SPAN Operation Chapter 3
SPAN-IGM User Manual Rev 2 35
3.2.5.3 Set up a Wheel Sensor
1. Send the following commands to setup the wheel sensor.
ENCLOSUREWHEELSENSOR ENABLE 1HZ
SETWHEELPARAMETERS ticks circ spacing
2. Send the following commands to log the wheel sensor data.
LOG TIMEDWHEELDATAB ONNEW
LOG WHEELSIZEB ONCHANGED
3.3 Azimuth Sources on a SPAN System
The SPAN system use three different methods to calculate the azimuth.
• Course Over Ground
• Inertial Azimuth
• ALIGN Azimuth
3.3.1 Course Over Ground
The course over ground azimuth is determined using the position delta between two position solutions
computed by the SPAN-IGM. This is the simplest way to compute an azimuth and is done using either
the GNSS solution or the INS solution. This method does not work when the vehicle is stationary as any
position difference is due to position error and the computed azimuth is meaningless.
Course over ground azimuth is of greatest advantage in aerial or marine environments where the actual
direction of travel may not match the forward axis of the aircraft/boat due to winds or currents. This effect
is known as the crab angle. Course over ground azimuth is a great way to compute the offset if another
means of computing the vehicle azimuth are available.
Course over ground azimuths are available in several different velocity logs. See Table 6, Logs with
Azimuth data on page 36.
3.3.2 Inertial Azimuth
The inertial azimuth computed by the SPAN inertial navigation filter. It uses the sensors in the IMU to
compute the azimuth of the IMU (this can be rotated to another reference if desired). For more
information, see the APPLYVEHICLEBODYROATION and VEHICLEBODYROTATION commands in the
SPAN on OEM6 Firmware Reference Manual (OM-20000144).
This azimuth is the one provided in the majority of the INS logs available to a SPAN user. See Table 6,
Logs with Azimuth data on page 36.
3.3.3 ALIGN Azimuth
On SPAN systems with dual antennas, an azimuth is available from the dual antenna baseline. This is
the same azimuth that is used as an update to the SPAN solution. It is noisier than the inertial azimuth
and is available at a much lower rate, but will have a stable mean. This azimuth is computed from the
master antenna to the rover antenna based on how the antennas are oriented on the vehicle.
There is a specific subset of logs that output this azimuth. See Table 6, Logs with Azimuth data on
page 36.
The parameters entered in the SETWHEELPARAMETERS command depend on the wheel
sensor being used. See the OEM6 Family Firmware Reference Manual (OM-20000129)
for more information about this command.
