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Hu’s calibration method. Two cameras and one laser level are placed in front of the 3D calibration board. The laser level generates two laser planes that are vertical to each other. Two crossing lines are generated from the laser planes on the 3D calibration board. The calibration point is the crossing point between two crossing lines. The 3D coordinates of the measurement point are reconstructed by the calibration results of two cameras.
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Equation construction of a laser plane demonstrates a remarkable importance for vision measurement systems based on the structured light. Here we create a simple 1D target with a cone at the bottom and a checkered pattern on the top to calibrate the equation of the laser plane in the view field of a camera. A group of 2D coordinates of the intersec...
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A robot-based three-dimensional (3D) measurement system is presented. In the presented system, a structured light vision sensor is mounted on the arm of an industrial robot. Measurement accuracy is one of the most important aspects of any 3D measurement system. To improve the measuring accuracy of the structured light vision sensor, a novel sensor...
Citations
... Due to the advantages of fast response, non-contact, high flexibility and abundant * Author to whom any correspondence should be addressed. perceptual information, the technology has been applied in the fields of nondestructive testing of industrial products, robot visual guidance, 3D target reconstruction and military industry [1][2][3]. Taking the automatic detection of abnormal state of steel coil strapping in iron and steel production enterprises as an example, the strapping state of steel coil is an auxiliary process for safe hoisting. It is very important to detect abnormal strapping in real time, which can avoid the problem of steel coil explosion caused by looseness or tear of steel coil strapping, affecting production efficiency and transportation quality. ...
In order to accurately detect the abnormal looseness of strapping in the process of steel coil hoisting, an accurate detection method of strapping abnormality based on CCD structured light active imaging is proposed. Firstly, a maximum entropy laser stripe automatic segmentation model integrating multi-scale saliency features is constructed. With the help of saliency detection model, the purpose is to reduce the interference of the environment to the laser stripe and highlight the distinguishability between the stripe and the background. Then, the maximum entropy is used to segment the fused saliency features and accurately extract the stripe contour. Finally, the stripe normal field is obtained by calculating the stripe gradient vector, the stripe center line is extracted based on the stripe distribution normal direction, and the abnormal strapping is recognized online according to the stripe center. Experiments show that the proposed method is effective in terms of detection accuracy and time efficiency, and has certain engineering application value.
... The main objective of the calibration is to find all the transformsT ⊂ {T ij , T wi } where T ij ∈T if the laser l j is visible by the camera c i . In order to calibrate the laser frames respect to the observing cameras, most methods use planar checkboards [12] or even 3D calibration boards [20], placed such that so that the laser lines cut across squares of the checkboard. The drawacks to this type of calibrations is that the intrinsic parameters of the cameras have to be estimated with high accuracy, especially in the case of Scheimpflug cameras. ...
This paper describes a method for calibrating multi camera and multi laser 3D triangulation systems, particularly for those using Scheimpflug adapters. Under this configuration, the focus plane of the camera is located at the laser plane, making it difficult to use traditional calibration methods, such as chessboard pattern-based strategies. Our method uses a conical calibration object whose intersections with the laser planes generate stepped line patterns that can be used to calculate the camera-laser homographies. The calibration object has been designed to calibrate scanners for revolving surfaces, but it can be easily extended to linear setups. The experiments carried out show that the proposed system has a precision of 0.1 mm
... Although some camera intrinsic matrix-free methods are proposed [16][17][18][19][20], the auxiliary devices such as 3D chessboard boxes [16][17][18][19] and guide rails [20] that have to be fixed on the ground are used in the calibration process. The need for such auxiliary devices makes the camera intrinsic matrix-free methods [16][17][18][19][20] impractical for on-site calibration. ...
... Although some camera intrinsic matrix-free methods are proposed [16][17][18][19][20], the auxiliary devices such as 3D chessboard boxes [16][17][18][19] and guide rails [20] that have to be fixed on the ground are used in the calibration process. The need for such auxiliary devices makes the camera intrinsic matrix-free methods [16][17][18][19][20] impractical for on-site calibration. ...
... Although some camera intrinsic matrix-free methods are proposed [16][17][18][19][20], the auxiliary devices such as 3D chessboard boxes [16][17][18][19] and guide rails [20] that have to be fixed on the ground are used in the calibration process. The need for such auxiliary devices makes the camera intrinsic matrix-free methods [16][17][18][19][20] impractical for on-site calibration. ...
