Issue 3

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https://diglib.eg.org/handle/10.2312/62

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Towards Context- Dependent Interpolation of Digital Elevation Models
(Blackwell Science Ltd and the Eurographics Association, 1994) Dixon, A.R.; Kirby, G.H.; Wills, D.P.M.
The fractional Brownian motion (fBm) model has become increasingly popular in recent years as a mechanism for the synthesis of many natural phenomena. Unfortunately, the required interdependence of neighbouring points over an unbounded area (context dependence) renders valid approximations to fBm extremely inefficient. This paper describes a technique for the interpolation of digital elevation models to an arbitrarily high spatial resolution. This is achieved using an efficient recursive subdivision algorithm which has the ability to permit some degree of context dependence within, and across the boundaries of interpolation areas. The application of this technique to flight simulation is described and the technique is evaluated based on its ability to reduce run-time storage requirements.
GKS-9x: The Design Output Primitive, an Approach to a Specification.
(Blackwell Science Ltd and the Eurographics Association, 1994) Nehlig, Ph. W.; Duce, D. A.
This paper describes an approach to the formal definition of the design primitive introduced in the revision of the ISO/IEC computer graphics standard, GKS. The paper starts with a general description of the design primitive and then describes the specification (which is given in the Z notation) and the motivation for the approach taken in some detail. The paper concludes with a reflection on the contribution of this work, and the descriptive style adopted an the GKS revision, to the role of formal description in the presentation of graphics standards.
Triangulating multiply-connected polygons: A simple, yet efficient algorithm.
(Blackwell Science Ltd and the Eurographics Association, 1994) Ronfard, Remi P.; Rossignac, Jarek R.
We present a new, simple, yet efficient algorithm for triangulating multiply-connected polygons. The algorithm requires sorting only local concave minima (sags). The order in which triangles are created mimics a flooding process of the interior of the polygon. At each stage, the algorithm analyses the positions and neighborhoods of two vertices only, and possibly checks for active sags, so as to determine which of five possible actions to take. Actions are based on a local decomposition of the polygon into monotonic regions, or gorges (raise the water level in the current gorge, spill into an adjacent gorge, jump to the other bank of a filled gorge, divide a gorge into two, and fill a gorge to its top). The implementation is extremely simple and numerically robust for a large class of polygons. It has been tested on millions of cases as a preprocessing step of a walkthrough and inspection program for complex mechanical and architectural scenes. Extensive experimental results indicate that the observed complexity in terms of the number of vertices, remains under in all cases.
Fast Wavelet Radiosity Method
(Blackwell Science Ltd and the Eurographics Association, 1994) Pattanaik, Sumanta N.; Bouatouch, Kadi
Wavelet analysis has been found [1] to be very useful for functional representation and accurate global solution of radiosity. In radiosity we deal with functions in 2D and 4D spaces. Under such conditions, the biggest bottleneck in applying this wavelet analysis seems to be the large number of multidimensional inner products. In this paper, we propose (i) the use of interpolating wavelets for fast inner product computation and consequently for faster wavelet radiosity solution (ii) the use of hierarchical decomposition technique for determining the smoothness of the radiosity function for optimal adaptive subdivision.
Chebyshev Polynomials for Boxing and Intersections of Parametric Curves and Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1994) Fournier, Alain; Buchanan, John
Parametric curves and surfaces are powerful and popular modelling tools in Computer Graphics and Computer Aided Design. Ray-tracing is a versatile and popular rendering technique. There is therefore a strong incentive in developing fast, accurate and reliable algorithms to intersect rays and parametric curves and surfaces.We propose and demonstrate the use of Chebyshev basis functions to speed up the computation of the intersections between rays and parametric curves or surfaces. The properties of Chebyshev polynomials result in the computation of better and tighter enclosing boxes. For surfaces they provide a better termination criterion to decide on the limits of subdivision, and allow the use of bilinear surfaces for the computation of the intersection when needed.The efficiency of the techniques used depends on the relative magnitude of the coefficients of the Chebyshev basis functions. We show from a statistical analysis of the characteristics of several thousands surfaces of different origin that these techniques will result most of the time in significant improvement in speed and accuracy over other other boxing and subdivision techniques.
