

[0073] The extreme value search algorithm proposed in this application can avoid the problem of falling into local peaks in the hill climbing algorithm. At the same time, it has fast focusing speed and high focusing accuracy, and can provide a reliable method support for camera calibration to obtain the distance-optimal focal plane position focusing tracking curve.

[0074] Furthermore, the automatic calibration device for the focus tracking curve provided by this application is applicable to a variety of fixed-focus cameras with integrated ranging functions. Cameras can be selected according to needs, making it highly universal and applicable to a wide range of situations. Furthermore, the automatic calibration device proposed in this application can calibrate different fixed-focus cameras and quickly and accurately obtain a focus tracking curve. After the depth sensor acquires depth data, the optimal focal plane position can be quickly determined based on the focus tracking curve within a large-span scene.

[0075] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An automatic calibration device for a focusing tracking curve, characterized in that: It includes a calibration plate, a fixing device, a slide rail, a supporting device, a depth detection module and an image acquisition and processing module, wherein the fixing device is used to support the calibration plate and rotate it, the slide rail is perpendicular to the calibration plate and fixed on the fixing device, the slide rail is extended in the horizontal direction, the supporting device is slidably set on the slide rail, the supporting device is used to fix the depth detection module and the image acquisition and processing module, the depth detection module is used to obtain depth distribution data and transmit the data to the image acquisition and processing module, and the image acquisition and processing module includes a camera and a microcontroller for image processing and drive control.

2. The automatic calibration device for a focusing tracking curve according to claim 1, characterized in that: The calibration plate includes a large calibration plate and a small calibration plate; wherein the small calibration plate is fixed on the large calibration plate, and the small calibration plate is perpendicular to the direction of the camera visual axis, and a sample set is laid on the small calibration plate.

3. The automatic calibration device for a focusing tracking curve according to claim 2, wherein: The fixing device includes a base and a bracket located on the base, the bracket is fixed at both ends of the large calibration plate in the length direction, and a rotating device is provided on the side of the two brackets away from the large calibration plate, and the rotating device is used to control the rotation of the large calibration plate.

4. The automatic calibration device for a focusing tracking curve according to claim 3, characterized in that: One end of the slide rail is fixed on the base, and the other end extends outward in the horizontal direction. A slider and a stepper motor are provided on the slide rail. The stepper motor is used to drive the slider to slide on the slide rail. The supporting device is fixed on the slider. A pull rope encoder is also provided on the slide rail. The main body of the pull rope encoder is located at the connection between the slide rail and the base, and one end of the pull rope of the pull rope encoder is fixed on the slider.

5. The automatic calibration device for a focusing tracking curve according to claim 4, characterized in that: The supporting device includes a supporting frame, a control box and a camera fixing device, wherein a microcontroller is placed in the control box, the supporting frame is extended upward in a vertical direction, the control box and the camera fixing device are both fixed on the supporting frame, the camera fixing device includes a camera housing and a cross rod frame, the cross rod frame is used to connect the camera housing and the supporting frame, the camera is set in the camera housing, and a depth sensor is also set on the camera housing.

6. The automatic calibration device for a focusing tracking curve according to claim 5, wherein: The slider remains parallel to the camera visual axis when moving horizontally; the camera visual axis and the vertically placed large calibration plate remain perpendicular to each other, and the intersection of the straight line where the camera visual axis is located and the plane where the calibration plate is located is located at the geometric center of the calibration plate; the pull rope of the pull rope encoder remains horizontal with the camera visual axis.

7. A method for quickly determining the optimal focal plane position of an imaging camera applicable to large-span scenarios, characterized in that: The method comprises the following contents: S1: using the automatic calibration device for the focus tracking curve according to any one of claims 1 to 6 to obtain a focus tracking curve of a distance-optimal focal plane position mapping relationship; S2: Provide an extreme value search algorithm based on an improved hill climbing algorithm.

8. A method for quickly determining the optimal focal plane position of an imaging camera applicable to large-span scenarios, characterized in that: The extreme value search algorithm uses an improved hill climbing search method to determine six image recording points, and applies a curve fitting method to these recording points. The peak point obtained by fitting the curve is used as the optimal focal plane position. The steps are as follows: Step S1: Given an initial focusing position P0, control the camera to drive the focusing value to search along the direction of increasing image sharpness with a constant step size ΔVF, and use the Laplacian focus evaluation function value La Pi to characterize the image sharpness at the corresponding position; Step S2: Continuously image, and determine the interval where the true peak is located through the focus evaluation function value La: If La P3 <La P2 <La P1 , that is, if the focus evaluation function value continuously decreases, record the focus evaluation function value La Pi corresponding to the focal plane position P1, and the focal plane positions corresponding to the continuous two decreases in image sharpness are P2 and P3; Step S3: If La P2 <La P1 and La P3 >La P2 , that is, a local peak appears, then using La P2 as the focal plane position demarcation point, change the step size ΔVF, and repeat Steps S1 to S2 for the left and right partitions to search for the focal plane position until La P3 <La P2 <La P1 ; Step S4: Search in the opposite direction at a constant step size ΔVF at the focal plane position of (P3 - P2) / 2, and repeat Step S1 to Step S2. When there is La P6 <La P5 <La P4 , record the corresponding focal plane position as P4. At this time, the focal plane positions where the clarity drops continuously twice are P5 and P6 respectively; Step S5: During the hill climbing search, record six focus evaluation function values and the corresponding focal plane positions, and use the discrete focus evaluation function values and the focal plane position parameters to perform curve fitting to obtain the optimal focal plane position; among them, the six focus evaluation function values are La Pi , where i = 1, 2, 3... 6; the corresponding focal plane positions are P1 to P6.

9. The method for quickly determining the optimal focal plane position of an imaging camera in a large-span scene according to claim 8, characterized in that: The experimental steps for the automatic calibration device to construct the focus tracking curve are as follows: Step S1: Set the depth range, and then divide the depth range into a set of depth of field intervals according to the large depth of field divided interval imaging method; Step S2: Place a small calibration plate within the divided depth of field intervals; Step S3: The microprocessor drives the stepper motor to adjust the camera to a specified distance according to the depth of field interval. The microprocessor controls the camera to focus and image, evaluates the image sharpness of the images collected by the camera, and obtains the position of the best focal plane corresponding to this distance; Step S4: Repeat Step S2 - Step S3 for the remaining set of depth of field intervals; Step S5: Change the depth range. The depth range needs to overlap with no less than 50% of the depth intervals of the previous depth range, and the length of the depth range is the same as that of the previous depth range. Repeat the above Steps S2 - S4; Step S6: Obtain multiple sets of distances and the corresponding positions of the best focal planes. The microprocessor performs curve fitting with the distances and the positions of the best focal planes as coordinate points to obtain the focus tracking curve of the distance - best focal plane position mapping relationship.

10. A method for quickly determining the optimal focal plane position of an imaging camera applicable to large-span scenarios, characterized in that, It includes: Using the automatic calibration device for the focus tracking curve described in any one of claims 1 - 6, and adopting an extreme value search algorithm based on an improved hill - climbing algorithm to obtain the focus tracking curve of the distance - best focal plane position mapping relationship; Determine the position of the best focal plane in the focus tracking curve of the distance - best focal plane position mapping relationship according to the depth distribution data obtained by the depth detection module in the automatic calibration device.

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