Horizontal surveys are performed for the purpose of determining precise relative horizontal positions of points. They have traditionally been accomplished by trilateration, triangulation, and traverse. These traditional types of surveys involve making distance, direction, and angle observations. As with all types of surveys, errors will occur in making these observations, and thus, they must be analyzed and, if acceptable, adjusted. The following three chapters describe procedures for adjusting trilateration, triangulation, and traverse surveys, in that order.

Recently, the global navigation satellite systems (GNSSs), such as GPS, have gradually been replacing these traditional procedures for conducting precise surveys. In fact, GNSS surveys not only yield horizontal positions but give ellipsoidal heights as well. Thus, GNSS surveys provide three-dimensional surveys. Again, as with all observations, GNSS surveys contain errors and must be adjusted. In Chapter 17 we discuss the subject of GNSS surveying in more detail and illustrate methods for adjusting networks surveyed by this procedure.

Horizontal surveys, especially those covering a large extent, must account for the systematic effects of Earth curvature. One way this can be accomplished is to do the computations using coordinates from a mathematically rigorous map projection system such as the state plane coordinate system (SPCS), universal transverse ...

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