Single-camera three-dimensional coordinate measurement method and system based on full-field distance measurement

Abstract

The invention relates to the technical field of optical three-dimensional measurement and metering, and discloses a single-camera three-dimensional coordinate measurement method and system based on full-field distance measurement, and the method comprises the following steps: S1, building a calibration field containing a control point, shooting an image of the calibration field through a monocular camera, extracting the image coordinate of the control point, carrying out the camera calibration, and obtaining a calibration field; obtaining internal parameters and external orientation parameters of the camera; and S2, controlling the laser range finder to aim at the control point in the calibration field through the non-orthogonal double-axis turntable. Submillimeter-level high-precision measurement can still be realized under the condition of a short baseline, and the problems that the precision in the depth direction is insufficient, the baseline requirement is long, parameters are easy to drift and the like in traditional stereoscopic vision measurement are effectively solved. By introducing a non-orthogonal double-shaft turntable and a visual guidance laser aiming mechanism, autonomous, rapid and accurate measurement of multiple measurement points in a large field of view is realized, and the automation degree and reliability of measurement in a complex environment are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of optical three-dimensional measurement and metrology technology, specifically to a single-camera three-dimensional coordinate measurement method and system based on full-field ranging. Background Technology

[0002] As remote sensing satellites achieve increasingly higher resolutions, wider swaths, and higher orbital altitudes, their on-orbit antenna deployment has exceeded 100 meters, posing new demands for "high precision, high stability, and long-duration" operation. However, due to the high flexibility of the antenna structure, its surface accuracy is easily affected by factors such as zero gravity environment, solar radiation pressure, attitude control errors, micro-vibrations, and extreme temperature changes, leading to deformation and vibration. Current materials and technologies are nearing their limits; therefore, high-precision on-orbit surface measurement technology has become a key support for achieving active adjustment and dynamic compensation of antenna performance.

[0003] To address these needs, scholars both domestically and internationally have proposed various antenna surface accuracy measurement schemes. For example, Guo Meng et al. proposed a satellite antenna deformation detection method based on strain measurement. This method establishes a strain-displacement conversion model using elasticity theory, acquires strain data from the panel surface using a strain gauge array, and then inversely determines the deformation configuration. However, this method is based on the theory of small deflection in thin plates, limiting its applicability. Furthermore, the installation accuracy of the strain gauges directly affects data reliability, making it difficult to meet sub-millimeter accuracy requirements. Gao Feixiong et al. used fiber optic sensors to measure the deformation of the radial ribs of an umbrella-shaped antenna under space loads and proposed an improved Ko displacement algorithm, verifying its effectiveness through simulation and experiments. However, its sensor deployment is complex and sensitive to local deformation, limiting overall measurement accuracy. NASA's Langley Research Center and Johnson Space Center utilized five in-service cameras on the International Space Station to construct an on-orbit photogrammetry system, achieving measurements of the shape, vibration modes, and structural motion parameters of a roll-deployable solar array, with a target point spatial coordinate measurement RMSE of 15 mm. Although this multi-camera system has a wide measurement range, it suffers from bottlenecks such as excessively long baselines, calibration parameter drift, and significantly lower depth accuracy compared to lateral accuracy.

[0004] In summary, existing technologies face three major challenges: First, it is difficult to construct long baselines in space-constrained environments, while short baselines limit measurement accuracy; second, the accuracy of depth measurements is significantly lower than that of lateral measurements, which is an inherent limitation of visual measurement; third, parameter calibration and maintenance of multi-sensor systems are difficult, and camera poses are prone to drift in space thermodynamic environments. To address these issues, this paper proposes a high-precision measurement method that integrates photogrammetry and laser ranging. High-precision depth information is directly acquired through a full-field scanning ranging system, combined with the advantages of monocular vision in planar measurement, and vision guidance is used to achieve autonomous, high-precision 3D measurement under short baseline conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a single-camera three-dimensional coordinate measurement method and system based on full-field ranging, which solves the problems of difficulty in constructing long baselines in space-constrained environments and the limitation of measurement accuracy by short baselines.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a single-camera three-dimensional coordinate measurement method based on full-field ranging, comprising the following steps: S1. Construct a calibration field containing control points, capture images of the calibration field using a monocular camera, extract the image coordinates of the control points, perform camera calibration, and obtain the camera's intrinsic and extrinsic parameters. S2. Control the laser rangefinder to aim at the control points in the calibration field through the non-orthogonal dual-axis turntable, record the turntable horizontal angle, pitch angle and laser ranging value corresponding to each control point, and perform full-field scanning ranging system calibration based on the three-dimensional coordinates of the control points, the turntable angle and the laser ranging value, and establish the coordinate transformation relationship between the turntable and the laser rangefinder. S3. During the measurement phase, the camera captures the target point, extracts the image coordinates of the target point, guides the turntable to rotate based on the camera calibration parameters, and enables the laser rangefinder to aim at the target point. The pointing error is reduced through iterative optimization, and the final turntable angle and laser ranging value are recorded. S4. Based on the camera calibration parameters, the coordinate transformation relationship, the turntable angle, and the laser ranging value, a triangulation model is constructed, and the three-dimensional coordinates of the target point in the world coordinate system are calculated through an optimization algorithm.

