(2) To establish an arc of triangulation between two widely separated locations, you must

measure a baseline at each location, connect these measured areas by a series of adjoining triangles

forming quadrilaterals, and compute the latitude and longitude for the vertex of each triangle. The

vertex is then called a triangulation or geodetic-control station. The end of the baseline is often called

the initial point, and the directions of the sides of the triangles are called azimuths (Figure 1-9).

(3) Triangulation may be extended to cover larger areas by connecting and extending a series of

arcs that form a network. The network, which forms the triangulation system, is mathematically

adjusted to reduce all errors to a minimum.

c. Trilateration. Recently, electronic and light wave distance-measuring equipment has been

applied to geodetic surveys in a technique known as trilateration. Trilateration is the measurement of

the sides of a triangle. Each side of the triangular net is measured repeatedly to ensure precision. The

angles of the triangle and geodetic positions are computed, as in triangulation (Figure 1-10, page 1-14).

These systems also permit surveying over large water barriers, allowing the connection of islands and

continents. Traditional electronic systems only measure distance.