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Start date: 2000 × Author: Straßer, Wolfgang ×

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Now showing 1 - 10 of 14
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    Selective Stylization for Visually Uniform Tangible AR
    (The Eurographics Association, 2008) Fischer, Jan; Flohr, Daniel; Straßer, Wolfgang; Robert van Liere and Betty Mohler
    In tangible user interfaces, physical props are used for direct interaction with a computer system. Tangible interaction applications often use augmented reality display techniques in order to overlay virtual graphical objects over the interaction area. This typically leads to the problem that the virtual augmentations have a distinct, simple computer-generated look, which makes them easily distinguishable from the real environment and physical props. Here, we present a new style of tangible interaction, which seamlessly combines real objects and graphical models. In the tangible user interaction zone of our system, physical objects and virtual models are displayed in the same technical illustration style. Regions outside of the interaction zone, and also the user's hands, are shown unaltered in order to maintain an unmodified visual feedback in these areas. Our example application is a tangible urban planning environment, in which the placement of both real and virtual building models affects the flow of wind and the casting of shadows. We describe the real-time rendering pipeline which generates the selectively stylized output images in the tangible interaction system and discuss the functionality of the urban planning application.
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    A Consistent Bending Model for Cloth Simulation with Corotational Subdivision Finite Elements
    (The Eurographics Association, 2006) Thomaszewski, Bernhard; Wacker, Markus; Straßer, Wolfgang; Marie-Paule Cani and James O'Brien
    Wrinkles and folds play an important role in the appearance of real textiles. The way in which they form depends mainly on the bending properties of the specific material type. Existing approaches fail to reliably reproduce characteristic behaviour like folding and buckling for different material types or resolutions. It is therefore crucial for the realistic simulation of cloth to model bending energy in a physically accurate and consistent way. In this paper we present a new method based on a corotational formulation of subdivision finite elements. Due to the non-local nature of the employed subdivision basis functions a C1-continuous displacement field can be defined. In this way, it is possible to use the governing equations of thin shell analysis leading to physically accurate bending behaviour. Using a corotated strain tensor allows the large displacement analysis of cloth while retaining a linear system of equations. Hence, known convergence properties and computational efficiency are preserved while convincing and detailed folding behaviour is obtained in the simualtion.
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    Anisotropic Friction for Deformable Surfaces and Solids
    (ACM SIGGRAPH / Eurographics Association, 2009) Pabst, Simon; Thomaszewski, Bernhard; Straßer, Wolfgang; Eitan Grinspun and Jessica Hodgins
    This paper presents a method for simulating anisotropic friction for deforming surfaces and solids. Frictional contact is a complex phenomenon that fuels research in mechanical engineering, computational contact mechanics, composite material design and rigid body dynamics, to name just a few. Many real-world materials have anisotropic surface properties. As an example, most textiles exhibit direction-dependent frictional behavior, but despite its tremendous impact on visual appearance, only simple isotropic models have been considered for cloth and solid simulation so far. In this work, we propose a simple, application-oriented but physically sound model that extends existing methods to account for anisotropic friction. The sliding properties of surfaces are encoded in friction tensors, which allows us to model frictional resistance freely along arbitrary directions. We also consider heterogeneous and asymmetric surface roughness and demonstrate the increased simulation quality on a number of two- and three-dimensional examples. Our method is computationally efficient and can easily be integrated into existing systems.
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    Screen Space Spherical Harmonic Occlusion
    (The Eurographics Association, 2012) Herholz, Sebastian; Schairer, Timo; Schilling, Andreas; Straßer, Wolfgang; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
    In this paper we present a new algorithm for real-time directional occlusion sampling. We combine the real-time capabilities of Screen Space Ambient Occlusion (SSAO) with the Spherical Harmonics (SH) representation of local directional occlusion. SH are well established and used in modern off-line rendering implementations such as PantaRay [PFHA10]. Through our combination we are able to transfer a method for realistic local directional occlusion effects from offline rendering to dynamic real-time applications. These local occlusion effects react to the environmental lighting situation and lead to dynamic and colored local occlusion shadows while only generating a small computational overhead compared to SSAO. Unlike other real-time directional occlusion algorithms such as Screen Space Direction Occlusion (SSDO) [RGS09] our occlusion sampling is separated from the actual lighting process and therefore can be easily integrated in existing SH lighting methods such as Irradiance Volumes [GSHG98]. We furthermore extend our algorithm to include first bounce indirect illumination effects.
