Interactive Architectural Walkthroughs

Overview:

Interactive computer programs that simulate the experience of "walking" through a building interior are useful for visualization and evaluation of building models before they are constructed. However, realistic-looking building 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 model, swap them into memory and render them at interactive frame rates (at leastfifteen frames per second) as the observer's viewpoint is moved under user control.

We have developed a system that supports interactive walkthroughs of such large, fully furnished building models. The system relies upon an efficient display database that describes the model as a set of objects, each of which is represented at multiple levels of detail; and contains an index of spatial cells with precomputed visibility information. Adaptive display algorithms are used to compute the set of objects potentially visible from each observer viewpoint, and to choose an appropriate level of detail at which to render each object to maintain an interactive frame rate. Real-time memory management algorithms are used to predict observer motion and pre-fetch objects from disk that may become visible in future few frames. Using these techniques, the system is able to maintain over 15 frames/second during walkthroughs of building models containing over one million polygons.

This is joint work with Carlo Sequin, Seth Teller, and the UC Berkeley Walkthru Group.