• “Surveying is the art of and science of determining the relative positions of various points or stations on the surface of the earth by measuring the horizontal and vertical distances, angles, and taking the details of these points and by preparing a map or plan to any suitable scale.”

Leveling

  • Leveling is a branch of surveying which deals with the measurement of relative heights of different points on, above or below the surface of the earth. Thus in leveling, the measurements (elevations) are taken in the vertical plane.

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3 Objective of Surveying

The object of surveying is to prepare a map or plan to show the relative positions of the objects on the surface of the earth. The map or plan is drawn to some suitable scale. It also shows boundaries of districts, states, and countries too. It also includes details of different engineering features such as buildings, roads, railways, dams, canals etc.56.jpgUses of Surveying

  • The surveying may be used for following purposes:
  • To prepare a topographical map which shows hills, valleys, rivers, forests, villages, towns etc.
  • To prepare a cadastral map which shows the boundaries of fields, plots, houses and other properties..
  • To prepare an engineering map which shows the position of engineering works such as buildings, roads, railways, dams, canals

Topographical Maps.

7.jpgCadastral Map

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  • To prepare a contour map to know the topography of the area to find out the best possible site for roads, railways, bridges, reservoirs, canals, etc.
  • Surveying is also used to prepare military map, geological map, archaeological map etc.
  • For setting out work and transferring details from the map on the ground.

Contour Map

9Military Map10.jpgGeological Map11Archaeological Map12

Primary Divisions of Surveying

We know that the shape of the earth is spheroidal. Thus the surface is obviously curved. Surveying is primarily divided into two types considering the curvature of the earth’s surface.

  • Plane Surveying
  • Geodetic Surveying
    • Plain Surveying
    • The plain surveying is that type of surveying in which earth surface is considered as a plane and the curvature of the earth is ignored. In such surveying a line joining any two stations is considered to be straight. The triangle formed by any three points is considered as a plane triangle, and the angles of the triangle are considered as plain angles.
    • Surveying is carried out for a small area of less than 250 km2 . It is carried out by local or state agencies like R & B department, Irrigation department, Railway department.
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    • Geodetic Surveying
    • The geodetic Surveying is that type of surveying in which the curvature of the earth is taken into account. It is generally extended over larger areas. The line joining any two stations is considered as curved line. The triangle formed by any three points is considered to be spherical and the angles of the triangle are considered to be spherical angles. Geodetic surveying is conducted by the survey of India Department and is carried out for a larger area exceeding 250 km215.jpgPlain Surveying Vs Geodetic Surveying16

Fundamental Principles of Surveying

Two basic principles of surveying are:

  • Always work from whole to the part, and
  • To locate a new station by at least two measurements ( Linear or angular) from fixed reference points.

Always work from whole to the part:

  • According to the first principle, the whole survey area is first enclosed by main stations (i.e.. Control stations) and main survey lines. The area is then divided into a number of divisions by forming well conditioned triangles.17.jpg
  • The main survey lines are measured very accurately with precise survey instruments. The remaining sides of the triangle are measured. The purpose of this method of working is to control accumulation of errors. During measurement, if there is any error, then it will not affect the whole work, but if the reverse process is followed then the minor error in measurement will be magnified.
  • To locate a new station by at least two measurements ( Linear or angular) from fixed reference points.
  • According to the second principle the points are located by linear or angular measurement or by both in surveying. If two control points are established first, then a new station can be located by linear measurement. Let A & B are control points, a new point C can be established.
  • Following are the methods of locating point C from such reference points A & B.
  • The distance AB can be measured accurately and the relative positions of the point can be then plotted on the sheet to some scale.
  • (a) Taking linear measurement from A and B for C.
  • (b) Taking linear measurement of perpendicular from D to C.
  • (c) Taking one linear measurement from B and one angular measurement as ∕ ABC
  • Taking two angular measurement at A & B as angles / CAB and / ABC.
  • Taking one angle at B as / ABC and one linear measurement from A as AC.18

Classification of Surveying

Survey can be classified into various categories depending on methods used and nature of the field.

  • Classification Based on Instruments.
  • Chain Survey:
  • This is the simplest type of surveying in which only linear measurements are made with a chain or a tape. Angular measurements are not taken.

Chain Survey19

Compass Survey:

  • In Compass Survey, the angles are measured with the help of a magnetic compass.

Chain and compass survey:

  • In this survey linear measurements are made with a chain or a tape and angular measurements with a compass.

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Plane Table Surveying

  • It is a graphical method of surveying in which field works and plotting both are done simultaneously.

Theodolite Survey:

  • In theodolite survey the horizontal angles are measured with the theodolite more precisely than compass and the linear measurements are made with a chain or tape.2324Theodolite Survey24

Tachometry Survey:

    • A special type of theodolite known as tachometer is used to determine horizontal and vertical distances indirectly.

