Surveying and Geomatics Solved Questions | QnA | Part 1 | Basic Surveying | By Akhand Dutta

Surveying or survey can be defined as the technique of determining the relative position of different features on, above or beneath the surface of the

Define Surveying in terms of Civil Engineering?

Ans- Surveying or survey can be defined as the technique of determining the relative position of different features on, above or beneath the surface of the earth by means of different types of measurements and finally representing them on a sheet of paper known as a plan or map.

It is a branch of civil engineering in which relative positions of ground points are determined by taking the linear and angular measurement.

List the Principle of the survey.

 Measuring Tape

Explain the two Principles of surveying.

Ans- (1) Working from whole to part:

According to this principle, it is always desirable to carry out survey work from whole to part. This means, when an area is to be surveyed, first a system of control points is to be established covering the whole area with very high precision. Then minor details are located by less precise methods.

(2) Location of a point by measurement from two points of reference:

According to 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.

What is Magnetic Bearing?

Ans- (1) True Bearing - The bearing expressed as the horizontal angle between a geographic meridian and a line on the Earth; esp. the horizontal angle measured clockwise from true north.

(2 ) Magnetic Bearing - The bearing expressed as the horizontal angle between the local magnetic meridian and a line on the Earth; a bearing measured clockwise from magnetic north. It differs from a true bearing by the amount of magnetic declination at the point of observation.

Explain the Principle of Plane table surveying.

Ans- Plane table surveying is based on the principle that lines were drawn during plotting always lie parallel to the corresponding lines actually present on the ground.

Eg- consider four ground stations A, B, C and D which on joining provides a rectangle ABCD. This has been plotted on a sheet of paper at a scale by plane table surveying. Here, the sides AB, BC, CD and DA are plotted in such a way that they are parallel to the sides actually available on the ground.

Write down some of the different instruments for linear measurement.

Ans- Some of the instruments for linear measurements are rulers, vernier callipers, vernier height gauges, vernier depth gauges, micrometres, dial indicators, trammels, telescopic gauges, surface gauges, straight edges, wire gauges, screw pitch gauges, radius gauges, thickness gauges, slip gauges etc.

What is Backsight?

Ans- (1) Fore Sight– It is the last staff reading taken from a setting of the level. It is also termed as minus sight. Foresight is the sight taken on a levelling staff held at a point of unknown elevation to ascertain the amount by which the point is above or below the line of sight. This is also called minus sight as the foresight reading is always subtracted from the height of the Instrument.

(2) Back sight- The first sight taken on a levelling staff held at a point of known elevation. B.S. enables the surveyor to obtain HI, +sight i.e. Height of Instrument or line of sight.

What is the classification of surveying on the basis of the Nature of the Field and state their objectives?

Ans- There are three types of surveying based upon the nature of the field which is as follows:

(1) Land Surveying: It can be further classified as i) Topographical survey ii) Cadastral Survey and iii) City Survey. It generally deals with natural or artificial features on land such as rivers, streams, lakes, wood, hills, roads, railways, canals, towns, water supply systems, buildings & properties etc.

(2) Marine Surveying: Marine or hydrographic survey deals with bodies of water for purpose of navigation, water supply, harbour works or for determination of mean sea level. The work consists of the measurement of discharge of streams, making a 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 Surveying: The astronomical survey offers the surveyor means of determining the absolute location of any point or the absolute location of and direction of any line on the surface of the earth. This consists of observations of the heavenly bodies such as the sun or any fixed star.

What are the functions of the Swivel joint, oval rings?

Ans- (1) Swivel Joint- A swivel joint for a pipe is often a threaded connection in between which at least one of the pipes is curved, often at an angle of 45 or 90 degrees. The connection is tightened enough to be water- or air-tight and then tightened further so that it is in the correct position.

(2) Oval Rings- The links are joined by 3 circular or oval wire rings. These rings provide flexibility to the chains.

What is the stepping method of chaining on Sloping Ground?

