Sketching in Gestalt Space: Interactive Shape Abstraction through Perceptual Reasoning

We present an interactive method that allows users to easily abstract complex 3D models with only a few strokes. The key idea is to employ well‐known Gestalt principles to help generalizing user inputs into a full model abstraction while accounting for form, perceptual patterns and semantics of the model. Using these principles, we alleviate the user's need to explicitly define shape abstractions. We utilize structural characteristics such as repetitions, regularity and similarity to transform user strokes into full 3D abstractions. As the user sketches over shape elements, we identify Gestalt groups and later abstract them to maintain their structural meaning. Unlike previous approaches, we operate directly on the geometric elements, in a sense applying Gestalt principles in 3D. We demonstrate the effectiveness of our approach with a series of experiments, including a variety of complex models and two extensive user studies to evaluate our framework.     

基于运动传播和Isomap分析的三维人脸动画编辑与合成

提出一种三维人脸动画数据编辑与合成的有效方法,使用户可以在三维人脸模型上选定控制点,并在二维平面上指定表情动作的约束条件.根据人脸动画数据训练一个先验概率模型,将较少的用户约束传播到人脸网格的其他部分,从而生成完整生动的人脸表情;通过Isomap学习算法对三维人脸动画知识进行建模,并结合用户指定的关键帧拟合高维曲面上的平滑测地线,以自动合成新的人脸动画序列.实验结果表明,该方法可以直观地对人脸动画的生成进行交互式控制,并能生成较为逼真的表情动画.     

A robust watermarking scheme for 3D triangular mesh models

Copyright protection of digital media has become an important issue in the creation and distribution of digital content. As a solution to this problem, digital watermarking techniques have been developed for embedding specific information identifying the owner in the host data imperceptibly. Most watermarking methods developed to date mainly focused on digital media such as images, video, audio, and text. Relatively few watermarking methods have been presented for 3D graphical models. In this paper we propose a robust 3D graphical model watermarking scheme for triangle meshes. Our approach embeds watermark information by perturbing the distance between the vertices of the model to the center of the model. More importantly, to make our watermarking scheme robust against various forms of attack while preserving the visual quality of the models our approach distributes information corresponds to a bit of the watermark over the entire model, and the strength of the embedded watermark signal is adaptive with respect to the local geometry of the model. We also introduce a weighting scheme in the watermark extraction process that makes watermark detection more robust against attacks. Experiments show that this watermarking scheme is able to withstand common attacks on 3D models such as mesh simplification, addition of noise, model cropping as well as a combination of these attacks.     

MCGIM-Based Model Streaming for Realtime Progressive Rendering

While most mesh streaming techniques focus on optimizing the transmission order of the polygon data,few approaches have addressed the streaming problems by using geometry images(GIM).In this paper,we present a new approach which firstly partitions a mesh into several surface patches,then converts these patches into multi-chart geometry images(MCGIM).After resampling the MCGIM and normal map atlas are obtained,we hierarchically construct the regular geometry image representation by adopting the quadtree structure.In this way,the encoded nodes can be transmitted in arbitrary order with high transmission flexibility.Also,the rendering quality of the partially transmitted models can be greatly improved by using the normal texture atlas.Meanwhile only the geometry on the silhouette to the current viewpoint are required to be refined and transmitted,therefore the amount of data is minimized for transferring each frame.In particular,our approach also allows users to encode and transmit the mesh data via JPEG2000 technique.Therefore,our mesh streaming method is suitable for transmitting 3D animation models with use of Motion JPEG2000 videos.Experimental results have demonstrated the effectiveness of our approach,which enables one server to stream the MCGIM texture atlas to the clients.Also,the transmitted model can be rendered in a multiresolution manner by GPU acceleration on the client side,due to the regular geometry structure of MCGIM.     

Exemplar-based statistical model for semantic parametric design of human body

This paper presents an exemplar-based method to provide intuitive way for users to generate 3D human body shape from semantic parameters. In our approach, human models and their semantic parameters are correlated as a single linear system of equations. When users input a new set of semantic parameters, a new 3D human body will be synthesized from the exemplar human bodies in the database. This approach involves simpler computation compared to non-linear methods while maintaining quality outputs. A semantic parametric design in interactive speed can be implemented easily. Furthermore, a new method is developed to quickly predict whether the parameter values is reasonable or not, with the training models in the human body database. The reconstructed human bodies in this way will all have the same topology (i.e., mesh connectivity), which facilitates the freeform design automation of human-centric products.     

基于混合频谱信号编码的网格纹理平滑

网格纹理平滑技术要求既能保持模型大尺度结构特征又能去除模型小尺度纹理.然而当模型小尺度纹理与噪声相差较大时,大多数网格光顺算法会将网格纹理识别为特征加以保持,而无法有效将其去除;现有的基于谱分析的网格光顺方法尽管能有效去除网格纹理,但又无法同时保持模型大尺度结构特征.为解决该问题,本文提出一种基于混合频谱信号编码的低通...     

