Method and apparatus for 3D reconstruction of conductors and calculation of sag based on monocular vision

Abstract

This invention discloses a method and apparatus for 3D reconstruction and sag calculation of conductors based on monocular vision. The method includes: S1, fixing a calibrated monocular camera to a tower; S2, acquiring necessary tower structural parameters; S3, establishing a 3D tower coordinate system and calibrating the camera's extrinsic parameters; S4, determining the 3D coordinates of the terminal block in the tower coordinate system, constructing the plane containing the conductor, and transforming this plane to the camera coordinate system; S5, marking a visible feature point on the conductor, performing distortion correction on the feature point, and generating a projection ray; S6, solving for the intersection point between the projection ray and the plane containing the conductor; S7, transforming the 3D coordinates of the intersection point back to the tower coordinate system; S8, fitting the spatial morphology of the conductor using a quadratic curve; and S9, calculating the conductor sag value. The method includes a monocular camera module, a parameter acquisition module, a coordinate system construction module, a plane construction and ray intersection module, a 3D reconstruction module, a sag calculation module, and a communication module. This method does not rely on complex binocular or multi-view vision systems, has advantages such as low cost and ease of deployment, and is suitable for long-term online monitoring and maintenance management of power systems.

Description

Technical Field

[0001] This invention relates to the fields of intelligent inspection of power systems and computer vision technology, specifically to a method and device for three-dimensional reconstruction of conductors and calculation of sag based on monocular vision, which is applicable to non-contact measurement of conductor spatial morphology and real-time evaluation of sag parameters in high-voltage / ultra-high-voltage overhead transmission lines during operation. Background Technology

[0002] Overhead transmission lines are a crucial component of power systems, and their safe and stable operation directly impacts the reliability of the power grid. Conductor sag, the amount of downward sag of a conductor between two suspension points due to its own weight and environmental loads, is a key indicator of the mechanical condition of a transmission line. Excessive sag may lead to insufficient safe distances to the ground or objects, potentially causing discharges or even short circuits; conversely, insufficient sag may cause excessive conductor tension, resulting in wire breaks or tower damage. Therefore, accurate, efficient, and real-time monitoring of conductor sag is of significant engineering importance.

[0003] Currently, the main methods for measuring conductor sag include the following categories: Traditional manual inspection methods involve maintenance personnel using tools such as telescopes and rangefinders to observe from the ground or climb towers, and then estimating sag using empirical formulas. This method is inefficient, highly subjective, and limited by terrain, weather, and safety distances, making it difficult to meet the high-frequency, high-precision monitoring requirements of modern smart grids.

[0004] Direct sensor measurement method: This method involves installing tilt sensors, tension sensors, or temperature sensors on the conductor to indirectly calculate the sag through physical quantities. While this method allows for online monitoring, it requires the deployment of active equipment on high-voltage conductors, which presents challenges such as installation difficulties, high maintenance costs, sensitivity to electromagnetic interference, and poor long-term operational reliability.

[0005] Binocular / multi-view stereo vision method: This method uses multiple cameras to simultaneously capture images of the conductor from different perspectives, and reconstructs the conductor's three-dimensional coordinates using the principle of triangulation. While this method offers high accuracy, it suffers from complex system structure, difficult calibration, stringent requirements for camera synchronization, and limitations in deploying multi-view cameras in narrow transmission lines, thus restricting its engineering applicability.

[0006] LiDAR or UAV photogrammetry: This method acquires point cloud data of the conductor using airborne LiDAR or oblique photography, and then fits the conductor curve to calculate the sag. Although it can cover a large area of ​​the line, the equipment is expensive, the operation cycle is long, and the data processing is complex, making it difficult to achieve continuous, real-time monitoring. It is usually only used for periodic inspections.

[0007] In recent years, monocular vision has been widely used in industrial measurement due to its advantages such as simple structure, low cost, and ease of deployment. However, monocular vision inherently suffers from a lack of depth information, and without additional constraints, it cannot directly recover the absolute three-dimensional position of an object. Existing technologies have attempted to combine known geometric priors for monocular reconstruction, but these often neglect the precise spatial relationship between the camera installation location and the tower structure, resulting in reconstruction results lacking a physical reference and significant errors in sag calculation.

