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2. Types of control surveys. Their application.
3. The geoid and ellipsoid.

Horisontal and Vertical Control survey

Control surveys establish precise horizontal and vertical
positions of reference monuments. These serve as the basis for
originating or checking subordinate surveys for projects such as

topographic and hydrographic mapping; property boundary
delineation; and route and construction planning, design, and layout.
They are also essential as a reference framework for giving locations

of data entered into Land Information Systems (LISs) and Geographic
Information Systems (GISs).
Control Surveying consists of research, measurements,

calculations and reports detailing the horizontal and vertical
reference systems established for the survey.
Traditionally there have been two general types of control

surveys: horizontal and vertical. Horizontal surveys generally
establish geodetic latitudes and geodetic longitudes of stations over
large areas. From these values, plane rectangular coordinates, usually
in a state plane or Universal Transverse Mercator (UTM) coordinate

system can be computed. On control surveys in smaller areas, plane
rectangular coordinates may be determined directly without obtaining
geodetic latitudes and longitudes.

Field procedures used in horizontal control surveys have
traditionally been the ground methods of triangulation, precise
traversing, trilateration, and combinations of these basic approaches.
In addition, astronomical observations have been made to determine

azimuths, latitudes, and longitudes. Rigorous photogrammetric
techniques have also been used to densify the control in an area.
Horisontal control is a system of control stations, local or

universal, which must be established to locate the positions of various
points, objects, or details on the surface of the Earth. The relative
positions of detail points can be easily determined if these points are

tired in to a local control station; or, if the control station is tied in to a
geodetic control, the positions of other detail points can also be
located relative to a worldwide control system. The main control

system is formed by a triangulation network supplemented by
traverse. A traverse that has been established and is used to locate
detail points and objects is often spoken of as a control traverse.

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