1. CIVIL DEPRATMENT

2. Plane table surveying Equipments Accessories Principle
Setting up the plane table
Methods
Advantages - disadvantages

3. Pen No.
Shefali Christain
Haridk Tailor
Ishita Bhatt
Keyur Jadav
Jay Patel

4. Plane Table Surveying
Plane Table Surveying is a graphical method of survey in which the field observations and plotting are done simultaneously.
It is simple and cheaper than theodolite survey. It is most suitable for small scale maps.
The plan is drawn by the surveyor in the field, while the area to be surveyed is before his eyes. Therefore, there is no possibility of omitting the necessary measurements.

5. Equipments :-
Plane Table
Tripod
Alidade

6. Plane table
The drawing board for plane tabling is made from well-seasoned wood with its upper surface exactly plane.
It is mounted on a tripod and clamps are provided to fix it in any direction.

7. Tripod The plane table is mounted on a tripod
The tripod is generally of open frame type.
The tripod may be made to fold for convenience of transportation.
Tripod is provided with three foot screws at its top for levelling of the plane table.

8. Alidade The alidade is useful for establishing a line of sight.
Simple Alidade
It is used for ordinary work .
It is generally consists of a gun metal or wooden rule with two vertical vanes at the ends.
The eye-vane is provided with a narrow slit while the object vane is open and carries a horse hair.

9. To draw the rays, one of the edge of alidade is bevelled and this perfectly smooth working edge is known as the fiducially edge.
The fiducially edge is graduated to facilitate the plotting of distances to a scale.

10. Accessories:- Trough Compass Spirit level U-Fork with Plumb bob
Water proof cover
Drawing paper
Pins
Drawing accessories

11. Trough compass
 The trough compass is required for drawing the line showing magnetic meridian on the paper.
It is used on orientation of the table to the magnetic meridian.
When the freely suspended needle shows 00 at each end, a line is drawn on the drawing paper which represents the magnetic north.

12. Spirit Level
A Spirit Level is used for ascertaining If the table is properly level.
The Table is levelled by placing the level on the board in two positions at right angles and getting the bubble central in both positions.

13. U Fork with Plumb Bob
 U-fork with plumb bob is used for centring the table over the point or station occupied by the plane table when the plotted position of that point is already on the sheet.
Also, in the beginning of the work, it is used for transferring the ground point on the sheet.

14. Water proof cover
An umbrella is used to protect the drawing paper from rain.

15. Drawing paper & accessories
Drawing paper is used for plotting the ground details.
For plotting the ground details on the paper we need drawing accessories.

16. Principle of plane table survey:-
“ All the lines drawn on the drawing sheet are parallel to the corresponding lines on the ground, if the table is in properly oriented position.”
Normally O,A,B,C etc represents the ground points and o ,a ,b , c etc represents the points on the drawing paper.

17. Setting Up the Plane table:-
 Three processes are involved in setting up the plane table over the station.
Levelling
Centring
Orientation

18. Leveling
The Table should be set up at convenient height for working on the board, say about 1 m. The legs of Tripod should be spread well apart and firmly into the ground.
For levelling the table ordinary spirit level may be used. The table is levelled by placing the level on the board in two positions at right angles and getting the bubble central in both directions.

19. Centering
The table should be so placed over the station on the ground that the point plotted on the sheet corresponding to the station occupied should be exactly over the station on the ground. The operation is known as centering the plane table. It is done by U-fork and plumb bob.

20. Orientation
This process involves positioning the plane table in such a manner that all lines on the paper are parallel to the corresponding lines on the ground.
There are two methods of orientation:
By magnetic needle
By back sighting

21. a. By magnetic needle
In this method, the magnetic north is drawn on paper at a particular station. At the next station, the trough compass is placed along the line of magnetic north and the table is turned in such a way that the ends of magnetic needle are opposite to zeros of the scale. The board is then fixed in position by clamps. This method is inaccurate in the since that the results are likely to be affected by the local attraction.

22. b. By back sighting
Suppose a line is drawn from station A on paper as ab, representing line AB on ground
The table is turned till the line of sight bisects the ranging rod at B. The board is then clamped at B and then alidade is kept on ba.
The table is turned till the line of sight bisects the ranging rod at A.
This method is better than the previous one and it gives perfect orientation.

23. Methods of Plane tabling:-
Method of Radiation
Method of Intersection
Method of Traversing
Method of Resection

24. Method of Radiation
This is the simplest method and it is useful only when the whole traverse can be commanded from a single station.
Do the whole procedure for setting up the plane table.
Then keep the alidade touching station and sight to A. Draw the ray along that edge, measure distance OA and take a suitable scale on paper which will give a point on a paper.

25. Similarly, obtain points b ,c , d,e,f on paper by drawing lines of sights for stations B,C,D,E,F and according to suitable scale.
Join a ,b ,c ,d ,e , f on the paper. For checking the accuracy of work , measure the distance AB , BC , CD , DE , EF , FA and compare them with the lengths on paper.

26. Method of Intersection
This method is useful where it is not possible to measure the distance on ground.
The location of an object is determined by the intersection of point taken from two different stations.
Follow the procedure for setting up the plane table.
Pivoting the alidade about o1 , sight it to O2 . Measure O1 O2 and plot it along the ray o2 . The base line o1 o2 is drawn.

27. Pivoting the alidade about o1 sight the A , B and draw corresponding rays.
Shift the table about O2 and set it there orient the table by back sighting O1.
Pivot the alidade about o2 , sight the details A, B and draw the corresponding rays to intersect the previously drawn rays at a , b etc.

28. Method of Traversing
This method is just like compass survey and it is useful for the survey work of roads, rivers etc.
Set the plane table at A. By use of plumbing fork transfer the A on the sheet.
With alidade pivoted about a, sight it to B and draw the ray.

29. Measure AB and scale off ab to some scale
Measure AB and scale off ab to some scale. Similarly draw a ray towards E, measure the AE and plot e.
Shift the table to B and set it. Orient it by back sighting of A. Clamp the table.
Sight to C. Measure BC and plot it on the drawn ray to some scale.
If there are n stations then table will have to be set on atleast (n-1) stations to know the error of closure.

30. Advantages :-
The plan is drawn by the surveyor himself while the area to be surveyed is before his eyes. Therefore, there is no possibility of omitting the necessary measurements.
The surveyor Can compare the plotted work with the actual features of the area.  
It is simple and cheaper than the theodolite survey.
It is most suitable for small scale maps.

31. No great skill is required to create map.
It is useful in magnetic areas where compass may not be used.
The mistakes in writing field books are eliminated.

32. Disadvantages :- It is not intended for very accurate work.
It is not suitable in monsoon.
It is essentially a tropical instrument.
Due to heaviness, it is inconvenient to transport.
Since there are so many accessories, there is likelihood of them being lost.