1. LEVELING

2. INTRODUCTION
Levelling is the process by which differences in height between two or more points can be determined.
For planning purposes they are used
to provide the information needed to develop the maps, charts and drawings necessary to layout buildings, roads, drains.
Layout used to establish the boundaries lines, elevation for the construction of those structures.

3. LEVELING TERMS Datum Bench Mark (BM) Back sight (BS)
Height of Instrument (HI)
Foresight (FS)
Intermediate Sight (IS)
Turning Point (TP)

4. DATUM
The most common surveying datum is mean sea-level (MSL)
Datum - This is an arbitrary level surface to which the heights of all points are referred.
An assumed datum, which is established by giving a benchmark an assumed value (e.g m) to which all levels in the local area will be reduced.
but as hydrological work is usually just concerned with levels in a local area, we often use:

5. BENCH MARK (BM)
An object whose elevation above mean sea level is known or assumed to be known
A bench mark must be an object that is dimensionally stable because it is reference point for all of the elevations for a survey
If the bench mark elevation is accidentally changed, all surveys that used it must be redone.

6. CONT
In many situations it is not necessary to know the exact elevation above sea level. For such surveys, a local benchmark is used.
Frequently, this bench mark is given the elevation of m
When using a local bench mark, the survey crew must select and establish its location
A typical local bench mark might be and ‘X’ chipped in a concrete curb or a bridge abutment, an iron pin driven firmly into the ground, or the rime of an electrical or sewer access holes.

7. BACKSIGHT (BS)
A rod reading taken on a point of known or assumed elevation
It is the vertical distance between the line of sight through the instrument and the point of known or assumed elevation on which the rod is set.
The back sight reading is used to establish height of the instrument
A back sight will always be taken on a bench mark or turning point.

8. CONT
The word back sight has nothing to do with the direction in which the instrument pointed.
It is important to remember that there is only one back sight for each setup of the instrument.

9. HEIGHT OF INSTRUMENT (HI)
HI is the elevation of the line of sight through the instrument when it is mounted on a tripod and leveled
It is found by adding the back sight reading to the elevation of the point on which the back sight was taken.
BM + BS = HI

10. FORESIGHT (FS) A rod reading taken on any point of unknown elevation
In differential leveling, there is only one foresight for each instrument setup, whereas profile leveling may have several foresights per instrument setup
The FS is subtracted from the HI to find the elevation of unknown point.
HI – FS= elevation

11. INTERMEDIATE SIGHT (IS)
Is a rod reading taken at any other point where elevation is required.
HI – IS = elevation

12. TURNING POINT
A temporary bench mark that is used to extend survey a greater distance
They are used any time it is necessary to move the instrument.
Whenever the instrument is moved to a different location a back sight is taken on a TP to establish the new instrument height
Turning points are usually used wherever the starting station and ending station can not be seen from one instrument position

13. CONT
The structure used for a turning point should be dimensionally stable just like a bench mark
A stake or permanent structure such as a curb must be used.
Do not set rod on the ground when making a turning point; doing so could result in a serious error.

15. LEVELING CREW AT WORK

16. LEVELING PRINCIPLE Height of A above datum is; 1.500 – 0.750 = 0.750 m
Height of C above datum is ; – = 0.450m

17. LEVELING PRINCIPLE Simple Levelling Differential Levelling
When it is required to find the differenced in elevation between two points, both of which are visible from a single position of the level.
Differential Levelling
Determine the difference in elevation between two or more points without any regard to the alignment of the points.
Use when:
Two point are a large distance apart.
The difference in elevation between two points is large.
Obstacle intervenes between points.

18. LEVELING PRINCIPLE

19. LEVELING PRINCIPLE

20. LEVELING PRINCIPLE

21. LEVELING PRINCIPLE

22. DATUM
Datum is a standard position or level that measurements are taken from.

23. LEVELING INSTRUMENT The basic equipment required in levelling is :
A device that gives a truly horizontal line
Dumpy level, automatic level.
A suitably graduated staff for reading vertical

25. LEVEL

26. Two "E" pattern staffs, note slight differences in the marking and numbers.
The "E" pattern is designed to make it easy to read a small section of the scale when seen through a telescope
STAFF

28. Usually the length of staff is 3m, 4m or 5m while the width is not less than 38mm.
Measurements are in metres and cm (10mm blocks) which enable heights to be estimated to 1 mm.
Different colours are used to differentiate each metre length, the most common being black and red on a white background.
Each observer will need to focus the reticule to allow for their own eye.

