Heading Angle Or Azimuth (A); Inclination (D); Declination (L); Fig 13 Earth's Magnetic Field - Nokia NPL-4 Series Manual

NPL-4/5/RM-104
System Module and User Interface
Heading angle or azimuth (α)
The angle between magnetic north and the heading direction. Magnetic north is the
direction of x
h
paper, x y will be referred to as "horizontal" component of the earth´s field.
h h
The compass heading is defined by:
The azimuth is the reading quantity of a compass. Throughout this paper, α is counted
clockwise from magnetic north, i.e. north is 360° or 0°, east is 90°, south is 180°, west is
270°.
Inclination (δ)
Also known dip. The angle between the earth´s field vector and the horizontal plane. As
already pointed out, the inclination varies with the actual location on earth, being zero
at the equator and approaching ±90° near the poles.
Declination (λ)
The angle between geographic or true north and magnetic north. Declination is depen-
dent on the actual position on earth. It also has a long-term drift. Declination can be to
the east or to the west and can reach values of about ±25°. The azimuth measured by a
compass has to be corrected by the declination in order to find the heading direction
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Page 44
Figure 13: Earth's Magnetic Field
y the earth´s field component perpendicular to gravity. Throughout this
h
α
Heading (
⎛ ⎞
y
⎜ ⎜ ⎟ ⎟
=
h
) arctan
⎝ ⎠
x
h
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