[0008] Furthermore, the characteristics of power transmission line scenarios, such as strong lighting variations, slender and low-texture conductors, and complex backgrounds, further increase the difficulty of extracting and locating conductor feature points in monocular images. How to fully utilize tower structure parameters as external constraints while using only a monocular camera to achieve high-precision reconstruction of conductor spatial position and reliable calculation of sag remains a pressing technical challenge.

[0009] Therefore, there is an urgent need to propose a three-dimensional reconstruction method for conductors that integrates prior knowledge of tower structures and monocular visual observation. This method can simplify hardware configuration while ensuring the accuracy and practicality of sag calculation, thus providing effective technical support for the intelligent operation and maintenance of transmission lines. Summary of the Invention

[0010] The purpose of this invention is to provide a method and apparatus for three-dimensional reconstruction of conductors and calculation of sag based on monocular vision, which overcomes the problems of insufficient accuracy caused by relying on multi-view cameras, needing to install sensors on the conductors, or lacking physical references in the prior art. Under the premise of using only a monocular camera, combined with tower structure parameters as geometric constraints, it can realize high-precision reconstruction of conductor spatial morphology and accurate calculation of sag.

[0011] To achieve the above objectives, the present invention provides the following technical solution.

[0012] On the one hand, this invention proposes a method for three-dimensional reconstruction of a conductor and calculation of its sag based on monocular vision, including the following steps: S1, will have known internal parameters And the distortion parameter D = \left [ {k1\, k2\, k3\, p1\, p2} \right ] The monocular camera is fixedly installed on one side of the transmission line tower so that the camera's field of view is along the direction of the transmission channel; S2. Obtain the structural parameters of the tower, the structural parameters including at least the horizontal distance between the wire terminal on the tower and the camera. The span between two adjacent towers and the vertical offset of the camera mounting height relative to the wiring terminals. ; S3. Establish a tower coordinate system with the center of the tower at the height of the camera as the origin. The tower coordinate system is a right-handed system. Along the route, Vertically upwards, and the camera coordinate system is calibrated. The attitude transformation relationship between the camera coordinate system and the tower coordinate system, where the camera coordinate system is a right-handed system. Along the optical axis of the imaging plane, Downward along the imaging plane: in A 3D point in the camera coordinate system A three-dimensional point in the tower coordinate system. and These represent rotational and translational transformations between two coordinate systems, respectively. S4. Determine the three-dimensional coordinates of the terminals at both ends of the conductor in the tower coordinate system based on the structural parameters:

[0013] in The height of the terminal block relative to the coordinate system can be obtained from installation parameter lookup or on-site measurement. Construct the plane containing the conductor within the tower coordinate system. The plane is then transformed to the camera coordinate system using coordinate transformation:

[0014] in The plane containing the conductor in the camera coordinate system; S5. Mark a visible feature point on the conductor. Using the camera's intrinsic parameters and distortion parameters The image coordinates of the feature points are subjected to distortion correction processing to obtain their distortion-free projection points on the camera's normalized imaging plane. :

[0015] in These are the normalized imaging plane projection points with distortion. This is the distortion correction function. Furthermore, from this... Generate a projection ray originating from the camera's optical center and passing through the distortion-free projection point. ; S6. In the camera coordinate system, solve for the intersection point of the projected ray and the plane containing the guide wire, and obtain the three-dimensional coordinates of the intersection point in the camera coordinate system. ; S7. Transform the three-dimensional coordinates of the intersection point back to the tower coordinate system using coordinate transformation. ; S8. Based on the coordinates of the terminals at both ends of the conductor in the tower coordinate system and the three-dimensional coordinates of the intersection point, a quadratic curve is used to fit the spatial shape of the conductor. S9. Based on the fitted quadratic curve, calculate the vertical sag distance of the lowest point of the conductor in the span relative to the line connecting the two ends, and use it as the sag value.

[0016] Furthermore, in step S4, the plane in which the conductor is located is constructed specifically by using the plane spanned by the two terminal points and the gravity direction vector as the theoretical suspension plane of the conductor.

[0017] Furthermore, in step S5, the distortion correction process uses the radial distortion coefficient and tangential distortion coefficient obtained from camera calibration to correct the original pixel coordinates to distortion-free coordinates through a reverse mapping model.

[0018] Furthermore, in step S8, the quadratic curve fitting employs the least squares method, constraining the curve to pass through two terminal points and minimizing the distance from the feature points to the curve. In the tower coordinate system, the curve's analytical expression is: The optimization function is:

[0019] Furthermore, the feature points are either high-contrast markers temporarily placed on the conductor or identifiable structural feature points inherent in the conductor itself.

