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GI Tables of Contents: 899091929394959697989900010203040506070809

Proceedings of the 1999 Conference on Graphics Interface

Fullname:Proceedings of the 1999 Conference on Graphics Interface
Editors:Scott I. MacKenzie; James Stewart
Location:Kingston, Ontario, Canada
Dates:1999-Jun-02 to 1999-Jun-04
Publisher:Canadian Information Processing Society
Standard No:ISBN 0-9695338-8-8; hcibib: GI99
Links:Conference Series Home Page | Online Proceedings
  1. Physical Simulation
  2. Interaction Design
  3. Invited Paper
  4. Invited Talk
  5. Global Illumination
  6. Interaction Techniques
  7. Image-based Techniques
  8. Invited Paper
  9. Modeling
  10. Non-photorealistic Rendering
  11. Invited Paper
  12. Physical Animations

Physical Simulation

Interactive Animation of Structured Deformable Objects BIBAPDFGI Online Paper 1-8
  Mathieu Desbrun; Peter Schröder; Alan Barr
In this paper, we propose a stable and efficient algorithm for animating mass-spring systems. An integration scheme derived from implicit integration allows us to obtain interactive realistic animation of any mass-spring network. We alleviate the need to solve a linear system through the use of a predictor-corrector approach: We first compute a rapid approximation of the implicit integration, then we correct this estimate in a post-step process to preserve momentum. Combined with an inverse dynamics process to implement collisions and other constraints, this method provides a simple, stable and tunable model for deformable objects suitable for virtual reality. An implementation in a VR environment demonstrates this approach.
Geometric Awareness for Interactive Object Manipulation BIBAGZGI Online Paper 9-17
  Min-Hyung Choi; James Cremer
This paper describes formulation and management of constraints that, combined with a nonlinear optimization algorithm, enable interactive geometrically aware manipulation of articulated objects. Going beyond purely kinematic or dynamic approaches, our solution method directly employs geometric constraints to ensure non-interpenetration during object manipulation. We present the formulation of the inequality constraints used to ensure nonpenetration, describe how to manage the set of active inequality constraints as objects move, and show how these results are combined with a nonlinear optimization algorithm to achieve interactive geometrically aware object manipulation. Our optimization algorithm handles equality and inequality constraints and does not restrict object topology. It is an efficient iterative algorithm, quadratically convergent, with each iteration bounded by O(nnz(L)), where nnz(L) is the number of non-zeros in L, a Cholesky factor of a sparse matrix.

Interaction Design

A User Centered Task Analysis of Interface Requirements for MRI Viewing BIBAPDFGI Online Paper 18-26
  Johanna E. van der Heyden; Kori M. Inkpen; M. Stella Atkins; M. Sheelagh T. Carpendale
This paper explores the viability of Magnetic Resonance Image (MRI) presentation on a computer screen. This includes investigating the feasibility of presenting the information on a desktop computer in a manner that facilitates MRI analysis and medical diagnosis. Two key objectives are identified: 1) understand the MRI analysis task and determine specific presentation issues and requirements through observations of radiologists; and 2) obtain user feedback on design alternatives. Observations of the MRI analysis task in the traditional light screen environment reveal three requirement categories: user control of films, easy navigation of images and simultaneous availability of detail and context. Design proposals, based on these requirements, include the use of windowing techniques, workspace and overview design, and detail-in-context concepts, as well as the adoption of metaphor and structure from the traditional light screen environment. The results from the preliminary user feedback support the value and feasibility of providing MRI analysis on a computer screen.
A Desktop Design for Synchronous Collaboration BIBAGZGI Online Paper 27-35
  Bogdan Dorohonceanu; Ivan Marsic
This paper presents a novel graphics user interface for desktop management of a synchronous groupware client. The interface is part of the Rutgers University DISCIPLE framework that enables sharing of applications. The interface presents an individual view of a collaboration space that contains collaboration artifacts, collaborators, their groupings and relationships. The conceptual model of the collaboration process is described since it strongly influences the design of the user interface. We establish the requirements, describe the components of the user interface and then discuss alternative approaches. JavaBeans applications are shared by being imported into the shared workspace, but additionally, importing Beans allows user tailoring of the interface and thus supports end-user programming. Interface customization is demonstrated with multimodal human/machine interfaces and the collaboration components (such as group awareness widgets, concurrency controllers, etc.). Another activity supported is multi-user visual programming using the JavaBeans technology. Users at geographically separate locations can collaboratively build complex applications using pre-existing components. This interface has been implemented and tested on a variety of Java applications.

