Weiwei Xu           中文主页

 

Zhejiang University

 

Room 516, Mengminwei Building, No. 388 Yuhangtang Road, Xihu District,

Hangzhou, P.R.China

Email: xww@ cad.zju.edu.cn

 

About Me

Weiwei Xu is currently a researcher at state key lab of CAD&CG in Zhejiang university. He was a Qianjiang Professor at Hangzhou Normal University and a researcher in Internet Graphics Group at Microsoft Research Asia from 2005 to 2012,  and he was a post-doc researcher at Ritsmeikan university in Japan for more than one year. He received Ph.D. Degree in Computer Graphics from Zhejiang University, Hangzhou, and B.S. Degree and Master Degree in Computer Science from Hohai University in 1996 and 1999 respectively.  

 

Research Interests

Physical simulation and computer animation, Computational geometry, 3D Printing, Virtual reality

 

Professional Activities

Program co-chair:

ACM VRST 2013,2014

Paper Committee Member:

Pacific Graphics, ACM Symposium on Geometry Processing, CASA, IEEE Virtual Reality, GMP, SPM

Paper Reviewer:

ACM SIGGRAPH, ACM SIGGRAPH Asia, IEEE Visualization, IEEE TVCG, SGP, Computers & Graphics

 

Publications

 

2016

 

Stress Constrained Thickness Optimization for Shell Object Fabrication

Haiming Zhao, Weiwei Xu, Kun Zhou, Yin Yang, Xiaogang Jin, Hongzhi Wu

We present an approach to fabricate shell objects with thickness parameters, which are computed to maintain the user-specified structural stability. Given a boundary surface and user-specified external forces, we optimize the thickness parameters according to stress constraints to extrude the surface. Our approach mainly consists of two technical components: First, we develop a patch-based shell simulation technique to efficiently support the static simulation of extruded shell objects using finite element methods. Second, we analytically compute the derivative of stress required in the sensitivity analysis technique to turn the optimization into a sequential linear programming problem. Experimental results demonstrate that our approach can optimize the thickness parameters for arbitrary surfaces in a few minutes and well predict the physical properties, such as the deformation and stress of the fabricated object.

 

Accepted by Computer Graphics Forum  [Paper] [Supplementary] [Video


 

 

All-hex Meshing using Closed-form Induced Polycube

Xianzhong Fang, Weiwei Xu, Hujun Bao, Jin Huang

The polycube based hexahedralization methods are robust to the generation of internal singularity free all-hex meshes. They avoid the difficulty to control the global singularity structure for a valid hexahedralization in frame-field based methods. To thoroughly utilize this advantage, we propose to use a frame field without internal singularities to guide the polycube construction. Theoretically, our method extends the vector fields associated with the polycube from exact forms to closed forms, which are curl free everywhere but may not be globally integrable. The closed forms give additional degrees of freedom to deal with the topological structure of high genus models, and also provide better initial axis alignment for subsequent polycube generation. We demonstrate the advantages of our method on various models, ranging from genus-zero models to high genus ones, from single-boundary models to multiple boundary ones.

 

ACM SIGGRAPH 2016  [ Paper (available soon)] [Supplementary] [Video


 

 

Make it swing: Fabricating personalized roly-poly toys

Haiming Zhao, Chengkuan Hong, Juncong Lin, Xiaogang Jin, Weiwei Xu

A roly-poly toy is considered as one of the oldest toys in history. People, both young and old, are fascinated by its unique ability to right itself when pushed over. There exist different kinds of roly-poly toys with various shapes. Most of them share a similar bottom which is a hollow hemisphere with a weight inside. However, it is not an easy task to make an arbitrary model to swing like a roly-poly due to the delicate equilibrium condition between the center of mass of the roly-poly toy and the shape of the hemisphere. In this paper, we present a computer-aided method to help casual users design a personalized roly-poly toy and fabricate it through 3D printing with reduced material usage and sufficient stability. The effectiveness of our method is validated on various models. Our method provides a novel easy-to-use means to design an arbitrary roly-poly toy with an ordinary 3D printing machine, extricating amateurs from the dilemma of finding extra weight to balance the shape.

