Issue 3

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/80

Browse

Now showing 1 - 20 of 41

Selective Pixel Transmission for Navigating in Remote Virtual Environments
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Mann, Yair; Cohen-Or, Daniel
This paper presents a technique to improve the performance of a walkthrough in remote virtual environments, where a scene is rendered jointly by the server and the client, in order to reduce the network requirements as much as possible. The client generates novel views by extrapolating a reference view based on the locally available geometric model, while the server transmits data necessary to prevent an accumulation of errors. Within this concept, we show that by transmitting only a selected subset of pixels, the quality of the extrapolated views can be improved while requiring less bandwidth. We focus on the selection process in which the visibility gaps between the reference view and novel view are detected, packed and transmitted compressed to the client.
A Framework for Interacting with Paper
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Robinson, Peter; Sheppard, Dan; Watts, Richard; Harding, Robert; Lay, Steve
This paper reports on ways of using digitised video from television cameras in user interfaces for computer systems. The DigitalDesk is built around an ordinary physical desk and can be used as such, but it has extra capabilities. A video camera mounted above the desk, pointing down at the work surface, is used to detect where the user is pointing and to read documents that are placed on the desk. A computer-driven projector is also mounted above the desk, allowing the system to project electronic objects onto the work surface and onto real paper documents. The animated paper documents project is considering particular applications of the technology in electronic publishing. The goal is to combine electronic and printed documents to give a richer presentation than that afforded by either separate medium.This paper describes the framework that has been developed to assist with the preparation and presentation of these mixed-media documents. The central component is a registry that associates physical locations on pieces of paper with actions. This is surrounded by a number of adaptors that assist with the creation of new documents either from scratch or by translating from conventional hypermedia, and also allow the documents to be edited. Finally the DigitalDesk itself identifies pieces of paper and animates them with the actions described in the registry.
Finally Everyone Can Work With Highly Complex 3D Models
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Rossignac, Jarek
In the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware.The availability of inexpensive graphics support on personal computers, the Internetâ s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialistâ s access to 3D databases.First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea - other more effective techniques show promise.The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly.The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.
Fast Analytic Shading and Shadowing for Area Light Sources
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Takahashi, Tokiichiro
This paper describes a fast analytic algorithm that generates exact highlights and soft shadows from area light sources. In order to realize fast shadowing, we propose the ray-oriented buffer which segments 3D space by following light rays from polygonal sources. Each cell of the buffer stores objects that intersect a related subspace. Candidate objects which may cast shadows onto a point are selected by referring to the buffer. The candidates are then tested with their shadow bounding volumes to suppress objects that never occlude light sources.In addition, we propose the cross scanline clipping algorithm. It quickly determines the exact regions of uncovered area light sources with simple silhouette generation. Both diffuse and specular reflections are computed by integrating light rays from the uncovered sources. Experimental results confirm the high performance of the proposed method.
Painting-like Image Emphasis based on Human Vision Systems
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Tanaka, Toshimitsu; Ohnishi, Noboru
Regional image emphasis is often evident in paintings and illustrations. This technique increases local contrast while reducing global contrast by amplifying image intensity on shadowed surfaces, reducing intensity on illuminated surfaces, and then expanding contrast at intensity edges. The effects are assumed to result from the visual processing needed to interpolate the real world onto canvas. Therefore, we propose an intensity emphasis method based on human vision. This method simulates the adaptation of photoreceptor cells and the lateral inhibition of receptive fields. These attributes of a vision system are realized by computation of relative intensity and differential intensity in small areas.The proposed method can successfully generate painting-like artifacts, which greatly improves the perception of visual elements displayed in an image. Since the method efficiently reduces the dynamic range of images, it can be used for displaying highlighted images on standard graphic monitors. Experiments on a computer-generated image and a photograph confirm the advantages of our method.
A Muscle-based Feed-forward Controller of the Human Body
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Komura, Taku; Shinagawa, Yoshihisa; Kunii, Tosiyasu L.