Invited Paper

Computer Games, Education And Interfaces: The E-GEMS Project BIBAPDFGI Online Paper 36-39
  Maria M. Klawe
For the past six years the E-GEMS project has studied the design and use of computer games and activities for mathematics education in grades 4 to 8. Our research has involved researchers in education and computer science, professional game developers, teachers and thousands of children. The outcomes of this collaboration include a wide range of research studies as well as innovative prototype games and a successful commercial product. Our results demonstrate that games can be very effective in increasing both motivation and achievement in mathematics learning. They also pinpoint the critical importance of detailed elements of game design, the role of the teacher, and the integration of computer games with other forms of mathematics education. Finally our work has identified important differences, as well as similarities, in girls' and boys' interactions with games and computers. In this paper we highlight some of the recent E-GEMS work with particular attention to the aspects related to interfaces and HCI.

Invited Talk

Will Anyone Really Use Radiosity? BIBAPDFGI Online Paper 40-41
  François Sillion
The radiosity technique for the simulation of energy exchanges in synthetic models has been continuously improved in the past 15 years, to the point where impressively realistic images can be produced, and the technology is being offered in commercial products. Does this mean it can be used in practice? Many obstacles remain, obviously, for non-expert users who may want to produce meaningful simulations, and radiosity can hardly be described as a mature technology. We consider here the potential applications where a user will want to use radiosity: we identify the remaining technological barriers, and present some avenues being explored to lift them.

Global Illumination

Stratified Wavelength Clusters for Efficient Spectral Monte Carlo Rendering BIBAPDFGI Online Paper 42-49
  Glenn F. Evans; Michael D. McCool
Wavelength dependent Monte Carlo rendering can correctly and generally capture effects such as spectral caustics (rainbows) and chromatic aberration. It also improves the colour accuracy of reflectance models and of illumination effects such as colour bleeding and metamerism. The stratified wavelength clustering (SWC) strategy carries several wavelength stratified radiance samples along each light transport path. The cluster is split into several paths or degraded into a single path only if a specular refraction at the surface of a dispersive material is encountered along the path. The overall efficiency of this strategy is high since the fraction of clusters that need to be split or degraded in a typical scene is low, and also because specular dispersion tends to decrease the source colour variance, offseting the increased amortized cost of generating each path.
Efficient Glossy Global Illumination with Interactive Viewing BIBAGZMOVGI Online Paper 50-57
  Marc Stamminger; Annette Scheel; Xavier Granier; Frederic Perez-Cazorla; George Drettakis; François X. Sillion
The ability to perform interactive walkthroughs of global illumination solutions including glossy effects is a challenging open problem. In this paper we overcome certain limitations of previous approaches. We first introduce a novel, memory- and compute-efficient representation of incoming illumination, in the context of a hierarchical radiance clustering algorithm. We then represent outgoing radiance with an adaptive hierarchical basis, in a manner suitable for interactive display. Using appropriate refinement and display strategies, we achieve walkthroughs of glossy solutions at interactive rates for non-trivial scenes. In addition, our implementation has been developed to be portable and easily adaptable as an extension to existing, diffuse-only, hierarchical radiosity systems. We present results of the implementation of glossy global illumination in two independent global illumination systems.
Controlling Memory Consumption of Hierarchical Radiosity with Clustering BIBAGZGI Online Paper 58-65
  Xavier Granier; George Drettakis
Memory consumption is a major limitation of current hierarchical radiosity algorithms, including those using clustering. To overcome this drawback we present a new algorithm which reduces the storage required for both the hierarchy of subdivided elements and the links representing light transfers. Our algorithm is based on a link hierarchy, combined with a progressive shooting algorithm. Links are thus stored only when they might transfer energy at subsequent iterations. The push-pull and refine/gather steps of hierarchical radiosity are then combined, allowing the simplification of subtrees of the element hierarchy during refinement. Subdivided polygons replaced by textures and groups of input objects contained in clusters may be deleted. A memory control strategy is then used, forcing links to be established higher in the link hierarchy, limiting the overall memory used. Results of our implementation show significant reduction in memory required for a simulation, without much loss of accuracy or visual quality.
Approximating the Location of Integrand Discontinuities for Penumbral Illumination with Linear Light Sources BIBAGZGI Online Paper 66-75
  Marc J. Ouellette; Eugene Fiume
One of the benefits of shading with linear light sources is also one of its major challenges: generating soft shadows. The primary difficulty in this task is determining the discontinuities in the linear light source integrals that are caused by occluding objects. We demonstrate in this paper that the computed location of each discontinuity only needs to be moderately accurate, provided that the expected value of this location is a continuous function of the actual value of the location. We introduce Random Seed Bisection (RSB), an algorithm that has this property. We use this algorithm to efficiently find the approximate location of a discontinuity, in order to partition the domain of integration into subintervals (panels) over which the integrand is naturally smooth, and approximate the integral efficiently over each panel using low-degree numerical quadratures. We demonstrate the effectiveness of this solution for shadowing problems with at most 1 discontinuity in the domain of integration. We also provide efficient heuristics that take advantage of the coherence in a scene to handle shadowing problems with at most 2 discontinuities in the domain of integration. This work is a first step toward a comprehensive approach to efficiently solving numerical integration problems for extended light sources.

