Navigation Procedures

For any type of acquisition, on any vehicle, navigation data is recorded following this general outline:

1. The first satellites are tracked and coarse time is solved.

2. Enough satellites are tracked to compute a position.

3. Receiver “fine time” is solved, meaning the time on board the receiver is accurate enough to begin timing IMU measurements.

4. Raw IMU measurements begin to be timed by the receiver and are available to the INS filter. The INS Status field changes from Inactive to awaitingAzimuth. This indicates that the navigation system is waiting on an azimuth (or heading). An azimuth is the direction that the system faces(the yaw component of attitude), where true north is represented as 0 degrees. With most systems, the azimuth must be determined through GPS course over ground, a process known as "inertial alignment".

5. Once the inertial alignment routine begins the INS Status field will change to Aligning. For rovers with dual antenna systems, alignment is complete once an RTK position is solved between both antennas. For single antenna setups, an alignment routine must be performed, either kinematically or statically.

6. The rover will transition to navigation mode when alignment is complete, indicating that the heading has been determined with sufficient certainty. The INS Status field will change to AlignmentComplete.

7. The solution is then refined using updates from GNSS. Once the system is operating within specifications and after some vehicle movement, the INS Status field changes to SolutionGood. This indicates that the estimated azimuth standard deviation is below the preset value. If it increases above the preset value, the status changes to HighVariance.

Before using the rover to collect lidar or camera data, the navigation system needs to be initialized and aligned (status of AlignmentComplete) in order to produce an accurate estimate of all of the system’s trajectories. Generally speaking, most of the above sequence is performed automatically by the navigation system, however a proper inertial alignment, or azimuth determination, requires some knowledge and competence by the lidar operator.

Inertial alignment is either static or kinematic. Most systems cannot align statically and require kinematic GNSS data to align. Static and kinematic alignment processes is described here.

All other navigation system statuses are described below:

INS Status	Description
Inactive	INS is inactive. The alignment routine has not started.
DeterminingOrientation	INS is determining which IMU axis is aligned with gravity.
Aligning	INS is in alignment mode.
AlignmentComplete	The INS filter is in navigation mode, however not enough vehicle dynamics have been experienced for the system to be within specifications.
SolutionGood	The INS filter is in navigation mode and the INS solution is good.
HighVariance	The INS solution is still being computed but the azimuth solution uncertainty has exceeded the threshold. The default threshold is IMU dependent. The solution is still valid but you should monitor the solution uncertainties. You may encounter this state during times when the GNSS, used to aid the INS, is absent.
WaitingInitialPos	The INS filter has determined the IMU orientation and is awaiting an initial position estimate to begin the alignment process.