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GI Tables of Contents: 888990919293949596979899000102030405060708

Proceedings of the 1998 Conference on Graphics Interface

Fullname:Proceedings of the 1998 Conference on Graphics Interface
Editors:Wayne A. Davis; Kellogg S. Booth; Alain Fournier
Location:Vancouver, B.C., Canada
Dates:1998-Jun-18 to 1998-Jun-20
Publisher:Canadian Information Processing Society
Standard No:ISBN 0-9695338-7-X; 1-55860-550-9; hcibib: GI98
Links:Conference Series Home Page | Online Proceedings
  1. Rendering
  2. Meshing Techniques
  3. Invited Speaker
  4. Modeling
  5. Invited Speaker
  6. Volume Visualization
  7. Animation
  8. Invited Speaker
  9. Human-Computer Interaction
  10. Invited Speaker
  11. Image-based Techiuques
  12. Image-based Techniques


Visibility Streaming for Network-based Walkthroughs BIBAFull-Text 1-7
  Daniel Cohen-Or; Eyal Zadicario
In network-based walkthroughs the server transmits online only the primitives which are potentially visible from the client's current viewpoint (visibility streaming). To reduce the bandwidth requirements it is necessary to minimize the set of view-dependent potentially visible primitives using occlusion culling techniques. However, even a slight change in the viewpoint might require the computation and transmission of many new primitives and thus latency is inevitable. In this paper we present an algorithm for determining a conservative superset of an epsilon-neighborhood of a given viewpoint. Having such an epsilon-superset, the client is free to render the model independently of the server as long as he moves within that epsilon-neighborhood.
Ray-Tracing Procedural Displacement Shaders BIBAGZ 8-16
  Wolfgang Heidrich; Hans-Peter Seidel
Displacement maps and procedural displacement shaders are a widely used approach of specifying geometric detail and increasing the visual complexity of a scene. While it is relatively straightforward to handle displacement shaders in pipeline based rendering systems such as the Reyes-architecture, it is much harder to efficiently integrate displacement-mapped surfaces in ray-tracers. Many commercial ray-tracers tessellate the surface into a multitude of small triangles. This introduces a series of problems such as excessive memory consumption and possibly undetected surface detail. In this paper we describe a novel way of ray-tracing procedural displacement shaders directly, that is, without introducing intermediate geometry. Affine arithmetic is used to compute bounding boxes for the shader over any range in the parameter domain. The method is comparable to the direct ray-tracing of Bezier surfaces and implicit surfaces using Bezier clipping and interval methods, respectively.
Lighting Networks -- A New Approach for Designing Lighting Algorithms BIBAGZ 17-25
  Philipp Slusallek; Marc Stamminger; Hans-Peter Seidel
In the past, new global illumination algorithms have usually been designed as a single module that was responsible for the simulation of all aspects of illumination in a scene. A recently developed alternative is the design of small and specialized algorithms (lighting operators) together with an infrastructure for creating more complex algorithms by connecting these building blocks - the Lighting Network.
   In this paper, we discuss the benefits of the Lighting Network approach for designing new and improved global illumination algorithms. Lighting Networks not only provide a flexible infrastructure for new algorithms, they also support a better theoretic understanding of the lighting simulation process. We show that a small number of global light propagation operators already provides the basis for creating many of todays illumination algorithms. Their illumination results are converted into more suitable representations by purely local conversion operators that are specific to an illumination algorithm. Varying the composition of these operators and introducing new elements allows us to create and explore the benefits of new simulation algorithms.
   We demonstrate the potential of Lighting Networks with several examples, implementing a diverse set of algorithms, such as density estimation, irradiance gradients, and a composite lighting simulation.