[0007] Preferably, in step S1, camera calibration specifically includes: The camera's intrinsic parameters, including focal length, principal point position, and distortion coefficient, are calibrated using a multi-image self-calibration bundle adjustment method. Based on the correspondence between the three-dimensional coordinates of the control points and their image coordinates, the exterior orientation parameters of the camera relative to the world coordinate system are calculated. The exterior orientation parameters include rotation matrices and translation vectors.

[0008] Preferably, in step S2, establishing the coordinate transformation relationship between the turntable and the laser rangefinder specifically includes: Establish transformation models between the world coordinate system, the horizontal turntable coordinate system, the pitch turntable coordinate system, and the laser rangefinder coordinate system; wherein, the transformation models describe the rotation and translation relationships between the world coordinate system and the horizontal turntable coordinate system, the horizontal turntable coordinate system and the pitch turntable coordinate system, and the pitch turntable coordinate system and the laser rangefinder coordinate system through parameters. Based on the aforementioned conversion model, an error equation is constructed using the three-dimensional coordinates of the control points, the turntable angle, and the laser ranging value. The pose parameters in the transformation model are solved using a least squares optimization algorithm.

[0009] Preferably, in step S3, reducing the pointing error through iterative optimization specifically includes: Convert the image coordinates of the target point into a direction vector in the laser rangefinder coordinate system; The offset of the target point in the plane perpendicular to the laser emission direction in the coordinate system of the laser rangefinder is calculated as the pointing error; Based on the pointing error, the horizontal and vertical angles of the turntable are iteratively adjusted until the offset is minimized.

[0010] Preferably, in step S4, constructing the triangulation model specifically includes: Based on the camera calibration parameters, the image coordinates of the target point are converted into the line-of-sight vector in the camera coordinate system; Based on the coordinate transformation relationship, the ranging starting point of the laser rangefinder is transformed to the camera coordinate system to obtain the baseline vector; By combining the laser ranging value, the baseline vector, and the line-of-sight vector, the three-dimensional coordinates of the target point in the camera coordinate system are solved using the law of cosines.

[0011] Preferably, the present invention also provides a single-camera three-dimensional coordinate measurement system based on full-field ranging, comprising: The calibration field is equipped with control points whose three-dimensional coordinates are known. A monocular camera is used to acquire images of the calibration field or the target point to be measured. Non-orthogonal dual-axis rotary table; The laser rangefinder is fixedly mounted on the dual-axis turntable; The data processing unit is in communication connection with the camera, turntable, and laser rangefinder. The data processing unit is configured to: perform camera calibration to obtain the camera's intrinsic and extrinsic parameters; perform full-field scanning ranging system calibration to establish the coordinate transformation relationship between the turntable and the laser rangefinder; generate control commands based on camera images to guide the turntable to aim at the target point; and calculate the three-dimensional coordinates of the target point based on the principle of triangulation.

[0012] This invention provides a single-camera three-dimensional coordinate measurement method and system based on full-field ranging. It has the following beneficial effects: 1. This invention achieves sub-millimeter level high-precision measurement even under short baseline conditions, effectively overcoming problems such as insufficient depth accuracy, long baseline requirements, and easy parameter drift in traditional stereo vision measurement. By introducing a non-orthogonal dual-axis turntable and a vision-guided laser aiming mechanism, it realizes autonomous, rapid, and accurate measurement of multiple measurement points within a large field of view, significantly improving the automation and reliability of measurements in complex environments. This method provides a feasible technical path and data support for engineering applications such as on-orbit antenna surface inspection and high-precision measurement of large structural components, and has strong practicality and promotional value.

[0013] 2. This invention integrates monocular vision and laser ranging technologies to construct a complementary measurement architecture, effectively improving the overall accuracy and reliability of the system. The vision system offers high resolution in planar measurements, while laser ranging directly provides high-precision depth distance information. This overcomes the inherent limitation of traditional pure vision measurements, where depth accuracy is significantly lower than lateral accuracy. The result achieves and maintains uniform sub-millimeter accuracy in the X, Y, and Z directions, ensuring comprehensive reliability of the measurement data.

