Abstract

Carl M. Erikson

Hierarchical Levels of Detail to Accelerate the Rendering of Large Static and
Dynamic Polygonal Environments

(Under the direction of Dinesh Manocha)

Interactive visualization of large three-dimensional polygonal datasets is an
important topic in the field of computer graphics and scientific visualization.
These datasets can be static, such as walkthrough applications, or dynamic,
such as CAD scenarios where a designer moves, adds, or deletes parts.  In many
cases, the number of primitives in these models overwhelms the rendering
performance of current graphics systems.  One method for accelerating the
rendering of these environments is polygonal simplification.  This dissertation
describes the creation and application of levels of detail, or LODs, and
hierarchical levels of detail, or HLODs, to accelerate the rendering of large
static and dynamic polygonal environments.  The principal idea of this work is
that simplification methods should not always treat objects, or collections of
polygons, in a scene independently.  Instead, they may be able to produce
higher quality and drastic approximations by simplifying disjoint regions of a
scene together.  This idea is applicable to the creation of LODs for individual
objects that consist of unconnected polygons, and for the construction of
HLODs, or approximations representing groups of static or dynamic objects.

We present a polygonal simplification algorithm called General and Automatic
Polygonal Simplification, or GAPS, that excels at merging disjoint polygons
through the use of an adaptive distance threshold and surface area
preservation.  We use GAPS to create LODs and HLODs for nodes in the scene
graphs of large polygonal environments.  These approximations enable two
rendering modes, one that allows the user to specify a desired image quality
and another that targets a frame-rate.  When objects in the scene move, our
algorithm updates HLODs that have become inaccurate or invalid using
asynchronous simplification processes.  Our algorithm currently handles scenes
with limited rigid-body dynamic movement.  We demonstrate its performance on
several large CAD environments including a 13 million polygon power plant
model.  Our approach has achieved nearly an order of magnitude improvement in
average rendering speed with little or no loss in image quality for several
viewing paths of complex environments.