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2.  Plane table is a graphical method of surveying in which the field works and the plotting is done simultaneously.  It is particularly adopting in small mapping.  Plane table surveying is used for locating the field computation of area of field.  The principle of plane tabling is parellelism,of rays of line on paper are parallel to the line on ground 2

3.  Plane Table  Alidade  Sprit Level  The Compass  U- fork or plumbing fork with plumb bob 3

4.  The plane table is a drawing board of size 750mm×600mmm and of well-seasoned wood like teak, pine, etc.  The top surface is well levelled.  The bottom surface consist of a threaded circular plate for fixing the table on the tripod stand by a wing nut. 4

5. Plane Alidade :  The plane alidade consist of a metal or wooden ruler of length about 50cm.  One of its edges is beveled, and is known as the fiducial edge.  It consist of two vanes at both end which are hinged with ruler  One is known as the ‘Object vane’ and caries a horse hair; the other is called the ‘Sight vane‘ and is pivoted with a narrow slit 5

6. Telescopic Alidade :  The telescopic alidade consist of a telescope meant for inclined sight or sighting distinct object clearly.  This alidade has no vanes at the end.  It is also provided with fiducial edge. 6

7.  The spirit level is a small metallic or made by other material tube containing a small bubble of spirit.  The bubble is visible on the top along a graduated glass tube.  The spirit is meant for levelling the plane table. 7

8. The Trough compass :  Trough compass is a rectangular box made of non-magnetic metal containing a magnetic needle pivoted at the center.  This compass consist of a ‘0’ mark at both end to locate the N – S direction. 8

9. The Circular box Compass:  It carries a pivoted magnetic needle at the center.  The circular box is fitted on a square base plate.  Sometime two bubble tube are fixed at right angle to each other on the base plate.  It is for marking the north direction on the map. 9

10.  The U – fork is a metal strip bent in the shape of a ‘U’ having equal arm length.  The top arm is pointed and the bottom arm carries a hook for suspending a plumb bob. 10

11. The procedures for working with the plane table are:  Fixing the table on the tripod stand  Leveling  Centering  Marking the north line  Orientation 11

12. Fixing the table on the tripod stand: The tripod stand is placed over the required station with its legs well apart. Then the table is fixed on it by wing nut at the bottom. Leveling: The table is levelled by placing the spirit level at different corners and various positions on the table. The bubble is brought to the center of its run at every positions of the table by adjusting the legs. 12

13. Centering : The drawing sheet is fixed on the table.A suitable point P is selected on the sheet to represent the station P on the ground. A pin is then fixed on this selected point. The upper point end of the U fork is made in content with the station pin and the plum bob which is suspended from hook at the lower end is brought just over the station P by turning the station clockwise or counterclockwise or slightly adjusting the legs. Then the table is clamped. The care should be taken not to disturb the leveling. 13

14. Marking the North line: The trough compass is placed on the right–hand top corner with its north end approximately towards the north. Then the compass is turned clockwise or anticlockwise so that the needle exactly coincides with the 0–0 mark. Now the line representing the north line is drawn through the edge of the compass. It should be ensured that the table is not turned. Orientation: When plane table survey is to be conducted by connecting several stations. The orientation must be performed at every successive station. The process of orientation is described in two methods. 14

15. The method is suitable when the local attraction is not suspected in the area. Procedure: The table is centered, levelled and the north direction is pointed on the right corner of the sheet at station A. With the alidade touching the point ‘a’ the ranging rod on point B is bisected and a ray is drawn with suitable scale. The table is shifted and adjusted over B. Now the trough compass is placed exactly along the north line drawn previously. The table is then turned clockwise or counterclockwise Until the needle coincides exactly with 0-0 mark of the compass 15

16. This method is accurate and is always preferred. Procedure: The table is centered, levelled and the north direction is pointed on the right corner of the sheet at station A. With the alidade touching the point ‘a’ the ranging rod on point B is bisected and a ray is drawn with suitable scale. The table is shifted and adjusted over B. Now alidade is placed along the line ba,and the ranging rod at A is bisected by turning the table clock or anticlockwise. When the centering, leveling, and bisection of the ranging rod at A are prefect, then the orientation is said to be perfect. 16

17.  There are four methods of plane tabling: 1. Radiation 2. Intersection 3. Traversing 4. Resection 17

18.  This method is suitable for locating the objects from a single station.  In this method, rays are drawn from the station to the objects, and the distance is measured and plotted to any suitable scale along the respective rays. 18

19. a) Suppose P is the station on the ground from where the objects A,B,C and D are visible. b) The plane table is set up over the station P. A drawing sheet is fixed on the table, which is then levelled and centered. A point p is selected on the sheet to represent the station P. c) The north line is marked on the right hand top corner of the sheet with the trough compass or circular box compass. d) With the alidade touching p, the ranging rod at A,B,C and D are bisected and the rays drawn. e) The distance PA,PB,PC, and PD are measured and plotted to any suitable scale to obtain the points a, b, c and d representing the objects A,B,C and D on paper. 19