[0020] On the other hand, the present invention also provides an apparatus for implementing the above method, comprising: 1. Monocular camera module, used to acquire images containing guide lines and feature points; 2. Parameter acquisition module, used to input or read camera intrinsic parameters, distortion parameters, and tower structure parameters; 3. Coordinate system construction module, used to establish the tower coordinate system and the camera coordinate system, and to realize the coordinate transformation between the two; 4. Plane Construction and Ray Intersection Module: This module is used to construct a traverse plane in the camera coordinate system and calculate the intersection point of the projected ray with the plane. 5. The 3D reconstruction module is used to transform the coordinates of the intersection points to the tower coordinate system and fit the quadratic curve of the conductor in combination with the terminal points; 6. Sag Calculation Module: Used to calculate sag values ​​based on the fitted curve.

[0021] Furthermore, the monocular camera module is fixedly installed on the crossarm or tower body of the tower, with its optical axis parallel to the direction of the power transmission line.

[0022] Furthermore, it also includes a communication module for uploading sag results to a remote monitoring platform to achieve online status assessment.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 3D reconstruction can be achieved with just a single camera: By introducing tower structure parameters as external geometric constraints, the deficiency of depth information in monocular vision can be effectively compensated, eliminating the need for binocular or multi-view systems and significantly reducing hardware costs and deployment difficulty.

[0024] High accuracy and clear physical meaning: The coordinate system is established based on the actual tower structure, and the reconstruction results have a clear engineering reference system, avoiding the problem of lack of absolute scale in pure image-driven methods. The sag calculation results are more practical.

[0025] Suitable for online monitoring scenarios: The system can be deployed on poles for a long time. Combined with automatic image recognition and calculation modules, it can realize automated, high-frequency, and remote monitoring of conductor sag, thereby improving the level of intelligent operation and maintenance of transmission lines.

[0026] The algorithm is robust: by utilizing the duct suspension plane constraint and quadratic curve prior, it can maintain high reconstruction stability and sag calculation accuracy even under conditions of image noise, illumination changes or partial occlusion.

[0027] In summary, this invention provides a conductor sag monitoring solution that is simple in structure, low in cost, reliable in accuracy, and easy to implement in engineering, and is particularly suitable for status perception and safety early warning of high-voltage / ultra-high-voltage overhead transmission lines. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the overall process of the monocular vision-based three-dimensional reconstruction and sag calculation method for conductors described in this invention. Figure 2 This is a system structure block diagram of the monocular vision-based 3D reconstruction and sag calculation device for conductors according to the present invention; Figure 3 This is a schematic diagram illustrating the spatial relationship and projection geometry between the tower coordinate system and the camera coordinate system in this invention. Detailed Implementation

[0029] The following describes the embodiments of the present invention through specific examples and in conjunction with the accompanying drawings. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific examples, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] The conductor sag monitoring device in this embodiment includes: a monocular camera module, a parameter acquisition module, a coordinate system construction module, a plane construction and ray intersection module, a three-dimensional reconstruction module, a sag calculation module, and a communication module.

[0031] The monocular camera was securely mounted on a crossarm of a tower on one side of the transmission line, at a height of approximately 30 m. Its optical axis was roughly parallel to the direction of the transmission line, with no pitch or yaw, ensuring that the conductor within the target span remained completely within the field of view. The camera's intrinsic parameter matrix had been obtained through offline calibration. With distortion parameters ,in:

[0032] like Figure 3 As shown, a tower coordinate system is established with the center of the tower at the camera installation height as the origin. Based on the installation drawings and actual measurements, the conductor span... The hanging points on both sides are at the same height, 1 meter higher than the camera. The horizontal distance between the wiring terminals and the camera. .

[0033] Acquire static images of the conductor and select feature points on the conductor. .

