Figure 8.
Scanning pattern.
c. Depth Perception. Periods of low illumination greatly reduce the
ability of the eve to determine distances. Therefore, various cues must be
used to estimate distances at night. These monocular cues are usually used
at the subconscious level. Awareness of these cues by crew members may
enable them to look for and use cues that they are not in the habit of
using.
(1) Geometric perspective: The size and shape of an object changes
depending on the distance and angle from which it is viewed. These apparent
changes give a geometric perspective that is evaluated in three different
ways.
(a) Linear perspective. Objects appear to converge over
distance. Therefore, you estimate the distance to an object by comparing
the apparent separation to the known separation. For example, if you know
the distance between the navigation lights of an aircraft, you can estimate
the distance to the aircraft by comparing their apparent separation distance
to the known separation distance.
(b) Apparent foreshortening. The shape of an object tends to
appear elliptical over distance. Therefore, you estimate the distance
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