 

Computer Aided Geometric Design 43: 226-236 (2016)  [Paper] [Supplementary] [Video


 

 

View-Aware Image Object Compositing and Synthesis from Multiple Sources

Xiang Chen, Weiwei Xu, Sai-Kit Yeung, Kun Zhou

Image compositing is widely used to combine visual elements from separate source images into a single image. Although recent image compositing techniques are capable of achieving smooth blending of the visual elements from different sources, most of them implicitly assume the source images are taken in the same viewpoint. In this paper, we present an approach to compositing novel image objects from multiple source images which have different viewpoints. Our key idea is to construct 3D proxies for meaningful components of the source image objects, and use these 3D component proxies to warp and seamlessly merge components together in the same viewpoint. To realize this idea, we introduce a coordinate-frame based single-view camera calibration algorithm to handle general types of image objects, a structure-aware cuboid optimization algorithm to get the cuboid proxies for image object components with correct structure relationship, and finally a 3D-proxy transformation guided image warping algorithm to stitch object components. We further describe a novel application based on this compositing approach to automatically synthesize a large number of image objects from a set of exemplars. Experimental results show that our compositing approach can be applied to a variety of image objects, such as chairs, cups, lamps, and robots, and the synthesis application can create novel image objects with significant shape and style variations from a small set of exemplars.

 

J. Comput. Sci. Technol. 31(3): 463-478 (2016)  [Paper] [Supplementary] [Video


 

 

Fast Nearest Neighbor Search in the Hamming Space

Zhansheng Jiang, Lingxi Xie, Xiaotie Deng, Weiwei Xu, Jingdong Wang

Recent years have witnessed growing interests in computing compact binary codes and binary visual descriptors to alleviate the heavy computational costs in large-scale visual research. However, it is still computationally expensive to linearly scan the large-scale databases for nearest neighbor (NN) search. In [15], a new approximate NN search algorithm is presented. With the concept of bridge vectors which correspond to the cluster centers in Product Quantization [10] and the augmented neighborhood graph, it is possible to adopt an extract-on-demand strategy on the online querying stage to search with priority. This paper generalizes the algorithm to the Hamming space with an alternative version of k-means clustering. Despite the simplicity, our approach achieves competitive performance compared to the state-of-the-art methods, i.e., MIH and FLANN, in the aspects of search precision, accessed data volume and average querying time.

 

International Conference on Multimedia Modeling (MMM) 2016: 325-336  [Paper] [Supplementary] [Video


 

 

2015

 

Lightweight wrinkle synthesis for 3D facial modeling and animation

Jun Li, Weiwei Xu, Zhi-Quan Cheng, Kai Xu, Reinhard Klein

We present a lightweight non-parametric method to generate wrinkles for 3D facial modeling and animation. The key lightweight feature of the method is that it can generate plausible wrinkles using a single low-cost Kinect camera and one high quality 3D face model with details as the example. Our method works in two stages: (1) offline personalized wrinkled blendshape construction. User-specific expressions are recorded using the RGB-Depth camera, and the wrinkles are generated through example-based synthesis of geometric details. (2) Online 3D facial performance capturing. These reconstructed expressions are used as blendshapes to capture facial animations in real-time. Experiments on a variety of facial performance videos show that our method can produce plausible results, approximating the wrinkles in an accurate way. Furthermore, our technique is low-cost and convenient for common users.

 

Computer-Aided Design 58: 117-122 (2015)  [Paper] [Supplementary] [Video


 

 

Agile structural analysis for fabrication-aware shape editing

Yue Xie, Weiwei Xu, Yin Yang, Xiaohu Guo, Kun Zhou

This paper presents an agile simulation-aided shape editing system for personal fabrication applications. The finite element structural analysis and geometric design are seamlessly integrated within our system to provide users interactive structure analysis feedback during mesh editing. Observing the fact that most editing operations are actually local, a domain decomposition framework is employed to provide unified interface for shape editing, FEM system updating and shape optimization. We parameterize entries of the stiffness matrix as polynomial-like functions of geometry editing parameters thus the underlying FEM system can be rapidly synchronized once edits are made. A local update scheme is devised to re-use the untouched parts of the FEM system thus a lot repetitive calculations are avoided. Our system can also perform shape optimizations to reduce high stresses in model while preserving the appearance of the model as much as possible. Experiments show our system provides users a smooth editing experience and accurate feedback.

 

Computer Aided Geometric Design 35-36: 163-179 (2015)  [Paper] [Supplementary] [Video


 

 

A Suggestive Interface for Sketch-based Character Posing

Pei Lv, Pengjie Wang, Weiwei Xu, Jinxiang Chai, Mingmin Zhang, Zhigeng Pan, Mingliang Xu

We present a user-friendly suggestive interface for sketch-based character posing. Our interface provides suggestive information on the sketching canvas in succession by combining image retrieval technique with 3D character posing, while the user is drawing. The system highlights the canvas region where the user should draw on and constrains the user's sketches in a reasonable solution space. This is based on an efficient image descriptor, which is used to measure the distance between the user's sketch and 2D views of 3D poses. In order to achieve faster query response, local sensitive hashing is involved in our system. In addition, sampling-based optimization algorithm is adopted to synthesize and optimize the retrieved 3D pose to match the user's sketches the best. Experiments show that our interface can provide smooth suggestive information to improve the reality of sketching poses and shorten the time required for 3D posing.