20.  This method is suitable for locating inaccessible points by the intersection of the rays drawn from two instrument station. 20

21. a) Suppose A and B are two station and P is an object on the far bank of the river. Now it is required to fix the position of P on the sheet by the intersection of rays, drawn from A and B. b) The table is set up at A. It is levelled and centered so that a point a on the sheet is just over the station A. The north line is marked on the right-hand top corner. The able is then clamped. c) With the alidade touching a, the object P and the ranging rod at B are bisected, and rays are drawn through the fiducial edge of the alidade. 21

22. d) The distance AB is measured and plotted in the suitable scale to obtain the point b. e) The table is shifted and centered over B and levelled properly. Now the alidade is placed along the line ba and orientation is done by back sighting. At this time it should be remembered that the centering, leveling and orientation must be perfect simultaneously. f) With the alidade touching b the object P is bisected and a ray is drawn. This ray will intersect the previous ray line at a point p. this point p is required plotted position of P. 22

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24.  This method is suitable for connecting the traverse station.  This is similar to compass traversing or Theodolite traversing.  Here the fielding and plotting are done simultaneously with the help of the radiation and traversing. 24

25. a) Suppose A,B,C,D and E are the traverse stations. b) The table is set up at station A and a suitable point a is selected on the sheet in such a way that the area may be plotted in the sheet. The table is centered, levelled and clamped. The north line is marked on the right hand corner of the sheet. c) With the alidade touching point a the ranging rod at B is bisected and a ray is drawn. The distance AB is measured and plotted to any suitable scale. d) The table is shifted and centered over B. It is then levelled, oriented by back sighting and clamped. e) With the alidade touching point b, the ranging rod at C is bisected and ray is drawn. The distance BC is measured and plotted to the same scale. 25

26. f) The table is shifted and the same procedure is repeated. g) In this same manner, all the stations of the traverse are connected. h) At the end, the finishing point may not coincide with the starting point and there may be some closing error. This error is adjusted graphically. 26

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28.  This method is suitable for establishing new station at a place in order to locate missing details. Procedure : a) Suppose it is required to establish a station at position P. let us select two points A and B on the ground. The distance AB is measured and plotted to any suitable scale. This line is known as base line. b) The table is setup at A. it is levelled, cantered and oriented by bisecting the ranging rod at B. The table is then clamped. 28

29. c) With the alidade touching point a, the ranging rod at P is bisected and a ray is drawn. Then a point P 1 is marked on this ray by estimating with the eye. d) The table is shifted and centered in such a way that P 1 is just over P. It is then oriented by back sighting the ranging rod at A. e) With the alidade touching point b, the ranging rod at B is bisected and a ray is drawn. Suppose this ray intersect the previous ray at a point P. This point represent the position of P on the sheet. Then the actual position of the station P is marked on the ground by U – fork and plumb bob. 29

30.  Sometime, after the completion of plane table traversing, it may be notice that an impotent object has not been located due to oversight. If no station pegs are found on the field, some special methods of resection are applied in order to establish a new station for plotting the missing object. As such 1. The Two point problem 2. The Three point problem. 30

31.  In this problem, two well-defined points whose positions have already been plotted on the plan, are selected.  Then by perfectly bisecting these points, a new station is established at required position. 31

32. a) Suppose P and Q are two well defined points whose position are plotted on map as p and q. it is required to locate a new station at A by perfectly bisecting P and Q. b) An auxiliary station B is selected at a suitable position. The table is set up at B, and levelled and oriented by eye estimation. It is then clamped. c) With the alidade touching p and q, the points P and Q are bisected and rays are drawn. Suppose these rays intersect at b. 32

33. d) With the alidade centered on b, the ranging rod at A is bisected and a ray is drawn. Then by eye estimation, a point a 1 is marked on this ray. e) The table is shifted and centered on A, with a 1 just over A. it is levelled and oriented by back sighting. With the alidade touching p, the point P is bisected and a ray is drawn, Suppose this ray intersects the line ba 1 at point a 1, as was assumed previously. f) With the alidade centered on a 1 the point Q is bisected and a ray is drawn. Suppose this ray intersects the ray bq at a point q 1. the triangle pqq 1 is known as the triangle of error, and is to be eliminated. 33

34. g) The alidade is placed along the line pq 1 and a ranging rod R is fixed at some distance from the table. Then, the alidade is placed along the line pq and the table is turned to bisect R. At this position the table is said to be perfectly oriented. h) Finally, with the alidade centered on p and q, the points P and Q are bisected and rays are drawn. Suppose these rays intersects at a point a. this would represent the exact position of the station A. then the station A is marked on the ground. 34

35.  In this problem three well defined points are selected whose positions have already been plotted on the map. then, by perfectly bisecting these three well defined points, a new station is established at the required position.  No auxiliary station is required in order to solve this problem. The table is directly placed at the required position. The problem may be solved by thee different methods as 1. Tracing Paper Method 2. Bassel’s Method 3. Lehman’s Method 35

