Short Presentations

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https://diglib.eg.org/handle/10.2312/231

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From Textual Chats to Interest Groups in 3D Virtual Space
(Eurographics Association, 2002) Masa, Michal; Zara, Jiri
While the textual chat is a highly popular tool for various kinds of social interactions, its extension to the visual three-dimensional domain remains almost untouched and without practical utilization yet. This paper discusses advantages and disadvantages of spatial virtual environment when used as a platform for connecting people and serving for social and cultural interaction. The differences between textual chat and interest groups in virtual reality are highlighted with the aim to overcome the gap between well-established chat technology and promising but still a bit exotic virtual reality approach. Theoretical analysis is followed by several examples taken from experimental setup.
Interpolating 2D Shape Hierarchically
(Eurographics Association, 2002) Johan, Henry; Nishita, Tomoyuki
Shape interpolation has been widely used in the field of computer graphics for modeling and for creating visual effects. This paper presents a novel hierarchical method to interpolate between two 2D shapes. A hierarchical representation, which is a hierarchy of triangles, is proposed to represent the interior and the details of each shape. By constructing the compatible hierarchical representations of the two shapes, the intermediate shapes are computed by interpolating the corresponding triangles at the lowest level to the highest level of the representations, From experimental results, the proposed method produces smooth interpolation sequences.
Feature interference in free form template matching
(Eurographics Association, 2002) Song, Y.; Vergeest, J. S. M.; Horvath, I.
Template matching is a useful method in the reconstruction of free form surfaces. In this paper, matching of free form surfaces with parameterized templates is studied with the emphasis on feature interference. By their definitions in 3- Dimensional space, free form features are introduced, analyzed and parameterized first. An optimization function based on a Hausdorff-like shape distance measuring method is proposed and applied as measuring method between the digitalized model surface and the parameterized feature template. The proposed method not only can fit isolated free form features, but also works when a feature is interfered by other free form features in some specified conditions. A series of numerical experiments have been conducted to demonstrate the proposed methods based on ACIS and Open Inventor. Fitting strategies are proposed as well.
Function-defined shape node for VRML
(Eurographics Association, 2002) Lai, Feng Min; Sourin, Alexei
This paper describes how the web-based visualisation can be greatly improved using the function-based shape modelling technique. We propose the function-defined VRML shape node, which allows the content creators to describe any complex models with relatively small functions compared to the large-size polygonal mesh based VRML nodes. The design, the implementation details, and the application examples of the proposed node are discussed. The software is available for downloading from the project website.
Improved Bump Mapping by using Quadratic Vector Interpolation
(Eurographics Association, 2002) Hast, Hans Anders; Barrera, Tony; Bengtsson, Ewert
Bump mapping is a technique that perturbs normals used in the illumination computation in order to make the surface appear rough or wrinkled. Standard graphics hardware linearly interpolates rotated vectors in the direction to the light source over the polygon. Then, a cube map is used to normalize these vectors. We propose the use of quadratic interpolation instead, which will make the normalization stage unnecessary. The result is faster bump mapping with quality near the quality obtained by using vector interpolation with normalization. Quadratic interpolation is already used for ordinary shading but has to our knowledge not previously been used for bump mapping. The fast setup we use in our new algorithm can also be applied to Phong shading resulting in increased performance. Similarly the same approach can be used for efficiently setting up the linear interpolation.
A Method for Creating Mosaic Images Using Voronoi Diagrams
(Eurographics Association, 2002) Dobashi, Yoshinori; Haga, Toshiyuki; Johan, Henry; Nishita, Tomoyuki
This paper proposes a non-photorealistic rendering method that creates an artistic effect called mosaicing. The proposed method converts images provided by the user into the mosaic images. Commercial image editing applications also provide a similar function. However, these applications often trade results for low-cost computing. It is desirable to create high quality images even if the computational cost is increased. We present an automatic method for mosaicing images by using Voronoi diagrams. The Voronoi diagrams are optimized so that the error between the original image and the resulting image is as small as possible. Next, the mosaic image is generated by using the sites and edges of the Voronoi diagram. We use graphics hardware to efficiently generate Voronoi diagrams. Furthermore, we extend the method to mosaic animations from sequences of images.
Hardware-Assisted Relief Texture Mapping
(Eurographics Association, 2002) Fujita, Masahiro; Kanai, Takashi
Image-Based Rendering by Warping (IBRW) creates three-dimensional scene by deforming several 2D images with depth information. Image-based rendering has an advantage compared to traditional polygon rendering that the rendering time is still constant even if a scene becomes complex. Relief texture mapping decomposes IBRWinto a very simple 1D image operation and a traditional texture mapping, which allows more effective computations. In this paper, we try to apply some hi-quality shading effects such as reflection mapping for relief texture mapping. Their effects can be realized by per-pixel shading technology of today’s graphics hardware. Our method for relief texture mapping allows fast and almost the same shading as well as traditional polygon rendering.
