EG1991Vienna, Austriahttps://diglib.eg.org/handle/10.2312/199https://diglib.eg.org/retrieve/fdaa7edb-a0d4-4010-9910-ce4fb6ee560d/2024-09-18T14:20:32Z2024-09-18T14:20:32Z401A Testbed for Image SynthesisTrumbore, BenLytle, WayneGreenberg, Donald P.https://diglib.eg.org/handle/10.2312/egtp199110352022-03-28T11:55:07Z1991-01-01T00:00:00Zdc.title: A Testbed for Image Synthesis
dc.contributor.author: Trumbore, Ben; Lytle, Wayne; Greenberg, Donald P.
dc.description.abstract: Image Synthesis research combines new ideas with existing techniques. A collection of software modules that provide such techniques is extremely useful for simplifying the development process. We describe the design and implementation of a new Testbed for Image Synthesis that provides such support. This Testbed differs from previous Testbeds in both its goals and its design decisions. The Testbed design addresses the problems of high model complexity, complicated global illumination algorithms and coarse grain parallel processing environments. The implementation is modular, portable and extensible. It allows for statistical comparison of algorithms and measurement of incremental image improvements, as well as quantitative comparison of Testbed images and light reflectance measured from physical models. The Testbed is designed to interface with any available modeling system. This compatibility was achieved through careful design of the data format that represents environments. The software modules of the Testbed are organized in a hierarchical fashion, simplifying application programming.
1991-01-01T00:00:00ZSolid-Interpolating Deformations: Construction and animation of PIPsKaul, AnilRossignac, Jarekhttps://diglib.eg.org/handle/10.2312/egtp199110372022-03-28T11:55:06Z1991-01-01T00:00:00Zdc.title: Solid-Interpolating Deformations: Construction and animation of PIPs
dc.contributor.author: Kaul, Anil; Rossignac, Jarek
dc.description.abstract: Computer programs that simulate the deformations of geometric shapes have played a key role in the increasing popularity of software tools for artistic animation. Previously published techniques for specifying and animating deformations are either limited in their domain or ill suited for interactive editing and visualization. This is because the effects of alterations performed by the animator on the model's parameters may not always be anticipated, and because realtime animation may only be produced by visualizing pre-computed sequences of 3D frames, which are obtained by a slow process and require vast amounts of storage. To support an interactive environment for animation design, we have developed a new, simple, and efficient animation primitive: a Parameterized Interpolating Polyhedron, or PIP for short. PIPs are easily specified and edited by providing their initial and final shapes, which may be any polyhedra, and need not have corresponding boundary elements. PIPs may be efficiently animated on standard graphic hardware because a PIP is a smoothly varying family of polyhedra bounded by faces that evolve with time. The faces have constant orientations and vertices that each move on a straight line between a vertex of the initial shape and a vertex of the final one. The cost of recalculating the time dependant information of a PIP is small in comparison to the display cost. We provide simple and efficient algorithms, based on Minkowski sum operations, for computing PIPs. When both the initial and final shapes are convex, the resulting faces are the true boundary of the deforming object, otherwise subsets of the resulting faces may lie inside the object. In both cases, correct images are automatically generated using standard depth-buffer hardware. The tools we have developed are convenient for interactively designing animation sequences that show the metamorphosis of 3D shapes. They may also be used to simulate the geometric effect of a variety of manufacturing operations, and for interactively selecting the optimal compromise between two or more shapes. They are being integrated in the LAMBADA design and inspection environment for animated assemblies, where deformations and rigid-body motions may be easily combined and synchronized using a hierarchical representation.
