Principle of surveying and scale & its types

Principle of surveying 

There are following types of principle of surveying are as follows 

1. Working from whole to part 
2. Location of a point by measurement from two points reference 

1. Working from whole to part 

According to this principle , the surveying is to work from whole to part either in plane or geodetic surveying. 

First, the whole area is enclosed by main stations, and main station line. The area is divided into a number of parts by forming well condition triangles (30°< α >120°). 

The main station lines are measured very accurately with standard chain or tape, then the side of the triangle are measured. The aim of this process is to be prevent accumulation of errors. 

During this procedure if there's any error within the measurement of any side of triangle then it will not be affect the whole work. The error will be always detected & eliminated .

2. Location of a point by measurement from two points reference 

According to this principle relative position of a point should always be fixed by measurement (linear or angular) from two points of reference through the help of chain, tape, compass, or theodolite. 

Let A & B be the two reference points on the ground. The distance of AB can be measured accurately and its relative position C can be plotted on the sheet paper with a suitable scale.

1. Distance AC and  BC can be measured and point C can be plotted by using the chain or tape.
   
2. A perpendicular CD can be measured on the reference line AB and length AD and BD are measured. The point C can be plotted with the help of Set Square or cross staff.
   
3. The distance AC and BC are not measured but angle BAC & angle ABC are measured with a theodolite or compass survey
   

What is scale :-

The drawing of objects are not possible to represents the actual length of an object on a drawing sheet paper.

Scale is that the fixed ratio that any distance on the plan with a corresponding distance on the surface. Scale is the generally necessary to draw then to a convenient scale.

There are following types of scales:-

1. Plane scale 
2. Diagonal scale 
3. Vernier scale 
4. Comparative scale 

1. Plane scale 

It is used to read only two dimensions successively of such as meter and decimeter.

2. Diagonal scale 

It is used to read only three dimensions successively of such as meter, decimeter, and centimeter.

3. Vernier scale 

It is used for the measuring fractional part of the smallest division of the main scale. 

4. Comparative scale 

A scale which is used for common representative fraction (R. F) but read in measure is called comparative scale. 

Note:- 

Representative fraction (R. F) 

It is the ratio of the corresponding distance of a map to the corresponding distance on the ground is known as representative fraction. 

Terms used in vernier scale 

* Direct vernier

            The smallest division of a vernier is shorter than a smallest division of the primary scale. 

* Retrograde

             The smallest division of a vernier is longer than the smallest division of the primary scale. 

* Least count

             The ratio of the smallest division on the main scale to the quantity of division on the vernier is known as least count. 

           

             Mathematically, 

     

   Least count = x/n

Where,    x = smallest division on main                            scale. 

                 n = No. of division on the                                    vernier.