Volume 20 (2001)

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A Novel Approach for Delaunay 3D Reconstruction with a Comparative Analysis in the Light of Applications
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Nonato, L.; Minghim, R.; Oliveira, M. C. F.; Tavares, G.
This paper presents a novel algorithm for volumetric reconstruction of objects from planar sections using Delaunay triangulation, which solves the main problems posed to models defined by reconstruction, particularly from the viewpoint of producing meshes that are suitable for interaction and simulation tasks. The requirements for these applications are discussed here and the results of the method are presented. Additionally, it is compared to another commonly used reconstruction algorithm based on Delaunay triangulation, showing the advantages of the reconstructions obtained by our technique.
Multiresolution for Algebraic Curves and Surfaces using Wavelets
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Esteve, Jordi; Brunet, Pere; Vinacua, Alvar
This paper describes a multiresolution method for implicit curves and surfaces. The method is based on wavelets, and is able to simplify the topology. The implicit curves and surfaces are defined as the zero-valued piece-wise algebraic isosurface of a tensor-product uniform cubic B-spline. A wavelet multiresolution method that deals with uniform cubic B-splines on bounded domains is proposed. In order to handle arbitrary domains the proposed algorithm dynamically adds appropriate control points and deletes them in the synthesis phase.
Modeling Dynamic Hair as a Continuum
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Hadap, Sunil; Magnenat-Thalmann, Nadia
In this paper we address the difficult problem of hair dynamics, particularly hair-hair and hair-air interactions. To model these interactions, we propose to consider hair volume as a continuum. Subsequently, we treat the interaction dynamics to be fluid dynamics. This proves to be a strong as well as viable approach for an otherwise very complex phenomenon. However, we retain the individual character of hair, which is vital to visually realistic rendering of hair animation. For that, we develop an elaborate model for stiffness and inertial dynamics of individual hair strand. Being a reduced coordinate formulation, the stiffness dynamics is numerically stable and fast. We then unify the continuum interaction dynamics and the individual hair's stiffness dynamics.
Interactive Computer Animation of Hand Gestures using Status Estimation with Multiple Regression Analysis
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Kitamura, Yoshifumi; Higashi, Tomohiko; Iida, Takayuki; Kishino, Fumio
This paper presents a method of interactively generating natural hand gesture animation using reduced dimensionality from multiple captured data sequences of finger motions conducting specific tasks. This method is achieved by introducing an estimation with multiple regression analysis. Even when the skeletal structure of the user who inputs the motion is different from that of the shape model in the computer, the motion that a user imagines is generated. Experimental results obtained from the interface applied to virtual object manipulation showed that the proposed method generates animation naturally, just as users would expect. This method enables us to make input devices that require minimal user training and computer calibration, and helps to make the user interface intuitive and easy to use.
Tour Into the Picture using a Vanishing Line and its Extension to Panoramic Images
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Kang, Hyung Woo; Pyo, Soon Hyoung; Anjyo, Ken-ichi; Shin, Sung Yong
Tour into the picture (TIP) proposed by Horry et al.13 is a method for generating a sequence of walk-through images from a single reference picture (or image). By navigating a 3D scene model constructed from the picture, TIP produces convincing 3D effects. Assuming that the picture has one vanishing point, they proposed the scene modeling scheme called spidery mesh. However, this scheme has to go through major modification when the picture contains multiple vanishing points or does not have any well-defined vanishing point. Moreover, the spidery mesh is hard to generalize for other types of images such as panoramic images. In this paper, we propose a new scheme for TIP which is based on a single vanishing line instead of a vanishing point. Based on projective geometry, our scheme is simple and yet general enough to address the problems faced with the previous method. We also show that our scheme can be naturally extended to a panoramic image.
3D Metamorphosis Between Different Types of Geometric Models
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Breen, David E.; Mauch, Sean; Whitaker, Ross T.; Mao, Jia
We present a powerful morphing technique based on level set methods, that can be combined with a variety of scan conversion/model processing techniques. Bringing these techniques together creates a general morphing approach that allows a user to morph a number of geometric model types in a single animation. We have developed techniques for converting several types of geometric models (polygonal meshes, CSG models and MRI scans) into distance volumes, the volumetric representation required by our level set morphing approach. The combination of these two capabilities allows a user to create a morphing sequence regardless of the model type of the source and target objects, freeing him/her to use whatever model type is appropriate for a particular animation.
