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.

Read More: What is Triangulation Surveying?

The common figures or system used in triangulation system are:

  1. Single Chain of Triangles
  2. Double Chain of Triangles
  3. Central Point Figures
  4. Quadrilaterals
  5. Combination of all the system

1. Single Chain of Triangles in Triangulation

Single chain of triangles are used to survey narrow strip of terrain. This figure or system is rapid and economical. The figures made in this method is not so accurate and is not used for primary works. The number of conditions that are used to fulfill the figure conditions is relatively small. 
In this method, two independent routes cannot be used to determine the solution of the triangles. Hence, to reduce the accumulation of errors, it is recommended to introduce baseline frequently. 

Single Chain of Triangles

2. Double Chain of Triangles

Double chain figures are used for covering larger area.

3. Centered Figures

It is used to cover area in a flat country. It provides satisfactory results. The centered figures can be quadrilaterals, hexagons, or pentagons with central stations. The figure provide desired checks during the computations. The progress of centered figures work is slow as they require more instrument setting.

4. Braced Quadrilaterals

The quadrilateral with four corner stations and observed diagonal forms the best figures. It is best suited for hilly country. Since the computed length of the sides can be carried through the system by different combinations of sides and angles, the system is most accurate.

Braced Quadrilateral-Triangulation Figure/Layout

In fact, braced quadrilateral consists of overlapping triangles. This system is treated to be the strongest and the best arrangement of triangles, and it provides a means of computing the lengths of the sides using different combinations of sides and angles. Most of the triangulation systems use this arrangement

5. Combination of all above systems

Sometimes a combination of above systems may be used which may be according to the shape of the area and the accuracy requirements.

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