Issue 3

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https://diglib.eg.org/handle/10.2312/111

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Ray Differentials and Multiresolution Geometry Caching for Distribution Ray Tracing in Complex Scenes
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Christensen, Per H.; Laur, David M.; Fong, Julian; Wooten, Wayne L.; Batali, Dana
When rendering only directly visible objects, ray tracing a few levels of specular reflection from large, low-curvaturesurfaces, and ray tracing shadows from point-like light sources, the accessed geometry is coherentand a geometry cache performs well. But in many other cases, the accessed geometry is incoherent and a standardgeometry cache performs poorly: ray tracing of specular reflection from highly curved surfaces, tracing rays thatare many reflection levels deep, and distribution ray tracing for wide glossy reflection, global illumination, widesoft shadows, and ambient occlusion. Fortunately, less geometric accuracy is necessary in the incoherent cases.This observation can be formalized by looking at the ray differentials for different types of scattering: coherentrays have small differentials, while incoherent rays have large differentials. We utilize this observation to obtainefficient multiresolution caching of geometry and textures (including displacement maps) for classic and distributionray tracing in complex scenes. We use an existing multiresolution caching scheme (originally developed forscanline rendering) for textures and displacement maps, and introduce a multiresolution geometry caching schemefor tessellated surfaces. The multiresolution geometry caching scheme makes it possible to efficiently render scenesthat, if fully tessellated, would use 100 times more memory than the geometry cache size.
A Fast Rendering Method for Refractive and Reflective Caustics Due to Water Surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Iwasaki, Kei; Dobashi, Yoshinori; Nishita, Tomoyuki
In order to synthesize realistic images of scenes that include water surfaces, the rendering of optical effectscaused by waves on the water surface, such as caustics and reflection, is necessary. However, rendering causticsis quite complex and time-consuming. In recent years, the performance of graphics hardware has made significantprogress. This fact encourages researchers to study the acceleration of realistic image synthesis. We present herea method for the fast rendering of refractive and reflective caustics due to water surfaces. In the proposed method,an object is expressed by a set of texture mapped slices. We calculate the intensities of the caustics on the objectby using the slices and store the intensities as textures. This makes it possible to render caustics at interactive rateby using graphics hardware. Moreover, we render objects that are reflected and refracted due to the water surfaceby using reflection/refraction mapping of these slices.Categories and Subject Descriptors (according to ACM CCS): I.3.1 [Computer Graphics]: Hardware Architecture I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Adaptive Ray Tracing of Subdivision Surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Müller, Kerstin; Techmann, Torsten; Fellner, Dieter W.
Subdivision Surfaces as well as (interactive) ray tracing have become an important issue in computer graphics.But ray tracing of subdivision surfaces has received only little attention. We present a new approach for raytracing of subdivision surfaces. The algorithm uses a projection of the ray onto the surface and works mainly intwo dimensions along this projection. While proceeding from patch to patch, we examine the bounding volume oftheir borders: the lower the distance between ray and subdivision surface, the more refinement steps are adaptivelyapplied to the surface but only along the projection of the ray. The adaptive refinement of a patch is controlled bycurvature, size, its membership to the silhouette, and its potential contribution to the light transport. The algorithmis simple and mainly consists of elementary geometric computations. Hence it is fast and easy to implementwithout the need for elaborate preprocessing. The algorithm is robust in the sense that it deals with all features ofsubdivision surfaces like creases and corners.Categories and Subject Descripters (according to ACM CCS): I.3.7 [Computer Graphics]: Raytracing
Volumetric cell-and-portal generation
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Haumont, D.; Debeir, O.; Sillion, F.
We present an algorithm to generate a cell-and-portal decomposition of general indoor scenes. The method is an adaptation of the 3D watershed transform, computed on a distance-to-geometry sampled field. The watershed is processed using a flooding analogy in the distance field space. Flooding originates from local minima, each minimum producing a region. Portals are built as needed to avoid the merging of regions during their growth. As a result, the cell-and-portal decomposition is closely linked to the structure of the models. In a building, the algorithm finds all the rooms, doors and windows. To restrict the memory load, a hierarchical implementation of the algorithm is presented. We also explain how to handle possible model degeneracies -such as cracks, holes and interpenetrating geometries- using a pre-voxelisation step. The hierarchical algorithm, preceded when necessary by the pre-voxelisation, was tested on a large range of models. We show that it is able to deal with classical architectural models, as well as cave-like environments and large mixed indoor/outdoor scenes. Thanks to the intermediate distance field representation, the algorithm can be used regardless of the way the model is represented: it deals with parametric curves, implicit surfaces, volumetric data and polygon soups in a unified way.
