Duplex fitting of zero-level and offset surfaces

Offset surfaces play an important role in various CAD/CAM applications. Given a set of oriented points, we propose a hierarchical method in this paper to fit both the zero-level surface and its offset surface with a single implicit function. The implicit function is formed by compactly supported radial basis functions (CSRBFs). Different from other existing methods in literature, our approach reconstructs an implicit function which interpolates or approximates both the zero-level surface and the offset surface of a given point set, simultaneously. Employing locally supported functions leads to an efficient computational procedure, while the coarse-to-fine hierarchy makes our approach insensitive to the density of scattered data and allows us to reconstruct large parts of missing data. The performance of our method is demonstrated by a number of examples and the application of adaptive slicing hollowed models in rapid prototyping.     

Inferring Solids Composed of Linear and Quadratic Surfaces from Incomplete Three Views

This paper introduces an automatically reasoning system for inferring linear and quadratic surface solids from incomplete three views,The method is based on human reasoning .Initially,quadratic surface primitives are fecognized and extracted according to possibility computation.Then ,the data relative only to quadratic surface primitives are femoved from the given three views and polyhedrons are constructed based on the remaining data.The final solid is constructed by assembling all the generated quadratic surface primitives and the polyhedrons.The system has been implemented in C and OpenGL on Windows NT.The constructed solid can be observed at any angle by rotating it using the keyboard.Many examples are tested and the experimental results show that the system is very robust,and can accurately and effectively construct a suitable solid composed of linear and quadratic surfaces from incomplete three views.     

CAD系统中公差信息建模技术综述

公差信息建模是指对某一些造型系统进行准确无误的公差表述,并对其语义作出正确合理的解释。由于某对CAD／CAPP／CAM的集成有着十分重要的作用。因此一直是CAD／CAM研究领域的热点,研究成果十分丰硕。另一方面,由于公差信息的建模有着相当的难度,该领域至今仍然有着许多问题有待解决。文中对当前CAD系统中公差信息建模技术的研究历史和现状进行了较为全面的综述,分析比较了目前各种模型的优点与不足,最后对公差信息建模中亟待解决的问题及可能对策进行了讨论。     

Generation of random non-overlapping dot patterns for light guides using molecular dynamics simulations with variable r-cut and reflective boundary techniques

This paper presents a molecular dynamics (MD) scheme for the automatic generation of dot patterns for the light guides used in LCD backlight modules. Several MD computational techniques are integrated with the conventional MD scheme to enable the adjustment of the dot density in specific regions of the light guide in order to create a dot distribution with a high dot density variation and a high spatial uniformity. These techniques include the cell division technique, the variable r-cut technique, the boundary smoothing technique and the reflective boundary condition. The reflective boundary condition enables a precise control of the dot density within each cell, and is instrumental in achieving a dot distribution with both a high dot density variation and a high spatial uniformity. The performance of the proposed dot generation scheme is verified by considering the practical example of the dot pattern design of a light guide with a single LED light source located in the lower-right corner. The numerical results confirm the ability of the proposed method to achieve an even luminance condition by establishing a dot pattern whose density increases concentrically with an increasing distance from the light source.     

Homogeneous bounding boxes as tools for intersection algorithms of rational bézier curves and surfaces

In the divide-and-conquer algorithm for detecting intersections of parametric rational Bézier curves (surfaces), we use bounding boxes in recursive rough checks. In this paper, we replace the conventional bounding box with a homogeneous bounding box, which is projectively defined. We propose a new rough check algorithm based on it. One characteristic of the homogeneous bounding box is that it contains a rational Bézier curve (surface) with weights of mixed signs. This replacement of the conventional bounding box by the homogeneous one does not increase the computation time.     

Piecewise generation of surfaces of curved ducts of varying cross-sectional area using patch shifting or overlap

Using the results of previous numerical experiments, it is shown how patch shifting or overlap can be used to produce a continuous surface for curved ducts of varying elliptical or circular cross-sectional area. It is shown that if two overlapping Bézier patches are bounded in the v-parametric direction, say, by the same two u-parametric curves, the derivatives of both patches can, indeed be equal over the overlapping portions of the patches. It is then deduced that the mathematical result may hold only over a limited area of the overlapping patches on which sections of the patches can be joined to produce a continuous duct surface.     

A Visibility Sphere Marching algorithm of constructing polyhedral models for haptic sculpting and product prototyping

This paper presents a Visibility Sphere Marching algorithm of constructing polyhedral models from Dexel volume models for haptic virtual sculpting. Dexel volume models are used as the in-process models representation during interactive modification in a haptic virtual sculpting system. The stock material represented in a Dexel volume model is sculpted into a designed model using a developed haptic sculpting system. The sculpted Dexel volume models are converted to polyhedral surface models in STL format by the proposed visibility sphere marching algorithm. The conversion turns out to be an interesting and challenging problem. The proposed visibility sphere marching algorithm consists of three sub-algorithms: (i) roof and floor covering, (ii) wall-building, and (iii) hole-filling algorithms. The polyhedral surface models converted from the Dexel volume models can then be input to and processed by available computer-aided manufacturing (CAM) or rapid prototyping systems. The presented technique can be used in virtual sculpting, CAD/CAM, numerically controlled machining verification and rapid prototyping.     

计算机辅助设计在工业设计的应用状况及发展前景

在工业设计进行的流程中,计算机辅助设计悄然的穿插在每一个相对独立的主题活动之中.从一个完整的设计流程审视,计算机辅助设计的作用显而易见.它在设计流程数据管理,产品效果表现以及计算机辅助模型制作等广泛应用,发挥了工具化的作用.在应用过程中,促进了其自身的发展和工业设计的发展.     

Habitat prediction and knowledge extraction for spawning European grayling (Thymallus thymallus L.) using a broad range of species distribution models

This study aims to apply seven data-driven methods (i.e. artificial neural networks [ANNs], classification and regression trees [CARTs], fuzzy habitat suitability models [FHSMs], generalized additive models [GAMs], generalized linear models [GLMs], random forests [RF] and support vector machines [SVMs]) to develop data-driven species distribution models (SDMs) for spawning European grayling (Thymallus thymallus), and to compare the predictive performance and the ecological relevance, quantified by the habitat information retrieved from these SDMs (i.e. variable importance and habitat suitability curves [HSCs]). The results suggest RF to yield the most accurate SDM, followed by SVM, CART, ANN, GAM, FHSM and GLM. However, inconsistencies between different performance measures were observed, indicating that different models may obtain a high score on a particular aspect and perform worse on other aspects. Despite their lower predictive ability, GAM, GLM and FHSM proved to be useful, since HSCs could be obtained and thus these techniques allow testing of ecological relevance and habitat suitability. Water depth and flow velocity appeared to be important variables for spawning grayling. The HSCs clearly indicate higher habitat suitability at a lower water depth, a low to medium flow velocity and a higher percentage of medium-sized gravel, whereas the models disagreed on the habitat suitability for the percentage of small-sized gravel. These findings demonstrate the applicability of data-driven SDMs for both habitat prediction and ecological knowledge extraction that are useful for management of a target species.