Issue 3

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https://diglib.eg.org/handle/10.2312/96

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Augmented Reality with Back-Projection Systems using Transflective Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Bimber, Oliver; Encarnacao, L. Miguel; Schmalstieg, Dieter
In this paper, we introduce the concept of Extended VR (extending viewing space and interaction space of back-projection VR systems), by describing the use of a hand-held semi-transparent mirror to support augmented reality tasks with back-projection systems. This setup overcomes the problem of occlusion of virtual objects by real ones linked with such display systems. The presented approach allows an intuitive and effective application of immersive or semi-immersive virtual reality tasks and interaction techniques to an augmented surrounding space. Thereby, we use the tracked mirror as an interactive image-plane that merges the reflected graphics, which are displayed on the projection plane, with the transmitted image of the real environment. In our implementation, we also address traditional augmented reality problems, such as real-object registration and virtual-object occlusion. The presentation is complemented by a hypothesis of conceivable further setups that apply transflective surfaces to support an Extended VR environment.
A Multiresolution Model for Soft Objects Supporting Interactive Cuts and Lacerations
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Ganovelli, Fabio; Cignoni, Paolo; Montani, Claudio; Scopigno, Roberto
Performing a really interactive and physically-based simulation of complex soft objects is still an open problem in computer animation/simulation. Given the application domain of virtual surgery training, a complete model should be quite realistic, interactive and should enable the user to modify the topology of the objects. Recent papers propose the adoption of multiresolution techniques to optimize time performance by representing at high resolution only the object parts considered more important or critical. The speed up obtainable at simulation time are counterbalanced by the need of a preprocessing phase strongly dependent on the topology of the object, with the drawback that performing dynamic topology modification becomes a prohibitive issue. In this paper we present an approach that couples multiresolution and topological modifications, based on the adoption of a particle systems approach to the physical simulation. Our approach is based on a tetrahedral decomposition of the space, chosen both for its suitability to support a particle system and for the ready availability of many techniques recently proposed for the simplification and multiresolution management of 3D simplicial decompositions. The multiresolution simulation system is designed to ensure the required speedup and to support dynamic changes of the topology, e.g. due to cuts or lacerations of the represented tissue.
An Adaptive Spectral Rendering with a Perceptual Control
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Claude Iehl, Jean; Peroche, Bernard
In this paper, we present a spectral rendering method based on a ray tracing algorithm and guided by a perceptual control of the error made. An adaptive representation of spectral data for light sources and materials is used and induces, for each pixel, the evaluation of an algebraic expression. For each visible wavelength, the computations of complex spread in refractive and dispersive materials, based on several photon maps, are locally restricted by an adaptive evaluation of the expression. This method allows to simulate high quality physically-based pictures and, in particular, some specific phenomena like dispersion in transparent objects, scattered caustics,. . .
LCTS: Ray Shooting using Longest Common Traversal Sequences
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Havran, V.; Bittner, J.
We describe two new techniques of ray shooting acceleration that exploit the traversal coherence of a spatial hierarchy. The first technique determines a sequence of adjacent leaf-cells of the hierarchy that is pierced by all rays contained within a certain convex shaft. This sequence is used to accelerate ray shooting for all remaining rays within the shaft. The second technique establishes a cut of the hierarchy that contains nodes where the hierarchy traversal can no longer be predetermined for all rays contained within a given shaft. This cut is used to initiate the traversal for all remaining rays contained in the shaft. The description of the methods is followed by results evaluated by their practical implementation.
Towards Blind Detection of Robust Watermarks in Polygonal Models
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Benedens, Oliver; Busch, Christoph
We describe a Digital Watermarking system dedicated for embedding watermarks into 3D polygonal models. The system consists of three watermarking algorithms, one named Vertex Flood Algorithm (VFA) suitable for embedding fragile public readable watermarks with high capacity and offering a way of model authentication, one realizing affine invariant watermarks, named Affine Invariant Embedding (AIE) and a third one, named Normal Bin Encoding (NBE) algorithm, realizing watermarks with robustness against more complex operations, most noticeably polygon reduction. The watermarks generated by these algorithms are stackable. We shortly discuss the implementation of the system, which is realized as a 3D Studio MAX plugin.
Subdivision Surface Tesselation on the Fly using a versatile Mesh Data Structure
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Muller, Kerstin; Havemann, Sven
Subdivision surfaces have become a standard technique for freeform shape modeling. They are intuitive to use and permit designers to flexibly add detail. But with larger control meshes, efficient adaptive rendering techniques are indispensable for interactive visualization and shape modeling. In this paper, we present a realization of tesselation-on-the-fly for Loop subdivision surfaces as part of a framework for interactive visualization.
Tone Reproduction for Interactive Walkthroughs
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Scheel, A.; Stamminger, M.; Seidel, H.-P.
