Issue 3

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/68

Browse

Now showing 1 - 20 of 39

Shading with Curve Light Sources1
(Blackwell Science Ltd and the Eurographics Association, 1995) Bao, Hujun; Ying, Jianguo; Peng, Qunsheng
A new shading model for curve light sources is presented. It accounts for both diffuse reflection and specular reflection of the illuminated surface. By regarding a linear light source as a directional quadrilateral light source with very small width, a simple formula is derived first for calculating the diffuse reflection component due to the illumination of the linear segment. The diffuse reflection of the surface by direct illumination of a curve light source is then evaluated by approximating the curve light with a series of linear segments. The specular reflection component due to a curve light source is represented by an integration taking Phong s specular model as the kernel and evaluated by summing the contributions from the linear segments. Finally, an efficient shadow detection algorithm for curve light sources is proposed. The images rendered with the shading model are very photo-realistic.
Thoughtful Drawings: A Computational Model of the Cognitive Nature of Children s Drawing
(Blackwell Science Ltd and the Eurographics Association, 1995) Burton, Ed
An interpretation of children s drawing is presented that is based on active perception of the world and the construction of an equivalent self contained two-dimensional world. This model is implemented in a computer program called Rose (Representation Of Spatial Experience). Inspired by the drawings of young children, Rose simulates the perception of the general form and structure of three-dimensional computer models and constructs equivalent childlike two-dimensional representations from them. Rose serves to illustrate the plausibility of the constructive process as a model for real children s drawing and in addition serves as an alternative approach to traditional computer graphic rendering.
Object Calibration for Augmented Reality
(Blackwell Science Ltd and the Eurographics Association, 1995) Whitaker, Ross T.; Crampton, Chris; Breen, David E.; Tuceryan, Mihran; Rose, Eric
Augmented reality involves the use of models and their associated renderings to supplement information in a real scene. In order for this information to be relevant or meaningful, the models must be positioned and displayed in such a way that they align with their corresponding real objects. For practical reasons this alignment cannot be known a priori, and cannot be hard-wired into a system. Instead a simple, reliable alignment or calibration process is performed so that computer models can be accurately registered with their real-life counterparts. We describe the design and implementation of such a process and we show how it can be used to create convincing interactions between real and virtual objects.
Fast Shadowing Algorithm for Linear Light Sources
(Blackwell Science Ltd and the Eurographics Association, 1995) Tanaka, Toshimitsu; Takahashi, Tokiichiro
This paper presents a fast shadowing algorithm for linear light sources that uses a ray-oriented buffer. Space segmentation by the buffer guarantees that if a point is included in a subspace, all light rays toward the point are also contained in the subspace. Each cell of the buffer stores a list of objects that lie within or intersect the subspace allocated to the cell. Therefore, candidate objects, those that may cast shadows onto a point, are determined by referring to the cell where the point is mapped. In addition, whether each candidate object actually casts shadows or not is tested with the bounding-volume of the shadow space to reduce the number of objects subjected to expensive light clipping. The bounding-volumes are also stored in the buffer. For efficiently generating the ray-oriented buffer, we present the cylindrical scan-conversion algorithm. The algorithm preconverts objects surfaces to trapezia to decrease the light clipping cost, then connects the trapezia to the buffer cells.Due to the above improvements, our algorithm achieves over 10 times faster shadow generation compared to the conventional methods. Experimental results confirm that our method can generate realistic images with soft shadows in a few minutes.
A Direct Manipulation Interface for 3D Computer Animation
(Blackwell Science Ltd and the Eurographics Association, 1995) Snibbe, Scott Sona
We present a new set of interface techniques for visualizing and editing animation directly in a single three-dimensional scene. Motion is edited using direct-manipulation tools which satisfy high-level goals such as"reach this point at this time" or"go faster at this moment". These tools can be applied over an arbitrary temporal range and maintain arbitrary degrees of spatial and temporal continuity.We separate spatial and temporal control of position by using two curves for each animated object: the motion path which describes the 3D spatial path along which an object travels, and the motion graph, a function describing the distance traveled along this curve over time. Our direct-manipulation tools are implemented using displacement functions, a straightforward and scalable technique for satisfying motion constraints by composition of the displacement function with the motion graph or motion path. This paper will focus on applying displacement functions to positional change. However, the techniques presented are applicable to the animation of orientation, color, or any other attribute that varies over time.
