Guest Editor's Introduction

Computer Graphics Tokyo 84Part 2: GeometricModelingTosiyasu L. Kunii

University of Tokyo

Computer Graphics Tokyo 84 at-tracted more than 14,000 participantsfrom all over the world. Of that number20 percent attended the excellenttechnical sessions that were offered.When we started to gather the best andmost representative papers from thatevent to share with those of you in thefield who could not be at ComputerGraphics Tokyo 84, it quickly becameapparent that there would be too manyfor a single issue of this magazine.Therefore, we brought you articles lastmonth on graphics language design,software, and geometric modeling. Thismonth it is my privilege to share withyou the rest of the papers on geometricmodeling that have been chosen by thereviewers to appear in IEEE CG&A.

First Ingrid Carlbom, IndranilChakravarty, and David Vanderscheldescribe a generalization of the octreedata structure for representing poly-hedral objects. This data structure,called the polytree, is a cellular spatialdecomposition of the object space intoprimitive cells, the increased complexityof which has several advantages over oc-trees, according to the authors, who alsopresent a recursive subdivision algorithmfor the creation of a polytree from aboundary representation.

Next Hiroaki Chiyokura andFumihiko Kimura propose a method forrepresenting the solid design process interms of a set of primitive operationsthat would result in a much more user-friendly modeling system. In theirsystem, Modif, high-level operationsmodify solid shapes through primitiveoperations, each of which has a cor-responding inverse operation. All arestored in a design process representation.When Modif is used with boundary re-presentation as the method of internalrepresentation, the authors show that

their system can quickly regenerate pre-viously designed solids at any stage oftheir design.Tapio Takala then brings us an in-

depth consideration of user interfacemanagement systems, or UIMSs, for in-teractive CAD systems. Takala looks atthe updating of models and the opera-tion of different tool algorithms, givingus suggestions about UIMS contents andthe changes needed to keep up withpresent-day user needs.

Next we are treated to a discussion ofthe use of a 4 x 4 determinant by FujioYamaguchi and Toshiya Tokieda. Theauthors also describe Boolean shapeoperations of a solid modeling system,Freedom II. This simple and efficientalgorithm makes use of the continuity ofa shape.Then Yoshimi Ota, Hiroshi Arai,

Shinji Tokumasu, and Toshio Ochi sug-gest that some computer graphics ap-plications can borrow from the color-shading data for 3-D objects used inCAD/CAM applications and not onlysave many man-hours of work but get

more precise results in the process. Bychoosing the proper division parameter,they tell us, they have attained a veryhigh degree of accuracy.

Steven G. Satterfield and David F.Rogers then bring us a procedure forgenerating accurate contour lines for aB-spline surface. This procedure includestwo steps: The first is a modification ofa traditional routine for contouring overa triangular mesh, and the second usesB-spline surface generation over alimited area to produce the contour ac-curately.

I extend many thanks to all thesescientists for their valuable contributionsto Computer Graphics Tokyo 84 andtheir contributions to this issue of IEEEComputer Graphics and Applications. Ithas been an excellent experience to workwith each of them. H

The computer graphics rendering is from thearticle by Carlbom, Chakravarty, and Vander-schel on page 24 of this issue.

Tosiyasu L. Kunii is currently a professor of information and computerscience at the University of Tokyo. He started work there in raster graphics in1968, which led to the Tokyo Raster Technology Project. His research in-terests include computer graphics, database systems, and software engineer-ing. He has authored and edited 20 computer science books and published 75refereed academic/technical papers in computer science and applicationsareas.

s_ ; ~~Kunii is president of the Computer Graphics Society, chairman of theboard of the Handheld Computer Society, and a member of the EditorialBoard of CG&A. He is active in IFIP, has organized and is ex-chair of the

Technical Committee on Software Engineering of the Information Processing Society of Japan,and has organized and is ex-president of the Japan Computer Graphics Association. He served asgeneral chairman of the Third International Conference on Very Large Data Bases in 1977, pro-gram chairman of Intergraphics 83, and program chairman of Computer Graphics Tokyo 84,which he will also chair in 1985.

Kunii received his BSc, MSc, and DSc in chemistry from the University of Tokyo in 1962, 1964,and 1967.

Kunii's address is Department of Information Science, Faculty of Science, the University ofTokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan.

0272-1716/85/0400-0023$01.00 © 1985 IEEEApril 1985 23