Introduction to surveying, types and methods of surveying

Surveying, to the majority of engineers is the process of measuring length, height difference and angles on site either for the preparation of large scale plans or in order that engineering works can be located in their correct position on ground. The correct term for this is engineering surveying and it falls under the general title of land surveying.

Land surveying :As with surveying in general land surveying can be broken down into several subsections which is:

·         GEODETIC SURVEYING

·         TOPOGRAPHICAL SURVEYING

·         PHOTOGRAMMETRY

·         HYDROGRAPHIC SURVEYING

·         CADASTRAL SURVEYING

·         ENGINEERING SURVEYING

     

GEODETIC SURVEYS:  Covers such large areas that the curved shape of the earth has to be taken into account. This survey involves advanced mathematical theory and requires precise measurement to be made to provide a framework of accurately located points. These points can be used to map entire continents, they can be used to measure the size and shape of earth or they can be used to carry out scientific studies such as the determination of the earth’s magnetic field and detection of continental drift.

TOPOGRAPHICAL SURVEYS: They establish the position and shape of natural and man-made features over a given area, usually for the purpose of producing a map of an area or for establishing a geographic information system. Such surveys are classified according to the scale of the final map or terrain model formed. small scale surveys cover large area such as an entire continent, country and may range from 1:1000000 to 1:50000, medium scale maps range from about 1:10000 to 1:1000 and may cover a small area like small town. Large scale 1:500 to 1:50 often provided to meet the needs of civil engineers, architects and government department.

PHOTOGRAMMETRY: surveys using photographs taken with special cameras mounted in an aircraft. The photographs produce three dimensional (3D) image of ground features from which maps or numerical data can be produced, usually done with the help of stereo plotting devices and computer.

HYDROGRAPHIC: In hydrographic surveying , surveyors gather information in the marine environment , mapping the coastlines and sea bed in other to produce navigational charts.  Recently much of their work has been for offshore oil exploration and production. Hydrographic surveys are also used in the design, construction and maintenance of harbors, inland water routes, river and sea defenses and in control of pollution and also in scientific studies of the ocean.

CADASTRAL SURVEYING: Surveys that involves establishment and keeping records of ownership and boundaries of land property.

ENGINEERING SURVEYING:  The term engineering surveying is a general expression for any survey work carried out in connection with the construction of civil engineering and building projects. Surveyors and engineers involve in site surveying are responsible for all aspects of dimensional control on such schemes.

v  Main Purpose Of Engineering Surveys ;

Ø  At the concept and design stage to provide large scale topographical survey and other measurements upon which projects are designed.

Ø  At the construction stage to provide the precise control from which it is possible to position the works and most importantly to ensure that engineering projects are built in their correct relative and absolute positions.( setting-out)

Ø  At the post construction stage to-monitor for structural movement on major retaining structures such as dams.