Planning Collision-Free Reaching Motions for Interactive Object Manipulation and Grasping
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Kallmann, Marcelo; Aubel, Amaury; Abaci, Tolga; Thalmann, Daniel
We present new techniques that use motion planning algorithms based on probabilistic roadmaps to control 22 degrees of freedom (DOFs) of human-like characters in interactive applications. Our main purpose is the automatic synthesis of collision-free reaching motions for both arms, with automatic column control and leg flexion. Generated motions are collision-free, in equilibrium, and respect articulation range limits. In order to deal with the high (22) dimension of our configuration space, we bias the random distribution of configurations to favor postures most useful for reaching and grasping. In addition, extensions are presented in order to interactively generate object manipulation sequences: a probabilistic inverse kinematics solver for proposing goal postures matching pre-designed grasps; dynamic update of roadmaps when obstacles change position; online planning of object location transfer; and an automatic stepping control to enlarge the character's reachable space. This is, to our knowledge, the first time probabilistic planning techniques are used to automatically generate collision-free reaching motions involving the entire body of a human-like character at interactive frame rates.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Volumetric Filtering, Modeling and Visualization for Nano-Medicine
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Bajaj, Chandrajit
The 3D structures of individual proteins or small complexes, such as most of the Protein Data Bank entries, are still unable to yield the 'full picture' of a functional biological complex. The study of large macromolecular complexes, such as viruses, ion channels, the ribosome and other macromolecular machines of various types, offer more complete structural and functional description of the nano-machinery of life.In addition to x-ray crystallography. NMR spectroscopy, electron cryomicroscopy (cryoEM) imaging of single particles, and in-vivo molecular tomographic imaging has become indispensable at revealing the structures of large macromolecular complexes at subnanometer resolutions.In this talk, I shall describe some of the recent computational advances in filtering, modeling, analysis and visualization, that have propelled structure determination by cryoEM and tomographic imaging, to steadily increasing accuracy.
Progressive Simplification of Tetrahedral Meshes Preserving All Isosurface Topologies
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Chiang, Yi-Jen; Lu, Xiang
In this paper, we propose a novel technique for constructing multiple levels of a tetrahedral volume dataset whilepreserving the topologies of all isosurfaces embedded in the data. Our simplification technique has two majorphases. In the segmentation phase, we segment the volume data into topological-equivalence regions, that is, thesub-volumes within each of which all isosurfaces have the same topology. In the simplification phase, we simplifyeach topological-equivalence region independently, one by one, by collapsing edges from the smallest to the largesterrors (within the user-specified error tolerance, for a given error metrics), and ensure that we do not collapseedges that may cause an isosurface-topology change. We also avoid creating a tetrahedral cell of negative volume(i.e., avoid the fold-over problem). In this way, we guarantee to preserve all isosurface topologies in the entiresimplification process, with a controlled geometric error bound. Our method also involves several additionalnovel ideas, including using the Morse theory and the implicit fully augmented contour tree, identifying typesof edges that are not allowed to be collapsed, and developing efficient techniques to avoid many unnecessary orexpensive checkings, all in an integrated manner. The experiments show that all the resulting isosurfaces preservethe topologies, and have good accuracies in their geometric shapes. Moreover, we obtain nice data-reductionrates, with competitively fast running times.
The Stringed Haptic Workbench: a New Haptic Workbench Solution
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Tarrin, N.; Coquillart, S.; Hasegawa, S.; Bouguila, L.; Sato, M.
