EG1988 Proceedings (Technical Papers)

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Animation of Stochastic Model-Based 3-D Textures
(Eurographics Association, 1988) Gagalowicz, Andre; Ma, Song D.
We have previously shown the validity of a statistical model proposed by us for realistic textures. We have also shown how to use this model to map realistic textures onto a still surface of any shape and extent, maintaining consistency and scaling without producing repeating patterns.The problem we have to solve in this paper is how to use this statistical model in order to produce animated objects while keeping temporal consistency. This problem a priori difficult to solve as our mapping technique is statistical.We propose two different techniques. The first method called the image space method creates texture directly on the image planes. The second one called the object space method performs the texture synthesis on the object surface itself which has to be sampled finelly beforehand.
Application Profiles for Computer Graphics Standards - A Touch of Realism
(Eurographics Association, 1988) Mumford, Anne M.
Computer graphics standards have become widely used and are now a fact of life. We have reached the stage of reviewing and extending the current standards. There is an important move within the user community which needs to be taken into consideration in these processes. This is the development of application profiles within user groups to make their use of the graphics standards easier and to ensure portability. This paper suggests that this move is important and cannot be ignored by users of standards or those involved with the current standards work.
Architectures for Mass Market 3D Displays
(Eurographics Association, 1988) Winser, Paul; Bonnet, Thierry; Dumont, Dominique; Mathieu, Yves
We discuss the specific architecture requirements of real time 3D display systems intended for low cost mass market products of the near future. Vertex transformation and polygon rendering are two processing aspects where hardware acceleration must be used to achieve the performance target. The use of one or more DSP chips as vertex processors is discussed, and two efficient z-buffer implementations described. Antialiasing and texture mapping greatly improve the visual impression at some processing cost.
Automatic Detection of Closed Parametric Surfaces without Interior
(Eurographics Association, 1988) Seidel, Hans-Peter
This paper presents an algorithm for the automatic detection of closed piecewise parametric surfaces without any inside or outside, e.g. a Klein bottle. The algorithm is able to decide whether a given closed surface is orientable or not. If non-orientable, the surface will not divide Euclidean 3-space into two halves. Therefore a non-orientable surface can never serve as the boundary of a solid object. The algorithm is based on results from algebraic topology and thus avoids the computation of derivatives and normal vectors. Several applications of the algorithm to rational tensor product B-spline surfaces are given.
Boundary to Constructive Solid Geometry: A Step Towards 3D Conversion
(Eurographics Association, 1988) Juan, R.
Several solid representation schemes exist today in solid modeling. As none of them has properties that are uniformly better than any other, the need for modeling systems working on two or more different schemes which perform every operation in the most suitable scheme, became evident. Then it is necessary to provide geometric modeling systems with the ability of converting from one scheme into another scheme. As most solid modellers use either, a boundary representation (BR) or a constructive solid geometry representation (CSG), conversion from one into the other appears to be of capital importance. Conversion from CSG into BR has been carefully studied but a few attention has been deserved to the conversion from BR to CSG. This paper presents an algorithm which generates CSG binary trees from BR representations over a restricted class of polyhedra. The tree is optimal in the output size. Unfortunately, the algorithm does not in general warrant a correct conversion and, consequently some open questions and ideas for further research are presented.
The Calculus of the Non-Exact Perspective Projection - Scene-Shifting for Computer Animation
(Eurographics Association, 1988) Hofmann, Georg Rainer
This paper shows the principle way to apply the, scene-shiftin technique of the classical film to computer animation. calculus is presented which is a modification of the well-known classical calculus of the perspective projection. However,, a given perspective view (which may be a frame in a computer animated film) of a three-dunensiona! scene does not change homogenous1 when the position of the viewer (i.e. the eyepoint, the location of the camera ... ) changes. So the subject of this paper is to ask for these parts of the frame with only little changes within a tolerance E. Based on the theorems of the presented calculus, a computer animated film as a sequence of single frames may no longer be computed frame by frame, one frame independent from another, and every frame passing through the whole visualization pipeline of the rendering system. In any frame, parts of the preceeding frame may be inserted, if necessary with two-dimensional modifications: scaling, shifting. This will decrease the computing costs for that frame significantly, since for these arts of the frame no new perspective transformahon and rendering is required. It is a shortening of the visualization pipeline. For the sake of the compactness of this paper we will give no detailed proofs of the theorems presented in here. The interested readers may obtain these information directly from the author.
COLOUR SECTION
(Eurographics Association, 1988) Various
A Compositional Semantics for Graphics
(Eurographics Association, 1988) Pineda, Luis A.
