EG1989Hamburg, Germanyhttps://diglib.eg.org/handle/10.2312/197https://diglib.eg.org/retrieve/e7c2ee47-3cfe-4f1a-83f3-25733cad4797/2024-08-03T09:49:13Z2024-08-03T09:49:13Z421Colour Section-https://diglib.eg.org/handle/10.2312/egtp198910412022-03-28T11:54:58Z1989-01-01T00:00:00Zdc.title: Colour Section
dc.contributor.author: -
1989-01-01T00:00:00ZGEO++ - A System for Both Modelling and DisplayWisskirchen, Peterhttps://diglib.eg.org/handle/10.2312/egtp198910302022-03-28T11:54:57Z1989-01-01T00:00:00Zdc.title: GEO++ - A System for Both Modelling and Display
dc.contributor.author: Wisskirchen, Peter
dc.description.abstract: We present a new concept for a graphics system which we call GEO++ . Apart from the manipulation of groups (structures in PHIGS-terminology), GEO++ permits a direct access to the tree structure required for display. With this concept we believe to have achieved a synthesis between the requirements of modelling in the sense of manipulation of building patterns and of display in the sense of editing individual objects (parts) on the screen.
1989-01-01T00:00:00ZSubdivisions of Surfaces and Generalized MapsLienhardt, Pascalhttps://diglib.eg.org/handle/10.2312/egtp198910332022-03-28T11:54:57Z1989-01-01T00:00:00Zdc.title: Subdivisions of Surfaces and Generalized Maps
dc.contributor.author: Lienhardt, Pascal
dc.description.abstract: The modeling of subdivisions of surfaces is of greatest interest in Geometric Modeling (in particular for Boundary Representation) , and many works deal with the definition of models, which enable the representation of closed, orientable subdivisions of surfaces, and with the definition of elementary operations, which can be applied to these models (Euler operators) . We study in this paper the notion of 2-dimensional generalized map (or 2-G-map), which make possible the definition of the topology of any subdivision of surface, orientable or not orientable, opened or closed ; reciprocally, the topology of any subdivision of any surface may be defined by a 2-G-map . Three characteristics are associated to any 2-G-map G (the most elementary being the number of boundaries, the most known being the genus ...), and can be directly computed on G . These characteristics define the subdivision of surface modelled by G (static classification of the subdivision) . We define also operations which can be applied to 2-G-maps . Any 2-G-map (and then any subdivision of surface) can be constructed by a sequence of operations . To these operations correspond variations of the characteristics associated to the 2-G-maps . These variations enable the control of the effect of an operation on the modelled subdivision (dynamic classification of the subdivision) . The notion of 2-G-map defines the different elements of a subdivision (vertex, edge, face, bound ary...) by using one unique kind of elements, in a rigorous and unambiguous manner. Data structures may be deduced from the notion of 2-G-map . These data structures make possible the representation of any subdivision of surface , in a way near to the well-known "windged-edge" data structure defined by B. Baumgart in [BA75] . The constraints of consistency about these data structures can be directly deduced from the definition of 2-G-maps . The set of the properties of 2-G-maps (rigour, consistency, possibility of static or dynamic classification) makes the greatest interest of the 2-G-maps, with respect to other models of subdivisions of surfaces used in Geometric Modeling .
1989-01-01T00:00:00Z2.5 Dimensional Graphics SystemsHerman, Ivanhttps://diglib.eg.org/handle/10.2312/egtp198910312022-03-28T11:54:57Z1989-01-01T00:00:00Zdc.title: 2.5 Dimensional Graphics Systems
dc.contributor.author: Herman, Ivan
dc.description.abstract: The outline of an extension of traditional 2D graphics systems is given. This extension is aimed at supporting a three dimensional application program, without incorporating full viewing into the general graphics system itself. The resulting system might be very advantageous for large application programs which have their own three dimensional facilities.
1989-01-01T00:00:00ZBlending Rational B-Spline SurfacesBardis, L.Patrikalakis, N.M.https://diglib.eg.org/handle/10.2312/egtp198910342022-03-28T11:54:58Z1989-01-01T00:00:00Zdc.title: Blending Rational B-Spline Surfaces
dc.contributor.author: Bardis, L.; Patrikalakis, N.M.
dc.description.abstract: A method for blendin non uniform rational B-spline surface patches, either open or periodic, is developed. he blending surface is expressed in terms of an integral, bicubic B-spline patch. The blend ensures position and normal vector continuity along linkage curves to within a specified accuracy. The linkage curves are either user-defined or are obtained by offsetting the intersection of the two patches using geodesics on each patch. An example illustrates the applicability of our method.