The workbench is an interesting semi-immersive configuration for interactive tasks. However, haptic feedback, i.e.force and tactile feedback, is one important cue which is missing. To the authors' knowledge, the sole proposedsolution consists in installing an arm force feedback device on one-screen workbenches. This solution, however,has several drawbacks. The arm can perturb the stereoscopic display, cross virtual objects or hide parts of thevisualization space. Furthermore, the interaction space is limited by the size of the arm, which may also damagethe screen or perturb the electromagnetic tracking system. Some of these difficulties may even be worth with a two-screenworkbench. This paper discusses an alternative solution, which consists in integrating a stringed hapticdevice on a workbench. This approach is less invasive, more flexible and well-suited to a two-screen workbench.
ShieldTester: Cell-to-Cell Visibility Test for Surface Occluders
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Navazo, I.; Rossignac, J.; Jou, J.; Shariff, R.
We present a novel Cell-To-Cell Visibility (C2CV) algorithm, which given two polyhedra, AandBand a connectedand oriented manifold triangle mesh, S offers a simple, fast and conservative test for detecting when A and B areoccluded from each other by S. Previously disclosed C2CV algorithms either relied on costly occlusion fusion orwere restricted to convex or "apparently convex" occluders, which makes them inappropriate for scenes wherepotential occluders are arbitrary triangulated surfaces, such as the body of a car or a portion of a terrain. Thesimplicity of our C2CV algorithm, named ShieldTester, stems from a new Occlusion Theorem, introduced herewhich permits to establish occlusion by computing the intersection of S with a single ray from a vertex ofAtoa vertex ofB. ShieldTester may be used to establish that pairs of cells in a subdivision of space are hidden fromeach other by a relatively large surface occluder, so that when the viewer is in one cell, the objects in the othercell need not be displayed.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Computational Geometryand Object Modeling: Occlussion Culling, Visibility Test, Triangle Meshes
Freeform Shape Representations for Efficient Geometry Processing
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Kobbelt, Leif
The most important concepts for the handling and storage of freeform shapes in geometry processing applications are parametric representations and volumetric representations. Both have their specific advantages and drawbacks. While the algebraic complexity of volumetric representations is independent from the shape complexity, the domain of a parametric representation usually has to have the same structure as the surface itself (which sometimes makes it necessary to update the domain when the surface is modified).On the other hand, the topology of a parametrically defined surface can be controlled explicitly while in a volumetric representation, the surface topology can change accidentally during deformation. A volumetric representation reduces distance queries or inside/outside tests to mere function evaluations but the geodesic neighborhood relation between surface points is difficult to resolve. As a consequence, it seems promising to combine parametric and volumetric representations to effectively exploit both advantages.In this talk, a number of projects are presented and discussed in which such a combination leads to efficient and numerically stable algorithms for the solution of various geometry processing tasks. Applications include global error control for mesh decimation and smoothing, topology control for level-set surfaces, and shape modeling with unstructured point clouds.
Interactive Cutaway Illustrations
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Diepstraten, J.; Weiskopf, D.; Ertl, T.
In this paper we discuss different approaches to generate cutaway illustrations. The purpose of such a drawingis to allow the viewer to have a look into an otherwise solid opaque object. Traditional methods to draw thesekinds of illustrations are evaluated to extract a small and effective set of rules for a computer-based renderingof cutaway illustrations. We show that our approaches are not limited to a specific rendering style but can besuccessfully combined with a great variety of well-known artistic or technical illustration techniques. All methodsof this paper make use of modern graphics hardware functionality to achieve interactive frame rates.
Particle-Based Simulation of Fluids
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Premzoe, Simon; Tasdizen, Tolga; Bigler, James; Lefohn, Aaron; Whitaker, Ross T.
Due to our familiarity with how fluids move and interact, as well as their complexity, plausible animation of fluidsremains a challenging problem. We present a particle interaction method for simulating fluids. The underlyingequations of fluid motion are discretized using moving particles and their interactions. The method allows simulationand modeling of mixing fluids with different physical properties, fluid interactions with stationary objects, andfluids that exhibit significant interface breakup and fragmentation. The gridless computational method is suitedfor medium scale problems since computational elements exist only where needed. The method fits well into thecurrent user interaction paradigm and allows easy user control over the desired fluid motion.
