SURVEYING

Defination of Surveying :-

Surveying is the an of detennining the relative positions of points on, above or beneath the surface of the earth by means of direct or indirect measuremenis of distance. direction and elevation. It also includes the an of establishing points by predetennined angular and linear measuremenis. The application of surveying requires skill as well as the knowledge of mathematics, physics, and to some extent, asttonomy.

PRIMARY DMSIONS OF SURVEY

1..1 The earth is an oblate spheroid of revolutions, the length of iiS polar axis (12,713.800 meters) being somewhal less than that of its equaiorial axis (12,756.750 meterl. Thus, the polar axis is shorter than the equatorial axis by 42.95 kilometres. Relative to the diamerer of the earth this is less than 0.34 percent. If we neglect the irregularities at' rhe earrh. the surface of the imaginary spheroid is a curved surface, every element of which is normal o the plumb line. The intersection of such a surface with a plaue passing through the centre of the earth will form a line continuous around the earth. The portion of such a line is known as 'level line' and the circle defined by the intersection is known as 'great circle'. 

 1.2 The surveying can be divided into two class:-

1. Plane Surveying 
2. Geodetic Surveying

Plane surveying is that type of surveying in which the mean surface of the earth considered as a plane and the spheroidal shape is neglected. All triangles formed by survey lines are considered as plane triangles. Trhe earth's surface having an area of 195 sq. km.

Geodetic surveying is that type of surveying in which the shape of the earth is taken into account all lines lying in the surface are curved lines and the triangles are spherical triangles. It, therefore, involves spherical trigonomeuy. All geodetic surveys include work of larger magnitude and high degree of precision.

1.3. Classification of Surveying

Classification based upon the nature of field survey

1)Land Surveying

 Topographical Surveys :- This consists of horizontal and vertical location of certain  points by linear and angular measurements and is made to determine the natural features of country such as rivers, streams, lakes, woods, hills, etc., and such artificial features as roads, railways, canals, towns and village.

  Cadastral Surveys :- Cadastral surveys are made incident to the fixing of property lines, the calculation of land area, or the transfer of land property from one owner to another. They are also made to frx the boundaries of municipalities and of State and Federal jurisdictions.

City Surveying : - They are made in connection with the construction of streets.
water supply systems, sewers and other works. 

2)  Marine or Hydrographic Survey. :- Marine or hydrographic survey deals with bndies

of water for pwpose of navigation, water supply, harbour works or for the deiermination
of mean sea level. The work consists in measurement of discharge of streams, making
topographic survey of shores and banks, taking and locating soundings to determine the
depth of water and observing the fluctuations of the ocean tide.

3) Astronomical Survey.:- The astronomical survey offers the surveyor means of determining the absolute location of any point or the absolute location and direction of any line on the surface of the earth.

CLASSIFICATION BASED ON THE OBJECT OF SURVEY

1)  Engineering Survey. :- This is undertaken for the determination of quantities or to afford sufficient data for the designing of engineering .works such as roads and reservoirs, or those connected with sewage disposal or water supply.

2)  Military Survey :- This is used for determined point of strategic importants.

3)  Mine Survey. This is used for the exploring -mineral wealth.

4) Geological Survey. This is used for determining different strata in the earth.

 5)  Archaeological ·Survey. This is used for unearthing relics of antiquity.

CLASSIFICATIONBASED ON INSTRUMENTS USED

An alternative classification may be based upon the instruments or methods employed,
the chief typeS being :-

1.  Chain survey
2. Theodolite survey
3. Traverse survey
4. Triangulatiqn survey
5.  Tacheometric survey
6. Planetable survey
7. Photogrammetric survey
   
8. Aerial Survey

PRINCIPLES OF SURVEYING

 

Following are the two basic principles of surveying :-

1. Working from whole to parts
2. Location of a point by measurement from two points of references. 

1) Working from whole to parts :- The second ruling principle of surveying, whether plane or geodetic, is to work from whole to part. It is very essential to esrablish first a system of control poinlS and to fix them with higher precision. Minor control points can then be established by less precise methods and the details can then be located using these minor control points by running minor traverses etc.

2) Location of a point by measurement from two points of references.