ground-surface installations and underground structures to which designated geodetic points are secured at the sites.
The surface part of geodetic marks on points of triangulation and polygonometry assures mutual visibility between them and serves as a support for installing geodetic measuring instruments and as an object for sighting.
Depending on the conditions of the locality and the distance between points, the surface part of the geodetic marks is of varying altitude and construction. If adjacent geodetic points are mutually visible at ground level, the external geodetic marks are stone posts or simple wooden or metal pyramids 6-8 m in height. If a height of from 6-8 m to 15-18 m is necessary, then the geodetic marks are built in the form of double truncated pyramids, the inner one being a support for the instrument and the outer one having a space for the observer and providing for the sighting aim. At heights greater than 15-18 m, the geodetic marks are complex signals in which the legs of the inner pyramid lean on the pillars of the outer pyramids.
The underground part of the geodetic mark at points of triangulation and polygonometry is a system of concrete pillars (or a secured metal pipe in a concrete base, with a stamp set into it), on which there is an aperture or a designated point. This point is the geodetic point proper and is called the center of the point. Points of leveling are designated and fixed by an analogous device and are installed in the bottom of the geodetic mark, in which case they are called reference (bench) marks, or are set into the walls of the stone structure with cast-iron stamps. On the marks there is an inscription, cast together with it, indicating the type and number of the geodetic point.
REFERENCEShishkin, V. N. Rukovodstvo po postroike geodezicheskikh znakov, 4th ed. Moscow, 1965.
A. V. BUTKEVICH