The HIVE is composed of several major sub-systems and components as depicted in the Figure below. These include: a.) a wearable rendering system, b.) a head-mounted displayand orientation tracking device, c.) eight infrared cameras, d.) a position processing system, e.) a control room for monitoring the VE state. All processing units are linked together by an 802.11b wireless network. Specialized system software interfaces with hardware devices, processes sensor data, and supports rapid development of virtual worlds.
Figure 1. Huge Immersive Virtual Environment System.
a.) Wearable rendering system. Users of the HIVE are completely un-tethered and encumbered as little as possible. HIVE users carry a portable rendering unit, orientation sensor for head-tracking, a custom-built video control unit for the HMD, and associated power supplies. The rendering computer, video control unit (VCU), and power supplies are mounted to a small backpack frame (see Figure to the right). The total weight of the backpack with a single battery for HMD power is approximately 9.8 kilograms.
b.) Head-mounted display. Immersion in the HIVE is achieved by presenting computer generated images to participants in an NVIS nVisor SX HMD. The unit is a light weight (1 kg), dual VGA frame-parallel HMD. The HMD has a stereo display with a resolution of 1024 x 1280 for each eye. Field of view is approximately 60° diagonal and 48° horizontal with an angular resolution is 2.25 arc minutes per pixel. Overlap between the displays is 100%. The dual reflective FLCOS (Ferroelectric Liquid-crystal-on-Silicon) displays produce 24 bit true color with a contrast ratio of 200:1. Head phones with frequency response ranging from 15 to 25,000 Hz are integrated into the unit. Correct synch information and voltage must be supplied to the HMD through a stereo video control unit (VCU).
c. Eight infrared cameras. In general, optical position tracking using triangulation can operate over longer distances with less interference than alternative tracking technologies. HIVE cameras work optimally in cool ambient lighting (e.g., fluorescent, mercury vapor lights, and sodium vapor lights). The use of eight cameras facilitates coverage of the large tracking area, increases precision, and reduces possible problems related to occlusions.
d.) Position processing system. The HIVE uses the infrared Precision Position Tracker (PPT X8) manufactured by WorldViz, LLC. It is capable of tracking the position of up to eight markers (infrared LEDs emitting light at 880 nm) simultaneously. The system updates position at 60 Hz; the manufacturer indicates that the total latency for the tracker (including RS232 communication) is 20 ms. For measurements within five meters of the center of the HIVE, position tracking error averages 2.09 cm ± .005 (for a 95% confidence interval). 80% of the tracking area has an absolute measurement error less than 7.49 cm, and overall RMS error is 6.68 cm. Variability in postition estimates averages 0.44 cm ± .28 (for a 95% confidence interval). 80% of the tracking area has a variability in position estimation of less than 0.63 cm.
e.) Control room. The rendering and position-tracking computers are controlled and monitored through a graphics workstation. This workstation provides remote access to the computer worn by the user as well as to another workstation dedicated to the position tracking system. It enables experimenters to monitor the visualizations that are displayed in the user’s HMD. HIVE software supports monitoring by creating a cluster-based network. This allows multiple viewpoints of a single virtual simulation to be rendered across more than one computer. Low-level synchronization of VE state across machines is handled automatically over the LAN via UDP packets.
Both Vizard (developed by WorldViz LLC) and Panda3D (developed jointly by Disney and Carnegie Mellon University ’s Entertainment Technology Center ) are currently used to support the HIVE. Both are Python based toolkits that provide a basic framework for quickly constructing real time 3D computer-simulated environments. With support for most standard 3D model and texture formats, visual and auditory content can be easily developed with third party modeling programs.
HIVE researchers have extended both Vizard and Panda 3D by implementing a HIVE application programming interface (API). The primary purpose of this API is to standardize portions of the VE software that interface with the various input devices of the HIVE, and to speed the implementation of research and other applications of the HIVE. The standardization further speeds development of virtual worlds to provide specialized functions that support experimental work conducted in the HIVE.
• Multi-user support