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CumInCAD is a Cumulative Index about publications in Computer Aided Architectural Design
supported by the sibling associations ACADIA, CAADRIA, eCAADe, SIGraDi, ASCAAD and CAAD futures

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_id	6733
authors	Bettels, Juergen and Myers, David R.
year	1986
title	The PIONS Graphics System
source	IEEE Computer Graphics and Applications. July, 1986. vol. 6: pp. 30-38 : col. ill. includes a short bibliography
summary	During 1979, CERN began to evaluate how interactive computer graphics displays could aid the analysis of high-energy physics experiments at the new Super Proton Synchrotron collider. This work led to PIONS, a 3D graphics system, which features the ability to store and view hierarchical graphics structures in a directed-acyclic-graph database. It is possible to change the attributes of these structures by making selections on nongraphical information also stored in the database. PIONS is implemented as an object-oriented message-passing system based on SmallTalk design principles. It supports multiple viewing transformations, logical input devices, and 2D and 3D primitives. The design allows full use to be made of display hardware that provides dynamic 3D picture transformation
keywords	visualization, computer graphics, database, systems, modeling
series	CADline
last changed	2003/06/02 13:58

_id	af53
authors	Boyer, E. and Mitgang, L.
year	1996
title	Building community: a new future for architecture education and practice
source	Carnegie Foundation for the Advancement of Teaching
summary	Internships, before and after graduation, are the most essential link connecting students to the world of practice. Yet, by all accounts, internship is perhaps the most troubled phase of the continuing education of architects. During this century, as architectural knowledge grew more complex, the apprenticeship system withered away and schools assumed much of the responsibility for preparing architects for practice. However, schools cannot do the whole job. It is widely acknowledged that certain kinds of technical and practical knowledge are best learned in the workplace itself, under the guidance of experienced professionals. All state accrediting boards require a minimum period of internship-usually about three years-before a person is eligible to take the licensing exam. The National Council of Architectural Registration Boards (NCARB) allows students to earn up to two years of work credit prior to acquisition of an accredited degree. The Intern Development Program (IDP), launched by NCARB and the American Institute of Architects in 1979, provides the framework for internship in some forty states. The program was designed to assure that interns receive adequate mentoring, that experiences are well-documented, and that employers and interns allocate enough time to a range of educational and vocational experiences to prepare students for eventual licensure. As the IDP Guidelines state, "The shift from school to office is not a transition from theory to pragmatism. It is a period when theory merges with pragmatism.... It's a time when you: apply your formal education to the daily realities of architectural practice; acquire comprehensive experience in basic practice areas; explore specialized areas of practice; develop professional judgment; continue your formal education in architecture; and refine your career goals." Whatever its accomplishments, however, we found broad consensus that the Intern Development Program has not, by itself, solved the problems of internship. Though we found mutually satisfying internship programs at several of the firms we visited or heard about around the country, at many others interns told us they were not receiving the continuing education and experience they needed. The truth is that architecture has serious, unsolved problems compared with other fields when it comes to supplying on-the-job learning experiences to induct students into the profession on a massive scale. Medicine has teaching hospitals. Beginning teachers work in actual classrooms, supported by school taxes. Law offices are, for the most part, in a better financial position to support young lawyers and pay them living wages. The architecture profession, by contrast, must support a required system of internship prior to licensure in an industry that has neither the financial resources of law or medicine, the stability and public support of teaching, nor a network of locations like hospitals or schools where education and practice can be seamlessly connected. And many employers acknowledged those problems. "The profession has all but undermined the traditional relationship between the profession and the academy," said Neil Frankel, FAIA, executive vice president of Perkins & Will, a multinational firm with offices in New York, Chicago, Washington, and London. "Historically, until the advent of the computer, the profession said, 'Okay, go to school, then we in the profession will teach you what the real world is like.' With the coming of the computer, the profession needed a skill that students had, and has left behind the other responsibilities." One intern told us she had been stuck for months doing relatively menial tasks such as toilet elevations. Another intern at a medium-sized firm told us he had been working sixty to seventy hours per week for a year and a half. "Then my wife had a baby and I 'slacked off' to fifty hours. The partner called me in and I got called on the carpet for not working hard enough." "The whole process of internship is being outmoded by economics," one frustrated intern told us. "There's not the time or the money. There's no conception of people being groomed for careers. The younger staff are chosen for their value as productive workers." "We just don't have the best structure here to use an intern's abilities to their best," said a Mississippi architect. "The people who come out of school are really problems. I lost patience with one intern who was demanding that I switch him to another section so that he could learn what he needed for his IDP. I told him, 'It's not my job to teach you. You are here to produce.'" What steps might help students gain more satisfying work opportunities, both during and after graduation?
series	other
last changed	2003/04/23 15:14

