Issue 3

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https://diglib.eg.org/handle/10.2312/101

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Real-Time Cloud Rendering
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Harris, Mark J.; Lastra, Anselmo
This paper presents a method for realistic real-time rendering of clouds suitable for flight simulation and games. It provides a cloud shading algorithm that approximates multiple forward scattering in a preprocess, and first order anisotropic scattering at runtime. Impostors are used to accelerate cloud rendering by exploiting frame-to-frame coherence in an interactive flight simulation. Impostors are shown to be particularly well suited to clouds, even in circumstances under which they cannot be applied to the rendering of polygonal geometry. The method allows hundreds of clouds and hundreds of thousands of particles to be rendered at high frame rates, and improves interaction with clouds by reducing artifacts introduced by direct particle rendering techniques.
Rendering Pearlescent Appearance Based On Paint-Composition Modelling
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Ershov, Sergey; Kolchin, Konstantin; Myszkowski, Karol
We describe a new approach to modelling pearlescent paints based on decomposing paint layers into stacks of imaginary thin sublayers. The sublayers are chosen so thin that multiple scattering can be considered across different sublayers, while it can be neglected within each of the sublayers. Based on this assumption, an efficient recursive procedure of assembling the layers is developed, which enables to compute the paint BRDF at interactive speeds. Since the proposed paint model connects fundamental optical properties of multi-layer pearlescent and metallic paints with their microscopic structure, interactive prediction of the paint appearance based on its composition becomes possible.
Walk-Through Illustrations: Frame-Coherent Pen-and-Ink Style in a Game Engine
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Freudenberg, Bert; Masuch, Maic; Strothotte, Thomas
In this paper we show how a game engine designed to generate photorealistic images can be extended to produce non-photorealistic and hybrid renditions. We introduce new hardware-based methods to accomplish pen-and-ink illustrations. The combination of the highly optimized processing of a game engine and the use of hardware for NPR algorithms yields real-time animation of pen-and-ink illustrations.The particular advance of this method is that it yields the first real-time, frame-coherent pen-and-ink animations which maintain both tone and texture.
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.
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
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.
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.
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.
PC-based Real-time Texture Painting on Real World Objects
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Iwakiri, Yuya; Kaneko, Toyohisa
The problem of texture mapping on real world objects has attracted attention11,8 recently. A work by Lensch et al.9 addressed the problem of locating a camera position in the celestial sphere and then mapping the acquired pictures on a real world object. The entire process took a half hour to one hour to map 10 to 15 pictures. In this paper, we propose a new innovative algorithm to speed up the texture mapping or painting process in real-time. We built a PC-based system using a commonly available video card with a geometry engine. Mapping of a picture required about 20 seconds. It is successful in giving an illusion to the operator to paint a colorless real world object with a color texture brush.
Streaming of Complex 3D Scenes for Remote Walkthroughs
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Teler, Eyal; Lischinski, Dani
We describe a new 3D scene streaming approach for remote walkthroughs. In a remote walkthrough, a user on a client machine interactively navigates through a scene that resides on a remote server. Our approach allows a user to walk through a remote 3D scene, without ever having to download the entire scene from the server. Our algorithm achieves this by selectively transmitting only small parts of the scene and lower quality representations of objects, based on the user's viewing parameters and the available connection bandwidth. An online optimization algorithm selects which object representations to send, based on the integral of a benefit measure along the predicted path of movement. The rendering quality at the client depends on the available bandwidth, but practical navigation of the scene is possible even when bandwidth is low.
Fast simulation and rendering techniques for fluid objects
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Kunimatsu, A.; Watanabe, Y.; Fujii, H.; Saito, T.; Hiwada, K.; Takahashi, T.; Ueki, H.
Movies with actions and light effects of fluid objects are aesthetically pleasing and interesting. Until now, the calculation costs of simulation and rendering of fluid objects have been very high. Using a modern PC system and appropriate methods, we achieved a time of 10-20 seconds per frame for this application. Our system uses a full Navier-Stokes equation solver with uniform Eulerian mesh, marching cube isosurface techniques, Catmull-Clark subdivision surface techniques, ray tracing techniques on each vertex and conventional polygon base rendering by HW accelerator. In this paper, we describe the components of our system and the reasons for choosing them. By measuring CPU times of each process for some movie scenes of fluid objects, we evaluate this system. We consider what factors are important for creating movies of fluid objects with short TAT.
Animation of Soap Bubble Dynamics, Cluster Formation and Collision
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Durikovic, Roman
What is happening when a soap bubble floats on the air? How do bubbles coalesce to form beautiful three-dimensional clusters? The physical-based model and animation described herein provide the answers. This paper deals with a complete computer simulation of soap bubbles from a dynamic perspective, which should prove to be of great interest to physicists and mathematicians. We discuss the dynamic formation of irregular bubble clusters and how to animate bubbles. The resulting model takes into account surface tension, film elasticity, and shape variations due to gravity and external wind forces.

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