 

Comput. Graph. Forum 34(7): 111-121 (2015)  [Paper] [Supplementary] [Video


 

 

Interactive design and simulation of tubular supporting structure

Ran Luo, Lifeng Zhu, Weiwei Xu, Patrick Gage Kelley, Vanessa Svihla, Yin Yang

This paper presents a system for design and simulation of supporting tube structure. We model each freeform tube component as a swept surface, and employ boundary control and skeletal control to manipulate its cross-sections and its embedding respectively. With the parametrization of the swept surface, a quadrilateral mesh consisting of nine-node general shell elements is automatically generated and the stress distribution of the structure is simulated using the finite element method. In order to accelerate the complex finite element simulation, we adopt a two-level subspace simulation strategy, which constructs a secondary complementary subspace to improve the subspace simulation accuracy. Together with the domain decomposition method, our system is able to provide interactive feedback for parametric freeform tube editing. Experiments show that our system is able to predict the structural character of the tube structure efficiently and accurately.

 

Graphical Models 80: 16-30 (2015)  [Paper] [Supplementary] [Video


 

 

Integrating 3D structure into traffic scene understanding with RGB-D data

Yingjie Xia, Weiwei Xu, Luming Zhang, Xingmin Shi, Kuang Mao

RGB Video now is one of the major data sources of traffic surveillance applications. In order to detect the possible traffic events in the video, traffic-related objects, such as vehicles and pedestrians, should be first detected and recognized. However, due to the 2D nature of the RGB videos, there are technical difficulties in efficiently detecting and recognizing traffic-related objects from them. For instance, the traffic-related objects cannot be efficiently detected in separation while parts of them overlap, and complex background will influence the accuracy of the object detection. In this paper, we propose a robust RGB-D data based traffic scene understanding algorithm. By integrating depth information, we can calculate more discriminative object features and spatial information can be used to separate the objects in the scene efficiently. Experimental results show that integrating depth data can improve the accuracy of object detection and recognition. We also show that the analyzed object information plus depth data facilitate two important traffic event detection applications: overtaking warning and collision avoidance.

 

Neurocomputing 151: 700-709 (2015)  [Paper] [Supplementary] [Video


 

 

Recognizing multi-view objects with occlusions using a deep architecture

Yingjie Xia, Luming Zhang, Weiwei Xu, Zhenyu Shan, Yuncai Liu

Image-based object recognition is employed widely in many computer vision applications such as image semantic annotation and object location. However, traditional object recognition algorithms based on the 2D features of RGB data have difficulty when objects overlap and image occlusion occurs. At present, RGB-D cameras are being used more widely and the RGB-D depth data can provide auxiliary information to address these challenges. In this study, we propose a deep learning approach for the efficient recognition of 3D objects with occlusion. First, this approach constructs a multi-view shape model based on 3D objects by using an encode–decode deep learning network to represent the features. Next, 3D object recognition in indoor scenes is performed using random forests. The application of deep learning to RGB-D data is beneficial for recovering missing information due to image occlusion. Our experimental results demonstrate that this approach can significantly improve the efficiency of feature representation and the performance of object recognition with occlusion.

 

Inf. Sci. 320: 333-345 (2015)  [Paper] [Supplementary] [Video


 

 

Boundary-dominant flower blooming simulation

Jianfang Li, Min Liu, Weiwei Xu, Haiyi Liang, Ligang Liu

This paper presents a new physics-based simulation method for flower blossom, which is based on biological observations that flower opening is usually driven by a boundary-dominant morphological transition in a curved petal. We use an elastic triangular mesh representing a flower petal and adopt in-plane expansion to induce global bending. Out-of-plane curl plays an auxiliary role in reducing the curvatures of cross-sections. We also propose to adapt semi-implicit Euler time integrator for fast simulation results, which has intrinsic damping and at least one order precision. Our system allows users to control the blossoming process by simply specifying a growth curve, which is easy to design because of the boundary-dominant property. Experimental results show that our physics-based system runs faster and generates more realistic and convincing blossom results than the existing simulation methods. Copyright ? 2015 John Wiley & Sons, Ltd.

