Body relative direction
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Direction (geometry, geography)
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Body relative directions (also known as egocentric coordinates)[1] are geometrical orientations relative to a body such as a human person's body or a road sign. The most common ones are: left and right; forward and backward; up and down. They form three pairs of
orthogonal
axes.
Traditions and conventions
Since definitions of left and right based on the geometry of the natural environment are unwieldy, in practice, the meaning of relative direction words is conveyed through
fall freely
. Up is then defined as the opposite direction of down. Another common definition uses a human body, standing upright, as a frame of reference. In that case, up is defined as the direction from feet to head, perpendicular to the surface of the Earth. In most cases, up is a directionally oriented position generally opposite to that of the pull of gravity.
In situations where a common frame of reference is needed, it is most common to use an egocentric view. A simple example is road signage. Another example is
type compositor, returning to an egocentric view. In medicine and science, where precise definitions are crucial, relative directions (left and right) are the sides of the organism, not those of the observer. The same is true in heraldry, where left and right in a coat of arms is treated as if the shield were being held by the armiger. To avoid confusion, Latin terminology is employed: dexter and sinister for right and left. Proper right and proper left
are terms mainly used to describe artistic images, and overcome the potential confusion that a figure's "own" right or "proper right" hand is on the left hand as the viewer sees it from the front.
Forward and backward may be defined by referring to an object's or organism's
motion. Forward is defined as the direction in which the object is moving. Backward is then defined as the opposite direction to forward. Alternatively, 'forward' may be the direction pointed by the observer's nose, defining 'backward' as the direction from the nose to the sagittal border in the observer's skull
. With respect to a ship 'forward' would indicate the relative position of any object lying in the direction the ship is pointing. For symmetrical objects, it is also necessary to define forward and backward in terms of expected direction. Many mass transit trains are built symmetrically with paired control booths, and definitions of forward, backward, left, and right are temporary.
Given significant distance from the
magnetic compass and the sun
. Facing the sun, before noon, the north pointer of the compass points to the "left" hand. After noon, it points to the "right".