[0014] 3. This invention forms a seamless closed loop from system calibration, visual guidance, automatic aiming to final calculation, reducing reliance on professional operators and manual intervention. It demonstrates good adaptability to complex on-orbit or industrial environments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the principle of the present invention; Figure 2 This is a schematic diagram of the overall structure of the full-field scanning measurement system of the present invention; Figure 3 This is a schematic diagram of the calibration field and control point layout of the present invention; Figure 4 This is a schematic diagram of image acquisition and feature point extraction according to the present invention; Figure 5 This is a schematic diagram illustrating the autonomous pointing of the target point in this invention; Figure 6 This is a flowchart of the method of the present invention; Figure 7 This is a system model diagram of the present invention; Figure 8 This is a schematic diagram of the system calibration method of the present invention; Figure 9 This is a schematic diagram of the triangle measurement method of the present invention; Figure 10 This is a schematic diagram of the calibration error histogram of the present invention; Figure 11 This is a schematic diagram of the measurement error histogram of the present invention; Figure 12 This is a schematic diagram of the spatial distribution of the measurement target points of the present invention. Detailed Implementation

[0016] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see the appendix Figure 1 - Appendix Figure 12 This invention provides a single-camera three-dimensional coordinate measurement method based on full-field ranging, comprising the following steps: S1. Construct a calibration field containing control points, capture images of the calibration field using a monocular camera, extract the image coordinates of the control points, perform camera calibration, and obtain the camera's intrinsic and extrinsic parameters. Furthermore, in S1, camera calibration specifically includes: The camera's intrinsic parameters, including focal length, principal point position, and distortion coefficient, are calibrated using a multi-image self-calibration bundle adjustment method. Based on the correspondence between the 3D coordinates of the control points and their image coordinates, the exterior orientation parameters of the camera relative to the world coordinate system are calculated. The exterior orientation parameters include the rotation matrix and the translation vector.

[0018] Specifically, a dedicated calibration field is first constructed, containing control points with known precise three-dimensional coordinates. A monocular camera fixed at the measurement station captures a series of images of this calibration field from multiple viewpoints. Advanced image processing algorithms automatically and accurately extract the coordinate positions of all control points on the image plane. Subsequently, the core intrinsic parameters of the camera, including focal length, principal point position, and critical lens distortion coefficients, are precisely solved using a multi-image self-calibration bundle adjustment method. Based on this, the system establishes collinearity condition equations according to the strict geometric relationship between the object-space three-dimensional coordinates of the control points in the world coordinate system and their corresponding coordinates on the image plane, thereby reliably calculating the camera's external orientation parameters relative to the world coordinate system and ultimately determining its precise rotational attitude and translational position in space. By precisely solving the camera's intrinsic parameters and reliably calculating the exterior orientation parameters, not only was clear image information obtained, but also accurate spatial angle perception capabilities were established. This process provides the necessary and reliable initial parameters for subsequent vision-guided laser aiming and 3D intersection calculations, significantly improving the system's absolute accuracy and overall stability in 3D coordinate measurement, and laying a solid foundation for achieving sub-millimeter-level measurement across the entire field of view.

[0019] S2. Control the laser rangefinder to aim at the control points in the calibration field through the non-orthogonal dual-axis turntable, record the turntable horizontal angle, pitch angle and laser ranging value corresponding to each control point, and perform full-field scanning ranging system calibration based on the three-dimensional coordinates of the control points, the turntable angle and the laser ranging value, and establish the coordinate transformation relationship between the turntable and the laser rangefinder. Furthermore, in S2, establishing the coordinate transformation relationship between the turntable and the laser rangefinder specifically includes: Establish transformation models between the world coordinate system, the horizontal turntable coordinate system, the pitch turntable coordinate system, and the laser rangefinder coordinate system; wherein, the transformation model describes the rotation and translation relationships from the world coordinate system to the horizontal turntable coordinate system, from the horizontal turntable coordinate system to the pitch turntable coordinate system, and from the pitch turntable coordinate system to the laser rangefinder coordinate system through parameters; Based on the transformation model, an error equation is constructed using the three-dimensional coordinates of the control points, the turntable angle, and the laser ranging value. The pose parameters in the transformation model are solved using the least squares optimization algorithm.

[0020] Specifically, the system controls a laser rangefinder mounted on a non-orthogonal dual-axis turntable to sequentially aim at multiple control points with known three-dimensional coordinates in the calibration field. During each aiming maneuver, the system simultaneously records the current horizontal rotation angle, pitch angle of the turntable, and the precise distance value returned by the laser rangefinder. By establishing a complete transformation chain from the world coordinate system, the horizontal turntable coordinate system, the pitch turntable coordinate system, to the laser rangefinder coordinate system, a parameterized model describing the rotation and translation relationships between these coordinate systems is constructed. Based on this model, error equations are constructed using the collected spatial coordinates of the control points, the turntable angles, and the distance measured. Finally, a least-squares optimization algorithm is used to accurately solve for all the pose parameters of the system.

[0021] Through multi-coordinate system modeling and parameter optimization, the angular displacement of the turntable and the linear displacement of the laser rangefinder are accurately correlated, forming a complete spatial measurement chain. This precise system calibration ensures spatial consistency between the laser beam direction and the ranging value, providing a reliable geometric basis for subsequent vision-guided automatic aiming and high-precision 3D coordinate calculation, significantly improving the accuracy and stability of the entire measurement system.

