The article provides information regarding the location of the dual GNSS antennas on the object and the setting of the corresponding parameters for dual-antenna systems. The article information below is related to the following systems:
- INS-D
- INS-DU
- INS-DL
- INS-DM
- MRU-PD
The generalized name “INS” is used hereinafter for convenience and clarity.
The Inertial Labs INS uses a heading calculated by a dual-antenna GNSS receiver for the correction. The INS and dual GNSS antennas can be installed in different places of the carrier object. Moreover, the placement of the antennas near the INS is undesirable due to the possible impact on the magnetometers (for the systems that utilize magnetometers). While the best place for the INS is the center of gravity of the carrier object, the GNSS antennas should be placed with a clear view of the sky with a sufficient ground plane.
The GNSS heading is the RTK solution of the secondary antenna based on the primary antenna. As such, it is very sensitive to all issues related to multipath.
There are the following ways to improve GNSS heading:
– to isolate any possible multipath sources.
– to install antennas on the grounding planes.
– to install antennas higher than surrounding objects/devices/parts of the carrier object.
– to check if any not-shielded USB3 devices nearby can interfere with GNSS L2.
– to extend the baseline if possible (the recommended baseline is 1. 5 meters).
Also, there is an option to use multipath-rejecting antennas (like NovAtel VEXXIS® GNSS-800 Series).
The GNSS antennas can be installed with virtually any orientation in the horizontal plane of the object. For example, the baseline can be aligned with the longitudinal axis of the object OR with the lateral axis of the object OR not aligned with any object’s axis. The key is that the position of the antennas should be measured as accurately as possible relative to the accelerometer mass-center of the INS and stored in the INS memory.
For the location of the accelerometer mass center of your device, please refer to the main ICD.
The position of the primary antenna is measured in the object axes – to the right, forward, and up. Then, it is necessary to enter these coordinates in appropriate fields in the IMU tab of the “Device option” menu of GUI and click “OK” to apply and save these settings (Figure 2).
It is possible to set the secondary antenna location in two ways: by specifying its position in meters relative to the accelerometer mass-center of the IMU in the “Secondary antenna position relative to the IMU (m)” fields or by specifying the antenna’s baseline orientation in degrees in the “Antennas baseline orientation (deg)” fields (Figure 3).
Fig. 4. shows Alpha and Beta angles of the antennas` baseline orientation relative to the INS unit. Alpha angle is measured in the horizontal plane of the object, with a clockwise direction positive. Beta angle is measured in a vertical plane of the object, with up positive. Note that in Fig. F.5 there are positive Alpha and negative Beta angles.
Fig. 5. shows Alpha and Beta angles of the antennas` baseline orientation relative to the MRU unit. Alpha angle is measured in the object’s horizon plane, and the clockwise direction is positive. Beta angle is measured in vertical plane, positive is up. Note that on the Fig. 5. there are positive Alpha and Beta angles.
Please note, that there is no possibility to enter the antenna position with a higher than centimeter resolution. However, this limitation does not prevent the device from providing position accuracy according to the specification.