Volume 23 (2004)

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Point Cloud Collision Detection
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Klein, Jan; Zachmann, Gabriel
In the past few years, many efficient rendering and surface reconstruction algorithms for point clouds have been developed. However, collision detection of point clouds has not been considered until now, although this is a prerequisite to use them for interactive or animated 3D graphics.We present a novel approach for time-critical collision detection of point clouds. Based solely on the point representation, it can detect intersections of the underlying implicit surfaces. The surfaces do not need to be closed.We construct a point hierarchy where each node stores a sufficient sample of the points plus a sphere covering of a part of the surface. These are used to derive criteria that guide our hierarchy traversal so as to increase convergence. One of them can be used to prune pairs of nodes, the other one is used to prioritize still to be visited pairs of nodes. At the leaves we efficiently determine an intersection by estimating the smallest distance.We have tested our implementation for several large point cloud models. The results show that a very fast and precise answer to collision detection queries can always be given.Categories and Subject Descriptors (according to ACM CCS): G.1.2 [Numerical Analysis]: Approximation of surfaces and contours I.3.5 [Computer Graphics]: Computational Geometry and Object-Modeling[Geometric algorithms, languages and systems; object hierarchy; physically-based modeling] I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism[Animation; virtual reality]
Dupin Cyclide Blends Between Quadric Surfaces for Shape Modeling
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Foufou, Sebti; Garnier, Lionel
We introduce a novel method to define Dupin cyclide blends between quadric primitives. Dupin cyclides are non-spherical algebraic surfaces discovered by French mathematician Pierre-Charles Dupin at the beginning of the 19th century. As a Dupin cyclide can be fully characterized by its principal circles, we have focussed our study on how to determine principal circles tangent to both quadrics being blended. This ensures that the Dupin cyclide we are constructing constitutes aG1blend. We use the Rational Quadratic Bezier Curve (RQBC) representation of circular arcs to model the principal circles, so the construction of each circle is reduced to the determination of the three control points of the RQBC representing the circle.In this work, we regard the blending of two quadric primitives A and B as two complementary blending operations: primitive A-cylinder and cylinder-primitive B; two Dupin cyclides and a cylinder are then defined for each blending operation. In general the cylinder is not useful and may be reduced to a simple circle. A complete shape design example is presented to illustrate the modeling of Eurographics'04 Hugo using a limited number of quadrics combined using Dupin cyclide blends.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
Image-based Relighting, and Computer Vision
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Dutre, Philip
Image-based techniques have become very popular over the past couple of years. Ranging from modeling to rendering and lighting, the use of images as direct input for graphics algorithms has become as important as processing polygons or other forms of data.This talk will focus on some of the challenges posed by Image-based relighting. Starting from a set of photographs of an object under various illumination conditions, Image-based relighting computes novel renderings of the objects. Also, the inverse problem stated as 'What is the required lighting configuration to reach a desired illumination on the object?' will be discussed, as well as some thoughts on how results from computer vision can be used to accelerate the process.
Fast Multipath Radiosity using Hierarchical Subscenes
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Castro, F.; Sbert, M.; Neumann, L.
This paper presents an efficient acceleration technique for the global line radiosity Multipath method. In this approach, the scene is subdivided in a hierarchy of box bounded subscenes, the boxes subdivided in a grid of virtual patches which store angular information. A new recursive (according to the hierarchy of subscenes) function allows to execute the Multipath algorithm at different levels of the hierarchy. A speed up factor up to 3-4 has been obtained on some of the tested scenes.
A Viewpoint-Dependent Approach to Ray Trace Free-Form Surfaces
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Formella, A.; Mueller, K.
For convincing realistic scenes objects with free-form surfaces are essential. Especially for photorealistic rendering pure polygonal models are often not sufficient. We present a new kind of algorithm to render free-form surfaces in a rendering system based on ray tracing. We describe a triangular patch as usual by its three points and normal vectors, but base the intersection calculation as well on the viewpoint of the camera (or, in general, on the ray itself). Hence, the shape of the object depends to some extent on the sampling rays. However, the resulting differences of, for instance, the shape of the silhouette to the shape of the corresponding shadow is usually not perceived by the observer of the rendered image. Because we perform a direct computation without a tessellation process, the resulting surface, its shadows, and its reflections appear smooth independent of the distance to the camera. Furthermore, the memory consumption depends only linearly on the number of input triangles. Special features like creases, T-vertices, and darts are also well supported. The computed uv-coordinates provide a direct means for texture mapping whose visual appearance improves significantly compared to triangle meshes of the same resolution.
