429664114-Plane-Table-Surveying-ppt.pptx

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1. Central Engineering College Imadol , Lalitpur DEPARTMENT OF CIVIL ENGINEERING Created By:- Pawan Sharma

2. Content Introduction of plane Table Surveying. Equipment Used in Plane Table Surveying. Working operations of Plane Table Surveying. Method of Plane Table Surveying. Two point Problem. Three point Problem.

3. Plane Table Surveying Plane Table Surveying is a graphical method of survey in which the field observations and plotting process simultaneously.

4. Equipments Used in Plane Table Surveying. The plane table Alidade U-Fork with Plumb bob Spirit Level Compass Drawing Paper

5. The Plane table A plane table is made of wooden or plywood and it is normally rectangular in shape. The size of plane table is 60cm*70cm. There are three types of Plane table:- The traverse table Johnson table The coast survey table

6. Tripod The plane table is mounted on a tripod Tripod is provided with three foot screws at its top for leveling of the plane table.

7. Alidade The alidade is useful for establishing a line of sight. There are two Types of alidade. Plane alidade 2. Telescopic alidade

8. U-Fork with Plumb bob U-fork with plumb bob is used for centering the table over the point or station occupied by the plane table when the plotted position of that point is already on the sheet.

9. Spirit Level The Table is leveled by placing the level on the board in two positions at right angles and getting the bubble central in both positions.

10. Compass The compass is required for drawing the line showing magnetic meridian on the paper. It is used to orient the table to the magnetic meridian.

11. Drawing Paper Drawing paper is used for plotting the ground details.

12. Working operations of Plane Table Surveying. Fixing Fixing the plane table on the tripod stand Setting Leveling Centering Orientation

13. Leveling Place the table over the station-point and spread out legs to make it level and at a convenient height, preferably not above the elbow. Centering The point on the paper representing the station being occupied should be vertically over the point on the ground. This operation is known as centering of the table. Orientation The table is said to be oriented when it is so placed that all lines on the paper are parallel to the corresponding lines on the ground.

14. Methods Of Plane Tabling Radiation Intersection Traversing Resection Compass Method Back-ray Method Two-point problem Three-point problem

15. Radiation

16. Intersection

17. Traversing

18. Two point Problem

19. Two point Problem A two-point problem is one of the methods of resection. Resection is the process of determining positions of an unknown point with other known points. The problem of finding plotted position of the station point occupied by the plane table with the help of plotted position of two well defined point is known as solving two point problem.

20. Procedure While choosing point Q the triangles formed APQ and BPQ should be well-conditioned. Point Q is roughly oriented, and A and B are plotted in it. Similarly, alidade is sighted to P and name it p1. Now orient the plane table back sighting to Q produces the ray from A to intersect which is named p. Also, draw the ray PB to intersect at line bp at b1. Now, b and b1 points might not coincide due to the presence of angular error in it. To correct it, fix the point R along with the AB and rotate the table till the ab line is sighted to R. which is the correct orientation of A and B. Again, the resector line aA and bB are drawn to get position p of point P.

21. Three point Problem The problem of finding plotted position of the station point occupied by the plane table with the help of plotted position of three well defined point is known as solving three point problem.   The method is based on the fact that, in a correctly oriented plane table, resectors through well defined points get intersected at a point which represents the location of the plane table station on the drawing   There are 3 method to solve three point problem. they are given below: Mechanical / tracing paper method Graphical method Trial and error method / lehman’s method

22. Three point Problem

23. Mechanical method: The method is based on the fact that, in a correctly oriented plane table, resectors through well defined points get intersected at a point which represents the location of the plane table station on the drawing The method is also called trace paper mehod .

24. Graphical method: 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. It is simple method of solving 3- point problem

25. Trial and error method/ lehman’s method / triangle of error: if the orientation of the plane table is not proper, the intersection of the resectors through the three points will not meet at a point but will form a triangle, known as triangle of error   The size of the triangle of error depends upon the amount of angular error in the orientation .   minimises the triangle of error to a point iteratively. The iterative operation consist of drawing of resectors from known points through their plotted position and the adjustment of orientation of the plane table.

26. Lehmann's rules If the position of plane table station is inside the great triangle, its plotted position should be chosen inside the triangle of error. If the position of plane table station is outside the great triangle, its plotted position should be chosen outside the triangle of error.   The point of plane table on the same side of the 3 resection line the distance of plane table from resection line is proportional to the length of that line. P1/pa=p2/ pb =p3/pc It mean that ratios must be equal For ex: 1/2=1/2=1/2 The plotted position of the plane table should be so chosen that it is to the same side of all the three rays.

27. If the position of plane table station is outside the great circle, its plotted position should be so chosen that It lies on the same side of ray to the most distant point as the intersection k of the other two rays. The intersection of two rays to the nearer points, is midway between the plotted position of the station and the ray to the most distant point .   If the position of plane table station is outside the great triangle but inside the great circle, the plotted position of the station is so chosen that the ray to the middle point lies between plotted station position and the intersection of the rays to the two extreme points.

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