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    Illustrative Hybrid Visualization and Exploration of Anatomical and Functional Brain Data
    (The Eurographics Association and Blackwell Publishing Ltd., 2008) Jainek, Werner M.; Born, Silvia; Bartz, Dirk; Straßer, Wolfgang; Fischer, Jan; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
    Common practice in brain research and brain surgery involves the multi-modal acquisition of brain anatomy and brain activation data. These highly complex three-dimensional data have to be displayed simultaneously in order to convey spatial relationships. Unique challenges in information and interaction design have to be solved in order to keep the visualization sufficiently complete and uncluttered at the same time. The visualization method presented in this paper addresses these issues by using a hybrid combination of polygonal rendering of brain structures and direct volume rendering of activation data. Advanced rendering techniques including illustrative display styles and ambient occlusion calculations enhance the clarity of the visual output. The presented rendering pipeline produces real-time frame rates and offers a high degree of configurability. Newly designed interaction and measurement tools are provided, which enable the user to explore the data at large, but also to inspect specific features closely. We demonstrate the system in the context of a cognitive neurosciences dataset. An initial informal evaluation shows that our visualization method is deemed useful for clinical research.
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    Photorealistic Real-Time Visualization of Cultural Heritage: A Case Study of Friedrichsburg Castle in Germany
    (The Eurographics Association, 2007) Kuchar, Robert; Schairer, Timo; Straßer, Wolfgang; David B. Arnold and Andrej Ferko
    This paper presents a novel highly immersive and interactive VR (virtual reality) installation targeted on photorealistic real-time visualization. Although applicable to many other scenarios, this work is focused primarily on virtual reconstructions in the context of cultural heritage projects. We address two shortcomings in most of the current virtual reconstructions, namely interactivity and realism. On the one hand many of them are presented either as a movie or using semi-interactive techniques. In both cases the imagery is pre-rendered and therefore the visualization is lacking interactivity. On the other hand interactive real-time presentations often are neither intuitive to navigate nor visually pleasant. We extended a real-time rendering software based on global illumination to adapt to the special needs of the visualization of virtual scenes that stem from the field of cultural heritage. A HDR (high dynamic range) daylight simulation was developed in conjunction with techniques and algorithms to significantly speed up the calculation time and increase the visual quality of the scene. To account for the different lighting situations encountered in the visualization of indoor and outdoor scenes, we developed a high dynamic range rendering pipeline that uses a dynamic tone mapping algorithm similar to human vision. To provide interactive access to the high quality 3D model even for unskilled users, we developed a very intuitive user interface based on a simple touchscreen for navigating the virtual scene. The combination of the real-time presentation of the photorealistic reconstruction and the intuitive navigation interface leads to a highly immersive and interactive VR installation. Since we are currently working on a virtual reconstruction of a Renaissance castle located in southern Germany, we will therefore use this reconstruction as a case study to present the developed features and to prove their relevance and usefulness. The virtual reconstruction is displayed using our VR installation and will be accessible to the public in the State Museum of Hohenzollern by August 2007
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    Model-based Hybrid Tracking for Medical Augmented Reality
    (The Eurographics Association, 2006) Fischer, Jan; Eichler, Michael; Bartz, Dirk; Straßer, Wolfgang; Ming Lin and Roger Hubbold
    Camera pose estimation is one of the most important, but also one of the most challenging tasks in augmented reality. Without a highly accurate estimation of the position and orientation of the digital video camera, it is impossible to render a spatially correct overlay of graphical information. This requirement is even more crucial in medical applications, where the virtual objects are supposed to be correctly aligned with the patient. Many medical AR systems use specialized tracking devices, which can be of limited suitability for real-world scenarios. We have developed an AR framework for surgical applications based on existing medical equipment. A surgical navigation device delivers tracking information measured by a built-in infrared camera system, which is the basis for the pose estimation of the AR video camera. However, depending on the conditions in the environment, this infrared pose data can contain discernible tracking errors. One main drawback of the medical tracking device is the fact that, while it delivers a very high positional accuracy, the reported camera orientation can contain a relatively large error. In this paper, we present a hybrid tracking scheme for medical augmented reality based on a certified medical tracking system. The final pose estimation takes the inital infrared tracking data as well as salient features in the camera image into account. The vision-based component of the tracking algorithm relies on a pre-defined graphical model of the observed scene. The infrared and vision-based tracking data are tightly integrated into a unified pose estimation algorithm. This algorithm is based on an iterative numerical optimization method. We describe an implementation of the algorithm and present experimental data showing that our new method is capable of delivering a more accurate pose estimation.
