A level set based segmentation approach for point-sampled surfaces

Segmenting a complex 3D surface model into some visually meaningful sub-parts is one of the fundamental problems in digital geometry processing. In this paper, a novel segmentation approach of point-sampled surfaces is proposed, which is based on the level set evolution scheme. To segment the model so as to align the patch boundaries with high curvature zones, the driven speed function for the zero level set inside narrow band is defined by the extended curvature field, which approaches zero speed as the propagating front approaches high curvature zone. The effectiveness of the proposed approach is demonstrated by our ex- perimental results. Furthermore, two applications of model segmentation are illustrated, such as piecewise parameterization and local editing for point-sampled geometry.     

板材激光弯曲成形规律的研究

本文用大变形弹塑性有限元法对金属板材柔性成形新工艺——激光弯曲进行了动态数值模拟。从热力学的观点出发，阐明了该工艺的变形机理；论证了板材厚度和光束移动速度对温度梯度和弯曲角度的影响，为该工艺进一步深入研究奠定了基础。模拟结果与试验吻合较好。     

基于VB.NET与AutoCAD的二次开发在双曲率钣金件展开中的应用

通过研究双曲率钣金件展开,以钢铁转炉设计中双曲率钣金件为例,利用VB.NET与AutoCAD2008软件开发钣金件展开为平面图形,进行二次开发。在工业生产中可以节约材料,降低生产成本,提高生产效率,从而取得很高的经济效益。     

Study on the deformation theory of a parabolic part based on solid granules medium forming

Solid granules medium forming (SGMF), a new flexible die forming technology, uses solid granules instead of a rigid male or female die (or elastomer, liquid) for sheet metal drawing. The good fluidity and compressive capacity of a solid granules medium can improve the forming limit of complex shell parts. The sheet metal drawing process of SGMF is a compound process of drawing and bulging, which is very different from the conventional drawing process. A parabolic part is used as the research object for a study of the forming process. Two concepts, drawing weight and bulging weight, are originally proposed in the sheet metal drawing of SGMF (replacing the rigid male die), and the corresponding expressions are obtained. The computational formulas of geometrical conditions and strain in the sheet metal drawing of SGMF are established, and the radius of the strain dividing circle is obtained by calculation. The established theoretical model is applied to the research object, an aircraft part, to analyze the forming process. The results show that the proposed theory can be applied to analyze the strain in different deformation regions of SGMF. This original theory provides a new theoretical analysis for studying the sheet metal drawing of SGMF.     

板料成形模拟及其在汽车覆盖件冲压过程中的应用

基于板料成形模拟的必要性和汽车覆盖件成形的复杂性 ,提出有限元分析是模拟复杂三维板料成形问题的有力工具 .介绍了动态显式有限元法的原理和特点 ,讨论了国际现有的各种商用软件 ,论述了汽车覆盖件模拟的国内外应用现状 .以某新型汽车前门外板为例 ,运用显示有限元分析软件Dynaform对前门外板冲压过程进行了计算机模拟分析 ,预测冲压过程中可能出现的各种工艺缺陷 ,例如坯料的破裂 ,并以模拟结果为依据提出改进方法 .     

Visible region extraction from a sequence of rational Bézier surfaces

A method for computing the visible regions of free-form surfaces is proposed in this paper. Our work is focused on accurately calculating the visible regions of the sequenced rational Bézier surfaces forming a solid model and having coincident edges but no inner-intersection among them. The proposed method calculates the silhouettes of the surfaces without tessellating them into triangle meshes commonly used in previous methods so that arbitrary precision can be obtained. The computed silhouettes of visible surfaces are projected onto a plane orthogonal to the parallel light. Then their spatial relationship is applied to calculate the boundaries of mutual-occlusion regions. As the connectivity of the surfaces on the solid model is taken into account, a surface clustering technique is also employed and the mutual-occlusion calculation is accelerated. Experimental results showed that our method is efficient and robust, and can also handle complex shapes with arbitrary precision. Project supported by the National Basic Research Program (973) of China (No. 2002CB312106) and the National Natural Science Foundation of China (Nos. 60533070, and 60403047). The third author was supported by the project sponsored by a Foundation for the Author of National Excellent Doctoral Dissertation of China (No. 200342) and a Program for New Century Excellent Talents in University (No. NCET-04-0088), China     