Laser triangulation sensors (LTS) are widely used to acquire depth information in industrial applications. However, the parameters of the components, e.g., the camera, of the off-the-shelf LTS are typically unknown. This makes it difficult to recalibrate the degenerated LTS devices during regular maintenance operations. In this paper, a novel one-dimensional target-based camera intrinsic matrix-free LTS calibration method is proposed. In contrast to conventional methods that calibrate the LTS based on the precise camera intrinsic matrix, we formulate the LTS calibration as an optimization problem taking all parameters of the LTS into account, simultaneously. In this way, many pairs of the camera intrinsic matrix and the equation of the laser plane can be solved and different pairs of parameters are equivalent for displacement measurement. A closed-form solution of the position of the one-dimensional target is proposed to make the parameters of the LTS optimizable. The results of simulations and experiments show that the proposed method can calibrate the LTS without knowing the camera intrinsic matrix. In addition, the proposed approach significantly improves the displacement measurement precision of the LTS after calibration. In conclusion, the proposed method proved that the precise camera intrinsic matrix is not the necessary condition for LTS displacement measurement.
... In addition, the camera was used to obtain color information of the object and fused with the point cloud. Compared with the method using single checkerboard pattern, Xu [29,30] put forward a novel calibration method with combined measurement target. Xu extracted annular orbit of the intersection feature points and intersection points between the laser plane and the centers with 1D target with a checkered pattern and a 3D calibration board [29]. ...
... Compared with the method using single checkerboard pattern, Xu [29,30] put forward a novel calibration method with combined measurement target. Xu extracted annular orbit of the intersection feature points and intersection points between the laser plane and the centers with 1D target with a checkered pattern and a 3D calibration board [29]. In Reference [30], Xu adopted two checkerboards as reference planes. ...
Line structured light system has made rapid progress in recent years owing to the improvement of camera resolution and image processing technology. The calibration of line structured light system and centerline extraction affect the imaging quality. Hence, numerous innovations have occurred in both line structured light calibration methods and centerline extraction methods. In this paper, key technologies of line structured light calibration are reviewed. Major calibration methods such as vector cross product, linear equation solution, cross ratio invariance, vanishing points and lines, Plücker matrix are analyzed and compared in detail. Methods of centerline extraction are analyzed furthermore. This review concludes with a discussion of the future development of line structured light system, providing a good reference for researchers.
... Zagorchev and Goshtasby utilized a dual frame structure to estimate the 3D plane of a moving slit laser, which corresponds to the camera coordinates [18]. Similarly, two or three mutually perpendicular planes provide enough information to estimate the position of the moving slit laser [19][20][21]. Consequently, the 3D positions of the cast features on a scanned object can be determined by a calibrated camera. ...
This study proposes an automatic three-dimensional (3D) color shape measurement system based on images recorded by a stereo camera. The system, comprising several off-the-shelf components, is cost-effective yet capable of obtaining quality color 3D objects. In the proposed system, a turntable carrying a checkerboard is used to assist the simultaneous calibration of the stereo camera and the turntable. A slit laser is driven to swing forward and backward for generating stripes on test objects. The stereo images are collected and analyzed for obtaining matching pixels, and, consequently, the 3D point coordinates based on epipolar geometry are obtained. Screened Poisson reconstruction is utilized to integrate and smooth the scanned surfaces. With additional color images from the same camera, several multi-view texturing methods are benchmarked. We concluded that our proposed system can successfully and automatically reconstruct quality 3D color shapes of various objects.
... Then, the parameters of the camera and the pose of the laser projector are calibrated by the planar references. Xu et al. [14] introduces a method to calibrate the laser plane by a 1D reference with a mark on its top. The intersection point of the three planes of the 3D reference is defined as the origin of the world-coordinatesystem. ...
A reconstruction approach is presented with a random laser plane and a cylindrical reference. A semi-cylinder reference with the known diameter is designed as the cylindrical-coordinate-system. The optimization function is provided by the parameterized re-projection errors of the feature points on the cylindrical reference, the laser intersection points on the cylindrical reference and the object. The reconstruction approach is tested and analyzed by contrasting the difference between the reconstructed value and the true value of the vernier caliper. The means of the root mean squares (RMS) of the optimization and initialization are 1.36 mm and 1.44 mm. The experiments indicate that the approach with the random laser plane and the cylindrical reference is a reliable method for the 3D reconstruction in the active vision system with the planar structured light. OAPA
... Therefore, the camera calibration has also attracted researchers to improve the 3D reconstruction accuracy. At present, the calibration methods are mainly divided into 1D calibration 25,26 , 2D calibration [27][28][29] and 3D calibration 30 . The 1D calibration reference is simple in structure and easy to be manufactured, but the calibration accuracy is the lowest due to the lack of information on the 1D reference. ...