Interaction Techniques

Design of Virtual 3D Instruments for Musical Interaction BIBAPDFGI Online Paper 76-83
  Axel G. E. Mulder; S. Sidney Fels; Kenji Mase
An environment for designing virtual instruments with 3D geometry has been prototyped and applied to real-time sound control and design. It was implemented by extending a realtime, visual programming language called Max/FTS, running on an SGI Onyx, with software objects to interface CyberGloves and Polhemus sensors and to compute human movement and virtual object features. Virtual input devices with behaviours of a rubber balloon and sheet were designed for the control of sound spatialization and timbre parameters. Informal evaluation showed that a sonification inspired by the physical world appears natural and effective. More research is required for a natural sonification of virtual input device features such as shape, taking into account possible co-articulation of these features. While both hands can be used for manipulation, left-hand-only interaction with a virtual instrument may be a useful replacement for and extension of the standard music synthesizer keyboard modulation wheel. More research is needed to identify and apply manipulation pragmatics and movement features, and to investigate how they are co-articulated, in the mapping of virtual object parameters.
A Handwriting-Based Equation Editor BIBAGZGZGI Online Paper 84-91
  Steve Smithies; Kevin Novins; James Arvo
Current equation editing systems rely on either text-based equation description languages or on interactive construction by means of structure templates and menus. These systems are often tedious to use, even for experts, because the user is forced to ''parse'' the expressions mentally before they are entered. This step is not normally part of the process of writing equations on paper or on a whiteboard. We describe a prototype equation editor that is based on handwriting recognition and automatic equation parsing. It is coupled with a user interface that incorporates a set of simple procedures for correcting errors made by the automatic interpretation. Although some correction by the user is typically necessary before the formula is recognized, we have found that the system is simpler and more natural to use than systems based on specialized languages or template-based interaction.
A Psychophysical Comparison of Two Stylus-Driven Soft Keyboards BIBAPDFGI Online Paper 92-97
  Michael Bohan; Chad A. Phipps; Alex Chaparro; Charles G. Halcomb
This study compared text entry performance of two stylus-driven soft keyboards for use in hand-held computing devices: the QWERTY and the T9. Participants transcribed text presented on a computer screen into a personal digital assistant (PDA) using a stylus and one of these two keyboards. We introduced a new psychophysical technique for measuring transcription rate that provides a composite measure of speed and accuracy. Using this technique, we calculated the maximum transcription rate for each keyboard. The results show that transcription rates were higher for the QWERTY keyboard than for the T9, despite the T9 keyboard's apparent superior physical characteristics. An ancillary experiment demonstrated that the poorer performance of the T9 layout may have resulted from an increase in visual scanning time due to perceptual grouping of the letters on the keys. Together these findings imply that the QWERTY keyboard layout remains the most effective of the currently available designs for stylus tapping on soft keyboards.

