Research On Mosaic Method Of Large Objects Three-dimensional Measurement Based On Unmarked Points

With its excellent advantages,structured light 3D measurement technology is widely used in industrial production and manufacturing fields such as industrial rapid measurement and reverse engineering.With the rapid development of modern industrial manufacturing,the demand for large object such as aircraft and engine blades,automobiles and ships,three-dimensional measurement of large object has become an important problem and development trend in industrial manufacturing.The increasing in measurement area,the complexity of the measurement surface,and the increased measurement accuracy requirements make traditional 3D measurement methods difficult to meet the measurement requirements of modern industrial manufacturing.Therefore,the three-dimensional splicing measurement method of structured light objects has a important significance for obtaining complete three-dimensional shape information.In the actual measurement process,the amount of 3D point cloud data acquired by3 D measurement technology based on structured light huge and accompanied by noise.At the same time,due to the large size of the measured object,a single measurement cannot meet the requirements of the complete 3D shape measurement,so it is measured from different angles.In this paper,the topological structure of the acquired disordered point cloud data is firstly established,then the Filter processing and the streamlining operation are performed,and finally the three-dimensional measurement data from different angles are spliced.The main research contents of this paper are divided into the following points.(1)The construction of intersecting axis measurement systems is set up,then camera calibration and calibration of system geometry parameters are calibrated.Then,the periodic fluttering on the reference plane is corrected,and the phase information of the surface of the complex object is solved by the theoretical model of temporal phase unwrapping method based on the fringe cycle correction.(2)Aimed at the problem of 3D point cloud data obtained by three-dimensional measurement of complex large objects is huge and accompanied by noise,it is necessary to establish a topological structure for the disordered point cloud data and filter operations is used on disordered point cloud.An adaptive grid method is proposedto streamline the point cloud data,which provides a powerful guarantee for the processing speed and accuracy of the subsequent 3D reconstruction and 3D stitching.(3)Since the single-format is limited by the measurement range and visual occlusion,it is impossible to obtain a complete three-dimensional shape of a large object in one measurement,so the image needs to be spliced.In this paper,the FPFH feature is used to detect the key points and search for the corresponding key points,the Ransac algorithm is used to remove the pair of mismatched points and set a certain threshold to retain the corresponding pairs of high-quality feature points.(4)Then using the precision rotating platform,vertical line angle centering method is used to determine the center of the rotation axis,and the error analysis and optimization of the three-dimensional stitching results are carried out.Therefore,a three-dimensional splicing method for large objects based on unmarked points is proposed,this method does not require the sticking of any marker points,it avoids the inaccurate problem of the rotation axis coordinates when using the turntable method for splicing measurement,and avoids the shortage of long calculation time because large amount of data is caused by the ICP algorithm when performing point cloud registration,which provides the possibility of real-time online detection.(5)Finally,a three-dimensional measurement experiment was performed on the complex large plaster image.The experimental results show that the three-dimensional splicing method of large objects based on unmarked points can effectively complete the 3D splicing measurement of complex large objects,and the splicing effect is good.And using a rectangular standard block as the measurement object,this method is used for splicing measurement and analysis measurement accuracy,the height accuracy is0.146 mm,and the splicing precision is 0.193 mm.