Leveling Survey:

    • This type of survey is used to determine the vertical distances (elevations) and relative heights of points with the help of an instrument known as level.25.jpg25.jpg25.jpg

Photogrammetric Survey:

Photogrammetry is the science of taking measurements with the help of photographs taken by aerial camera from the air craft.25.jpg

EDM Survey:

In this type of survey all measurements ( length, angles, co-ordinates) are made with the help of EDM instrument ( i.e.. Total Station).25

Classification Based on methods.

Triangulation:

  • Triangulation is basic method of surveying, when the area to be surveyed is large, triangulation is adopted. The entire area is divided into network of triangles.25.jpg

Traversing:

  • A Traversing is circuit of survey lines. It may be open or closed. When the linear measurements are done with a chain and a tape and the directions or horizontal angles are measured with a compass or a theodolite respectively the survey is called traversing.25

Classification based on Purpose

    • Geological Survey:
    • In this both surface and subsurface surveying are conducted to locate different minerals and rocks. In addition, geological features of the terrain such as folds and faults are located.25.jpg

Mine Survey

Mine Survey includes include both surface and underground surveys. It is conducted for the exploration of mineral deposits and to guide tunneling and other operations associated with mining.25.jpg

Archaeological Survey

  • It is conducted to locate relics of antiquity, civilization, kingdoms, forts, temples, etc.

Military Survey

  • It has very important and critical applications in the military. Aerial surveys are conducted for this purpose. It is conducted to locate strategic positions for the purpose of army operations.25

Classification based on Nature of field

Land Survey

    • Land Survey is done on land to prepare plan and maps of a given area. Topographical, city and cadastral surveys are some of the examples of land surveying.

Hydrological Surveying

    • This survey is conducted on or near the body of water such as lake, river, coastal area. This Survey consists of locating shore lines of water bodies.

Astronomical Survey

This survey is conducted for the determining of latitudes, longitudes, azimuths, local time, etc. for various places on earth by observing heavenly bodies ( sun or the stars).

Aerial Survey

An aerial survey is conducted from aircraft. Aerial cameras take photographs of the surface of the earth in overlapping strips of land. This is also known as photographic survey.25Plan and Maps

  • One of the basic objective of surveying is to prepare plans and maps.

Plan

  • A plan is the graphical representation to some scale, of the features on, near or below the surface of the earth as projected on a horizontal plane. The horizontal plane is represented by plane of drawing sheets on which the plan is drawn to some scale However the surface of the earth is curved it cannot be truly represented on a plane without distortion. In plane surveying the area involved are small, the earth’s surface may be considered as plane and hence plan is constructed by orthographic projections. A plan is drawn on a relatively large scale.

Map

    • If the scale of the graphical projection on a horizontal plane is small, the plan is called a map. Thus graphical representation is called a plan if the scale is large while it is called a map if the scale is small.
    • On plan, generally only horizontal distances and directions or angles are shown. On topographical map, however the vertical distances (elevations) are also represented by contour lines.

Scale

It is basic requirement for the preparation of plan or map Scale is used to represent large distances on paper. The ratio by which the actual length of the object is reduced or increased in the drawing is known as the ‘Scale’ for example., if 1 cm on a map represents a distance of 10 metres on the ground, the scale of the map is said to be 1 cm = 10 m.25.jpg

Types of Scales

(a) Plain Scale

(b) Diagonal Scale

(c) Chord Scale

(d) Vernier Scale

  • Plain Scale
  • The plain Scale is the most commonly used in maps, this scale is used to represent two successive units, such as tenths, metres, decimetres, etc.25
  • Diagonal Scale
  • Using a diagonal scale, one can measure three dimensions such as “ Units, tenths and hundredths”, i.e. metre, decimeter, and centimetres, and so on.25
  • Chord Scale
  • A scale of chord is used to measure or to set off angles. It is marked either on rectangular or on an ordinary wooden scale.25

Vernier Scale

  • In 1631, Pierre Vernier invented a device for the purpose of measuring a fractional part of a graduated scale. It consists of two approximating scales, one of them is fixed and is called the primary scale. The other movable and is called the vernier.25.jpg

Choice of Scale of a Map

  • Scale of a map is the ratio of the distance drawn on the map to the corresponding distance on the ground. As the area involved are rather large, it is essential to select a suitable scale for representing the area on a map. Selection of the scale depends upon the purpose, size and the required precision of plotting.
  • Scales are generally classified as large, medium and small as under.
  • Large Scale: 1 cm= 10 m or less than 10 m
  • Medium Scale: 1 cm = 10 m to 100 m
  • Small Scale: 1 cm= 100 or more than 100 m
  • For most of engineering projects, the scale varies from 1 cm = 2.5 m to 100 m Small scale topographical maps are usually drawn to scale 1 cm = 1 km, a scale of 1 cm= 5 m to 50 m is generally used for plans prepared for subdivisions of land.

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Units of Measure

  • The system of units in India in the recent years in M.K.S. and S.I. but all the records available in surveying done in the past are in F.P.S. units therefore, for an engineer it becomes necessary to know the conversion of units from one system to another, a few are listed below.25.jpg
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