Short Presentations

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An Accurate Illumination Model for Objects Coated with Multilayer Films
(Eurographics Association, 2000) Hirayama, H.; Kaneda, K.; Yamashita, H.; Monden, Y.
This paper proposes an accurate illumination model for rendering objects coated with multilayer films. Optical phenomenaof multilayer films are caused by reflection, refraction, interference, and absorption of light inside each layer of multiple films, and these physical phenomena are complicatedly related with each other. The proposed method calculates composite reflectance and transmittance of multilayer films, taking into account all the physical phenomena described above, and visualizes the optical phenomena caused by the multilayer films accurately. The illumination model proposed in the paper can handle both smooth surface and locally smooth rough surfaces. Several examples of objects coated with various kinds of films demonstrate the usefulness of the proposed method.
Adding a scalar value to 2D vector field visualization: the BLIC (Bumped LIC)
(Eurographics Association, 2000) Sanna, A.; Montrucchio, B.
Visualization of vector data produced from application areas such as computational fluid dynamics (CFD), environmental sciences, and material engineering is a challenging task. Texture-based methods reveal to be effective, versatile, and suitable for a large spectrum of applications since they allow to obtain high resolution output textures where direction, orientation, and magnitude of the flow can be displayed. In this paper we present a new method called BLIC (Bumped LIC), which allows both to characterize and visualize interesting structures in the flow and to map an additional scalar value in the output texture by bumps and depressions, leaving colors for further information mapping. Some examples show how the proposed method can enhance the quality of output textures with respect to the classical texture-based approaches.
ALOHA : Adaptive Level Of Detail for Human Animation Towards a new framework
(Eurographics Association, 2000) Giang, Thanh; Mooney, Robert; Peters, Christopher; Sullivan, Carol O.
The task of animating and rendering virtual humans in real-time is challenging. One must first establish a sense of realism through appearance, and then maintain this realism through correct and plausible motion, while continually satisfying the real-time constraint imposed. One technique that aids in achieving such a task is to take advantage of the viewer’s perception to compute less accurate models when loss of accuracy is unlikely to be noticed. Traditionally, these ‘level of detail’ techniques have been used primarily for geometric modelling. However, more recently, they have also been applied to animation. This paper seeks to amalgamate animation and geometric level of detail research in order to produce an integrated framework on which to build a totally scalable system for virtual human animation.
Automatic Fitting of Digitised Contours at Multiple Scales through Curvature Scale Space
(Eurographics Association, 2000) Mokhtarian, Farzin; Ung, Yoke Khim
The Curvature Scale Space (CSS) technique has been used in conjunction with Hermite curves for automatic fitting of digitised contours at multiple scales. CSS is a powerful contour shape descriptor which is expected to be in the MPEG-7 standard. A parametric representation of the input contour is convolved with Gaussian functions in order to obtain multi-scale descriptions of the contour. Curvature can be computed directly at each point of the smoothed contours. As a result, a set of curvature zero-crossing points can be recovered from each smoothed contour. Hermite curves were used since each Hermite curve is defined by two endpoints and the tangent vectors at those points. No points external to the input contour are required for Hermite curves. Hermite endpoints are defined as consecutive curvature zero-crossing points extracted at multiple scales using the CSS method. Hermite tangent vectors can also be determined using the CSS technique. The only data stored are the endpoints and the tangent vectors needed by the Hermite curves in order to arrive at an approximate reconstruction of the original contour. Approximation Error and Compression Ratio are computed at each scale. The graph of compression ratio as a function of approximation error is smoothed to remove noise and small fluctuations. The bending point of that function is then defined as the largest maximum of its second derivative. The bending point can be considered as the boundary between the mostly vertical and the mostly horizontal segments of the graph. It can be used for automatic selection of an optimal scale.
Combining finite element deformation with cutting for surgery simulations
(Eurographics Association, 2000) Nienhuys, Han-Wen; van der Stappen, A. Frank
Interactive surgery simulations have conflicting requirements of speed and accuracy. In this paper we show how to combine a relatively accurate deformation model—the Finite Element (FE) method—and interactive cutting without requiring expensive matrix updates or precomputation. Our approach uses an iterative algorithm for an interactive linear FE deformation simulation. The iterative process requires no global precomputation, so runtime changes of the mesh, i.e. cuts, can be simulated efficiently. Cuts are performed along faces of the mesh; this prevents growth of the mesh. We present a provably correct method for changing the mesh topology, and a satisfactory heuristic for determining along which faces to perform cuts. The incision surface will be jagged; this problem is a subject of current research.
Component Based Human Animation Architecture
(Eurographics Association, 2000) Jing, Huang; Fi, Chin Kah; Prakash, Edmond C.
This paper describes a method to predict the free reach movement of different components of the human body. Since the human body is composed of the following components: arms, legs, torso, head & neck, and each of these components has similar features, the same geometric inverse kinematics algorithm can be used in different parts of the body to realize free reach movement task. The main advantage of the proposed method is that it avoids matrix inverse calculation, which is very time consuming. And by using this method, the task can be mostly simplified.
