A multi-focal combined camera tilt imaging calibration method, medium and device

Abstract

This invention relates to the field of bridge deformation measurement technology. It provides a multi-focal-length combined camera tilt imaging calibration method. Utilizing multiple cameras with different focal lengths, and employing a tilted shooting method along the side of the bridge, it achieves clear, high-resolution combined imaging from near to far along the camera's line of sight. This effectively expands the camera's effective imaging range in the depth direction, meeting the needs of large-scale bridge measurements. Compared to conventional single-camera visual imaging methods, this invention expands the effective imaging range in the camera's depth (line of sight) direction. Compared to tilt-shift imaging, this invention is still based on conventional imaging, with the camera's depth-of-field distribution conforming to conventional understanding, making focusing easier and more practical. Compared to existing multi-camera combined imaging methods, this invention focuses on addressing the imaging blur problem caused by insufficient depth of field in the camera's line of sight direction, thus expanding the effective imaging range in the camera's depth (line of sight) direction.

Description

Technical Field

[0001] This invention relates to the field of bridge deformation measurement technology, specifically to a method, medium, and equipment for calibrating tilt imaging using a multi-focal length combined camera. Background Technology

[0002] Bridges are constantly exposed to harsh environmental conditions and subjected to various loads, making them highly susceptible to vertical displacement, or bridge deflection. Measuring bridge deflection or vertical displacement is a crucial component of assessing bridge structural condition and a key auxiliary means of identifying potential hazards and ensuring bridge safety and durability. Traditional displacement measurement equipment, such as accelerometers, strain gauges, inclinometers, total stations, Global Navigation Satellite Systems (GNSS), fiber optic sensors, and laser scanners, faces limitations in practical applications, including destructive contact installation, high deployment costs, and restrictions on measurement locations.

[0003] In recent years, significant progress has been made in vision-based bridge deflection or displacement measurement research, proving the effectiveness of vision methods in non-destructive bridge displacement measurement applications. However, due to limitations in camera field of view, depth of field, and resolution, single-camera vision systems struggle to achieve high-resolution imaging of large targets such as bridges that are tens or hundreds of meters long, covering a wide range of multiple points. Therefore, in recent years, some scholars have focused their research on monocular tilt-shift imaging methods. Based on existing monocular vision systems, they have introduced the tilt-shift imaging principle based on Scham's law, proposing a high-precision monitoring method for large-scale, multi-point displacement based on monocular tilt-shift imaging. Unlike the imaging method in conventional cameras where the image plane is orthogonal to the lens optical axis, tilt-shift cameras can significantly expand the camera's depth of field without reducing the image magnification by tilting the lens relative to the image plane (non-orthogonal). This allows the camera to simultaneously possess high resolution and large depth of field imaging characteristics. Therefore, when the monocular tilt-shift vision system and measurement points are arranged in a linear array, high-resolution, clear imaging of all measurement points on the linear array can be achieved using only the monocular vision system. However, while tilt-shift imaging expands the depth of field, it also narrows the width of the depth of field. In practical applications, the camera and measurement points must be arranged in a strictly linear array; otherwise, the image will still be blurry. In addition, the depth of field distribution of tilt-shift imaging does not conform to conventional understanding, which also makes its focusing operation more difficult, thus limiting the widespread application of tilt-shift imaging to some extent. Some researchers are also studying imaging methods using multiple cameras, but most existing studies focus on expanding the imaging range (field of view) without considering the imaging blur caused by insufficient depth of field in the direction of the camera's line of sight.

[0004] In summary, there is an urgent need to provide a method, medium, and device for calibrating tilt imaging of a multi-focal length combined camera to solve the technical problems existing in the prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a method, medium, and device for calibrating tilt imaging of a multi-focal length combined camera, in order to solve the technical problems existing in the prior art. The specific technical solution is as follows:

[0006] A method for calibrating tilt imaging of a multi-focal length combined camera, characterized by comprising the following steps:

[0007] Multiple measurement targets were set up on the side of the bridge along the direction of its extension.

[0008] A multi-focal-length combined camera was used to obliquely photograph a target on the side of a bridge, achieving oblique imaging calibration of the multi-focal-length combined camera. Specifically:

[0009] Step S1: Determine the effective imaging range [d1,d2] of each camera in the line of sight direction according to the preset image resolution requirements;

[0010] Step S2: Based on the geometric relationship between the camera and the side of the bridge, calculate the effective imaging range S of each camera on the side of the bridge.

[0011] Step S3: Verify whether the effective imaging range of each camera on the side of the bridge meets the overlapping coverage condition; if it does, the imaging calibration is completed; if it does not, proceed to step S4.

[0012] Step S4: Dynamically adjust the mounting position of the multi-focal length combined camera, and repeat steps S2 and S3 until the imaging range of all measurement targets is completely covered.