[0022] S3. During the measurement phase, the camera captures the target point, extracts the image coordinates of the target point, guides the turntable to rotate based on the camera calibration parameters, and enables the laser rangefinder to aim at the target point. The pointing error is reduced through iterative optimization, and the final turntable angle and laser range value are recorded. Furthermore, in S3, reducing the pointing error through iterative optimization specifically includes: Convert the image coordinates of the target point into a direction vector in the laser rangefinder coordinate system; The offset of the target point in the plane perpendicular to the laser emission direction in the coordinate system of the laser rangefinder is calculated as the pointing error; Based on the pointing error, the horizontal and vertical angles of the turntable are iteratively adjusted until the offset is minimized.

[0023] Specifically, the system captures an image of the target point using a calibrated monocular camera and accurately extracts its pixel coordinates. Using the pre-calibrated camera parameters, the system calculates the expected direction of the target point in the laser rangefinder coordinate system. This direction information is then converted into control commands to drive a non-orthogonal dual-axis turntable for initial positioning. The system calculates the offset of the laser beam from the target point in real time on a plane perpendicular to the emission direction, and iteratively adjusts the turntable's horizontal and vertical angles based on this error until the laser spot precisely coincides with the target point on the image sensor.

[0024] Through closed-loop adjustment of visual feedback and turntable control, the system can quickly eliminate aiming errors, ensuring that the laser beam is precisely aligned with the target point. This technology not only significantly improves measurement efficiency and avoids uncertainties caused by manual intervention, but more importantly, it provides highly reliable angle and distance observations for subsequent three-dimensional coordinate calculations, providing a key guarantee for achieving sub-millimeter precision measurements.

[0025] S4. Based on camera calibration parameters, coordinate transformation relationships, turntable rotation angle, and laser ranging values, a triangulation model is constructed, and the three-dimensional coordinates of the target point in the world coordinate system are calculated through an optimized algorithm.

[0026] Furthermore, in S4, constructing the triangulation model specifically includes: Based on the camera calibration parameters, the image coordinates of the target point are converted into the line-of-sight vector in the camera coordinate system; Based on the coordinate transformation relationship, the ranging starting point of the laser rangefinder is transformed to the camera coordinate system to obtain the baseline vector; By combining the laser rangefinder value, baseline vector, and line-of-sight vector, the three-dimensional coordinates of the target point in the camera coordinate system are solved using the law of cosines.

[0027] Specifically, a triangulation measurement model is constructed by comprehensively utilizing calibrated camera parameters, coordinate system transformation relationships, real-time acquired turntable angles, and laser rangefinder values. First, the image coordinates of the target point are transformed to the camera coordinate system using camera intrinsic and extrinsic parameters, forming a precise line-of-sight direction vector. Simultaneously, based on the calibrated coordinate transformation relationships, the starting point of the laser rangefinder is precisely transformed to the camera coordinate system, obtaining the baseline vector connecting the camera's optical center and the starting point. Then, combining the precise distance value provided by the laser rangefinder, a spatial triangle is constructed using the baseline vector and the line-of-sight direction vector as two sides, employing the law of cosines. Finally, the precise three-dimensional coordinates of the target point in the camera coordinate system are obtained.

[0028] By organically combining high-precision absolute distance information with accurate line-of-sight direction, the inherent limitation of insufficient depth measurement accuracy in traditional monocular vision is effectively overcome. This model achieves deep fusion and mutual verification of data from different sensors, enabling the system to obtain uniform and reliable sub-millimeter-level measurement accuracy in all directions even under short baseline conditions, providing an effective technical solution for precision 3D measurement over large spatial areas.

[0029] This embodiment also provides a single-camera three-dimensional coordinate measurement system based on full-field ranging, including: The calibration field is equipped with control points whose three-dimensional coordinates are known. A monocular camera is used to acquire images of the calibration field or the target point to be measured. Non-orthogonal dual-axis rotary table; The laser rangefinder is fixedly mounted on a dual-axis rotary table. The data processing unit is in communication connection with the camera, turntable, and laser rangefinder. The data processing unit is configured to: perform camera calibration to obtain the camera's intrinsic and extrinsic parameters; perform full-field scanning ranging system calibration to establish the coordinate transformation relationship between the turntable and the laser rangefinder; generate control commands based on camera images to guide the turntable to aim at the target point; and calculate the three-dimensional coordinates of the target point based on the principle of triangulation.

[0030] Specifically, the system first uses a calibration field to calibrate camera parameters, and then establishes a complete coordinate transformation relationship by controlling a turntable to scan calibration points. In actual measurement, the system visually identifies the target point and automatically guides the laser beam to point precisely. Finally, based on the principle of triangulation, it fuses visual direction and laser ranging data to accurately calculate the three-dimensional coordinates of the target point. This organic combination of hardware configuration and software algorithm enables the system to possess both the large field of view advantage of visual measurement and the high precision characteristics of laser ranging.