Meshing Techniques

Triangle Mesh Compression BIBAGZ 26-34
  Costa Touma; Craig Gotsman
A novel algorithm for the encoding of orientable manifold triangle mesh geometry is presented. Mesh connectivity is encoded in a lossless manner. Vertex coordinate data is uniformly quantized and then losslessly encoded. The compression ratios achieved by the algorithm are shown to be significantly better than those of currently available algorithms, for both connectivity and coordinate data. Use of our algorithm may lead to significant reduction of bandwidth required for the transmission of VRML files over the Internet.
An Improved Parametric Side-Vertex Triangle Mesh Interpolant BIBAZ 35-42
  Stephen Mann
There are many schemes for fitting triangular surface patches to a triangular net of data. In general, local schemes produce surfaces with poor surface quality. Although variational techniques construct surfaces of higher quality, such techniques tend to be computationally expensive. In this paper, I will present modifications to Nielson's side-vertex method that improve its surface quality without resorting to variational techniques.
A General Framework for Mesh Decimation BIBAGZ 43-50
  Leif Kobbelt; Swen Campagna; Hans-Peter Seidel
The decimation of highly detailed meshes has emerged as an important issue in many computer graphics related fields. A whole library of different algorithms has been proposed in the literature. By carefully investigating such algorithms, we can derive a generic structure for mesh reduction schemes which is analogous to a class of greedy-algorithms for heuristic optimization. Particular instances of this algorithmic template allow to adapt to specific target applications. We present a new mesh reduction algorithm which clearly reflects this meta scheme and efficiently generates decimated high quality meshes while observing global error bounds.

Invited Speaker

The α-γ-δ's of Digital Media Convergence BIBAPS 51-56
  Alvy Ray Smith
There is no theoretical roadblock obstructing the integration of different media types into a single digital medium - after all, bits are bits - but there are several real problems hindering the so-called digital convergence. The alpha problem is that between premultiplied and non-premultiplied alpha. The gamma problem concerns the nonlinearity that many of today's applications insist on burning into their image data. The delta problem is about the integration of the discrete and the continuous - eg, samples (pixels) and geometry. The subtleties of these are explored - eg, square pixels" and non-rectangular images - and a current example of how wrong things can get - the US digital television transmission formats battle - is elaborated."


Multiresolution Surface Reconstruction for Hierarchical B-splines BIBAGZ 57-64
  David Forsey; David Wong
This paper presents a method for automatically generating a hierarchical B-spline surface from an initial set of control points. Given an existing mesh of control points, a mesh with half the resolution, is constructed by simultaneously approximating the finer mesh while minimizing a smoothness constraint using weighted least squares. Curvature measures of are used to identify features that need only be represented in the finer mesh. The resulting hierarchical surface accurately and economically reproduces the original mesh, is free from excessive undulations in the intermediate levels and produces a multiresolution representation suitable for animation and interactive modelling.
On Approximating Rough Curves with Fractal Functions BIBAGZGIF 65-72
  Wayne O. Cochran; John C. Hart; Patrick J. Flynn
Fractal functions are explored as a representation for rough data in computer graphics. Two new techniques for using fractal interpolation functions to approximate rough functions and curves are introduced. The first is based on a Hough transform of fractal function transformation parameters. The second is based on previous techniques in fractal image compression. These techniques are then demonstrated on the task of recovering the parameters of a fractal function, approximating a rough function and approximating the boundary of a leaf.
Software Tools for Craniofacial Growth and Reconstruction BIBAGZ 73-81
  Katrina Archer; Kevin Coughlan; David Forsey; Sonja Struben
Forensic artists use tissue thicknesses at well known landmarks on the craniofacial skeleton to generate a potential likeness of an individual from a skull. This is a very subjective and time consuming process. We present two prototype software packages: one for simulating the growth of a craniofacial skeleton either forwards or backwards in time, and the other for generating a facial reconstruction over a skeleton. The craniofacial growth model uses three-dimensional data from specific landmarks through time to drive the growth process. Tissue depth markers on the craniofacial model determine the interpolated shape of the facial reconstruction and can be altered to cover the range of potential likenesses. Examples of a facial reconstruction and a grown craniofacial skeleton are shown.
Clonal Mosaic Model for the Synthesis of Mammalian Coat Patterns BIBAGZ 82-91
  Marcelo Walter; Alain Fournier; Mark Reimers
We introduce the Clonal Mosaic model for the synthesis of mammalian coat patterns, present its implementation for modeling and display purposes, and give a few examples of generated patterns. The model is based on cell division and cell-to-cell interactions, and it can generate repeating spotted and striped patterns occurring in several species of mammals, especially the big cats and giraffes. From a biological perspective, the model has a strong appeal in light of recent experimental evidence on pigment cells and other pigment related mechanisms; from a computer graphics perspective, the model can not only deliver many patterns which are visually similar to real patterns and can be used as textures, but it is also amenable to simulation on arbitrary surfaces.

