Helmet-Mounted Displays: - USAARL - The - U.S. Army

igure 4.2. AH-64 EO tracker.
Visual Coupling 83
high frequency background noise and the requirement for demanding high
component mounting accuracy during installation (Cameron, Trythall, and
Barton, 1995).
Regardless of the technology, an HTS must provide defined measures
of accuracy. System parameters include motion box size, pointing angle
accuracy, pointing angle resolution, update rate (of tracker, not display),
and jitter. The motion box size defines the linear dimensions of the space
volume within which the HTS can accurately maintain a valid line-of-sight.
The box is referenced to the design eye position of the cockpit. It is
desirable that this box provide angular coverage at least equal to that of
normal head movement, i.e., ±180º in azimuth, ±90 in elevation, and ±45º
in roll (Task and Kocian, 1995). The motion box size for the AH-64
IHADSS is 12 inches forward, 1.5 inches aft, ±5 inches laterally, and ±2.5
inches vertically from the design eye position. From a human factors
viewpoint, it is important that the motion box be able to accommodate
multiple seat positions and aviator posture variances.
Pointing accuracy, also referred to as static accuracy, usually means
F