Issue 3

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https://diglib.eg.org/handle/10.2312/106

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Now showing 1 - 20 of 46

Flattening 3D objects using silhouettes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Martin, D.; Fekete, J.D.; Torres, J. C.
An important research area in non-photorealistic rendering is the obtention of silhouettes. There are many methods to do this using 3D models and raster structures, but these are limited in their ability to create stylised silhouettes while maintaining complete flexibility. These limitations do not exist in illustration, as each element is plane and the interaction between them can be eliminated by locating each one in a different layer. This is the approach presented in this paper: a 3D model is flattened into plane elements ordered in space, which allows the silhouettes to be drawn with total flexibility.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation
Metamorphosis of Polyhedral Surfaces using Decomposition
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Shlafman, Shymon; Tal, Ayellet; Katz, Sagi
This paper describes an algorithm for morphing polyhedral surfaces based on their decompositions into patches. The given surfaces need neither be genus-zero nor two-manifolds. We present a new algorithm for decomposing surfaces into patches. We also present a new projection scheme that handles topologically cylinder-like polyhedral surfaces. We show how these two new techniques can be used within a general framework and result with morph sequences that maintain the distinctive features of the input models.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computational Geometry and Object Modeling]: Boundary representations I.3.7 [Three-Dimensional Graphics and Realism]: Animation
Free-form sketching with variational implicit surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Karpenko, Olga; Hughes, John F.; Raskar, Ramesh
With the advent of sketch-based methods for shape construction, there's a new degree of power available in the rapid creation of approximate shapes. Sketch [Zeleznik, 1996] showed how a gesture-based modeler could be used to simplify conventional CSG-like shape creation. Teddy [Igarashi, 1999] extended this to more free-form models, getting much of its power from its 'inflation' operation (which converted a simple closed curve in the plane into a 3D shape whose silhouette, from the current point of view, was that curve on the view plane) and from an elegant collection of gestures for attaching additional parts to a shape, cutting a shape, and deforming it.But despite the powerful collection of tools in Teddy, the underlying polygonal representation of shapes intrudes on the results in many places. In this paper, we discuss our preliminary efforts at using variational implicit surfaces [Turk, 2000] as a representation in a free-form modeler. We also discuss the implementation of several operations within this context, and a collection of user-interaction elements that work well together to make modeling interesting hierarchies simple. These include 'stroke inflation' via implicit functions, blob-merging, automatic hierarchy construction, and local surface modification via silhouette oversketching. We demonstrate our results by creating several models.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Modeling packages I.3.6 [Computer Graphics]: Interaction techniques
Hardware-Based Volumetric Knit-Wear
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Daubert, Katja; Seidel, Hans-Peter
We present a hardware-based, volumetric approach for rendering knit wear at very interactive rates. A single stitch is represented by a volumetric texture with each voxel storing the main direction of the strands of yarn inside it. We render the knit wear in layers using an approximation of the Banks model. Our hardware implementation allows specular and diffuse material properties to change from one voxel to the next. This enables us to represent yarn made up of different components or render garments with complicated color patterns. Furthermore, our approach can handle self-shadowing of the stitches, and can easily be adapted to also include view-independent scattering. The resulting shader lends itself naturally to mip-mapping, and requires no reordering of the base geometry, making it versatile and easy to use.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Hardware Applications Volumetric Textures
Efficient Multidimensional Sampling
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Kollig, Thomas; Keller, Alexander
Image synthesis often requires the Monte Carlo estimation of integrals. Based on a generalized concept of stratification we present an efficient sampling scheme that consistently outperforms previous techniques. This is achieved by assembling sampling patterns that are stratified in the sense of jittered sampling and N-rooks sampling at the same time. The faster convergence and improved anti-aliasing are demonstrated by numerical experiments.Categories and Subject Descriptors (according to ACM CCS): G.3 [Probability and Statistics]: Probabilistic Algorithms (including Monte Carlo); I.3.2 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.
Geometric Approximations Towards Free Specular Comic Shading
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Winnemoller, Holger; Bangay, Shaun
We extend the standard solution to comic rendering with a comic-style specular component. To minimise the computational overhead associated with this extension, we introduce two optimising approximations; the perspective correction angle and the vertex face-orientation measure. Both of these optimisations are generally applicable, but they are especially well suited for applications where a physically correct lighting simulation is not required. Using our optimisations we achieve performances comparable to the standard solution. As our approximations favour large models, we even outperform the standard approach for models consisting of 10,000 triangles or more, which we can render exceeding 40 frames per second, including the specular component.Categories and Subject Descriptors (according to ACM CSS): I.3.3 [Computer Graphics] Picture/Image Generation: Display algorithms; I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism: Color, shading, shadowing, and texture; I.4.3 [Image Processing and Computer Vision] Enhancements: Geometric Correction.