Invited Speaker

Perception and Data Visualization: The Foundations of Experimental Semiotics BIBAFull-Text 92-98
  Colin Ware
Data Visualization is a new discipline involving the application of computer graphics to the understanding of information. It is successful because it can take advantage of the remarkable pattern finding capability of the human visual system. Visualization techniques are applied in medicine, software engineering, stock market analysis and many areas of science. But is it a science or a design discipline? If it is a science, how should research be conducted? In this paper it is argued that visualization can be productively regarded as an area of applied perception research, building on new advances in our understanding of how people see. The intellectual basis for such a discipline is outlined and illustrated with three example relating to color, object perception and stereoscopic space perception respectively.

Volume Visualization

Interactive Volume Cutting BIBAGZ 99-106
  Kevin Chun-Ho Wong; Yu-Hang Siu Siu; Pheng-Ann Heng; Hanqiu Sun
In 2D, Intelligent Scissors is an efficient interactive tool for image segmentation. By interactive use of a dynamic-programming graph-searching algorithm, a region of interest in the image can be accurately obtained. In this paper, we introduce the use of Intelligent Scissors for contour detection on a volumetric data surface. It is fast enough to be used in an interactive virtual environment, in which the user can intuitively select the contours in volumetric data in an accurate and robust manner. Moreover, we extend our work to the volume data manipulation, cutting off the interesting part of the volume by providing a contour on its surface. The cutting surface is computed by a fast dynamic programming algorithm. By using this tool, many new volumetric data models can be created from an existing one in an effective way.
Wavelet-Based 3D Compression Scheme for Very Large Volume Data BIBAZ 107-116
  Insung Ihm; Sanghun Park
Visualizing very large volume data has been recognized as a task requiring great effort in a variety of science and engineering fields. In particular, such data usually places considerable demands on run-time memory space. This paper describes an effective 3D compression scheme for very large volume data that exploits the power of wavelet theory. In designing our compression method, we have compromised between two important factors: high compression ratio and fast run-time random access. Our experimental results on the Visual Human data sets show that our method achieves fairly good compression ratios. In addition, it minimizes the overhead caused during run-time reconstruction of voxel values. This 3D compression scheme will be useful in developing many interactive visualization systems for huge volume data, and will make visualization technology accessible to a much wider range of users, as it can be based on personal computers or low-end workstations with limited memory.
A Graph Based Interface for Representing Volume Visualization Results BIBAGZ 117-124
  James Patten; Kwan-Liu Ma
This paper discusses a graph based user interface for representing the results of the volume visualization process. As images are rendered, they are connected to other images in a graph based on their rendering parameters. The user can take advantage of the information in this graph to understand how certain rendering parameter changes affect a dataset, making the visualization process more efficient. Because the graph contains more information than is contained in an unstructured history of images, the image graph is also helpful for collaborative visualization and animation.


Animating Sand, Mud, and Snow BIBAGZHTML 125-132
  Robert Sumner; James O'Brien; Jessica Hodgins
Computer animations often lack the subtle environmental changes that should occur due to the actions of the characters. Squealing car tires usually leave no skid marks, airplanes rarely leave jet trails in the sky, and most runners leave no footprints. In this paper, we describe a simulation model of ground surfaces that can be deformed by the impact of rigid body models of animated characters. To demonstrate the algorithms, we show footprints made by a runner in sand, mud, and snow as well as bicycle tire tracks, a bicycle crash, and a falling runner. The shapes of the footprints in the three surfaces are quite different, but the effects were controlled through only five essentially independent parameters. To assess the realism of the resulting motion, we compare the simulated footprints to video footage of human footprints in sand.
Simulating the Flow of Liquid Droplets BIBAGZ 133-142
  Patrick Fournier; Arash Habibi; Pierre Poulin
The ever-changing nature of liquids makes them very difficult to model and animate. This paper addresses the simulation of one aspect of liquids, i.e. droplets running down surfaces. We present a model oriented towards a visually-satisfying simulation and efficiency. The efficiency results from the separation between the shape and the motion of a droplet. The motion accounts for all changes encountered along the path followed over a mesh of triangles. It is affected by various properties modeled as friction, adhesion, roughness, and collisions between droplets. Streaks are also added along the paths. We characterize the shape of a droplet by a small set of properties, such as volume conservation, surface tension, etc. We model them as constraints to satisfy. The shape model is mainly based on mass-springs. It is simple and efficient, and it guarantees that whatever the values of the unconstrained parameters, all produced shapes satisfy the characteristic properties, and thus, can represent different types of droplets. Rendered animations of various liquids illustrate the resulting simulation.
Active Implicit Surface for Animation BIBAGZ 143-150
  Mathieu Desbrun; Marie-Paule Cani-Gascuel
This paper introduces a new model of deformable surfaces designed for animation, which we call active implicit surfaces. The underlying idea is to animate a potential field defined by discrete values stored in a grid, rather than directly animating a surface. This surface, defined as an iso-potential of the field, has the ability to follow a given object using a snake-like strategy. Surface tension and other characteristics such as constant surface area or constant volume may be added to this model. The implicit formulation allows the surface to easily experience topology changes during simulation. We present an optimized implementation: computations are restricted to a close neighborhood around the surface. Applications range from the coating of deformable materials simulated by particle systems (the surface hides the granularity of the underlying model) to the generation of metamorphosis between shapes that may not have the same topology.
Footprint-based Quadruped Motion Synthesis BIBAGZ 151-160
  Nick Torkos; Michiel van de Panne
This paper applies trajectory-based optimization techniques to the synthesis of quadruped motions. The animator specifies hard constraints, consisting of footprint locations and their timings, and soft constraints that encode both physically-plausible behavior and the notion of comfortable positions. By dealing first and foremost with the spline trajectories representing the gross motion of the quadruped, the resulting optimization problem can be solved efficiently and robustly. Results include walking, jumping, and galloping quadrupeds.