Adaptive Implicit Surface Polygonization Using Marching Triangles
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Akkouche, Samir; Galin, Eric
This paper presents several improvements to the marching triangles algorithm for general implicit surfaces. The original method generates equilateral triangles of constant size almost everywhere on the surface. We present several modifications to adapt the size of the triangles to the curvature of the surface. As cracks may arise in the resulting polygonization, we propose a specific crack-closing method invoked at the end of the mesh growing step. Eventually, we show that the marching triangles can be used as an incremental meshing technique in an interactive modeling environment. In contrast to existing incremental techniques based on spatial subdvision, no extra data-structure is needed to incrementally edit skeletal implicit surfaces, which saves both memory and computation time.
Implementation and Complexity of the Watershed-from-Markers Algorithm Computed as a Minimal Cost Forest
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Felkel, Petr; Bruckschwaiger, Mario; Wegenkittl, Rainer
Displacement Mapping using Scan Conversion Hardware Architectures
(Blackwell Publishers Ltd and the Eurographics Association., 2001) Doggett, Michael; Kugler, Anders; Strasser, Wolfgang
This paper presents a novel algorithm and architectures for perspective correct displacement of the surface geometry of a polygonal model using a displacement map. This new displaced surface geometry is passed onto a traditional rendering pipeline. The algorithm uses a multiple pass approach in which the geometry is displaced in the first pass and then the displaced geometry is rendered. The significant features of the algorithm are that the surface is displaced after its triangle mesh is transformed into screen space and that it uses only bi-linear interpolation for calculating the displaced geometry allowing a cheap incremental scan-line implementation. A hardware architecture based on this algorithm is presented along with possible alternative implementations. The technique presented here allows greater photorealism by using increased detail without an increase in bandwidth for geometry or calculation time for transformation.
Rendering: Input and Output
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Rushmeier, H.
Rendering is the process of creating an image from numerical input data. In the past few years our ideas about methods for acquiring the input data and the form of the output have expanded. The availability of inexpensive cameras and scanners has influenced how we can obtain data needed for rendering. Input for rendering ranges from sets of images to complex geometric descriptions with detailed BRDF data. The images that are rendered may be simply arrays of RGB images, or they may be arrays with vectors or matrices of data defined for each pixel.The rendered images may not be intended for direct display, but may be textures for geometries that are to be transmitted to be rendered on another system. A broader range of parameters now need to be taken into account to render images that are perceptually consistent across displays that range from CAVEs to personal digital assistants. This presentation will give an overview of how new hardware and new applications have changed traditional ideas of rendering input and output.
A Unified Subdivision Scheme for Polygonal Modeling
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Maillot, Jerome; Stam, Jos
Subdivision rules have traditionally been designed to generate smooth surfaces from polygonal meshes. In this paper we propose to employ subdivision rules as a polygonal modeling tool, specifically to add additional level of detail to meshes. However, existing subdivision schemes have several undesirable properties making them ill suited for polygonal modeling. In this paper we propose a general set of subdivision rules which provides users with more control over the subdivision process. Most existing subdivision schemes are special cases. In particular, we provide subdivision rules which blend approximating spline based schemes with interpolatory ones. Also, we generalize subdivision to allow any number of refinements to be performed in a single step.
Tensor Topology Tracking: A Visualization Method for Time-Dependent 2D Symmetric Tensor Fields
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Tricoche, X.; Scheuermann, G.; Hagen, H.
Topological methods produce simple and meaningful depictions of symmetric, second order two-dimensional tensor fields. Extending previous work dealing with vector fields, we propose here a scheme for the visualization of time-dependent tensor fields. Basic notions of unsteady tensor topology are discussed. Topological changes - known as bifurcations - are precisely detected and identified by our method which permits an accurate tracking of degenerate points and related structures.
Rendering Natural Waters
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Premoze, Simon; Ashikhmin, Michael
Creating and rendering realistic water is one of the most daunting tasks in computer graphics. Realistic rendering of water requires that the sunlight and skylight illumination are correct, the water surface is modeled accurately and that the light transport within water body is properly handled. This paper describes a method for wave generation on a water surface using a physically-based approach. The wave generation uses data from the oceanographical observations and it is controlled by intuitive parameters such as wind speed and wind direction. The optical behavior of the water surfaces is complex but is well-described in the ocean science literature. We present a simple and intuitive light transport approach that is easy to use for many different water types such as deep ocean water, muddy coastal water, and fresh water bodies. We demonstrate our model for a number of water and atmospheric conditions.
Fast and Controllable Simulation of the Shattering of Brittle Objects
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Smith, Jeffrey; Witkin, Andrew; Baraff, David
We present a method for the rapid and controllable simulation of the shattering of brittle objects under impact. An object is represented as a set of point masses connected by distance-preserving linear constraints. This use of constraints, rather than stiff springs, gains us a significant advantage in speed while still retaining fine control over the fracturing behavior. The forces exerted by these constraints during impact are computed using Lagrange multipliers. These constraint forces are then used to determine when and where the object will break, and to calculate the velocities of the newly created fragments. We present the details of our technique together with examples illustrating its use.An earlier version of this paper was presented at Graphics Interface 2000, held in Montreal, Canada.
