The number of polygons comprising interesting architectural models is many more than can be rendered at interactive frame rates. However, due to occlusion by opaque surfaces (e.g., walls), only a small fraction of atypical model is visible from most viewpoints. We describe a method of visibility preprocessing that is efficient andeffective foraxis-aligned oril.ria / architectural m[}dels, A model is subdivided into rectangular cc//.$whose boundaries coincide with major opaque surfaces, Non-opaque p(~rtc~/.rare identified rm cell boundaries. and used to form ana~ju{~’n~y,q)f~/>//con nectingthe cells nfthesubdivisicm. Next. theccl/-r/~-cc/ / visibility is computed for each cell of the subdivisirrn, by linking pairs of cells between which unobstructed.si,q/~t/inr. ~exist. During an interactive ww/krhrm/,q/~phase, an observer with a known ~~sition and\it)M~~~)~t>mov esthrc>ughthe model. At each frame, the cell containingthe observer is identified, and the contents {]fp{>tentially visible cells areretrieved from storage. The set of potentially visible cells is further reduced by culling it against theobserver’s view cone, producing the ~)yt>-r~]-t(>// \ i,$ibi/ify, The contents of the remaining visible cells arc then sent to a graphics pipeline for hidden-surface removal and rendering, Tests onmoderatelyc mnplex 2-D and 3-D axial models reveal substantially reduced rendering loads,

An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Z-buffer scan conversion does well on criterion (b), but poorly on criterion (a). Here we present a hierarchical Z-buffer scan-conversion algorithm that does well on both criteria. The method uses two hierarchical data structures, an object-space octree and an image-space Z pyramid, to accelerate scan conversion. The two hierarchical data structures make it possible to reject hidden geometry very rapidly while rendering visible geometry with the speed of scan conversion. For animation, the algorithm is also able to exploit temporal coherence. The method is well suited to models with high depth complexity, achieving orders of magnitude acceleration in some cases compared to ordinary Z-buffer scan conversion.

This paper explores the issues involved in designing and developing network software architectures for large scale virtual environments. We present our ideas in the context of NPSNET-IV, the first 3D virtual environment that incorporates both the IEEE 1278 Distributed Interactive Simulation (DIS) application protocol and the IP Multicast network protocol for multi-player simulation over the Internet.

Visibility algorithms for walkthrough and related applications have grown into a significant area, spurred by the growth in the complexity of models and the need for highly interactive ways of navigating them. In this survey, we review the fundamental issues in visibility and conduct an overview of the visibility culling techniques developed in the last decade. The taxonomy we use distinguishes between point-based and from-region methods. Point-based methods are further subdivided into object and image-precision techniques, while from-region approaches can take advantage of the cell-and-portal structure of architectural environments or handle generic scenes.

this paper is to provide the reader with a good understanding of the types of interaction that are possible in a virtual environment. The main body of the paper consists of a discussion of the fundamental forms of interaction and includes numerous examples of interaction techniques that can be used as building blocks in the development of virtual worlds applications. Included as an appendix to this paper is an overview of coordinate system transformations and examples of using coordinate system diagrams in the implementation of virtual worlds interaction techniques. Though every effort has been made to avoid a bias towards a particular type of virtual environments system, the paper does assume some form of display to present images to a user, a tracking system which can be used to measure the position and orientation of the user's head and hand, and some form of input device such as a hand-held button device or an instrumented glove which can be used to signal the user's intentions. 2 Mark R. Mine TR95-018 May 5, 1995

We present an algorithm for performing adaptive real-time level-of-detail-based rendering for triangulated polygonal models. The simplifications are dependent on viewing direction, lighting, and visibility and are performed by taking advantage of image-space, object-space, and frame-to-frame coherences. In contrast to the traditional approaches of precomputing a fixed number of level-of-detail representations for a given object our approach involves statically generating a continuous level-ofdetail representation for the object. This representation is then used at run-time to guide the selection of appropriate triangles for display. The list of displayed triangles is updated incrementally from one frame to the next. Our approach is more effective than the current level-of-detail-based rendering approaches for most scientific visualization applications where there are a limited number of highly complex objects that stay relatively close to the viewer. Our approach is applicable for scalar (such as distance from the viewer) as well as vector (such as normal direction) attributes.

While large investments are made in sophisticated graphics hardware, most realistic rendering is still performed off-line using ray trace or radiosity systems. A coordinated use of hardware-provided bitplanes and rendering pipelines can, however, approximate ray trace quality illumination effects in a user-interactive environment, as well as provide the tools necessary for a user to declutter such a complex scene. A variety of common ray trace and radiosity illumination effects are presented using multi-pass rendering in a pipeline architecture. We provide recursive reflections through the use of secondary viewpoints, and present a method for using a homogeneous 2-D projective image mapping to extend this method for refractive transparent surfaces. This paper then introduces the Dual Z-buffer, or DZ-buffer, an evolutionary hardware extension which, along with current framebuffer functions such as stencil planes and accumulation buffers, provides the hardware platform to render non-refr...

We present a z-buffered image-space-based rendering technique that allows navigation in complex static environments. The rendering speed is relatively insensitive to the complexity of the scene as the rendering is performed apriori, and the scene is converted into a bounded complexity representation in the image space. Realtime performance is attained by using hardware texture mapping to implement the image-space warping and hardware affine transformations to compute the viewpoint--dependent warping function. Our proposed method correctly simulates the kinetic depth effect (parallax), occlusion, and can resolve the missing visibility information by combining z-buffered environment maps from multiple viewpoints. CRCategories and Subject Descriptors: I.3.3 [Computer Graphics ]: Picture/Image Generation - Display Algorithms, Viewing Algorithms; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - Animation, Texture; I.4.8 [Image Processing]: Scene Analysis - Range data. A...

Genus-reducing simplifications are important in constructing multiresolution hierarchies for level-of-detail-based rendering, especially for datasets that have several relatively small holes, tunnels, and cavities. We present a genus-reducing simplification approach that is complementary to the existing work on genus-preserving simplifications. We propose a simplification framework in which genus-reducing and genus-preserving simplifications alternate to yield much better multiresolution hierarchies than would have been possible by using either one of them. In our approach we first identify the holes and the concavities by extending the concept of #- hulls to polygonal meshes under the L1 distance metric and then generate valid triangulations to fill them. CR Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image Generation --- Display algorithms; I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling --- Curve, surface, solid, and object represent...

Database and Display Algorithms for Interactive Visualization of Architectural Models by Thomas Allen Funkhouser Doctor of Philosophy in Computer Science University of California at Berkeley Professor Carlo H. S'equin , Chair This thesis describes a system for interactive walkthroughs of large, fully furnished architectural models. Realistic-looking architectural models with furniture may consist of millions of polygons and require gigabytes of data -- far more than today's workstations can render at interactive frame rates or fit into memory simultaneously. In order to achieve interactive walkthroughs of such large building models, a system must store in memory and render only a small portion of the model in each frame; that is, the portion seen by the observer. As the observer "walks" through the model, some parts of the model become visible and others become invisible; some objects appear larger and others appear smaller. The challenge is to identify the relevant portions of the m...