SUBCOURSE EDITION - Modern Prepper

Section II. CONTROL4-6. Types of ControlThe term "control" as used in mapping refers to the established system of coordinated data whichdetermines both the horizontal and vertical positions of specific points or features on the earth's surface.Control may be classified in several different ways, such as degree of accuracy (1st order, 2nd order,etc.), type of survey (classical or electronic), nature of survey (horizontal or vertical), and whethermonumented or nonmonumented. Detailed instructions on the establishment of such control are givenin TM 5-441, Geodetic and Topographic Surveying. A brief description of the kinds of control mostgenerally used in mapping projects follows.a. Horizontal control is the network of stations of fixed position, referred to a commonhorizontal datum, which relates the horizontal positions of these stations to the graticule or the grid insuch terms that they can be plotted in their correct positions on a map base. It is usually established bytriangulation or traverse methods, or by a combination of the two. Trilateration, or the measurement ofsides of triangles rather than the angles, accomplished by electronic devices, is also used to extendhorizontal control. Airborne distance measurement systems, such as Shoran, Hiran, and Shiran, whichutilize pulsed radio signals transmitted from an aircraft and received and returned by groundtransponders, are also used to establish and extend horizontal control.b. Vertical control is a network of stations whose elevations have been related to a commonvertical datum, usually an imaginary level line representing mean sea level. The values of all contoursand spot elevations on a map are based on this vertical datum. For military mapping, vertical control isobtained by direct or trigonometric leveling, depending upon the existing control and the requiredaccuracy. The Terrain Profile Recorder, an airborne electronic device, is also used to obtain elevationdata, but this normally is used only for medium and small scale mapping.c. Picture Point control is supplementary control which is field-identified on aerial photography,but not permanently marked on the ground. It is generally established as part of the control net forstereophotogrammetric projects, but is also used for controlling photo mosaics and photo revisionprojects.d. Map Control consists of geographic coordinates or grid coordinates on existing maps ofestablished accuracy which can be used to position detail on medium or small scale mapping. This ismost often used when a large scale series covering a given area has been compiled according to accuracystandards, and is then reduced in scale and used as basic source for a map-compiled, medium- or smallscaleseries. It is also used as an expedient method of positioning when no other control data isavailable or obtainable.130