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 Edited by: Editorial Board of Journal Of Computer Science and Technology P.O. Box 2704, Beijing 100190, P.R. China Sponsored by: Institute of Computing Technology, CAS & China Computer Federation Undertaken by: Institute of Computing Technology, CAS Published by: SCIENCE PRESS, BEIJING, CHINA Distributed by: China: All Local Post Offices Other Countries: Springer

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• Table of Content
 15 March 2006, Volume 21 Issue 2 Previous Issue    Next Issue
Articles
 Select Inflatable Models Ling Li and Vasily Volkov Journal of Computer Science and Technology, 2006, 21 (2): 154-158 .  Abstract   PDF(596KB) ( 1389 )   Chinese Summary A physically-based model is presented for the simulation of a new type of deformable objects---inflatable objects, such as shaped balloons, which consist of pressurized air enclosed by an elastic surface. These objects have properties inherent in both 3D and 2D elastic bodies, as they demonstrate the behaviour of 3D shapes using 2D formulations. As there is no internal structure in them, their behaviour is substantially different from the behaviour of deformable solid objects. We use one of the few available models for deformable surfaces, and enhance it to include the forces of internal and external pressure. These pressure forces may also incorporate buoyancy forces, to allow objects filled with a low density gas to float in denser media. The obtained models demonstrate rich dynamic behaviour, such as bouncing, floating, deflation and inflation.
 Select Real-Time Watercolor for Animation Thomas Luft and Oliver Deussen Journal of Computer Science and Technology, 2006, 21 (2): 159-165 .  Abstract   PDF(1863KB) ( 1391 )   Chinese Summary We present algorithms that allow for real-time rendering of 3D-scenes with a watercolor painting appearance. Our approach provides an appropriate simplification of the visual complexity, imitates characteristic natural effects of watercolor, and provides two essential painting techniques: the wet-on-wet and the wet-on-dry painting. We concentrate on efficient algorithms based on image space processing rather than on an exact simulation. This allows for the real-time rendering of 3D-scenes. During an animation a high frame-to-frame coherence can be achieved due to a stable segmentation scheme. Finally, we seamlessly integrate a smooth illumination into the watercolor renderings using information from the 3D-scene.
 Select Reflection and Refraction on Implicit Surfaces Wei Hu, Kai-Huai Qin, Hua-Wei Wang, and Ya-Feng Li Journal of Computer Science and Technology, 2006, 21 (2): 166-172 .  Abstract   PDF(2254KB) ( 1421 )   Chinese Summary Implicit surfaces are often used in computer graphics. They can be easily modeled and rendered, and many objects are composed of them in our daily life. In this paper, based on the concept of virtual objects, a novel method of real-time rendering is presented for reflection and refraction on implicit surface. The method is used to construct virtual objects from real objects quickly, and then render the virtual objects as if they were real objects except for one more step of merging their images with the real objects images. Characteristics of implicit surfaces are used to compute virtual objects effectively and quickly. GPUs (Graphics Processing Units) are used to compute virtual vertices quickly and further accelerate the computing and rendering processes. As a result, realistic effects of reflections and refractions on implicit surfaces are rendered in real time.
 Select Texture Pattern Generation Using Clonal Mosaic Texture Pattern Generation Using Clonal Mosaic How Jiann Teo and Kok Cheong Wong Journal of Computer Science and Technology, 2006, 21 (2): 173-180 .  Abstract   PDF(2031KB) ( 1263 )   Chinese Summary In this paper, an effective system for synthesizing animal skin patterns on arbitrary polygonal surfaces is developed. To accomplish the task, a system inspired by the Clonal Mosaic (CM) model is proposed. The CM model simulates cells reactions on arbitrary surface. By controlling the division, mutation and repulsion of cells, a regulated spatial arrangement of cells is formed. This arrangement of cells shows appealing result, which is comparable with those naturalpatterns observed from animal skin. However, a typical CM simulation process incurs high computational cost, where the distances among cells across a polygonal surface are measured and the movements of cells are constrained on the surface. In this framework, an approach is proposed to transform each of the original 3D geometrical planes of the surface into its Canonical Reference Plane Structure. This structure helps to simplify a 3D computational problem into a more manageable 2D problem. Furthermore, the concept of Local Relaxation is developed to optimally enhance the relaxation process for a typical CM simulation. The performances of the proposed solution methods have been verified with extensive experimental results.
