This document provides information on contour surveying or levelling. It discusses the objectives of levelling which are to find elevations of points and establish points at given elevations. It describes levelling equipment such as the level, tripod, staff, tape measure and umbrella. It explains key levelling terms including benchmark, backsight, foresight, reduced level and change point. Rules of levelling are outlined including starting and ending on a benchmark and keeping lines of sight short. The document shows an example of booking levelling observations and reducing the levels.

1. Surveying & Levelling – S1C4
Contour Surveying (Levelling)
Done by: Eng.S.Kartheepan (M.Sc, B.Eng, AMIESL)
Department of Civil Engineering
IET, Katunayake

2. 2
 There are 2 main objectives
1. Find the elevations of given points with respect to
a given or assumed reference surface (datum)
2. Establish points at a given elevation or at different
elevations with respect to a given or assumed
datum.
Difference in height
H
Levelling – Purpose
Introduction

3. 3
Objective 1 – Enable engineering works to be
designed
Establish new vertical control
Determine the heights of discrete points
Provide spot heights or contours on a plan
Provide data for road cross-sections or volumes of
earthworks
Levelling – Objectives
Introduction…

4. 4
 Level: The purpose of a level is to provide a
horizontal line of sight
 A telescope which can be extremely accurately set
so it is horizontal, has a set of cross-hairs, and can
be turned through 360 horizontally.
 Provides line of sight
 A level tube to make a line of sight horizontal
 A levelling head to bring the bubble in its centre of
run
Levelling – Equipment

5. Levelling Equipment (Cont.)Telescope
Telescope
eyepiece
object lensobject lensfocusing lens
diaphragm focusing screw
line of
collimation
Focusing:
1. Rotate eyepiece to give a sharp,
clear image of the cross hairs
2. Rotate focusing screw to give a
sharp, clear image of the object
being observed.
The aim of focusing is
to remove (eliminate)
PARALLAX

6. 6
Objective 2 - Required in the setting out of all
kinds of engineering works
Provide a level or inclined plane to set out of
construction work
Levelling – Objectives

7. 7
A fully adjustable 3-legged
stand on which the level sits, so
that the level:
• is roughly horizontal,
prior to fine adjustment
• is at a height at which
the user can see
through it easily
Levelling – Equipment –Tripod

8. 8
 Staff
 A measuring stick, usually 4m tall, and clearly
marked in divisions of 10 mm (allowing
readings to be taken to 1mm by
interpolation), which is held vertically
 Tape measure
 Gig Umbrella
Levelling – Equipment – Staff,Tape,
Umbrella

9. 9
BS FS
 A measurement process whereby the
difference in height between two or
more points can be determined
Difference in height
H = BS - FS
Levelling – Definition
Note that it is not
necessary set up the LEVEL
on the line of BS & FS

10. 10
 Level surface
◦ A surface over which water will not flow
◦ The direction of gravity is always normal to a
level surface
 Horizontal surface
◦ A horizontal surface will be tangent to a level
surface
◦ Over short distances (<100 m) the horizontal
surface and the level surface will coincide
Levelling – Keywords

11. 11
Limit of practical
coincidence (~100 m)
direction of gravity
Level surface
Horizontal
surface
Levelling – Keywords

12. 12
 Datum
◦ A reference surface to which the heights of all
points in a survey or on a site are referred
◦ May be arbitrary or a national height datum
◦ In Sri Lanka we have a National Datum as
MSL
◦ The surface which defines the MSL is
(approximately) Mean Sea Level
Levelling – Keywords

13. 13
RL
Levelling – Keywords – Datum (MSL)
RL – Reduced Level –The Height of a Point Above the Datum

14. 14
Levelling – Keywords – Height

15. 15
 Reduced Level (RL)
◦ The height of a point above the datum
 Benchmark (BM)
◦ A stable reference point of known RL
◦ Usually used as the starting and finishing point
when levelling
 Temporary Bench Mark (TBM)
◦ A point placed (e.g. peg, nail, spike) to provide a
temporary reference point
Levelling – Keywords

16. Types of SDSL Benchmarks

17. Types of SDSL Benchmarks….

18. Types of SDSL Benchmarks…

19. 19
 Backsight (BS)
◦ Always the first reading from a new
instrument station
 Foresight (FS)
◦ Always the last reading from the current
instrument station
 Intermediate sight (IS)
◦ Any sighting that is not a backsight or
foresight
Levelling – Keywords

20. 20
 Change point (CP)
◦ Location of the staff when the level is moved
◦ Change points should be
 Stable
 Well defined
 Recoverable
 e.g. sharp rock, nail, change plate
Levelling – Keywords

21. 21
0.3
0.33
0.339
Read value at
The horizontal
cross hair
Levelling – Reading an E-face Staff

22. 22
The value is ?
1.900
1.910
1.920
1.9301.932
Levelling – Reading an E-face Staff
Read value at
The horizontal
cross hair

23. 23
1.100
1.110
1.120
1.1301.133
The value is ?
Levelling – Reading an E-face Staff
Read value at
The horizontal
cross hair

24. 24
 Always commence and finish a level run on a
Benchmark (BM or TBM)
 Keep foresight and backsight distances as equal as
possible
 Keep lines of sight short (normally < 50m)
 Use stable, well defined change points
Levelling – Rules

