131 lines
7.8 KiB
Plaintext
131 lines
7.8 KiB
Plaintext
Published in Dec 1992 CyberEdge Journal
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CyberEdge Journal is published by Ben Delaney, bdel@well.sf.ca.us
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A SUMMARY OF VIRTUAL ENVIRONMENTS RESEARCH AT UNC-CHAPEL HILL
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by Mark A. DeLoura, deloura@cs.unc.edu
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The University of North Carolina at Chapel Hill's Computer Science
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department has been doing research into immersive head-mounted virtual
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environment systems since 1986, when their first head-mounted display
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prototype was completed. Since that time, one of the major goals of the
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department has been improving the realism of virtual worlds, by advancing
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the state of the art in both software and hardware systems.
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In this article I'll briefly outline UNC's concentrations for the year, as
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well as describe the current system used for developing VR-based
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applications.
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Fall 1992 sees the continuation of work on building PixelFlow, the newest
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machine in a line of graphics multicomputers built by members of the
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department. PixelFlow, detailed in a SIGGRAPH '92 paper by Fuchs and
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Molnar, will combine partial images produced by multiple independent
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rendering pipelines in a high-speed image composition network to produce
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the final image. Performance of this machine is expected to be linearly
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scalable to well over 10 million anti-aliased, textured polygons per
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second, supporting advanced shading models and multiple shaped light
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sources. A working prototype of the PixelFlow system is expected to be
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operational by early 1994.
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The current rendering machine used by most VR-based applications in the
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department is Pixel-Planes 5. The Pixel-Planes 5 multicomputer was part of
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the equipment brought to SIGGRAPH '91 by UNC, and was the graphics
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workhorse used in all of the demos that were shown there. (For more
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information on the SIGGRAPH '91 "Tomorrow's Realities" demos, see CyberEdge
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Journal issue #5.) Pixel-Planes 5 is programmed in C or C++ with a subset
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of PHIGS+, and can produce in excess of 2 million Phong-shaded, z-buffered
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triangles per second. VR applications are most commonly built using
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various libraries created by students, such as PPHIGS (graphics), trackerlib
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(tracking mechanisms), adlib (analog/digital devices), and vlib (virtual
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world-specific routines, such as maintenance of standard transformations).
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The Tracking group has developed a working optoelectronic tracking ceiling,
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made up of many 2- by 2-foot ceiling tiles with 32 infrared LEDs per tile.
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The special head-mounted display used with this ceiling tracker has four
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cameras attached to it which point at the ceiling-- these provide enough
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information for the computer to resolve the user's position to within 2 mm,
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and orientation to 0.2 degrees. Update rates depend on the mode the
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ceiling is in, but 50-80 Hz is typical, as is a lag of 15-30 ms. The
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ceiling is currently 10- by 12-feet, but plans are in the works to increase
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the size of the ceiling to 15- by 30-feet. Research is underway to
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develop a Self-Tracker, which can determine changes in position and
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orientation by viewing the existing environment.
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Head-mounted displays (HMDs) used by the department include a see-through
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prototype, a video-merge HMD, VPL EyePhones, and the Virtual Research
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Flight Helmet. For more complex user interactions, a variety of
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manipulators are available for use; these include an Argonne Remote
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Manipulator (ARM) force-feedback arm, a billiard ball, a Python joystick, a
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modified bicycle glove, a "wand", and a pair of analog joysticks. All of
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the hand-held input devices and HMDs (except for the optoelectronic tracking
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ceiling) are tracked by Polhemus 6-D magnetic trackers (3SPACE and FASTRAK
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models).
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Work on software for improving the stability of virtual environments this
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year is being led by Gary Bishop and the HMD group. This year's motto is
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"No Swimming", where swimming refers to the manner in which objects in
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virtual worlds appear to slosh around when the user turns their head.
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Swimming is the visible result of tracker lag, latency in the rendering
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pipeline, and other bottlenecks in the system. Several different areas are
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being actively worked on to improve the images we see in the head-mounted
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display: motion prediction using Kalman filters, beam-racing and
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"just-in-time-pixel display" to get rid of the inaccuracies due to the
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image-scanout time, examination of static and dynamic jitter in the
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trackers, and correction of the distortion in the HMD due to the optics
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used to achieve a wide field-of-view.
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Aside from the war on swimming objects in virtual worlds, there are several
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applications actively being worked on. The three major application projects
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at this time are the Nanomanipulator, the ultrasound volume-visualization
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project, and the architectural walkthrough.
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The Nanomanipulator, Russell Taylor's projected Ph.D dissertation topic, is
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a joint project between the UNC Computer Science Department and the UCLA
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Chemistry Department. UCLA provided a Scanning-Tunneling Microscope (STM),
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which Russell has created an inclusive interface to so that one can don the
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HMD and actually change the surface of an object on a molecular level, as
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well as feel the forces of the molecules via the ARM. The display will
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come up on an HMD or projection screen with cross-polarized shutter
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glasses, and the user can interact with either the ARM or the billiard
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ball. The hand-input device has various modes attached to it, which
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include feeling the surface, zooming in on a certain part of it, or
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altering it.
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The ultrasound project was shown in a paper at SIGGRAPH '92. The
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department has acquired an old ultrasound machine, and the goal is to be
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able to construct a volume-visualization of the object being examined,
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which would then be overlayed on top of live video and viewed with an
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HMD. This would make it seem as if a person had X-ray vision. Testing is
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commonly performed on a baby doll lying in an aquarium in the center of the
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graphics lab, but tests with live subjects have been performed as well.
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Closely associated with this project is the difficulty of overlaying
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computer-generated imagery on top of the real world. The real world is
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inherently real-time, while the computer-generated objects are going to be
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a bit slower due to the various bottlenecks of the tracking and
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image-generation systems. Different approaches for this application are
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being examined, such as using a see-through HMD instead of viewing the
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image overlayed on live video.
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The architectural walkthrough originally was not in the plan for work this
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year, but this decision was changed when it was pointed out as the only
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application being worked on by UNC that made it apparent when
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graphics algorithms were incorrect. Most people have never seen surfaces
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at a nanometer scale, or complex protein molecules, whereas an indoor scene
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is something which nearly everyone experiences for large durations each day.
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This makes debugging the shading models developed for use on the new
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graphics machines easier to debug, since almost anyone can look at an image
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and tell whether or not it appears realistic. This year's approach to the
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walkthrough deals largely with modelling details. Through a cooperation with
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Virtus Corporation, the Walkthrough project team is developing a much more
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intricate model of the upcoming expansion of Fred Brooks' house. The
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models are created on Virtus Walkthrough software for the Macintosh, and
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they are then uploaded to a Unix machine and converted to a Pixel Planes
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5-specific format. It is the hope that this new model will also be a great
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test for the upcoming PixelFlow machine.
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Other work being pursued at this time includes the addition of Focal Point
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software for producing directional sound, inclusion of TiNi ticklers for
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tactile feedback, expansion of the current 3DM inclusive world-building
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tool, and continued work on Richard Holloway's excellent vlib package.
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