Collaborative CAD (Co-CAD) systems can be constructed based on either 3D kernel or legacy stand-alone CAD systems, which are typically commercial CAD systems such as CATIA, Pro/E and so on. Most of synchronous Co-CAD systems, especially these based on legacy stand-alone CAD systems, adopt the lock mechanism or the floor control as concurrency controls which are very restrictive and stagnant. A flexible concurrency control method is proposed to support the flexible concurrency control in Co-CAD systems based on legacy stand-alone CAD systems. At first, a model of operation relationship is proposed with special consideration for the concurrency control of these kinds of Co-CAD system. Then two types of data structure, the Collaborative Feature Dependent Graph (Co-FDG) and the Collaborative Feature Operational List (Co-FOL), are presented as the cornerstone of flexible concurrency control. Next a Flexible Concurrency Control Algorithm (FCCA) is proposed. Finally a Selective Undo/Redo Algorithm is proposed which can improve the flexibility of Co-CAD furthermore.

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Based on the V-system, an orthogonal function system over triangular domain, we proposed a retrieval method for 3D model group consisting of several separate parts. The V-system is an efficient tool to precisely represent either continuous or separate geometric objects, which is its striking characteristic. The V-system can transform a 3D object to the frequency domain based on its triangular mesh, and generate related eigenvector which is invariant to rotation, translation, and scaling. With the V-system, we can successfully extend the orthogonal transformation methods widely used in 2D image retrieval to 3D model retrieval. Retrieval experimental results show that the proposed approach is practical and effective; and it has distinct advantage for model group retrieval. Comparing with the existed 3D model retrieval measures which can only be used to retrieve single model, this new approach can be used to retrieve a model group consisting of several separate parts, which is significant and has important application value in the reuse of model groups.

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In this paper, we propose a novel quad remeshing algorithm for articulated shapes. Different from existing methods that are essentially based on local analysis to align with local geometric features, our method focuses on the global structure and generates quad mesh with edge flow aligning with the skeleton. To achieve this, we firstly extract the skeleton from 3D shape. It captures the global structure of the shape and decomposes the shape into feature parts. We detect tube-like parts and build sweeping surface on them. For joint part connecting tube-like parts, we generate a smooth cross field interpolating the directions from its adjacent tube-like parts. Using this cross field, we generate the quad mesh of joint part. It smoothly connects adjacent sweep surfaces. The mesh models generated in our system greatly benefit the sculpting operators for sculpting modeling and skeleton-based animation.

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In the fields of computer aided geometric design, computer graphics and so on, curvature variation minimization has been widely used for constructing curve and surface. This paper investigates the minimal curvature variation in constructing the cubic Hermite curve that interpolates the given positions and unit tangent vectors at two points, while the magnitudes of the tangent vectors are unknown. The computation of this problem is very hard to handle and a very time-consuming task. To reduce the computing cost, simpler models are used to approximate it, but the existing simpler models can't give a good approximation, and hence make the curves constructed have unsatisfactory shapes. So a new model is presented in this paper. In the new model, the magnitude of each tangent vector is expressed as polynomial function of the tangent vector angles, which is easy to compute, and the shapes of constructed curves are visually similar to the ones constructed by minimizing the accurate curvature variation.

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Patch-based texture synthesis techniques from a small sample texture generate a new texture image efficiently, but one significant problem is that these existing texture synthesis algorithms suffer from structure mismatching across patch boundaries due to inaccurate similarity measure. In this paper, we propose a desired distance metric to measure structural similarity when especially handling textures with salient features, which has the ability to find best matches during the patch-based sampling. To do this, we introduce the concept of “layers” to describe the correlation of pixels through computing each pixel weight, and construct the orientation fields to capture the inherent direction and variation of texture features through computing the dominant local orientation angle and the degree of anisotropy of each pixel. Our experimental results demonstrate that the proposed method can significantly alleviate structure discontinuities in synthesized textures.

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Molecular shape is one of the most critical factors that determines molecular function. Therefore, it is frequently desirable to understand geometric characteristics of a molecule more precisely and efficiently. In this paper, we introduce the BetaMol, a molecular modeling, analysis, and visualization software based on the recent theory of the beta-complex and the quasi-triangulation that are derived from the Voronoi diagram of three-dimensional spherical atoms. The powerful features of the BetaMol are solely based on a unified, single framework of the mathematically rigorous and computationally efficient beta-complex theory. The BetaMol is implemented in the standard C++ language with OpenGL graphics library and freely available at Voronoi Diagram Research Center web site (http://voronoi.hanyang.ac.kr).

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