When a rendering algorithm has created a pixel array of radiance values the task of producing an image is not yet completed. In fact, to visualize the result the radiance values still have to be mapped to luminances, which can be reproduced by the used display. This step is performed with the help of tone reproduction operators. These tools have mainly been applied to still images, but of course they are just as necessary for walkthrough applications, in which several images are created per second. In this paper we illuminate the physiological aspects of tone reproduction for interactive applications. It is shown how tone reproduction can also be introduced into interactive radiosity viewers, where the tone reproduction continuously adjusts to the current view of the user. The overall performance is decreased only moderately, still allowing walkthroughs of large scenes.
Floating Points: A Method for Computing Stipple Drawings
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Deussen, Oliver; Hiller, Stefan; Van Overveld, Cornelius; Strothotte, Thomas
We present a method for computer generated pen-and-ink illustrations by the simulation of stippling. In a stipple drawing, dots are used to represent tone and also material of surfaces. We create such drawings by generating an initial dot set which is then processed by a relaxation method based on Voronoi diagrams. The point patterns generated are approximations of Poisson disc distributions and can also be used for integrating functions or the positioning of objects. We provide an editor similar to paint systems for interactively creating stipple drawings. This makes it possible to create such drawings within a matter of hours, instead of days or even weeks when the drawing is done manually.
Modelling virtual cities dedicated to behavioural animation
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Thomas, Gwenola; Donikian, Stephane
In order to populate virtual cities, it is necessary to specify the behaviour of dynamic entities such as pedestrians or car drivers. Since a complete mental model based on vision and image processing cannot be constructed in real time using purely geometrical information, higher levels of information are needed in a model of the virtual environment. For example, the autonomous actors of a virtual world would exploit the knowledge of the environment topology to navigate through it. In this article, we present a model of virtual urban environments using structures and information suitable for behavioural animations. Thanks to this knowledge, autonomous virtual actors can behave like pedestrians or car drivers in a complex city environment. A city modeler has been designed, using this model of urban environment, and enables complex urban environments for behavioural animation to be automatically produced.
Real Time Local Approximation of Deformations using Rotations
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Maillot, Jerome
Additional realism can be achieved in computer generated images using smooth and increasingly complex deformations. Though significant effort has been spent on improving these deformations, no general method has been proposed yet to deal with rigid pieces connected to soft objects. This paper proposes a general framework to solve this problem. We will present several types of applications, such as flowing small objects in a deformation field, animating rigid features connected to some deformed object, or smoothly attached limbs to a deforming body. All the calculations presented here can be applied to any type of deformation, provided that the deformation at each point only depends on the point itself. Even though we can directly compute the result for some analytical deformation fields, we will show that a good sampling of the deformation in the area of interest is generally enough. One intermediate result consists of a practical method to find the best rotation that approximates a linear transformation. The proposed method is a superset of the Gram-Schmidt orthonormalization process, and is much easier to compute than global methods based on Taylor series.
Integrating Occlusion Culling and Levels of Detail through Hardly-Visible Sets
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Andujar, Carlos; Saona-Vazquez, Carlos; Navazo, Isabel; Brunet, Pere
Occlusion culling and level-of-detail rendering have become two powerful tools for accelerating the handling of very large models in real-time visualization applications. We present a framework that combines both techniques to improve rendering times. Classical occlusion culling algorithms compute potentially visible sets (PVS), which are supersets of the sets of visible polygons. The novelty of our approach is to estimate the degree of visibility of each object of the PVS using synthesized coarse occluders. This allows to arrange the objects of each PVS into several Hardly-Visible Sets (HVS) with similar occlusion degree. According to image accuracy and frame rate requirements, HVS provide a way to avoid sending to the graphics pipeline those objects whose pixel contribution is low due to partial occlusion. The image error can be bounded by the user at navigation time. On the other hand, as HVS offer a tighter estimation of the pixel contribution for each scene object, it can be used for a more convenient selection of the level-of-detail at which objects are rendered. In this paper, we describe the new framework technique, provide details of its implementation using a visibility octree as the chosen occlusion culling data structure and show some experimental results on the image quality.
Interactive High-Quality Maximum Intensity Projection
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Mroz, Lukas; Hauser, Helwig; Groller, Eduard
Maximum Intensity Projection (MIP) is a volume rendering technique which is used to visualize high-intensity structures within volumetric data. At each pixel the highest data value, which is encountered along a corresponding viewing ray is depicted. MIP is, for example, commonly used to extract vascular structures from medical data sets (angiography). Due to lack of depth information in MIP images, animation or interactive variation of viewing parameters is frequently used for investigation. Up to now no MIP algorithms exist which are of both interactive speed and high quality. In this paper we present a high-quality MIP algorithm (trilinear interpolation within cells), which is up to 50 times faster than brute-force MIP and at least 20 times faster than comparable optimized techniques. This speed-up is accomplished by using an alternative storage scheme for volume cells (sorted by value) and by removing cells which do not contribute to any MIP projection (regardless of the viewing direction) in a preprocessing step. Also, a fast maximum estimation within cells is used to further speed up the algorithm.
Color Distribution - A New Approach to Texture Compression
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Ivanov, Denis V.; Kuzmin, Yevgeniy P.
