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The azimuth is usually measured from 000°
at the reference direction clockwise through 360°. An azimuth is often
designated as true, magnetic, compass grid, or relative
as the reference direction is true, magnetic, compass,
or grid north, or heading, respectively. Unless otherwise
specified, the term is generally understood to apply to true azimuth,
which may be further defined as the arc of the horizon, or the
angle at the zenith, between the north part of the celestial meridian
or principal vertical circle and a vertical circle, measured
from 000° at the north part of the principal vertical circle clockwise
through 360°. Azimuth taken directly from a table, before interpolation,
is called tabulated azimuth. After interpolation, or, if determined
by calculation, mechanical device, or graphics, it is called computed
azimuth. When the angle is measured in either direction from north
or south, and labeled accordingly, it is properly called azimuth angle;
when measured either direction from east or west, and labeled accordingly,
it is called amplitude. An azimuth determined by solution of the
navigational triangle with altitude, declination, and latitude
then is called an altitude azimuth; if meridian angle, declination,
and latitude are given, it is called a time azimuth; if meridian
angle, declination and altitude are given, it is called a time and
altitude azimuth. |
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