29. Failure to do so will cause parallax, where a small movement of the eye's position will cause the horizontal lines to give a different staff reading.

30. With the eye piece focused you will see a vertical and a horizontal line dividing the field of view.
The middle horizontal line marks the horizontal plane through the telescope (height of collimation) and is the reference for all height readings.
There may also be two short stadia lines. Stadia are used for measuring the distance to the staff by multiplying the difference between the two stadia readings by a constant (usually 100).

31. In this view the staff reading is = _____
Check that the spirit level bubble is within the central portion of the scale before reading the staff.
In this view the staff reading is = _____
Upper stadia = ____ Lower stadia = ____ Stadia difference = _____

32. It is essential that readings are taken when the staff is vertical
Even with a spirit level it is difficult to hold a staff vertical. This difficulty increases in wind
Some staffs are fitted with a spherical spirit level and handles to help the staff person keep it vertical.
It is essential that readings are taken when the staff is vertical
CHECK THE STAFF

34. To read the staff when vertical the surveyor use the vertical reticule line to direct the staff person to move the top of the staff left or right of the sight line.

35. The level is an optical instrument that provides a height reference
The level is an optical instrument that provides a height reference. This reference is a horizontal plane through the axis of the telescope, known as the "Height of Collimation".
Once the height of collimation (or instrument height) has been measured the height of other stations can be found by measuring from this plane with a staff.
The height of collimation is found by taking a backsight to a staff placed on a bench mark. The staff reading is added to the bench mark value to obtain the height of collimation.
PRINCIPLE OF LEVELING

36. CONT
Once the height of collimation has been found ground height at any spot below this plane can be found by observing the staff and subtracting the staff reading from the height of collimation.

37. Temporary Adjustment Setting up Levelling Elimination of parallax.
Leg adjustment, Fixing instrument over tripod.
Levelling
Elimination of parallax.

38. Setting Up Leg Adjustment
Each leg of a tripod is adjustable for length. The legs are locked by a lever clamp (left) or screw (right).
Set tripod in position - if the ground is sloping place two legs on the down hill side

39. Firmly press the two tripod feet on the down hill side into the ground using your own foot on the tripod's foot plate. (This will tilt the head)
Fine adjustments can be made by changing the length of each leg.
Make sure that the clamp or locking screw is tight when finished.

40. Fixing the instrument over tripod

41. SETTING UP A LEVEL
The head must be screwed snugly on the tripod. If the head too lose, the instument is unstable, if too tight, it may “freeze”
A level should be removed from its container by lifting from the base, not by grasping the telescope.
The safest way to transport a leveling instrument in a vehicle is to leave it in the container.

42. Levelling Up
Spherical level is a bubble spirit level attached to the tribrach and referenced to the axis of the telescope.
In use the bubble must be within the circle for the instrument to give a horizontal sight line
The eye piece is adjustable and should be set for each observer to bring the cross hairs in to sharp focus.

43. ADJUSTING THE LEVELLING HEAD
The bubble will probably be against the side of the circular spirit level, and needs moving in to the centre.
The bubble moves in the direction of the left thumb.
Facing the instrument rotate both foot screws in opposite directions at the same time. Either thumbs moving inwards or thumbs moving outwards.
Align the telescope parallel to two foot screws.

44. The first two screws are level so they must not be touched.
CONT
As a check rotate the instrument through 90°. If necessary re-level the original two foot screws and repeat the rotation to check the third one.
Using the left hand adjust the third levelling screw to centre the bubble. Again the bubble will move in the same direction as the left thumb.
The first two screws are level so they must not be touched.

46. Elimination of Parallax
Focussing the eyepiece
To make the cross-hairs appear distinct and cleary visible.
Hold white paper in front of the objective. Move eyepiece in or out till cross hair appear distinct.
Focussing the objective
To bring image of the object in the plane of the cross hair.
Direct telescope towards the staff. Turn focussing screw until image appears clear and sharp.

47. Permanent Adjustment
Done to set the essential parts of the instrument in true position relative to each other.
The desired relationship of the fundamental lines are:
The vertical axis of the level should be perpendicular to the axis of the plate bubble tube
The line of collimation should be perpendicular to the vertical axis
The axis of the telescope and the line of collimation should coincide.