[0031] Example Device system composition: To verify the effectiveness of the proposed fusion measurement method, this embodiment constructs a full-field scanning measurement system including a camera, a laser rangefinder, and a dual-axis turntable. Its overall structure is as follows: Figure 2 As shown. All components of the system are mounted on an optical platform. The hardware used includes: an AVTGE4900 industrial camera (CMOS sensor resolution of...). The pixel size is DEN-10-500 laser rangefinder (typical ranging accuracy) Repeatability ) and the ARS-6036-GM high-precision turntable (angular resolution 0.01°, repeatability accuracy is °).

[0032] To achieve system calibration, this embodiment constructs a planar control field with dimensions of 6m × 3m, as follows: Figure 3 As shown. The control field contains 78 coded control points and 640 ordinary points. The three-dimensional coordinates of the control points were obtained using the VSTARS high-precision photogrammetry system.

[0033] Method and Flow: The measurement method proposed in this invention includes three stages: calibration, autonomous target point orientation, and three-dimensional coordinate calculation. The specific process is as follows: Figure 6 As shown, there are clear input and output relationships between each stage, forming a complete closed-loop measurement process.

[0034] Image acquisition and preprocessing: First, a monocular industrial camera captures multiple high-resolution images of the control field or measurement object, including control points and target points. The system then uses image processing algorithms to extract the image coordinates of the points and performs distortion correction and error removal to obtain the two-dimensional image information required for subsequent calibration and measurement.

[0035] System calibration: With the assistance of the control field, the camera's intrinsic parameters were first calibrated, obtaining the focal length, principal point position, and distortion coefficients. Then, using the collinearity condition equation and beam adjustment method, combined with the three-dimensional coordinates of the control points, the camera's exterior orientation parameters were calculated. Based on this, a dual-axis turntable was controlled to drive the laser rangefinder to aim at the control points point by point, recording the corresponding rotation angles and distance values. The relative pose relationship between the turntable and the rangefinder was then derived through least-squares optimization, thereby establishing a unified transformation model between the laser rangefinder, the turntable, and the world coordinate system.

[0036] Autonomous direction: After calibration, the system enters the target measurement phase. The camera acquires the image coordinates of the target point, and combined with the aforementioned calibration parameters, calculates the target point's orientation in the laser rangefinder coordinate system. Based on this orientation, the control system calculates the required horizontal and vertical angles and drives the dual-axis turntable to automatically adjust the laser beam direction. Through iterative optimization, the pointing error is continuously reduced until the laser point completely coincides with the target point in the image, thereby achieving precise aiming at the target point. Figure 5 As shown, the laser point is located at the center of the target point, verifying the accuracy and robustness of the visual guidance algorithm.

[0037] 3D coordinate calculation: After the target point is precisely aimed, the laser rangefinder outputs the spatial distance to the target point, the turntable provides the corresponding rotation angle, and the camera provides the line-of-sight direction. The system integrates these observations and constructs geometric constraint equations based on the triangulation principle of "baseline-distance-line-of-sight direction" to solve for the three-dimensional coordinates of the target point. Least-squares iterative optimization is then used to further reduce errors. Finally, high-precision spatial coordinates of the target point in the world coordinate system are obtained.

[0038] Through the above steps, the method of this invention forms a complete closed loop from image acquisition and system calibration to autonomous pointing and 3D calculation. Image processing provides initial information for autonomous pointing, autonomous pointing ensures the correspondence between laser ranging and target point position, and triangulation calculation ultimately outputs accurate 3D coordinates. Each link is interconnected, enabling the system to achieve autonomous, high-precision 3D measurement of a large range of target points under short baseline conditions.

[0039] The system calibration is specifically as follows: This system contains five rigidly connected coordinate systems, namely: the world coordinate system... Camera coordinate system Laser rangefinder coordinate system Horizontal turntable coordinate system and the pitch and turntable coordinate system ,like Figure 7 As shown. The transformation relationships between these coordinate systems are the foundation for realizing three-dimensional coordinate calculation.

[0040] The transformation relationships between coordinate systems are described using rotation matrices and translation vectors. Theoretically, each rigid body has 6 degrees of freedom in three-dimensional space. However, due to the existence of structural coupling in this system, reasonable constraints can be applied to the model to reduce the degrees of freedom. Specifically, let the rotation axis of the horizontal turntable be the z-axis, and its intersection with the xoy plane of the world coordinate system be the origin of the horizontal turntable coordinate system. By rotating the world coordinate system around the x-axis and y-axis, aligning its z-axis with the rotation axis of the turntable; then translating the world coordinate system in the x and y directions, aligning its origin with the origin of the horizontal turntable coordinate system. Coincidence. Based on this modeling method, coordinate system alignment can be achieved by retaining only the rotation angles and translations in two directions, requiring a total of 4 parameters. Describe the transformation relationship.