 Select View Dependent Sequential Point Trees Wen-Cheng Wang, Feng Wei, and En-Hua Wu Journal of Computer Science and Technology, 2006, 21 (2): 181-188 .  Abstract   PDF(1857KB) ( 1322 )   Chinese Summary Sequential point trees provide the state-of-the-art technique for rendering point models, by re-arranging hierarchical points sequentially according to geometric errors running on GPU for fast rendering. This paper presents a view dependent method to augment sequential point trees by embedding the hierarchical tree structures in the sequential list of hierarchical points. By the method, two kinds of indices are constructed to facilitate the points rendering in an order mostly from near to far and from coarse to fine. As a result, invisible points can be culled view-dependently in high efficiency for hardware acceleration, and at the same time, the advantage of sequential point trees could be still fully taken. Therefore, the new method can run much faster than the conventional sequential point trees, and the acceleration can be highly promoted particularly when the objects possess complex occlusion relationship and viewed closely because invisible points would be in a high percentage of the points at finer levels.
 Select Real-Time Optimal Reach-Posture Prediction in a New Interactive Virtual Environment Jingzhou Yang, R. Timothy Marler, Steven Beck, Karim Abdel-Malek, and Joo Kim Journal of Computer Science and Technology, 2006, 21 (2): 189-198 .  Abstract   PDF(2878KB) ( 1410 )   Chinese Summary Human posture prediction is a key factor for the design and evaluation of workspaces, in a virtual environment using virtual humans. This work presents a new interface and virtual environment for the direct human optimized posture prediction (D-HOPP) approach to predicting realistic reach postures of digital humans, where reach postures entail the use of the torso, arms, and neck. D-HOPP is based on the contention where depending on what type of task is being completed, and human posture is governed by different human performance measures. A human performance measure is a physics-based metric, such as energy or discomfort, and serves as an objective function in an optimization formulation. The problem is formulated as a single-objective optimization (SOO) problem with a single performance measure and as multi-objective-optimization (MOO) problem with multiple combined performance measures. We use joint displacement, change in potential energy, and musculoskeletal discomfort as performance measures. D-HOPP is equipped with an extensive yet intuitive user-interface, and the results are presented in an interactive virtual environment.
 Select Bernoulli Embedding Model and Its Application in Texture Mapping Hong-Xin Zhang, Ying Tang, Hui Zhao, and Hu-Jun Bao Journal of Computer Science and Technology, 2006, 21 (2): 199-203 .  Abstract   PDF(1412KB) ( 1264 )   Chinese Summary A novel texture mapping technique is proposed based on nonlinear dimension reduction, called Bernoulli logistic embedding (BLE). Our probabilistic embedding model builds texture mapping with minimal shearing effects. A log-likelihood function, related to the Bregman distance, is used to measure the similarity between two related matrices defined over the spaces before and after embedding. Low-dimensional embeddings can then be obtained through minimizing this function by a fast block relaxation algorithm. To achieve better quality of texture mapping, the embedded results are adopted as initial values for mapping enhancement by stretch-minimizing. Our method can be applied to both complex mesh surfaces and dense point clouds.
 Select Representation of Urban Buildings Using Modified Relief Mapping Byounghyun Yoo and Soonhung Han Journal of Computer Science and Technology, 2006, 21 (2): 204-208 .  Abstract   PDF(1740KB) ( 1646 )   Chinese Summary This paper describes the real-time mapping displacement of buildings onto the polygon model of base terrain of geo-spatial information. The buildings are represented as height maps, leading to low memory requirements and not involving changes of the original geometry (i.e., no vertices are created or displaced). The displacement of buildings is mapped toward the protruding direction. The base of texture which represents the ground in topography is correctly mapped onto base polygon without any distortion. This approach can exhibit the correct occlusions between buildings and ground due to parallax and correct self-occlusion.