Image-Swept Volumes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Winter, Andrew S.; Chen, Min
Many graphical objects can be represented by swept volumes (including its subset - generalised cylinders) by sweeping 2D or 3D templates along 3D trajectories. In this paper, we present a new approach for constructing swept volumes using image templates. We utilise scalar fields as our underlying data type, and employ volume ray casting techniques for rendering swept volumes in their original sweeping specifications as well as in their voxelised approximations. In addition to some simple image-swept volumes, we also treat multi-channel image templates, video templates, generalised sweeps, and self-intersecting trajectories. This approach enables us to model swept volumes with heterogeneous interiors and amorphous effects. It also facilitates the use of constructive volume geometry for creating complex scenes in both modelling and rendering space.
Grid Based Final Gather for Radiosity on Complex Clustered Scenes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Scheel, Annette; Stamminger, Marc; Seidel, Hans-Peter
Radiosity methods handle large scenes and complex objects using clustering techniques. To reconstruct a high quality image, usually a second very time consuming final gather pass is applied which exactly recomputes the last light transport before reaching the eye. We propose a new final gather technique which is especially suited for scenes with fine polygonal geometry. In such scenes, substantial parts of the incident illumination vary only smoothly across the surfaces and can be reconstructed on a much coarser structure. We therefore propose a final gather reconstruction based on an object-independent 3D grid. The illumination of each sender is investigated separately: If it varies smoothly across a grid cell, it is interpolated between the vertices of the grid cell, or recomputed exactly, otherwise. We further reduce the number of required samples using view-dependent optimizations. So complex objects with a very detailed structure-plants are good example here-exhibit strong masking effects, which can be exploited by our method. Finally, the estimation of penumbra screen sizes can be used to further reduce costly visibility reevaluations.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Copmuter Graphics]: Picture/Image generation I.3.7 [Copmuter Graphics]: Three-Dimensional Graphics and Realism
Fast Continuous Collision Detection between Rigid Bodies
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Redon, Stephane; Kheddar, Abderrahmane; Coquillart, Sabine
This paper introduces a fast continuous collision detection technique for polyhedral rigid bodies. As opposed to most collision detection techniques, the computation of the first contact time between two objects is inherently part of the algorithm. The method can thus robustly prevent objects interpenetrations or collisions misses, even when objects are thin or have large velocities. The method is valid for general objects (polygon soups), handles multiple moving objects and acyclic articulated bodies, and is efficient in low and high coherency situations. Moreover, the method can be used to speed up existent continuous collision detection methods for parametric or implicit rigid surfaces. The collision detection algorithms have been successfully coupled to a real-time dynamics simulator. Various experiments are conducted that show the method's ability to produce high-quality interaction (precise objects positioning for example) between models up to tens of thousands of triangles, which couldn't have been performed with previous continuous methods.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation - Virtual Reality
Transparency in Interactive Technical Illustrations
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Diepstraten, J.; Weiskopf, D.; Ertl, T.
This paper describes how technical illustrations containing opaque and non-opaque objects can be automatically generated. Traditional methods to show transparency in manual drawings are evaluated to extract a small and effective set of rules for computer-based rendering of technical illustrations, leading to a novel view-dependent transparency model. We propose a hardware-accelerated depth sorting algorithm in image-space which specifically meets the requirements of our transparency model. In this way, real-time rendering of semi-transparent technical illustrations is achieved. Finally, it is described how our approach can be combined with other methods in the field of non-photorealistic rendering in order to enhance the visual perception of technical illustrations.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing and texture
Intrinsic Parameterizations of Surface Meshes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Desbrun, Mathieu; Meyer, Mark; Alliez, Pierre
Parameterization of discrete surfaces is a fundamental and widely-used operation in graphics, required, for instance, for texture mapping or remeshing. As 3D data becomes more and more detailed, there is an increased need for fast and robust techniques to automatically compute least-distorted parameterizations of large meshes. In this paper, we present new theoretical and practical results on the parameterization of triangulated surface patches. Given a few desirable properties such as rotation and translation invariance, we show that the only admissible parameterizations form a two-dimensional set and each parameterization in this set can be computed using a simple, sparse, linear system. Since these parameterizations minimize the distortion of different intrinsic measures of the original mesh, we call them Intrinsic Parameterizations. In addition to this partial theoretical analysis, we propose robust, efficient and tunable tools to obtain least-distorted parameterizations automatically. In particular, we give details on a novel, fast technique to provide an optimal mapping without fixing the boundary positions, thus providing a unique Natural Intrinsic Parameterization. Other techniques based on this parameterization family, designed to ease the rapid design of parameterizations, are also proposed.
