CLASSIFICATION OF SURVEYING

Surveys may be classified in four different ways, they are discussed as under

1. Classification Based on Instruments Used:

(a) Chain Survey:

It is done by using chain or tape, by measuring linear distances. Metric chains 20 or 30 m are used. The principle used is chain triangulation, in this method the given area is divided into no. of triangles and the sides of the triangle lengths are measured using chain and details are located by taking perpendicular or oblique offsets from the chain line.

(b)Compass Survey:

The Compass works on the principle that a freely pivoted magnetic needle points in the magnetic North-South direction. The bearings of the lines are measured with the reference to magnetic North. To Totate detail and to survey the given area a series of connected lines are formed either closed or open traversing. The bearings of the lines are measured with compass and lengths with chain or tape.

(c) Plane Table Survey:

In plane table surveying both the fieldwork and plotting is done simultaneously. A plane table is drawing board can be fixed over tripod with help of clamp. With an alidade the direction of a line can be plotted and distance and measure with chain or tape and marked on drawing sheet kept over the board.The main principle used is parallelism, meaning that the rays drawn from stations to objects on the paper are parallel to the lines from the stations to the objects on the ground. Due to inaccuracy and difficulty in carrying no. of accessories to the field, this method is obsolete now.

(d) Theodolite Survey:

Vernier theodolites are used to measure the horizontal and vertical angles accurately with least count of 20. The line of sight can be established with telescope and it is used for all types of survey work like triangulation, traversing and filling in details.

(e) Levelling:

A level has a telescope attached with a bubble tube, to keep the line of sight horizontal in all directions. To keep line of sight horizontal the telescope is supported over a levelling head which consists of three foot screws. A graduated pole, known as the levelling staff, is used with a level to find the difference in elevation between points.

(f) Tacheometric Surveying:

PA tacheometer is similar t theodolite, but it has a stadia diaphragm having three cross hairs The reading taken by a levelling staff or stadia rod calculated. By knowing the constants of instruments, the horizontal distance and vertical distances can be calculated, from the instrument station to objects.

(g) EDM Survey:

Different types of instruments are used in Electromagnetic Distance Measurement Survey. EDM instruments generates and transmits the electromagnette wave signals, which are reflected back to the instrument by keeping a reflector at remote station. The phase difference between the transmitted and received signals, enables to calculate the slope distance. In built programmes in the instrument. Calculate the horizontal distance and difference in elevation, between the stations, is displayed and stored.

(h), Photogrammetry (or) Aerial Survey:

In this survey aerial photographs are taken from cameras mounted on aircraft. By interpreting these photographs, large area maps can be prepared within short duration.

(i) Remote Sensing:

It involves two operations, these are data acquisition and data analysis. Data acquisition Involves the source of energy (electromagnetic waves) propagated through atmosphere, the interaction of waves with the objects and the reflected waves are sensed by suitable sensor system mounted on the satellite. By interpreting, the data analysis is carried out, which is used for different purposes (ex: land use, land cover, mineral exploration, urban planning, etc.),

(j) Total Station Survey:

It is a advanced surveying. Instrument and is a combination of an electronic theodolite and an EDM. Using total station we can measure both horizontal & vertical angles and distances. It can display the data on screen and it can be stored or transfer to computer through data card or wireless for further processing. It can be used for establishing major control points with high level of precision.

(k) GPS Survey:

The Global Positioning System (GPS) is operated by US department of Defence. In this system a number of satellites (about 28) are placed around the globe and each satellite is having on board atomic clocks, transmits radio signals, These signals are received by the GPS receiver (hand held or fixed over tripod), which analysis and gives position of the receiver as well as time. It is basically used for navigation control and other survey works

2. Classification Based on Methods Employed

(a) Triangulation Surveying: In this method of surveying the selected survey stations are connected with survey lines in such a way resulting in the formation of network of triangles.
(b) Traverse Surveying: In this method of surveying the whole area of field is divided into connected traverses. A traverse is a geometrical figure consisting of more than three sides.

3. Classification Based on the Object of Survey

(a) Geological Survey This is used to determine different strata in the earth’s crust.
(b) Archaeological Survey: This is used to trace relics of the past
(c) Mine Survey: This is used to explore the mineral wealth such as gold, coal, Iron ore etc.
(d) Military Survey: This is used for locating points of strategic importance.

4.Classification Based on the Nature of the Field Survey:

(a) Marine Surveying or Hydrographic Surveying(this survey deals with bodies of water for purpose of navigation, water supply, harbour works etd, The work consists in measurement of discharges of streams preparing topographic survey of shores and banks, taking and locating surrounding to determine the depth of wate and observing the fluctuations of the ocean tide.
(b) Astronomical Surveying: The astronomical survey offers the surveyor means of Cetermining the absolute location of any point ort the absolute location and direction of any line on the surface of the earth) This consists in observations made with respect to the sun or any fixed star
(c) Land Surveying Land surveying can be further sub. divided into the following classes:
• Topographical Surveying Is done to determine the natural features of a country such as lakes, rivers, hills, forests, etc.
•Cadastral Surveying Is conducted to determine the boundaries of fields, estates, houses etc. They are also made to fix the boundaries of municipalities and state and federal jurisdictions
•City Surveying: Is carried out to locate the streets water supply systems, sanitary sewers and other works.
•Engineering Surveying Is done to prepare designs, detailed drawings and estimates for work such as Roads, Bridges Reservoirs etc.

(In civil engineering the engineering survey plays an important role) Engineering survey may be further sub-divided into.

1. Reconnaissance Survey :This is conducted for determining the feasibility of work and to prepare a rough cost of the project or scheme.
2. Preliminary Survey: This survey is conducted for collecting more precise data to find the best location or route for the work and to estimate exact quantities and costs.
3. Location Survey: This survey is conducted for setting out the work on the ground.