There is an increasing demand for human body motion data. Motion capture and physical animation have been used to generate such data. It is, however, apparent that such methods cannot automatically generate arbitrary human body motions. A human body is a redundant multi-linked body controlled by a number of muscles. For this reason, the muscles must work appropriately and cooperatively for controlling the whole body. It is well-known that the human body control system is composed of two parts: The open-loop feed-forward control system and the closed-loop feedback control system. Many researchers have investigated the characteristics of the latter by analyzing the response of a human body to various external perturbations. However, for the former, very few studies have been done. This paper proposes an open-loop feed-forward model of the lower extremities which includes postural control for accurate animation of a human body. Assumptions are made here that the feed-forward controller minimizes a certain objective value while keeping the balance of the body stable. The actual human motion data obtained using a motion capturing technique is compared with the trajectory calculated using our method for verification. The best criteria which is based on muscle dynamics is proposed. Using our method, dynamically correct human animation can be created by merely specifying a few key postures.
Animation by Deformation of Space-Time Objects
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Aubert, Fabrice; Bechmann, Dominique
This article presents the properties of animation with space-time objects. A space-time object means here a geometrical object embedded in R4 with a volumic topology. Resulting animations are obtained by deforming space-time objects with a free-form deformation model. In this way topological modifications, such as disconnecting or hole making, as well as classical geometrical modifications, can be created in an animated object.
Virtually Documented Environments: A New Interface Paradigm for Task-oriented Access to Information
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Kakez, Samory; Conan, Vania; Bisson, Pascal
We present a suitable virtually documented environment system providing the user with high level interaction possibilities. The system is dedicated to applications where the operator needs to have his hands free in order to access information, carry out measurements and/or operate on a device (e.g. maintenance, instruction). The system merges video images acquired through a head-mounted video camera with synthetic data (multimedia documents including CAD models and text) and presents these merged images to the operator. Registration techniques allow the operator to visualise information properly correlated to the real world: this is an essential aspect in order to achieve a feeling of presence in a real environment.We increase the sense of immersion through high level Human-Computer Interaction (HCI) allowing hands-free access to information through vocal commands as well as multimodal interaction associating speech and gesture. In this way, the user can access information and manipulate it in a very natural manner. We discuss the construction of the documentation system and the requested functionalities which led to the system architecture.
Computing Volumes of Solids Enclosed by Recursive Subdivision Surfaces
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Peters, Jorg; Nasri, Ahmad
The volume of a solid enclosed by a recursive subdivision surface can be approximated based on the closed-form representation of regular parts of the subdivision surface and a tight estimate of the local convex hull near extraordinary points. The approach presented is efficient, i.e. non-exponential, and robust in that it yields rapidly contracting error bounding boxes. An extension to measuring higher-order moments is sketched.
Preface and Table of Contents (EG 1997, CGF 16-3)
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Fellner, Dieter W.; Szirmay-Kalos, László
-
Normal Computation for Discrete Surfaces in 3D Space
(Blackwell Publishers Ltd and the Eurographics Association, 1997) ThÃ¼rmer, Grit; WÃ¼thrich, Charles A.
Associating normal vectors to surfaces is essential for many rendering algorithms. We introduce a new method to compute normals on discrete surfaces in object space. Assuming that the surface separates space locally into two disjoint subsets, each of these subsets contains implicitly information about the surface inclination. Considering one of these subsets in a small neighbourhood of a surface point enables us to derive the surface normal from this set. We show that this leads to exact results for C1 continuous surfaces in R3. Furthermore, we show that good approximations can be obtained numerically by sampling the considered area. Finally, we derive a method for normal computation on surfaces in discrete space.
Tunnel-Free Supercover 3D Polygons and Polyhedra
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Andres, Eric; Nehlig, Philippe; Francon, Jean
A new discrete 3D line and 3D polygon, called Supercover 3D line and Supercover 3D polygon, are introduced. Analytical definitions are provided. The Supercover 3D polygon is a tunnel free plane segment defined by vertices and edges. An edge is a Supercover 3D line segment. Two different polygons can share a common edge and if they do, the union of both polygons is tunnel free. This definition of discrete polygons has the "most" properties in common with the continuous polygons. It is particularly interesting for modeling of discrete scenes, especially using tunnel-free discrete polyhedra. Algorithms for computing Supercover 3D Lines and Polygons are given and illustrated.
A Multiscale Approach to Integrated Volume Segmentation and Rendering
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Westermann, Rudiger; Ertl, Thomas
A number of techniques have been proposed for rendering volumetric scalar data sets. Techniques have also been proposed for analyzing the three dimensional information contents of the underlying domain, but traditionally the data analysis part is left as a post-processing step which only involves the rendered two dimensional images. In this paper, we describe a visualization method for scalar volume data which integrates explicit knowledge of the underlying domain into the rendering process. The key of this approach lies in a hierarchical description of the discrete signal, which is decomposed into a sequence of multiscale representations. We describe a technique for the analysis of structures within the data. This allows for the segmentation and classification of the relevant features and can be used to improve their visual sensation. We also address the problem of accelerating the final rendering pass by integrating the extracted object space information into the ray traversal process.
An Algorithmic Reflectance and Transmittance Model for Plant Tissue
