Figure 2 Earth Field Vector - Philips KMZ51 Application Note

Philips Semiconductors
Electronic Compass Design using
KMZ51 and KMZ52
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 or dip δ
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. If a
compass is tilt, then inclination has to be considered, as explained in section 9.
• Declination λ
The angle between geographic or true north and magnetic north. Declination is dependent 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 with respect to geographic north. This is pointed out in section 8.
azimuth
inclination
or dip
Hex
α
δ
Hez
z
(down)
Figure 2
x
(heading
direction)
declination
Heh
λ
HEVECTOR.AI
Hey
He
Earth field vector
9
Application Note
AN00022
magnetic
north
true
north
y y
(right) (right)