Geodetic control surveys are usually performed to establish a basic control network (framework) from which supplemental surveying and mapping work are performed. The required accuracy for a control survey depends primarily on its purpose. Factors that affect accuracy are type and condition of equipment used, field procedures adopted, and the experience and capabilities of personnel employed.
Geodetic Control Standard (2008 FGDC Standard)
Geodetic Network Standards (1998 FGDC Standard)
Horizontal Control Networks
Horizontal geodetic control networks can be established by a number of different methods, however GPS has become the most widely used method due to its efficiency and superior results. These networks provide positional information (latitude/longitude) with reference to a mathematical surface called an ellipsoid (horizontal datum) defined to model the size and shape of (all or some part of) the Earth.
Vertical Control Networks
Vertical control networks are a series of points on which precise heights, or elevations, have been established. Vertical control stations are typically called bench marks. As a part of a vertical information network, the bench mark’s elevation is known relative to a datum, usually mean sea level.
When working with geodetic control points, high accuracy is essential, although the points can be widely scattered. When attempting to model features or processes across the landscape (e.g., flood response to a rainfall event in a watershed), a much denser pattern of reasonably accurate points that together faithfully represent the overall terrain is more important. There is no single technology that can economically yield data that supports both geodetic and landscape analysis needs, and there may never be such a single solution. Nevertheless, current technologies can better meet each of these needs than just 10 years ago and even more promising technologies are emerging.