i. Additional support for other topographic missions is defined in AR 115-11, FM 5-105, unit
table(s) of organization and equipment (TOE), and directives from higher headquarters (HQ). These
missions--
Provide precise positioning to support updating the MOS 81T (Terrain Analyst) database.
Support construction surveyors (when projects require real-world coordinates).
Establish and extend basic control for field surveys.
Allow survey data and station description cards to be forwarded to NIMA, the organization's
survey information center (SIC), and collocated terrain analyst teams upon request.
PART B - SURVEY OPERATIONS
2-2. General. The actual shape of the earth's solid mass is referred to as topography. A geoid is
defined as the surface of the earth's gravity (attraction and rotation) which coincides with the MSL in the
open undisturbed ocean. A spheroid (an ellipsoid of revolution) appears as a figure that is flattened at
the poles and bulging at the equator. It can be described using a mathematical formula that defines a
part of the surface of the geoid. However, because of the great variations in topography, many different
spheroids exist. Because the earth's surface is irregular and pieces of mathematical computations are
unreliable, the type of survey conducted depends on the purpose or the level of accuracy required.
PART C - SURVEY TYPES
2-3. General. In plane surveys, all points are referenced to a flat plane with the curvature completely or
partially ignored. In geodetic surveys, all established points are referenced to the curved surface of a
spheroid and, in all computations, the effect of curvature is computed.
a. Plane Survey. Plane surveys ignore the actual shape of the earth and apply the principles of
plane geometry and trigonometry. These surveys are treated as if the measurements were made on a flat
plane, with all lines being straight. When the survey area is less than 250 square kilometers and less
accuracy is needed, curvature can be ignored. Most localized construction projects (highway and
railroad) and boundary projects use plane surveys.
b. Geodetic Survey. Geodetic surveys take into account the size and shape of the earth. Since the
stations in geodetic surveys are routinely spaced over extended distances, more precise instruments and
techniques are required than for plane
EN0593
2-4
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