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

Visual Coupling 4
Clarence E. Rash
Introduction
One HMD enhancement to mission effectiveness is the providing of
video imagery used for pilotage (most effective during night and foul
weather missions). This pilotage imagery is generated from sensors. These
sensors can either be head/helmet-mounted, as with ANVIS, or aircraftmounted,
as with the FLIR on the AH-64 Apache. With head-mounted
sensors, the resulting imagery is inherently correlated with the direction of
head line-of-sight. However, to obtain this spatial correlation for aircraftmounted
sensors, it is necessary to slave the sensor to head motion; the
sensor must be “visually coupled” to the head. [It should be noted that true
line-of-sight is defined by eye gaze direction as well as head direction.] To
accomplish this task, a head/eye tracking system is incorporated into the
HMD. This visual coupling also provides the capability to point (aim) fire
control systems (weapons). Visual coupling takes advantage of the natural
psycho-motor skills of the aviator (Brindle, 1996).
Tracking Systems
The fundamental concept of a visually coupled system (VCS) is that the
line-of-sight-direction of the aviator is continuously monitored, and any
change is replicated in the line-of-sight-direction of the (aircraft-mounted)
sensor (Task and Kocian, 1995). The subsystem which detects these
changes in head/eye position is called a tracking system (or tracker). As
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