 

Journal of Visualization and Computer Animation 26(3-4): 433-443 (2015)  [Paper] [Supplementary] [Video


 

 

Online Structure Analysis for Real-Time Indoor Scene Reconstruction

Yizhong Zhang, Weiwei Xu, Yiying Tong, Kun Zhou

We propose a real-time approach for indoor scene reconstruction. It is capable of producing a ready-to-use 3D geometric model even while the user is still scanning the environment with a consumer depth camera. Our approach features explicit representations of planar regions and nonplanar objects extracted from the noisy feed of the depth camera, via an online structure analysis on the dynamic, incomplete data. The structural information is incorporated into the volumetric representation of the scene, resulting in a seamless integration with KinectFusion's global data structure and an efficient implementation of the whole reconstruction process. Moreover, heuristics based on rectilinear shapes in typical indoor scenes effectively eliminate camera tracking drift and further improve reconstruction accuracy. The instantaneous feedback enabled by our on-the-fly structure analysis, including repeated object recognition, allows the user to selectively scan the scene and produce high-fidelity large-scale models efficiently. We demonstrate the capability of our system with real-life examples.

 

ACM Trans. Graph. 34(5): 159 (2015)  [Paper] [Supplementary] [Video


 

 

Expediting precomputation for reduced deformable simulation

Yin Yang, Dingzeyu Li, Weiwei Xu, Yuan Tian, Changxi Zheng

Model reduction has popularized itself for simulating elastic deformation for graphics applications. While these techniques enjoy orders-of-magnitude speedups at runtime simulation, the efficiency of precomputing reduced subspaces remains largely overlooked. We present a complete system of precomputation pipeline as a faster alternative to the classic linear and nonlinear modal analysis. We identify three bottlenecks in the traditional model reduction precomputation, namely modal matrix construction,cubature training, and training dataset generation, and accelerate each of them. Even with complex deformable models, our method has achieved orders-of-magnitude speedups over the traditional precomputation steps, while retaining comparable runtime simulation quality.

 

ACM Trans. Graph. 34(6): 243 (2015)  [Paper] [Supplementary] [Video


 

 

2014

 

Transductive 3D Shape Segmentation using Sparse Reconstruction

Weiwei Xu, Zhouxu Shi, Mingliang Xu, Kun Zhou, Jingdong Wang, Bin Zhou, Jinrong Wang, Zhenming Yuan

We propose a transductive shape segmentation algorithm, which can transfer prior segmentation results in database to new shapes without explicitly specification of prior category information. Our method first partitions an input shape into a set of segmentations as a data preparation, and then a linear integer programming algorithm is used to select segments from them to form the final optimal segmentation. The key idea is to maximize the segment similarity between the segments in the input shape and the segments in database, where the segment similarity is computed through sparse reconstruction error. The segment-level similarity enables to handle a large amount of shapes with significant topology or shape variations with a small set of segmented example shapes. Experimental results show that our algorithm can generate high quality segmentation and semantic labeling results in the Princeton segmentation benchmark.

 

Comput. Graph. Forum 33(5): 107-115 (2014)  [Paper] [Supplementary] [Video


 

 

Automatic 3D Indoor Scene Updating with RGBD Cameras

Zhenbao Liu, Sicong Tang, Weiwei Xu, Shuhui Bu, Junwei Han, Kun Zhou

Since indoor scenes are frequently changed in daily life, such as re-layout of furniture, the 3D reconstructions for them should be flexible and easy to update. We present an automatic 3D scene update algorithm to indoor scenes by capturing scene variation with RGBD cameras. We assume an initial scene has been reconstructed in advance in manual or other semi-automatic way before the change, and automatically update the reconstruction according to the newly captured RGBD images of the real scene update. It starts with an automatic segmentation process without manual interaction, which benefits from accurate labeling training from the initial 3D scene. After the segmentation, objects captured by RGBD camera are extracted to form a local updated scene. We formulate an optimization problem to compare to the initial scene to locate moved objects. The moved objects are then integrated with static objects in the initial scene to generate a new 3D scene. We demonstrate the efficiency and robustness of our approach by updating the 3D scene of several real-world scenes.

 

Comput. Graph. Forum 33(7): 269-278 (2014)  [Paper] [Supplementary] [Video


 

 

An asymptotic numerical method for inverse elastic shape design

Xiang Chen, Changxi Zheng, Weiwei Xu, Kun Zhou

Inverse shape design for elastic objects greatly eases the design efforts by letting users focus on desired target shapes without thinking about elastic deformations. Solving this problem using classic iterative methods (e.g., Newton-Raphson methods), however, often suffers from slow convergence toward a desired solution. In this paper, we propose an asymptotic numerical method that exploits the underlying mathematical structure of specific nonlinear material models, and thus runs orders of magnitude faster than traditional Newton-type methods. We apply this method to compute rest shapes for elastic fabrication, where the rest shape of an elastic object is computed such that after physical fabrication the real object deforms into a desired shape. We illustrate the performance and robustness of our method through a series of elastic fabrication experiments.