[0013] Furthermore, in step S1, determining the effective imaging range of each camera in the line-of-sight direction specifically includes:

[0014] Image resolution constraints are established based on the pinhole imaging model and depth-of-field calculation formula;

[0015] The required image resolution is calculated by back-calculating the preset displacement measurement accuracy.

[0016] Calculate the effective imaging range of each camera in the line-of-sight direction.

[0017] Furthermore, step S2 specifically involves:

[0018] The installation baseline parameters of each camera are obtained by laser ranging;

[0019] Establish a geometric model between the camera and the bridge;

[0020] Calculate the effective imaging range of each camera on the side of the bridge.

[0021] Furthermore, the calculation process for the effective imaging range of each camera on the side of the bridge is as follows:

[0022] First, calculate the distance u from the right edge of each camera's field of view to the effective imaging range d1 position in the line of sight direction.

[0023]

[0024] In the formula, θ represents the field of view of the camera;

[0025] Next, calculate the angle β between the left edge of the field of view of each camera and the side edge of the bridge.

[0026]

[0027] In the formula, J is the vertical distance between the camera and the side of the bridge;

[0028] Then, calculate the distance n from the point perpendicular to the side line of the bridge to the effective imaging range s1 of the bridge, and the distance m from the point perpendicular to the side line of the bridge to the effective imaging range d2 of the bridge.

[0029]

[0030] In the formula, σ is the camera tilt angle, σ=90°-β;

[0031] Finally, the effective imaging range S of the camera on the side of the bridge is calculated.

[0032] S = mn.

[0033] Furthermore, step S3 specifically includes:

[0034] Construct a distribution map of the effective imaging range of each camera on the side of the bridge;

[0035] Detect whether there are overlapping areas between adjacent intervals;

[0036] Verify that all measurement target locations fall within the joint coverage area.

[0037] Furthermore, methods for adjusting the mounting position of the multi-focal length combination camera include:

[0038] Move the multifocal distance camera along a direction perpendicular to the side of the bridge to change the distance between the multifocal distance camera and the bridge;

[0039] Rotate the multifocal combination camera to change its tilt angle.

[0040] Furthermore, the multi-focal length combined camera includes multiple cameras with different focal lengths arranged in parallel, and the multiple cameras with different focal lengths are arranged in ascending order of focal length along the extension direction of the bridge.

[0041] Furthermore, at least three spatially distributed measurement targets are set on the side of the bridge, each containing multiple reflective feature points.

[0042] A readable storage medium storing a computer program, wherein a processor executes the computer program to implement the multi-focal length combined camera tilt imaging calibration method as described above.

[0043] An electronic device includes a memory and a processor, wherein the memory stores a computer program; the processor executes the computer program to implement the multi-focal length combined camera tilt imaging calibration method as described above.

[0044] The application of the technical solution of the present invention has the following beneficial effects:

[0045] This invention provides a multi-focal-length combined camera tilt imaging calibration method. Utilizing multiple cameras with different focal lengths, and employing a tilted shooting method along the side of the bridge, it achieves clear, high-resolution combined imaging from near to far along the camera's line of sight. This effectively expands the camera's effective imaging range in the depth direction, meeting the needs of large-scale bridge measurements. Compared to conventional single-camera visual imaging methods, this invention expands the effective imaging range in the camera's depth (line of sight) direction. Compared to tilt-shift imaging, this invention is still based on conventional imaging, with the camera's depth-of-field distribution conforming to conventional understanding, making focusing easier and more practical. Compared to existing multi-camera combined imaging methods, this invention focuses on addressing the imaging blur problem caused by insufficient depth of field in the camera's line of sight direction, thus expanding the effective imaging range in the camera's depth (line of sight) direction.

[0046] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0047] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0048] Figure 1 This is a flowchart of the tilt imaging calibration method for multi-focal length combined cameras in this invention;

[0049] Figure 2 This is a schematic diagram of a multi-focal length combination camera setup;

[0050] Figure 3 This is a schematic diagram of the geometric model between the camera and the bridge in this invention. Detailed Implementation

[0051] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered.

[0052] In the description of this invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "front", "back", "lateral", "longitudinal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0053] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0054] Example:

[0055] See Figure 1 This invention provides a method for calibrating tilt imaging of a multi-focal length combined camera, comprising the following steps:

[0056] Multiple measurement targets were set up on the side of the bridge along the direction of its extension.

