APPENDIX F Frequently Asked Questions
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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 log such as BESTPOS. When the time status reaches FINETIME, the inertial fil-
ter starts and IMU data is available.
5. How can I access the inertial solution?
The GNSS+INS solution is available from a number of specific logs dedicated to the inertial filter. The
INSPOS
log,
INSPVA
log,
INSVEL
log,
INSSPD
log and
INSATT
log 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 (100, 125 or
200 Hz depending on your IMU model). The solution can also be triggered by the mark input signal by
requesting the
MARKxPVA
logs.
6. Can I still access the GNSS-only solution while running SPAN?
The GNSS only solution used when running the OEM7 receiver without the IMU is still available when run-
ning SPAN. Logs such as the
PSRPOS
log and
RTKPOS
log 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 max-
imum rate of 5 Hz when running SPAN. Only INS-specific logs should be logged at rates higher than 5 Hz
when running SPAN.
7. What will happen to the INS solution when I lose GNSS satellite visibility?
When GNSS tracking is interrupted, the INS 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 meas-
urements accumulate over time to degrade the solution accuracy. For example, after one minute of GNSS
outage, the horizontal position accuracy is approximately 2.5 m when using an HG1700 AG58. 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
INSSTDEV
log or
INSSTDEVS
log.
8. Why can SPAN not align with my IMU-KVH1750?
SPAN requires that the IMU-KVH1750 be configured with non-default settings. If you have obtained your
IMU-KVH1750 directly from KVH, or have manually changed the IMU configuration, refer to
on page 52 for information about configuring the IMU for operation with SPAN.
Further details on the command and logs in this section are available in the
.