Raycasting of Nonregularly Structured Volume Data
(Blackwell Science Ltd and the Eurographics Association, 1994) Fruhauf, Thomas
Raycasting is an efficient, but computation-intensive technique for the direct rendering of volumetric data. Nonregularly structured volume data is produced in a variety of applications, such as numerical simulation, ultrasonic inspection, or seismic measurement. Unfortunately, in raycasting nonregulary structured grids, sampling data along the rays is even more computation-intensive. One idea might be to resample the data onto a regular grid for further processing. It is shown, that resampling typical grids results either in extreme sub- sampling of the most interesting areas or in data sets too huge to handle. Additionally, no better hardware will overcome the fact that all topology and context information is lost through resampling. Therefore, dedicated algorithms for the raycasting of nonregularly structured volumes are required.We present a new approach for this task, which is based on sending rays through the computational space of a nonregular grid, instead of conventionally raycasting the physical space. This technique overcomes the difficulties in sampling data along the rays, since the computational space is regular by definition. The paper outlines the mathematical operations of this technique as well as its embedding in a rendering algorithm. We have implemented the new raycasting strategy as a module of our interactive visualization system, providing the users with an additional tool for the efficient exploration of their data.
Beyond WYSIWYG: Display of Hidden Information in Graphics Editors
(Blackwell Science Ltd and the Eurographics Association, 1994) Schleich, R.; Durst, M.J.
Graphics editors such as computer aided design systems are complex and difficult to use. We attribute this to the fact that only a small part of the information is visible and therefore accessible and understandable. Only the graphics objects themselves are visible, but the relations between these objects remain hidden. We propose an effective way to visualise this information in the form of trees and graphs in so-called structure browsers. A prototype implements this proposal based on an object-oriented application framework for graphics editors.
Sketching 3D models with 2D interaction devices
(Blackwell Science Ltd and the Eurographics Association, 1994) Branco, Vasco; Costa, Antonio; Ferreira, F. Nunes
The creation of a 3D shape using CAD tools, namely solid modelers, is difficult and time-consuming. Therefore, these systems are kept away from the conceptual phases of design, perhaps the most important in any product life cycle.The sketch is considered by many people as one of the fundamental techniques during a design s conceptual stages, as it enables high level design options to be explored at low cost. In general, this technique IS under-appreciated in the computer graphics world.In this paper, we present a system called IDeS that tries to combine simplicity and intuition while drawing, with the useful features of the solid modelers, for example, CSG operators.
Improved Visualisation of Marine Data: Algae and Acid Rain
(Blackwell Science Ltd and the Eurographics Association, 1994) Day, A.M.; Turner, S.M.; Arnold, D.B.
Reducing The Latency In Head-Mounted Displays By A Novel Prediction Method Using Grey System Theory
(Blackwell Science Ltd and the Eurographics Association, 1994) Wu, Jiann-Rong; Ouhyoung, Ming
In this paper we propose a novel prediction method for the head motion using Grey System theory, where a 6D tracker is attached to an HMD on a user s head in virtual reality applications. Our prediction method using Grey System Model can greatly reduce the latency by at least one half and reduce image jittering. A system latency below 100 ms or even 50 ins can be achieved, even though without prediction the latency is around 200 ms. Using 6 points in prediction with Grey System Model is currently the best in tracker prediction as we tried from 2 points to 10 points.In order to measure the latency, we also propose a way to measure it in an HMD system precisely and conveniently. During the process, we have implemented four different prototypes respectively on a PC486, a SUN SparcStation10, an SGI IndigoR4000, and a high performance computer image generator. The computation complexity of our prediction method is relatively low and therefore real time requirement is easily met.
Spectral Data Modeling for a Lighting Application
(Blackwell Science Ltd and the Eurographics Association, 1994) Deville, Pascal M.; Merzouk, Slimane; Cazier, Dorothee; Paul, Jean C.