Image-based Techniques

Multi-layered image-based rendering BIBAZGI Online Paper 98-106
  Sing Bing Kang; Huong Quynh Dinh
In this paper, we describe a multi-layered image-based rendering system that can use different types of input to produce and render new environments. Each separate input that can be manipulated independently is called a layer. In our implementation, the types of layers that can be manipulated are the image-based and 3-D-based layers. The computation required for rendering the newly-crafted environment is reduced by using cached composite snapshots of that environment at reference poses. These cached snapshots are used to directly generate novel views, and the original layers are used only when necessary. Another key concept is the identification of types of holes generated as a result of pixel transfer from the composite snapshots to the generated view. For optimal rendering quality, the algorithm used in filling these holes is specific to the hole type (either intralayer or interlayer). The ideas embodied in our multi-layered IBR system are useful in augmenting the capabilities of applications that require fast and geometrically consistent rendering of 3-D scenes such as video editing.
Interactive Rendering of Wavelet Projected Light Fields BIBAGZGI Online Paper 107-114
  Paul Lalonde; Alain Fournier
Light field techniques allow the rendering of objects in time complexity unrelated to their geometric complexity. The technique discretely samples the space of light rays exiting the boundary around an object and then reconstructs a requested view from these data. In order to generate high quality images a dense sampling of the space is required which leads to large data sets. These data sets exhibit a high degree of coherence and should be compressed in order to make their size manageable. We present a wavelet-based method for storing light fields over planar domains. The parameterization is based on the Nusselt embedding, which leads to simplifications in shading computations when the light fields are used illumination sources. The wavelet transform exploits the coherence in the data to reduce the size of the data sets by factors of 20 times or more without objectionable deterioration in the rendered images. The wavelet representation also allows a hierarchical representation in which details can be added incrementally, and in which each coarser view is an appropriately filtered version of the finer detail. By blending between the two seemless transitions are possible. The wavelet coefficients are compressed by thresholding the coefficients and storing them in a sparse hexadecary tree. The tree encoding allows random access over the compressed wavelet coefficients which is essential for extracting slices and point samples from the light field.
Imaging all Visible Surfaces BIBAGZGI Online Paper 115-122
  Wolfgang Stuerzlinger
Today many systems exist to generate geometric models of existing scenes and objects. However, very few systems store accurate data about surface appearance such as colors and textures. One way to capture surface texture data is to record a series of images that, collectively, captures all visible surfaces of the object. Finding good viewpoints for this task is not easy. This paper presents a new heuristic method to find a good set of viewpoints for a given geometric model. Taking images from the computed viewpoints will show every visible part of every surface at least once. The approach uses a hierarchical visibility algorithm to preprocess the scene. A good set of viewing regions is identified with simulated annealing and then good viewpoints are derived. Results and visualizations of the computed solutions are presented.

Invited Paper

Style and Function of Graphic Tools BIBAPDFGI Online Paper 123-131
  Ted Selker
Shouldn't the future be a place where our graphical interfaces disencumber computer use? We should be developing a library of graphical presentation and interface techniques relative to where they are useful. We should work to make things respect the ergonomic and psychophysical realities of people. We should work to make things that look like what they do or represent. When these goals over constrain design, we need good teaching tools - prosthetics - to help the user share the designer's vision.
   When should the user interface should slink out of the way to allow us to focus our attention on our tasks and when should it be stylish and playful? The sea-green institutional paint of the 50s was supposed be a relaxing color. Interfaces also might suffer from being offensively bland. We choose and use things to make a social statement of status, style, and knowledge. This paper discusses how tools should give designers the latitude to create brand and style statements, while making reasoned and motivated choices of interface techniques in scenarios.