[0057] A multi-focal-length combined camera was used to obliquely photograph a target on the side of a bridge, achieving oblique imaging calibration of the multi-focal-length combined camera. Specifically:

[0058] Step S1: Determine the effective imaging range [d1,d2] of each camera in the line of sight direction according to the preset image resolution requirements;

[0059] Step S2: Based on the geometric relationship between the camera and the side of the bridge, calculate the effective imaging range S of each camera for the side of the bridge;

[0060] Step S3: Verify whether the effective imaging range of each camera on the side of the bridge meets the overlapping coverage condition; if it does, the imaging calibration is completed; if it does not, proceed to step S4.

[0061] Step S4: Dynamically adjust the mounting position of the multi-focal length combined camera, and repeat steps S2 and S3 until the imaging range of all measurement targets is completely covered.

[0062] Preferably, at least three spatially distributed measurement targets are arranged on the side of the bridge along the bridge's extension direction (the number of measurement targets can be arranged according to actual needs, see [reference]). Figure 2 In this embodiment, three measurement targets are set, each containing multiple reflective feature points to enhance detectability and improve measurement accuracy and reliability.

[0063] In this embodiment, see Figure 2 The multi-focal-length combined camera includes multiple cameras with different focal lengths arranged in parallel. The multiple cameras with different focal lengths are arranged in order of increasing focal length along the extension direction of the bridge. In this embodiment, taking a combination of three cameras as an example, the focal lengths of the three cameras are 25mm, 50mm and 75mm respectively.

[0064] Furthermore, in step S1, determining the effective imaging range of each camera in the line-of-sight direction specifically includes:

[0065] Image resolution constraints are established based on the pinhole imaging model and depth-of-field calculation formula; the required image resolution is inversely calculated based on the preset displacement measurement accuracy; and the effective imaging range of each camera in the line-of-sight direction is calculated. The above calculation process is existing technology. Given the known camera parameters, the effective imaging range [d1, d2] of the camera in the line-of-sight direction can be considered as a known value.

[0066] Furthermore, step S2 specifically involves:

[0067] The installation baseline parameters of each camera, such as the vertical distance between the camera and the side of the bridge, are obtained using a laser rangefinder; a geometric model between the camera and the bridge is then established (see [reference needed]). Figure 3 Based on this geometric model, the effective imaging range of each camera on the side of the bridge is calculated, specifically:

[0068] First, calculate the distance u from the right edge of each camera's field of view to the effective imaging range d1 position in the line of sight direction.

[0069]

[0070] In the formula, θ represents the field of view of the camera;

[0071] Next, calculate the angle β between the left edge of the field of view of each camera and the side edge of the bridge.

[0072]

[0073] In the formula, J is the vertical distance between the camera and the side of the bridge, which is obtained by laser ranging;

[0074] Then, calculate the distance n from the perpendicular point of the camera's optical center O to the side line of the bridge to the effective imaging range d1 of the bridge, and the distance m from the perpendicular point of the camera's optical center O to the side line of the bridge to the effective imaging range d2 of the bridge.

[0075] n = u·cosβ;

[0076] m = J·tan(σ+θ);

[0077] In the formula, σ is the camera tilt angle, σ=90°-β;

[0078] Finally, the effective imaging range S of the camera on the side of the bridge is calculated.

[0079] S = mn.

[0080] Furthermore, step S3 specifically includes:

[0081] Step S2 calculates the effective imaging range of the three cameras on the side of the bridge and constructs an interval distribution map of the effective imaging range of each camera on the side of the bridge. It detects whether there are overlapping areas between adjacent intervals and verifies whether all measurement target positions fall within the joint coverage area. If there are no non-overlapping areas between adjacent intervals and all measurement target positions fall within the joint coverage area, the calibration is completed. If there are non-overlapping areas or the measurement target positions do not fall within the joint coverage area, a camera installation position adjustment suggestion is generated.

[0082] Preferably, the method for adjusting the mounting position of the multifocal length combined camera includes: moving the multifocal length combined camera in a direction perpendicular to the side of the bridge to change the distance J between the multifocal length combined camera and the bridge; rotating the multifocal length combined camera to change the tilt angle σ of the multifocal length combined camera. Through the above adjustment method, the mounting position of the multifocal length combined camera can be quickly adjusted, improving the efficiency of tilt imaging calibration of the multifocal length combined camera.

[0083] The multi-focal-length combined camera tilt imaging calibration method provided by this invention utilizes multiple cameras with different focal lengths, employing a tilted shooting method from the side of the bridge, to achieve clear, high-resolution combined imaging along the camera's line of sight from near to far. This effectively expands the camera's effective imaging range in the depth direction, meeting the needs of large-scale bridge measurements. Compared to conventional single-camera visual imaging methods, this invention can expand the effective imaging range in the camera's depth (line of sight) direction; compared to tilt-shift imaging, this invention is still based on conventional imaging, the camera's depth-of-field distribution conforms to conventional understanding, the focusing operation is less difficult, and it is more practical; compared to existing multi-camera combined imaging methods, this invention focuses on addressing the imaging blur problem caused by insufficient depth of field in the camera's line of sight direction, thus expanding the effective imaging range in the camera's depth (line of sight) direction.

