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w-Test:
The w-test entails normalizing the residuals of a GPS pseudorange solution and
testing these against a 99% confidence limit for outliers. This limit is 2.576. If
outliers are found, they are removed and the solution is re-executed excluding
that satellite data pertaining to the outlier. If more than one satellite is found to
produce a residual outlier, only that satellite with the largest normalized residual
is eliminated. This continues until no outliers are present or until the exclusion of
any more data would result in insufficient data for a solution (four satellites for 3D
and three for 2D). Since the normalized residuals tend towards being equal with
reduced redundancy (as the number of satellites used in the solution approaches
the minimum required), it is unlikely that WinFrog will ever have to stop the
exclusion of data due to insufficient satellites. Nonetheless, WinFrog still checks
for this condition.
Caution should be exercised when using this option. If the vessel is too far away
from the selected reference stations and/or there are few satellites in common
with the vessel and the reference station(s) the w-test option may eliminate data
to the point where the solution approaches the minimum required.
F-Test:
The F-test is a check of the unit variance of the GPS pseudorange solution. This
confirms the validity of the model used for the solution and the weighting of the
observations used. Note that it is only a confirmation check, no data or solution
results are thrown out based on the results of the test.
The unit variance is the sum of the weighted, squared residuals, divided by the
degrees of freedom (number of redundant measurements) in the solution. The F-
Test should result in unity. If the unit variance is consistently different from unity,
it indicates that there may be a problem with the stochastic model used, or an
unmodeled bias in the data.
RefStns:
Click the RefStns button in the Pseudorange Calculation dialog box to open the
Select DGPS Reference Stations dialog box, as seen below.
WinFrog User's Guide - Appendix C – GPS/NovAtel Con
Page 15 of 22
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