Volume 06 (1987)https://diglib.eg.org/handle/10.2312/172024-10-13T10:26:33Z2024-10-13T10:26:33Z1141Splines for EngineersOhlin, S.C.https://diglib.eg.org/handle/10.2312/egtp198710412022-03-28T11:54:49Z1987-01-01T00:00:00Zdc.title: Splines for Engineers
dc.contributor.author: Ohlin, S.C.
dc.description.abstract: This paper introduces the concept of interpolation consistency. It is claimed that this property is an essential one for splines that are intended for use in Computer Aided Design. Consistency is defined as the property of an interpolation algorithm that, if the given set of points is extended by any point on the interpolated curve, the algorithm applied to the extended set of points will yield exactly the same curve as before. A clear distinction is made between function interpolation, where y is a function of x, and curve interpolation, where x and y are Cartesian coordinates in the geometric plane. The class of consistent curve interpolating planear splines that corresponds to cubic function interpolation is discussed in some detail and includes the Cornu spiral, the lemniscate, and the tension-free mechanical spline. Next the class that corresponds to pentic function interpolation is considered, and an efficient algorithm is presented for the calculation of one such spline, a planar spline where the curvature is a cubic polynomial in the arclength. This algorithm produces curves where the curvature is, loosely speaking, as constant as possible. Some examples illustrating the desirable properties of this spline are given.
1987-01-01T00:00:00ZA New Algorithm for Contour-plottingBrinkkernper, SjaakHendriks, Harriehttps://diglib.eg.org/handle/10.2312/egtp198710382022-03-28T11:54:52Z1987-01-01T00:00:00Zdc.title: A New Algorithm for Contour-plotting
dc.contributor.author: Brinkkernper, Sjaak; Hendriks, Harrie
dc.description.abstract: A new algorithm for contour-plotting is introduced. The input function, tabulated or in a subroutine description, is approximated by an interpolation function. The contours of this approximating function are drawn piecewise on a subdivision of the given domain. The algorithm is based on the iterated solution of Initial Value Problems defined by applying the Implicit Function Theorem. Estimates on the dependence of the contourlines on the approximating function are presented using the method of gradient lines. Finally some examples are shown.
1987-01-01T00:00:00ZAn Intersection-Sensitive Hidden-Surface AlgorithmDevai, Ferenchttps://diglib.eg.org/handle/10.2312/egtp198710362022-03-28T11:54:49Z1987-01-01T00:00:00Zdc.title: An Intersection-Sensitive Hidden-Surface Algorithm
dc.contributor.author: Devai, Ferenc
dc.description.abstract: Given a set of pairwise disjoint planar polygonal faces with altogether N edges in the three-dimensional space. Let k be the number of intersection points of the projections of the edges in a projection plane, 0 < k < N(N-1)/2. An algorithm for the elimination of hidden surfaces in O((N+k)log N) time and O(N+k) space is proposed. If k is O(N), which is often the case in practice, the algorithm has O(N log N) expected time, regardless of the probability distribution of the input data. The constants of proportionality are low enough to make this algorithm of practical use. The method is a three-dimensional generalization of a two-dimensional scan-line algorithm, called the NlogN algorithm. A total order hide of faces is introduced. By determining the intersections of the projected edges, regions are designated within which visibility is unvaried. Then each region is visited, maintaining the total order hide, from which visible surfaces and rendering of partially transparent objects can be inferred.
1987-01-01T00:00:00ZA Fast Antialiasing Method with a Z-BufferGhazanfarpour, DjamchidPeroche, Bernardhttps://diglib.eg.org/handle/10.2312/egtp198710372022-03-28T11:54:51Z1987-01-01T00:00:00Zdc.title: A Fast Antialiasing Method with a Z-Buffer
dc.contributor.author: Ghazanfarpour, Djamchid; Peroche, Bernard
dc.description.abstract: This paper describes a new antialiasing method when a z-buffer is used. Good quality antialiasing is achieved in spite of unavoidable approximations. Compared to an ordinary z-buffer, only a little extra memory space and processing time are required. In particular, this fast method can be beneficial when used on a raster graphics system equipped with a hardware-implemented z-buffer. Our approach, however, offers appropriate treatment for certain problems left unsolved by previous methods.
1987-01-01T00:00:00ZInteraction Management in CAD Systems with History MechanismYamaguchi, YasushiKimura, FumihikoTen Hagen, Paul J. W.https://diglib.eg.org/handle/10.2312/egtp198710402022-03-28T11:54:51Z1987-01-01T00:00:00Zdc.title: Interaction Management in CAD Systems with History Mechanism
dc.contributor.author: Yamaguchi, Yasushi; Kimura, Fumihiko; Ten Hagen, Paul J. W.
dc.description.abstract: User friendliness is one of the unresolved problems in CAD systems. There are many possible directions for improving user friendliness. Understanding of the modeling process is one of the most important directions. It is natural for a user to describe the model in terms of its evolution. We call this concept model derivation. To construct and use model derivation, we propose a history mechanism which keeps and manipulates the history of the modeling process. The history mechanism manages high level interactions by introducing powerful symbolic computation to manipulate the history. Since the history representation is based on the operation's syntax and separated from the internal model representation, it is easy to apply the history mechanism to any modeling system which uses established techniques. Thus the system designer can easily introduce model derivation without reducing efficiency of the implementation.
