[talks] J Terrace preFPO

Melissa M. Lawson mml at CS.Princeton.EDU
Thu Apr 5 09:07:06 EDT 2012

Jeff Terrace will present his preFPO on Thursday April 12 at 4PM 
in Room 302 (note room!).  The members of his committee are:  
Michael Freedman, advisor; Adam Finkelstein and Phil Levis (Stanford), 
readers; Vivek Pai and Szymon Rusinkiewicz, nonreaders.  Everyone 
is invited to attend his talk.  His abstract follows below.


Metaverses are three-dimensional virtual worlds where anyone can add
and script new objects. Metaverses today, such as Second Life, are
dull, lifeless, and stagnant because users can see and interact with
only a tiny region around them, rather than a large and immersive
world. Current metaverses impose this distance restriction on
visibility and interaction in order to scale to large worlds, as the
restriction avoids appreciable shared state in underlying distributed
systems. We present a brief summary of the design and implementation
of the Sirikata metaverse server. The Sirikata server scales to
support large, complex worlds, even as it allows users to see and
interact with the entire world. It achieves both goals simultaneously
by leveraging properties of the real world and 3D environments in its
core systems, such as a novel distributed data structure for virtual
object queries based on visible size.

A virtual-world environment becomes a truly engaging platform when
users have the ability to insert 3D content into the world. However,
arbitrary 3D content is often not optimized for real-time rendering,
limiting the ability of clients to display large scenes consisting of
hundreds or thousands of objects. We present the design and
implementation of an automatic, unsupervised conversion process that
transforms 3D content into a format suitable for real-time rendering
while minimizing loss of quality. The resulting progressive format
includes a base mesh, allowing clients to quickly display the model,
and a progressive portion for streaming additional detail as desired.
Sirikata’s public, open-source content repository is currently using
this method and has processed over 700 3D models.

3D meshes are large--often several megabytes in size. When a client
enters a scene containing many objects, it can take a long time to
download meshes, resulting in poor visual fidelity. A progressive mesh
format allows a client to download a low-resolution version of a mesh
at a much lower cost in bandwidth, but deciding how to order downloads
has a huge impact on performance. Should a client download a higher
texture resolution for one model, or stream additional vertices for
another? Worse, underpowered clients might not be able to display a
high resolution mesh, resulting in wasted time downloading unneeded
content. We present the design and implementation of a framework for
evaluating scheduling algorithms for progressive meshes and we perform
this evaluation on several different algorithms. The result is a mesh
scheduling algorithm that optimizes for visual fidelity given a fixed
bandwidth constraint.

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