23-Issue 2
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Item Computer Graphics forum(The Eurographics Association and Blackwell Publishing, Inc, 2004) Duke, David; Scopigno, RobertoItem Distributed and Collaborative Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2004) Brodlie, K. W.; Duce, D. A.; Gallop, J. R.; Walton, J. P. R. B.; Wood, J. D.Visualization is a powerful tool for analyzing data and presenting results in science, engineering and medicine. This paper reviews ways in which it can be used in distributed and/or collaborative environments. Distributed visualization addresses a number of resource allocation problems, including the location of processing close to data for the minimization of data traffic. The advent of the Grid Computing paradigm and the link to Web Services provides fresh challenges and opportunities for distributed visualization-including the close coupling of simulations and visualizations in a steering environment. Recent developments in collaboration have seen the growth of specialized facilities (such as Access Grid) which have supplemented traditional desktop video conferencing using the Internet and multicast communications. Collaboration allows multiple users-possibly at remote sites-to take part in the visualization process at levels which range from the viewing of images to the shared control of the visualization methods. In this review, we present a model framework for distributed and collaborative visualization and assess a selection of visualization systems and frameworks for their use in a distributed or collaborative environment. We also discuss some examples of enabling technology and review recent work from research projects in this field.Item Image Interpolation by Pixel-Level Data-Dependent Triangulation(The Eurographics Association and Blackwell Publishing Ltd., 2004) Su, Dan; Willis, PhilipWe present a novel image interpolation algorithm. The algorithm can be used in arbitrary resolution enhancement, arbitrary rotation and other applications of still images in continuous space. High-resolution images are interpolated from the pixel-level data-dependent triangulation of lower-resolution images. It is simpler than other methods and is adaptable to a variety of image manipulations. Experimental results show that the new 'mesh image' algorithm is as fast as the bilinear interpolation method. We assess the interpolated images' quality visually and also by the MSE measure which shows our method generates results comparable in quality to slower established methods. We also implement our method in graphics card hardware using OpenGL which leads to real-time high-quality image reconstruction. These features give it the potential to be used in gaming and image-processing applications.Item An Integer One-Pass Algorithm for Voxel Traversal(The Eurographics Association and Blackwell Publishing Ltd., 2004) Liu, Y. K.; Zalik, B.; Yang, H.Voxel traversing along a line in a uniformly divided voxel space is frequently needed in different applications of computer graphics. The paper presents a new integer one-pass algorithm for this problem. In 2D, the proposed approach is based on a modification of the well-known Bresenham algorithm. The algorithm is then extended in 3D where a special case may occur. It is characterized by a simple discriminator. A derivation for this discriminator given in the paper confirms that all calculations can be realized using only integer arithmetic. In this way, the accumulation of rounding errors is completely eliminated, and a robust and compact implementation can be easily achieved. One of the main advantages of the proposed algorithm is that it visits 1-3 voxels during each iteration thus assuring its efficiency. The algorithm has been compared with other algorithms for voxel traversing by measuring spent CPU time. For comparison, Cleary and Wyvill's, Amanatides and Woo's, and Code-based algorithm have been used. The proposed algorithm is faster than the referenced algorithms.Item Modeling Trees with Hypertextures(The Eurographics Association and Blackwell Publishing Ltd., 2004) Strnad, D.; Guid, N.In the paper, a new method for modelling trees at medium detail is presented. The method is based on a volumetric representation of trees, generated by an iterated function system (IFS). Alleviating the modeling restrictions of fractal techniques, extensions to the standard IFS are introduced. Practical aspects of modeling and rendering of trees, such as data structures and bounding volumes, are discussed. The advantages of the new method are described at the end together with some results.Item Space-Time Hierarchical Radiosity with Clustering and Higher-Order Wavelets(The Eurographics Association and Blackwell Publishing Ltd., 2004) Damez, Cyrille; Holzschuch, Nicolas; Sillion, Francois X.We address in this paper the issue of computing diffuse global illumination solutions for animation sequences. The principal difficulties lie in the computational complexity of global illumination, emphasized by the movement of objects and the large number of frames to compute, as well as the potential for creating temporal discontinuities in the illumination, a particularly noticeable artifact. We demonstrate how space-time hierarchical radiosity, i.e. the application to the time dimension of a hierarchical decomposition algorithm, can be effectively used to obtain smooth animations: first by proposing the integration of spatial clustering in a space-time hierarchy; second, by using a higher-order wavelet basis adapted for the temporal dimension. The resulting algorithm is capable of creating time-dependent radiosity solutions efficiently.Item The State of the Art in Flow Visualization: Dense and Texture-Based Techniques(The Eurographics Association and Blackwell Publishing Ltd., 2004) Laramee, Robert S.; Hauser, Helwig; Doleisch, Helmut; Vrolijk, Benjamin; Post, Frits H. and Weiskopf, DanielFlow visualization has been a very attractive component of scientific visualization research for a long time. Usually very large multivariate datasets require processing. These datasets often consist of a large number of sample locations and several time steps. The steadily increasing performance of computers has recently become a driving factor for a reemergence in flow visualization research, especially in texture-based techniques. In this paper, dense, texture-based flow visualization techniques are discussed. This class of techniques attempts to provide a complete, dense representation of the flow field with high spatio-temporal coherency. An attempt of categorizing closely related solutions is incorporated and presented. Fundamentals are shortly addressed as well as advantages and disadvantages of the methods.Item A Viewpoint-Dependent Approach to Ray Trace Free-Form Surfaces(The Eurographics Association and Blackwell Publishing Ltd., 2004) Formella, A.; Mueller, K.For convincing realistic scenes objects with free-form surfaces are essential. Especially for photorealistic rendering pure polygonal models are often not sufficient. We present a new kind of algorithm to render free-form surfaces in a rendering system based on ray tracing. We describe a triangular patch as usual by its three points and normal vectors, but base the intersection calculation as well on the viewpoint of the camera (or, in general, on the ray itself). Hence, the shape of the object depends to some extent on the sampling rays. However, the resulting differences of, for instance, the shape of the silhouette to the shape of the corresponding shadow is usually not perceived by the observer of the rendered image. Because we perform a direct computation without a tessellation process, the resulting surface, its shadows, and its reflections appear smooth independent of the distance to the camera. Furthermore, the memory consumption depends only linearly on the number of input triangles. Special features like creases, T-vertices, and darts are also well supported. The computed uv-coordinates provide a direct means for texture mapping whose visual appearance improves significantly compared to triangle meshes of the same resolution.Item Visualizing Objects with Mirrors(The Eurographics Association and Blackwell Publishing Ltd., 2004) Hurtado, F.; Noy, M.; Robert, J.-M.; Sacristan, V.; Skiena, S.We present an automatic camera and mirrors placement method for visualizing 3D scenes such that complete and nonredundant visibility is guaranteed, as well as highest image resolution. We provide algorithms and geometries for optimal object-independent mirrors and viewpoint placement for all objects in a specific class. We also briefly consider object-dependent algorithmic problems, where mirrors and viewpoints are positioned as a function of the object.