Triangulation surveying is the branch of trigonometrical or geodetic surveying. Triangulation surveying is based on trigonometric formulas. If the one side and two angles are known then the other sides and angle to be computed from trigonometric formulas. In this method, suitable points called triangulation stations are selected and established throughout the area to be surveyed. The vertices of stations are connected by the number of triangles. The complete figure is called a triangulation system.

There are three types of generally used in triangulation.

There are three types of generally used in triangulation.

**1.Triangles**

Triangles |

**2.Quadrilaterals**

Quadrilaterals |

**3.Pentagons or hexagons.**

HEXAGON |

Every triangulation system is made up of a network of triangles. Angles of the triangle should be well shaped or well proportioned, the angle has not less than 30 degrees and not greater than 120 degrees.

Classification of triangulation systems.(1) first-order first order tube notion.(2) Secondary or be computers(3) Tertiary or third order .1. In primary or first order triangulation are a very large area covered or whole of the country,and highest possible degree of precision is required to have an average triangle closure minimum one second and the maximum three seconds. The measurements of base 5 to 20 km and the sides are

30 to 160 km. The degree of accuracy 1 in 500000 baseline check on the base 1in 25000.

2.With in primary triangles other points are fixed at closer intervals that is formed secondary

series of triangles. It has an average triangle closure of 3 seconds and a maximum of 8 seconds. The

length of the baseline 2 to 5 km and the sides of the triangle 8 to 70 km. It has a degree of accuracy

is 50,000 and the checking base 1in 10000.

**3.**Within the secondary triangle points established for details survey.The average triangle of closure 6 sec to12 sec. The length of the baseline is 1 to 3 km and has a side of the triangle is 1.5 to 10 km. The check base is 1 in 5000 and a degree of more than 1 in 5000.

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