48. Instrumental errors
Collimation Error
Error due to Parallax Error
Levelling Staf; not held vertical, graduation not correct,
Natural errors
Error due to Earth Curvature
Error due to Refraction
Error due to wind, type of ground.
Personal errors
Mistakes in setting up level, focussing eyepiece, objective, setting the collimation, holding staff.
LEVELING ERRORS

49. Collimation Error
The Automatic Prism compensator goes out of alignment.
The level provides readings outside of its specification

50. Collimation Error

51. Parallax Error
When using an optical instrument — both the image and cross hairs can be focused- if either is imprecisely focused, the cross hairs will appear to move with respect to the object focused, if one moves one's head horizontally in front of the eyepiece.

52. Parallax Error

53. Correction of Parallax Error
Adjust Focus of lens to infinity
Focus of Cross Hairs to a sharp setting Note every users parallax focus is different
Refocus on Target and check for parallax

54. Curvature of the Earth
Due to the curvature of the Earth, the line of sight at the instrument will deviate from a horizontal line as one moves away from the level

55. CORRECTION FOR CURVATURE AREA
For a sight length of 100m the effect is only 1mm.
Keep Sight lengths under 50m
the effect is eliminated by using equal sight lengths for fore- and backsights.

56. The variable density of the Earth's atmosphere causes a bending of the ray from the staff to the level.
May also be caused by heat emitted by plant
May be caused by heat haze
REFRACTION

57. 8. Repeat steps 5 to 7 until a foresight is taken on the last station.
7. Move the instrument, and set up again.
6. Establish the next TP, and take the FS reading.
5. Take the BS on the TP.
4. Move the instrument, and set up again.
3. Establish the TP, and take the FS reading.
2. Take the BS reading on BM1.
1. Set up the instrument.
In summary, the procedure for differential leveling is as follows:

58. The process of taking a plus sight, followed by minus sight, is repeated over and over until the curcuit is completed.
Running closed curcuits can be made either by returning to the starting bench mark, or by ending the curcuit at any other bench mark.

59. If a closure is made by returning to the initial bench mark, then the final elevation should agree with the strating elevation.
The amount by which they differ is the loop misclosure
If closure is made to another bench mark, the section misclosure is the difference between the closing bench mark’s given elevation and its elevation obtained after leveling through the section

60. Recommendeds the following formula to compute allowable misclosures:-
Precise levelling
C = 4 x √K
Accurate levelling
C = 12 x √K
Where C is a allowable loop or section misclosure, in mm; and K is the total length leveled, in km
MISCLOSURES

61. EXAMPLE The misclosure is +30 mm The length of the loop is 0.7 km
The misclosure of +30 mm is too big
The loop must be repeated (or find the error)
The misclosure limit is…

62. The procedure for differential levelling will be described using this type of circuit, illustrated schematically .

64. ANSWER

65. PRECISION Precision in leveling is increased by Repeating measurement,
Making frequenties to established bench marks,
Using high quality equipment,
Keeping it in good adjustment, and
Performing the measurements carefully

66. ERROR CONTROL
In surveying, it is important to control as many errors as possible.
For differential leveling surveys three error checks should be completed:
close the loop,
note check,
and calculation of the allowable error of closure.
The survey is closed to provide the information for the other two checks.

67. TWO METHOD OF RECORDING
RISE AND FALL
HEIGHT OF COLLIMATION

68. RECORDING FIELD NOTES (RF RECORDING SYTLE)BS IS FS
Rise
Fall
ELE
Remark
1.32
50.00
BM A
2.56
3.98
2.66
47.34
TP 1
1.25
1.31
48.65 C
3.65
2.40
46.25 D
3.49
0.67
2.98
49.23
TP 2
2.58
0.91
50.14 E
2.64
1.54
1.04
51.18
TP 3
3.79
1.15
50.03
Ʃ10.01
Ʃ9.98
Ʃ6.24
Ʃ6.21
Check = ƩB.S. – ƩF.S. = Ʃrise – Ʃfall = Last R.L. – First R.L.

69. RECORDING FIELD NOTES (HC RECORDING SYTLE)BS IS FS HC
ELE
Remark
1.32
51.32
50.00
BM A
2.56
3.98
49.9
47.34
TP 1
1.25
48.65 C
3.65
46.25 D
3.49
0.67
52.72
49.23
TP 2
2.58
50.14 E
2.64
1.54
53.82
51.18
TP 3
3.79
50.03
Ʃ10.01
Ʃ9.98
Check = ƩB.S. – ƩF.S. = Last R.L. – First R.L.

70. Example

71. Rise and Fall

72. Height of Collimation

73. THANK YOU
Edited From Original Notes by Puan Liyana