Designing 2D Vector Fields of Arbitrary Topology
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Theisel, H.
We introduce a scheme of control polygons to design topological skeletons for vector fields of arbitrary topology. Based on this we construct piecewise linear vector fields of exactly the topology specified by the control polygons. This way a controlled construction of vector fields of any topology is possible. Finally we apply this method for topology-preserving compression of vector fields consisting of a simple topology.
A Frequency-Domain Approach to Watermarking 3D Shapes
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Ohbuchi, 1 Ryutarou; Mukaiyama, 1 Akio; Takahashi, 2 Shigeo
This paper presents a robust watermarking algorithm with informed detection for 3D polygonal meshes. The algorithm is based on our previous algorithm [22] that employs mesh-spectral analysis to modify mesh shapes in their transformed domain. This paper presents extensions to our previous algorithm so that (1) much larger meshes can be watermarked within a reasonable time, and that (2) the watermark is robust against connectivity alteration (e.g., mesh simplification), and that (3) the watermark is robust against attacks that combine similarity transformation with such other attacks as cropping, mesh simplification, and smoothing. Experiment showed that our new watermarks are resistant against mesh simplification and remeshing combined with resection, similarity transformation, and other operations..
Surface reconstruction based on a dynamical system?
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Giesen, Joachim; John, Matthias
We present an efficient algorithm that computes a manifold triangular mesh from a set of unorganized sample points in. The algorithm builds on the observation made by several researchers that the Gabriel graph of the sample points provides a good surface description. However, this surface description is only one-dimensional. We associate the edges of the Gabriel graph with index 1 critical points of a dynamical system induced by the sample points. Exploiting also the information contained in the critical points of index 2 provides a two-dimensional surface description which can be easily turned into a manifold.
3D Scanning Technology: Capabilities and Issues
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Scopigno, Roberto
The recent evolution of graphics technology makes it possible to manage very complex models on inexpensive platforms. These impressive rendering capabilities should be paired with detailed and accurate digital models. The construction of high quality 3D models is made easier by the increasing diffusion of automatic 3D measuring devices (often called 3D scanners). These allow to build highly accurate models of real 3D objects in a cost- and time-effective manner. The talk will present the capabilities of this technology focusing mainly on a particular application context: the acquisition of Cultural Heritage artifacts. The peculiar requirements of this domain (high accuracy in the acquisition of both shape and surface appearance, expected low cost and easiness of use of the tools) make it a perfect application example. This talk aims also at presenting and discussing the main issues in the acquisition of accurate 3D models, together with some limitations of current hardware and software tools. Some examples of the results of current projects will be shown.
Sculpturing on Discrete Displacement Fields
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Ayasse, Jorg; Muller, Heinrich
A displacement field can be defined by a vector field and a height field on an orientable surfaceS, describing the direction and the amount of displacement to be applied toSin order to get a surface represented by the displacement field.Stogether with the vector field can also be considered as a representation of a volume by a 'surface crust'. The crust allows the application of sculpturing operations for designing detailed structure. For conventional height fields over the plane, sculpturing can be reduced to the task of finding the minimum or maximum of the height values of a surface and the height values stored. Over the plane, depth-buffering with parallel projection has been used for calculation. For displacement fields over curved surfaces the projection is more complicated. In this contribution, an efficient solution is presented for displacement fields over triangular meshes. The central task is to insert a triangle in space into the curved depth-buffer represented by the displacement field.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computational Geometry and Object Modeling]: Curve, surface, solid, and object representations
A Solid Model Based Virtual Hairy Brush
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Xu, Songhua; Tang, Min; Lau, Francis; Pan, Yunhe
We present the detailed modeling of the hairy brush used typically in Chinese calligraphy. The complex model, which includes also a model for the ink and the paper, covers the various stages of the brush going through a calligraphy process. The model relies on the concept of writing primitives, which are the smallest units of hair clusters, to reduce the load on the simulation. Each such primitive is constructed through the general sweeping operation in CAD and described by a NURBS surface. The writing primitives dynamically adjust themselves during the virtual writing process, leaving an imprint on the virtual paper as they move. The behavior of the brush is an aggregation of the behavior of all the writing primitives. A software system based on the model has been built and tested. Samples of imitation artwork from using the system were obtained and found to be nearly indistinguishable from the real artwork.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Methodology and Techniques]: Interaction techniques I.3.5 [Computational Geometry and Object Modeling]: Physically based modeling I.3.4 [Graphics Utilities]: Paint systems
Slow Growing Subdivision (SGS) in Any Dimension: Towards Removing the Curse of Dimensionality
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Pascucci, V.