 Select The Number of Independent Kruppa Constraints from N Images Zhan-Yi Hu, Yi-Hong Wu, Fu-Chao Wu, and Song-De Ma Journal of Computer Science and Technology, 2006, 21 (2): 209-217 .  Abstract   PDF(424KB) ( 1218 )   Chinese Summary It is well known that without any priori knowledge on the scene, camera motion and camera intrinsic parameters, the only constraint between a pair of images is the so-called epipolar constraint, or equivalently its fundamental matrix. For each fundamental matrix, at most two independent constraints on the cameras intrinsic parameters are available via the Kruppa equations. Given N images, N(N-1)/2 fundamental matrices appear, and N(N-1) Kruppa constraints are available. However, to our knowledge, a formal proof of how many independent Kruppa constraints exist out of these N(N-1) ones is unavailable in the literature. In this paper, we prove that given N images captured by a pinhole camera with varying parameters and under general motion, the number of independent Kruppa constraints is (5N-9) (N>2), and it is less than that of independent constraints from the absolute quadric by only one. This one-constraint-less property of the Kruppa equations is their inherent deficiency and is independent of camera motion. This deficiency is due to their failure of automatic enforcement of the rank-three-ness on the absolute quadric.
 Select A New Method of Manifold Mosaic for Large Displacement Images Xian-Yong Fang, Ming-Min Zhang, Zhi-Geng Pan, and Peng Wang Journal of Computer Science and Technology, 2006, 21 (2): 218-223 .  Abstract   PDF(1868KB) ( 1537 )   Chinese Summary In the traditional manifold mosaic, a single center strip is clipped out from each source image to create a large image. Therefore the displacement between neighboring views should be very small in order to fulfill effective strips cutting. In this paper, a method is proposed to create a manifold mosaic by images with relative large displacement by means of cutting out multiple strips in the overlap area according to the homography between images. These strips are then warped together to create a smooth mosaic. An improved RANSAC algorithm is also presented in order to improve the precision of homography calculation. Experimental results demonstrate the efficiency of the method.
 Select A Novel Variational Image Model: Towards a Unified Approach to Image Editing Yun Zeng, Wei Chen, and Qun-Sheng Peng Journal of Computer Science and Technology, 2006, 21 (2): 224-231 .  Abstract   PDF(3116KB) ( 2105 )   Chinese Summary In this paper we propose a unified variational image editing model. It interprets image editing as a variational problem concerning the adaptive adjustments to the zero- and first-derivatives of the images which correspond to the color and gradient items. By varying the definition domain of each of the two items as well as applying diverse operators, the new model is capable of tackling a variety of image editing tasks. It achieves visually better seamless image cloning effects than existing approaches. It also induces a new and efficient solution to adjusting the color of an image interactively and locally. Other image editing tasks such as stylized processing, local illumination enhancement and image sharpening, can be accomplished within the unified variational framework. Experimental results verify the high flexibility and efficiency of the proposed model.
 Select Automatic Shape Control of Triangular B-Splines of Arbitrary Topology Ying He, Xian-Feng Gu, and Hong Qin Journal of Computer Science and Technology, 2006, 21 (2): 232-237 .  Abstract   PDF(2190KB) ( 1204 )   Chinese Summary Triangular B-splines are powerful and flexible in modeling a broader class of geometric objects defined over arbitrary, non-rectangular domains. Despite their great potential and advantages in theory, practical techniques and computational tools with triangular B-splines are less-developed. This is mainly because users have to handle a large number of irregularly distributed control points over arbitrary triangulation. In this paper, an automatic and efficient method is proposed to generate visually pleasing, high-quality triangular B-splines of arbitrary topology. The xperimental results on several real datasets show that triangular B-splines are powerful and effective in both theory and practice.
 Select Radial Supershapes for Solid Modeling Yohan D. Fougerolle, Andrei Gribok, Sebti Foufou, Frederic Truchetet, and Mongi A. Abidi Journal of Computer Science and Technology, 2006, 21 (2): 238-243 .  Abstract   PDF(1056KB) ( 1459 )   Chinese Summary In the previous work, an efficient method has been proposed to represent solid objects as multiple combinations of globally deformed supershapes. In this paper, this framework is applied with a new supershape implicit function that is based on the notion of radial distance and results are presented on realistic models composed of hundreds of hierarchically globally deformed supershapes. An implicit equation with guaranteed differential properties is obtained by simple combinations of the primitives implicit representations using R-function theory. The surface corresponding to the zero-set of the implicit equation is efficiently and directly polygonized using the primitives parametric forms. Moreover, hierarchical global deformations are considered to increase the range of shapes that can be modeled. The potential of the approach is illustrated by representing complex models composed of several hundreds of primitives inspired from CAD models of mechanical parts.
