Triangulation is a technique followed in surveying to achieve horizontal control. In a triangulation system, a number of interconnected triangles are traced and their angles are 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 the baseline and the angles are measured using an instrument, and the length of all the sides is determined using trigonometric formula.
Principal of Triangulation in Surveying
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 the 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 the sine rule,
a/sin A = b/ sin B = c/ sin C;
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Triangulation System in Surveying
As mentioned, a series of interconnected triangles form the survey area. If we know the length of one side and the three angles, the length of the other sides of each triangle can be computed.
In this system, the apex of the triangle is called the triangulation station, and the whole figure is called as triangulation system or triangulation figure.
The common types of figures that are used in triangulation systems are:
- 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.
1. Triangles for Triangulation
Triangles for Triangulation
2. Quadrilateral for Triangulation
3. Polygons for Triangulation
|Polygons with Central Points
Triangulation Figures or Layouts in Triangulation Survey
A triangulation figure is a group of triangles, with a single and common side to the preceding and following figures used in the triangulation technique in construction surveying.
The common figures or systems used in triangulation systems are:
- Single Chain of Triangles
- Double Chain of Triangles
- Central Point Figures
- Combination of all the system
1. Single Chain of Triangles in Triangulation
|Single Chain of Triangles