ABSTRACT
This paper describes the development of a
"next generation" high performance, flexible, relatively inexpensive,
commodity based, spatially immersive visualization environment.
Current and near-future technologies and computational economics allow the development of better and more cost effective spatially immersive visualization systems. The systems being developed focuses on configurations utilizing a large number of identical modular components. For the most part these components are off the shelf, relatively inexpensive, commodity items.
KEYWORDS Spatial Immersive Environments, Fully Immersive Visualization, Virtual Reality
INTRODUCTION
Today, immersive virual environment systems
fall into two categories - head mounted displays and spatially immersive
displays (SIDs) such as the CAVE developed at the University of Illinois at
Chicago [1]. Head mounted displays
(HUDs) are designed to present two separate synthetic views of the virtual
environment to the user. One view is
for the right eye and the other view is for the left eye. These two stereo views are fused by the
viewer's perceptual system in the same way as right and left eye views of
natural scenes. HUD systems must, in
addition to computing the synthetic displays, track the viewer's location and
viewing orientation in the virtual world to create the correct right and left
eye views.
In SIDs, such as CAVE installations, the right and left head mounted displays are
replaced by multiple projected displays that form the walls of an environment
cube. Current CAVEs have at most six planar surfaces, each representing a large
portion of the possible field of view.
Most CAVE installations have fewer than the maximum six display
surfaces. Each of the projection surfaces is usually driven from an expensive,
high performance graphics system such as SGI Onyx2 with one or more Infinite
RealityTM graphics processors. Figure 1 illustrates
the CAVE approach using three display surfaces and three image projectors.
Figure 2 shows adding a fourth floor surface and a fourth projector
utilizing a relecting mirror. Figure 3 shows a CAVE configuration with all six
display surfaces.
In spatially immersive systems, the projected
displays are usually presented as time sequential stereo images. The user is required to wear special glasses
that have liquid crystal shutters whose operation is synchoronized to the
diplay frame rate. As in the head
mounted display version, the position and perhaps oreintation of the viewer
must be tracked [2] if correct stereo views are to be projected on the CAVE
walls.
An alternative to the active, time
sequential, stereo presenation is a passive diplay approach that uses two
projectors for each diplay screen.
Polarized filters are placed in front of each projector. These filters are oriented at 90 degree
angles. The viewer also wears 
Figure 1 - A
3-sided CAVE
Figure 2 - A 4-sided CAVE
Figue 3 - A
6-sided CAVE
glasses
with polarized lenses. These lenses are
also oriented at 90 degree angles so that the right eye sees only the right eye
projected image while the left eye sees only the left eye image.
While fully immersive visualization
facilities are still relatively rare, they are becoming key facilitators for
many research and industrial projects. This paper describes the development of
"next generation" high performance, flexible, relatively inexpensive,
commodity based, spatially immersive visualization systems.
THE IDEAL SYSTEM
It can be argued that the ideal
spatially immersive environment would be one where the user is
surrounded by a seamless spherical display surface that provides very high
resolution, high update rate, 360 degree panoramic stereo views of extremely
high complexity data. The current CAVE
immersive environments are poor approximations to this ideal. Domed spatially immersive environments have
been used for many years in flight training simulators [3] and dodecahedron
approximations to spherical projections have been developed [4].
Current and near future technologies and
computational economics allow the development of better and more cost
effective spatially immersive visualization systems. The systems we are
developing focus on configurations utilizing a large number of identical modular
components. For the most part these
components are off the shelf, relatively inexpensive, commodity items.
MAJOR COMPONENTS
A spatially immersive visualization system
consists of three major elements - 1) the computational infrastructure, 2) the surrounding display surfaces, and 3)
the viewer tracking and interaction elements. We are exploring new approaches
to both the computational infrastructure and the display surface geometries to
be used. We have not focused on the
viewer tracking and interactive
elements and expect to use the approaches in current practice.
In our new approach, the computational
infrastructure used is a visual computing extension of the Beowulf
concept [5]. A Beowulf system consists
of a collection of commodity computers networked to form an inexpensive but
powerful distributed parallel computing engine. The Beowulf concept generally
makes use of extentions to the Linux [6] operating system.
The visual computing extension is to add a
high performance commodity graphics processor to each of the computational
nodes. The result is a powerful
parallel distributed visualization system. Based on published performance
benchmark results, collections of relatively low cost commodity visual systems
compare very favorably in both cost and aggregate performance with the
expensive high-end graphics systems typically used to support immersive systems
[7]. For example, an entry level SGI
Onyx2 Infinite RealityTM system with an approximate cost of $170,000
has a measured DX benchmark performance of about 36. A high-end Pentium III based workstation costing about $13,700
has a DX performance of about 25. The
cost ratio is about 12 to 1 while the performance ratio is only about 3 to 2,
yielding a 8 to 1 cost perfomance
advantage for the commodity workstation. While one must be cautious when
using such single measure comparisons, the trend is clear.
Having the visual computing distributed over
a collection of processors allows innovation in the structure of the display
surfaces. In our approach, the
aggregate display surface is composed of many display faces or facets. In such configurations, each facet need only
display a relatively small portion of the total virtual environment. The
graphics computation needed for each facet will fall within the capacity of
today's, and certainly tomorrow's, high-end commodity graphics systems.
The envisioned faceted display elements could
be arranged in a number of configurations.
In fact, the display configurations could be tailored to meet specific
applications. There are a number of
polyhedral configurations whose faceted surfaces are good approximations to the
ideal spherical display surface.
Several of these are formed using many instances of only a single planar
shape. These polyhedra require from 12 up to 60 or more planar faces [8][9].
Among these is the 24 facet Trapezoidal Icositetrahedra illustrated below. In
addition to the solid form, Figure 4 shows the 24 identical facets unfolded
onto a plane.