 Select DBSC-Based Grayscale Line Image Vectorization Konstantin Melikhov, Feng Tian, Jie Qiu, Quan Chen,and Hock Soon Seah Journal of Computer Science and Technology, 2006, 21 (2): 244-248 .  Abstract   PDF(741KB) ( 1458 )   Chinese Summary Vector graphics plays an important role in computer animation and imaging technologies. However present techniques and tools cannot fully replace traditional pencil and paper. Additionally, vector representation of an image is not always available. There is not yet a good solution for vectorizing a picture drawn on a paper. This work attempts to solve the problem of vectorizing grayscale line drawings. The solution proposed uses Disk B-Spline curves to represent strokes of an image in vector form. The algorithm builds a vector representation from a grayscale raster image, which can be a scanned picture for instance. The proposed method uses a Gaussian sliding window to calculate skeleton and perceptive width of a stroke. As a result of vectorization, the given image is represented by a set of Disk B-Spline curves.
 Select Specification of Initial Shapes for Dynamic Implicit Curve/Surface Reconstruction Zhou-Wang Yang, Chun-Lin Wu, Jian-Song Deng,and Fa-Lai Chen Journal of Computer Science and Technology, 2006, 21 (2): 249-254 .  Abstract   PDF(1422KB) ( 1243 )   Chinese Summary The dynamic implicit curve/surface reconstruction demands no special requirement on the initial shapes in general. In order to speed up the iteration in the reconstruction, we discuss how to specify the initial shapes so as to reflect the geometric information and the topology structure of the given data. The basic idea is based on the combination of the distance function and the generalized eigenvector fitting model.
 Select Connolly Surface on an Atomic Structure via Voronoi Diagram of Atoms Joonghyun Ryu, Rhohun Park, and Deok-Soo Kim Journal of Computer Science and Technology, 2006, 21 (2): 255-260 .  Abstract   PDF(1266KB) ( 1788 )   Chinese Summary One of the most important geometric structures of a protein is the Connolly surface of protein since a Connolly surface plays an important role in protein folding, docking, interactions between proteins, amongst other things. This paper presents an algorithm for precisely and efficiently computing the Connolly surface of a protein using a proposed geometric construct called \beta-shape based on the Voronoi diagram of atoms in the protein. Given the Voronoi diagram of atoms based on the Euclidean distance from the atom surfaces, the proposed algorithm first computes a \beta-shape with an appropriate probe. Then, the Connolly surface is computed by employing the blending operation on the atomic complex of the protein by the given probe.
 Select Determining Knots by Minimizing Energy Cai-Ming Zhang, Hui-Jian Han, and Fuhua Frank Cheng Journal of Computer Science and Technology, 2006, 21 (2): 261-264 .  Abstract   PDF(648KB) ( 1033 )   Chinese Summary A new method for determining knots to construct polynomial curves is presented. At each data point, a quadric curve which passes three consecutive points is constructed. The knots for constructing the quadric curve are determined by minimizing the internal strain energy, which can be regarded as a function of the angle. The function of the angle is expanded as a Taylor series with two terms, then the two knot intervals between the three consecutive points are defined by linear expression. Between the two consecutive points, there are two knot intervals, and the combination of the two knot intervals is used to define the final knot interval. A comparison of the new method with several existing methods is included.
 Select Generation of Discrete Bicubic G^1 B-Spline Ship Hullform Surfaces from a Given Curve Network Using Virtual Iso-Parametric Curves Joong-Hyun Rhim, Doo-Yeoun Cho, Kyu-Yeul Lee, and Tae-Wan Kim Journal of Computer Science and Technology, 2006, 21 (2): 265-271 .  Abstract   PDF(2719KB) ( 1897 )   Chinese Summary We propose a method that automatically generates discrete bicubic G^{1 continuous B-spline surfaces that interpolate the curve network of a ship hullform. First, the curves in the network are classified into two types: boundary curves and reference curves''. The boundary curves correspond to a set of rectangular (or triangular) topological type that can be represented with tensor-product (or degenerate) B-spline surface patches. Next, in the interior of the patches, surface fitting points and cross boundary derivatives are estimated from the reference curves by constructing virtual'' iso-parametric curves. Finally, a discrete G^1 continuous B-spline surface is generated by a surface fitting algorithm. Several smooth ship hullform surfaces generated from curve networks corresponding to actual ship hullforms demonstrate the quality of the method.