New method for distinguishing planar rational cubic B-spline curve segments as monotone curvature variation

In order to fair and optimize rational cubic B-spline curves used frequently in engineering, and to improve design system function, some formulae on the degree and the knot vector, of the product of three B-spline functions, are presented; then Marsden’s identity is generalized, and by using discrete B-sline theory, the product of three B-spline functions is converted into a linear combination of B-splines. Consequently, a monotone curvature variation (MCV) discriminant for uniform planar rational cubic B-spline curves can be converted into a higher degree B-spline function. Applying the property of positive unit resolution of B-spline, an MCV sufficient condition for the curve segments is obtained. Theoretical reasoning and instance operation showed that the result is simple and applicable in curve design, especially in curve fair processing.     

Alternative 3D Modeling Approaches Based on Complex Multi-Source Geological Data Interpretation简

Due to the complex nature of multi-source geological data, it is difficult to rebuild every geological struc-ture through a single 3D modeling method. The multi-source data interpretation method put forward in this analysis is based on a database-driven pattern and focuses on the discrete and irregular features of geological data. The geological data from a variety of sources covering a range of accuracy, resolution, quantity and quality are classified and inte-grated according to their reliability and consistency for 3D modeling. The new interpolation-approximation fitting construction algorithm of geological surfaces with the non-uniform rational B-spline （NURBS） technique is then pre-sented. The NURBS technique can retain the balance among the requirements for accuracy, surface continuity and data storage of geological structures. Finally, four alternative 3D modeling approaches are demonstrated with reference to some examples, which are selected according to the data quantity and accuracy specification. The proposed approaches offer flexible modeling patterns for different practical engineering demands.     

《板材冲压成形技术》课程改革的探索

通过调研和论证,确定了模具设计与制造专业人才培养目标,进而召开实践专家访谈会,确定典型工作任务是板材冲压成形工艺制订和板材冲压成形模具设计。依据学习目标、学习内容、教学条件、理论知识覆盖性、职业生涯可持续发展及本课程特点,确定出6个学习情境,并以一个学习情境为例简述教学过程。     

A Learning Model That Stimulates Geometric Thinking Through Use of PCLogo and Geometer's Sketchpad

Summary

PCLogo and Geometer's Sketchpad are powerful tools that may be used by mathematics teachers who want to integrate technology with geometry instruction in the elementary classroom. The purpose of this study was to examine the usefulness of PCLogo and Geometer's Sketchpad to stimulate thinking about geometric concepts in elementary age children. We used a collective case study design that included four cases, two girls (ages 8 and 10) and two boys (ages 10 and 11). All participants were trained to use PCLogo and Geometer's Sketchpad to construct geometric shapes and measure the attributes of the shapes. After the training, participants used these technologies as tools to stimulate thinking about geometric concepts. As a result of our observations of children's performances as they reasoned about geometric concepts, we developed a learning model for teaching children about geometry.     

A comparative study on the effectiveness of the computer assisted method and the interactionist approach to teaching geometry shapes to young children

The purpose of this study is to compare and evaluate the effectiveness of computer assisted teaching of geometry shapes and an interactionist approach to teaching geometry in kindergarten versus other more traditional teaching methods. Our research compares the improvement of the children’s geometrical competence using two teaching approaches. The first one employs our ICT oriented learning method specifically targeting Realistic Mathematics Education (RME) and the van Hiele model for geometry shapes. The second method is based on the interactionist approach of teaching children in kindergarten. The sample consisted of 139 Greek kindergarten children from Crete. We conducted interventions based on the above two methods, in two experimental groups. The first experimental group consisted of 50 children who were taught geometry shapes according to the principles of Realistic Mathematics Education with the use of appropriate educational software. The second experimental group consisted of 45 children who were taught about geometry shapes with an interactionist approach without the use of computers. The control group consisted of 44 children and was taught about geometry shapes following the ways teachers chose to put the basic pedagogical principles of Curriculum for kindergarten into practice without the use of ICT. Children in all groups were pre-tested and post-tested for their geometry performance. The results showed that the teaching approaches of our interventions, the one with the additional use of ICT and the interactionist one, contribute significantly more to the development of kindergarten children’s geometry competence as compared to other traditional methods.     

