5.2 LD8 output sentences
TRINAV version 3 definitions commentary
1. The "Nav point no." is a unique integer identifying the position. It should be manually entered into
the software according to requests from Positioning Engineers. Alternatively, this should start
from 1 and be incremented if several positions are output from the same system.
2. The system name should identify the system (or contractor) and software version (e.g. "SEADIFF
2.1" or "MFIX 1.2.3").
3. The "Age of fix" is the time of the first character of the data string being output to WesternGeco’s
positioning system minus the time of position.
4. WGS84 ellipsoid and datum must be used. The height must be antenna height above the WGS84
ellipsoid.
5. The variance and covariance terms are elements from the variance-covariance matrix of the
position fix computation (un-scaled).
6. The external reliability is the maximum positional effect of an undetectable error in an
observation. This quantity is related to the power of the test (the probability that the MDE would
be detected) and the significance level used.
1. The values recommended by UKOOA should be used (see UKOOA Guidelines for the use of
Differential GPS in offshore surveying, Issue no. 1, Sept. 1994) i.e. a significance level of test
1% and the power of the test 80%.
2. If values other than those given above are used, this must be explicitly stated by the
contractor.
7. TRINAV V3 fix status codes:
Status code Meaning
0 No or bad fix
1 Altitude aiding (Weighted height used in fix)
2 Altitude hold (2D fix)
3 3D fix
4 3D fix INS aided
5 INS only (dead reckoning)
8. TRINAV V3 computation type codes
Type code Meaning
0 No corrections
1 Single frequency DGNSS
2 Dual frequency DGNSS
3 PPP (satellite orbit and clock corrections)
4 PPP-AR (ambiguity resolution) using phase bias information.
5 Other
9. TRINAV V3 source codes:
Type code Meaning
L L-band only, always followed by 1 (i.e. L1)
M L-band multi-channel, followed by number of links tracked (e.g. M3)
I Internet source, always followed by 0 (i.e. I0)
O Other, always followed by 0 (i.e. O0)
10. "No. of ref. stations" gives the number of reference stations in use for this fix, not the number of
stations available. This field must be set to 0 if the fix is not differential.
53
LD8 Operations Manual
To Next Page