1991-01-01T00:00:00ZC 2 Gregory patchMiuraa, Kenjiro TakaiWangb, Kuo-Kinghttps://diglib.eg.org/handle/10.2312/egtp199110362022-03-28T11:55:09Z1991-01-01T00:00:00Zdc.title: C 2 Gregory patch
dc.contributor.author: Miuraa, Kenjiro Takai; Wangb, Kuo-King
dc.description.abstract: G² continuity of free-form surfaces is sometimes very important in engineering applications. The conditions for G2 continuity between two Bezier patches has been studied and methods developed to ensure such continuity. However, certain restrictions on the shapes of such patches arise within the Bezier-patch formulation. The Gregory patch is a kind of free-form surface patch which is an extension of the Bezier patch such that cross-boundary first derivatives can be specified without restrictions on the compatibility condition. In this paper, we extend the idea of the Gregory patch and develop a formulation for the C² Gregory patch. The properties of the C² Gregory patch are discussed as well as its connection with a Bezier patch and a G² continuous interpolation method based upon such patches.
1991-01-01T00:00:00ZVariable-Radius Blending by Using Gregory Patches in Geo- metric ModelingHarada, T.Konnoa, K.Chiyokura, H.https://diglib.eg.org/handle/10.2312/egtp199110382022-03-28T11:55:08Z1991-01-01T00:00:00Zdc.title: Variable-Radius Blending by Using Gregory Patches in Geo- metric Modeling
dc.contributor.author: Harada, T.; Konnoa, K.; Chiyokura, H.
dc.description.abstract: Blending surfaces, which connect two curved surfaces smoothly, often appear in geometric modeling. Many of the blending surfaces are variable-radius blends. Variableradius blending surfaces are very important in the design process, but it is difficult to generate such surfaces with existing geometric modelers. This paper proposes a new method to generate variable-radius blends. Instead of the popular rolling-ball method, we adopt “sliding-circle” blending. A circle slides on two curved surfaces so that the circle is perpendicular to a specified control curve, and its trajectory defines a blending surface. A variable-radius blend can be generated if the radius of the circle changes smoothly. In our method, the shape of the variable-radius blend is represented by Gregory patches. The Gregory patch is an extension of a Bezier patch and two Gregory patches can be connected together with tangential continuity. The characteristics of the Gregory patch are suitable for representing blending surfaces with geometric modelers.
1991-01-01T00:00:00ZTime Complexity of Monte Carlo RadiosityShirley, Peterhttps://diglib.eg.org/handle/10.2312/egtp199110342022-03-28T11:55:10Z1991-01-01T00:00:00Zdc.title: Time Complexity of Monte Carlo Radiosity
dc.contributor.author: Shirley, Peter
dc.description.abstract: The time complexity of Monte Carlo radiosity is discussed, and a proof is given that the expected number of rays required to produce a satisfactory radiosity solution for N zones is O(N). A satisfactory solution is defined to be one in which the variance of radiance estimates for each zone is below a predefined threshold. The proof assumes that the radiance is bounded, and the area ratio of the largest to smallest zone is bounded.
1991-01-01T00:00:00ZMOVE-X: A System for Combining Video Films and Computer AnimationErtl, GerhardMüller-Seelich, HeimoTabatabai, Behnamhttps://diglib.eg.org/handle/10.2312/egtp199110222022-03-28T11:55:06Z1991-01-01T00:00:00Zdc.title: MOVE-X: A System for Combining Video Films and Computer Animation
dc.contributor.author: Ertl, Gerhard; Müller-Seelich, Heimo; Tabatabai, Behnam
dc.description.abstract: The objective of the presented project was to implement a system for the visualization of buildings. The system is used to create movies of buildings and interior rooms before they are built. For a realistic impression of a building it is very important to show its actual environment in the film. The designed software solution permits to create films where real images of the environment are overlaid with computer generated images of the building. In order to overlay the video film with computer generated images, it is necessary to compute the exact position, the viewing direction and the adjustment of the zoom for every frame of the film. These parameters can be calculated from the video images. This paper describes the algorithms used to calculate the camera parameters and to track passpoints in a sequence of video images. Some problems resulting from interlaced video and low resolution are discussed in detail. The rendering techniques used to generate images of the new building are also discussed.