Figure 4 A 24 facet Trapezoidal Icositetrahedra
(also known as a Deltoidal Icositetrahedra)
Figure
5 shows the array of projectors needed for a display environment using the
Trapezoidal Icositetrahedra form.
Compare this figure with Figures 1, 2, and 3 above. Each of these projectors
would be driven from its own graphics computational node. The set of these 24 computational nodes
would form a visually extended Beowulf system as discussed above.
Figure 5 - A
24 facet immersive environment with projector positions indicated.
Figure 6 shows an illustration of how such a
system might be located within a high ceiling building. The human figure show the scale of this 15
foot diameter display structure. The building entrance shown is approximately
18 feet wide.
Figure 6 How a 24-facet immersive display structure
might be located within a high ceiling room.
The entrance shown is about 18 feet wide.
Figure
7 shows a cross-section through the 24 facet structure. The human figure is included to give scale
to the illustration and to show where the viewer would be located relative to
the display surfaces. A set of
simulated molecular images is shown projected on the display surfaces.
Figure 7 A simulated cross-sectional view of a 15 foot diameter
24 facet immersive display environment.
OBJECTIVES
We are focused on exploring and evaluating this
new class of spatially immersive visualization systems. We are concerned with
determining whether these new visualization environments are practical and
effective.
The objectives in this research can be summarized
as follow:
1)
Explore and
evaluate, at the conceptual level, possible geometric display structures and
their implications for next generation spatially immersive environments.
2)
Develop and evaluate
software simulations of some of the more promising configurations identified in
the conceptual phase.
3)
Construct and
evaluate operational prototype systems for the most promising geometric
configurations.
4)
Develop the
software need to support simulated and operational prototype systems. Some of
the issues to be addresses include; effective distribution of the graphic
computation, dynamic data partitioning, synchronization of the displays, the
required projection and image clipping algorithms, and automated display system
calibration.
5)
Develop a deeper
understanding of the technical and effectiveness issues and trade-offs of these
systems. How are technical considerations and user effectiveness related to
geometric configuration?
6)
Investigate the
feasibility of mass replicated, modular, implementations of these systems.
7)
Develop
experimental designs to be used to evaluate prototype systems and
experimentally measure the effectiveness of the systems.
We are currently in the conceptual development
and initial simulation phases of this project. Simulation and small-scale
prototypes will be used to verify conceptual results prior to committing to the
construction of full-scale prototype designs.
Selection and development of the prototypes
involves detailed simulation, physical structure design, supporting software
design, physical fabrication and assembly, and software implementation.
Prototype evaluation will include both a
technical evaluation of the system and an effectiveness evaluation. The
technical evaluation will address issues such as computational complexity,
computational loading, dynamic performance, and cost/performance.
EFFECTIVENESS EVALUATION
In addition to the design and development of
prototypes systems of this new class, we are concerned with the effectiveness
of the immerse experiences they will provide. That is, do they empower the
participant by affording new insights and deeper understandings, as well as by
facilitating performance generally?
It remains the case that relatively little
published research has attempted to characterize either the immersive
experience in a simulated environment or establish whether an enhanced sense of
immersion results in either improved or less effortful task performance [10].
Our approach to this evaluation will be to
measure the concomitant cognitive, affective and physiological processes
occurring during and after immersive experiences. Physiological activity such
as heart rate and skin conductance have proven to be useful indicators of
effort and attention in complex settings [11], and the electromyographic
measurement of facial muscle activity has proven to be a robust indicator of
affective processes [12]. Continuous response measurement and secondary
reaction time techniques have also proven to be useful measures of such ongoing
psychological processes. Traditional measures of task performance, such as
error rates, as well as somewhat novel measures of such performance, such as
standardized performance trajectories, along with measures of the encoding,
recall or recognition of information, will also be explored to assess the
cognitive concomitants of immersive experiences.
EXPECTED OUTCOMES
We expect that this work will result in:
1)
The development of an improved class of spatially immersive
environments, including the construction and evaluation of several polyhedral
prototypes utilizing low cost commodity components.
2)
Specialized
graphics software to support these prototypes.
3)
System software to
manage graphics data distribution, coordinated operation of many graphic
computation nodes, display synchronization, and user interaction.
4)
A much deeper
understanding of the issues related to polyhedral immersive virtual
environments.
5)
Suggested designs
for modular mass replicated immersive environments
This work has the potential to fundamentally
influence the economics, availability, and pervasive-ness of spatially
immersive environments. It has the potential to influence the design,
development, and viability of future spatially immersive systems. It will
contribute to the availability of these environments across a wide range of
users in many disciplines.
FUTURE DIRECTIONS
In addition to the 24 facet polyhedra used above to illustrate the basic concepts, there are many other polyhedra formed from larger numbers of identical planar shapes. Two of these with 60 facets each are shown in Figure 8. These, and polyhedra with even larger numbers of facets, could be the basis for future spatially immersive systems. In fact, the larger the number of facets, the larger the number of computational nodes used. This increases the overall aggregate visual computational power of the system. It also decreases the size of each display facet for an environment of given size. More facets also result in a better approximation to the ideal spherical environment.
Figure 8 Two
60 facet polyhedra -the Deltoidal Hexecontahedron on the left, the Pentagonal
Hexecontahedron on the right.
Faceted display configurations hold the
promise of truly modular systems where the immersive environment is created by
literally bolting together mass replicated modules. Each module containing the required
structural, computational, and display elements. The display elements of these modules could possibly eventually be flat
panel displays similar to those currently used in laptop computers.
REFERENCES
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ACKNOWLEDGEMENT
Figures 5, 6 and 7 were created by Christina
Garcia at the Texas A&M Visualization Laboratory.