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

Introductory Overview 11
aviator to perform a certain number of complex tasks. The performance of
these tasks is impacted by aviator skills and capabilities (user properties),
and by the characteristics of the HMD. The operational environment may
include high speed, low level flight, during low illumination and/or adverse
weather conditions. Eggleston (1997) developed a model which maps
aviator tasks (e.g., navigation, unmasking maneuver, etc.), user properties
(e.g., perception, organization, etc.), and HMD characteristics (e.g., FOV,
resolution, etc.) for specific missions and mission elements. This type of
analysis is essential in ensuring an optimal HMD design which meets the
needs of the aviator and the mission.
In summary, the design specifications for any system must be guided
by these criteria convolved with hardware limitations, human performance
strengths and weaknesses, and good human factors engineering practices.
[Note: This book does not tackle the complex, and still unresolved, issue
of HMD imagery information content, which includes the selection of types
and quantity of data to be presented, the symbols used, or their placement
within the displayed imagery. Interested readers may find information in
these areas in Craig, Marshall, and Jordan (1997), Drewery, Davy, and
Dudfield (1997), and Murray (1997).]
Helmet-Mounted Displays Overview
Melzer and Moffitt (1997) describe an HMD as minimally consisting
of “an image source and collimating optics in a head mount.” For the
purpose of this book, we expand this description to include a visual
coupling system, which performs the function of slaving head and/or eye
positions and motions to one or more aircraft systems. Figure 1.5 presents
the basic Army aviation HMD as a block diagram in which there are four
major elements: image source (and associated drive electronics), display
optics, helmet, and head/eye tracker. The image source is a display device
upon which sensor imagery is produced. These sources typically have been
miniature CRTs or I 2 tubes. Other miniature displays based on FP
technologies rapidly are becoming alternate choices. The display optics
are used to couple the display imagery to the eye. The optics generally
magnify and focus the display image. The helmet, while providing the
protection for which it was designed originally, serves additionally as a
platform for mounting the image source and display optics. The tracking