Visibility preprocessing for interactive walkthroughs

Abstract

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, CR Categrsries and Subject Descriptors: [Computer {;raphics]: l.3.5Compuiational GeonletW and Object Model ing-,qe~~~~~efri( a (,qorilhnf.j, /<In,qMJ,qes, and ,sv.stetiI,s:1.3.7 Three-Dimensional Graphics and Realism -~i.siblc /irrc/.rrfi:fiwr'u/,cywi/hms.Additional Key Words and Phrases: architectural simulation, linear progmmming. superset visibility.Permwmmlocopy wnhout leeall(~r part f>fthis material isgrantcd provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice mrd the title of the fsubl icatitrn and ih date appear. and notice is given that copying is by permission ,,( the Association for Comput ing Machinery. To copy otherwise, ormrcpuh[ish. requmcs a fee mrd/orspec itic pm-mission.ACM-O-X9791-436-WI m)7mrl I KS) 75

Visibility Preprocessing with Occluder Fusion for Urban Walkthroughs

“…To calculate occlusion for regions, a general method is to break down the view space into cells and precompute for each cell a set of objects that are potentially visible (potentially visible sets, PVS). For general scenes, visibility precomputation can become quite costly with respect to time and memory, but for certain scenes, like terrains [20] or building interiors [22] it is possible to use the a priori knowledge about the scene structure for visibility calculation. Cohen-Or et al [2] show an algorithm for densely occluded scenes that does not make use of occluder fusion.…”

Topological Space Partition for Fast Ray Tracing in Architectural Models

“…The subdivision is performed using a kd-tree. It has been extended for general convex cells (non necessarily axis-aligned) using a BSP-tree by Teller et al (Teller and Séquin, 1991). Meneveaux et al (Meneveaux et al, 1998) used a rule-based system which consists in finding the openings (i.e.…”

“…Figure 9(a)). Cells-and-portals structures are used in (Airey et al, 1990), (Teller and Séquin, 1991), (Luebke and Georges, 1995) or (Meneveaux et al, 1998) to compute the potentially visible set (or PVS) in architectural environments. From the same perspective and for efficiency purpose, we choose to compute the set of potential visible lights for each cell making up our scenes.…”

Interactive 3-D virtual colonoscopy system

“…One exploits a hierarchical Z-buffer to efficiently cull unseen objects [21]. The other approach in [17], [19] divides the whole scene into many cells. Each cell has a predetermined PVS.…”