TRIANGULATION

in navigation, surveying, and civil engineering, a technique for precise determination of distances and angles for location of a ship's or aircraft's position, and in such endeavours as road building, tunnel alignment, and other construction. It is based on the laws of plane trigonometry, that if one side and two angles of a triangle are known, the other two sides and angle can be readily calculated. One side of the selected triangle is measured; this is the baseline. The two adjacent angles are measured by means of a surveying device known as a theodolite, and the entire triangle is established. By constructing a series of such triangles, each adjacent to at least one other, values can be obtained for distances and angles not otherwise measurable. Triangulation was used by the ancient Egyptians, Greeks, and other peoples at a very early date, with crude sighting devices that were improved into the diopter, or dioptra (an early theodolite), in the 1st century AD by Hero of Alexandria.