Research On Key Technologies Of Photogrammetry For Large-Scale Equipment And Its Application In Port Machinery

At present,there is an urgent need for efficient and fast measurement technology in monitoring and structural optimization of large-scale equipment.The research shows that photogrammetry has non-contact,high efficiency,low cost and high measurement accuracy,but it is difficult to be widely used in large-scale equipment.Because largescale equipment are with large size,lack of surface texture,unable to stick markers and without enough measurement time.This paper summarizes the characteristics and limitations of large-scale equipment,studies the key technologies of photogrammetric method applied in the measurement process of large-scale equipment,and puts forward the camera calibration method,pose estimation method,geometric dimension measurement method and the calculation method of the center of special cylindrical components for large-scale equipment.The experimental results show that it can meet the engineering needs.The main work includes:(1)Aiming at the difficulty of establishing calibration field for large-scale equipment in field operation,a two-step calibration method is proposed.Firstly,the radial distortion coefficient of the camera is calibrated by checkerboard method.Sub pixel image location method based on optical distortion and error probability is proposed to solve the problem of increasing image location error of large-scale equipment control points.The effective focal length of each photograph is calibrated and calculated accurately in the measurement field.The experimental results of six scenarios show that the improved effective focal length calibration method proposed in this paper has a significant effect.When the distance is 63.21 m from the portal crane,the measurement accuracy of the algorithm is improved by 98.84% compared with the traditional method.(2)Aiming at the problems of large-scale equipment,such as large tilt of shooting angle,few control points and large change of photo depth,a method of establishing objective function based on depth information weighting and projection operator to solve the optimal camera pose is proposed.At the same time,the multi-solution problem in pose estimation is solved through geometric relationship.The simulation results show that the method is superior to other commonly used methods.The experimental results of gantry crane show that the relative errors of camera position and attitude angle are 6.77e-6 and 0.455% respectively when the control points are coplanar,and 4.67e-6 and 0.373% when the control points are not coplanar,respectively.It shows that the method can work well under Limited conditions.Accurate and stable camera pose estimation.(3)Aiming at the problem that large-scale equipment lacking texture is difficult to match homonymous points,a measurement method of contour constraint and image edge extraction is proposed.This method effectively utilizes the known conditions of the geometric characteristics of large-scale equipment,establishes errors by combining the geometric contour constraints of the measured object with the edge of the image,and solves the precise values of the geometric parameters of the measured object by iteration.In this process,the LSD straight line extraction algorithm is improved according to the characteristics of mechanical equipment contour,which solves the problem that the original LSD algorithm can not extract straight lines and curves with obtuse angles.The experimental results of grab ship unloader used in port show that the relative error is better than 1/5000 under the measurement distance of 112.49 m,and the continuous geometric dimensions of the measured object can be obtained.(4)Aiming at the problem that some cylindrical parts of large-scale equipment can not directly measure the center,but can only indirectly measure the stiffeners,a composite weighted central precise location algorithm based on optical distortion and point selection is proposed.This method fits the spatial circle by weighting the optical distortion in the process of obtaining the measured data of stiffeners,and then fits the center and radius of the cylinder accurately by weighting the deviations of the fitting centers of different data in the process of selecting points and combining.Compared with reliable measurements,the accuracy error of the fitting radius is 0.15%.The experimental results of portal crane show that the relative error of the algorithm is less than 2.5,and the radius deviation is less than 5 mm,compared with the calculation of circle center and radius by manual labeling.