_id	ga0015
id	ga0015
authors	Daru, R., Vreedenburgh, E. and Scha, R.
year	2000
title	Architectural Innovation as an evolutionary process
source	International Conference on Generative Art
summary	Traditionally in art and architectural history, innovation is treated as a history of ideas of individuals (pioneers), movements and schools. The monograph is in that context one of the most used forms of scientific exercise. History of architecture is then mostly seen as a succession of dominant architectural paradigms imposed by great architectural creators fighting at the beginning against mainstream establishment until they themselves come to be recognised. However, there have been attempts to place architectural innovation and creativity in an evolutionary perspective. Charles Jencks for example, has described the evolution of architectural and art movements according to a diagram inspired by ecological models. Philip Steadman, in his book "The Evolution of Designs. Biological analogy in architecture and the applied arts" (1979), sketches the history of various biological analogies and their impact on architectural theory: the organic, classificatory, anatomical, ecological and Darwinian or evolutionary analogies. This last analogy "explains the design of useful objects and buildings, particularly in primitive society and in the craft tradition, in terms of a sequence of repeated copyings (corresponding to inheritance), with small changes made at each stage ('variations'), which are then subjected to a testing process when the object is put into use ('selection')." However, Steadman has confined his study to a literature survey as the basis of a history of ideas. Since this pioneering work, new developments like Dawkins' concept of memes allow further steps in the field of cultural evolution of architectural innovation. The application of the concept of memes to architectural design has been put forward in a preceding "Generative Art" conference (Daru, 1999), showing its application in a pilot study on the analysis of projects of and by architectural students. This first empirical study is now followed by a study of 'real life' architectural practice. The case taken has a double implication for the evolutionary analogy. It takes a specific architectural innovative concept as a 'meme' and develops the analysis of the trajectory of this meme in the individual context of the designer and at large. At the same time, the architect involved (Eric Vreedenburgh, Archipel Ontwerpers) is knowledgeable about the theory of memetic evolution and is applying a computer tool (called 'Artificial') together with Remko Scha, the authoring computer scientist of the program who collaborates frequently with artists and architects. This case study (the penthouse in Dutch town planning and the application of 'Artificial') shall be discussed in the paper as presented. The theoretical and methodological problems of various models of diffusion of memes shall be discussed and a preliminary model shall be presented as a framework to account for not only Darwinian but also Lamarckian processes, and for individual as well as collective transmission, consumption and creative transformation of memes.
keywords	evolutionary design, architectural innovation, memetic diffusion, CAAD, penthouses, Dutch design, creativity, Darwinian and Lamarckian processes
series	other
more	http://www.generativeart.com/
last changed	2003/08/07 17:25