Field Functions for Blending Range Controls on Soft Objects
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hsu, P. C.; Lee, C.
This paper proposes new field functions that have adjustable inner radius and outer radius of influence. Incorporatingthe proposed field functions with soft object modeling, soft blending, Ricci's super-ellipsoid blends, Perlin'sset operations, and R-functions, etc. can have blending range controls by adjusting the inner and the outer radiiof influence of given field functions. As a result, the sizes of the resulting blending surfaces on soft objects willnot be restricted by the sizes of the blended primitive soft objects and can be enlarged and shrunk freely withoutdeforming the overall shapes of blended primitive soft objects. In addition, a small soft object can have a largeblending region, and a large one can have a small blending regionCategories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling - Curve, surface, solid and object representations
A Scalable Approach to Interactive Global Illumination
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Benthin, Carsten; Wald, Ingo; Slusallek, Philipp
The addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.In particular with interactive applications we expect the environment to reflect changes in the scenedue to global lighting effects instead of it being just a static backdrop. However, a sufficiently fast and accuratecomputation of global illumination at interactive rates has been difficult even with recent approaches based onrealtime ray tracing.In this paper we present a highly scalable approach to interactive global illumination. It fully recomputes a high-qualitysolution for each frame and thus offers immediate feedback even for dynamic scenes, achieving more than20 fps for simple scenes. Compared to previous systems we increased the raw performance by a factor of up toeight and removed the bottlenecks that were limiting scalability. The system now scales linearly in quality andavailable computing resources, tested with up to 48 CPUs in a commodity PC-cluster. Due to its logarithmicscaling property with respect to scene complexity it even supports lighting simulation in complex scenes with morethan 50 million triangles. This scalability allows applications to perform flexible performance trade-offs. We alsoargue that the realism achievable through interactive global illumination will make it a standard feature of future3D graphics systems once the required computing resources are readily available.
Visyllable Based Speech Animation
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Kshirsagar, Sumedha; Magnenat-Thalmann, Nadia
Visemes are visual counterpart of phonemes. Traditionally, the speech animation of 3D synthetic faces involvesextraction of visemes from input speech followed by the application of co-articulation rules to generate realisticanimation. In this paper, we take a novel approach for speech animation - using visyllables, the visual counterpartof syllables. The approach results into a concatenative visyllable based speech animation system. The key contributionof this paper lies in two main areas. Firstly, we define a set of visyllable units for spoken English along withthe associated phonological rules for valid syllables. Based on these rules, we have implemented a syllabificationalgorithm that allows segmentation of a given phoneme stream into syllables and subsequently visyllables. Secondly,we have recorded the database of visyllables using a facial motion capture system. The recorded visyllableunits are post-processed semi-automatically to ensure continuity at the vowel boundaries of the visyllables. We defineeach visyllable in terms of the Facial Movement Parameters (FMP). The FMPs are obtained as a result of thestatistical analysis of the facial motion capture data. The FMPs allow a compact representation of the visyllables.Further, the FMPs also facilitate the formulation of rules for boundary matching and smoothing after concatenatingthe visyllables units. Ours is the first visyllable based speech animation system. The proposed technique iseasy to implement, effective for real-time as well as non real-time applications and results into realistic speechanimation.Categories and Subject Descriptors (according to ACM CCS): 1.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Reanimating Faces in Images and Video
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Blanz, V.; Basso, C.; Poggio, T.; Vetter, T.