Discrete Analysis for Antialiased Lines
(Eurographics Association, 2000) Boyer, V.; Bourdin, J. J.
This paper presents a new fast and smooth antialiasing technique. Drawing straight line is the graphic tool’s main primitive. Previous antialiasing techniques improve smoothness but slow down computation.
Efficient Evaluation of the Field Functions of Soft Objects Using Interval Tree
(Eurographics Association, 2000) Min, Kyung-Ha; Lee, In-Kwon; Park, Chan-Mo
We present an algorithm to evaluate the field function of a soft object efficiently. Instead of using a global field function that is defined by the sum of all local field functions, we consider only the set of local field functions that affects a point at which we want to evaluate the field function. To find the affecting local field functions efficiently, we exploit a data structure called interval tree based on the bounding volume of the component corresponding to the primitives (skeletons) of a soft object. The bounding volume of each component is generated with respect to the radius of a local field function of the component, threshold value, and the relations between the components and other neighboring components. The proposed scheme of field function evaluation can be used in many applications for soft objects such as modeling and rendering, especially in interactive modeling process.
A Facial Repertoire for Animation
(Eurographics Association, 2000) ten Hagen, Paul J. W.
Character design and facial animation of characters is among the most tedious parts of creation of animations. In contrast to body animations, performer data have not been successfully used for faces. The CharToon system provides a facility to create a powerful repertoire of reusable components at several levels for the construction of faces and face animations. The knowledge embedded in the system allows for reuse of facial architectures, motion methods and animation definitions for newly constructed or adapted faces. These methods cover among other things, expressions, speech animations and changing view points. This paper describes the organization of the repertoire, how it can be built and extended, and gives examples of its usage. The repertoire offers a perspective of how a higher level system of animation behaviors can be created on top. The presentation will show many animated examples of the contents and working of the repertoire.
An Image Processing Approach to Detection of Ridges and Ravines on Polygonal Surfaces
(Eurographics Association, 2000) Belyaev, Alexander; Ohtake, Yutaka
Surface creases, ridges and ravines, provide us with important information about the shapes of 3D objects and can be intuitively defined as curves on a surface along which the surface bends sharply. Exploring similarity between edges of 2D grey-scale images and curvature extrema of 3D shapes and generalizing a basic edge detection approach to triangular meshes, we develop a method for detection of ridges and ravines on a smooth surface approximated by a triangular mesh. We also sketch three potential applications of our approach: mesh fairness evaluation, improving mesh decimation techniques, and simulating artistic pen-and-ink drawings of 3D objects.
Imaging Geometry for Concentric Mosaics
(Eurographics Association, 2000) Watson, G. C.; Vaughan, N.; Wright, M. W.
Image-based models of environments can be captured with the use of a rotating video camera. In this paper we consider the nature of the display to develop a simple quantitative measure of the quality of ray sampling which we use to compare different imaging geometries for concentric mosaics. We propose a novel arrangement for the rotating camera, which we show to produce a better sampling of rays for viewing on displays where the display surface is fixed in space and the view position is varied. We show how this improved capture geometry can be employed in a head tracked display to produce a display that resembles a virtual window through which a captured environment can be viewed.
Interactive Modelling of Convolution Surfaces with an Extendable User Interface
(Eurographics Association, 2000) Goto, Yuichiro; Pasko, Alexander
Convolution surfaces enable the user to model complex free-form shapes. Due to analytical solutions for some kernel functions and skeletal elements, it is possible to model convolution surfaces interactively. An extendable user interface allows the user to design models using different types of convolution surfaces. New primitives can be easily bound to the modeller using the proposed binding technique. Models generated in HyperFun language can be exchanged between modelling tools on several platforms.
Interactive Vegetation Rendering with Slicing and Blending
(Eurographics Association, 2000) Jakulin, Aleks
Detailed and interactive 3D rendering of vegetation is one of the challenges of traditional polygon-oriented computer graphics, due to large geometric complexity even of simple plants. In this paper we introduce a simplified image-based rendering approach based solely on alpha-blended textured polygons. The simplification is based on the limitations of human perception of complex geometry. Our approach renders dozens of detailed trees in real-time with off-the-shelf hardware, while providing significantly improved image quality over existing real-time techniques. The method is based on using ordinary mesh-based rendering for the solid parts of a tree, its trunk and limbs. The sparse parts of a tree, its twigs and leaves, are instead represented with a set of slices, an imagebased representation. A slice is a planar layer, represented with an ordinary alpha or color-keyed texture; a set of parallel slices is a slicing. Rendering from an arbitrary viewpoint in a 360 degree circle around the center of a tree is achieved by blending between the nearest two slicings. In our implementation, only 6 slicings with 5 slices each are sufficient to visualize a tree for a moving or stationary observer with the perceptually similar quality as the original model.
MeshSweeper: From Closest Point to Hausdorff Distance Between Meshes
(Eurographics Association, 2000) Gueziec, A.
