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Declination Value
Declination, also called magnetic variation, is the difference between true and magnetic north, relative to
a point on the earth. It is measured in degrees east or west of true north. Correcting for declination is
accomplished by storing the correct declination angle, and then changing the heading reference from
magnetic north to true north. Declination angles vary throughout the world, and change very slowly over
time. For the greatest possible accuracy, go to the National Geophysical Data Center web page below to
get the declination angle based on your latitude and longitude:
http://www.ngdc.noaa.gov/cgi-
bin/seg/gmag/fldsnth1.pl
Pitch and Roll
The TCM2.5/2.6 uses accelerometers to measure the orientation of the compass with respect to gravity.
Since the compass also measures the complete magnetic field, the TCM2.5/2.6 can correct for the tilt of
the compass to provide an accurate heading.
The TCM2.5/2.6 utilizes Euler angles as the method for determining accurate orientation. This method is
the same used in aircraft orientation where the outputs are Heading (Yaw), Pitch and Roll.
When using
Euler angles pitch and roll are defined as the angle rotated around an axis through the center of the
fuselage; pitch is rotation around an axis through the center of the wings. These two rotations are
independent of each other since the rotation axes rotate with the plane body.
For the TCM2.5/2.6 a
positive pitch
is when the
front edge of the board is rotated upward
and a
positive
roll
is when the
right edge of the board is rotated downward.
Figure 3: TCM2.5 Pitch & Roll Axes
Figure 4: TCM2.6 Pitch & Roll Axes
