# Triangle Definitions for Land Surveyors

**triangle equation—**See *equation, angle.*

**triangle of error—**The triangle formed when three plotted lines fail to intersect at a common point; triangle of misclosures, cocked hat. The center of the triangle may be considered to be the adjusted location, i.e., the true or correct location. See also *resection.*

**Triangulated Irregular Network (TIN)—**A network of triangles whose vertices are points of known elevation and whose sides represent a line of constant slope. Using these lines, elevations between known points can be interpolated.

**triangulation—**A method of surveying in which the stations are points on the ground at the vertices of a chain or network of triangles. The angles of the triangles are measured instrumentally and the sides are derived by computation from selected sides or bases, the lengths of which are obtained by direct measurement on the ground or by computation from other triangles. A triangulation system of limited width (generally that of one triangle), designed to progress in a single general direction, is designated arc triangulation, and the chain of triangles (or polygons composed of abutting or overlapping triangles) is called a triangulation arc. A triangulation network covering an area with abutting or overlapping triangles is designated area triangulation, and the resulting configuration is called a triangulation net. See also *Appendix A, Standards for Geodetic Control Surveys.*

**triangulation, arc—**A system of triangulation of limited width designed to progress in a single general direction.

**triangulation, flare—**A method of triangulation in which simultaneous observations are made on parachute flares. This method is used for extending triangulation over lines too long to be observed by ordinary methods.

**triangulation, ship-to-shore—**A method of triangulation involving simultaneous observations from three shore stations on a target carried by a ship offshore of the middle station. The middle station must be visible from each of the two end stations.

**triangulation, Shoran—**A method of triangulation in which the sides of appropriate figures are measured by the Shoran line-crossing method.

**triangulation base line—**See *base line, triangulation. *See also *Appendix A, Standards for Geodetic Control Surveys.”*

**triangulation signal—**See *signal, triangulation. *

**triangulation station—**See *station.*

**triangulation tower—**A triangulation signal consisting of two separate structures, independent of one another; an inner structure which supports the theodolite and sometimes the target or signal lamps, and an outer structure which supports the observer and his assistants and sometimes the target or signal lamps. Some portable metal towers were called “Bilby towers.”

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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