Real-Time

A common problem in inertial sensor configuration and usage is setting-up properly the GNSS lever arm and other external sensor installation parameters: A precise lever arm (within 1cm) is a key to ensure optimal precision. Angle between inertial sensor an a dual antenna system should also be accurately measured within less than 0.05° to ensure proper navigation performance.

However measuring angles and lever arms with such precision is generally not practically feasible, unless using a total station. In challenging conditions, this expensive solution might not be able to account for small misalignment between a short baseline dual antenna and a miniature inertial sensor (typical UAV setup).

To overcome these issues, SBG Systems have developed efficient algorithms and procedures to calibrate precisely the installation lever arms and small angles. GNSS lever arms and DVL alignment are estimated through this procedure.

This procedure can be performed in Qinertia post-processing software for optimal performance, or for high performance navigation systems (Ekinox, Apogee, Navsight, Quanta), through the integrated web interface.

The procedure is slightly different in real time and in Qinertia, but the main steps are the following:

1. Enter a rough “a priori” configuration, with 10cm precision on each lever arm

2. Run a calibration sequence, with higher dynamics than usual operation to allow the EKF observing the various lever arms and angles (moving typically through figure of eights).

3. Compute the refined calibration parameters using Qinertia or using the real-time calibration interface, and apply these parameters in the sensor non-volatile memory

4. Use the sensor normally, with the precise lever arm setup to ensure high performance and robustness

You can click on [calibration procedure to link when available] to see the see the real-time calibration procedure for SBG Systems high performance units.

Ellipse series

On the Ellipse series, the default operation includes automatic lever arm estimation to allow easy setup. Once refined parameters are obtained through Qinertia, it’s possible to stop this automatic lever arm estimation to enable best performance.

Post-Processing

As for real-time, it is possible to estimate lever arms and alignment using Qinertia post-processing software. Qinertia offers the best solution available on the market to efficiently estimate mechanical installation parameters. Please read the dedicated Lever Arm Estimation article in the Qinertia User Manual to get more details.

In Qinertia, this is easily done by telling Qinertia that the external sensor lever arms are not accurately measured. A simple box in the GNSS configuration window must be unchecked:

The next time Qinertia processes the data, it will estimate the lever arms and possible alignment between the two antennas. This estimation will appear in a window automatically once the processing is done and will show the current settings compared to the estimated settings. You can then choose to use these new settings or not and to launch a new processing. These steps can be done multiple times to converge towards the best lever arms which is usually when the current lever arms are equal to the estimated lever arms.


Of course as in real-time there are things to take into consideration when estimating lever arms and alignment in post-processing. As in real time it is important to have dynamics to have a good estimation in 3D. It is also important to do this while in PPK accuracy to measure these lever arms as accurately as possible.