TRIANGULATION IN SURVEYING

    TRIANGULATION

Triangulation is a method used in providing controls for the connection of future surveys. It involves the use of interconnected triangles hence the name triangulation. In a triangulation scheme, all the angles of the triangle must be measured while the only distance measured is the base line.

There are various orders of the scheme, which are :

1.       Primary Triangulation

2.       Secondary Triangulation

3.       Tertiary Triangulation

4.       Minor Triangulation

ORDER OF TRIANGULATION

Order of triangulation refers to the classification of triangulation into different types. Essential principles remaining the same, triangulation is carried out with different types of instruments and methods. The different types of triangulations differ only in the accuracy stipulated for the work. Thus we have : first order or primary triangulation, second- order or secondary triangulation, and third- order or tertiary triangulation.

Ø     FIRST- ORDER TRIANGULATION

First – order triangulation is done on extensive areas, such as country, for which the highest level of accuracy is stipulated. The lengths of the sides of the triangle are large. Triangulation stations are precisely located using first- order triangulation. A stringent control is exercised in all the measurements. The instruments used must be precise and should be tested and adjusted daily.

                In primary triangulation, care is taken to minimize errors by using very high precision equipments, methods used are commensurate with the equipment, and the criteria for permissible errors are equally stringent. This is necessary because all the other surveys are based on such a triangulation.

Ø      SECOND – ORDER TRIANGULATION

Second – order triangulation is carried out within the primary triangulation stations. He extent of area covered is small and the sides of the triangle are also small. The instruments and methods used are not as précised as in first-order triangulation. The accuracy limits specified are not as stringent as in first case.

Ø     THIRD- ORDER TRIANGULATION

Third – order or tertiary triangulation is performed within the area covered by second- order triangulation stations. This triangulation gives a set of control points which are normally used by agencies conducting engineering surveys. The equipments and methods used are of lower precision. The accuracy limits are also not as stringent as in the case of the other two methods of triangulation.

                The requirements and the extent of area for the three types of triangulation are given.