Research And Application Of Non-contact Measurement Method Of Zokor Skull Shape Index Based On Three-dimensional Point Cloud Data

The shape index of the zokor skull is an important basis for identifying the age composition of the zokor.The traditional measurement of the shape index of the zokor skull is directly measured manually by using a vernier caliper.This way not only is a large workload,but also cannot avoid direct contact with the skull specimen during measurement,which will cause different degrees of damage to the specimen and affect subsequent research and use.At the same time,in this process,measurement errors occur,which reduces the accuracy of the measurement results.For the above problem,this thesis takes zokor skull specimens of different genders and ages as the research object.Using three-dimensional laser scanning technology,the method and application of non-contact measurement of zokor skull shape indicators based on three-dimensional point cloud data are studied.The main research contents are as follows:(1)Aiming at the problems of under-segmentation and over-segmentation caused by traditional point cloud segmentation algorithm for point cloud data of zokor skull with complex background,a three-dimensional point cloud segmentation method based on normal estimation is proposed.First,improve the random sampling consistency(RANSAC)algorithm,and introduce normal constraints to remove most of the plane point clouds in the background,so that the target point cloud and the background point cloud are separated.Then the target point cloud is efficiently and accurately extracted from the remaining point cloud by Euclidean clustering segmentation.(2)Aiming at the problem of inaccurate recognition of measurement points caused by incomplete cloud contours of the dorsal and ventral view of the zokor skull obtained after segmentation,a bounding box-based measurement point recognition and extraction algorithm was proposed.First,the dorsal view and ventral view are projected to a two-dimensional plane,and the boundary contour is extracted from the point cloud of the dorsal view.Then,on the basis of the OBB bounding box and the convex hull of the boundary contour,the measurement points of the zokor skull are identified,and the six measurement points of the total length of the skull,the zygomatic breadth and the greatest mastoid breadth are extracted.Finally,compared with the actual measured value of the zokor skull index,the average relative error of the rear view index based on the two-dimensional projection plane is less than 2.5%.(3)Aiming at the problem that the distortion of the cloud features of the ventral view projected to the two-dimensional plane causes the measurement of the three-dimensional index based on the ventral view,a method of non-contact measurement of the shape index of the zokor skull based on the three-dimensional reconstruction model is proposed.First,use a method based on the combination of FPFH features and improved ICP algorithm to register the dorsal view and ventral view clouds.Then,greedy projection triangulation algorithm is used to reconstruct the zokor skull model.Finally the shape indexes such as the greatest length of the nasals,the length of the diastema,and the length of tooth row are extracted.The average relative error of the shape index detection based on the 3D reconstruction model is less than 2%,and the error is smaller.(4)The random forest algorithm was used to analyze the three indexes of the total length of the skull,the zygomatic breadth and the greatest mastoid breadth based on two-dimensional projection plane and three-dimensional reconstruction model respectively,and the total length of the skull,the zygomatic breadth,the greatest mastoid breadth,the condy lobasal length,the greatest length of the nasals,the length of tooth row,the length of the diastema seven indicators to establish age classification model.The analysis of the results showed that,the accuracy of the first model is 83.3%,the accuracy of the second model is 91.6%,and the accuracy of the third model is 100%.However,the calculation time of the first model is shorter than that of the latter two,and it has certain advantages in calculation speed.In practical applications,according to different conditions and requirements,different shape indicators and non-contact measurement methods can be selected to identify the age of the zokor.