_id	c584
authors	Gerzso, Miguel J.
year	1979
title	Spacemaker : A Computer Language for Modelling Architectural Physical Form
source	Application of Computers in Architecture, Building Design and Urban Planning, International Conference Proceedings. 1979. pp. 573-582 : ill. includes bibliography
summary	The paper describes a modeling technique of architectural form. The technique is divided into two parts. A diagrammatic production system and a computer language. The production notation serves as a representation of underlying organization of building groups. The computer language -- SPACEMAKER -- facilitates the coding of such rules for computer programming. The particular version of the diagrammatic production system as presented first began by attempting to apply two picture grammars to architectural problems. The first effort was based on PDL developed by Allen Shaw and was called SNARQ I and the second one grew out of work done by Yun-chung Cho and was called SNARQ II. A few years later, these notations evolved into the notation presented after adapting ideas from A. Lindenmeyer. Numerous models of architectural systems were then constructed
keywords	architecture, languages, modeling
series	CADline
last changed	2003/06/02 13:58

_id	8e4d
authors	Hartley, P.J. and Judd, C.J.
year	1979
title	Curve and Surface Representations for Bezier B-spline Systems
source	1979? pp. 226- 236 : ill. includes bibliography
summary	The Bezier approach to the computer-aided design of surfaces, using interactive design of curves to construct surface sections, can be implemented using spline curves just as well as the original polynomial curves, and with some advantages. In the paper, some problems are considered that arise when a Bezier system is formulated and describe possible solutions for a spline-based system
keywords	curves, representation, CAD, curved surfaces, B-splines, Bezier,
series	CADline
last changed	2003/06/02 13:58

_id	2ccd
authors	Kalisperis, Loukas N.
year	1994
title	3D Visualization in Design Education
doi	https://doi.org/10.52842/conf.acadia.1994.177
source	Reconnecting [ACADIA Conference Proceedings / ISBN 1-880250-03-9] Washington University (Saint Louis / USA) 1994, pp. 177-184
summary	It has been said that "The beginning of architecture is empty space." (Mitchell 1990) This statement typifies a design education philosophy in which the concepts of space and form are separated and defined respectively as the negative and positive of the physical world, a world where solid objects exist and void-the mere absence of substance-is a surrounding atmospheric emptiness. Since the beginning of the nineteenth century, however, there has been an alternative concept of space as a continuum: that there is a continuously modified surface between the pressures of form and space in which the shape of the space in our lungs is directly connected to the shape of the space within which we exist. (Porter 1979). The nature of the task of representing architecture alters to reflect the state of architectural understanding at each period of time. The construction of architectural space and form represents a fundamental achievement of humans in their environment and has always involved effort and materials requiring careful planning, preparation, and forethought. In architecture there is a necessary conversion to that which is habitable, experiential, and functional from an abstraction in an entirely different medium. It is often an imperfect procedure that centers on the translation rather than the actual design. Design of the built environment is an art of distinctions within the continuum of space, for example: between solid and void, interior and exterior, light and dark, or warm and cold. It is concerned with the physical organization and articulation of space. The amount and shape of the void contained and generated by the building create the fabric and substance of the built environment. Architecture as a design discipline, therefore, can be considered as a creative expression of the coexistence of form and space on a human scale. As Frank Ching writes in Architecture: Form, Space, and Order, "These elements of form and space are the critical means of architecture. While the utilitarian concerns of function and use can be relatively short lived, and symbolic interpretations can vary from age to age, these primary elements of form and space comprise timeless and fundamental vocabulary of the architectural designer." (1979)
series	ACADIA
email
last changed	2022/06/07 07:52

