The Normalized Residual Wi is a local test statistic that is used to detect gross errors.
They are calculated for each observation, and they are not affected by the weight of the measurement. A large value indicates that a large residual is possibly caused by a measurement error. For example, significant values are:
- Wi > 4 = gross error is likely
- Wi < 2.5 = measurements are of good quality.
According to local regulations, other limits may apply for geodetic networks, or polar mappings. You specify a maximum value for Wi in the Advanced Options of the Calculation Project Settings. See also Calculation Project Settings.
Estimated size of a gross error Gi
If Wi exceeds the maximum value, the system calculates estimates for the size of the gross error Gi. A gross error of this size would explain the calculated Wi. Gi indicates the size and algebraic sign of a possible gross error.
Click the Analyze Normalized Residual link to open the Result dialog box. On the Measurement Results tab, click the header of the Wi column to sort for the Wi values.
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Green light indicates that no measurement errors have been detected, and that Wi < Wi max for all values. -
Yellow light alerts you that for some observations no Wi value could be determined. For example, for points that have no over determination. Continue, if you want to include detail points that are only measured once. If your measurements do not contain single measurements, check the configuration, or the tolerances.
If you want to allow single measurements for some points, modify the field code list, and select the Single option. See Field Code Settings for Calculation.
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Red light indicates that measurement errors have been detected. The list displays the 5 observations that have the largest Wi > Wi max. Click the Show link, to open the Result dialog box, and to check the measurements.
To resolve the measurement errors, you can do the following:
- In the Measurement dialog box, on the Measurement Data tab, deactivate the measurement.
- Use the Gi value to modify the measurement accordingly.
- In the Measurement dialog box, on the Measurement Data tab, modify the standard deviation accordingly.