Discrete Parametrization for Deforming Arbitrary Meshes BIBAGZGZGI Online Paper 132-139
  Shigeru Kuriyama; Toyohisa Kaneko
Techniques for deforming polygonal meshes are demonstrated by using two-dimensional lattices of control points or functions for pasting features. The deformations use a shape-preserving parametrization that embeds the mesh's vertices in a normalized two-dimensional space while preserving shape consistency for non-flat surfaces. A discrete smoothing used for the parametrization has inefficient iterative calculations, which is unsuitable for manipulations of dense meshes, and an initial approximation for the smoothing is therefore proposed in order to reduce the number of iterations. The approximation uses a graph-searching algorithm and a discrete normalization whose computational costs are negligible in comparison with that of the iterative calculations.
A General Model of Animated Shape Perturbation BIBAGZGI Online Paper 140-147
  Jean-Michel Dischler
Stochastic shape-perturbation, called shape- or hyper-texturing, represents an attractive way for rendering many complex surface structures including fur, fire, cotton or rocks. While current methods often limit applications to static, isolated and rather simple objects, this paper attempts to provide a more general approach, based on projection schemes. The presented technique not only permits to deal with various shapes, but furthermore combines perturbation with animation using 3D deformation models based on a principle of smoothed particles. The parameters of the deformation are controlled by the user through projection primitives". Examples of animated surface behaviors (applied to usual polyhedrons such as the Utah teapot) including morphing, fluttering, burning and waving illustrate the possibilities of the approach."
Interactive Mesh Fusion Based on Local 3D Metamorphosis BIBAGZGI Online Paper 148-156
  Takashi Kanai; Hiromasa Suzuki; Jun Mitani; Fumihiko Kimura
This paper proposes a new mesh modeling scheme, called mesh fusion, based on three-dimensional (3D) mesh-based metamorphosis. We establish the attachment from a part of one mesh to a part of another with smooth boundaries, employing the traditional cutting and pasting operation in conjunction with a combination of meshes, applying the idea of 3D metamorphosis. We also offer an algorithm for adjusting two boundaries by using the combination of three geometrical operations rigid transformation, scaling and deformation. Our schematic offers a computation time swift enough that the user can create various shapes with interactive speed.

Non-photorealistic Rendering

Observational Model of Blenders and Erasers in Computer-Generated Pencil Rendering BIBAGZGI Online Paper 157-166
  Mario Costa Sousa; John William Buchanan
In this paper we present a blender and eraser model that extends our graphite pencil and paper model. This blender and eraser model enhances the rendering results producing realistic looking graphite pencil tones and textures. Our model is based on observations on the absorptive and dispersive properties of blenders and erasers interacting with lead material deposited over drawing paper. The parameters of our model are the particle composition of the lead over the paper, the texture of the paper, the position and shape of the blender and eraser, and the pressure applied to them. We demonstrate the capabilities of our approach with a variety of pencil swatches and compare them to digitized pencil drawings. We also present automatic and interactive image-based rendering results implementing traditional graphite pencil tone rendering methods.
Halftoning with Image-Based Dither Screens BIBAGZGI Online Paper 167-174
  Oleg Veryovka; John Buchanan
Continuous tone images must be halftoned to be displayed on binary output devices such as printers. The ordered dither algorithm is a popular approach to halftoning. This algorithm uses a threshold matrix to approximate gray scale values. The arrangement of thresholds in the matrix determines texture artifacts introduced into the halftoned image. Thus, the challenge of research in ordered dithering is to find a matrix that results in the least visible texture artifacts. In this work we control the halftoning texture by generating a threshold matrix from an arbitrary image. We demonstrate that processing images using adaptive histogram equalization results in pixel distributions similar to traditional dither screens. Ordered dithering with the resulting threshold matrix enables us to define texture in the halftoned image. We control the appearance of this texture by a combination of the ordered dither algorithm with an error diffusion process. We present applications of the image-based dither screens to both photorealistic and artistic rendering. In the case of photorealistic tone reproduction this technique preserves textures and edges of the original image. The ability to define an arbitrary texture enables us to introduce a variety of artistic effects. A halftoned image can be embossed with another image, texture, or text. Also, halftoning with textures clipped from the existing art works approximates the look of traditional illustration media.
An illustration technique using hardware-based intersections and skeletons BIBAGZGI Online Paper 175-182
  Oliver Deussen; Jörg Hamel; Andreas Raab; Stefan Schlechtweg; Thomas Strothotte
We present a method for generating line drawings of complex geometries in the style of crosshatched illustrations. Hatching lines are generated by intersecting the geometry with a set of planes. Half-toning on the basis of the generated curves is used to represent a given intensity distribution. Computing a geometric skeleton allows us to determine automatically the orientation of the intersection planes for a wide variety of models. By using predefined line styles different types of illustrations can be generated. Applications of the method are discussed, examples are given.

