Importance of Antenna Location for ALIGN

To achieve the best SPAN performance when using dual antenna (ALIGN):

  • the two GNSS antennas should be mounted on the vehicle securely in a stable location

  • the two GNSS antennas should be mounted as far apart as possible

  • the two GNSS antennas should be mounted away from other vehicle obstructions resulting in a clear view of the sky

  • the primary GNSS antenna should be mounted as close as possible to the IMU

The primary and secondary GNSS antenna can be mounted anywhere on the vehicle with a fixed distance (baseline) between them. The baseline between the two antennas does not need to be aligned with the vehicle axes or with the axes of the IMU.

The heading accuracy is dependent on the antenna baseline length. For best performance, mount the antennas as far part as possible. A separation of 1 metre is the minimum recommended distance. At a baseline length of 1 metre, the ALIGN accuracy is 0.20°. If the baseline length were 0.5 metre, the ALIGN accuracy would be 0.40°. A 2 metre baseline results in an ALIGN accuracy of 0.08°.

Finally, the primary antenna should be mounted as close as possible to the IMU while still maintaining a maximum antenna baseline length. This may lead to some compromise being made for the primary antenna location. Preference should be put on keeping the primary antenna closer to the IMU even it results in a shorter baseline between the two GNSS antennas.

As with the primary antenna lever arm, it is also important to have the best possible accuracy on the IMU to the secondary antenna lever arm (refer to the Importance Of Lever Arms). However, as measuring lever arms can be difficult, an alternative is to calibrate the IMU Body frame to ALIGN frame rotation using the INSCALIBRATE command or to measure that rotation directly and enter it using the SETINSROTATION command.