Texture compression is recently one of the most important topics of 3D scene rendering techniques, because it allows rendering more complicated high-resolution scenes. However, because of some special requirements for these type of techniques, the commonly used block decomposition approach may introduce visual degradation of image details due to lack of colors. We present here a new approach to texture compression, which allows sharing of one color by several blocks providing a larger number of unique colors in each particular block and the best compression ratio. We also present an iterative algorithm for obtaining distributed colors on a texture, and discuss some advantages of our approach. The paper concludes with comparison of our technique with S3TC and other block decomposition methods.
Fast Volume Rendering and Data Classification Using Multiresolution in Min-Max Octrees
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Dong, Feng; Krokos, Meleagros; Clapworthy, Gordon
Haptic Cues for Image Disambiguation
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Faconti, G.; Massink, M.; Bordegoni, M.; De Angelis, F.; Booth, S.
Haptic interfaces represent a revolution in human computer interface technology since they make it possible for users to touch and manipulate virtual objects. In this work we describe a cross-model interaction experiment to study the effect of adding haptic cues to visual cues when vision is not enough to disambiguate the images. We relate the results to those obtained in experimental psychology as well as to more recent studies on the subject.
Context-based Space Filling Curves
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Dafner, Revital; Cohen-Or, Daniel; Matias, Yossi
A context-based scanning technique for images is presented. An image is scanned along a context-based space filling curve that is computed so as to exploit inherent coherence in the image. The resulting one-dimensional representation of the image has improved autocorrelation compared with universal scans such as the Peano-Hilbert space filling curve. An efficient algorithm for computing context-based space filling curves is presented. We also discuss the potential of improved autocorrelation of context-based space filling curves for image and video lossless compression.
Integration of Multidimensional Interaction Devices in Real-Time Computer Graphics Applications
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Frohlich, Torsten; Roth, Marcus
Modern CAD/CAM and Virtual Reality applications cannot be imagined without the new class of interaction devices allowing the user direct interaction with computer generated scenes. Integrating such devices into existing or newly developed software is a complex task for a number of reasons. The set of devices is very heterogeneous in functionality and data formats. Most devices are difficult to handle by inexperienced users or need careful handling and calibration. After reviewing a number of existing systems, a novel approach to this problem is presented. A device interface that allows the flexible, hardware independent configuration and error robust operation, even reconfiguration and exchanges of interaction devices during operation, will be introduced. The system structure is discussed and novel communication protocols reducing latency are invented.
Unsteady Flow Visualization by Animating Evenly-Spaced Streamlines
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Jobard, Bruno; Lefer, Wilfrid
In recent years the work on vector field visualization has been concentrated on LIC-based methods. In this paper we propose an alternative solution for the visualization of unsteady flow fields. Our approach is based on the computation of temporal series of correlated images. While other methods are based on pathlines and try to correlate successive images at the pixel level, our approach consists in correlating instantaneous visualizations of the vector field at the streamline level. For each frame a feed forward algorithm computes a set of evenly-spaced streamlines as a function of the streamlines generated for the previous frame. This is achieved by establishing a correspondence between streamlines at successive time steps. A cyclical texture is mapped onto every streamline and textures of corresponding streamlines at different time steps are correlated together so that, during the animation, they move along the streamlines, giving the illusion that the flow is moving in the direction defined by the streamline. Our method gives full control on the image density so that we are able to produce smooth animations of arbitrary density, covering the field of representations from sparse, that is classical streamline-based images, to dense, that is texture-like images.
Collaborative Virtual Simulation Environment for Radiotherapy Treatment Planning
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Cai, Wenli; Walter, Stefan; Karangelis, Grigorios; Sakas, Georgios
The simulation of Radiotherapy Treatment Planning (RTP) is a normal procedure in oncology clinics carried out on a Simulator machine. The Virtual Simulation of RTP replaces the real Simulator machine with a virtual one by using the CT data sets of a patient instead of the real patient. In this paper, we present a collaborative virtual simulation environment of RTP, named EU-VIRTUOSO, which is based on volume rendering and telecommunication techniques. The RTP procedure is visualised on a virtual patient, which is created by using the CT data of the patient. Different volume rendering and volume interaction techniques, such as DRR, MIP, gradient surface, and iso-surface, supply physicians with high quality rendering images to simulate the real working environment of the Simulator machine. In the collaborative environment, physicians distributed at different locations can work together via network to plan the treatment or to validate the treatment plan on-line by a collaborative application sharing approach. Both concepts virtualised planning and collaborative planning improve the efficiency and accuracy of a radiotherapy treatment while reducing the effort for an individual patient.
Real Time, Accurate, Multi-Featured Rendering of Bump Mapped Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Tarini, M.; Cignoni, P.; Rocchini, C.; Scopigno, R.
We present a new technique to render in real time objects which have part of their high frequency geometric detail encoded in bump maps. It is based on the quantization of normal-maps, and achieves excellent result both in rendering time and rendering quality, with respect to other alternative methods. The method proposed also allows to add many interesting visual effects, even for object with large bumb maps, including non-s rendering, chrome effects, shading under multiple lights, rendering of different materials within a single object, specular reflections and others. Moreover, the implementation of the method is not complex and can be eased by software reuse.

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