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Item Modelling and Rendering Graphics Scenes Composed of Multiple Volumetric Datasets(Blackwell Publishers Ltd and the Eurographics Association, 1999) Leu, Adrian; Chen, MinThis paper presents a method for modelling graphics scenes consisting of multiple volumetric objects. A two-level hierarchical representation is employed, which enables the reduction of the overall storage consumption as well as rendering time. With this approach, different objects can be derived from the same volumetric dataset, and 2D images can be trivially integrated into a scene. The paper also describes an efficient algorithm for rendering such scenes on ordinary workstations, and addresses issues concerning memory requirements and disk swapping.Item Extending Graphics Hardware For Occlusion Queries In OpenGL(The Eurographics Association, 1998) Bartz, Dirk; Meißner, Michael; Hüttner, Tobias; S. N. SpencerFor interactive rendering of large polygonal objects, fast visibility queries are necessary to quickly decide whether polygonal objects are visible and need to be rendered. None of the numerous published algorithms provide visibility performance for interactive rendering of large models. In this paper, we propose an OpenGL extension for fast occlusion queries. Added after the depth test stage of the OpenGL rendering pipeline. our algorithm provides fast queries to establish the occlusion of polygonal objects. Furthermore, hardware aspects of this proposal are discussed and possible implementations on two different graphics architectures are presented.Item ve99(1999)Item Virtual Dunhuang Art Cave: A Cave within a CAVE(Blackwell Publishers Ltd and the Eurographics Association, 1999) Lutz, B.; Weintke, M.Virtual Reality can present historical places in a three-dimensional and interactive way, giving visitors a photorealistic impression of objects. Not only existing scenarios can be shown, but VR can also be used to rebuild scenarios that were damaged or destroyed a long time ago, giving new life to the cultural heritage. We used Virtual Reality to present the Mogao Grottos in Dunhuang. This cave site is one of the most important cultural and religious places by the ancient Silk Road. The presentation is to give visitors the impression of visiting the cave site and provide information about the caves, paintings and statues in an interesting way. To achieve this, we developed a new, intuitive interaction paradigm, which enables the user to explore the caves. To give observers a photorealistic impression of the caves and to create a feeling of immersion, innovative rendering techniques were integrated.The resulting presentation combines Virtual Reality and archaeology to give tourists a realistic experience of this cave site and to support scientists in their research work.Item WebTalk: a 3D collaborative environment to access the Web(Eurographics Association, 1999) Paolini, P.; Barbieri, T.; Loiudice, P.; Alonzo, F.; Arru, M.; Zanti, M.; Gaia, G.The notion of cooperative visit and interaction within a web site, both at 2D and 3D level, could add decisive motivation to pursue exploitation of the third dimension in networked environments. A prototype developed at the HOC laboratory in Politecnico of Milan, WEBTALK, allows development of custom 3D environments in which actions and situations can be shared throughout a network. The current prototype makes use of standard web-based Internet/Intranet technology: it is composed of a VRML (Virtual Reality Modeling Language) graphical engine and a Java-based TCP/IP (the Internet Protocol) communication layer. The technique has proven itself successful and has given rise to several interesting applications, such as the creation of Virtual 3D Museum Spaces at the National Science Museum (www.museoscienza.org), in which visitors can visit the museum interacting with the exhibits themselves and sharing their experiences with other visitors - even joining a guided tour with the virtual museum guide. A new prototype will make use of a completely Java-based environment, using Sun’s Java 2 and Java 3D. The new WEBTALK will stress even further the issues of third party external authoring of virtual worlds and of cooperation patterns within the shared environments, with a distinction between shared object geometries, shared object behaviors, shared object data (stored in an on-line DBMS), and cooperation metaphors within the virtual world. Linking to 2D-based web sites resources will lead cooperation patterns to be extended also to regular web-space.Item Improved Laplacian Smoothing of Noisy Surface Meshes(Blackwell Publishers Ltd and the Eurographics Association, 1999) Vollmer, J.; Mencl, R.; Muller, H.This paper presents a technique for smoothing polygonal surface meshes that avoids the well-known problem of deformation and shrinkage caused by many smoothing methods, like e.g. the Laplacian algorithm. The basic idea is to push the vertices of the smoothed mesh back towards their previous locations. This technique can be also used in order to smooth unstructured point sets, by reconstructing a surface mesh to which the smoothing technique is applied. The key observation is that a surface mesh which is not necessarily topologically correct, but which can efficiently be reconstructed, is sufficient for that purpose.Item Three-Dimensional Visualization of Atomic Collision Cascades(The Eurographics Association, 1998) Sroubek, Filip; Slavik, Pavel; Bartz, DirkThe paper describes a new approach to the visualization of atomic collision cascades and using the interaction with visualized data. The collision cascade is a physical phenomenon initiated by bombarding the surface of a solid with accelerated atomic particles. The process evolves in time and therefore it is necessary to develop some tools that would allow to investigate and visualize the dynamics of the process. Such tools are classi ers ( lters) that enable to select and visualize objects with specific dynamic properties. As the visualization has been done in a 3D environment a question arises how to specify effectively and user friendly both the properties and the objects in the 3D space. Several techniques are available that allow interaction in the 3D space. It has been necessary to test some of these techniques and to determine which one is the most suitable for the given application class.Item Texturing 3D Models of Real World Objects from Multiple Unregistered Photographic Views(Blackwell Publishers Ltd and the Eurographics Association, 1999) Neugebauer, Peter J.; Klein, KonradAs the efficiency of computer graphic rendering methods is increasing, generating realistic models is now becoming a limiting factor. In this paper we present a new technique to enhance already existing geometry models of real world objects with textures reconstructed from a sparse set of unregistered still photographs. The aim of the proposed technique is the generation of nearly photo-realistic models of arbitrarily shaped objects with minimal effort. In our approach, we require neither a prior calibration of the camera nor a high precision of the user's interaction. Two main problems have to be addressed of which the first is the recovery of the unknown positions and parameters of the camera. An initial estimate of the orientation is calculated from interactively selected point correspondences. Subsequently, the unknown parameters are accurately calculated by minimising a blend of objective functions in a 3D-2D projective registration approach. The key point of the proposed method of registration is a novel filtering approach which utilises the spatial information provided by the geometry model. Second, the individual images have to be combined yielding a set of consistent texture maps. We present a robust method to recover the texture from the photographs thereby preserving high spatial frequencies and eliminating artifacts, particularly specular highlights. Parts of the object not seen in any of the photographs are interpolated in the textured model. Results are shown for three complex example objects with different materials and numerous self-occlusions.Item Prefetching in a Texture Cache Architecture(The Eurographics Association, 1998) lgehy, Homan; Eldridge, Matthew; Proudfoot, Kekoa; S. N. SpencerTexture mapping has become so ubiquitous in real-time graphics hardware that many systems are able to perform filtered texturing without any penalty in fill rate. The computation rates available in hardware have been outpacing the memory access rates, and texture systems are becoming constrained by memory bandwidth and latency. Caching in conjunction with prefetching can be used to alleviate this problem. In this paper, WC introduce a prefetching texture cache architecture designed to take advantage of the access characteristics of texture mapping. The structures needed are relatively simple and arc amenable to high clock rates. To quantify the robustness of our architecture, we identify a set of six scenes whose texture locality varies over nearly two orders of magnitude and a set 01 four memory systems with varying bandwidths and latencies. Through the use of a cycle-accurate simulation, we demonstrate that even in the presence of a high-latency memory system, our architecture can attain at least 97% of the performance of a zerolatency memory system.Item mm99(1999)