a marker or tower erected at triangulation stations and, sometimes, at traverse stations. Surveying signals are used in mounting geodetic instruments, such as transits, at a height that provides for line of sight to adjacent markers. The distance to the adjacent markers depends on the order of precision of triangulation and ranges from 5–10 km to 30–50 km. Sighting targets are mounted on the surveying signals.
Surveying signals may be simple or complex. A simple signal consists of two pyramids that do not touch—an inner one and an outer one. The inner pyramid is usually trihedral and serves as a base or mounting for the geodetic instrument. The outer pyramid is tetrahedral and serves as the base upon which the observer stands and as a mounting for the sighting target. In complex signals the inner pyramid is fastened to the same posts as the observer’s base. Simple signals are 6 to 15 m high, and combined signals 16 to 55 m high. In forested regions surveying signals are built of wood; in unforested regions fixed or portable metal signals are used. Simple pyramids that carry only the sighting target are used in open areas. In this case, the geodetic instrument is mounted beneath the pyramid on a conventional tripod.