Abstract: The representation method of heterogeneous material information is one of the key technologies of heterogeneous object modeling, but almost all the existing methods cannot represent non-uniform rational B-spline (NURBS) entity. According to the characteristics of NURBS, a novel data structure, named NURBS material data structure, is proposed, in which the geometrical coordinates, weights and material coordinates of NURBS heterogeneous objects can be represented simultaneously. Based on this data structure, both direct representation method and inverse construction method of heterogeneous NURBS objects are introduced. In the direct representation method, three forms of NURBS heterogeneous objects are introduced by giving the geometry and material information of control points, among which the homogeneous coordinates form is employed for its brevity and easy programming. In the inverse construction method, continuous heterogeneous curves and surfaces can be obtained by interpolating discrete points and curves with specified material information. Some examples are given to show the effectiveness of the proposed methods. Keywords: heterogeneous object; non-uniform rational B-spline (NURBS); material data structure; direct representation method; inverse construction method
This paper deals with the background and significance of working on heterogeneous objects modeling and briefly introduces the architecture of ACIS and HOOPS and their corresponding functional modules. Based on inverse-distance weighting algorithm to determine the material composition within the object, the general approach to modeling the heterogeneous objects by using ACIS and HOOPS is introduced and demonstrated via some simple examples.
According to the requirement of heterogeneous object modeling in additive manufacturing (AM), the Non-Uniform Rational B-Spline (NURBS) method has been applied to the digital representation of heterogeneous object in this paper. By putting forward the NURBS material data structure and establishing heterogeneous NURBS object model, the accurate mathematical unified representation of analytical and free heterogeneous objects have been realized. With the inverse modeling of heterogeneous NURBS objects, the geometry and material distribution can be better designed to meet the actual needs. Radical Basis Function (RBF) method based on global surface reconstruction and the tensor product surface interpolation method are combined to RBF-NURBS inverse construction method. The geometric and/or material information of regular mesh points is obtained by RBF interpolation of scattered data, and the heterogeneous NURBS surface or object model is obtained by tensor product interpolation. The examples have shown that the heterogeneous objects fitting to scattered data points can be generated effectively by the inverse construction methods in this paper and 3D CAD models for additive manufacturing can be provided.
This paper presents a CAD system, termed as HO-CAD, for heterogeneous object modeling based on ACIS and HOOPS. The HO-CAD system is composed of four modules which are used for creation, representation and visualization of geometry and material composition information, respectively. In the process of the software designing and programming, such considerations as interactivity, open ability, integrating ability, independence and extensibility are taken by combining the geometric modeling function of ACIS with rendering and visualization functions of HOOPS in the environment of VC++ 6.0. The architectures of ACIS and HOOPS as well as the implementation of three key modules, i.e. interactive module, modeling module, and data management module, are briefly introduced. At last, some examples of heterogeneous objects modeled by this system are illustrated.
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