iWalk: Interactive Out-of-Core Rendering of Large Models

We present iWalk, a system for interactive out-of-core rendering of large models on an inexpensive PC. The system uses a new outof -core preprocessing algorithm and a new multi-threaded out-ofcore rendering approach. The out-of-core preprocessing algorithm is incremental and fast, and it builds an on-disk hierarchical representation for a model larger than main memory. The out-of-core rendering approach uses multiple threads to overlap rendering, visibility computation, and disk operations. A rendering thread uses a from-point visibility algorithm to find the nodes of the model hierarchy that the user sees, and sends fetch requests to a geometry cache, which reads nodes from disk into memory. To avoid bursts of disk operations, a look-ahead thread guesses the nodes that the user may see next, and sends prefetch requests to the geometry cache. The system can run in approximate mode for interactive rendering, or in conservative mode for rendering with guaranteed accuracy. On a commodity PC, iWalk can preprocess a 13-million-polygon model in 17 minutes, and then render it in approximate mode with 98% accuracy at 9 frames per second. Thus, iWalk allows us to use an inexpensive PC to visualize models that would typically require expensive high-end graphics workstations or parallel machines