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    Two-Handed Through-the-Lens-Techniques for Navigation in Virtual Environments
    (The Eurographics Association, 2001) Stoev, Stanislav L.; Schmalstieg, Dieter; Straßer, Wolfgang; B. Froehlich and J. Deisinger and H.-J. Bullinger
    We present a tool set of techniques for navigation in virtual environments. Based on a through-the-lens concept, the user is enabled to simultaneously view the surrounding virtual world and an arbitrary location of the virtual world as seen through an interactively defined window. For the manipulation and the adjustment of this virtual window we propose three different strategies, loosely based on the well-known eyeball-in-hand, scene-in-hand, and world-in-miniature techniques. Since our technique provides a preview area with controllable size and position, the occluded part of the scene can be flexibly managed, while enabling intuitive and precise work with the proposed tools. The proposed techniques provide powerful tools that are easy to implement and can be applied in any type of virtual environments.
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    Advanced Topics in Virtual Garment Simulation
    (The Eurographics Association, 2007) Thomaszewski, Bernhard; Wacker, Markus; Straßer, Wolfgang; Lyard, Etienne; Luible, C.; Volino, Pascal; Kasap, M.; Muggeo, V.; Magnenat-Thalmann, Nadia; Karol Myszkowski and Vlastimil Havran
    For more than two decades, cloth simulation has been an active research area in computer graphics. In order to create efficient high-quality animations, techniques from many research fields have to be thoroughly combined. The ongoing interest in this field is also due to the multidisciplinary nature of cloth simulation which spurs development and progress in collision detection, numerical time integration, constrained dynamics, or motion control, to name just a few areas. Beyond the very basic approaches, the complexity of the material can be daunting if no guidance is given. It is therefore the goal of this tutorial to provide the reader with an introduction and a guideline to the relevant matter. In order to provide a concise review, we will focus on advanced topics in cloth simulation, shedding light on both theoretical and practical aspects. This will pave the ground for those willing to implement a contemporaneous cloth simulation system as well as researchers who consider to start working in this area.
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    Perceptual Reparameterization of Material Properties
    (The Eurographics Association, 2007) Cunningham, Douglas W.; Wallraven, Christian; Fleming, Roland W.; Straßer, Wolfgang; Douglas W. Cunningham and Gary Meyer and Laszlo Neumann
    The recent increase in both the range and the subtlety of computer graphics techniques has greatly expanded the possibilities for synthesizing images. In many cases, however, the relationship between the parameters of an algorithm and the resulting perceptual effect is not straightforward. Since the ability to produce specific, intended effects is a natural pre-requisite for many scientific and artistic endeavors, this is a strong drawback. Here, we demonstrate a generalized method for determining both the qualitative and quantitative mapping between parameters and perception. Multidimensional Scaling extracts the metric structure of perceived similarity between the objects, as well as the transformation between similarity space and parameter space. Factor analysis of semantic differentials is used to determine the aesthetic structure of the stimulus set. Jointly, the results provide a description of how specific parameter changes can produce specific semantic changes. The method is demonstrated using two datasets. The first dataset consisted of glossy objects, which turned out to have a 2D similarity space and five primary semantic factors. The second dataset, transparent objects, can be described with a non-linear, 1D similarity map and six semantic factors. In both cases, roughly half of the factors represented aesthetic aspects of the stimuli, and half the low-level material properties. Perceptual reparameterization of computer graphics algorithms (such as those dealing with the representation of surface properties) offers the potential to improve their accessibility. This will not only allow easier generation of specific effects, but also enable more intuitive exploration of different image properties.