Coordinate
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Coordinate
One of a set of measures defining a point in space.
If the point is know to be on a given line, only one coordinate is
needed; if on a surface, two are required; if in space, three. Cartesian
coordinates define a point relative to two intersecting lines, called axes. If
the axes are perpendicular, the coordinates are rectangular; if not
perpendicular, they are oblique coordinates. A three-dimensional system of
Cartesian coordinates is called space coordinates. Polar coordinates define a
point by its distance and direction from a fixed point called the pole.
Direction is given as the angle between a reference radius
vector and a radius vector to the point. If three dimensions are involved,
two angles are used to locate the radius vector. Space-polar coordinates
define a point on the surface of a sphere by (1) its distance from a fixed
point at the center, the pole; (2) the colatitude or angle between the polar
axis (a reference line through the pole) and the radius vector (a straight
line connecting the pole and the point); and (3) the longitude or angle
between a reference plane through the polar axis and a plane through the
radius vector and the polar axis. Spherical coordinates define a point on a
sphere or spheroid by its angular distances from a primary great circle and
from a reference secondary great circle. Geographical or terrestrial
coordinates define a point on the surface of the earth. Celestial coordinates
define a point on the celestial sphere.
Table VI
summarizes the terms used in four geocentric celestial coordinate systems and
the terrestrial (geographic) coordinate system and indicates the analogous
terms under each system.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use