Unit 1 :- Introduction to Surveying

Fundamental of Surveying.

Surveying is the art of determining the relative position of points on, above and beneath the surface of earth by the means of direct or indirect measurement of distance, direction and elevation. It also includes the art of representing natural or physical structure for preparing map on a suitable scale.

Objective of Surveying 

1. To prepare a topographical map which shows the hills, valleys, rivers, Forest etc. of a place.

2. To prepare a cad-astral map showing the boundary of a field, house and other property.

3. To prepare an engineering map which shows the details of engineering work such as road, railway, irrigation Canal, building etc.

4. To prepare a military map showing the road and railway communication with different parts of country.

5.  To prepare a contour map of any location to determine the capacity of reservoir and to find the alignment of railway, roadway, irrigation canal etc.

 Classification of Surveying

1. Primary Classification

A) Plain Surveying 

 It is the type of surveying in which the curvature of earth is not taken into the consideration. This is because plain surveying carried out in small areas. Plain surveying is carried out on the area less than 250 Sq. Km.

B) Geodetic Surveying

In the geodetic surveying the curvature of earth is taken into consideration. The line joining two points on the geodetic surveying is considered as curved line. It is carried out in an area exceeding 250 Sq. Km.

2. Secondary Classification

A. Based on Instrument Used

i) Chain Surveying

ii) Compass Surveying

iii) Plane Table Surveying

iv) Theodolite Surveying

v) Tacheometric Surveying

vi) Photographic Surveying

 

B) Based on Method

i) Triangulation Method

ii) Traverse Method

 

C) Based on Object

i) Geological Survey

ii) Mine Survey

iii) Archeological Survey

iv) Military Survey

 

D) Based on Nature of Field

 i) Land Surveying

ii) Marine Surveying

iii) Astronomical Surveying

 

Principle of Surveying 

Working from Whole to Part:

This principle is fundamental to surveying and is followed to prevent the accumulation of errors. The idea is to first cover a large area in surveying to establish control points with a higher degree of precision. Then, surveying is carried out within this area. This approach localizes errors and prevents their accumulation. If the reverse process is followed (i.e., working from part to whole), the errors would accumulate and expand to a greater magnitude, making the work uncontrollable at the end. This principle involves laying down an overall system of stations whose positions are fixed to a fairly high degree of accuracy as control, and then the survey of details between the control points may be added on the frame by less elaborate methods. Once the overall size has been determined, the smaller areas can be surveyed in the knowledge that they must (and will if care is taken) fit into the confines of the main overall frame. Errors which may inevitably arise are then contained within the framework of the control points and can be adjusted to it.

Location of Point by Measurement from Two Points of Reference:  

As per this principle, the relative position of a point to be surveyed should be located by measurement from at least two points of reference, the positions of which have already been fixed or known. This method is commonly used in triangulation. If P and Q are the two reference points on the ground surface, any other point, like R, can be located by any of the direct methods. But, although a single method is adequate to locate the relative position of ‘R’ with respect to reference points P and Q, it is essential to adopt at least any two methods to fix the position of point 'R’. While the measurements made in either of the first method or second method will be useful in locating the point ‘R’, the measurements made in the other method will act as a check.