A heads up display (HUD) is a computerized readout displayed on a transparent surface, such as a windshield, which displays information while maintaining the view. Originally developed for utilization in military applications, this display has many uses — including flight simulators, automobiles, commercial aircraft and motorcycle helmets. In gaming, many first-person shooters feature HUD displays.
The purpose of a heads up display is to provide critical data to the viewer while not distracting him or her from the primary task for which the data is needed. It informs a fighter jet pilot of heading, altitude, air speed and orientation to the horizon line, among other data, which lessens the need for the pilot to look down at the instrument panel. Commercial planes have similar HUDs, and some automobiles feature one showing speed. Motorcycle helmets with a heads up display on the visor shield project speed and gear number.
The type of display used in aircraft requires three basic parts: a computer, combiner and an overhead projector unit (OPU). The computer interfaces with the aircraft to collect and format data from the flight management system as well as other systems, while the OPU projects the data on to a combiner. A combiner is made of coated, transparent glass that only reflects light in the green wavelength. The OPU is installed behind the pilot’s head, while the combiner is installed in the field of vision. In some models, the OPU and combiner are one unit.
Refocusing the eyes can cause fatigue, so an aircraft’s heads up display is “focused at infinity” allowing the pilot to read the display without shifting focus. When used in automobiles, the display is focused closer, somewhere near the end of the hood. Motorcycle helmets also have a relative focal point for maximum comfort.
This type of display can also be ocular, worn as a portable device over one eye. This type of HUD is most often used by military in the field to display tactical information. Experiments are also ongoing for development of a heads up display that would send information directly to the eye’s retina.
Other types of HUD devices in development will use Synthetic Vision Systems (SVS) to display real-world computer-generated terrain from high-resolution databases. When an aircraft is in flight with no visibility, for example, this type would render surrounding land on the display. If the aircraft’s vector were headed for an obstacle, the obstacle would change color in the display to warn the pilot, providing ample time to change course.