[0041] Using the same modeling principles, four parameters can be used. Describe the pose relationship between the pitch turntable and the horizontal turntable using 5 parameters. Describe the transformation between the laser rangefinder and the pitch turntable. A total of 13 parameters are required. Describe a full-field scanning ranging system.

[0042] According to the definition of a full-field scanning ranging system, it controls the horizontal... , looking up Aim at the spatial target point P from two angles and obtain the distance d from the ranging starting point to the target point. Since the laser emission direction is along the negative x-axis of the coordinate system, the target point's coordinates in the laser rangefinder coordinate system are as follows upon aiming: The coordinates are then transformed to the world coordinate system, as shown in formula (1): (1) in, For laser ranging coordinates; World coordinates; , It is the rotation matrix and translation vector between the laser ranging coordinate system and the pitch turntable coordinate system; It is the rotation matrix and translation vector between the pitch table coordinate system and the horizontal table coordinate system; It is the rotation matrix and translation vector between the horizontal turntable coordinate system and the world coordinate system; The horizontal and vertical turntables rotate separately. , The rotation matrix corresponding to the angle.

[0043] To address the complex pose calibration problem between the camera, turntable, and laser rangefinder, this embodiment proposes a step-by-step calibration strategy: A calibration control field is established, and first, the camera's intrinsic and extrinsic parameters are calibrated independently. Then, the dual turntable and laser rangefinder system are jointly modeled and calibrated. Based on these parameters, the image coordinates of the target point are obtained using a vision system. Combined with distance information provided by the full-field scanning rangefinder system, a baseline-distance-line-of-sight triangulation model is constructed, thereby achieving sub-millimeter accuracy in three-dimensional coordinate measurement under short baseline conditions. Figure 8 As shown.

[0044] Camera intrinsic parameters were calibrated using bundle adjustment. Based on this, using the collinearity condition equation and known intrinsic parameters, the rotation matrix and translation vector of the camera relative to the world coordinate system were inverted and solved by matching the image coordinates and 3D coordinates of the control points, yielding six exterior orientation parameters. .

[0045] Further control the laser rangefinder to sequentially aim at multiple target points with known three-dimensional coordinates in space, and record the turntable angles. , With laser ranging value d Using the transformation model established by formula (1), the implicit expression for the transformation of the target point from the laser rangefinder coordinate system to the world coordinate system can be obtained as shown in formula (2): ; (2) in, For the parameters to be estimated in the system, , For the turntable angle, d This is the distance measurement value.

[0046] The calculated values ​​are compared with the actual coordinates of the target point to construct the error vector (3).

[0047] (3) in, These are the actual coordinates of the target point; The calculated value is the coordinate of the target point; Formula (4) takes the partial derivative of the unknown parameter and uses the Taylor expansion formula to linearize the first term.

[0048] (4) in, These are the initial values ​​of the parameters; This is the linearization error composition term. Multiple target points can be written in matrix form: (5) (6); in, The true coordinates of the nth target point; It is the initial value Substitute the coordinates of the nth target point into formula (2); It is the linearization error synthesis term at the nth point; is the model function at the nth point; J is the Jacobian matrix of the model function with respect to the partial derivatives of each parameter; Let these be the increments of each parameter. Use the least squares method to find the optimal solution for the parameter increments: (7) The parameter update formula is: (8) in, The parameters are obtained from k iterations; for The parameters obtained from the next iteration. Through the above step-by-step calibration process, 13 parameters of the full-field scanning ranging system are obtained. From these, the exterior orientation parameters between the camera and the world coordinate system, the exterior orientation parameters between the horizontal coordinate system and the world coordinate system, and the exterior orientation parameters between the pitch stage and the horizontal stage can be derived. Exterior orientation parameters between the laser rangefinder and the pitch turntable .

[0049] Based on the above calibration results, the external orientation parameter relationship between the camera and the horizontal turntable can be further derived as shown in equation (9): (9) in , These are the rotation matrix and translation vector for the camera coordinate system and the horizontal turntable coordinate system, respectively.

[0050] Autonomous direction: The laser ranging system controls the direction of the laser beam through a dual-axis turntable. Its goal is to automatically adjust the turntable angle according to the specified three-dimensional coordinates so that the laser is accurately pointed at the target. The core is to solve the direction that the laser beam should have under the current system attitude from the estimated coordinates of the known target point.

