Least Squares - Standard Errors Dialog

Generally, standard deviations for initial coordinate positions and observations are not available before adjustment, so TPC uses estimates called A Priori values.

When TPC analyzes the survey and builds the network, it must assign some estimate of standard error to each record. TPC gets those estimates from this dialog.

Horizontal Dist

Horizontal distance is specified both as a constant and a part per million (PPM). Distance precisions for each observation are computed as the const value plus the PPM value multiplied by the distance measured.

Horizontal Angle

Specifies the standard error of a horizontal angle measurement in seconds.

Vertical Angle

Specifies the standard error of a vertical angle measurement in seconds. TPC uses both Vertical (horizontal = 0 degrees) and Zenith (horizontal = 90 degrees). Both use the same Vertical Angle standard error shown here.

Azimuth/Bearing

Specifies the standard error of an azimuth or bearing measurement.

Elevation Difference

Elevation difference is specified both as a constant and a part per million (PPM). Distance precisions for each observation are computed as the const value plus the PPM value multiplied by the distance measured.

Save as Defaults / Recall Defaults

Choose these options to save and recall the default APriori values. When you start a new Least Squares analysis, TPC uses the default values.

Once a Least Squares analysis is performed, it stores its APriori values in the .LSA file. The next time you access that analysis, you will see the APriori values stored with the analysis, not the default values you have saved here.