Triangulation is a method followed in surveying to achieve horizontal control. In triangulation system, a number of interconnected triangles is traced and their angles measured to determine the relative positions of the points spread over an area. In this system, the length of only one line is determined, called as the **base line **and the angles are measured using an instrument and length of all the sides are determined using trigonometric formula.Â

### Principal of Triangulation

The principle of triangulation in surveying is that, "if one side and three angles are known for a triangle, then the remaining sides can be calculated using sine rule."

In the above figure, if the anyone side for example c and the angles A, B and C are known, then as per sine rule,

a/sin A = b/ sin B = c/ sin C;

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### Triangulation System in Surveying

As mentioned, as series of interconnected triangles form the survey area. If we know the length of one side and the three angles, the length of other sides of each triangle can be computed.Â

In this system, the apex of the triangle are called as the **triangulation stations, **and the whole figure is called as **triangulation system or triangulation figure.**

The common types of figures that are used in triangulation system are:

- Triangles
- Quadrilaterals
- Polygons

- The sum of the interior angles should be (2n-4) x 90, where the number of sides of the figure is given by 'n'.
- The total sum of the angles joining at a station must be equal to 360 degrees.
- The length of the sides that are calculated through more than one route should match and agree.

#### Triangles for Triangulation

## Â Â Â Â Â Â Â Â Â Triangles for Triangulation |

#### Quadrilateral for Triangulation

#### Polygons for Triangulation

Polygons with Central Points |

**Where are Triangulation Survey Used?**

Also Read:Â

- What is Compass Surveying?
**What is Principle of Surveying?**- What is Chain Surveying?
- Reconnaissance Survey and Index Sketch in Chain Surveying
- What is a Site Plan? What is the Purpose of Site Plan? When is Site Plan Required? What are the Types of Site Plans?
- Linear Measurements in SurveyingÂ