Invited Speaker

Cognitive Modeling in Human-Computer Interaction BIBAFull-Text 161-167
  Bonnie John
The field of Human-Computer Interaction (HCI), whose goal is to make computers support human activity in much more satisfying ways than they currently do, has three main uses for cognitive modeling. A cognitive model can substitute for a human user to predict how users will perform on a system before it is implemented or even prototyped. A system can generate a cognitive model of the user currently interacting with the system in order to modify the interaction to better serve that user. Finally, cognitive models can substitute directly for people so groups of individuals can be simulated in situations that require many participants, e.g., for training or entertainment. This paper presents some instances of such models and the implications for GI design.

Human-Computer Interaction

A Probabilistic Character Layout Strategy for Mobile Text Entry BIBAPS 168-176
  Tom Bellman; I. Scott MacKenzie
We present a text entry strategy designed for small, input-limited devices in mobile situations. In an existing text entry interaction style, arrow keys move a cursor around the character set, displayed on a 3 or 4 line liquid crystal display, and a select key outputs the highlighted character to the display. The Fluctuating Optimal Character Layout (FOCL) strategy aims to improve entry rates with this interaction technique. After each character c entered, the layout is rearranged so that the most likely next characters are closer to the cursor. Each new layout is optimal with respect to c, given digram (letter-pair) probabilities in common English. FOCL significantly reduces kspc-the average number of keystrokes per character-, a non-empirical measure that partly accounts for text entry speed. However, it also requires the user to locate each character in an unfamiliar layout, thus adding visual search time to the task. In a longitudinal experiment comparing the fluctuating layout approach to a fixed QWERTY layout, we found no significant difference in entry speeds. We discuss our design rationale and various modifications to the design that may yield a performance improvement.
On the Use of Perceptual Cues and Data Mining for Effective Visualization of Scientific Datasets BIBAGZ 177-184
  Christopher G. Healey
Scientific datasets are often difficult to analyse or visualize, due to their large size and high dimensionality. We propose a two-step approach to address this problem. We begin by using data mining algorithms to identify areas of interest within the dataset. This allows us to reduce a dataset's size and dimensionality, and to estimate missing values or correct erroneous entries. We display the results of the data mining step using visualization techniques based on perceptual cues. Our visualization tools are designed to exploit the power of the low-level human visual system. The result is a set of displays that allow users to perform rapid and accurate exploratory data analysis. In order to demonstrate our techniques, we visualized an environmental dataset being used to model salmon growth and migration patterns. Data mining was used to identify significant attributes and to provide accurate estimates of plankton density. We used colour and texture to visualize the significant attributes and estimated plankton densities for each month for the years 1956 to 1964. Experiments run in our laboratory showed that the colours and textures we chose support rapid and accurate element identification, boundary detection, region tracking, and estimation. The result is a visualization tool that allows users to quickly locate specific plankton densities and the boundaries they form. Users can compare plankton densities to other environmental conditions like sea surface temperature and current strength. Finally, users can track changes in any of the dataset's attributes on a monthly or yearly basis.
Pain and Fatigue in Desktop VR: Initial Results BIBAGZ 185-192
  Christopher D. Shaw
This paper describes a comprehensive experimental evaluation of a two-handed free-form surface editor called THRED, which uses a pair of Polhemus 3D trackers with added buttons in a complementary two-handed style. On top of the underlying free-form surface editor application was built two other user interfaces that provide reasonable competition for the two-handed style. The second interface uses one button-enhanced 3D tracker in the dominant hand, with the non-dominant hand selecting commands from the keyboard. The third style is a mouse-based interface that is a simplified clone of the Alias modeler. This user study evaluates these interfaces in terms of pain and fatigue. The results show that experienced minimal pain and fatigue with THRED, an a par with that experienced in the mouse-based interface, but there was statistically significant fatigue in the use of the One-Handed interface. The pain and fatigue surveys clearly indicate that THRED and the Mouse-Based interface yield low discomfort, which contradicts the established wisdom that bat-based interfaces are likely to be painful or fatiguing to use.
Multi-Granularity Noise for Curvilinear Grid LIC BIBAGZ 193-200
  Xiaoyang Mao; Lichan Hong; Arie Kaufman; Noboru Fujita; Makoto Kikukawa
A major problem of the existing curvilinear grid Line Integral Convolution (LIC) algorithm is that the resulting LIC textures may be distorted after being mapped onto the parametric surfaces, since a curvilinear grid usually consists of cells of different sizes. This paper proposes a way for solving the problem through using multi-granularity noise as the input image for LIC. A stochastic sampling technique called Poisson ellipse sampling is employed to resample the computational space of a curvilinear grid into a set of randomly distributed points. From this set of points, we are able to reconstruct a noise image with its local noise granularity being adapted to the physical space cell size of the grid.