 

ACM Trans. Graph. 33(4): 95:1-95:11 (2014)  [Paper] [Supplementary] [Video


 

 

Imagining the unseen: stability-based cuboid arrangements for scene understanding

Tianjia Shao, Aron Monszpart, Youyi Zheng, Bongjin Koo, Weiwei Xu, Kun Zhou, Niloy J. Mitra

Missing data due to occlusion is a key challenge in 3D acquisition, particularly in cluttered man-made scenes. Such partial information about the scenes limits our ability to analyze and understand them. In this work we abstract such environments as collections of cuboids and hallucinate geometry in the occluded regions by globally analyzing the physical stability of the resultant arrangements of the cuboids. Our algorithm extrapolates the cuboids into the un-seen regions to infer both their corresponding geometric attributes (e.g., size, orientation) and how the cuboids topologically interact with each other (e.g., touch or fixed). The resultant arrangement provides an abstraction for the underlying structure of the scene that can then be used for a range of common geometry processing tasks. We evaluate our algorithm on a large number of test scenes with varying complexity, validate the results on existing benchmark datasets, and demonstrate the use of the recovered cuboid-based structures towards object retrieval, scene completion, etc.

 

ACM Trans. Graph. 33(6): 209:1-209:11 (2014)  [Paper] [Supplementary] [Video


 

 

Sensitivity-optimized rigging for example-based real-time clothing synthesis

Weiwei Xu, Nobuyuki Umetani, Qianwen Chao, Jie Mao, Xiaogang Jin, Xin Tong

We present a real-time solution for generating detailed clothing deformations from pre-computed clothing shape examples. Given an input pose, it synthesizes a clothing deformation by blending skinned clothing deformations of nearby examples controlled by the body skeleton. Observing that cloth deformation can be well modeled with sensitivity analysis driven by the underlying skeleton, we introduce a sensitivity based method to construct a pose-dependent rigging solution from sparse examples. We also develop a sensitivity based blending scheme to find nearby examples for the input pose and evaluate their contributions to the result. Finally, we propose a stochastic optimization based greedy scheme for sampling the pose space and generating example clothing shapes. Our solution is fast, compact and can generate realistic clothing animation results for various kinds of clothes in real time.

 

ACM Trans. Graph. 33(4): 107:1-107:11 (2014)  [Paper] [Supplementary] [Video


 

 

2013

 

As-Rigid-As-Possible Distance Field Metamorphosis

Yanlin Weng, Menglei Chai, Weiwei Xu, Yiying Tong, Kun Zhou

Widely used for morphing between objects with arbitrary topology, distance field interpolation (DFI) handles topological transition naturally without the need for correspondence or remeshing, unlike surface-based interpolation approaches. However, lack of correspondence in DFI also leads to ineffective control over the morphing process. In particular, unless the user specifies a dense set of landmarks, it is not even possible to measure the distortion of intermediate shapes during interpolation, let alone control it. To remedy such issues, we introduce an approach for establishing correspondence between the interior of two arbitrary objects, formulated as an optimal mass transport problem with a sparse set of landmarks. This correspondence enables us to compute non-rigid warping functions that better align the source and target objects as well as to incorporate local rigidity constraints to perform as-rigid-aspossible DFI. We demonstrate how our approach helps achieve flexible morphing results with a small number of landmarks.

 

Comput. Graph. Forum 32(7): 381-389 (2013)  [Paper] [Supplementary] [Video


 

 

Interpreting concept sketches

Tianjia Shao, Wilmot Li, Kun Zhou, Weiwei Xu, Baining Guo, Niloy J. Mitra

Concept sketches are popularly used by designers to convey pose and function of products. Understanding such sketches, however, requires special skills to form a mental 3D representation of the product geometry by linking parts across the different sketches and imagining the intermediate object configurations. Hence, the sketches can remain inaccessible to many, especially non-designers. We present a system to facilitate easy interpretation and exploration of concept sketches. Starting from crudely specified incomplete geometry, often inconsistent across the different views, we propose a globally-coupled analysis to extract part correspondence and inter-part junction information that best explain the different sketch views. The user can then interactively explore the abstracted object to gain better understanding of the product functions. Our key technical contribution is performing shape analysis without access to any coherent 3D geometric model by reasoning in the space of inter-part relations. We evaluate our system on various concept sketches obtained from popular product design books and websites.