Visibility Preprocessing Using Spherical Sampling of Polygonal Patches
(Eurographics Association, 2002) Meruvia Pastor, Oscar E.
A technique is presented that permits fast view-reconstruction of individual objects. This method improves a previous approach to solve the problem of approximated view reconstruction by combining clustering of polygons with visibility bitfields to determine visibility for novel viewpoints. The technique consists of three steps: patch creation, spherical sampling, and rendering. In the first stage, the input 3D model is tiled in polygonal patches. In the sampling stage images of the model are taken from several points on the surface of a viewing sphere. Patch-ID bitfields, which are structures that contain visibility information, are computed for each picture. In the rendering stage, a subset of the viewpoints computed for sampling is selected depending on the viewers position on the viewing sphere and the bitfields of the selected viewpoints are used to rebuild the visible parts of the model from the new viewpoint. The overall system presented here makes a very efficient use of memory resources, and involves practically no overhead during rendering while significantly improving frame rate during interaction with large models. Although the technique is not conservative, our results show that the reconstructed views are practically identical to the original views of the model.
Simulation of Cumuliform Clouds Based on Computational Fluid Dynamics
(Eurographics Association, 2002) Miyazaki, Ryo; Dobashi, Yoshinori; Nishita, Tomoyuki
Simulation of natural phenomena is one of the important research fields in computer graphics. In particular, clouds play an important role in creating images of outdoor scenes. Fluid simulation is effective in creating realistic clouds because clouds are the visualization of atmospheric fluid. In this paper, we propose a simulation technique, based on a numerical solution of the partial differential equation of the atmospheric fluid model, for creating animated cumulus and cumulonimbus clouds with features formed by turbulent vortices.
Dynamic Motion Models
(Eurographics Association, 2002) Grünvogel, Stefan Michael; Lange, Thorsten; Piesk, Jens
Real-time animation of virtual characters is a demanding task. We propose dynamic motion models which can create the motion of a virtual character in different styles and have the ability to change the animation while it is played. The motions are created by blending and changing given base motions which contain animation data and additional information. The blending and manipulation operations on the animation data build up a motion tree which can be altered dynamically in real-time. This allows to change the animation of a motion model while its animation is played. Motion trees of different motion models are blended together to build a motion tree which represents the complete animation of the character. This tree is constructed and dynamically changed according to user commands.
Distance fields applied to character animation
(Eurographics Association, 2002) Rudomin, Isaac; Castillo, J.
A general hybrid geometric-physical method that is useful for animating characters with skin, clothing and a MPEG-4 compatible face is presented. This method uses an approximation to the underlying musculo-skeletal structure of the body and face to generate a distance field, used for collision detection purposes, and skin/clothing consisting of a particle-spring mesh. The results obtained deliver animation with plausible dynamics for fairly detailed models at around 60fps on a PIII computer with Nvidia Gforce2 graphics. The main contribution is to show that similar algorithms can be used for skin, clothing and facial animation, at interactive rates.
Adaptive Tessellation for Trimmed NURBS Surface
(Eurographics Association, 2002) YingLiang, Ma; Hewitt, Terry
We present an adaptive method for tessellating the trimmed NURBS surface in the parametric domain. Given a model space tolerance ε, the algorithm first splits the NURBS surface in both the U and V directions to fit within the bounding box of the outer trimming loop. Then we subdivide the surface into Bézier patches recursively until the control net of the Bézier patch is flat enough and within the tolerance ε. By building up the quadtrees of inner trimming loops, we use the scanline algorithm to remove the patches inside the inner trimming loops. Finally, we close the inner trimming loops with a set of triangles. The resulting tessellation contains both quadrilaterals and triangles.
Improved Integration for Cloth Simulation
(Eurographics Association, 2002) Parks, David L.; Forsyth, David A.
Most methods of cloth simulation produce animations that do not move very freely; the result often looks like the material is “swimming”. The primary sources of this phenomenon are the non-physical dissipation terms often added to the mechanics to ensure stability in the simulation, and the numerical damping that is implicit in the choice of ODE integration schemes. By disposing of the additional dissipation terms and choosing a new integrator, the generalized-a method, that was designed to safely integrate mechanical systems with extraneous high-frequency signals in their temporal component, we obtain more realistic results often with the about the same amount of computation.
Extraction of Critical Points and Nets Based on Discrete Gradient Vector Field
(Eurographics Association, 2002) De Floriani, Leila; Mesmoudi, Mohammed Mostefa; Danovaro, Emanuele
In this paper we address the problem of representing the topology of discrete scalar fields defined on triangulated domains. To this aim, we use the notion of discrete gradient vector field that we have introduced in [4] to classify the critical points of a scalar field defined over a two-dimensional domain that generalizes the nature of critical points in the differentiable case. Then we sketch an algorithm for extracting a critical net in the discrete case.