1989-01-01T00:00:00ZA Reference Model for the Visualisation of Multi-Dimensional DataBergeron, R. DanielGrinstein, Georges G.https://diglib.eg.org/handle/10.2312/egtp198910292022-03-28T11:54:58Z1989-01-01T00:00:00Zdc.title: A Reference Model for the Visualisation of Multi-Dimensional Data
dc.contributor.author: Bergeron, R. Daniel; Grinstein, Georges G.
dc.description.abstract: This paper presents a reference model for the development of systems for the visualization of multidimensional data. The purpose of the reference model is to build a conceptual basis for thinking about multi-dimensional visualization and for use in developing visualization environments. We describe the reference model in terms of the fundamental concepts of PHIGS (Programmer’s Hierarchical Interactive Graphics System), but extend those concepts to the representation of objects of arbitrary dimensionality.
1989-01-01T00:00:00ZVisualizing Curvature Discontinuities of Free-Form SurfacesPottmann, Helmuthttps://diglib.eg.org/handle/10.2312/egtp198910402022-03-28T11:54:58Z1989-01-01T00:00:00Zdc.title: Visualizing Curvature Discontinuities of Free-Form Surfaces
dc.contributor.author: Pottmann, Helmut
dc.description.abstract: A new method for the visualization of curvature discontinuities of free-form surfaces is presented. It is based upon an improvement and refinement of the well-known technique of displaying isophotes.
1989-01-01T00:00:00ZVariations on a Dither AlgorithmPins, MarkusHild, Hermannhttps://diglib.eg.org/handle/10.2312/egtp198910282022-03-28T11:54:59Z1989-01-01T00:00:00Zdc.title: Variations on a Dither Algorithm
dc.contributor.author: Pins, Markus; Hild, Hermann
dc.description.abstract: Mapping continuous-tone pictures into digital halftone pictures, i.e. 0/1-pictures, for printing purposes is a well explored technique. In this paper, one of these algorithms, the two-dimensional error-diffusion algorithm is extended to color pictures and animated pictures. The color picture algorithm is superior to existing algorithms by considering extreme color values as well as adjacent color values. The animation algorithm eliminates the noise created by the correct but varying pixel patterns generated by applying a single picture dithering algorithm on every frame. The power of the algorithms is demonstrated by experiments carried out on synthetic images generated by ray tracing.
1989-01-01T00:00:00ZAn Analysis of Modeling ClipO Bara, Robert M.Abi-Ezzi, Salimhttps://diglib.eg.org/handle/10.2312/egtp198910272022-03-28T11:55:00Z1989-01-01T00:00:00Zdc.title: An Analysis of Modeling Clip
dc.contributor.author: O Bara, Robert M.; Abi-Ezzi, Salim
dc.description.abstract: Modeling clip gives an application the ability to remove sections of an object in order to view internal detail. The clipping volume defied by modeling clip can be concave and disjoint, and is composed of a set of volumes that are specified in modeling coordinates. The modeling clip functionality has been included in the PHIGS specification [4], Some interesting peculiarities arise from the fact that most graphics pipelines (such as PHIGS) are algebraically based and that modeling clip regions are specified in modeling coordinates. One such peculiarity occurs when the transformation relating the coordinate system of the clip region to world coordinates is singular. A study on the algorithmic and architectural issues of implementing modeling clip is presented. The resulting algorithm to implement the modeling clip mechanism represents the clip volume as a pipeline of filters with each filter representing one of the sub-volumes. The method handles all of the sixteen possible set combinations between two regions in space. The effects of transformations on modeling clip have been examined, and has resulted in identifying when modeling clip can be efficiently performed in device coordinates as well as the cases when it can not. When handling singular modeling transformations, it is shown that it i
1989-01-01T00:00:00ZRepresenting Tolerance Information in Feature-Based Solid ModellingFalcidieno, BiancaFossati, Brunohttps://diglib.eg.org/handle/10.2312/egtp198910352022-03-28T11:54:59Z1989-01-01T00:00:00Zdc.title: Representing Tolerance Information in Feature-Based Solid Modelling
dc.contributor.author: Falcidieno, Bianca; Fossati, Bruno
dc.description.abstract: In this paper a system for defining dimensions and tolerances is presented which deals with the geometric representation of the objects in a coherent and compact way. This model is a combination of a hierarchical boundary model to represent geometry of the object with features and a relational graph model to encode dimensions and tolerances. In this way, the proposed model can be considered a ”product model” that, besides geometric and topological information about the feature components of a solid object, also codifies information about dimensions represented by relative positron operators connected to faces which are the primitive geometric entities of the object model. The method can automatically control the validity of the geometric and topological model of the object each tame that a new tolerance node is added to the structure or a tolerance constraint already existing is modified. In this case, it also translates changes in dimensional values into corresponding changes an geometry and topology.
1989-01-01T00:00:00Z