36.  Suppose A, B and C are three well defined points which have been plotted on the map as a, b and c. It is required to locate a station at P.  The table is placed and levelled. A tracing paper is fixed on the map and a point p is marked on it.  With the alidade centered on P, the points A,B and C are bisected and rays are drawn. These rays may not pass through the points a,b and c because orientation is not done.  Now the tracing paper is unfastened and moved over the map in such a way that the three rays simultaneously pass through the plotted positions a,b and c. 36

37.  Now the point p is pricked with a pin to give an impression p on the map. p is the required point on the map. The tracing paper is then removed.  The alidade is centered on p and the rays are drawn towards A,B and C. These rays must pass through the points a,b and c. 37

38.  Suppose A,B and C are three well condition points which have been plotted as a,b and c. Now it is required to locate a station at P.  The table is placed at the required station P and levelled. The alidade is placed along ca and the point A is bisected. The table is clamped. With the alidade centered an C the point B is bisected and a ray is drawn.  Again the alidade is placed along the line ac, and a point C is bisected and the table is clamped with the alidade touching a, the point B is bisected and a ray is drawn. Suppose this ray intersects the previous ray at a point d 38

39.  The alidade is placed along db and the point B is bisected. At this position the table is said to be perfectly oriented. Now the ray Aa,Bb and Cc are drawn. These three rays must meet at a point p which is the required point on map. This point is transferred to the ground by U-fork and plumb bob. 39

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41.  Suppose A,B and C are three well defined points which have been plotted as a,b and c on the map. It is required to establish a station at P.  The table is set up at P and levelled. Orientation is done by eye estimation.  With the alidade, rays Aa,Bb and Cc are drawn. As the orientation is approximate, the rays may not intersect at a point, but will may form a small triangle of error.  To get the actual point, this triangle of error is to be eliminate. By repeatedly turning the table clock or anticlockwise, the triangle is eliminated in such a way that the rays Aa,Bb and Cc finally meet at a point p. This is the required point on the map. This point is transferred to the ground by U-fork and plumb bob. 41

42. Triangle of error CB A 42

43. The following are the common errors in plane tabling.  Instrumental error  Personal error  Plotting error 43

44. 1. The surface of the table may not be perfectly level. 2. The fiducial edge of the alidade might not be straight. 3. The vanes may not be vertical. 4. The horsehair may be loose and inclined. 5. The table may be loosely joined with the tripod stand. 6. The needle of the trough compass may not be perfectly balanced. Also it may not be able to move freely due to sluggishness of two pivot point. 44

45. 1. The leveling of the table may not be perfect. 2. The table may not be centered properly. 3. The orientation of the table may not be proper. 4. The table might not be perfectly clamped. 5. The object may not be bisected perfectly. 6. The alidade may not be correctly centered on the station point. 7. The rays may not be drawn accurately. 45

46. 1. A good quality pencil with a very fine pointed end may not have been used. 2. An incorrect scale may be used by mistake. 3. Error may result from failure to observe the correct measurement from the scale. 4. Unnecessary hurry at the time of plotting may lead to plotting error 46

47. 1. Before starting the work the equipments for survey work should be verified. 2. The centering should be perfect. 3. The leveling should be perfect. 4. The orientation should be accurate. 5. The alidade should be centered on the same side of the station pin until the work is completed. 6. While shifting the plane table from one station to another, the tripod stand should be kept vertical to avoid damage to the fixing arrangement. 47

48. 7. Several accessories have to be carried, so care should be taken to ensure that nothing is missing. 8. The pencil should have a sharp point. 9. The distance of the object or lines should be written temporally along the respective rays until the plotting is completed. 10. Only the selected scale should be on the table. 11. Measurements should be taken carefully. 12. The stations on the ground are marked as A,B,C,D, etc. while the station points on the map are marked a,b,c,d, etc. 48

49. Reconnaissance: The area to be surveyed is thoroughly examined to find the best possible of traversing. The traverse stations should cover the whole and should be intervisible.The provisions of check line should be kept in mind Marking the stations: The selected stations are marked by wooden pegs on the ground. Reference stations should be prepared for the stations so that they can be readily located in case the stations pegs Connecting the traverse legs and marking details. 49

50.  It is most rapid method of surveying  There is no need for the field book as plotting is done along with the field work. So the problem of mistakes in booking field notes does not arise.  Plotted work can be compared with actual object regardless of whether or not they are properly represented.  There is no possibility of overlooking any important object.  There is no possibility of overlooking any measurement as plotting is done in the field. 50

51.  Irregular object may be represented accurately.  It is suitable in magnetic areas.  The map can be prepared easily, and does not require any great skill.  Error in the measurement and plotting can be detected by check lines  Inaccessible points can be easily located by intersection. 51

52.  The plane table is not suitable for accurate work as the fitting arrangement is not perfect.  Plane table surveying is not suitable in wet climate, in the rainy season, on foggy mornings and in windy weather.  The number of accessories required in such survey is large, and they are likely to lost.  The instrument is very heavy and difficult to carry.  The map cannot be repotted to a different scale as there is no field book. 52

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