EG1988

Permanent URI for this community

https://diglib.eg.org/handle/10.2312/196

Browse

Now showing 1 - 20 of 41

Free-Form Surfaces Modeling by Evolution Simulation
(Eurographics Association, 1988) Lienhardt, Pascal
We present in this paper a procedural method for modeling free-form, planar surfaces subdivisions, which allows simulating evolutions of such subdivisions. This method is founded on the common principles deduced from corpuscular phenomena modeling method (particle systems), and method for vegetal trees modeling by simulation of evolution. These principles are : - use of a discrete model, which is a set of basic elements, from which time discretization is deduced, -proper activity of basic elements; these methods consists in simulating the behaviour of these elements; - characterization of modelled object evolution, which is achieved by "functions" associated to basic elements; - priority of topology over geometry. A surface is defined as a set of surface elements, supported by a rooted, planar tree. A surface is initially reduced to a point. Surface evolution characterization and control are exclusively exerted through this tree. This method is applied to image synthesis and animation of natural shapes, especially vegetal shapes.
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.
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.
G1 Smoothing Solid Objects by Bicubic Bezier Patches
(Eurographics Association, 1988) Liang, Youdong; Ye, Xiuzi; Fang, Shiaofen
A general and unified method is presented for generating a wide range of 3D objects by smoothing the vertices and edges of a given polyhedron with arbitrary topology using bicubic Bezier patches. The common solution to the compatibility equations of geometric continuity between two Bezier patches is obtained and employed as the foundation of this new method such that this new solid and surface model is reliable and compatible with the solid modeling and surface modeling system in the most common use. The new method has been embeded in an algorithm supported by our newly developed solid modeling system MESSAGE. The performance and implementation of this new algorithm show that it is efficient, flexible and easy to manipulate.
A Procedural System for the Definition and Storage of Technical Drawings in Parametric Form
(Eurographics Association, 1988) Cugini, U.; Folini, F.; Vicini, I.
The construction of a truly USER-FRIENDLY CAD system requires the acquisition and management of a tremendous amount of information which cannot be. and must not be. directly requested from the user, but which has to be obtained by intelligently interpreting the sequence of operations performed by him. The system described here is out forward as a USERFRIENDLY tool for the definition. storage and modification of technical drawings in parametric form. The system that has been implemented (GIPS Graphic Interactive Parametric System) assists the user during the steps of definition and modification. taking advantage of the abiIity to interpret the procedure the user follows in describing the object he wants to design.
A System for Graphical Interaction on Parametrized Models
(Eurographics Association, 1988) Van Emmerik , Maarten J.G.M.
A system that enables the definition of parametrized solid models by means of graphical interaction is presented. The position, orientation and dimensions of primitive volumes for Constructive Solid Geometry (CSG) are determined by a number of control points. All control points are linked to nodes in a tree of local coordinate systems. The relations between control points is therefore determined by the relations of the nodes in this geometric tree. The user can create nodes and define geometric relations between them by graphical interaction on the geometric tree. With the system described in this paper, it is possible to define relations
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.
Optimal Texture Mapping
(Eurographics Association, 1988) De Ma, Song; Lin, Hong
Texture mapping is one of the most important techniques for highquality image synthesis. It can enhance immensely the visual richness of raster-scan images. We address in this paper the problem of mapping planar texture pattern onto arbitrarily curved surfaces. It is well known that such a mapping will inevitably produce distortion for any undevelopable surface. Although many techniques for texture mapping have been presented in the literature [1], to our knowledge, no general method existed which could control or minimize this distortion. We present in this paper a new method for texture mapping. The main idea is to develop the given curved surface approximately on a two-dimensional plane using an approximate locally isometric mapping while minimizing the distortion by an optimization technique. Our experience has shown that by using this technique, one can reduce considerably the distortion and thus improve the quality of the generated images.
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.
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.
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.
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.
Tools for Efficient Photo-Realistic Computer Animation
(Eurographics Association, 1988) Stößer, Achim; Schmitt, Alfred; Neidecker, Burkhard; Müller, Heinrich; Maus, Thomas; Leister, Wolfgang
The goal of the project “Occursus Cum Novo” was to generate a complex photo-realistic animation of nontrivial length in reasonable time at reasonable cost. Photographic realism comprises complex geometric models as well as the implementation of several optical effects. Both can be achieved by simulation. Simulations guaranteeing high quality, as ray tracing does for rendering, are known to be very time consuming. They require the design of powerful data structures and algorithms taking the abilities of todays hardware into account. The first part of this paper is devoted to rendering, here carried out by the raytracing method. An organizing scheme for a network of work stations is described which enabled us to generate 5-minutes of raytraced animation within 2 months without affecting any regular user of the work stations. The second part is devoted to the simulative modeling tools applied in “Occursus Cum Novo”. The recursive generator WAXI and a motion simulator METAMORPHOSIS are described to some detail. The results of the project are of general interest since they show a way leading to efficient high quality photo-realistic animation synthesis in the future.
Towards a System for Exploring the Universe of Polyhedral Shapes
(Eurographics Association, 1988) Colin, Christian
It is often easier to model a shape by giving its properties rather than describing it explicitly. Thus, we are interested in methods which allow us to create shapes automatically by only giving a set of properties. We propose a certain number of thoughts on the creation of objects achieved by the gluing together of elementary polyhedra. The formal approach that we develop is based on an exploration of the universe of polyhedral shapes. We also discuss techniques to automatically compute viewpoints, which emphasize the properties of the structures which have been created. These methods are one of the advantages of such a modeling.
A Simple Spectral Approach to Stochastic Modelling for Natural Objects
(Eurographics Association, 1988) Anjyo, Ken-ichi
Stochastic modeling has been widely used in computer graphics to depict natural objects or phenomena. Various techniques are available, depending on what object is to be represented and what extent of realism to be achieved. This paper presents a simple approach to stochastic spectral synthesis for producing a large range of natural objects and scenes at low computational cost. By considering a wide class of power spectra, the method can provide twodimensional stochastic models for various objects, involving terrains, clouds and sea waves. Moreover, some functional operations and parameters for the models are introduced, which can make the models more flexible in describing a three-dimensional complex scene.
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.
Liberation from Rectangles: A Tiling Method for Dynamic Modification of Objects on Raster Displays
(Eurographics Association, 1988) Slater, Mel; Davison, Allan; Smith, Mark
When graphics objects (also called segments) are used on raster display hardware, problems arise because of the mismatch between the high level requirements of object manipulation, and the low level representation from which the image is refreshed. This paper describes a tiling algorithm which provides a solution to the problems of damage repair and hit detection. In particular methods for handling object priority are discussed and experimental results showing the performance of the algorithm for a number of cases are presented.
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.
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.
A Method for Providing Full Interactive Control of the Shape of 3-D Curves and Surfaces
(Eurographics Association, 1988) Cros, Frederic; Brock, Philip J.
This paper presents a new method for providing an interactive local control on 3-D curves and surfaces. The possibility of interacting directly on the vector tangent to the curve at each control point (e.g. changing its magnitude and direction) gives the user a more intuitive control for shaping a curve than if he has to manipulate "abstract" parameters (like bias or tension). This technique is based on the use of Cardinal-splines and can also provide a means to obtain local control on surfaces.

Browse

Browsing EG1988 by Issue Date

Results Per Page

Sort Options