In this paper a theory for developing "intelligent" interactive graphic systems is detailed. The Fregean compositionality principle is enunciated for graphical representations. Geometrical symbols and relations receive semantic interpretations which are expressed as first order relations in the first order logical language. These interpretations are introduced with the help of deictic expressions. Deictic expressions constitute one associative mechanism between analogical representational systems used in graphics, and functional representational systems commonly used in AI applications. Interpretations of graphical symbols and geometrical relations between them constitute an ontology upon which complex linguistic interpretations are assigned to graphics. A concept of graphical grammar is introduced. Frege's compositionality principle, and the notion of graphical grammar lead to a concept of meaningful drawing. The graphical grammar constitutes a second associative mechanism between the two representational systems that have been mentioned. The truth conditions for relations in the graphical grammar are computed through geometrical knowledge. Computational geometry algorithms are associated with the high level representational system by means of the graphical grammar. Semantic interpretations of graphics are useful in carrying out natural language-like dialogue about graphical representations. Dialogues refer to true facts in particular interactive states, A notion of interactive state as a function of time and situation is then developed. One example of how this theory can be used in linking interactive graphics with AI applications is given. In the example, the semantic interpretation of a geographical map is constructed. This theory has been tested with an experimental program called GRAFLOG. The program is implemented in PROLOG and GKS.
Conic Beta-Splines with Local Tension Control for Interactive Curve Fitting
(Eurographics Association, 1988) Pham, Binh
Polynomial Beta-splines were introduced by Barsky as an extension of polynomial B-splines with bias and tension parameters which allow more flexibility in controlling shape in curve fitting. It is possible to show that a quadratic Beta-spline segment is equivalent to a quadratic B-spline segment with suitably modified control vertices. This provides a simple method for evaluating quadratic Beta-splines using De Boor's algorithm for calculating polynomial B-splines. A representation for conic Beta-splines with one tension parameter is introduced and some properties are derived. They form a basis for an efficient algorithm for interactive curve fitting with conic Beta-splines. The results are extended further to cover the case of conic Beta-splines with varying tension where the tension parameter is an interpolating function between the tension values at each end of a segment.
Construction and Animation of a Synthetic Actress
(Eurographics Association, 1988) Magnenat-Thalmann, N.; Thalmann, D.
This paper describes a method for creating and animating a synthetic actress. It emphasizes the methodology used to generate realistic images and motions. In particular, points which are often ignored in the literature are explained in detail: for example, the planning and preparation of models for digitizing, composition, skeleton installation and the animation process itself.
Conversion of Boundary Representations to Bintrees
(Eurographics Association, 1988) Diehl, Rabanus
Methods for the conversion from boundary-representations to approximation models (especially the bintree model) are examined. A new algorithm for the conversion to the bintree model is presented. It employs an inheritence mechanism during the subdivision, and reduces the block classification of leaf nodes by taking over the colours of the block corners calculated in advance.
The Development of PHEX, a 3D Graphics Extension to X11
(Eurographics Association, 1988) Clifford Jr., William H.; McConnell, John I.; Saltz, Jeffrey S.
Today, many computer applications require both 3 dimensional (3D) graphics and window management. The new ISO PHIGS [1] and GKS-3D [2] standards define functional interfaces for applications needing 3D graphics but do not provide control over windows. The X Windowing System (tm), Version 11 [3], is a de facto standard that provides control over windows but has limited 2D graphics capabilities. A consortium of organizations under the auspices of MIT has developed X3D PEX [4], an extension to the X11 standard, that supports PHIGS and GKS3D. The goal of PEX is to provide the best of both worlds: a high performance foundation for PHIGS and GKS-3D within the heterogeneous, distributed, X11 windowing environment. The underlying concept in PEX is that every X11 window has the capability to be a PHIGS or GKS-3D workstation.
Efficient Adaptive Subdivision of Bezier Surfaces
(Eurographics Association, 1988) Clay, Reed D.; Moreton, Henry P.
The support of free-form surfaces by modem solid modeling systems has necessitated the development of hardware and algorithms for the interactive display of surface patches. This paper describes an algorithm for the display of multiple surface patches at frame rates capable of providing smooth motion. The algorithm runs on the Silicon Graphics IRIS 4D GT workstation. Real-time motion is achieved by exploiting a microcodable pipeline of floating point processors and existing support for the display of Gouraud shaded Z-buffered polygons. The paper presents tradeoffs in the development of a high performance rendering algorithm. We discuss issues related to hardware support, surface representation, adaptive display, and the minimization of display artifacts such as faceting and cracking. More detailed discussion addresses the choice of Bezier surface patches and subdivision criteria.
