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Item Cross Scan Buffer and its Applications(Blackwell Science Ltd and the Eurographics Association, 1994) Tanaka, Toshimitsu; Takahashi, TokiichiroWe 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.Item Real Time Fitting of Hand-Sketched Pressure Brushstrokes(Blackwell Science Ltd and the Eurographics Association, 1994) Pudet, ThierryA 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.Item A New Approach to the Construction of Surfaces from Contour Data(Blackwell Science Ltd and the Eurographics Association, 1994) Jones, Mark W.; Chen, MinThis 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.Item A Robust and Consistent Algorithm for Intersecting Convex Polyhedra(Blackwell Science Ltd and the Eurographics Association, 1994) Sugihara, KokichiThis 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.Item A Hand Control and Automatic Grasping System for Synthetic Actors(Blackwell Science Ltd and the Eurographics Association, 1994) Sanso, Ramon Mas; Thalmann, DanielIn 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.Item 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, AnneMost 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.Item 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.Item Solid Modeling Based on a New Paradigm(Blackwell Science Ltd and the Eurographics Association, 1994) Yoshida, Norimasa; Shiokawa, Masato; Yamaguchi, FujioThe 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.Item 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.Item 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.