In recent years subdivision methods have been one of the most successful techniques applied to the multi-resolution representation and visualization of surface meshes. Extension these techniques to the volumetric case would enable their use in a broad class of applications including solid modeling, scientific visualization and mesh generation. Unfortunately, major challenges remain unsolved both in the generalization of the combinatorial structure of the refinement procedure and in the analysis of the smoothness of the limit mesh.In this paper we mainly tackle the first part of the problem introducing a subdivision scheme that generalizes to 3D and higher dimensional meshes without the excessive vertex proliferation typical of tensor-product refinements. The main four qualities of our subdivision procedure are: (i) the rate of refinement does not grow with the dimension of the mesh, (ii) adaptive refinement of the mesh is possible without introducing special temporary cell decompositions, (iii) the cells of the base meshes can have virtually unrestricted topology, and (iv) 'sharp' features of different dimensions can be incorporated naturally.We use a narrow averaging mask that is applied to the vertices of the mesh and/or to eventual functions defined on the mesh. The general study of the limit smoothness of the approach requires new analysis techniques that are beyond the scope of this paper.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curve, surface, solid, and object representations. Volumetric meshes, recursive subdivision methods.
Local Physical Models for Interactive Character Animation
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Oore, Sageev; Terzopoulos, Demetri; Hinton, Geoffrey
Our goal is to design and build a tool for the creation of expressive character animation. Virtual puppetry, also known as performance animation, is a technique in which the user interactively controls a character's motion. In this paper we introduce local physical models for performance animation and describe how they can augment an existing kinematic method to achieve very effective animation control. These models approximate specific physically-generated aspects of a character's motion. They automate certain behaviours, while still letting the user override such motion via a PD-controller if he so desires. Furthermore, they can be tuned to ignore certain undesirable effects, such as the risk of having a character fall over, by ignoring corresponding components of the force. Although local physical models are a quite simple approximation to real physical behaviour, we show that they are extremely useful for interactive character control, and contribute positively to the expressiveness of the character's motion. In this paper, we develop such models at the knees and ankles of an interactively-animated 3D anthropomorphic character, and demonstrate a resulting animation. This approach can be applied in a straight-forward way to other joints.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism, Interaction Techniques
Object Space EWA Surface Splatting: A Hardware Accelerated Approach to High Quality Point Rendering
(Blackwell Publishers, Inc and the Eurographics Association, 2002) Ren, Liu; Pfister, Hanspeter; Zwicker, Matthias
Elliptical weighted average (EWA) surface splatting is a technique for high quality rendering of point-sampled 3D objects. EWA surface splatting renders water-tight surfaces of complex point models with high quality, anisotropic texture filtering. In this paper we introduce a new multi-pass approach to perform EWA surface splatting on modern PC graphics hardware, called object space EWA splatting. We derive an object space formulation of the EWA filter, which is amenable for acceleration by conventional triangle-based graphics hardware. We describe how to implement the object space EWA filter using a two pass rendering algorithm. In the first rendering pass, visibility splatting is performed by shifting opaque surfel polygons backward along the viewing rays, while in the second rendering pass view-dependent EWA prefiltering is performed by deforming texture mapped surfel polygons. We use texture mapping and alpha blending to facilitate the splatting process. We implement our algorithm using programmable vertex and pixel shaders, fully exploiting the capabilities of today's graphics processing units (GPUs). Our implementation renders up to 3 million points per second on recent PC graphics hardware, an order of magnitude more than a pure software implementation of screen space EWA surface splatting.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Display Algorithms

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