A novel progressive modelling algorithm for 3D models

This paper presents a novel progressive modelling algorithm for 3D models to generate progressive meshes. We propose a forest clustering simplification method to generate a progressive mesh of a model with the efficient and smooth transitions between meshes at different resolutions. Our approach can also integrate and balance the appearance attributes to preserve features of a model in the simplification process. We have applied our progressive modelling technique to several different kinds of input models and results show that our approach only generates efficient and smooth progressive meshes of a given model, but also preserves the features. The proposed method is very suitable for progressive transmission and real‐time rendering of 3D models in networked virtual environments. Copyright © 2002 John Wiley & Sons, Ltd.     

Efficient spectral watermarking of large meshes with orthogonal basis functions

Allowing for copyright protection and ownership assertion, digital watermarking techniques, which have been successfully applied to classical media types like audio, images, and video, have recently been adapted for the newly emerged multimedia data type of 3D geometry models. In particular, the widely used spread-spectrum methods can be generalized for 3D datasets by transforming the original model to a frequency domain and perturbing the coefficients of the most dominant basis functions. Previous approaches employing this kind of spectral watermarking are mainly based on multiresolution mesh analysis, wavelet domain transformation, or spectral mesh analysis. Though they already exhibit good resistance to many types of real-world attacks, they are often far too slow to cope with very large meshes due to their complicated numerical computations. In this paper, we present a novel spectral watermarking scheme using new orthogonal basis functions based on radial basis functions. With our proposed fast basis function orthogonalization, while observing a persistence with respect to various attacks that is similar to that of other related approaches, our scheme runs faster by two orders of magnitude and thus can efficiently watermark very large models.     

Fully Convolutional Graph Neural Networks for Parametric Virtual Try-On

We present a learning-based approach for virtual try-on applications based on a fully convolutional graph neural network. In contrast to existing data-driven models, which are trained for a specific garment or mesh topology, our fully convolutional model can cope with a large family of garments, represented as parametric predefined 2D panels with arbitrary mesh topology, including long dresses, shirts, and tight tops. Under the hood, our novel geometric deep learning approach learns to drape 3D garments by decoupling the three different sources of deformations that condition the fit of clothing: garment type, target body shape, and material. Specifically, we first learn a regressor that predicts the 3D drape of the input parametric garment when worn by a mean body shape. Then, after a mesh topology optimization step where we generate a sufficient level of detail for the input garment type, we further deform the mesh to reproduce deformations caused by the target body shape. Finally, we predict fine-scale details such as wrinkles that depend mostly on the garment material. We qualitatively and quantitatively demonstrate that our fully convolutional approach outperforms existing methods in terms of generalization capabilities and memory requirements, and therefore it opens the door to more general learning-based models for virtual try-on applications.     

Mesh repair with user-friendly topology control

Limitations of current 3D acquisition technology often lead to polygonal meshes exhibiting a number of geometrical and topological defects which prevent them from widespread use. In this paper we present a new method for model repair which takes as input an arbitrary polygonal mesh and outputs a valid 2-manifold triangle mesh. Unlike previous work, our method allows users to quickly identify areas with potential topological errors and to choose how to fix them in a user-friendly manner. Key steps of our algorithm include the conversion of the input model into a set of voxels, the use of morphological operators to allow the user to modify the topology of the discrete model, and the conversion of the corrected voxel set back into a 2-manifold triangle mesh. Our experiments demonstrate that the proposed algorithm is suitable for repairing meshes of a large class of shapes.     

From laser-scanned data to feature human model: a system based on fuzzy logic concept

This paper describes the development of a prototype system using fuzzy logic concept for constructing a feature human model, which is to be stored in a 3D digital human model database. In our approach, the feature human model is constructed by unorganized cloud points obtained from 3D laser scanners. Firstly, noisy points are removed, and the orientation of the human model is adjusted; secondly, a feature based mesh generation algorithm is applied on the cloud points to construct the mesh surface of a human model; lastly, semantic features of the human model are extracted from the mesh surface. Compared with earlier approach, our method strongly preserves the topology of a human model; more details can be constructed; and both the robustness and the efficiency of the algorithm are improved. At the end of the paper, in order to demonstrate the functionality of feature human models, potential applications are given.     

真实感人脸模型的细分曲面重建

提出一种利用2张正交照片和细分曲面进行真实感三维人脸建模的方法,并实现了不同模型间的三维变形.为了构造个性化的人脸几何模型,将网格简化、自由曲面变形和细分结合起来,得到多个层次细节下的人脸模型;再经过纹理融合和映射,完成个性化的真实感三维人脸建模;同时利用线性插值实现了同拓扑真实感模型间的光滑变形.实验结果表明：该方法不仅可以进行有效的真实感三维人脸建模,而且变形简单流畅,具有广阔的应用前景.     

Evaluation for Small Visual Difference Between Conforming Meshes on Strain Field

This paper gives a method of quantifying small visual differences between 3D mesh models with conforming topology, based on the theory of strain fields. Strain field is a geometric quantity in elasticity which is used to describe the deformation of elastomer. In this paper we consider the 3D models as objects with elasticity. The further demonstrations are provided: the first is intended to give the reader a visual impression of how our measure works in practice; and the second is to give readers a visua...     

