My research interests lie in the field of computer graphics. Currently, I am working on the following projects :

• OcTree-based topology repair and editing
• Geodesic computation on meshes: implementation and application
• Feature sensitive mesh processing

Editing The Topology of 3D Models by Sketching

ACM SIGGRAPH 2007. (Paper, Movie)
Tao Ju, Qian-Yi Zhou and Shi-Min Hu

We present a method for modifying the topology of a 3D model with user control. The heart of our method is a guided topology editing algorithm. Given a source model and a user-provided target shape, the algorithm modifies the source so that the resulting model is topologically consistent with the target. Our algorithm permits removing or adding various topological features (e.g., handles, cavities and islands) in a common framework and ensures that each topological change is made by minimal modification to the source model. To create the target shape, we have also designed a convenient 2D sketching interface for drawing 3D line skeletons. As demonstrated in a suite of examples, the use of sketching allows more accurate removal of topological artifacts than previous methods, and enables creative designs with specific topological goals.

Video: Download video here (31.8MB). (Cannot open the video? Cannot hear the audio? Get latest QuickTime player.)

Software: A software MendIT based on this paper is currently available at: http://graphics.usc.edu/~qianyizh/software.html

Topology Repair of Solid Models Using Skeletons

IEEE Trans. Vis. Comput. Graph., Vol. 13, pp. 675-685, 2007. (Paper, Slides)
Qian-Yi Zhou, Tao Ju and Shi-Min Hu

We present a method for repairing topological errors on solid models in the form of small surface handles, which often arise from surface reconstruction algorithms. We utilize a skeleton representation that offers a new mechanism for identifying and measuring handles. Our method presents two unique advantages over previous approaches. First, handle removal is guaranteed not to introduce invalid geometry or additional handles. Second, by using an adaptive grid structure, our method is capable of processing huge models efficiently at high resolutions.

Slides: Download slides here (24.8MB). A poster for this paper is also available, download poster here (7.5MB).

Software: A software TopoMender based on this paper is now available, please refer to webpage:
http://graphics.usc.edu/~qianyizh/software.html

Handling Degenerate Cases in Exact Geodesic Computation on Triangle Meshes

Computer Graphics International, 2007, to appear. (Paper)
Yong-Jin Liu, Qian-Yi Zhou and Shi-Min Hu

The computation of exact geodesics on triangle meshes is a widely used operation in computer-aided design and computer graphics. Practical algorithms for computing such exact geodesics have been recently proposed by Surazhsky et al (2005). By applying these geometric algorithms to real-world data, degenerate cases frequently appear. In this paper we classify and enumerate all the degenerate cases in a systematic way. Based on the classification, we present solutions to handle all the degenerate cases consistently and correctly. The common users may find the present techniques useful when they implement a robust code of computing exact geodesic paths on meshes.

Robust Feature Classification and Editing

IEEE Trans. Vis. Comput. Graph., Vol. 13, pp. 34-45, 2007. (Paper)
Yu-Kun Lai, Qian-Yi Zhou, Shi-Min Hu, Johannes Wallner and Helmut Pottmann

Sharp edges, ridges, valleys and prongs are critical for the appearance and an accurate representation of a 3D model. In this paper, we propose a novel approach that deals with the global shape of features in a robust way. Based on a remeshing algorithm which delivers an isotropic mesh in a feature sensitive metric, features are recognized on multiple scales via integral invariants of local neighborhoods. Morphological and smoothing operations are then used for feature region extraction and classification into basic types such as ridges, valleys and prongs. The resulting representation of feature regions is further used for feature-specific editing operations.

Feature Sensitive Mesh Segmentation

ACM Symp. Solid and Physical Modeling, pp. 7-16, 2006. (Paper)
Yu-Kun Lai, Qian-Yi Zhou, Shi-Min Hu and Ralph R. Martin

Segmenting meshes into natural regions is useful for model understanding and many practical applications. In this paper, we present a novel, automatic algorithm for segmenting meshes into meaningful pieces. Our approach is a clustering-based top-down hierarchical segmentation algorithm. We extend recent work on feature sensitive isotropic remeshing to generate a mesh hierarchy especially suitable for segmentation of large models with regions at multiple scales. Using integral invariants for estimation of local characteristics, our method is robust and efficient. Moreover, statistical quantities can be incorporated, allowing our approach to segment regions with different geometric characteristics or textures.