Fair Surface Reconstruction Using Quadratic Functionals
(Blackwell Science Ltd and the Eurographics Association, 1995) Kolb, Andreas; Pottmann, Helmut; Seidel, Hans-Peter
An algorithm for surface reconstruction from a polyhedron with arbitrary topology consisting of triangular faces is presented. The first variant of the algorithm constructs a curve network consisting of cubic Bezier curves meeting with tangent plane continuity at the vertices. This curve network is extended to a smooth surface by replacing each of the networks facets with a split patch consisting of three triangular Bezier patches. The remaining degrees of freedom of the curve network and the split patches are determined by minimizing a quadratic functional. This optimization process works either for the curve network and the split patches separately or in one simultaneous step. The second variant of our algorithm is based on the construction of an optimized curve network with higher continuity. Examples demonstrate the quality of the different methods.
Syntax Channelling and Other Issues affecting Innovation in the Graphical User Interface
(Blackwell Science Ltd and the Eurographics Association, 1995) King, Mike
Does the modern commercial Graphical User Interface constrain the developer of graphics applications into certain interaction styles? This paper looks at the Microsoft Windows environment as an example, with particular reference to the question of interaction modes, screen real-estate and visual appearance. The concept of syntax channelling is introduced to help analyse the problem of modality, and the question of button-down versus button-up dragging is debated in the context of a range of commercial applications, and possible consequences for upper limb disorder. A Windows application developed by the author involving the implementation of a variety of innovative interfacing techniques is presented.
Filtering, Clustering and Hierarchy Construction: a New Solution for Ray-Tracing Complex Scenes
(Blackwell Science Ltd and the Eurographics Association, 1995) Cazals, Frederic; Drettakis, George; Puech, Claude
Data structures that handle very complex scenes (hundreds of thousands of objects) have in the past either been laboriously built by hand, or have required the determination of unintuitive parameter values by the user. It is often the case that an incorrect choice of these parameters can result in greedy memory requirements or severely degraded performance. As a remedy to this problem we propose a new data structure which is fully automatic since it does not require the user to determine any input parameters. The structure is built by first filtering the input objects by size, subsequently applying a clustering step to objects of the same size and finally building a hierarchy of uniform grids . We then show that this data structure can be efficiently constructed. The implementation of the shows that the new structure is stable since it s memory requirements grow linearly with the size of the scene, and that it presents a satisfactory compromise between memory usage and computational efficiency. A detailed comparison with previous data structures is also presented in the results.
The MADE Help System
(Blackwell Science Ltd and the Eurographics Association, 1995) Haindl, Michal; de Ruiter, Behr
MADE is the acronym for the ESPRIT project 6307, whose aim is to develop an object oriented multimedia application development environment. As part of this project the MADE help system is designed to be a distributed hypermedia system with additional support for run-time object monitoring and contextual help.
A Real-time Continuous Alphabetic Sign Language to Speech Conversion VR System
(Blackwell Science Ltd and the Eurographics Association, 1995) Liang, Rung-Huei; Ouhyoung, Ming
Many ways of communications are used between human and computer, while using gesture is considered to be one of the most natural way in a virtual reality system. Because of its intuitiveness and its capability of helping the hearing impaired or speaking impaired, we develop a gesture recognition system. Considering the world-wide use of ASL (American Sign Language), this system focuses on the recognition of a continuous flow of alphabets in ASL to spell a word followed by the speech synthesis, and adopts a simple and efficient windowed template matching recognition strategy to achieve the goal of a real-time and continuous recognition. In addition to the abduction and the flex information in a gesture, we introduce a concept of contact-point into our system to solve the intrinsic ambiguities of some gestures in ASL. Five tact switches, served as contact-points and sensed by an analogue to digital board, are sewn on a glove cover to enhance the functions of a traditional data glove.
Three Architectures for Volume Rendering
(Blackwell Science Ltd and the Eurographics Association, 1995) Hesser, Jurgen; Manner, Reinhard; Knittel, Gunter; Strasser, Wolfgang; Pfister, Hanspeter; Kaufman, Arie
