Plane Table Survey MCQ Quiz in বাংলা - Objective Question with Answer for Plane Table Survey - বিনামূল্যে ডাউনলোড করুন [PDF]

Concept:

Methods of Plane Table Surveying:

Generally there are four methods are available to perform plane table surveying. They are

1. Radiation
2. Intersection
3. Traversing
4. Resection

The following steps in ascending order of radiation method of plane table surveying:

1. Select a point "O" so that all points to be located are visible from it.
2. Set up the table at "O", level it, select a point "O" on the sheet so that it is exactly over station "O" on the ground.
3. Mark the direction of the magnetic meridian.
4. Centering the alidade on "O" BISECT the objects of traverse A, B, C, D, and E.

5. Measure the distances OA, OB, OC, OD, and OE and plot to convenient scale to locate a, b, c, d, and e respectively.

6. Join the points a, b, c, d, and e on the paper.

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Figure: Radiation Method

Explanation:

Instrument	Used for measuring
Frequency meter	Frequency of periodic signal
Lux meter	Light Intensity (illumination level of light)
Harmonic analyzer	Frequencies and amplitudes
Digital multimeter	Electric parameter

Concept:

Trial and error method or Lehman’s method:

This method is very commonly used in field measurements as it is very accurate. The position of a plane table is estimated by judgement. This tringle is reduced to point by trial and error.

This is the quickest and most accurate method to solve three-point problem in resection of plane tabling.

Bessel’s Graphical method:

There are various graphical methods to solve the three point problem. But the simple and the best one is the bessel’s solution by the inscribed quadrilateral.

It is based on the geometric principle that in any inscribed quadrilateral the angle made by one of the sides with one of the diagonals is equal to the angle made by the opposite side with the other diagonal.

Tracing paper or mechanical method:

In this method a tracing paper is fixed on the plane table and the station is approximately transferred on the tracing paper and all the three sections are sighted by drawing rays.

After removing the tracing paper, it is moved on the drawing sheet in such a way that the three rays on the tracing paper pass through the plotted positions of the ground stations and required point is plotted.

Concept:

Methods of Plane Table Surveying:

Generally, there are four methods are available to perform plane table surveying. They are

1. Radiation
2. Intersection
3. Traversing
4. Resection

Intersection method:

• This method is preferred when the distance between the stations is too large or the grounds are undulating. Example: Hilly areas or Hillock without vegetation.

The procedure of intersection method:

• In this method, we can locate the point by plotting two rays from two known stations. As shown in the figure, P and Q are the known stations.

• First, the equipment is placed on P and plot the lines by sighting the stations A, B, and Q.
• Then shift the equipment to station Q and plot the lines by sighting stations A, B, and P.
• Finally, the intersection of A and B rays is the required location of the point of intersection.

Concept:

Resection: 

• Resection is defined as the process of locating the instrument station occupied by the plane table by drawing rays from the stations whose positions have already been plotted on the drawing sheet.
• Two-point problems and Three-point problems are methods of orientation & resection.
• In the three-point problem method, three well-defined points, having locations already being plotted on the drawing are involved.
• These are used to find and subsequently plot the location of the plane table station.

There are several methods for the solution of the three-point problem:

1. Trial and Error method (Lehman’s method)
2. Mechanical method (Tracing paper method)
3. Graphical method (Bessel’s method)
4. Analytical method
5. geometrical construction method

 

Explanation:

An Alidade is an instrument used for sighting the point in plane table surveying. One edge of the ruler is bevelled or Fiducial and other is graduated (used for drawing line of sight).

It is a wooden or brass ruler of 50-60 cm in length. Two vanes are hinged at its two ends i.e Object vane and sight vane. A scale is attached to the fiducial edge so as to plot distances to the needle.

Alidades are of two types:

1. Plain Alidade: It is very simple and is used for ordinary work.

2. Telescopic Alidade: It is used to take inclined sights.

Explanation:

There are four methods of plane tabling:

1) Radiation:

• In this ray is drawn from the instrument towards the point, then the distance measured is located by plotting to some scale.
• More suitable when the distance is small and one instrument can control the points to be detailed.

2) Intersection/Graphic triangulation:

• Used when the distance between two points is large and cannot be measured accurately due to some field condition.
• The location of the object is determined by sighting at the object from two plane table stations, which were previously plotted and drawing the rays.
• The intersection of these rays gives the location of the object.
• The point of intersection of two rays forms a vertex of a triangle having two rays as two sides and a base as the third side.
• Due to this reason, this is also called graphic triangulation.

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3) Traversing:

• Similar to theodolite traversing, the table is set up at each station in succession.
• Foresight is taken to the next station and the required distance is measured to a suitable scale.
• This method is suited when the narrow strip of the terrain is to be surveyed.

4) Resection:

• This method is used when the plane table occupies a position not yet plotted on the drawing sheet.
• It is the process of determining the plotted positions of the station occupied by the plane table, by means of sights taken towards known points, the location of which has been plotted

Plane table surveying is the graphical method of survey in which the field observations and plotting are done simultaneously. Plane table surveying is based on the principle that lines drawn during plotting always lie parallel to the corresponding lines actually present on the ground i.e the principle of plane table surveying is parallelism.

Explanation:

• An Alidade is an instrument used for sighting the point in plane table surveying. One edge of the ruler is beveled or Fiducial and the other is graduated (used for drawing line of sight).
• It is a wooden or brass ruler of 50-60 cm in length. Two vanes are hinged at its two ends i.e Object vane and sight vane. A scale is attached to the fiducial edge so as to plot distances to the needle.
• The Object vane is open & it carries a hair or thin wire at its center. The two sight vanes are open and it carries a hair or thin wire at its center. The two sight vanes provide a Definite line of sight.

This fig is representing the edge point below it,

Alidades are of two types:

1. Plain Alidade: It is very simple and is used for ordinary work.

2. Telescopic Alidade: It is used to take inclined sights.

Concept:

The fixing of a plane table from three known points:

• The accuracy with which a plane table station can be located through a three-point problem is known as its fix.
• The degree of accuracy of the solution of the three-point problem is designated as its strength i.e., if the accuracy is high, the fix is termed as strong and for low accuracy, the fix is called poor.
• The accuracy of the fix depends on the relative positions of the plotted points and that of the location of the plane table station. Thus, the choice of plotted objects and the location of the table should be made to get a strong fix.

(a) The strength of fix is good if

• The location of the station is chosen within the great triangle formed by joining the three well-defined objects X;
• The middle object is nearer to the position of the plane table than the other two objects; of the two interior angles subtended by the three objects at the plane table stations, one is small and the other is large. However, the objects subtending small angles should be widely separated from each other.

(b) The strength of fix is poor if

• The location of the plane table is on or near the circumference of the great circle.
• Both the interior angles, subtended, by well-defined objects, at the plane table stations, are small.