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

Report ID:
June 2002
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We present iWalk, a system for interactive out-of-core rendering of
large models on an inexpensive PC. The system uses a new out-of-core
preprocessing algorithm and a new multi-threaded out-of-core 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.

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