Explain the stepping method of chaining on Sloping Ground.

Ans- The method consists of measuring the line in short horizontal lengths called steps. Suppose it is required to measure the horizontal distance between points A and B. For convenience and to obtain better results, chaining is done from the top of the hill to the toe i.e. downhill.

The follower holds the zero end of the chain at A on the ground and the leader with the other handle of the chain and a ranging rod moves in the forward direction at a convenient distance apart.

The leader then stops and the follower directs him to be in line with B. The leader then stretches the chain in the horizontal position and transfers the endpoint of the chain on the ground with the help of a plumb-bob or ordinarily with a ranging rod or by dropping a piece of stone.

The follower then moves and reaches the station occupied by the leader and then the leader moves in the forward direction. The process is repeated several times until the whole line is chained. The lengths of all the steps are added up so as to obtain the total horizontal distance. In this case, the horizontal distance between AB = Ap + Pq + Qr + Rb.

What is the significance of baseline and tie-line in chain triangulation?

Ans- (1) Baseline - Longest survey line passing through the centre of the are to be surveyed is called a baseline.

In triangulation, the baseline is of prime importance because it is the only horizontal distance to be measured. It should be measured very accurately since the accuracy of the computed sides of the triangulation system depends on it. Length of baseline varies from a fraction of (0.5-10) km and a fraction of a mile to 10 miles.

(2) Tie line – Line joining some fixed points as a Tie station on the main survey line is called a Tie line.

The significance of a tie line is two-fold, i.e., firstly it enables checking of the accuracy of the network and secondly locating the interior details which are comparatively far away from the main survey lines.

Write down the Procedure of setting Offsets with open cross-staff.

Ans- Procedure for setting offset with open cross-staff :

1. Keep the ranging rods at point P (fixed on survey line) and at

point A1 approximately.

2. The cross-staff with stadia rod is fixed at point B.

3. Now two surveyors will observe both rods at A1 and P

simultaneously.

4. If both rods are not bisecting at a time, then rod at A1

should move towards the right parallel to the survey line (towards

left if the rod is at A2) as shown in above fig.

5. Once both rods are bisected simultaneously then point A

can be fixed and perpendicular offset AB is said to be set to

given survey line PQ on the left side.

What is the use of Chain/tape, ranging rod, Peg, Arrows in the chaining process?

Ans- (1) Chain- Chains are commonly used to directly measure the linear distance between two points during the survey process.

(2) Ranging Rod- The ranging rods are used for making the positions of stations and for ranging the lines. They are made of ell seasoned straight-grained timber teak. The circular in cross-section of 3cm diameter and have a length of either 2 or 3cm, the length being more common.

(3) Peg- Pegs or Wooden pegs are used in measuring a length of a line to mark the endpoints of the line. The pegs are made of hardwood of 25 mm × 25 mm section, 150 mm long with one end tapered.

(4) Arrows- These are also called marking or chaining pins. Accompanying each chain are ten arrows, these are used to mark the end of the chain during the process of chaining.

Differentiate between the W.C.B. system and the R.B. system on four points.

Ans-

 W.C.B. R.B. 1.    The horizontal angle made by a line with the magnetic north in the clockwise direction is the whole circle bearing of the line The horizontal angle made by a line with the magnetic north or south (whichever is closer from the line) in the eastward or westward direction is the Quadrantal Bearing or Reduced Bearing of the line 2.   Only the magnetic north line is considered as a reference line in the whole circle bearing system. Both magnetic north and south lines are considered as reference line in the quadrantal bearing system. 3.   The clockwise angle from the reference, the line is Only taken Both clockwise and anticlockwise angle from the reference line is Only taken 4.   The value of the whole circle bearing varies from 0° to 360° The value of the reduced bearing varies from 0° to 90° 5.   Example: 26°, 121°, 245°, 350° etc. Example: N26°E, S59°E, S65°W, N10°W etc.

*Self Typed
*Source- Books, Internet, Self-Analysis

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