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Curvature-aware simplification for point-sampled geometry
Zhi-xun Su, Zhi-yang Li, Yuan-di Zhao, Jun-jie Cao
Front. Inform. Technol. Electron. Eng., 2011, 12(3): 184-194.
https://doi.org/10.1631/jzus.C1000068
We propose a novel curvature-aware simplification technique for point-sampled geometry based on the locally optimal projection (LOP) operator. Our algorithm includes two new developments. First, a weight term related to surface variation at each point is introduced to the classic LOP operator. It produces output points with a spatially adaptive distribution. Second, for speeding up the convergence of our method, an initialization process is proposed based on geometry-aware stochastic sampling. Owing to the initialization, the relaxation process achieves a faster convergence rate than those initialized by uniform sampling. Our simplification method possesses a number of distinguishing features. In particular, it provides resilience to noise and outliers, and an intuitively controllable distribution of simplification. Finally, we show the results of our approach with publicly available point cloud data, and compare the results with those obtained using previous methods. Our method outperforms these methods on raw scanned data.
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Sketch based garment modeling on an arbitrary view of a 3D virtual human model
Yu-lei Geng, Jin Wang, Guo-dong Lu, Zheng Liu, Gang Chen
Front. Inform. Technol. Electron. Eng., 2011, 12(3): 195-203.
https://doi.org/10.1631/jzus.C1000049
This paper presents a new approach for modeling a virtual garment intuitively and simply by sketching garment style lines. The user sketches directly onto the surface of 3D virtual human from arbitrary viewing directions, and the 3D garment suited to the virtual human can be created automatically. First, a distance field based allocation algorithm is proposed to find the 3D point which has the shortest given distance to the virtual human along the view direction. Then, the 3D style lines are generated by transforming from the 2D strokes on the human model and all the garment pieces are recognized from the 3D style lines. Finally, the 3D garment model is constructed by using the angle and offset based interpolation and Delaunay triangulation. In addition, we propose a body feature based template reusing method to fit the 3D garment to different virtual human models. The method can be adapted to designer habits and improve the usefulness of garment design. Examples show that the method is useful and efficient.
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A self-optimizing QoS-aware service composition approach in a context sensitive environment
Yuan-hong Shen, Xiao-hu Yang
Front. Inform. Technol. Electron. Eng., 2011, 12(3): 221-238.
https://doi.org/10.1631/jzus.C1000031
QoS-aware service composition is aimed to maximize the global QoS of a composite service when selecting candidate services. In a context sensitive service execution environment in pervasive computing, the context information for service composition is not static: device, policy, and user constraints, and QoS requirements may change, new services may be deployed, old ones withdrawn, or existing ones change their QoS parameters. This results in the current service composition plan failing or its QoS degrading from the optimum. In this paper, a runtime self-optimizing service composition framework is proposed. An implementation of a prototype for this framework is presented, addressing the issues of reducing extra delay while increasing global QoS in service composition in a dynamic context environment. Three service re-plan algorithms are compared that can be used in dynamic context environment, i.e., minimal-conflict hill-climbing repair genetic algorithm (MCHC-repair GA), an improved penalty-based GA, and our multi-population conflicts sorted repair genetic algorithm (MP-CS-repair GA), as well as three kinds of service composition mechanisms—with backup, without backup, and our context-aware service re-selection mechanisms. The results show that our MP-CS-repair GA and context-aware service re-selection method can reduce more extra delay while acquiring a higher global QoS for the composite service in a context sensitive environment. This context-aware service re-selection mechanism also shows some adaptability to different context change frequencies and user requirements for reducing computation cost in the self-optimizing process.
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Using concurrent lines in central catadioptric camera calibration
Lei Zhang, Xin Du, Ji-lin Liu
Front. Inform. Technol. Electron. Eng., 2011, 12(3): 239-249.
https://doi.org/10.1631/jzus.C1000043
Central catadioptric cameras have been extensively adopted in robotics and surveillance due to their extensive field of view. To attain precise 3D information in these applications, it is important to calibrate the catadioptric cameras accurately. The existing calibration techniques either require prior knowledge of the mirror types, or highly depend on a conic estimation procedure, which might be ruined if there are only small portions of the conic visible on calibration images. In this paper, we design a novel planar pattern with concurrent lines as a calibration rig, which is more robust in conic estimation since the relationship among lines is taken into account. Based on the line properties, we propose a rough-to-fine approach suitable for the new planar pattern to calibrate central catadioptric cameras. This method divides the nonlinear optimization calibration problem into several linear sub-problems that are much more robust against noise. Our calibration method can estimate intrinsic parameters and the mirror parameter simultaneously and accurately, without a priori knowledge of the mirror type. The performance is demonstrated by both simulation and a real hyperbolic catadioptric imaging system.
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8 articles
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