Interpreting the network adjustment report

The network adjustment output is an ASCII file that can be viewed and printed from GrafNet.

Input Stations

This is a list of the control (GCP) and check points in the project. Their associated geographic coordinates and standard deviations are also shown.

Input Vectors

This is the ECEF vector components for each session that has a Good status. The lower triangular of the ECEF covariance matrix is shown next to the vector components. The value in brackets is the standard deviation of the ECEF X, Y or Z axis in meters. The covariance values are not scaled by the Scale Factor entered at the start.

Output Vector Residuals

This indicates how well the session vectors fit in the network. The residual values are shown in local level, where RE is the east axis residual, RN is the north axis residual and RH is the Z axis residual. These values are expressed in meters and should ideally be a few centimeters or less. Larger values may be acceptable for larger networks.

In addition to the residual values, a parts-per-million (PPM) value is shown. This indicates the size of the residuals as a function of distance. 1 PPM corresponds to a 1 cm error at a distance of 10 km. The baseline length is also shown in kilometers. Baselines less than 1 km can have large PPM values. This is because other errors such as antenna centering become an influencing issue. This might not indicate an erroneous session solution. The last value is the combined (east, north and up) standard deviation (STD).

Check Point Residuals

If check points have been added, this section shows how well the known coordinates compare to those computed by the network adjustment.

Control Point Residuals

This section shows the adjustment made to control point residuals. When just one control point is used, then the adjustment will always be zero. With two or more points, the adjustment depends on the input control point standard deviation and the session vector standard deviations.

Output Station Coordinates

This shows the computed coordinates for each of the stations both in geographic and ECEF coordinate systems. The output datum is indicated by the Datum parameter at the top of this file.

Output Variance / Covariance

This section shows the local level (SE, SN and SZ) standard deviations along with ECEF covariance values. The standard deviation values are scaled by both the input scale factor and the statistical (confidence) scale factor. The covariance values are only scaled by the input scale factor. If error ellipse parameters are desired, then the Write Coordinates feature should be used.

Variance factor

See Variance Factor and Input Scale Factor for information.