EG 1994 Conference Proceedings

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https://diglib.eg.org/handle/10.2312/13893

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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.
Real Time Fitting of Hand-Sketched Pressure Brushstrokes
(Blackwell Science Ltd and the Eurographics Association, 1994) Pudet, Thierry
A method is described for fitting the outline of hand-sketched pressure brushstrokes with Bezier curves. It combines the brush-trajectory model, in which a stroke is generated by dragging a brush along a given trajectory, with a fast curve fitting algorithm.The method has been implemented for a vector-based drawing program in which the user draws with a cordless pressure-sensitive stylus on a digitizing tablet. From the trajectory followed by the stylus, its associated pressure data, and a specified brush, a stroke of variable width is computed and displayed in real time.First, the digitized trajectory is fitted, thus removing noise. Then, from polygonal approximations of the fitted trajectory and the brush outline, a polygonal approximation of the stroke outline is computed. Working with polygonal approximations reduces computations to simple geometric operations and greatly simplifies the treatment of dynamic, pressure-controlled brushes. Last, the polygonal approximation of the stroke outline is fitted. The result is a closed piecewise Bezier curve approximating the brushstroke outline to within an arbitrary error tolerance.Several examples of hand-sketched drawings realized with this method are presented.
A New Approach to the Construction of Surfaces from Contour Data
(Blackwell Science Ltd and the Eurographics Association, 1994) Jones, Mark W.; Chen, Min
This paper presents a new approach to the construction of a surface from a stack of contour slices. Unlike most existing methods, this new approach handles ambiguous conditions consistently without employing an algorithm to establish a correspondence between vertices on one contour and those on the next. It is easy to implement and fast to compute, requiring only basic geometric properties, namely closedness and simplicity, to be available with contour data. The advantages of this new approach have also been demonstrated with solutions to a few classical problems from the literature and some practical problems in medical imaging. It can also be applied to geographical surveying and keyframe animations.
A Robust and Consistent Algorithm for Intersecting Convex Polyhedra
(Blackwell Science Ltd and the Eurographics Association, 1994) Sugihara, Kokichi
This paper presents a numerically robust and topologically consistent algorithm for intersecting convex polyhedra. This algorithm is new in the sense that the consistency issue is completely separated from the numerical error issue. The intersection operation is combinatorially abstracted as the operation of changing the vertex-edge graphs associated with the input polyhedra, and numerical computation is employed only for choosing the branch of processing which is most likely to lead to the correct solution of the problem. Hence, the resultant algorithm is completely free from topological inconsistency.
A Hand Control and Automatic Grasping System for Synthetic Actors
(Blackwell Science Ltd and the Eurographics Association, 1994) Sanso, Ramon Mas; Thalmann, Daniel
In the computer animation field, the interest for grasping has appeared with the development of synthetic actors. Based on a grasp taxonomy, we propose a completely automatic grasping system for synthetic actors. In particular, the system can decide to use a pinch when the object is too small to be grasped by more than two fingers or to use a two-handed grasp when the object is too large. The system also offers both direct and inverse kinematics to control the articulations. In order to ensure realistic looking closing of the hand, several of the joints are constrained. A brief description of the system and results are also presented.
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.
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.
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.
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.
Volume Rendering on Non-regular Grids
(Blackwell Science Ltd and the Eurographics Association, 1994) Tabatabai, Behnam; Sessarego, Emanuela A.; Mayer, Harald F.
In this article we present the principle methods for volumerendering of non-regular grids as used in the Finite Element Method or the Method of Control Volumes. Besides linear element types, the methods discussed here also cover the handling of commonly used non-linear element types but little considered in the Computer Graphics community. The very basic operation in the whole rendering process, namely the interpolation of the geometry and function values is fully based on the element type specific shape functions, ensuring a consistent mathematical treatment of the object in the sense of the underlying numerical simulation. We discuss the implications of this approach and propose optimizations justified by general assumptions on the qualify of the simulation model.
Magicsphere: an insight tool for 3D data visualization
(Blackwell Science Ltd and the Eurographics Association, 1994) Cignoni, P.; Montani, C.; Scopigno, R.
How to render very complex datasets, and yet maintain interactive response times, is a hot topic in computer graphics. The MagicSphere idea originated as a solution to this problem, but its potential goes much further than this original scope. In fact, it has been designed as a very generical 3D widget: it defines a spherical volume of interest in the dataset modeling space. Then, several filters can be associated with the Magicsphere, which apply different visualization modalities to the data contained in the volume of interest. The visualization of multi-resolution datasets is selected here as a case study and an ad hoc filter has been designed, the MultiRes filter. Some results of a prototipal implementation are presented and discussed.
A Median Cut Algorithm for Efficient Sampling of Radiosity Functions
(Blackwell Science Ltd and the Eurographics Association, 1994) Feda, Martin; Purgathofer, Werner
This paper presents an efficient method for sampling the illumination functions in higher order radiosity algorithms. In such algorithms, the illumination function is not assumed to be constant across each patch, but it is approximated by a function which is at least C1 continuous. Our median cut sampling algorithm is inspired by the observation that many form factors are computed at higher precision than is necessary. While a high sampling rate is necessary in regions of high illumination, dark areas can be sampled at a much lower rate to compute the received radiosity within a given precision. We adaptively subdivide the emitter into regions of approximately equal influence on the result. Form factors are evaluated by the disk approximation and a ray tracing based test for occlusion detection. The implementation of a higher order radiosity system using B-splines as radiosity function is described. The median cut algorithm can also be used for radiosity algorithms based on the constant radiosity assumption.
Fast Dynamic Tessellation of Trimmed NURBS Surfaced1
(Blackwell Science Ltd and the Eurographics Association, 1994) Abi-Ezzi, Salim S.; Subramaniam, Srikanth
Trimmed NURBS (non-uniform rational B-splines) surfaces are being increasingly used and standardized in geometric modeling applications. Fast graphical processing of trimmed NURBS at interactive speeds is absolutely essential to enable these applications. which poses some unique challenges in software, hardware, and algorithm design. This paper presents a technique that uses graphical compilation to enable fast dynamic tessellation of trimmed NURBS surfaces under highly varying transforms.We use the concept of graphical data compilation. through which we preprocess the NURBS surface into a compact, view-independent form amenable for fast per-frame extraction of triangles. Much of the complexity of processing is absorbed during compilation. Arbitrarily complex trimming regions are broken down into simple regions that are specially designed to facilitate tessellation before rendering. Potentially troublesome cases of degeneracies in the surface are detected and dealt with during compilation. Compilation enables a clean separation of algorithm-intensive and compute-intensive operations, and provides for parallel implementations of the latter. Also, we exercise a classification technique while processing trimming loops. which robustly takes care of geometric ambiguities and deals with special cases while keeping the compilation code simple and concise.
Variational Design and Fairing of Spline Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1994) Greiner, Gunther
Variational principles have become quite popular in the design of free form surfaces. Among others they are used for fairing purposes. The choice of the right fairness functional is a crucial step. There is always a tradeoff between high quality and computational effort. In this paper we present fairness functionals that allow fairing efficiently, i.e., produce high quality surfaces in a reasonable amount of time. These functionals can be considered as simplified thin plate energy functionals for parametric surfaces or as simplified MVC functionals.

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