A System for View-Dependent Animation
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Chaudhuri, Parag; Kalra, Prem; Banerjee, Subhashis
In this paper, we present a novel system for facilitating the creation of stylized view-dependent 3D animation. Our system harnesses the skill and intuition of a traditionally trained animator by providing a convivial sketch based 2D to 3D interface. A base mesh model of the character can be modified to match closely to an input sketch, with minimal user interaction. To do this, we recover the best camera from the intended view direction in the sketch using robust computer vision techniques. This aligns the mesh model with the sketch. We then deform the 3D character in two stages - first we reconstruct the best matching skeletal pose from the sketch and then we deform the mesh geometry. We introduce techniques to incorporate deformations in the view-dependent setting. This allows us to set up view-dependent models for animation.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - Animation 7Our system takes as input a sketch (a), and a base mesh model (b), then recovers a camera to orient the base mesh (c), then reconstructs the skeleton pose (d), and finally deforms the mesh to find the best possible match with the sketch (e).
25th EUROGRAPHICS General Assembly
(The Eurographics Association and Blackwell Publishing Ltd., 2004)
DiFi: Fast 3D Distance Field Computation Using Graphics Hardware
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Sud, Avneesh; Otaduy, Miguel A.; Manocha, Dinesh
We present an algorithm for fast computation of discretized 3D distance fields using graphics hardware. Given a set of primitives and a distance metric, our algorithm computes the distance field for each slice of a uniform spatial grid baly rasterizing the distance functions of the primitives. We compute bounds on the spatial extent of the Voronoi region of each primitive. These bounds are used to cull and clamp the distance functions rendered for each slice. Our algorithm is applicable to all geometric models and does not make any assumptions about connectivity or a manifold representation. We have used our algorithm to compute distance fields of large models composed of tens of thousands of primitives on high resolution grids. Moreover, we demonstrate its application to medial axis evaluation and proximity computations. As compared to earlier approaches, we are able to achieve an order of magnitude improvement in the running time.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Distance fields, Voronoi regions, graphics hardware, proximity computations
Cultural Heritage Preservation Using Constructive Shape Modeling
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Vilbrandt, C.; Pasko, G.; Pasko, A.; Fayolle, P.-A.; Vilbrandt, T.; Goodwin, J. R.; Goodwin, J. M.; Kunii, T. L.
Issues of digital preservation of shapes and internal structures of historical cultural objects are discussed. An overview of existing approaches to digital preservation related to shape modeling is presented and corresponding problems are considered. We propose a new digital preservation paradigm based on both constructive modeling reflecting the logical structure of the objects and open standards and procedures. Constructive Solid Geometry (CSG) and Function Representation (FRep) are examined and practically applied as mathematical representations producing compressed yet precise data structures, thus providing inter-operability between current and future computer platforms crucial to archiving. Examples of CSG reconstruction of historical temples and FRep modeling of traditional lacquer ware are given. We examine the application of fitting of a parameterized FRep model to a cloud of data points as a step towards automation of the modeling process. Virtual venues for public access to cultural heritage objects including real time interactive simulation of cultural heritage sites over the Web are discussed and illustrated.
Approximate Soft Shadows win an Image-Space Flood-Fill Algorithm
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Arvo, Jukka; Hirvikorpi, Mika; Tyystjaervi, Joonas
Most former soft shadow algorithms have either suffered from restricted self-shadowing capabilities, been too slow for interactive applications, or could only be used with a limited types of geometry. In this paper, we propose an efficient image-based approach for computing soft shadows. Our method is based on shadow mapping and provides the associated benefits. We use pixel-based visibility computations for rendering penumbra regions directly into the screen-space. This is accomplished by using a modified flood-fill algorithm which enables us to implement the algorithm using programmable graphics hardware. Even though the resulting images are most often high quality, we do not claim that the proposed method is physically correct. The computation time and memory requirements for soft shadows depend on image resolution and the number of lights, not geometric scene complexity.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Three-Dimensional Graphics and Realism]: Color, shading, shadowing, and texture
Eurographics 2003
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Duce, David; Torres, Juan Carlos
Fast Hybrid Approach for Texturing Point Models
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Haitao Zhang; Feng Qiu; Arie Kaufman
We present three methods for texturing point models from sample textures. The first method, the point parameterization method, uses a fast distortion-bounded parameterization algorithm to flatten the point model's surface into one or more 2D patches. The sample texture is mapped onto these patches and alpha blending is used to minimize the discontinuity in the gaps between the patches. The second method is based on neighborhood matching where a color is assigned to each point by searching the best match within an irregular neighborhood. The hybrid method combines the former two methods, capitalizing on the advantages of both. The point parameterization method is used first to color most of the points, and the point neighborhood-matching method is then applied to the points belonging to the gaps between the parameterized patches to minimize the discontinuity. We opt for fast texture generation, while some discontinuities may appear in the gaps of anisotropic textures.