1991-01-01T00:00:00ZShading with Area Light SourcesTanaka, ToshimitsuTakahashi, Tokiichirohttps://diglib.eg.org/handle/10.2312/egtp199110172022-03-28T11:55:07Z1991-01-01T00:00:00Zdc.title: Shading with Area Light Sources
dc.contributor.author: Tanaka, Toshimitsu; Takahashi, Tokiichiro
dc.description.abstract: This paper derives a shading model for area light sources which covers both diffuse and specular reflection. The shading model assumes ideally diffuse polygonal light sources and uses Phong’s reflection model. The model can accurately integrate the intensities of diffuse and specular reflection without simulating an area light source as an array of point light sources. To simplify the reflection integration, each light source is transformed from the Cartesian coordinate system into the polar system. The light source is projected onto a unit sphere and then triangulated along great circles of the unit sphere. Finally, the integration value is calculated by polynomial approximation. Since our method can accurately integrate both diffuse and specular reflection, it can generate images that are more photorealistic than conventional methods. Because point light sources are not employed, highlight roughness is completely suppressed. Several images are presented that show the advantages of our method.
1991-01-01T00:00:00ZAn Algorithm of hidden Surface Removal based on Frame-To- Frame CoherenceTost, Danielehttps://diglib.eg.org/handle/10.2312/egtp199110192022-03-28T11:55:06Z1991-01-01T00:00:00Zdc.title: An Algorithm of hidden Surface Removal based on Frame-To- Frame Coherence
dc.contributor.author: Tost, Daniele
dc.description.abstract: Frame-to-frame coherence capitalizes on the continuity existing between successive frames in order to predict the visibility of the scene at a given instant on the basis of its visibility at the previous instant. It is shown that all the algorithms based on frame-to-frame coherence share a common model and involve similar data structures. This model is used as a framework for a discussion of possible frame-to-frame coherence algorithms. A specific solution based on a partition of the image space into several 2-D regions is then presented. A temporal graph of the depth priority relationship of the objects is first computed in a pre-process along with a temporal BSP tree of each object. In the first frame a total traversal of both data structures is required in order to establish the priority list of the faces of the scenes. In successive frames, the priority list is easily updated with partial traversals and with no geometrical computations. The complexity of the proposed algorithm is discussed. Some examples are presented with comments on the results of their implementation.
1991-01-01T00:00:00ZTimewarps: A Temporal Reparameterization Paradigm for Parametric AnimationSmith, JeffDrewery, Karinhttps://diglib.eg.org/handle/10.2312/egtp199110302022-03-28T11:55:06Z1991-01-01T00:00:00Zdc.title: Timewarps: A Temporal Reparameterization Paradigm for Parametric Animation
dc.contributor.author: Smith, Jeff; Drewery, Karin
dc.description.abstract: The ability to reparameterize the temporal axis in an animated sequence is a powerful and underexplored tool. Timewarps are described as extensions to previous work and the advantages of this tool are outlined. Timewarps allow an animator to progressively refine the timing of all or part of an animation. Problems inherent to this new concept were brought to light by the authors' implementation and are described in terms of both user interface and development issues. Solutions are discussed and directions for further study are outlined.
1991-01-01T00:00:00ZInteractive Conformance Testing for PHIGSCugini, John V.https://diglib.eg.org/handle/10.2312/egtp199110262022-03-28T11:55:06Z1991-01-01T00:00:00Zdc.title: Interactive Conformance Testing for PHIGS
dc.contributor.author: Cugini, John V.
dc.description.abstract: Conformance testing for the Programmer’s Hierarchical Interactive Graphics System (PHIGS) standard presents certain novel difficulties, especially the indirect effect of many functions, and the inaccessibility to the program of visual effects. The PHIGS Validation Tests (PVT) incorporate several innovative design features in order to address these difficulties. The model of deductive inference suggests ways to organize a system as logically complex as the PVT. This complexity makes the use of certain database concepts quite valuable in allowing users to navigate within the system. The problem of inaccessible effects can be addressed by careful design of the user interface, so as to minimize the subjectivity and operational difficulty inherent in testing such features. Subjectivity is minimized by posing short simple questions to the operator, in which the expected answer is randomized. Several design features enhance ease of use, including a customizable interface, self-explanatory displays, and automatic capture of results.
1991-01-01T00:00:00Z