 Select Modeling in Multi-Resolution and Its Applications Sungchan Kim, Kunwoo Lee, Taesik Hong, and Moonki Jung Journal of Computer Science and Technology, 2006, 21 (2): 272-278 .  Abstract   PDF(2542KB) ( 1664 )   Chinese Summary It is becoming common for many designers to work together on very complex assemblies in a collaborative environment. To work efficiently in this environment, the capabilities to simplify the portions of an assembly and to reset it to the original resolution should be added to the current CAD systems. Thus operators realizing multi-resolution on B-rep were proposed in previous work. This paper illustrates a prototype multi-resolution system to integrate the proposed operators and its applications. The multi-resolution system can be used in similarity comparisons to reduce the calculation load and to get the full comparison result in the overall shape. Then the features recognized with this system can be used in more detailed comparisons. This system also can be used conceptually to solve security problems in collaborative design.
 Select Geometric Properties of Ribs and Fans of a Bezier Curve Joo-Haeng Lee and Hyungjun Park Journal of Computer Science and Technology, 2006, 21 (2): 279-283 .  Abstract   PDF(1021KB) ( 1349 )   Chinese Summary Ribs and fans are interesting geometric entities that are derived from a given Bezier curve or surface based on the recent theory of rib and fan decomposition. In this paper, we present some of new geometric properties of ribs and fans for a Bezier curve including composite fans, rib-invariant deformation, and fan-continuity in subdivision. We also give some examples for the presented properties.
 Select Efficient Computation of k-Medians over Data Streams Under Memory Constraints Zhi-Hong Chong, Jeffrey Xu Yu, Zhen-Jie Zhang, Xue-Min Lin, Wei Wang, and Ao-Ying Zhou Journal of Computer Science and Technology, 2006, 21 (2): 284-296 .  Abstract   PDF(2180KB) ( 1586 )   Chinese Summary In this paper, we study the problem of efficiently computing k-medians over high-dimensional and high speed data streams. The focus of this paper is on the issue of minimizing CPU time to handle high speed data streams on top of the requirements of high accuracy and small memory. Our work is motivated by the following observation: the existing algorithms have similar approximation behaviors in practice, even though they make noticeably different worst case theoretical guarantees. The underlying reason is that in order to achieve high approximation level with the smallest possible memory, they need rather complex techniques to maintain a sketch, along time dimension, by using some existing off-line clustering algorithms. Those clustering algorithms cannot guarantee the optimal clustering result over data segments in a data stream but accumulate errors over segments, which makes most algorithms behave the same in terms of approximation level, in practice. We propose a new grid-based approach which divides the entire data set into cells (not along time dimension). We can achieve high approximation level based on a novel concept called (1-\epsilon)-dominant. We further extend the method to the data stream context, by leveraging a density-based heuristic and frequent item mining techniques over data streams. We only need to apply an existing clustering once to computing k-medians, on demand, which reduces CPU time significantly. We conducted extensive experimental studies, and show that our approaches outperform other well-known approaches.
 Select PMC: Select Materialized Cells in Data Cubes Hong-Song Li and Hou-Kuan Huang Journal of Computer Science and Technology, 2006, 21 (2): 297-305 .  Abstract   PDF(2676KB) ( 1338 )   Chinese Summary QC-Tree is one of the most storage-efficient structures for data cubes in an MOLAP system. Although QC-Tree can achieve a high compression ratio, it is still a fully materialized data cube. In this paper, an improved structure PMC is presented allowing us to materialize only a part of the cells in a QC-Tree to save more storage space. There is a notable difference between our partially materialization algorithm and traditional materialized views selection algorithms. In a traditional algorithm, when a view is selected, all the cells in this view are to be materialized. Otherwise, if a view is not selected, all the cells in this view will not be materialized. This strategy results in the unstable query performance. The presented algorithm, however, selects and materializes data in cell level, and, along with further reduced space and update cost, it can ensure a stable query performance. A series of experiments are conducted on both synthetic and real data sets. The results show that PMC can further reduce storage space occupied by the data cube, and can shorten the time to update the cube.
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