The HIVE is composed of several major sub-systems and components as depicted in Figure 1 below:
Figure 1: Huge Immersive Virtual Environment System.
Figure 2: The wearable rendering 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 2 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 (HMD) and Orientation Tracker
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) Twelve Infrared Cameras
In general, optical position tracking using triangulation can operate over longer distances with less interference than alternative tracking technologies. HIVE cameras (Figure 3) work optimally in cool ambient lighting (e.g., fluorescent, mercury vapor lights, and sodium vapor lights). The use of twelve cameras facilitates coverage of the large tracking area, increases precision, and reduces possible problems related to occlusions.
Figure 3: A HIVE camera
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 researchers to monitor the visualizations that are displayed in the user's HMD. The 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 the VE state across machines is handled automatically over the Local Area Network via UDP packets.
Currently, we use Unity 3D to support the HIVE. Unity provides a basic framework for quickly constructing real time 3D computer-simulated environments. With support for most standard 3D model and texture formats, visual content can be easily developed with third party modeling programs.
HIVE researchers have implemented a HIVE application programming interface (API). The primary purpose of this API is to standardize the way software interfaces 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.