Sperry Marine Visionmaster FT ECDIS User Manual page 503

ECDIS User Guide
Questionable
Unaligned
Unavailable
Uncompensated
Uncorroborated
65900012
There is a possibility that the data is not valid, usually
because no mechanism is being applied to ensure that the
data was not corrupted during transmission. For example,
this may be indicated if the NMEA messages providing the
data have no checksum (if the system is configured to
allow such messages). Questionable data is considered
usable, but degraded.
The data is received in a form that requires alignment, and
this alignment has not been performed yet. This would
typically apply to heading data received via a synchro or
stepper interface. When this applies, the data is
considered unusable.
No data is being received from the source or too few
samples have been received recently. When this applies,
the data is considered unusable.
The system could not adjust the data to be valid at the
consistent common reference point (CCRP) for the ship.
This adjustment is often referred to as a lever arm
correction. This is easiest to understand as it applies to
position data. When the system receives position data
from a GPS, the position applies to the position of the
GPS antenna, and must be adjusted to apply to the
CCRP. If the system has no heading data, it cannot
perform this adjustment. Compensation can also apply to
course over ground and speed over ground. When data is
Uncompensated, it is considered usable, but degraded.
The data does not match the data received via other
sensors that provide the same type of data. When half or
more than half of all sensors providing a given data type
disagree with the data from one sensor, then that sensor
is considered to be "not corroborated". For example, if we
have 2 GPS sensors, and GPS1 disagrees with GPS2,
then both will be "not corroborated". If we have 3 GPS
sensors, and GPS2 and GPS3 agree with each other, but
disagree with GPS1, then just GPS 1 will be "not
corroborated". When data is Uncorroborated, it is
considered usable, but degraded.
System
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