In computer graphics, image generation uses the RGB colorimetric system. However, this system does not produce an accurate simulation of the spectral characteristics of both light and material, due to the fact that it is device dependent. Indeed, to get realistic images, the image calculation process must deal with spectral characteristics of lights and materials and with the problem of sampling the wavelength domain. Methods have been shown that are a good way to solve the two problems mentioned above, however, these approaches do not take into account complex spectrums (discontinuous). In this paper, we propose a method which removes the constraints imposed by the current methods. Our method is based upon an algorithm of spectrum analysis.
3D Visualization for 2D GIS: an Analysis of the Users Needs and a Review of Techniques*
(Blackwell Science Ltd and the Eurographics Association, 1994) Giertsen, Christopher; Lucas, Anne
Most of the existing geographical information systems (GIS) make limited use of algorithms for advanced computer graphics and visualization. One explanation is that few attempts are made to identify the visualization needs for different uses of GIS, and to couple such needs to the available algorithms. Another explanation is that most GIS are designed to handle two-dimensional (20) data with few obvious relationships to three-dimensional (30) visualization.In an attempt to provide a better understanding of the application of visualization in GIS, we propose a conceptual framework linking several aspects of the two fields. At the user-level, we link different uses of GIS to different categories of audience and presentation styles. At the level of implementation, we first propose different ways to create 3D data for visualization from 2D GIS data, and then we review algorithms and techniques for 3D visualization with respect to support of different presentation styles.
A Formal Approach to the Specification of Graphic Object Functions
(Blackwell Science Ltd and the Eurographics Association, 1994) Torres, J.C.; Clares, B.
Graphic objects are an abstract mathematical model for graphic systems. The model is an algebraic approach to represent graphic information, which include modelling operations. This formalism require some method to describe normal graphic procedures, such as changing the object colour or texture mapping, as these procedures are essential to represent graphic processes.This paper extends the theory by introducing the concept of graphic object functions. A graphic object function transforms one graphic object into another, changing its visual appearance or its geometric properties. A formal definition of graphic functions is given, with a characterization of two special kinds of graphic object functions: filters and object transference functions. These two kinds of functions can be used to perform normal graphic operations, such as changing colours, texture mapping or clipping.Equivalence relationships between graphic objects induced by functions are also studied. These relationships establish an hierarchical structure on the graphic object set.
Solid Modeling Based on a New Paradigm
(Blackwell Science Ltd and the Eurographics Association, 1994) Yoshida, Norimasa; Shiokawa, Masato; Yamaguchi, Fujio
The technique of solid modeling is essential in CAD/CAM applications, and is currently well established. However, problems remain, such as the lack of uniformity in geometric computations and the lack of stability of Boolean operations of two solids. In this paper, we introduce a theoretical solid modeling system that operates on boundary representations of polyhedral objects and is based on a new paradigm. The characteristics of the system are the following: (I) in Boolean Operations and modeling transformations, all geometric computations are performed by the 4 ? 4 determinant method or the 4 ? 4 matrix method in homogeneous space, which allows the system to avoid division operations, (2) all geometric computations are performed by the exact integer arithmetic, which makes the geometric algorithms stable and simple, and (3) primitive solids are constructed consistently in the integer domain, and the consistency is assured throughout Boolean operations and transformations.
How to Render Frames and Influence People
(Blackwell Science Ltd and the Eurographics Association, 1994) Strothotte, Thomas; Preim, Bernhard; Raab, Andreas; Schumann, Jutta; Forsey, David R.
Rendering systems generally treat the production of images as an objective process governed by the laws of physics. However, perception and understanding on the part of viewers are subjective processes influenced by a variety offactors. For example, in the presentation of architectural drawings, the apparent precision with which the drawings are made will affect whether the viewer considers the design as part of a preliminary design or as part of a final polished project, and to some extent the level of confidence the viewer has in the encoded information.In this paper we develop techniques for rendering images in a way that differs from the usual photorealistic or wire-frame output of renderers. In particular, our techniques allow a user to adjust the rendering of a scene to produce images using primitives with variable degrees of precision, from approximations that resemble vague"five-minute-sketches" to more mature but still hand-drawn images. We provide a theoretical framework for analysing the information flow from the computer to the user via such images. Finally, we describe the design and implementation of a prototypical renderer and show examples of its output.
