Research And Application Of The Vertex Normal Vector Estimation Methods For Discrete Triangular Mesh Model

Triangular mesh model is an important approximate form for free-form surface in CAD/CAM system. It is widely used in reverse engineering, rapid prototyping and CNC machining as its fast flexibility and topological flexibility. The vertex normal vector of triangular mesh model as a bias data for surface offset, surface reconstruction and surface blending, which always acts as the known condition. Vertex normal vector estimation accuracy will directly influence the accuracy of these processing results. Therefore, it is necessary to improve the estimation accuracy of triangular mesh vertex normal vector.In order to provide more accurate and reliable vertex normal vector estimation information, the estimate precision of vertex normal vector is studied in this thesis, which plays an import role in reverse engineering, rapid prototyping, CNC machining and other industrial fields. Some details investigated in this paper are stated as follows:(1) The structure and logical rules of the STL file are investigated and the common errors and the solution in STL files are analyzed in this thesis. On the basis of establishing reasonable data structure of STL model, a new topology reconstruction algorithm based on the first order neighbor triangle of the vertex is developed, which can improve the search capabilities of the vertex’s neighbor triangle information and promote efficiency on vertex normal vector estimation.(2) A rapid extraction algorithm for triangular mesh boundary vertex is proposed based on the new topology reconstruction.(3) By analyzing the limitation of current vertex normal vector estimation methods, a new estimation method of triangular mesh vertex normal vector is proposed, which chooses the shape and the gravity as the weight of each triangle patches normal in the first order neighbor triangle of the vertex. Take the spherical, ellipsoid and paraboloid as the research object, analyse the estimate precision of vertex normal vector. And the method of calculation is proved to be more accurate and reasonable by the examples results and error analyses.(4) The application of vertex normal vector to surface offset is investigated, analyzed the interference checking and corrected based on vertex offset, and the interference based on vertex offset is analyzed. Then the methods to checking and correct the interference are introduced. Taking the spherical, ellipsoid and paraboliod as the research object, then the application of the vertex normal vector to curved surface offset is investigated. Example parts are designed and the results are analyzed to demonstrate that new algorithm is more accurate and more robust than other methods, and also it can show value in the actual engineering.