Invited Paper

Computer Aided Serendipity: The Role of Autonomous Assistants in Problem Solving BIBAGZGI Online Paper 183-192
  James Arvo
Pencil and paper are perhaps the most effective problem-solving tools ever invented. Why is this so, and what does this portend for computer-assisted problem solving? In this paper we investigate why the computer has not made more significant inroads into many aspects of problem solving, even in domains ostensibly concerned with purely formal methods. We observe that for many problem-solving activities computers are currently more constraining than enabling, particularly during problem formulation. We identify some of the obstacles that must be overcome in making the computer a more attractive medium for problem solving, and explore some of the tools that will likely play a part in bringing this about.

Physical Animations

A Visual Model For Blast Waves and Fracture BIBAGZGI Online Paper 193-202
  Michael Neff; Eugene Fiume
The expense, danger, planning and precision required to create explosions suggests that the computational visual modelling of explosions is worthwhile. However, the short time scale at which explosions occur, and their sheer complexity, poses a difficult modelling challenge. After describing the basic phenomenology of explosion events, we present an efficient computational model of isotropic blast wave transport and an algorithm for fracturing objects in their wake. Our model is based on the notion of a blast curve that gives the force-loading profile of an explosive material on an object as a function of distance from the explosion's centre. We also describe a technique for fracturing materials loaded by a blast. Our approach is based on the notion of rapid fracture: that microfractures in a material together with loading forces seed a fracturing process that quickly spreads across the material and causes it to fragment.
Animating Lava Flows BIBAGZGI Online Paper 203-210
  Dan Stora; Pierre-Olivier Agliati; Marie-Paule Cani; Fabrice Neyret; Jean-Dominique Gascuel
Animating lava flowing down the slopes of a volcano brings several challenges: modeling the mechanical features of lava and how they evolve over time depending on temperature; computing, in a reasonable time, the interactions inside the flow, and between the flow and a complex terrain data-base; and lastly, rendering the visual aspect of the flow. The methods described rely on smoothed particles governed by a state equation for animating the flow. We adapt this model to the animation of lava by linking viscosity to a temperature field and by simulating heat transfers. We propose particular data-structures that lead to linear computational time with respect to the number of particles. Lastly, we study a model based on a color-and-displacement procedural texture controlled by the flow for the realistic rendering of lava.
Animating Exploding Objects BIBAPDFJPGJPGGI Online Paper 211-218
  Oleg Mazarak; Claude Martins; John Amanatides
The paper explores the physically-based modeling of a blast wave impact on surrounding objects. We propose a connected voxel representation of objects to model explosions that result in realistic solid debris, rather than flat polygons. The paper also presents improved fracture algorithms capable of accounting for the damage of multiple explosions. The important implementation issues and the results of the simulation are discussed.