Volume rendering is a key technique in scientific visualization that lends itself to significant exploitable parallelism. The high computational demands of real-time volume rendering and continued technological advances in the area of VLSl give impetus to the development of special-purpose volume rendering architectures. This paper presents and characterizes three recently developed volume rendering engines which are based on the ray-casting method. A taxonomy of the algorithmic variants of ray-casting and details of each ray-casting architecture are discussed. The paper then compares the machinefeatures and provides an outlook onfuture developments in the area of volume rendering hardware.
Spherical Triangular B-splines with Application to Data Fitting
(Blackwell Science Ltd and the Eurographics Association, 1995) Pfeifle, Ron; Seidel, Hans-Peter
Triangular B-splines surfaces are a tool for representing arbitrary piecewise polynomial surfaces over planar triangulations, while automatically maintaining continuity properties across patch boundaries. Recently, Alfeld et al. [1] introduced the concept of spherical barycentric coordinates which allowed them to formulate Bernstein-Bezier polynomials over the sphere.In this paper we use the concept of spherical barycentric coordinates to develop a similar formulation for triangular B-splines, which we call spherical triangular B-splines. These splines defined over spherical triangulations share the same continuity properties and similar evaluation algorithms with their planar counterparts, but possess none of the annoying degeneracies found when trying to represent closed surfaces using planar parametric surfaces. We also present an example showing the use of these splines for approximating spherical scattered data.
Realizing 3D Visual Programming Environments within a Virtual Environment
(Blackwell Science Ltd and the Eurographics Association, 1995) Van Reeth, F.; Coninx, K.; De Backer, S.; Flerackers, E.
In the visual programming community, many interesting graphical metaphors have been reported upon for representing computer programs graphically. Most of them have a 2D or 2.5D appearance on the screen in order to reflect the inherent multi-dimensionality of the programming constructs being represented. By going into a three-dimensional representation, this reflection can go a stepfurther. With ever increasing3D graphics rendering capabilities on todays computers, it moreover becomes feasible to extend the dimensionality of the program (and data structure) depiction. We follow this approach by realizing 3D graphical programming techniques within CAEL, our interactive Computer Animation Environment Language. The paper elucidates how several concepts, traditionally found within the Virtual Environments area, can be utilized in the realization of three-dimensional Programming Environments.
Sketching 3D Animations
(Blackwell Science Ltd and the Eurographics Association, 1995) Balaguer, Jean-Francis; Gobbetti, Enrico
We are interested in providing animators with a general-purpose tool allowing them to create animations using straight-ahead actions as well as pose-to-pose techniques. Our approach seeks to bring the expressiveness of real-time motion capture systems into a general-purpose multi-track system running on a graphics workstation. We emphasize the use of high-bandwidth interaction with 3D objects together with specific data reduction techniques for the automatic construction of editable representations of interactively sketched continuous parameter evolution. In this paper, we concentrate on providing a solution to the problem of applying data reduction techniques in an animation context. The requirements that must be fulfilled by the data reduction algorithm are analyzed. From the Lyche and Morken knot removal strategy, we derive an incremental algorithm that computes a B-spline approximation to the original curve by considering only a small piece of the total curve at any time. This algorithm allows the processing of the user s captured motion in parallel with its specification, and guarantees constant latency time and memory needs for input motions composed of any number of samples. After showing the results obtained by applying our incremental algorithm to 3D animation paths, we describe an integrated environment to visually construct 3D animations, where all interaction is done directly in three dimensions. By recording the effects of user s manipulations and taking into account the temporal aspect of the interaction, straight-ahead animations can be defined. Our algorithm is automatically applied to continuous parameter evolution in order to obtain editable representations. The paper concludes with a presentation offuture work.
Synthetic Vision and Audition for Digital Actors
(Blackwell Science Ltd and the Eurographics Association, 1995) NOSER, Hansrudi; THALMANN, Daniel
We present an overview of some principles of synthetic vision and audition for digital autonomous actors in virtual worlds. After a short review of the state-of-the-art we focus on some aspects of synthetic vision and virtual world constraints. Then, we present a simple real time structured sound renderer. This sound renderer is used as audition channel for synthetic and real actors and synchronized sound track generator for video film productions.