 

ACM Trans. Graph. 32(4): 56:1-56:10 (2013)  [Paper] [Supplementary] [Video


 

 

Boundary-Aware Multidomain Subspace Deformation

Yin Yang, Weiwei Xu, Xiaohu Guo, Kun Zhou, Baining Guo

In this paper, we propose a novel framework for multidomain subspace deformation using node-wise corotational elasticity. With the proper construction of subspaces based on the knowledge of the boundary deformation, we can use the Lagrange multiplier technique to impose coupling constraints at the boundary without overconstraining. In our deformation algorithm, the number of constraint equations to couple two neighboring domains is not related to the number of the nodes on the boundary but is the same as the number of the selected boundary deformation modes. The crack artifact is not present in our simulation result, and the domain decomposition with loops can be easily handled. Experimental results show that the single-core implementation of our algorithm can achieve real-time performance in simulating deformable objects with around quarter million tetrahedral elements.

 

IEEE Trans. Vis. Comput. Graph. 19(10): 1633-1645 (2013)  [Paper] [Supplementary] [Video


 

 

2012

 

Motion-Guided Mechanical Toy Modeling

Lifeng Zhu, Weiwei Xu, John Snyder, Yang Liu, Guoping Wang, Baining Guo

We introduce a new method to synthesize mechanical toys solely from the motion of their features. The designer specifies the geometry and a time-varying rotation and translation of each rigid feature component. Our algorithm automatically generates a mechanism assembly located in a box below the feature base that produces the specified motion. Parts in the assembly are selected from a parameterized set including belt-pulleys, gears, crank-sliders, quick-returns, and various cams (snail, ellipse, and double-ellipse). Positions and parameters for these parts are optimized to generate the specified motion, minimize a simple measure of complexity, and yield a well-distributed layout of parts over the driving axes. Our solution uses a special initialization procedure followed by simulated annealing to efficiently search the complex configuration space for an optimal assembly.

 

ACM SIGGRAPH Asia 2012  [Paper] [Supplementary] [Video


 

 

An Interactive Approach to Semantic Modeling of Indoor Scenes with an RGBD Camera

Tianjia Shao, Weiwei Xu, Kun Zhou, Jingdong Wang, Dongping Li, Baining Guo

We present an interactive approach to semantic modeling of indoor scenes with a consumer-level RGBD camera. Using our approach, the user first takes a RGBD image of an indoor scene, which is automatically segmented into a set of regions with semantic labels. If the segmentation is not satisfactory, the user can draw some strokes to guide the algorithm to achieve better results. After the segmentation is finished, the depth data of each semantic region is used to retrieve a matching 3D model from a database. Each model is then transformed according to the image depth to yield the scene. For large scenes where a single image can only cover one part of the scene, the user can take multiple images to construct other parts of the scene. The 3D models built for all images are then transformed and unified into a complete scene. We demonstrate the efficiency and robustness of our approach by modeling several real-world scenes.

 

ACM SIGGRAPH Asia 2012  [Paper] [Video] [Data


 

 

All-Hex Meshing using Singularity-Restricted Field

Yufei Li, Yang Liu, Weiwei Xu, Wenping Wang, Baining Guo

Decomposing a volume into high-quality hexahedral cells is a challenging task in geometric modeling and computational geometry. Inspired by the use of cross field in quad meshing and the CubeCover approach in hex meshing, we present a complete all-hex meshing framework based on singularity-restricted field that is essential to induce a valid all-hex structure. Given a volume represented by a tetrahedral mesh, we first compute a boundary-aligned 3D frame field inside it, then convert the frame field to be singularity-restricted by our effective topological operations. In our all-hex meshing framework, we present an enhanced CubeCover approach that reduces degenerate elements appearing in the volume parameterizations via tetrahedral split operations and handle flipped elements effectively in hex-mesh extraction. Experimental results show that our algorithm generates high-quality all-hex meshes from a variety of 3D volumes robustly and efficiently.

 

ACM SIGGRAPH Asia 2012  [Paper] [Video


 

 

Diffusion Curve Textures for Resolution Independent Texture Mapping

Xin Sun, Guofu Xie, Yue Dong, Stephen Lin, Weiwei Xu, Wencheng Wang, Xin Tong, Baining GUo

We introduce a vector representation called diffusion curve tex-tures for mapping diffusion curve images (DCI) onto arbitrary surfaces. In contrast to the original implicit representation of DCIs [Orzan et al. 2008], where determining a single texture value requires iterative computation of the entire DCI via the Poisson equation, diffusion curve textures provide an explicit representa-tion from which the texture value at any point can be solved di-rectly, while preserving the compactness and resolution indepen-dence of diffusion curves. This is achieved through a formulation of the DCI diffusion process in terms of Green’s functions. This formulation furthermore allows the texture value of any rectangular region (e.g. pixel area) to be solved in closed form, which facilitates anti-aliasing. We develop a GPU algorithm that renders anti-aliased diffusion curve textures in real time, and demonstrate the effective-ness of this method through high quality renderings with detailed control curves and color variations.

