Using Multiple Control Points

When multiple control points are present, it is suggested to initially use only one. This prevents errors in the existing control from causing otherwise correct session vectors not to fit. Therefore, large tie errors in the traverse solution or large residuals in the network adjustment are attributed to GNSS processing and not poorly fitting base station coordinates.

The variance factor is only truly valid as a scale factor for a minimally constrained adjustment. See Interpreting the network adjustment report for information about interpreting the output. Once satisfied with the quality of the GNSS data and the fit of the session vectors, you can add additional control points with File | Add / remove Control Points or by right-clicking on a station in the Map Window and selecting Add as Control Point.

Since the network adjustment is a least-squares adjustment, it will move control point coordinates to make the network fit better. This is an undesirable effect for many applications. To avoid it, give control points very low standard deviations. The default value is 5 mm, which might have to be lowered if the network fit is poor. Lowering the standard deviation to 0.0001 m forces the control point to “stay put”. A standard deviation of zero is not allowed. Change the standard deviation for control points via File | Add and Remove Control Points. Select the desired control point and click Edit.