[0034] The traverse is reconstructed and its sag is calculated using a monocular vision-based 3D reconstruction and sag calculation method. Mark visible feature points Using the camera's intrinsic parameters With distortion parameters The image coordinates of the feature points are then subjected to distortion correction processing to obtain their distortion-free projection points on the camera's normalized imaging plane. :

[0035] in These are the normalized imaging plane projection points with distortion. This is the distortion correction function. Furthermore, from this... Generate a projection ray originating from the camera's optical center and passing through the distortion-free projection point. ; In the camera coordinate system, the intersection point of the projected ray and the plane containing the guide wire is determined, and the three-dimensional coordinates of the intersection point in the camera coordinate system are obtained. ; The three-dimensional coordinates of the intersection point are transformed back to the tower coordinate system using coordinate transformation. ; Based on the coordinates of the terminals at both ends of the conductor in the tower coordinate system and the three-dimensional coordinates of the intersection point, a quadratic curve is used to fit the spatial shape of the conductor. Based on the fitted quadratic curve, the vertical sag distance of the conductor at its lowest point in the span relative to the line connecting the two ends is calculated and used as the sag value.

[0036] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can make modifications and changes to the above embodiments without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be as set forth in the claims.

Claims

1. A method for wire three-dimensional reconstruction and sag calculation based on monocular vision, characterized in that, The method comprises the following steps: S1, a monocular camera with known intrinsic and distortion parameters is fixedly installed on a side tower of a power transmission line, so that the field of view of the camera is along the direction of the power transmission channel; S2, the structural parameters of the tower are obtained, the structural parameters at least including the horizontal distance between the line terminal on the tower and the camera, the span between two adjacent towers, and the vertical offset of the camera installation height relative to the line terminal; S3, a tower coordinate system is established with the center of the tower at the height of the camera as the origin, and the attitude transformation relationship between the camera coordinate system and the tower coordinate system is calibrated; S4, the three-dimensional coordinates of the line terminals at both ends of the line in the tower coordinate system are determined according to the structural parameters, and a plane in which the line is located is constructed in the tower coordinate system, and the plane is converted to the camera coordinate system through coordinate transformation; S5, a visible feature point is marked on the line, the image coordinates of the feature point are de-distorted by using the distortion parameters and intrinsic parameters of the camera, the non-distorted projection point of the feature point on the normalized imaging plane of the camera is obtained, and a projection ray is generated from the optical center of the camera and passing through the non-distorted projection point; S6, in the camera coordinate system, the intersection point of the projection ray and the plane in which the line is located is solved, and the three-dimensional coordinates of the intersection point in the camera coordinate system are obtained; S7, the three-dimensional coordinates of the intersection point are converted back to the tower coordinate system through coordinate transformation; S8, based on the three-dimensional coordinates of the intersection point and the line terminals at both ends of the line in the tower coordinate system, a quadratic curve is used to fit the spatial form of the line; S9, according to the fitted quadratic curve, the vertical sag of the lowest point of the line in the span relative to the line connecting the two terminals is calculated as the sag value.

2. The method of claim 1, wherein, In the step S4, the plane in which the line is located is constructed by taking the plane formed by the two line terminals and the gravity direction vector as the theoretical suspension plane of the line.

3. The method of claim 1, wherein, In the step S5, the de-distortion processing uses the radial distortion coefficient and the tangential distortion coefficient obtained by camera calibration to correct the original pixel coordinates to non-distorted coordinates through an inverse mapping model.

4. The method of claim 1, wherein, In the step S8, the least square method is used for quadratic curve fitting, the curve is constrained to pass through the two line terminals, and the distance from the feature point to the curve is minimized.

5. The method of claim 1, wherein, The feature point is a high-contrast marker temporarily set on the line, or a recognizable structural feature point of the line itself.

6. An apparatus for implementing the method of any one of claims 1-5, characterized by It comprises: 6.1, a monocular camera module for collecting images containing the line and the feature point; 6.2, a parameter acquisition module for inputting or reading the camera intrinsic parameters, distortion parameters and tower structural parameters; 6.3, a coordinate system construction module for establishing the tower coordinate system and the camera coordinate system and realizing the coordinate transformation between them; 6.4, a plane construction and ray intersection module for constructing the line plane in the camera coordinate system and calculating the intersection point of the projection ray and the plane; 6.5, a three-dimensional reconstruction module for converting the intersection point coordinates to the tower coordinate system and fitting the line quadratic curve in combination with the line terminal points; 6.6, a sag calculation module for calculating the sag value according to the fitted curve.

7. The apparatus of claim 6, wherein, The monocular camera module is fixedly installed on the crossarm or tower body of the tower, and its optical axis is parallel to the direction of the power transmission line.

8. The apparatus of claim 6, wherein, It also includes a communication module for uploading the calculated sag value to a remote monitoring platform.

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