Morphological Operations for Color-Coded Images
(Blackwell Science Ltd and the Eurographics Association, 1995) Busch, Christoph and Eberle, Michael
The subject of this paper is the semantically based postprocessing of color-coded images such as classification results. We outline why the classical definition of mathematical morphology suffers if it is used for processing of coded image data. Therefore we provide an extension for morphological operations such as dilation, erosion, opening, and closing. With a new understanding of morphology we introduce bridging and tunneling as further combinations of dilation and erosion. The extensions are applied to medical image data, where the semantic rules stem from basic anatomical knowledge.
A Quick Rendering Method Using Basis Functions for Interactive Lighting Design
(Blackwell Science Ltd and the Eurographics Association, 1995) Dobashi, Yoshinori; Kaneda, Kazufumi; Nakatani, Hideki; Yamashita, Hideo; Nishita, Tomoyuki
When designing interior lighting effects, it is desirable to compare a variety of lighting designs involving different lighting devices and directions of light. It is, however, time-consuming to generate images with many different lighting parameters, taking interreflection into account, because all luminances must be calculated and recalculated. This makes it difficult to design lighting effects interactively. To address this problem, this paper proposes a method of quickly generating images of a given scene illustrating an interreflective environment illuminated by sources with arbitrary luminous intensity distributions. In the proposed method, the luminous intensity ditribution is expressed with basis functions. The proposed method uses a series of spherical harmonic functions as basis functions, and calculates in advance each intensity on surfaces lit by the light sources whose luminous intensity distribution are the same as the spherical harmonic functions. The proposed method makes it possible to generate images so quickly that we can change the luminous intensity distribution interactively. Combining the proposed method with an interactive walk-through that employs intensity mapping, an interactive system for lighting design is implemented. The usefulness of the proposed method is demonstrated by its application to interactive lighting design, where many images are generated by altering lighting devices and/or direction of light.
Synthesizing Feather Textures in Galliformes
(Blackwell Science Ltd and the Eurographics Association, 1995) Dai, Wen-Kai; Shih, Zen-Chung; Chang, Ruei-Chuan
The texture of feather is one of the most fascinating, complicated, and beautiful texture patterns in nature. In this paper, we propose a new and effective texture generation approach that uses the traits of iteration behavior to synthesize the textures of Galliformes feathers realistically. We also propose an interactive feather modeling approach which provides a close connection between the user s intuition and the resulting branching pattern. In texturing the feather structure, we use an object-space mapping technique. Experimental results are presented to show the effectiveness of our method.
The HUMANOID Environment for Interactive Animation of Multiple Deformable Human Characters
(Blackwell Science Ltd and the Eurographics Association, 1995) Boulic, R.; Capin, T.; Huang, Z.; Kalra, P.; Lintermann, B.; Magnenat-Thalmann, N.; Moccozet, L. and Molet, T. and Pandzic, I. and Saar, K. and Schmitt, A. and Shen, J. and Thalmann, D.
We describe the HUMANOID environment dedicated to human modeling and animation for general multimedia, VR, and CAD applications integrating virtual humans. We present the design of the system and the integration of the various features: generic modeling of a large class of entities with the BODY data structure, realistic skin deformation for body and hands, facial animation, collision detection, integrated motion control and parallelization of computation intensive tasks.
Discrete Ray-Tracing of Huge Voxel Spaces
(Blackwell Science Ltd and the Eurographics Association, 1995) Stolte, Nilo; Caubet, Rene
The quality of images produced by Discrete Ray-Tracing voxel spaces is highly dependent on 3d grid resolution. The huge amount of memory needed to store such grids often discards discrete Ray-Tracing as a practical visualization algorithm. The use of an octree can drastically change this when most of space is empty, as such is the case in most scenes.Although the memory problem can be bypassed using the octree, the performance problem still remains. A known fact is that the performance of discrete traversal is optimal for quite low resolutions. This problem can be easily solved by dividing the task in two steps, working in two low resolutions instead of just one high resolution, thus taking advantage of optimal times in both steps. This is possible thanks to the octree property of representing the same scene in several different resolutions. This article presents a two step Discrete Ray-Tracing method using an octree and shows, by comparing it with the single step version, that a substantial gain in performance is achieved.

Browse

Browsing Issue 3 by Issue Date

Results Per Page

Sort Options