 

ACM Transactions on Graphics (SIGGRAPH 2012)  [Paper][Video][bibtex


 

 

2011

 

General Planar Quadrilateral Mesh Design Using Conjugate Direction Field

Yang Liu, Weiwei Xu, Lifeng Zhu, Jun Wang, Baining Guo, Falai Chen, Guoping Wang

We present a novel method to approximate a freeform shape with a planar quadrilateral (PQ) mesh for modeling architectural glass structures. Our method is based on the study of conjugate direction fields (CDF) which allow the presence of k/4 singularities. Starting with a triangle discretization of a freeform shape, we first compute an as smooth as possible conjugate direction field satisfying the user’s directional and angular constraints, then apply mixed-integer quadrangulation and planarization techniques to generate a PQ mesh which approximates the input shape faithfully. We demonstrate that our method is effective and robust on various 3D models.

 

ACM SIGGRAPH Asia 2011  [Paper] [Video][bibtex


 

 

Discriminative Sketch-based 3D Model Retrieval via Robust Shape Matching

Tianjia Shao, Weiwei Xu, Kangkang Yin, Jingdong Wang, Kun Zhou, Baining Guo

We propose a sketch-based 3D shape retrieval system that is substantially more discriminative and robust than existing systems, especially for complex models. The power of our system comes from a combination of a contourbased 2D shape representation and a robust sampling-based shape matching scheme. They are defined over discriminative local features and applicable for partial sketches; robust to noise and distortions in hand drawings; and consistent when strokes are added progressively. However, our robust shape matching algorithm requires dense sampling and registration, which incurs a high computational cost. We thus devise critical acceleration methods to achieve interactive performance: precomputing kNN graphs that record transformations between neighboring contour images and enable fast online shape alignment; pruning sampling and shape registration strategically and hierarchically; and parallelizing shape matching on multi-core platforms or GPUs. We demonstrate the effectiveness of our system through various experiments, comparisons, and a user study.

 

Computer Graphics Forum (PG 2011)  [Paper] [Video][Bibtex


 

 

2010

 

Sampling-based Contact-Rich Motion Control

Libin Liu, KangKang Yin, Michiel van de Panne, Tianjia Shao, Weiwei Xu

Human motions are the product of internal and external forces, but these forces are very difficult to measure in a general setting. Given a motion capture trajectory, we propose a method to reconstruct its open-loop control and the implicit contact forces. The method employs a strategy based on randomized sampling of the control within user-specified bounds, coupled with forward dynamics simulation. Sampling-based techniques are well suited to this task because of their lack of dependence on derivatives, which are difficult to estimate in contact-rich scenarios. They are also easy to parallelize, which we exploit in our implementation on a compute cluster. We demonstrate reconstruction of a diverse set of captured motions, including walking, running, and contact rich tasks such as rolls and kip-up jumps. We further show how the method can be applied to physically based motion transformation and retargeting, physically plausible motion variations, and reference trajectory-free idling motions. Alongside the successes, we point out a number of limitations and directions for future work.

 

ACM SIGGRAPH 2010  [Paper] [Video 46MB][Bibtex


 

 

Deformation Transfer to Multi-component Objects

Kunzhou, Weiwei Xu, Yiying Tong, Mathieu Desbrun

We present a simple and effective algorithm to transfer deformation between surface meshes with multiple components. The algorithm automatically computes spatial relationships between components of the target object, builds correspondences between source and target, and finally transfers deformation of the source onto the target while preserving cohesion between the target’s components. We demonstrate the versatility of our approach on various complex models.

Computer Graphics Forum (Eurographics 2010) [Paper] [Video 22MB][Bibtex

 

 

 

2009

 

Joint-aware Manipulation of Deformable Model

Weiwei Xu, Jun Wang, KangKang Yin, Kun Zhou, Michiel van de Panne, Falai Chen, Baining Guo

 

Complex mesh models of man-made objects often consist of multiple components connected by various types of joints. We propose a joint-aware deformation framework that supports the direct manipulation of an arbitrary mix of rigid and deformable components. We apply slippable motion analysis to automatically detect multiple types of joint constraints that are implicit in model geometry. For single-component geometry or models with disconnected components, we support user-defined virtual joints. We integrate manipulation handle constraints, multiple components, joint constraints, joint limits, and deformation energies into a single volumetric-cell based space deformation problem. An iterative, parallelized Gauss-Newton solver is used to solve the resulting non-linear optimization. Interactive deformable manipulation is demonstrated on a variety of geometric models while automatically respecting their multi-component nature and the natural behavior of their joints.

