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Various parameters are used to calculate the positional accuracy of a point compared to the imagery or other data being used as a point of reference. You can adjust the calculations by changing parameters or by making points inactive. You can change the confidence level and calculation methods used to obtain the statistics. When either of these parameters is changed, the statistics for the set of points can be automatically recalculated, or the analyst can choose when to recalculate. This also happens when you uncheck a point in the table to make it inactive.
Residuals
Fields associated with the residuals
| Field name | Description |
|---|---|
3 Sigma | A value that represents the mean residual plus three times the standard deviation. Any residual value that is greater than the three sigma threshold is considered to lie outside the valid values. |
Mean | The average of all the residual values for the points digitized. |
Standard Deviation | A measurement that describes the way points have been dispersed. The more widely the points have been digitized on the map, the larger this value will be. |
Active vs. Total Points | The number of points that are active versus the total number of points digitized during the PAAT session. |
Accuracy
Fields associated with the accuracy
| Field name | Description |
|---|---|
Absolute CE | The absolute circular error (CE), or horizontal accuracy, expressed in the reporting units, based on the x- and y-values. |
Relative CE | The National Geospatial-Intelligence Agency (NGA) definition of relative circular error, expressed in the reporting units. This is a measure of the consistency of horizontal error direction and magnitude of the points picked in the layer being evaluated. |
RMSE | The root mean square error (RMSE). This is a statistical measurement of the variance between the residual values. |
Absolute LE | The absolute linear error (LE), or vertical accuracy, of the evaluation points to the reference points based on the z-values. |
Relative LE | The NGA definition of relative linear error (LE), expressed in the reporting units. This is a measure of the consistency of vertical error direction and magnitude of the points picked in the layer being evaluated. |
Settings
Fields associated with the settings
| Field name | Description |
|---|---|
Reporting Units | The unit of measurement associated with the statistics. This applies to the Absolute CE, Relative CE, Absolute LE, Relative LE, RMSE, Mean, Standard Deviation, and 3 Sigma values. |
Confidence Level | The statistical confidence level for the accuracy assessment. The value for this field can be 90, 95, or 99. The statistics are recalculated appropriately when this value is changed. |
Calculation Method | The calculation method used for the statistics. You can use the NGA standard or United States Geological Survey (USGS) standard calculation method. |