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Baranoski, Gladimir V.G.; Rokne, Jon G.
Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.
Growing and Animating Polygonal Models of Animals
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Walter, Marcelo; Fournier, Alain
While there exist many computer models of animal bodies, as polygonal meshes and parametric surfaces, these are difficult to modify to take growth into account, or to animate. Growth data available from the literature usually is expressed as very sparse measurements over the body at various ages of the animal. We present here basic techniques to transfer growth data to computer models (especially polygonal meshes), which allows animation of the growth as well as animation of the body in the traditional sense.The main technique consists of defining local coordinate systems around the growing parts of the body, each one being transformed according to the relevant growth data while maintaining their relationship with the adjoining parts and the continuity of the surface. The local coordinates also permit ordinary animation mainly as relative rotation such as in articulated objects.We present examples with polygonal models of horses and cows, growth data from same, and motion from Muybridgeâ s classic photographic data.
Polyhedral Surface Modeling with a Diffusion System
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Kuriyama, Shigeru; Tachibana, Keihachiro
This paper presents a method of generating polyhedral surfaces by using a diffusion system that calculates the positional and normal vectors on their vertices. The system generates smooth shapes that satisfy the minimum norm property, and can be extended to imitate the shape controls of curvature continuous surfaces with bias and tension parameters. The shape of a surface is determined by the stable state of nonlinear and local calculations between vertices, and is easily controlled by adding constraints on arbitrary vertices. Such bottom-up calculation of surfaces enhances flexibility in the interactive design of complicated free-form shapes.
Orthogonal Decomposition of Non-Uniform Bspline Spaces using Wavelets
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Kazinnik, Roman; Elber, Gershon
We take advantage of ideas of an orthogonal wavelet complement to produce multiresolution orthogonal decomposition of nonuniform Bspline (NUB) spaces. The editing of NUB curves and surfaces can be handled at different levels of resolutions.Applying Multiresolution decomposition to possibly C1 discontinuous surfaces, one can preserve the general shape on one hand and local features on the other of the free-form models, including geometric discontinuities. The Multiresolution decomposition of the NUB tensor product surface is computed via the symbolic computation of inner products of Bspline basis functions. To find a closed form representation for the inner product of the Bspline basis functions, an equivalent interpolation problem is solved.As an example for the strength of the Multiresolution decomposition, a tool demonstrating the Multiresolution editing capabilities of NUB surfaces was developed and is presented as part of this work, allowing interactive 3D editing of NUB free-form surfaces.
An Analysis of Quasi-Monte Carlo Integration Applied to the Transillumination Radiosity Method
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Szirmay-Kalos, Laszlo; Foris, Tibor; Neumann, Laszlo; Csebfalvi, Balazs
This paper presents an enhanced transillumination radiosity method that can provide accurate solutions at relatively low computational cost. The proposed algorithm breaks down the double integral of the gathered power to an area integral that is computed analytically and to a directional integral that is evaluated by quasi-Monte Carlo techniques. Since the analytical integration results in a continuous function of finite variation, the quasi-Monte Carlo integration that follows the analytical integration will be efficient and its error can be bounded by the Koksma-Hlawka inequality. The paper also analyses the requirements of the convergence, presents theoretical error bounds and proposes error reduction techniques. The theoretical bounds are compared with simulation results.
The Personal Interaction Panel - a Two-Handed Interface for Augmented Reality
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Szalavari, Zsolt; Gervautz, Michael
This paper describes the introduction of a new interaction paradigm to augmented reality applications. The everyday tool handling experience of working with pen and notebooks is extended to create a three dimensional two-handed interface, that supports easy-to-understand manipulation tasks in augmented and virtual environments. In the design step we take advantage from the freedom, given by our very low demands on hardware and augment form and functionality to this device. On the basis of examples from object manipulation, augmented research environments and scientific visualization we show the generality of applicability. Although being in the first stages implementation, we consider the wide spectrum of suitability for different purposes.
Generating Reflected Directions from BRDF Data
(Blackwell Publishers Ltd and the Eurographics Association, 1997) Lalonde, Paul; Fournier, Alain
Monte-Carlo path tracing algorithms for computer graphics require that given an incident light ray at a surface an outgoing direction can be computed with a distribution given by the magnitude of the bidirectional reflectance distribution function (BRDF). For analytic reflectance functions this can be done using various techniques including inverting the function, or tabulating some representation of the inverse. However, measured BRDF data sets are too large for this to be practical.We present a method to generate reflection rays distributed according to the magnitude of the BRDF. The method relies on a wavelet-based representation of the BRDF. This representation is efficient and compact, allowing large, anisotropic measured BRDF data sets to be represented with a few thousand coefficients. In particular, we exploit the wavelet representation to quickly compute integrals over ranges of the BRDF.

Browse

Browsing Issue 3 by Issue Date

Results Per Page

Sort Options