Selective Visualization of Vector Fields
(Blackwell Science Ltd and the Eurographics Association, 1994) van Walsum, Theo; Post, Frits H.
In this paper, we present an approach to selective vector field visualization. This selective visualization approach consists of three stages: selectdon creation, selection processing and selective visualization mapping. It is described how selected regions, called selections, can be represented and created, how selections can be processed and how they can be used in the visualization mapping. Combination of these techniques with a standard visualization pipeline improves the visualization process and offers new facilities for visualization. Examples of selective visualization of fluid flow datasets are provided.
PREMO - An Initial Approach to a Formal Definition
(Blackwell Science Ltd and the Eurographics Association, 1994) DUCE, D.A.; DUKE, D.J.; ten HAGEN, P.J.W.; REYNOLDS, G.J.
Many descriptions of multimedia programming systems are starting to appear in the literature, but little work has yet been done on how to formally specify and reason about such systems. This paper is a contribution on the use of formal description techniques for the specification of multimedia systems and explores a style in which the Object-Z notation from the University of Queensland can be used to specify some of the properties and functionality of such systems. The work has been carried out with reference to the role of formal description techniques in the presentation of ISO/IEC International Standards and in particular to the Premo project in ISO/IEC JTCl/SC24.
The Mesh Propagation Algorithm for Isosurface Construction
(Blackwell Science Ltd and the Eurographics Association, 1994) Howic, C.T.; Blake, E.H.
A new algorithm, Mesh Propagation, is presented for the generation of isosurfaces from three-dimensional discrete data sets. While producing the same surface mesh as that generated by a corrected Marching Cubes algorithm, its characteristic is that it constructs an isosurface using connected strips of dynamically triangulated polygons. This compact data structure speeds up surface construction and reduces surface storage requirements. The surface can also be displayed more quickly, particularly where there is hardware support for rendering triangle strips.With engineering as well as medical imaging applications in mind, the algorithm can be used with both irregular and rectilinear grids of data, the primitive volume elements need not be hexahedral only, and volumes of heterogeneous polyhedral elements are supported without traversal complications.The algorithm propagates through the cells in the grid and uses the same lookup table topologies as Marching Cubes to determine patches of surface-element intersection- additional tables are used for non-hexahedral elements. The surface patches are dynamically coded into triangle strips which are then concatenated and linked to construct the surface. The data structures used for propagating through the volume overcome the topological ambiguities associated with table-based methods of surface construction and no holes are generated in the final mesh.
A Semantics-based Approach for the Design and Implementation of Interaction Objects
(Blackwell Science Ltd and the Eurographics Association, 1994) Paterno , F.; Leonardi, A.
Although tools for developing graphical user interfaces are becoming increasingly popular, they do not usually highlight precisely which key elements developers should take into account. This still entails considerable expertise in developing user interfaces. In this paper we present an approach to overcome these problems. Our approach is based on a model for interaction objects and a corresponding design space. This is supported by a toolkit where the available interaction objects are initially classified by their semantics whereas in most current toolkits they are investigated by their appearance. This facilitates designers and developers in identifying the interactors needed in order to obtain an Interactive System supporting user tasks.
Cross Scan Buffer and its Applications
(Blackwell Science Ltd and the Eurographics Association, 1994) Tanaka, Toshimitsu; Takahashi, Tokiichiro
We propose the Cross Scanline Buffer which preserves the result of hidden surface removal as performed by the Cross Scanline Algorithm. The Cross Scan Buffer reduces image re-generation time and eliminates aliasing artifacts even if the image is arbitrarily scaled. Perfect anti-aliasing is achieved because the Cross Scanline Algorithm analytically determines visible polygonal surfaces and divides them into sets of triangles and trapezia. The Cross Scan Buffer supports the various applications that currently use the conventional buffering methods for anti-aliasing. This paper introduces and tests three applications: image scaling, shadow creation, and texture mapping. Experimental results verify that the Cross Scan Buffer is very powerful yet efficient.

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