Invited Speaker

Layered Deformable Models with Implicit Surfaces BIBAGZ 201-208
  Marie-Paule Cani-Gascuel
Several challenging problems in the animation of deformable objects can be solved by combining existing models with implicit surfaces. The latter are used as an extra layer which coats any kind of structure that moves and deforms over time. Implicit surfaces detect collisions, model local deformations, and transmit response forces to the inner structures. They also control the variations of the object's volume. We present several applications from the animation of organic shapes to the simulation of soft inelastic substances that can separate into smaller pieces or fuse into larger ones.

Image-based Techiuques

Edge Enhancement Issues in Half-Toning BIBAGZ 209-216
  John. W. Buchanan; Lisa M. Streit; Oleg Veryovka
A post-processing edge enhancement technique that is applicable to all half-toning algorithms is proposed. Two types of edge pixels, dark and light edge pixels, are identified. Edges in an image are highlighted by setting the dark/light edge pixels to black/white. The method is tested on a laser printed and the evaluation technique is restricted to clustered half-toning methods.

Image-based Techniques

Globally Optimal Image Mosaics BIBAGZ 217-222
  Kirk L. Duffin; William A. Barrett
In this paper we examine the simultaneous solution of a set of image transformations with the goal of creating a globally optimal image mosaic. We examine an alternative parameterization of the full projective matrix transformation that leads to elimination of independent skew and aspect ratio parameters for each image. We also create a scale-free distance error metric which prevents the tendency of simultaneously solved systems to tend toward the zero solution.
Virtual navigation of complex scenes using clusters of cylindrical panoramic images BIBAGZ 223-232
  Sing Bing Kang; Pavan Kumar Desikan
The traditional approach of generating novel virtual views of an object or a scene is to render the appropriate 3-D model. The alternative is to render directly from the original images; this approach, which is based on pixel interpolation or reprojection, is called image-based rendering. In this paper, we describe a technique that enables virtual navigation within a complex environment using an image-based rendering technique. In particular, we make use of clusters of cylindrical panoramic images. Each cluster of panoramic images allows the user to smoothly navigate within a particular area, say within a single room. Having a collection of such interconnected clusters would enable the user to seamlessly navigate within a complex environment, such as an entire floor of a building, with each cluster representing a room. To achieve this goal, we examine a few techniques for image-based rendering using a cluster of cylindrical panoramic images to synthesize views from virtual viewpoints. We also describe our method for enabling smooth transition between clusters.
Rendering Generalized Cylinders with Paintstrokes BIBAGZ 233-242
  Ivan Neulander; Michiel van de Panne
We present an efficient technique for dynamically tessellating generalized cylinders. We make direct use of the generalized cylinder's screen-space projection in order to minimize the number of polygons required to construct its image. Used in conjunction with our A-Buffer polygon renderer, our technique strikes a good balance between speed and image quality when used at small to medium scales, generally surpassing other methods for rendering generalized cylinders.