Uncertainty Field Analysis Section
USMN does not by default calculate the uncertainties of the resulting optimal (USMN Composite) points, because this calculation can take a fair amount of time. As a result, you must initiate this calculation yourself.
Uncertainty field analysis works by using the instrument uncertainty characteristics to slightly perturb measurements following a realistic Gaussian distribution. Each iteration of perturbed measurements is then treated as a separate USMN network. Each iteration is solved in turn, which allows for statistical generation of optimal point uncertainties.
-
Samples. Specify the number of perturbations, or iterations, to perform. Higher numbers take proportionately longer to solve, but have more accurate uncertainty values. It has been statistically determined that 300 or more samples will provide results within 5% of the “statistically true” value, so 300 is considered the default. About 10,000-15,000 samples are required to get a result within 1% of the statistically true value.
-
Time Limit. When checked, the uncertainty field analysis will time out at this limit, regardless of the number of samples requested. In this case, the number of completed iterations will be used.
-
Begin. Initiates the Uncertainty Field Analysis.