_id	98bd
authors	Pea, R.
year	1993
title	Practices of Distributed Intelligence and Designs for Education
source	Distributed Cognitions, edited by G. Salomon. New York, NY: CambridgeUniversity Press
summary	v Knowledge is commonly socially constructed, through collaborative efforts... v Intelligence may also be distributed for use in designed artifacts as diverse as physical tools, representations such as diagrams, and computer-user interfaces to complex tasks. v Leont'ev 1978 for activity theory that argues forcibly for the centrality of people-in-action, activity systems, as units of analysis for deepening our understanding of thinking. v Intelligence is distributed: the resources that shape and enable activity are distributed across people, environments, and situations. v Intelligence is accomplished rather than possessed. v Affordance refers to the perceived and actual properties of a thing, primarily those functional properties that determine how the thing could possibly be used. v Norman 1988 on design and psychology - the psychology of everyday things" v We deploy effort-saving strategies in recognition of their cognitive economy and diminished opportunity for error. v The affordances of artifacts may be more or less difficult to convey to novice users of these artifacts in the activities to which they contribute distributed intelligence. v Starts with Norman's seven stages of action Ø Forming a goal; an intention § Task desire - clear goal and intention - an action and a means § Mapping desire - unable to map goal back to action § Circumstantial desire - no specific goal or intention - opportunistic approach to potential new goal § Habitual desire - familiar course of action - rapidly cycle all seven stages of action v Differentiates inscriptional systems from representational or symbol systems because inscriptional systems are completely external, while representational or symbol systems have been used in cognitive science as mental constructs. v The situated properties of everyday cognition are highly inventive in exploiting features of the physical and social situation as resources for performing a task, thereby avoiding the need for mental symbol manipulations unless they are required by that task. v Explicit recognition of the intelligence represented and representable in design, specifically in designed artifacts that play important roles in human activities. v Once intelligence is designed into the affordances properties of artifacts, it both guides and constrains the likely contributions of that artifact to distributed intelligence in activity. v Culturally valued designs for distributed intelligence will change over time, especially as new technology becomes associated with a task domain. v If we treat distributed intelligence in action as the scientific unit of analysis for research and theory on learning and reasoning... Ø What is distributed? Ø What constraints govern the dynamics of such distributions in different time scales? Ø Through what reconfigurations of distributed intelligence might the performance of an activity system improve over time? v Intelligence is manifest in activity and distributed in nature. v Intelligent activities ...in the real world... are often collaborative, depend on resources beyond an individual's long-term memory, and require the use of information-handling tools... v Wartofsky 1979 - the artifact is to cultural evolution what the gene is to biological evolution - the vehicle of information across generations. v Systems of activity - involving persons, environment, tools - become the locus of developmental investigation. v Disagrees with Salomon et al.'s entity-oriented approach - a language of containers holding things. v Human cognition aspires to efficiency in distributing intelligence - across individuals, environment, external symbolic representations, tools, and artifacts - as a means of coping with the complexity of activities we often cal "mental." "
series	other
last changed	2003/04/23 15:14

_id	0424
authors	Uno, Sakae and Matsuka, Hido
year	1979
title	A General Purpose Graphic System for Computer Aided Design
source	SIGGRAPH '79 Conference Proceedings. August, 1979. vol. 13 ; no. 2: pp. 25-32 : ill. some col. includes bibliography
summary	The paper describes the experimental Advanced Integrated Designer's Activity Support (A-IDAS) system that is intended to be a base for a total engineering system rather than a pure graphic system. The system provides a database in which graphic data, geometric data and engineering data are stored in a relational data model. It also provides a graphic management facility which can manipulate not only pictures drawn with lines but those drawn as areas. Areas are represented by crosshatched lines or color. With this experimental system, it has been found that one can develop an engineering system having fairly general purpose capabilities
keywords	CAD, computer graphics, engineering, relational database, drafting, user interface
series	CADline
last changed	2003/06/02 13:58

_id	f42f
authors	Baer, A., Eastman, C. and Henrion, M.
year	1979
title	Geometric modeling: a survey
source	Computer Aided Design; 11: 253
summary	Computer programs are being developed to aid the design of physical systems ranging from individual mechanical parts to entire buildings or ships. These efforts highlight the importance of computer models of three dimensional objects. Issues and alternatives in geometric modelling are discussed and illustrated with comparisons of 11 existing modelling systems, in particular coherently-structured models of polyhedral solids where the faces may be either planar or curved. Four categories of representation are distinguished: data representations that store full, explicit shape information; definition languages with which the user can enter descriptions of shapes into the system, and which can constitute procedural representations; special subsets of the information produced by application programs; and conceptual models that define the logical structure of the data representation and/or definition language.
series	journal paper
last changed	2003/04/23 15:14

