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Princeton COS 598B - A Dynamic Graphics System

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A INTERACTIVE 3D GRAPHICS %@ Walkthrough - A Dynamic Graphics System for Simulating Virtual Buildings Frederick P. Brooks, Jr. Department of Computer Science University of North Carolina at Chapel Hill 0.1 Abstract As part of our graphics research into virtual worlds, we are building a tool for an architect and his client to use for rapid prototyping of buildings by visually “walking through” them in order to refine specifications. Our first prototype simulated the new UNC Computer Science building with some 8000 polygons. BSP-tree software on the Adage Ikonas gave a colored, shaded perspective view every 3-5 seconds while the user moved a cursor in real-time over floorplans shown on the Vector-General 3300. The current (third) version uses Pixel-Planes to generate 9 updates/second, view images shown 4’ x 6’ by projector. Active short- and long-term research questions include speed-up, stereo, a 6-DoF interface with eye-level defaults, and an interactive model-building, model-changing system. 0.2 Application Concept At the 1965 IFIP Congress, Ivan Sutherland challenged computer graphicists to look beyond “the picture in the window” toward creating virtual environments in which the viewer is immersed, and where he sees, feels, and manipulates the virtual objects as if they were real. Much of the research at Chapel Hill has been aimed at this objective. The Walkthrough Project aims at providing a tool in which virtual buildings, designed but not yet constructed, can be explored by “walking through” them in the same way that simulated airplanes “fly” over virtual terrain. The object is not training, as it is with flight simulators, but visualization to permit the architect to OCTOBER 23-24,1986 9 )_.. -2.“prototype” a building and to iterate with his client on the detailed desiderata for it. Today’s CAD-CAE systems for building architecture aim primarily at assisting the designer in recording his decisions in a database and in producing standard blueprints and specifications. We envision another, complementary, computer graphics tool to help the designer visualize and explore the spaces he is creating, as part of the design process. Such a tool could be especially useful for designer-client dialogues. Whereas the designer is trained and experienced in imagining spaces, the client is not. He needs visualizations to aid his thinking and his communication with the designer. So the objective is a system that allows the user to visually experience the spaces in a virtual building, a vision first articulated by Donald Greenberg: For architects the ability to simulate motion is highly useful. One of the principal concerns of architectural design is space: the internal spaces of a building and the external space of the building and its setting. One does not react to space from a static position, as one might view a painting. To obtain a deeper understanding of architectural space it is necessary to move through the space, experiencing new views and discovering the sequence of complex spatial relations. [Greenberg, 19741 Given this objective, what can be done? The fielded state of the art offers two extremes: moving views and user-steered pre-computed high-quality views. Color wire-frame models of great intricacy can be moved and rotated in real time by vector displays. Skidmore-Owings-Merrill’s vector model of the Chicago Loop is a most impressive example. (We define real-time to be twelve updates/second or better, matching silent movies). Alternatively, one can select a fixed view of a virtual building or other model and produce a precisely rendered, color-shaded, illuminated, textured, anti-aliased image of high quality. Each such frame takes at least 20 minutes on a l-MIPS computer. One can make video of a succession of such frames along a preplanned cruise path, at 30 frames, or 10 hours of computing, per second of video. Today the technology puts an attractive intermediate within striking distance: real-time user-directed cruising through a virtual building, with continuous real- time production of TV-cartoon-quality shaded, colored, stereo views. 10 CHAPELHILL,NC92 INTERACTWE 3D GRAPHICS ‘++d 0.3 Ikonas Walkthrough Last year we built a prototype of such a system for our new Computer Science building. The user gets a floorplan view on the vector display, with eye position and direction marked by a cursor, and he gets a rendered view on the Ikonas display. Thus the user can steer himself down corridors, peer into offices, even see the several floors as he rides in the elevator - all before the building has been constructed. This work was initially motivated by our own needs for our interactions with our architects, the firm of O’Brien and Atkins. This prototype has been useful to us in decision-making, especially about the lobby layout and the balcony width. The user sees the spaces in 3-D stereo perspective, properly solid, colored, and lighted. The program was still too slow for real-time viewing, by a factor of about 35. One did get real-time updating of the floorplan cursor, so navigation was not difficult. The eye view got updated about every 3 seconds, at best, if the computer had no other load. By stopping for three seconds at a desired viewpoint, one could get any arbitrary view. This architectural tool was a lash-up of some in-hand advanced technology, namely l The Fuchs, Naylor, Kedem binary-space-partitioning algorithm, and Gre- gory Abram’s software for it, l an Adage Ikonas 3000 video frame buffer and a VG 3303 vector display, l a very fast bit-sliced microprocessor in the Adage Ikonas, l new stereo viewing devices. This prototype is demonstrated on the videotape, made with an earlier


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Princeton COS 598B - A Dynamic Graphics System

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