[0051] By transforming equation (1), the target point can be transformed from the world coordinate system to the laser rangefinder coordinate system, as shown in equation (10): (10) The three-dimensional coordinates of the target point in the laser coordinate system are given by the current turntable angle. , The transformation relationship can be simplified into a function based on equation (10), determined jointly by the system calibration parameters and the system calibration parameters: (11) Since the laser rangefinder emits light along the negative direction of the X-axis of the laser rangefinder coordinate system, the target point should ideally fall on a straight line. Therefore, the pointing error is defined as the offset of the target point in the Y and Z directions of the laser coordinate system, as shown in equation (12).

[0052] (12) in, This refers to the pointing error; This is the calculated value of the component coordinates of the target point in the laser rangefinder coordinate system.

[0053] To find the optimal pointing angle, a nonlinear error function is constructed for iterative calculation. Ultimately, the optimal turning angle that minimizes the pointing error can be obtained, achieving high-precision automatic pointing of the target point.

[0054] Coordinate measurement: After calibrating the camera and the full-field scanning ranging system, and controlling the rangefinder to automatically aim at the target and complete the ranging, the three-dimensional spatial coordinates of the target point can be further solved based on the principle of baseline-distance-line-of-sight trigonometric intersection. For example... Figure 9 As shown.

[0055] The coordinates of the starting point of the distance measurement in the coordinate system of the laser rangefinder are: Its coordinates can be transformed to the camera coordinate system using the aforementioned equation (10), resulting in equation (13): (13) Furthermore, baseline vector Let it be represented as a vector from the camera to the starting point of the ranging, with a length of: (14) in, It transforms the starting point of the ranging measurement into coordinates in the camera coordinate system.

[0056] Baseline Direction vector : (15) Image points captured by the camera The coordinates are The vector that determines the corresponding spatial line of sight direction can be determined. : (16) Angle between baseline vector and camera line-of-sight vector It can be calculated using the dot product of two vectors: (17) The other two included angles and They can be represented as: (18) The target distance provided by the full-field scanning ranging system, along with the aforementioned angular relationship, allows us to determine the intersection point between the camera's line of sight and the target point using the law of cosines. The side length can then be calculated. Length: (19) Based on this, the unit vector of the camera's line of sight can be... Extend proportionally Thus, the three-dimensional coordinates of the target point in the camera coordinate system are obtained, and their expression is shown in equation (20): (20) Experimental results: The system calibration consisted of two stages: camera calibration and full-field scanning ranging system calibration. First, the camera intrinsic parameters were calibrated using a control point-based bundle adjustment method. A total of 65 images were acquired by capturing the control field from multiple perspectives, and the focal length, principal point position, and distortion parameters were solved using the least squares method. The calibration results are shown in Table 1.

[0057] Table 1. Camera Intrinsic Parameter Calibration Results Subsequently, the camera's exterior orientation parameters were calculated using the resection method, and the results are shown in Table 2: Table 2. Camera exterior orientation parameter calibration results Based on this, the extrinsic parameters of the ranging system were calibrated. The control turntable was sequentially aimed at 20 control points with known three-dimensional coordinates in the control field, and the corresponding horizontal rotation angle, pitch angle, and ranging value were recorded. The least squares method was used to invert the 13 extrinsic parameters of the system. The obtained parameters are shown in Table 3.

[0058] Table 3. Calibration results of the full-field scanning ranging system parameters Substitute the calibration results into the model function to calculate the back projection error of the three-dimensional coordinates of each target point, and statistically calculate the mean and standard deviation in the X, Y, and Z directions. The results are shown in Table 4.

[0059] Table 4 Statistical results of system calibration error To more intuitively illustrate the error characteristics, histograms of error distribution in each direction are plotted, such as... Figure 10 Show.

[0060] It can be seen that the errors in the X, Y, and Z directions all exhibit a good normal distribution, indicating that the systematic error is mainly affected by random noise and the systematic error is small.

[0061] After pointing is completed, the distance measurement value is recorded, and the three-dimensional coordinates of the target point are solved using a triangulation model. The results are compared with the actual coordinates provided by the VSTARS system, and the error statistics are shown in Table 5.

[0062] Table 5 Statistical results of three-dimensional coordinate measurement errors Error histogram as follows Figure 11 As shown in the measurement error histogram, it can be observed that the three-dimensional measurement error exhibits a near-normal distribution in the X, Y, and Z directions, further confirming that the system measurement error mainly originates from random disturbances, indicating that the system modeling accuracy is high.

[0063] Figure 12 The diagram illustrates the three-dimensional distribution of the target points in space. Blue "+" symbols represent the true coordinate values ​​obtained from the VSTARS system, while red "×" symbols represent the measured three-dimensional coordinate values ​​obtained by the system in this embodiment. The two symbols highly overlap, verifying the accuracy of the proposed triangulation model and system calibration.