Mesh composition on models with arbitrary boundary topology

This paper presents a new approach for the mesh composition on models with arbitrary boundary topology. After cutting the needed parts from existing mesh models and putting them into the right pose, an implicit surface is adopted to smoothly interpolate the boundaries of models under composition. An interface is developed to control the shape of the implicit transient surface by using sketches to specify the expected silhouettes. After that, a localized Marching Cubes algorithm is investigated to tessellate the implicit transient surface so that the mesh surface of composed model is generated. Different from existing approaches in which the models under composition are required to have pairwise merging boundaries, the framework developed based on our techniques have the new function to fuse models with arbitrary boundary topology.     

An asymmetric and optimized encryption method to protect the confidentiality of 3D mesh model

3D models are widely used in computer graphics, design and manufacture engineering, art animation and entertainment. With the universal of acquisition equipment and sensors, a huge number of 3D models are generated, which are becoming the major source of engineering data. How to preserve the privacy of the 3D models is a challenge issue. In this paper, an asymmetric and optimized encryption method is presented to protect the 3D mesh models. Firstly, we propose an asymmetric encryption method for 3D mesh models to overcome the drawbacks of traditional symmetric encryption. The primary benefit is that our approach can enhance the security of the key. Secondly, we extend the typically asymmetric encryption algorithm from integer domain to float domain. In our method, we present a normalization function to map the float DC (Discrete Cosine) coefficients to integer domain. Thirdly, considering that the shape error and encryption/decryption computation cost are contradictory in the normalization mapping, we formulate the contradiction as a multi-objective optimization problem. And then, we propose a multi-objective solution to find an optimized mapping range for encryption/decryption efficiently. Furthermore, benefiting from the proposed asymmetric encryption framework, we continue to put forward a method to check the integrity of the encrypted 3D mesh model, in which the digest is encrypted twice to generate digital signature more safely. The proposed method has been tested on 3D mesh models from Stanford university and other sources to demonstrate the effect of the proposed encryption method and optimization mechanism.     

Mesh fusion using functional blending on topologically incompatible sections

Three-dimensional mesh fusion provides an easy and fast way to create new mesh models from existing ones. We introduce a novel approach of mesh fusion in this paper based on functional blending. Our method has no restriction of disk-like topology or one-ring opening on the meshes to be merged. First of all, sections with boundaries of the under-fusing meshes are converted into implicit representations. An implicit transition surface, which joins the sections together while keeping smoothness at the boundaries, is then created based on cubic Hermite functional blending. Finally, the implicit surface is tessellated to form the resultant mesh. Our scheme is both efficient and simple, and with it users can easily construct interesting, complex 3D models.     

A new approach to automatic and a priori mesh adaptation around circular holes for finite element analysis

Through our research on the integration of finite element analysis in the design and manufacturing process with CAD, we have proposed the concept of mesh pre-optimization. This concept consists in converting shape and analysis information in a size map (a mesh sizing function) with respect to various adaptation criteria (refining the mesh around geometric form features, minimizing the geometric discretization error, boundary conditions, etc.). This size map then represents a constraint that has to be respected by automatic mesh generation procedures. This paper introduces a new approach to automatic mesh adaptation around circular holes. This tool aims at optimizing, before any FEA, the mesh of a CAD model around circular holes. This approach, referred to as “a priori” mesh adaptation, should not be regarded as an alternative to adaptive a posteriori mesh refinement but as an efficient way to obtain reasonably accurate FEA results before a posteriori adaptation, which is particularly interesting when evaluating design scenarios. The approach is based on performing many offline FEA analyses on a reference case and deriving, from results and error distributions obtained, a relationship between mesh size and FEA error. This relationship can then be extended to target user specified FEA accuracy objectives in a priori mesh adaptation for any distribution of circular holes. The approach being purely heuristic, fulfilling FEA accuracy objectives, in all cases, cannot be theoretically guaranteed. However, results obtained using varying hole diameters and distributions in 2D show that this heuristic approach is reliable and useful. Preliminary results also show that extension of the method can be foreseen towards a priori mesh adaptation in 3D and mesh adaptation around other types of 2D features.     

面向移动计算终端的渐进几何简化方法

在移动计算终端上进行移动三维图形计算是一个重要的课题.针对移动计算终端屏幕小、计算能力低、无线网络带宽受限等特点,研究如何进行移动三维图形的渐进显示具有十分重要的意义.提出了利用Kobbelt四边形细分算法的逆过程迭代地进行简化的方法,通过迭代地把模型分割为奇点和作为简化模型的偶点,实现了对四边形网格几何模型的渐进式简化;提出了渐进显示的模式,通过把每一层的奇点作为可添加的细节信息,可以支持在终端上渐进显示不同细节模型并实现原模型的无损还原.完整的简化方法简单快速,可以高效地实现移动三维图形的渐进简化显示.最后在型号为Mio 336的PDA上的实验结果表明,研究成果在移动计算终端上进行实时交互等方面具有很好的应用前景.