_id	60d4
authors	Baer, A., Eastman, C.M. and Henrion, M.
year	1979
title	Geometric Modeling : a Survey
source	business Press. September, 1979. vol. 11: pp. 253-271 : ill. includes bibliography
summary	Computer programs are being developed to aid the design of physical systems ranging from individual mechanical parts to entire buildings or ships. These efforts highlight the importance of computer models of three dimensional objects. Issues and alternatives in geometric modeling are discussed and illustrated with comparisons of 11 existing modelling systems, in particular coherently-structured models of polyhedral solids where the faces may be either planar or curved. Four categories of representation are distinguished: data representations that store full, explicit shape information; definition languages with which the user can enter description of shapes into the system, and which can constitute procedural representations; special subsets of the information produced by application programs; and conceptual models that define the logical structure of the dada representation and/or definition language
keywords	solid modeling, B-rep, CSG, languages, CAD, programming, data structures, boolean operations, polyhedra
series	CADline
email
last changed	2003/05/17 10:15

_id	fcd6
authors	Berger, S.R.
year	1979
title	Artificial Intelligence and its impact on Coimputer-Aided Design
source	Design Studies, vol 1, no. 3
summary	This paper provides, for readers unfamiliar with the field, an introductory account of research which has been carried out in artificial intelligence. It attempts to distingussh between an artificial intelligence and a conventional computing approach and to assess the future influence of the former on computer-aided design.
series	journal paper
last changed	2003/04/23 15:14

_id	819a
authors	Brassel, Kurt E. and Fegeas, Robin
year	1979
title	An Algorithm for Shading of Regions on Vector Display Devices
source	SIGGRAPH '79 Conference Proceedings. August, 1979. vol. 13 ; no. 2: pp. 126- 133 : ill. includes bibliography
summary	The display of shaded polygons by line, cross-hatch, and dot patterns on vector devices is a task frequently used in computer graphics and computer cartography. In applications such as the production of shaded maps polygon shading turns out to be critical with respect to time requirements, and the development of efficient algorithms is of importance. Given an arbitrary polygon in the plane without self-crossing edges (simply-connected polygon), the task at hand is to shade this polygon with one or two sets of parallel lines where for each set a shading angle and a line distance are given. The basic concept of this new algorithm is to decompose the polygon into a set of mutually exclusive trapezoids (in special cases triangles) where the parallel edges of the trioxides are parallel to the desired shading lines. These trapezoids and triangles are then shaded in a fast procedure. In its present form the algorithm handles regions with up to 300 islands. Possible extensions include the construction of dash and cross patterns
keywords	algorithms, polygons, software, computer graphics, shading, GIS, mapping, drafting, information
series	CADline
last changed	2003/06/02 13:58

_id	9d45
authors	Ching, F.D.K.
year	1979
title	Architecture: Form, Space and Order
source	Van Nostrand Reinhold. New York
summary	The Second Edition of this classic introduction to the principles of architecture is everything you would expect from the celebrated architect, author, and illustrator, Francis D. K. Ching. Each page has been meticulously revised to incorporate contemporary examples of the principles of form, space, and order-the fundamental vocabulary of every designer. The result is a beautifully illustrated volume that embraces today's forms and looks at conventional models with a fresh perspective. Here, Ching examines every principal of architecture, juxtaposing images that span centuries and cross cultural boundaries to create a design vocabulary that is both elemental and timeless. Among the topics covered are point, line, plane, volume, proportion, scale, circulation, and the interdependence of form and space. While this revision continues to be a comprehensive primer on the ways form and space are interrelated and organized in the shaping of our environment, it has been refined to amplify and clarify concepts. In addition, the Second Edition contains: * Numerous new hand-rendered drawings * Expanded sections on openings and scale * Expanded chapter on design principles * New glossary and index categorized by the author * New 8 1/2 ? 11 upright trim In the Second Edition of Architecture: Form, Space, and Order, the author has opted for a larger format and crisper images. Mr. Ching has retained the style of his hand-lettered text, a hallmark of each of his books. This rich source of architectural prototypes, each rendered in Mr. Ching's signature style, also serves as a guide to architectural drawing. Doubtless, many will want this handsome volume for the sheer beauty of it. Architects and students alike will treasure this book for its wealth of practical information and its precise illustrations. Mr. Ching has once again created a visual reference that illuminates the world of architectural form.
series	other
last changed	2003/04/23 15:14

