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60 SPAN-IGM User Manual Rev 2
Appendix B Frequently Asked Questions
1. Why don’t I have any INS logs?
On start-up, the INS logs are not available until the system has solved for time. This requires that an
antenna is attached, and satellites are visible, to the system. You can verify that time is solved by
checking the time status in the header of any standard header SPAN log such as BESTPOS. When
the time status reaches FINETIME, the inertial filter starts and INS messages are available.
2. How can I access the inertial solution?
The INS/GNSS solution is available from a number of specific logs dedicated to the inertial filter. The
INSPOS, INSPVA, INSVEL, INSSPD, and INSATT logs are the most commonly used logs for
extracting the INS solution. These logs can be logged at any rate up to the rate of the IMU data (125
or 200 Hz). The solution can also be triggered by the mark input signal by requesting the MARKxPVA
logs. Further details on these logs are available in the SPAN on OEM6 Firmware Reference Manual
(OM-20000144).
3. Can I still access the GNSS-only solution while running SPAN?
The GNSS only solution used when running the OEM6 receiver without the IMU is still available
when running SPAN. Logs such as PSRPOS, RTKPOS and OMNIPOS are still available. The
BESTGNSSPOS log is also available to provide the best available GNSS only solution. Any non-INS
logs should be logged at a maximum rate of 5 Hz when running SPAN. Only INS-specific logs
documented in the SPAN on OEM6 Firmware Reference Manual (OM-20000144) should be logged
at rates higher than 5 Hz when running SPAN.
4. What will happen to the INS solution when I lose GNSS satellite visibility?
When GNSS tracking is interrupted, the INS/GNSS solution bridges through the gaps with what is
referred to as free-inertial navigation. The IMU measurements are used to propagate the solution.
Errors in the IMU measurements accumulate over time to degrade the solution accuracy. For
example, after ten seconds of GNSS outage, the horizontal position accuracy is approximately 3 m.
The SPAN solution continues to be computed for as long as the GNSS outage lasts, but the solution
uncertainty increases with time. This uncertainty can be monitored using the INSCOV log, see the
SPAN on OEM6 Firmware Reference Manual (OM-20000144).