Horizon Map Capture
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Rushmeier, Holly; Balmelli, Laurent; Bernardini, Fausto
We present a method for computing horizon maps from captured images of a bumpy surface. 1Horizon maps encode surface self-shadowing effects, and can be used with bump or normals maps to realistically render surfaces with small height perturbations. The method does not rely on complete surface reconstruction, and requires only eight captured images as input. In this paper we discuss how shadow information is extrapolated from the eight captured images to compute the horizon map. Our implementation accounts for the noise and uncertainties in physically acquired data.
Resampling Feature and Blend Regions in Polygonal Meshes for Surface Anti-Aliasing
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Botsch, Mario; Kobbelt, Leif
Efficient surface reconstruction and reverse engineering techniques are usually based on a polygonal mesh representation of the geometry: the resulting models emerge from piecewise linear interpolation of a set of sample points. The quality of the reconstruction not only depends on the number and density of the sample points but also on their alignment to sharp and rounded features of the original geometry. Bad alignment can lead to severe alias artifacts. In this paper we present a sampling pattern for feature and blend regions which minimizes these alias errors. We show how to improve the quality of a given polygonal mesh model by resampling its feature and blend regions within an interactive framework. We further demonstrate sophisticated modeling operations that can be implemented based on this resampling technique.
Recent Advances in Volume Visualization
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Brodlie, Ken; Wood, Jason
In the past few years, there have been key advances in the three main approaches to the visualization of volumetric data: isosurfacing, slicing and volume rendering, which together make up the field of volume visualization.In this survey paper we set the scene by describing the fundamental techniques for each of these approaches, using this to motivate the range of advances which have evolved over the past few years.In isosurfacing, we see how the original marching cubes algorithm has matured, with improvements in robustness, topological consistency, accuracy and performance. In the performance area, we look in detail at pre-processing steps which help identify data which contributes to the particular isosurface required. In slicing too, there are performance gains from identifying active cells quickly.In volume rendering, we describe the two main approaches of ray casting and projection. Both approaches have evolved technically over the past decade, and the holy grail of real-time volume rendering has arguably been reached.The aim of this review paper is to pull these developments together in a coherent review of recent advances in volume visualization.
Valence-Driven Connectivity Encoding for 3D Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Alliez, Pierre; Desbrun, Mathieu
In this paper, we propose a valence-driven, single-resolution encoding technique for lossless compression of triangle mesh connectivity. Building upon a valence-based approach pioneered by Touma and Gotsman22 , we design a new valence-driven conquest for arbitrary meshes that always guarantees smaller compression rates than the original method. Furthermore, we provide a novel theoretical entropy study of our technique, hinting the optimality of the valence-driven approach. Finally, we demonstrate the practical efficiency of this approach (in agreement with the theoretical prediction) on a series of test meshes, resulting in the lowest compression ratios published so far, for both irregular and regular meshes, small or large.
Real-Time Volume Deformations
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Westermann, Rudiger; Rezk-Salama, Christof
Real-time free-form deformation tools are primarily based on surface or particle representations to allow for interactive modification and fast rendering of complex models. The efficient handling of volumetric representations, however, is still a challenge and has not yet been addressed sufficiently. Volumetric models, on the other hand, form an important class of representation in many applications. In this paper we present a novel approach to the real-time deformation of scalar volume data sets taking advantage of hardware supported 3D texture mapping. In a prototype implementation a modeling environment has been designed that allows for interactive manipulation of arbitrary parts of volumetric objects. In this way, any desired shape can be modeled and used subsequently in various applications. The underlying algorithms have wide applicability and can be exploited effectively for volume morphing and medical data processing.
A Camera Engine for Computer Games: Managing the Trade-Off Between Constraint Satisfaction and Frame Coherence
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Halper, Nicolas; Helbing, Ralf; Strothotte, Thomas
Many computer games treat the user in the "1st person" and bind the camera to his or her view. More sophistication in a game can be achieved by enabling the camera to leave the users' viewpoint. This, however, requires new methods for automatic, dynamic camera control. In this paper we present methods and tools for such camera control. We emphasize guiding camera control by constraints; however, optimal constraint satisfaction tends to lead to the camera jumping around too much. Thus, we pay particular attention to a trade-off between constraint satisfaction and frame coherence. We present a new algorithm for dynamic consideration of the visibility of objects which are deemed to be important in a given game context.

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