Azimuth Sources on a SPAN System
The SPAN system use three different methods to calculate the azimuth.
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Course Over Ground
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Inertial Azimuth
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ALIGN Azimuth
Course Over Ground
The course over ground azimuth is determined using the position delta between two position solutions computed by the OEM7 receiver. 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 is available.
Course over ground azimuths are available in several different velocity logs. See Table: Logs with Azimuth Data.
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 SETINSROTATION command.
This azimuth is the one provided in the majority of the INS logs available to a SPAN user. See Table: Logs with Azimuth Data.
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 base 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: Logs with Azimuth Data.