An Evaluation of CSG Trees Based on Polyhedral Solids
(Eurographics Association, 1988) Badouel, Didier; Hegron, Gerard
Set operation on polyhedra is an important component of Geometric Modeling System (GMS) when a Constructive Solid Geometry (CSG) representation with polyhedral solid primitives is used. Output data will be the unique resulting polyhedron which provides an efficient data structure for displaying objects. With no use of spatial coherency, computational complexity of a set operation is quadratic. The new evaluation scheme called Boolean Octree limits set operation evaluation in a ‘minimal space of calculation’ where primitive boundaries intersect each other and where resulting evaluation participates in the construction of the final resulting object. Boolean Octree computes set operations in a local level providing a linear complexity for geometric calculations. During space subdivision, Boolean Octree has a global view on local CSG tree (projection of the CSG tree in local space) taking into account simplifications of the boolean expression. Set evaluation is done in the local volumes containing only two operands the configurations of which are ‘simple’, that is to say for a local description of an object there is only one vertex with any face number, one edge, or one face.
A Evalution of Some Three-Color Tiling Patterns
(Eurographics Association, 1988) Alt, Paul; Cordonnier, Vincent
Some new technologies for information display use discrete arrays of cells or picture elements. Each cell displays a single color and the colors do not overlap as they do on a CRT screen. Colored cells are distributed on the two dimension display surface by repeating a basic model called a pattern. Patterns can be evaluated by observing images displayed using them. However, such approaches usually do not give numerical results and depend strongly on the selected images and the observers. In this paper, we suggest and examine some pattern evaluation criteria which relate only to the pattern and its geometrical aspect: Fidelity of color location, the quality of white area and the fidelity of shapes used for lines drawing or characters. Numerical and geometrical approaches are proposed to evaluate the quality of several patterns. The result is a classification of the test patterns. Some of them seem to be better than frequently used patterns. In addition, comments are offered on future pattern design.
Experimenting with a Parallel Ray-Tracing Algorithm on a Hypercube Machine
(Eurographics Association, 1988) Priol, Thierry; Bouatouch, Kadi
A parallel space tracing algorithm is presented. It subdivides the scene into regions. These latter are distributed among the processors of an iPSC hypercube machine designed by Intel company. Each processor subdivides its own region into cells to accelerate the ray tracing algorithm. Processors communicate by means of messages. The pyramidal shape of the regions allows the deletion of the primary ray messages. A method of performing a roughly uniform load distribution is proposed.
An Expert System for Polyhedra Modelling
(Eurographics Association, 1988) Martin, Philippe; Martin, Dominique
Very often we wish to construct shapes according to some criteria, which are properties we want the object to possess. In this case explicit construction becomes an inadapted way of working. One would wish to obtain the result just by giving the desired properties. This is the approach we try to develop here, limiting the problem, for a start, to a special class of solids: the polyhedra. The aim of this study is to demonstrate the general principles which lead to a definition of solids through their properties, and not through an explicit construction. This leads us to the idea that giving a set of properties is a means to model solids, which allows us to talk about declarative modelling.
Fast Algorithm for Polygon Clipping with 3D Windows
(Eurographics Association, 1988) Burkert, Andreas; Noll, Stefan
Many applications which use 3D graphics, need 3D geometric modeling and hence polygon clipping against 3D Windows or general volumes. The disadvantages of existing clipping algorithms are that they are 2D, slow or produce incorrect results. This paper describes a new 3D clipping algorithm for concave polygons with one contour. The new algorithm is an extension to the algorithm of Liang and Barsky: The necessary condition for the appearance of a corner of the clipping rectangle in the output polygon is replaced by a necessary and sufficient condition and then extended to the three dimensional case. Another advantage of the presented algorithm is the the removal of degenerated edges. The algorithm is useful for implementing the draft international standards GKS-3D and PHIGS and also for 3D Window Systems.
Form-Factors for General Environments
(Eurographics Association, 1988) Shao, Ping-Pine; Peng, Qun-Sheng; Liang, You-Done
A new algorithm, based on the hemi-cube formulation, which calculates the form-factors required by the solution of the rendering equation, is presented. The concept of form-factors of the standard radiosity method is developed, In particular, the concept of specular form-factors is proposed. These new form-factors are also purely geometric terms describing the transfer of energy from one surface to another within a non-diffuse environment. The new form-factor is evaluated by numerical integrations based on the hemi-cube algorithm. The equations of the effective diffuse radiosity are presented and solved by numerical methods. The extension fully develops the characteristic of radiosity method and successfully solves the view-independent energy transfer in a general environment.
A Formal Specification of a Boundary Representation
(Eurographics Association, 1988) Baumann, Peter
Geometric modellers are used in a wide spectrum of applications in computer graphics. As many other applications use the generated internal representation of solids, semantic correctness is of special importance. On the other hand, the methodology of formal specification offers, in particular, the advantage of ensuring correctness by mathematical means. It is therefore a good idea to formally specify a geometric modeller. This paper describes an abstract data type defining a boundary representation. Special attention is paid to the operations for manipulating solids, i.e. the so-called Euler operations. The operation mfe (make face & edge) is used to show in detail how pre- and post-condition can be derived. Finally, mappings of this abstract data type onto implementations with different data models are discussed.

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