[0084] The present invention also provides an electronic device corresponding to the above embodiments. The electronic device may be a processing device for a client, such as a mobile phone, a laptop, a tablet computer, a desktop computer, etc., to execute the methods of the above embodiments.

[0085] The electronic device of this embodiment includes a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method described in the above embodiment.

[0086] In some implementations, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0087] In other implementations, the processor can be any type of general-purpose processor, such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation here.

[0088] The present invention also provides a readable storage medium corresponding to the above embodiments, wherein a computer program / instructions are stored thereon. When the computer program / instructions are executed by a processor, they implement the steps of the methods described in the above embodiments.

[0089] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0090] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0091] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0092] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for calibrating tilt imaging of a multi-focal length combined camera, characterized in that, Includes the following steps: Multiple measurement targets were set up on the side of the bridge along the direction of its extension. A multi-focal-length combined camera was used to obliquely photograph a target on the side of a bridge, achieving oblique imaging calibration of the multi-focal-length combined camera. Specifically: Step S1: Determine the effective imaging range of each camera in the line-of-sight direction according to the preset image resolution requirements. ; Step S2: Based on the geometric relationship between the camera and the side of the bridge, calculate the effective imaging range of each camera on the side of the bridge. ; Step S3: Verify whether the effective imaging range of each camera on the side of the bridge meets the overlapping coverage condition; if it does, the imaging calibration is completed; if it does not, proceed to step S4. Step S4: Dynamically adjust the mounting position of the multi-focal length combined camera, and repeat steps S2 and S3 until the imaging range of all measurement targets is completely covered. Step S2 is as follows: The installation baseline parameters of each camera are obtained by laser ranging; Establish a geometric model between the camera and the bridge; Calculate the effective imaging range of each camera on the side of the bridge; The calculation process for the effective imaging range of each camera on the side of the bridge is as follows: First, calculate the effective imaging range from the right edge of the field of view of each camera to the line of sight. Distance at location , ； In the formula, Indicates the camera's field of view; Next, calculate the angle between the left edge of the field of view of each camera and the side edge of the bridge. , ； In the formula, This is the vertical distance between the camera and the side of the bridge; Then, the distance from the perpendicular point of the camera's optical center to the side line of the bridge to the effective imaging range of the bridge is calculated. Distance at location And the effective imaging range of the bridge from the perpendicular point of the camera's optical center to the side line of the bridge. Distance at location , ； ； In the formula, For the camera tilt angle, ; Finally, the effective imaging range of the camera on the side of the bridge is calculated. , 。 2. The method for calibrating tilt imaging of a multi-focal length combined camera according to claim 1, characterized in that, In step S1, determining the effective imaging range of each camera in the line-of-sight direction specifically includes: Image resolution constraints are established based on the pinhole imaging model and depth-of-field calculation formula; The required image resolution is calculated by back-calculating the preset displacement measurement accuracy. Calculate the effective imaging range of each camera in the line-of-sight direction.

3. The method for calibrating tilt imaging of a multi-focal length combined camera according to claim 1, characterized in that, Step S3 specifically includes: Construct a distribution map of the effective imaging range of each camera on the side of the bridge; Detect whether there are overlapping areas between adjacent intervals; Verify that all measurement target locations fall within the joint coverage area.

4. The method for calibrating tilt imaging of a multi-focal length combined camera according to claim 1, characterized in that, Methods for adjusting the mounting position of a multi-focal length combination camera include: Move the multi-focal-length camera along a direction perpendicular to the side of the bridge to change the distance between the multi-focal-length camera and the bridge; rotate the multi-focal-length camera to change its tilt angle.

5. A method for calibrating tilt imaging of a multi-focal length combined camera according to any one of claims 1-4, characterized in that, The multi-focal-length combined camera includes multiple cameras with different focal lengths arranged in parallel, and these cameras are arranged in ascending order of focal length along the extension direction of the bridge.

6. A method for calibrating tilt imaging of a multi-focal length combined camera according to any one of claims 1-4, characterized in that, At least three spatially distributed measurement targets are set on the side of the bridge, and each measurement target contains multiple reflective feature points.

7. A readable storage medium, characterized in that, The readable storage medium stores a computer program, and the processor executes the computer program to implement the multi-focal length combined camera tilt imaging calibration method as described in any one of claims 1-4.

8. An electronic device, characterized in that, The device includes a memory and a processor, wherein the memory stores a computer program; the processor executes the computer program to implement the multi-focal length combined camera tilt imaging calibration method as described in any one of claims 1-4.

Images