Multi-sensor image registration using multi-resolution shape analysis

INTRODUCTION Image registration plays an important role in the fusion of remote sensing, video panorama, medical image processing, etc. (Li et al., 1995; 2004; Brown, 1992; Belongie et al., 2001; Rui et al., 2001). More different than video panorama, the registration of multi-sensor image needs to align the multi-sensor images of the same scene from different sources (Rignot et al., 1991). Multi-sensor image registration is widely used in the fusion of panchromatic images with infrared i…     

Numerical analysis of surface plasmons excited on a thin metal grating

INTRODUCTION It is widely known that a metal grating supports plasmon surface waves in the optics region (Raeter, 1982; Nevier, 1980). Excitation of a plasmon surface wave causes resonance absorption, which can be observed as partial or total absorption of incident light accompanied by an abrupt change of diffraction effi- ciency called resonance anomaly. If the grating is thick enough, the surface waves can be excited on the lit surface alone and the surface waves in this case are called…     

加工孔的利器——几种钻型

针对不同的加工要求，我们研制几款钻型精孔钻、半孔钻等以满足加工要求。     

Symmetric alteration of four knots of B-spline and NURBS surfaces

INTRODUCTION Modification of knots of a B-spline curve changes the shape of the curve. In some recent pub-lications (Juhász and Hoffmann, 2001; 2003; Hoff-mann and Juhász, 2004; Li and Wang, 2005), the authors studied the effect of the alteration of a single knot on the shape of the curve. Hoffmann (2004) and Li & Wang (2006) applied these theories into the constrained shape modification of B-spline and NURBS curves. Juhász (2001) and Hoffmann & Ju-hász (2005) studied the effe…     

全脐点弯曲曲面及其上曲线的若干性质

本文论证了全脐点曲面必为球面或平面 ,并讨论了球面曲线的一系列性质 ,揭示了这类曲线的曲率和挠率之间的特殊关系 ,从而刻画出其几何特征。     

金属板材的激光弯曲成形技术及其应用

激光弯曲成形是通过局部瞬态加热产生不均匀内部热应力，而导致板材变形的一种无模成形技术。章介绍了这种金属板材的激光弯曲成形技术常见的4种成形机理：温度梯度机理、墩粗机理、塑性皱曲机理和弹性膨胀机理；总结了激光弯曲成形国内外的发展状况；展望了该技术的研究趋势与应用前景。     

Designing Bézier surfaces minimizing the L2-norm of the Gaussian curvature

In freeform surface modelling, developable surfaces have much application value. But, in 3D space, there is not always a regular developable surface which interpolates the given boundary of an arbitrary piecewise smooth closed curve. In this paper, tensor product Bézier surfaces interpolating the closed curves are determined and the resulting surface is a minimum of the functional defined by the L2-integral norm of the Gaussian curvature. The Gaussian curvature of the surfaces is minimized by the method of solving nonlinear optimization problems. An improved approach trust-region form method is proposed. A simple application example is also given.     

曲面上非直线的渐近曲线的挠率与第Ⅰ、Ⅱ基本量的关系

曲线的挠率和曲面的第Ⅰ、Ⅱ基本量在微分几何中占有重要的地位,本文简单陈述了曲面上非直线的渐近曲线的挠率与第Ⅰ、Ⅱ基本量的关系.     

几何思想融入向量组线性相关性的教学探讨

代数与几何是不可分割的两个部分,借助于平面几何图形,可对线性相关性及其判别方法进行形象而又生动的描述．将几何思想融入线性代数的教学,使抽象的问题具体化,以提高课堂教学的趣味性,有助于学生对线性相关性概念的理解．