This paper presents a method for photo-realistic animation that can be applied to any face shown in a single imageor a video. The technique does not require example data of the person's mouth movements, and the image to beanimated is not restricted in pose or illumination. Video reanimation allows for head rotations and speech in theoriginal sequence, but neither of these motions is required.In order to animate novel faces, the system transfers mouth movements and expressions across individuals, basedon a common representation of different faces and facial expressions in a vector space of 3D shapes and textures.This space is computed from 3D scans of neutral faces, and scans of facial expressions.The 3D model's versatility with respect to pose and illumination is conveyed to photo-realistic image and videoprocessing by a framework of analysis and synthesis algorithms: The system automatically estimates 3D shape andall relevant rendering parameters, such as pose, from single images. In video, head pose and mouth movements aretracked automatically. Reanimated with new mouth movements, the 3D face is rendered into the original images.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation
Hierarchical Context-based Pixel Ordering
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Bar-Joseph, Ziv; Cohen-Or, Daniel
We present a context-based scanning algorithm which reorders the input image using a hierarchical representationof the image. Our algorithm optimally orders (permutes) the leaves corresponding to the pixels, by minimizing thesum of distances between neighboring pixels. The reordering results in an improved autocorrelation betweennearby pixels which leads to a smoother image. This allows us, for the first time, to improve image compressionrates using context-based scans. The results presented in this paper greatly improve upon previous work in bothcompression rate and running time.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometryand Object Modeling I.3.6 [Computer Graphics]: Methodology and Techniques
Narrative Use of Sign Language by a Virtual Character for the Hearing Impaired
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Rieger, Thomas; Braun, Norbert
This paper describes the concept and control of a 3d virtual character system with facial expressions and gesturesas a conversational user interface with narrative expressiveness for the hearing impaired. The gestures and facialexpressions are based on morphing techniques. The system allows the generation of sign language and mouthmotion in real time from text at the level of lip reading quality. The concept of Narrative Extended Speech Acts(NESA) is introduced, based on Interactive Storytelling techniques and the concepts of Narrative Conflict andSuspense Progression. We define a choice of annotation tags to be used with NESAs. We use the NESAs to classifyconversation fragments and to enhance computer generated sign language. We note, how the sign language gesturesare generated and show the possibilities for editing sign language gestures. Furthermore, we give details onhow the NESAs are mapped to gestures. We show the possibilities of controlling the virtual character's behaviourand gestures in a human-oriented way and provide an outlook on future work.Categories and Subject Descriptors (according to ACM CCS): 1.3.6 [Computer Graphics]: Methodology and Techniques
Advanced Design for a Realistic Virtual Brush
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Xu, Songhua; Lau, Francis C.M.; Tang, Feng; Pan, Yunhe
This paper proposes a novel algorithmic framework for an advanced virtual brush to be used in interactive digitalpainting. The framework comprises the following components: a geometry model of the brush using a hierarchicalrepresentation that leads to substantial savings in every step of the painting process; fast online brush motionsimulation assisted by offline calibration that guarantees an accurate and stable simulation of the brush's dynamicbehavior; a new pigment model based on a diffusion process of random molecules that considers delicateand complex pigment behavior at dipping time as well as during painting; and a user-adaptation component thatenables the system to cater for the personal painting habits of different users. A prototype system has been implementedbased on this framework. Compared with other virtual brushes, this new system is designed to presenta realistic brush in the sense that the system accurately and stably simulates the complex painting functionalityof a running brush, and therefore is capable of creating high-quality digital paintings with minute aesthetic detailsthat can rival the real artwork. The advanced features also give rise to a high degree of expressiveness ofthe virtual brush that the user can comfortably manipulate. http://www.csis.hku.hk/songhuale-brush/ providessupplementary materials for this paper.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Methodology and Techniques]: Interactiontechniques; I.3.5 [Computational Geometry and Object Modeling]: Physically based modeling; I.3.4 [GraphicsUtilities]: Paint systems;
Automatic texture atlas generation from trimmed NURBS models
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Guthe, M.; Klein, R.
A Texture Atlas is a two dimensional representation of a 3D model usable for paint systems or as a sewing pattern.The field of texture atlas generation from polygonal models has been well exploited in the recent years. The developedalgorithms work on piecewise linear surface representations, but not on parametric surfaces like NURBS,that are still the main surface representation in CAD systems. If a texture atlas is generated from a triangulatedNURBS model, the result cannot be edited further in a CAD system, since the separation into charts is not basedon the separate NURBS patches of the original model. We present a method for automatic generation of a textureatlas directly from trimmed NURBS models, while preserving the original NURBS representation. The resultingtexture atlas is build of several charts, each consisting of the original NURBS patches sewn together.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation;I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling; I.3.7 [Computer Graphics]: Three-DimensionalGraphics and Realism - Color, Shading and Texture; J.6 [Computer-aided Engineering]: Computer-aideddesign (CAD)

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