Real-Time Animated Grass
(Eurographics Association, 2002) Bakay, Brook; Lalonde, Paul; Heidrich, Wolfgang
We present a simple method to render fields of grass, animated in the wind, in real-time. The technique employs vertex shaders to render displacement maps with Russian-doll style transparent shells. Animation is achieved by translating the surface according to a local wind vector while preserving the length of the blades of grass. This technique achieves convincing results on current consumer graphics hardware and can be applied to other similar surfaces such as hair and fur.
Dynamics-Based Motion Synthesis by Simple Learning Control
(Eurographics Association, 2002) Kiriazov, Petko
Point-to-point motion of a humanoid agent (or any mobile creature) is considered as a composition of basic movements related to the degrees of freedom. With time/energy performance criteria, such movements can be synthesized by using simple control functions. Natural looking animation can be achieved employing even very simplified dynamics models. Their parameters can be estimated or identified using motion capture data. In case no appropriate dynamic model is available, we propose an efficient procedure of direct motion editing. The captured motion can be re-used in order to animate the original or other characters in a variety of similar motion tasks. The proposed approach for motion synthesis is applied in the case of a six-link biped. Two examples are considered: one for editing captured walking motion and the other of direct motion synthesis for climbing stairs. The proposed methodology is very appropriate for interactive character animation.
Texture Mapping on Doo-Sabin Subdivision Surfaces Using Multiple Images
(Eurographics Association, 2002) Huang, Zhiyong; Neo, Chee Seng
We propose a texture mapping method on subdivision surfaces using multiple images and have implemented it on Doo- Sabin scheme. At the beginning, one texture map is specified for each control mesh face respectively. In a subdivision process, a new face of control meshes may fall into a region of multiple texture maps. To correctly texture map on such faces, we need to further split the new faces into multiple parts so that each of them falls into a region of only one texture map. A splitting algorithm is devised. The novelty of our work is on a generalization of the method of DeRose et al. for the treatment of the use of multiple images.
Image Editing with Intelligent Paint
(Eurographics Association, 2002) Reese, Jack; Barrett, William
Intelligent Paint provides a new tool for interactively selecting image objects or regions of interest, while simultaneously applying filters or effects directly to the selection(s). By coupling adaptive cost-ordered region growing with the high-level visual expertise of the user to indicate which objects are of interest, we are able to accurately select and edit complex, non-homogeneous objects in only a few seconds using simple mouse input gestures. Prior to selection, the image is oversegmented using a watershed (tobogganing) algorithm. Watershed catchment basins are assembled into an hierarchical image partition by grouping basins using the student’s t-distribution. Grouped basins, referred to as TRAPs (Tobogganed Region Accumulation Plateaus), reasonably capture sub-object detail. Object selection is accomplished by user-steered, adaptive, cost-ordered collection of TRAPs. Tinting or application of filters during object selection provides immediate visual feedback as to what is being selected as well as the suitability of the chosen digital effect. Intelligent Paint selection compares favorably with popular commercial tools in terms of efficiency, accuracy and reproducibility with the added benefit of on-the-fly filtering, while raising the granularity of image editing from the pixel to the object-level. Novel tools for object-centered image editing such as Intelligent Eraser and Intelligent Clone tools are also possible with this technique.
Automated Enhancement of 3D Models
(Eurographics Association, 2002) Torres-Mendez, L.A.; Dudek, G.
The acquisition of a 3D model of a real environment can be accomplished using range sensors. In practice, suitable sensors to densely cover a large environment are often impractical. This paper presents ongoing work on the synthesis of 3D environment models from as little as one intensity image and sparse range data. Our method is based on interpolating the available range data using statistical inferences learned from the available intensity image and from those (sparse) regions where both range and intensity information is available. Since we compute the relationship between extisting range data and the images we start with, we do not need to make any strong assumptions about the kind of surfaces in the world (for example we do not need to assume the world exhibits only diffuse reflectance). Experimental results show the feasibility of our method.
Rendering of Japanese Artcraft
(Eurographics Association, 2002) Durikovic, Roman; Kolchin, Kostantin; Ershov, Sergey
We present several methods for simulation of Japanese lacquer ware, a prominent Far East Asian handicraft art. We consider two most popular kinds of Japanese lacquer ware made by the makie and nashiji techniques. For rendering makie, we propose a method for preparing RGBA textures from digital photos of art items. The alpha channels of these textures control the weight with which color channels are blended with the measured biderectional reflectance distribution function (BRDF) of a metallic finish. Both ray tracing and hardware based rendering are demonstrated. In the latter case, we show how the calculation of a sphere map texture used for BRDF visualization can be accelerated using a special coordinate system for tabulated BRDF. The depth effect manifested by nashiji lacquer is simulated by the explicit modeling of metal platelets immersed in absorptive material.

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