20
Theory of Operation
FORESHORTENING
The discussion earlier about perspective and the screwdriver example assumed that the screwdriver (or
target) was “normal” to your eye. Normal means the object is being viewed straight on (perpendicular or at 90
degrees), so its full length is observed.
Look what happens to the observed size of the screwdriver when it is rotated away from 90 degrees to your
eye– it appears smaller.
The observed size of the screwdriver becomes shorter. The more it is rotated, the smaller it appears to be.
This effect is called foreshortening. As before, if you know the actual size of the screwdriver is 6 inches, by
measuring the observed size and applying mathematics it is possible to determine the screwdriver’s angle of
orientation with respect to the normal view.
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