ACM SIGGRAPH 2009, [Paper] [Video 66MB][Bibtex]

 

 

 

2008

 

Keyframe-based Video Object Deformation

Yanlin Weng, Weiwei Xu, Shichao Hu, Jun Zhang, Baining Guo

 

This paper presents a novel deformation system for video objects. The system is designed to minimize the amount of user interaction, while providing flexible and precise user control. It has a keyframe-based user interface. The user only needs to manipulate the video object at some keyframes. Our algorithm will smoothly propagate the editing result from the keyframes to the rest frames and automatically generate the new video object. The algorithm is able to preserve the temporal coherence as well as the shape features of the video objects in the original video clips.

IEEE Cyber World 2008, [Paper] [Video 32MB][Bibtex]

 

2007

 

Gradient Domain Editing of Deforming Mesh Sequence

Weiwei Xu, Kun Zhou, Yizhou Yu, Qifeng Tan, Qunsheng Peng, Baining Guo.

 

Many graphics applications, including computer games and 3D animated films, make heavy use of deforming mesh sequences. In this paper, we generalize gradient domain editing to deforming mesh sequences. Our framework is keyframe based. Given sparse and irregularly distributed constraints at unevenly spaced keyframes, our solution first adjusts the meshes at the keyframes to satisfy these constraints, and then smoothly propagate the constraints and deformations at keyframes to the whole sequence to generate new deforming mesh sequence. To achieve convenient keyframe editing, we have developed an efficient alternating least-squares method. It harnesses the power of subspace deformation and two-pass linear methods to achieve high-quality deformations. We have also developed an effective algorithm to define boundary conditions for all frames using handle trajectory editing. Our deforming mesh editing framework has been successfully applied to a number of editing scenarios with increasing complexity, including footprint editing, path editing, temporal filtering, handle-based deformation mixing, and spacetime morphing.

ACM Transactions on Graphics (SIGGRAPH 2007) [Paper] [Video 80MB][Bibtex]

Direct Manipulation of Subdivision Mesh

Kun Zhou, Xin Huang, Weiwei Xu, Baining Guo.

 

We present an algorithm for interactive deformation of subdivision surfaces, including displaced subdivision surfaces and subdivision surfaces with geometric textures. Our system lets the user directly manipulate the surface using freely-selected surface points as handles. During deformation the control mesh vertices are automatically adjusted such that the deforming surface satisfies the handle position constraints while preserving the original surface shape and details. To best preserve surface details, we develop a gradient domain technique that incorporates the handle position constraints and detail preserving objectives into the deformation energy. For displaced subdivision surfaces and surfaces with geometric textures, the deformation energy is highly nonlinear and cannot be handled with existing iterative solvers. To address this issue, we introduce a shell deformation solver, which replaces each numerically unstable iteration step with two stable mesh deformation operations. Our deformation algorithm only uses local operations and is thus suitable for GPU implementation. The result is a real-time deformation system running orders of magnitude faster than the state-of-the-art multigrid mesh deformation solver. We demonstrate our technique with a variety of examples, including examples of creating visually pleasing character animations in real-time by driving a subdivision surface with motion capture data.

 

ACM Transactions on Graphics (SIGGRAPH 2007) [Paper] [Video 80MB][Bibtex]

 

 

 

 

 

 

2003~2010

 

Gradient Domain Mesh Deformation – A Survey

Weiwei Xu, Kun Zhou

Journal of Computer Science and Technology, 24(1):6-18, 2009

 

 

 

2D Shape Deformation using Nonlinear Least Squares Optimization

Yanlin Weng, Weiwei Xu, Kun Zhou, Baining Guo

The visual Computer, 22(9-11):653-660, 2006, [Paper 2MB]

 

 

Footprint Sampling based Motion Editing

Weiwei Xu, Zhigeng Pan, Mingmin Zhang

Int. J. Image Graphics 3(2): 311-324 (2003)

 

 

Easybowling: a small bowling machine based on virtual simulation

Zhigeng Pan, Weiwei Xu, Jin Huang, Mingmin Zhang, Jiaoying Shi

Computers & Graphics 27(2): 231-238 (2003)

 

 

 

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