_id	e7b8
authors	Dahl, Veronica
year	1983
title	Logic Programming as a Representation of Knowledge
source	IEEE Computer. IEEE Computer Society, October, 1983. vol. 16: pp. 106-110 : ill. includes bibliography
summary	Logic has traditionally provided a firm conceptual framework for representing knowledge. As it can formally deal with the notion of logical consequence, the introduction of Prolog has made it possible to represent knowledge in terms of logic and also to expect appropriate inferences to be drawn from it automatically. This article illustrates and explores these ideas with respect to two central representational issues: problem solving knowledge and database knowledge. The technical aspects of both subjects have been covered elsewhere (Kowalski, R. Logic for problem solving, North- Holland pub. 1979 ; Dahl, V. on database system development through logic ACM Trans.vol.7/no.3/Mar.1982 pp.102). This explanation uses simple, nontechnical terms
keywords	PROLOG, knowledge, representation, logic, programming, problem solving, database
series	CADline
last changed	1999/02/12 15:08

_id	eb8e
authors	Fowler, Robert J. and Little, James J.
year	1979
title	Automatic Extraction of Irregular Network Digital Terrain Models
source	SIGGRAPH '79 Conference Proceedings. August, 1979. vol. 13 ; no. 2: pp. 199- 207 : ill. includes bibliography
summary	For representation of terrain, an efficient alternative to dense grids is the Triangulated Irregular Network (TIN), which represents a surface as a set of non-overlapping contiguous triangular facets, of irregular size and shape. The source of digital terrain data is increasingly dense raster models produced by automated orthophoto machines or by direct sensors such as synthetic aperture radar. A method is described for automatically extracting a TIN model from dense raster data. An initial approximation is constructed by automatically triangulating a set of feature points derived from the raster model. The method works by local incremental refinement of this model by the addition of new points until a uniform approximation of specified tolerance is obtained. Empirical results show that substantial savings in storage can be obtained
keywords	GIS, mapping, computational geometry, data structures, mapping, representation, computer graphics, triangulation
series	CADline
last changed	2003/06/02 13:58

_id	0868
authors	Gero, John S. and Volfneuk, M.
year	1979
title	Building Fuzzy CAD Systems
source	1979? pp. 74-79 : ill. includes bibliography
summary	The paper introduces the need to include subjectivities in computer aided design systems. It commences with the differences between uncertainty, which has been used to model subjectivity, and imprecision. The former provides the basis of probability theory, whilst the latter the basis of fuzzy set theory. The thesis is that subjectivities introduce imprecision. It shows that subjectivities can be included in the description of the interactions between parts of the system. After presenting a brief introduction to fuzzy set theory the paper shows how a fuzzy CAD system can be built. An example is presented which demonstrates the approach
keywords	CAD, fuzzy logic
series	CADline
email
last changed	2003/06/02 13:58

_id	a7b0
authors	Gips, J.
year	1979
title	Artificial Intelligence
source	Environment and Planning B. 1979. vol. 6: pp. 353-364 : ill. includes bibliography
summary	The field of artificial intelligence and its subfields of computer vision, games, natural language understanding, speech understanding, mathematics, medicine and robotics is reviewed. The work of George Stiny and the author on design and criticism is discussed briefly in terms of a paradigm of artificial intelligence research
keywords	AI
series	CADline
last changed	2003/06/02 10:24

