STEP 10: Adjust Networks

  1. If no Project Tracking ID (real or “dummy”) has been associated with the project, network adjustments are performed on all selected sessions. Typically the CORS are held fixed in 3D. Any vertical user marks with known or published orthometric heights may be constrained vertically at those heights. See Section 11, Network Adjustments.

B. If a Project Tracking ID was used, then the next step is a series of five sequential network adjustments (see below). After each step, carefully review the results and especially the shifts in the coordinates. You may have to go back and reject some observations (or remove some constraints) and reprocess some sessions. Figure

Network adjustment window showing sequence of five network adjustments when a NGS Tracking ID is used.

Fig. 24 Network adjustment window showing sequence of five network adjustments when a NGS Tracking ID is used.

  1. Preliminary network adjustment: constrain the hub(s) (3D) and float all other stations. Make sure you have at least two good occupations (>2 hrs) per user mark.

  2. Horizontal free network adjustment (minimally constrained - same design as the Preliminary): constrain only one station (3D), typically a hub. This adjustment uses a different processing engine compared to the Preliminary adjustment. Analyze residuals, make sure they are small.

  3. Horizontal constrained network adjustment: constrain all CORSs (3D) except the distant CORS. Constrain the (published) adjusted horizontal coordinates for all observed user marks with published lat/lon’s. Evaluate the coordinate shifts for the signs of any outliers. Evaluate the F-test result (see Section 12 for more guidance on applying the F-test).

  4. Vertical free network adjustment (minimally constrained): constrain one hub in 2D; constrain to one (published) adjusted orthometric height (1D). Analyze residuals, make sure they are small.

  5. Vertical constrained network adjustment: constrain one hub (2D), float all other CORSs. Constrain all user marks that have published, adjusted orthometric heights. Evaluate the vertical shifts as well as the results of the F-test.