Hardware Lighting and Shading: a Survey
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Kautz, Jan
Traditionally, hardware rasterizers only support the Phong lighting model in combination with Gouraud shading using point light sources. However, the Phong lighting model is strictly empirical and physically implausible. Gouraud shading also tends to undersample the highlight unless a highly tesselated surface is used. Hence, higher-quality hardware accelerated lighting and shading has gained much interest in the recent five years. The research on hardware lighting and shading is two-fold. On the one hand, better lighting models for local illumination (assuming point light sources but evaluated per pixel) were demonstrated to be amenable to hardware implementation. On the other hand, recent research has demonstrated that even area lights, represented as environment maps, can be combined with complex lighting models. In both areas, many articles have been published, making it hard to decide which algorithm is well-suited for which application. This state-of-the-art report will review all relevent articles in both areas, and list advantages and disadvantages of each algorithm.
Volume Graphics 2003
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Fujishiro, Issei; Mueller, Klaus; Kaufman, Arie
Real-time Rigid Body Simulation for Haptic Interactions Based on Contact Volume of Polygonal Objects
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Hasegawa, S.; Sato, M.
This paper proposes a new method for real-time rigid body simulations for haptic interactions based on a penalty method regarding contact volume. Analytical methods for calculation of contact forces require too much time to maintain fast update rates for haptic controls. In addition, they prohibit direct connection of haptic interfaces.Penalty methods, which employ spring-damper models for calculation of contact forces, offer a very rapid rate of iterations. In addition, they permit direct connection of haptic interfaces. Penalty methods are good for haptic interactions. However, previous penalty methods do not regard distribution of contact forces over the contact area. For that reason, they can't calculate normal and friction forces on face-face contacts correctly.We propose a distributed spring-damper model on a contact area to solve these problems. We analyze three-dimensional geometries of the intersecting portion on the polyhedral objects. Then, we integrate forces and torques of distributed spring-damper models.We implement a proposed simulator and compare it with a point-based penalty method and constraint method. The comparison shows that the proposed simulator improves accuracy of the simulation of face-face contact and friction forces and the simulation speed. In addition, we attach a six degree-of-freedom (6-DOF) haptic interface to the simulator. Users can feel 6-DOF force feedback and input 6-DOF motions.Categories and Subject Descriptors (according to ACM CCS): I.6.5 [Model Development]: Modeling methodologies, H.5.2 [User Interfaces]: Haptic I/O, I.3.6 [Methodology and Techniques]: Interaction techniques
High Quality Hatching
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Zander, Johannes; Isenberg, Tobias; Schlechtweg, Stefan; Strothotte, Thomas
Hatching lines are often used in line illustrations to convey tone and texture of a surface. In this paper we present methods to generate hatching lines from polygonal meshes and render them in high quality either at interactive rates for on-screen display or for reproduction in print. Our approach is based on local curvature information that is integrated to form streamlines on the surface of the mesh. We use a new algorithm that provides an even distribution of these lines. A special processing of these streamlines ensures high quality line rendering for both intended output media later on. While the streamlines are generated in a preprocessing stage, hatching lines are rendered either for vector-based printer output or on-screen display, the latter allowing for interaction in terms of changing the view parameters or manipulating the entire line shading model at run-time using a virtual machine.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation-Display algorithms; I.3.3 [Computer Graphics]: Picture/Image Generation-Line and curve generation
Siggraph 2004
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Laycock, S. D.; Laycock, R. G.; Ryder, G.; Juarez-Comboni, J.; Montes de Oca, C.
Placement of Deformable Objects
(The Eurographics Association and Blackwell Publishing Ltd., 2004) S. Schein; G. Elber
With the increasing complexity of photorealistic scenes, the question of building and placing objects in three-dimensional scenes is becoming ever more difficult. While the question of placement of rigid objects has captured the attention of researchers in the past, this work presents an intuitive and interactive scheme to properly place deformable objects with the aid of free-form deformation tools. The presented scheme can also be used to animate the locomotion of nonrigid objects, most noticeably animals, and adapt the motion to arbitrary terrain. The automatic construction of our free-form deformation tool is completely hidden from the end user, and hence, circumvents the difficulties typically faced in manipulating these deformation functions. Further, a precise bound on the error that is introduced by applying free-form deformations to polygonal models is presented, along with an almost-optimal adaptive refinement algorithm to achieve a certain accuracy in the mapping.
Combined Correlated and Importance Sampling in Direct Light Source Computation and Environment Mapping
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Szecsi, Laszlo; Sbert, Mateu; Szirmay-Kalos, Laszlo
This paper presents a general variance reduction method that is a quasi-optimal combination of correlated and importance sampling. The weights of the combination are selected automatically in order to keep the merits of both importance and correlated sampling. The proposed sampling method is used for efficient direct light source computation of large area sources and for the calculation of the reflected illumination of environment maps. Importance sampling would be good in these cases if the sources are hidden, while correlated sampling is efficient if the sources are fully visible. The proposed method automatically detects the particular case and provides results that inherit the advantages of both techniques.
Second Symposium on Geometry Processing
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Scopigno, Roberto; Zorin, Denis; Alliez, Pierre; Boissonnat, Jean-Daniel

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