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Computer Graphics and Applications, IEEE

Issue 6 • Date Nov. 1990

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Displaying Results 1 - 8 of 8
  • A note on ray tracing mirages (comments and author's reply)

    Page(s): 10 - 12
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB)  

    The author comments on an article by M. Berger et al. (ibid., vol.10, no.3, p.36-41, 1990), which describes a model for forming a mirage. In particular, he makes some points regarding their interpretation of the model and their description of their implementation of a version of it. He points out that the primary bending agent in mirage formation is total reflection, not refraction, as Berger et al. suggest. This in turn indicates that a purely reflective model, without refraction might well be sufficient. The author asserts that this would be beneficial, as dispersive ray tracing is not particularly easy or inexpensive to implement, and it would obviate the statement by Berger et al. that the use of layers allows a digitized approach to the continuous spectrum. A response by M. Berger, essentially agreeing with the author, is included.<> View full abstract»

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  • A survey of shadow algorithms

    Page(s): 13 - 32
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    The various types of shadows are characterized. Most existing shadow algorithms are described, and their complexities, advantages, and shortcomings are discussed. Hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives are considered. For each type, shadow algorithms within various rendering techniques are examined. The aim is to provide readers with enough background and insight on the various methods to allow them to choose the algorithm best suited to their needs and to help identify the areas that need more research and point to possible solutions.<> View full abstract»

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  • Adaptive polygonalization of implicitly defined surfaces

    Page(s): 33 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (763 KB)  

    A method for finding an adaptive polygonal approximation of an implicitly defined surface is presented. For algebraic surfaces, the method yields an approximation guaranteed accurate to within some user-specified tolerance of the actual surface. This polygonalization can then be rendered using standard shaded polygon drawing techniques. A method for eliminating or improving the aspect ratios of the 'skinny' polygons that often arise in traditional polygonalization methods is also presented. This method has proved particularly useful in the creation of polygonalization for finite-element analysis.<> View full abstract»

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  • Ray tracing with polarization parameters

    Page(s): 44 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1244 KB)  

    Incorporating polarization parameters into the lighting model can enhance the physical realism of images rendered with a ray tracer. Polarization effects can be important in certain scenes, and the difference in rendering even simple scenes with and without proper treatment of polarization can be striking. All light waves possess a state of polarization, which changes almost every time light reflects off a material surface. A single reflection partially polarizes and may even completely polarize previously unpolarized light. Polarization influences the rendering of a scene because the reflected radiant intensity depends largely on the incident light waves's polarization state. E. Wolf's (1959) coherence matrix formalism of polarization has been incorporated into the Torrance-Sparrow reflectance model. This combination allows elegant quantitative derivations of the altered polarization state of light upon reflection in a ray tracer. Comparisons of identical scenes rendered with a conventional ray tracer and the ray tracer presented incorporating a polarization model show that the present method renders specular interobject reflections more accurately with respect to reflected radiance and color.<> View full abstract»

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  • A realistic lighting model for computer animators

    Page(s): 56 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1382 KB)  

    Because of the problems inherent in modeling the physics of light transmission, all lighting models used in computer graphics are approximations. Each model provides a different balance between image realism, model complexity, and runtime efficiency. A model that balances these factors and is easier than its predecessors for inexperienced animators to use is presented.<> View full abstract»

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  • A critical evaluation of PEX

    Page(s): 65 - 75
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    PEX, the PHIGS extension to the X Window System, is evaluated in the context of assumptions inherent in the PHIGS output, modeling, input, user interface, and system environment models. Problems not previously discussed arise when examining PEX this way. The problems not only pertain to the implementation of PEX, but also to implementing a 3-D library in a distributed windowing system in general. The University of Illinois PEX implementation serves as a reference to discuss the solutions proposed.<> View full abstract»

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  • Set models and Boolean operations for solids and assemblies

    Page(s): 76 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    Applications of solid modeling in computer-aided design, computer-aided manufacturing, and robotics, which often involve aggregates or assemblies of disconnected pieces, are addressed. Models for such assemblies must be subjected to some of the same operations as models for single parts. The mathematical basis of constructive solid geometry (CSG), the usual formalism in solid modelers, leads to difficulties in dealing with assemblies. An alternative CSG-like formalism based on open sets, in which both assemblies and connected pieces are modeled as point sets is presented. Consequently the same Boolean operations apply uniformly to connected pieces and assemblies.<> View full abstract»

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  • The ultimate design tool

    Page(s): 90 - 92
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    The author design tools from a tool user's point of view. The author considers the creative process and where design tools fit into that process. He considers pencil and paper as a tool and argues that they are better than computers as an ideation tool.<> View full abstract»

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IEEE Computer Graphics and Applications bridges the theory and practice of computer graphics.

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Editor-in-Chief
L. Miguel Encarnação
University of Iowa