1987-01-01T00:00:00ZDynamic Management of 3D ScenesHegron, Gerardhttps://diglib.eg.org/handle/10.2312/egtp198710392022-03-28T11:54:50Z1987-01-01T00:00:00Zdc.title: Dynamic Management of 3D Scenes
dc.contributor.author: Hegron, Gerard
dc.description.abstract: When simulating a moving observer or sensor in a 3D scene which contains a large number of objects, only the objects lying in the field of view or of interaction, named the local data base, have to be taken into account in order to decrease, at each step, computation time necessary for either image generation or various processings. This paper presents an algorithm which achieves the dynamic management of the local data base, that is to say which manages the set of objects which enter or leave the field of view of an observer (camera, sensor) during its displacement. This method consists, broadly, of the following two steps: a binary space partitioning of the 3D space is performed off-line from the object bounding boxes by means of planes perpendicular to the X, Y and Z axes and a subregion adjacency graph is created; the dynamic management of the local data base is achieved on-line by modelling the bounded bearing volume of the sensor by a cube of R "radius" (half-edge), and by using the adjacency graph, and inclusion and intersection criteria in order to exploit spatial and temporal coherences between each displacement. When the scene data base is very large, the dynamic management of the RAM memory can be done simultaneously by using this method reasoning from the bounding boxes of disjoined sub - scenes.
1987-01-01T00:00:00ZUnifying Vector and Polygon Algorithms for Scan Conversion and ClippingKilgour, AIistairhttps://diglib.eg.org/handle/10.2312/egtp198710282022-03-28T11:54:49Z1987-01-01T00:00:00Zdc.title: Unifying Vector and Polygon Algorithms for Scan Conversion and Clipping
dc.contributor.author: Kilgour, AIistair
dc.description.abstract: In both scan conversion and clipping, algorithm for dealing with polygons are generally presented independently of those for vectors, although many of the operations performed are similar. This paper shows how polygon algorithms for both problems can be developed from the corresponding vector algorithm. As well as yielding a unification at the conceptual level, this approach can lead to reduced code size in graphics system implementation, and produces polygon algorithms which are comparable in both robustness and efficiency with those previously presented.
1987-01-01T00:00:00ZThe Clockworks: An Object-Oriented Computer Animation SystemBreen, David E.Getto, Phillip H.Apodaca, Anthony A.Schmidt, Daniel G.Sarachan, Brion D.https://diglib.eg.org/handle/10.2312/egtp198710212022-03-28T11:54:49Z1987-01-01T00:00:00Zdc.title: The Clockworks: An Object-Oriented Computer Animation System
dc.contributor.author: Breen, David E.; Getto, Phillip H.; Apodaca, Anthony A.; Schmidt, Daniel G.; Sarachan, Brion D.
dc.description.abstract: The Clockworks is an object-oriented computer animation system developed at RPl's Center for Interactive Computer Graphics (CICG). The Clockworks has the ability to model and graphically simulate complex 3-D engineering processes, Its interactive capabilities also allow it be used as a design tool. Object-oriented concepts have been utilized in developing its high level architecture and its low level implementation. The Clockworks is defined as a collection of objects which communicate with the user and each other via messages. The actual implementation involved the creation of an object-oriented programming methodology using C and Unix. The complete system provides a rich research environment for exploring modelling, scripting and rendering. It also provides an interactive environment for design and a simulation environment for visual analysis of complex interacting structures.
1987-01-01T00:00:00ZDisplay of Solid Models with a Multi-Processor SystemJansen, Frederik W.Sutherland, Robert J.https://diglib.eg.org/handle/10.2312/egtp198710292022-03-28T11:54:50Z1987-01-01T00:00:00Zdc.title: Display of Solid Models with a Multi-Processor System
dc.contributor.author: Jansen, Frederik W.; Sutherland, Robert J.
dc.description.abstract: There is a growing need for fast high-quality display of solid objects. Recently-developed custom-VLSI hardware offers high-speed display but lacks the flexibility and processing power at the pixel level to sustain the calculations and filter operations needed for realistic reflection models, texture mapping and anti-aliasing. Multi-processor systems built with general-purpose components of relatively high capacity and moderate cost provide an alternative; they also offer higher performance than single processor systems but retain their flexibility. A CSG hidden-surface algorithm based on depth-buffering and image subdivision is presented which is suitable for use with such a multi-processor system.
1987-01-01T00:00:00ZViz: A Production System Based User Interface Management Systemvan Harmelen, MarkWilson, Stephanie M.https://diglib.eg.org/handle/10.2312/egtp198710262022-03-28T11:54:50Z1987-01-01T00:00:00Zdc.title: Viz: A Production System Based User Interface Management System
dc.contributor.author: van Harmelen, Mark; Wilson, Stephanie M.
dc.description.abstract: A production system based User Interface Management System (UIMS) is discussed. The UIMS, called Viz, has been designed and implemented in a windowed workstation environment, and (a) capitalises on the graphical facilities of the workstation while (b) being designed for both textual and graphical applications. The paper considers interaction, the appearance of Viz generated interfaces, and dialogue descriptions which parameterise Viz.
1987-01-01T00:00:00Z