Interactive Visualization of Large Architectural Models
Thomas A. Funkhouser
Bell Laboratories
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 least ten
frames per second) as the observer's viewpoint is moved under user
control.
I will describe 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 and Seth Teller.
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