Data Partition And Model Reconstruction Of Reverse Engineering

This paper is mainly focused on data segmentation and model reconstruction problems in Reverse Engineering fields,The main contents include Sharp Featurebased quadrilateral domain extraction from a mesh model,connectivity between multiple B-spline surfaces,fast algorithm for fitting multiple B-spline surfaces on model with arbitrary topology,setting up a hierarchically structured constraintbased data model and binary cubic interpolation of splines with C² connectivity for type-â…¡triangulations on rectangular domain.First this paper reviews the application of reverse engineering and main processes of reverse engineering are discussed and problems on data segmentation and model reconstruction are analyzed in detail.To segment a mesh data and extract quadrilateral domains,we take use of sharp features of the mesh.The procedure starts from an optimal triangulation based on the network of sharp features,and a method named idea angle reservation is provided to pre-treat the triangulated domains.Later,all triangles are converted into quadrilaterals under some defined rules for definite type of connected triangular patches.For unorganized points or mesh without any sharp feature,our software system named CTMod provides a user-interface for defining sharp features and creating boundaries.Comparing with manual method,our algorithm increases the partition speed greatly;Comparing with methods based on mesh simplification,our algorithm get fewer reasonable patches over sharp feature.The connectivity between surfaces is still one important problem for model reconstruction in the realm.After analyzing relationship between surfaces around normal corner or extraordinary corner,we present an algorithrn to setup combined connectivity which means G¹ connectivity is maintained near the extraordinary corner and G^k-2 connectivity is achieved in the left.In the implementation of our algorithm,linear constraints on check points are added avoiding deal with non-linear problems.While dealing with complex module reconstruction, we should face to calculate a quantity of control points,and solve a huge linear equation problem.For the reason of deficiency on data sampling and features of spline base,the coefficient matrix of the linear equations often turns to be ill.In order to get steady solution we present a fast algorithm based on dividing and controlling technique,this method can quickly solve the problem without loosing precision.The author also studies the problems of smooth connection between surfaces in type-â…¡triangulations using B-Net method.Spline surfaces have a great application on CAD,till now C-connectivity between surfaces are only related to high degree splines.In this chapter we discussed the existence,uniqueness and approximation degree of binary cubic splines with C² connectivity for type-â…¡triangulations on rectangular domain,and we also gave a analysis of approximation of the interpolation splines.A hierarchically structured and constraint-based data model for intuitive and precise solid modeling is also presented.The data model is based on a hybrid BREP/CSG strueture.Constraints are embedded in the solid model and are organized at hierarchical levels as feature constraints among internal feature elements,part constraints among internal features and assembly constraints between individual parts The proposed data model permits modeling on different levels and works well especially for virt(?)al prototype on a VR environment.At last the author developed a small reverse engineering software system to show the presented algorithms work well.Choosing VC++ as the developing language and making use of MFC framework and OpenGL techniques,the system can use point cloud,point contour and mesh data as input files,and processed models can be output in OBJ format.A Curve rendering technique is also presented.