We introduce a new algorithm for computing the distance from a point to an arbitrary polygonal mesh. Our algorithm uses a multi-resolution hierarchy of bounding volumes generated by geometric simplification. Our algorithm is dynamic, exploiting coherence between subsequent queries using a priority process (without caching the closest point), and achieving constant time queries in some cases. The method also applies to a mesh that deforms nonrigidly. Achieving from about 500 to several thousand queries per second for a complex polygonal shape on a PC, our method has applications both for interactive and photo-realistic graphics. In particular, we study in this paper the application to computing the Hausdorff distance between two polygonal shapes, with an arbitrary precision.
A Novel Image-Based Rendering System With A Longitudinally Aligned Camera Array
(Eurographics Association, 2000) Li, Jiang; Zhou, Kun; Wang, Yong; Shum, Heung-Yeung
A Procedural Approach to Solving Constraints of Articulated Bodies
(Eurographics Association, 2000) Lee, J. Won; Baek, Nakhoon; Kim, Dongho; Hahn, James K.
Realistic motions of articulated bodies are usually generated by using physically-based animation methods such as constrained dynamics. However, these methods involve heavy computations and complicated numerical methods. We present an alternative way of solving constraints of articulated bodies. Our objective is not physically correct motions but visually plausible animation. In our method, each object of the constrained body is first moved according to their physical parameters and external forces, without considering any constraints. Then the objects are translated and rotated to satisfy the given constraints. Instead of strict simulation of physical laws, we suggest procedural formulations for solving constraints. This formulation has the power of generating visually plausible motions as presented in our example animation sequences. Since our method is free from complex numerical methods, it is fast enough to be used in real-time applications such as virtual reality, computer games and real-time simulations. Numerical stability is another merit of our method. This procedural approach can be an alternative to strict physically-based animation methods.
Robust Polygons Clipping to Model Complex Objects
(Eurographics Association, 2000) Segura, Rafael J.; Feito, Francisco R.
One of the most important problems to solve in Solids Modelling is computing the boolean operations for solids (union, intersection and difference). In order to implement these three operations an algorithm to compute the intersection between faces is needed (polygons clipping). In the case of solids with planar faces there are many solutions, although most of them are valid only when the faces are convex. In this paper we present an algorithm to determine the intersection between polygons of any nature (concave or convex, manifol or non-manifold, with or without holes, etc.) based on the idea of simplicial coverings proposed by Feito 11. One of the advantages of this approach is the robustness of algorithms, since decompositions or complex operations that may alter the results obtained are not avoided. A very interesting application of this algorithm is the modelling of complex solids with this type of polygons as faces.
Scene understanding techniques using a virtual camera
(Eurographics Association, 2000) Barral, Pierre; Dorme, Guillaume; Plemenos, Dimitri
An automatic computation of the path for a camera around a three-dimensional scene is discussed. Previous work on automatic virtual camera, based on a heuristic evaluation function, is reviewed, and new methods to improve this work are presented. Theses methods consist of additional criteria in the evaluation function as well as new ways to determine the camera’s path. Ideas to animate automatically a camera inside a scene are presented, and in the end, results are discussed.
Selecting Effective Occluders for Visibility Culling
(Eurographics Association, 2000) Koltun, Vladlen; Cohen-Or, Daniel
This paper deals with the problem of identifying effective occluders for visibility culling. The solid-angle metric is commonly used for measuring the potential significance of occluders from a single viewpoint. In this paper, we show that it does not extend properly to from-region occlusion calculations. We propose to measure the effectiveness of an occluder by means of the size of its umbra. We first present an analytic object-space algorithm to accurately compute this measure. We then define an approximation which reflects the effectiveness of an occluder, and introduce a hardware-assisted algorithm to rapidly compute it.
Spreading of the cultural heritage by means of multi-configurable, low cost virtual reality techniques
(Eurographics Association, 2000) Flores, J.; Arias, J.; Saavedra, S.; Varela, E.; Ferro, J. M.; Taboada, J.
In the last few years, computer graphics techniques have been applied to preserve and promote the cultural heritage. In this first steps the bottleneck of these applications developed was the price of the hardware that limited the use of these tools to museums or exhibition rooms. Nevertheless, the fast increase of graphic capacity of the computers allows the development of high -quality complex applications which can be visualized in personal computers. This is completed by multidisciplinary research groups that focus their efforts on the most relevant aspect of the learning and presence sense in virtual environments. In this paper, an application of V.R. techniques to the promotion of heritage patrimony bases, in a PC platform, is presented. Focus has been put into high screen quality, multiple screen, multi-user, stereoscopic image, 3D sound and multisensorial environments as well as the high transportability, scalability and low price aiming at a quite widespread use of this hardware. The virtual reality application developed shows the old part of Santiago de Compostela, European City of Culture for the year 2000. The model of t he city is complex enough to prove that it is possible to use PC´s as visualization engine, over high quality and complex models.

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