Reference information
LD8 Operations Manual 40
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.
a. 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%.
b. If values other than those given above are used, this must be explicitly stated by the contractor.
7. TRINAV V3 fix status codes:
8. TRINAV V3 computation type codes:
9. TRINAV V3 source codes:
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.
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