INTRODUCTION TO SURVEYING

 

INTRODUCTION TO SURVEYING

 

  Surveying is the art of making measurements of objects on, above or beneath the ground to show their relative positions on paper. The relative position required is either horizontal or vertical.

APPLICATIONS OF SURVEYING

 

Some of the important applications of surveying are listed below:

 

1.   Astronomical survey helps in the study of astronomical movements of planets and for calculating local standard times.

2.   Maps prepared for countries, states and districts, etc. avoid disputes.

3.   Plans prepared record the property boundaries of private, public and government which help in avoiding unnecessary controversies.

4.   Topographical maps showing natural features like rivers, streams, hills, forests help in planning irrigation projects and flood control measures.

5.   Road maps help travelers and tourists to plan their programmers.

6.   Locality plan help in identifying location of houses and offices in the area

7.   Maps and plans help in planning and estimating various transportation projects like roads, bridges, railways and airports.

8.   For planning and executing water supply and sanitary projects one has to go for surveying first.

9.   Marine and hydrographic surveys help in planning navigation routes and harbours.

 

10. For making final payments in large projects surveying is to be carried out

11. Military surveys help in strategic planning

12. For exploring mineral wealth mine surveys are required.

13. Geological surveys are necessary for determining different strata in the earth’s crust so

                                 that proper location is found for reservoirs.

14. Archaeological surveys are required for unearthing relics of antiquity.

 

 PRIMARY DIVISIONS IN SURVEYING

 

 The survey in which earth’s curvature is considered is called geodetic surveying and the survey in which earth’s curvature is neglected is called Plane surveying.

 

CLASSIFICATION OF SURVEYING

 

Surveying may be classified based on the following three points:

 

1.   Natural of the field of survey

 

 

 

2.   Objects of survey

 

 

 

3.   Instrument used

 

 

 

4.   The methods employed

 

 

Classification Based on Nature of the Field of Survey

 

 

 

On this basis field of survey may be classified as land survey. Marine or hydraulic survey and astronomical survey.

 

 

Land survey: It involves measurement of various objects on land. This type of survey may be further classified as given below:

 

 

i.    Topographic surveys: They consist of measurement of various points to plot natural features such as rivers, streams, lakes, hill and forests as well as man  – made features like roads, railways, towns, villages and canals.

 

 

ii.  Cadastral survey: These surveys are for marking boundaries of municipalities, states, etc. the surveys made to mark properties of individual also come under this category.

 

 

iii. City survey: The surveys made in connection with the construction of streets, water supply and sewage lines fall under this category.

 

 

Marine of Hydrographic Surveys: The survey conducted to find depth of water at various points in bodies of water like sea, river and lakes fall under this category of surveying. Finding depth of water at specified points is known as soundings.

 

 

Astronomical Surveys: Observations made to heavenly bodies like sun and stars to locate absolute position of points on the earth and for the purpose of calculating local times is known as astronomical survey.

 

 

Classification Based on Object of Surveying

 

 

 

On the basis of objective of surveying, the classification can be as engineering survey. Military survey, mines survey, geological survey and archaeological survey.

 

 

1.   Engineering survey: The objective of this type of surveying is to collect data for designing roads, railways, irrigation, water supply and sewage disposal projects. These surveys may be further subdivided into:

 

 

a.   Reconnaissance survey for determining feasibility ad estimation of the scheme.

 

 

 

b.   Preliminary survey for collecting more information to estimate the cost o the project selected, and

 

 

c.   Location survey to set the work on the ground.

 

 

 

2.   Military Survey: This survey is meant for working out points of strategic importance.

 

 

 

3.   Mine survey: This is used for exploring mineral wealth.

 

 

 

4.   Geological survey: this survey is for finding different strata in the earth’s crust.

 

 

 

5.   Archaeological survey: this survey is for unearthing relics of antiquity.

 

 

 

Based on the instruments used, surveying may be classified into the following:

 

 

 

1.   Chain Survey

 

 

 

2.   Compass Survey

 

 

 

3.   Plane Table Survey

 

 

 

4.   Theodolite Survey

 

 

 

5.   Tacheometric Survey

 

 

 

6.   Modern Survey using electronic equipment like distance metres and total stations.

 

 

 

 

7.   Photographic and Aerial Survey.

 

 

 

Classification Based on the Methods Employed

 

 

 

Based  on  the  methods  employed,  surveying  may  be  classified  as  triangulation  and traversing.

 

 

1.   Triangulation:  In  this  method  control  points  are  established  through  a  network  of triangles

 

 

2. Traversing: In this scheme of control points consist of a series of connected points established through linear and angular measurements. If last line meets the starting point it is called as closed traverse. If it does not meet, it is known as open traverse.

 

 

MEASUREMENTS

 

 

 

Linear measurements are horizontal or vertical only. Here angular measurements are also  involved.  Commonly  used  linear  units  in  surveying  are  kilometre,  metre  and millimetres. For measurement of angles sexagesimal system is used. In this 1 circumference

= 360 degrees

 

SCALES

 

 

 

It is not possible and also not desirable to make maps to full scale. All distances are reduced by fixed proportion and drawings are made. The scale of a map or the drawing is the fixed proportion which every distance on the map bears to he corresponding distance on the ground. Thus, if 1 mm on the paper represents 1m on the ground, then the scale is 1 mm = 1 m ( or 1 cm = 10m or 1: 1000.

 

 

To make scale independent of units it is preferable to use representative factor, which is defined as the ratio of distance of one unit on paper to one unit on ground. Thus,

1mm = 1m is equivalent to RF=1/1000.

 

 

 

 

Plain Scale: On a plain scale it is possible to read two dimensions directly such as unit and tenths.

 

 

Diagonal Scale: In plain scales only units and tenths could be shown whereas in diagonal scales it is possible to show units, tenths and hundredths. Units and tenths are shown as in plain scale. To show hundredths, principle of similar triangles is used

 

 

PRINCIPLES OF SURVEYING

 

 

 

To get accurate results one should follow the two basic principles explained below:

 

 

 

1.  Work from whole to part

 

 

 

In surveying large areas, a system of control points is identified and they are located with high precision. Then secondary control points are located using less precise methods. With respect the secondary control point’s details of the localized areas are measured and plotted. This is called working from whole t part. This principle in surveying helps in localizing the errors. If the surveying is carried out by adding localized areas, errors accumulate.

 

 

2.  Fixing positions of new control points

 

 

 

For fixing new control points with respect to already fixed points, at least two independent processes should be followed. IF A and B are two already located control points and with respect  to  them  new  control  point  C  is  to  be  located,  apart  from  the  minimum  two measurements required, one more reading should be taken. Fixing of check lines and tie lines will also serve this purpose.