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 a typical model is visible from most viewpoints.We describe a method of visibility preprocessing that is efficient and effective for axis-aligned oraxialarchitectural models. A model is subdivided into rectangularcellswhose boundaries coincide with major opaque surfaces. Non-opaqueportalsare identified on cell boundaries, and used to form anadjacency graphconnecting the cells of the subdivision. Next, thecell-to-cellvisibility is computed for each cell of the subdivision, by linking pairs of cells between which unobstructedsightlinesexist.During an interactivewalkthroughphase, an observer with a known position andview conemoves through the model. At each frame, the cell containing the observer is identified, and the contents of potentially visible cells are retrieved from storage. The set of potentially visible cells is further reduced by culling it against the observer's view cone, producing theeye-to-cell visibility. The contents of the remaining visible cells are then sent to a graphics pipeline for hidden-surface removal and rendering.Tests on moderately complex 2-D and 3-D axial models reveal substantially reduced rendering loads.