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HMR3500 User's Guide
Figure 7: Initialization Dialog Box
4.6 MAGNETIC DECLINATION AND AZIMUTH OFFSET
Magnetic declination (also known as magnetic variation), is the angle between true north and magnetic north and is a
function of location and, to lesser extents, date and altitude. Azimuth offset is defined as the horizontal angle between the
forward axis of the module and the reference axis of the platform on which it is mounted. Azimuth offset is a constant that
is a function of the mechanical mounting and installation of the compass. Both declination and offset angles directly affect
azimuth accuracy, and the compass applies both corrections by adding them to the raw magnetic azimuth measurement.
Both angles are provided as separate quantities to permit keeping track of them individually, even though their effect is
simply additive. The sign convention used for both angles is positive for east. For example, if magnetic north is east of
true north, the declination is positive.
If you don't know the magnetic declination for your current location, you can ask the compass to calculate it using the
World Magnetic Model. See 4.12 Magnetic Declination, on page 21.
4.7 ROLL AND PITCH OFFSET
Roll and pitch offsets are defined as the angle between the horizontal plane of the module and the reference plane that is
nominally "level" when the platform is stationary. It is a function of how the module is mounted with respect to the platform.
For both angles, they can be either positive or negative. A positive roll offset means the left side of the module is lower
than the reference plan. A positive pitch offset means the front side of the module is lower than the reference plan. The
numbers in the boxes will be added to the final roll and pitch values calculated from the compass.
4.8 ORIENTATION RATE
The output rate of the orientation data provided by the compass may be set by the user from less than 0.1 Hz to 50 Hz.
The specified frequency must have a period that is a multiple of five milliseconds. For this reason, the frequency you enter
may be adjusted to the nearest integer value and will be shown.
4.9 RESET MODULE
The Reset command is equivalent to cycling the compass power, and will cause the power-up message to be displayed.
The RSET command sent to the module is described on page 8). Also, serial number and version information stored in
the CompassHost program will be reset. The module should respond with a DPOWER, which will cause CompassHost to
solicit version information again.
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