[0064] Experimental results and accuracy analysis reveal that this invention proposes a high-precision measurement method integrating photogrammetry and laser ranging, which has been validated in a large-scale planar calibration field. This method constructs a parameterized model based on a non-orthogonal two-axis turntable system and achieves high-precision calibration through a large-scale planar calibration field. Visually guided laser aiming technology, combined with a proposed novel triangulation measurement algorithm, enables autonomous and accurate measurement of the target point's three-dimensional coordinates. Experiments show that the system can achieve autonomous multi-point measurement over a large field of view, achieving a three-dimensional measurement accuracy of 0.3 mm for a 6m × 3m antenna target at a measurement distance of 4 meters.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A single-camera three-dimensional coordinate measurement method based on full-field ranging, characterized in that, Includes the following steps: S1. Construct a calibration field containing control points, capture images of the calibration field using a monocular camera, extract the image coordinates of the control points, perform camera calibration, and obtain the camera's intrinsic and extrinsic parameters. S2. Control the laser rangefinder to aim at the control points in the calibration field through the non-orthogonal dual-axis turntable, record the turntable horizontal angle, pitch angle and laser ranging value corresponding to each control point, and perform full-field scanning ranging system calibration based on the three-dimensional coordinates of the control points, the turntable angle and the laser ranging value, and establish the coordinate transformation relationship between the turntable and the laser rangefinder. S3. During the measurement phase, the camera captures the target point, extracts the image coordinates of the target point, guides the turntable to rotate based on the camera calibration parameters, and enables the laser rangefinder to aim at the target point. The pointing error is reduced through iterative optimization, and the final turntable angle and laser ranging value are recorded. S4. Based on the camera calibration parameters, the coordinate transformation relationship, the turntable angle, and the laser ranging value, a triangulation model is constructed, and the three-dimensional coordinates of the target point in the world coordinate system are calculated through an optimization algorithm.

2. The single-camera three-dimensional coordinate measurement method based on full-field ranging according to claim 1, characterized in that, In step S1, camera calibration specifically includes: The camera's intrinsic parameters, including focal length, principal point position, and distortion coefficient, are calibrated using a multi-image self-calibration bundle adjustment method. Based on the correspondence between the three-dimensional coordinates of the control points and their image coordinates, the exterior orientation parameters of the camera relative to the world coordinate system are calculated. The exterior orientation parameters include rotation matrices and translation vectors.

3. The single-camera three-dimensional coordinate measurement method based on full-field ranging according to claim 1, characterized in that, In step S2, establishing the coordinate transformation relationship between the turntable and the laser rangefinder specifically includes: Establish transformation models between the world coordinate system, the horizontal turntable coordinate system, the pitch turntable coordinate system, and the laser rangefinder coordinate system; wherein, the transformation models describe the rotation and translation relationships between the world coordinate system and the horizontal turntable coordinate system, the horizontal turntable coordinate system and the pitch turntable coordinate system, and the pitch turntable coordinate system and the laser rangefinder coordinate system through parameters. Based on the aforementioned conversion model, an error equation is constructed using the three-dimensional coordinates of the control points, the turntable angle, and the laser ranging value. The pose parameters in the transformation model are solved using a least squares optimization algorithm.

4. The single-camera three-dimensional coordinate measurement method based on full-field ranging according to claim 1, characterized in that, In S3, reducing the pointing error through iterative optimization specifically includes: Convert the image coordinates of the target point into a direction vector in the laser rangefinder coordinate system; The offset of the target point in the plane perpendicular to the laser emission direction in the coordinate system of the laser rangefinder is calculated as the pointing error; Based on the pointing error, the horizontal and vertical angles of the turntable are iteratively adjusted until the offset is minimized.

5. The single-camera three-dimensional coordinate measurement method based on full-field ranging according to claim 1, characterized in that, In S4, constructing the triangulation model specifically includes: Based on the camera calibration parameters, the image coordinates of the target point are converted into the line-of-sight vector in the camera coordinate system; Based on the coordinate transformation relationship, the ranging starting point of the laser rangefinder is transformed to the camera coordinate system to obtain the baseline vector; By combining the laser ranging value, the baseline vector, and the line-of-sight vector, the three-dimensional coordinates of the target point in the camera coordinate system are solved using the law of cosines.

6. A single-camera three-dimensional coordinate measurement system based on full-field ranging, characterized in that, A single-camera three-dimensional coordinate measurement method based on full-field ranging, as described in any one of claims 1-5, comprises: The calibration field is equipped with control points whose three-dimensional coordinates are known. A monocular camera is used to acquire images of the calibration field or the target point to be measured. Non-orthogonal dual-axis rotary table; The laser rangefinder is fixedly mounted on the dual-axis turntable; The data processing unit is in communication connection with the camera, turntable, and laser rangefinder. The data processing unit is configured to: perform camera calibration to obtain the camera's intrinsic and extrinsic parameters; perform full-field scanning ranging system calibration to establish the coordinate transformation relationship between the turntable and the laser rangefinder; generate control commands based on camera images to guide the turntable to aim at the target point; and calculate the three-dimensional coordinates of the target point based on the principle of triangulation.

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