_id	c3b5
authors	Hinds, John K. and Kuan, L.P.
year	1979
title	Sculptured Surface Technology as a Unified Approach to Geometric Definition
source	CASA - The Computer and Automated System Association of SME. 23 p. : ill Dearborn: SME, 1979. MS79-146. includes bibliography.
summary	The purpose of this paper is to describe a comprehensive approach to representing and machining complex surface shapes in an APT programming system. The APT (Automatically Programmed Tools) user language was extended to permit the definition of a hierarchy of curves and surfaces. Much of the logic has been implemented using matrix canonical forms which are closed under the full family of projective transformations, permitting family of parts storage and retrieval and part compensation. The area of numerical control machining was addressed, but the solutions for tool positioning were only partially successful due to the complexity of the algorithmic problem. This paper first outlines some of the mathematical methods adopted and then illustrates how these have been implemented with an APT part programming example
keywords	curved surfaces, representation, geometric modeling, mechanical engineering, CAM
series	CADline
last changed	2003/06/02 13:58

_id	4966
authors	Kaplan, Michael and Greenberg, Donald P.
year	1979
title	Parallel Processing Techniques for Hidden Surface Removal
source	SIGGRAPH '79 Conference Proceedings. 1979. vol. 13 ; no. 2: pp. 300-307 : ill. includes bibliography
summary	Previous work in the hidden-surface problem has revealed two key concepts. First, the removal of non-visible surfaces is essentially a sorting problem. Second, some form of coherence is essential for the efficient solution of this problem. In order to provide real-time simulations, it is not only the amount of sorting which must be reduced, but the total time required for computation. One potentially economic strategy to attain this goal is the use of parallel processor systems. This approach implies that the computational time will no longer be dependent on the total amount of sorting, but more on the appropriate division of responsibility. This paper investigates two existing algorithmic approaches to the hidden-surface problem with a view towards their applicability to implementation on a parallel machine organization. In particular, the statistical results of a parallel processor implementation indicate the difficulties stemming from a loss of coherence and imply potentially important design criteria for a parallel configuration
keywords	computer graphics, rendering, display, hidden surfaces, parallel processing, algorithms
series	CADline
last changed	2003/06/02 13:58

_id	c6a9
authors	Kay, Douglas Scott and Greenberg, Donald P.
year	1979
title	Transparency for Computer Synthesized Images
source	SIGGRAPH '79 Conference Proceedings. August, 1979. vol. 13 ; no. 2: pp. 158-164 : ill. (some col.). includes bibliography
summary	Simple transparency algorithms which assume a linear transparency over an entire surface are the type most often employed to produce computer synthesized images of transparent objects with curved surfaces. Although most of the images created with these algorithms do give the impression of transparency, they usually do not look realistic. One of the most serious problems is that the intensity of the light that is transmitted through the objects is generally not proportional to the amount of material through which it must pass. Another problem is that the image seen behind the objects is not distorted as would naturally occur when the light is refracted as it passes through a material of different density. Use of a non-linear transparency algorithm can provide a great improvement in the realism of an image at a small additional cost. Making the transparency proportional to the normal to the surface causes it to decrease towards the edges of the surface where the path of the light through the object is longer. The exact simulation of refraction, however, requires that each sight ray be individually traced from the observer, through the picture plane and through each transparent object until an opaque surface is intersected. Since the direction of the ray would change as each material of differing optical density was entered, the hidden surface calculations required would be very time consuming. However, if a few assumptions are made about the geometry of each object and about the conditions under which they are viewed, a much simpler algorithm can be used to approximate the refractive effect. This method proceeds in a back-to-front order, mapping the current background image onto the next surface, until all surfaces have been considered
keywords	computer graphics, shading, transformation, display, visualization, algorithms, realism
series	CADline
last changed	2003/06/02 13:58

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