An optimization method to reconstruct the object profile is performed by using a flexible laser plane and bi-planar references. The bi-planar references are considered as flexible benchmarks to realize the transforms among two world coordinate systems on the bi-planar references, the camera coordinate system and the image coordinate system. The laser plane is confirmed by the intersection points between the bi-planar references and laser plane. The 3D camera coordinates of the intersection points between the laser plane and a measured object are initially reconstructed by the image coordinates of the intersection points, the intrinsic parameter matrix and the laser plane. Meanwhile, an optimization function is designed by the parameterized differences of the reconstruction distances with the help of a target with eight markers, and the parameterized reprojection errors of feature points on the bi-planar references. The reconstruction method with the bi-planar references is evaluated by the difference comparisons between true distances and standard distances. The mean of the reconstruction errors of the initial method is 1.01 mm. Moreover, the mean of the reconstruction errors of the optimization method is 0.93 mm. Therefore, the optimization method with the bi-planar references has great application prospects in the profile reconstruction.
... Active vision with the structured light is considered as one of the most promising approach for the optical detection and profile reconstruction, where the line-structured light is attractive due to the high accuracy and efficiency [1][2][3][4][5][6][7][8] . In the vision-based measurement, the calibration methods with the 1D references 9,10 , 2D references [11][12][13][14][15][16] or 3D references [17][18][19] are previously studied to construct the projection geometry of a camera in the measurement. The 1D-reference-based calibration was proposed by Zhang 9 for the first time. ...
A 3D reconstruction method is presented for the laser projective point of a laser line, which is located by an orthogonal reference. The laser line is initially expressed by the Plücker matrix generated from two random points on the line and then transformed to the dual Plücker matrix representation. The initial solution of the 3D laser point is obtained by the non-homogeneous linear equations, which are derived from the projection geometry of the 3D feature point on the reference and the 3D laser point on the laser line represented by the dual Plücker matrix. The optimization function is constructed by minimizing the sums of the re-projection errors of the reference points and the laser point. The average absolute error of the initial solution is 1.07 mm while the one of the optimization solution is 1.01 mm. The average relative error of the initial solution is 4.14% while the one of the optimization solution is 3.86%. Thus, the optimization reconstruction of the projective point contributes the accuracy and the prospect in the vision-based inspection fields.
... Nevertheless, the previous work focuses on two projective laser lines on two fixed planes or many captured laser lines in the camera coordinate system. Recently, the method of the distance between the origin point and feature points is presented to solve the laser plane equation, by which the laser plane is directly calibrated in the world coordinate system [7]. In this paper, we propose a calibration approach by the constant distance from the coordinate axis to the feature points on the laser plane, which takes the advantages of both high accuracy and global results in the world coordinate system. ...
... The world coordinates of the reconstructed feature points can be derived from the laser plane coefficients and image coordinates of the feature points as [7] ( Therefore, we construct the difference square between the measured length of the target and the reconstructed distance from the feature points to the ox axis by ...
... The distances from the right end of the cylinder to the yoz plane in the experiments are 60 mm, 120 mm, 180 mm, and 240 mm, respectively. 20 feature points are extracted for the comparisons with the point-origin method that takes the distance from the feature points to the origin as the optimization object [7]. ...
Laser plane solution is one of the key points in optical metrology. A solution method is presented to calibrate a laser plane by optimizing the difference between the measured length of the target and the reconstructed length with the arguments of the equation coefficients of the laser plane. An experimental study of the reconstruction errors of the developed method shows a higher precision compared with the point-origin method in the calibration of a laser plane.
... In the main improvements of the calibration target, a crenellated gauge object with calibration points [11], a plane with a triangular hole [12], a target moving on a plane [14], a 3D calibration board with a height gauge [13], and with a 1D target [15] are reported to achieve accurate laser plane calibration. As complicated setups are required in the calibrations adopting 3D and 1D targets, a 2D target is reasonable for calibrating a laser plane. ...
A calibration method adopting Plücker matrices is proposed to explore the laser plane in a structured light measurement. The calibration model establishes the geometrical relationship among the camera, 2D target, and laser plane. The laser plane is constructed by multiple Plücker matrices of the dual 3D crossing lines between the laser plane and target planes in the camera coordinate system. Moreover, the validity of this calibration method is experimentally analyzed through the impact factors of noise magnitude and number of images. The mean errors of three directional angles of the normal vector to the laser plane are − 0.174 ° , 0.170°, and − 0.022 ° , respectively. The variances of the errors of three directional angles are 0.069°, 0.046°, and 0.160°, respectively. The maximal absolute errors of three directional angles are 1.362°, 1.351°, and 1.347°, respectively. The experiments prove that the calibration method is available to provide an accurate calibration for the laser plane.