25. A Sample Looped Level Line
Setup 1
Setup 2
Setup 3
Setup 4
BS
IS
FS
BM A
CP 1
CP 2
CP 3
Culvert
Post
MDn

26. Booking the observations
BM A
CP 1
CP 2
CP 3
Culvert
MDn
Back Inter Fore Point
BM A
CP 1
1.32
3.98
Setup 1

27. Post
Booking the observations
BM A
CP 1
CP 2
CP 3
Culvert
MDn
Setup 2
Back Inter Fore Point
1.32 BM A
3.98 CP 1
Culvert
Post
CP 2
2.56
1.25
3.65
0.67
Post

28. Booking the observations
BM A
CP 1
CP 2
CP 3
Culvert
MDn
Setup 2
Setup 3
Back Inter Fore Point
1.32 BM A
2.56 3.98 CP 1
1.25 Kerb
3.65 Post
0.67 CP 2
MDn
CP 3
3.49
2.58
1.54
Post
Setup 1

29. Booking the observations
BM A
CP 1
CP 2
CP 3
Culvert
Post
MDn
Setup 1
Setup 4
Setup 2
Setup 3
Back Inter Fore Point
1.32 BM A
2.56 3.98 CP 1
1.25 Culver
t
3.65 Post
3.49 0.67 CP 2
2.58 MDn
1.54 CP 3
BM A
2.64
3.79

30. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 CP 1
1.25 Culvert
3.65 Post
3.49 0.67 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A



31. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 Culvert
3.65 Post
3.49 0.67 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A



32. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 Post
3.49 0.67 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A



33. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A



34. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A



35. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 CP 3
3.79 BM A



36. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 BM A



37. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A



38. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A
10.01 9.98 


39. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A
10.01 9.98 
(0.03) 

40. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A
10.01 9.98 6.24 6.21 
(0.03) 

41. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A
10.01 9.98 6.24 6.21 
(0.03) (0.03) 

42. Reducing levels (Rise and Fall)
Back Inter Fore Rise Fall RL Comment
1.32 50.00 BM A
2.56 3.98 2.66 47.34 CP 1
1.25 1.31 48.65 Culvert
3.65 2.40 46.25 Post
3.49 0.67 2.98 49.23 CP 2
2.58 0.91 50.14 MDn
2.64 1.54 1.04 51.18 CP 3
3.79 1.15 50.03 BM A
10.01 9.98 6.24 6.21 
(0.03) (0.03) (0.03) 

43. Back Inter Fore IH RL Comment
1.32 50.00 BM A
2.56 3.98 CP 1
1.25 Culvert
3.65 Post
3.49 0.67 CP 2
2.58 MDn
2.64 1.54 CP 3
3.79 BM A


Reducing levels (Instrument Height) - HOC

44. Back Inter Fore IH RL Comment
1.32 51.32 50.00 BM A
2.56 3.98 49.90 47.34 CP 1
1.25 48.65 Culvert
3.65 46.25 Post
3.49 0.67 52.72 49.23 CP 2
2.58 50.14 MDn
2.64 1.54 53.82 51.18 CP 3
3.79 50.03 BM A
10.01 9.98 

Reducing levels (Instrument Height)

45. Back Inter Fore IH RL Comment
1.32 51.32 50.00 BM A
2.56 3.98 49.90 47.34 CP 1
1.25 48.65 Culvert
3.65 46.25 Post
3.49 0.67 52.72 49.23 CP 2
2.58 50.14 MDn
2.64 1.54 53.82 51.18 CP 3
3.79 50.03 BM A
10.01 9.98 
(0.03) 
Reducing levels (Instrument Height)

46. Back Inter Fore IH RL Comment
1.32 51.32 50.00 BM A
2.56 3.98 49.90 47.34 CP 1
1.25 48.65 Culvert
3.65 46.25 Post
3.49 0.67 52.72 49.23 CP 2
2.58 50.14 MDn
2.64 1.54 53.82 51.18 CP 3
3.79 50.03 BM A
10.01 9.98 
(0.03) 0.03 
Reducing levels (Instrument Height)

47. Misclosure
►Misclosure
▪ The amount by which the measured height
difference (H measured) differs from the
known height difference derived from the
RLs of the starting and finishing benchmarks
(H known)
Misclosure = H known – H measured

48. An Acceptable Miscloser?
 Small misclosures in closed level loops are
expected because of the accumulation of
errors
 If the misclosure is small, it can be
adjusted
 If the misclosure is large, the loop (or part
of it) must be repeated
 Misclosures can also result from errors in
published BM levels and from BM
instability

49. Testing the Misclose
 The amount of misclosure we are
prepared to accept depends on the
accuracy we are hoping to achieve
 For routine levelling, the third order
levelling standard is adopted…
 misclosure  24k mm
◦ where k is the length of the loop in km

50. Continuing the Example
 The misclosure is +30 mm (i. e. +0.03 m)
 The length of the loop is 0.7 km
(Assumed)
 The misclosure limit is…
 24(0.7) = ±20 mm
 The misclosure of +30 mm is too big
 The loop must be repeated

51. Adjusting the misclose
 Adjustment is carried out to ensure that
the measured and known RLs of the
closing benchmark agree
 The misclosure is linearly distributed
according to the number of set-ups
 The adjustment per set-up for the
previous example is (0.03/4) m...

52. Adjusting the Misclose
Measured
RL
Point Adjustment Adjusted
RL
50.00 BM A
47.34 CP 1
48.65 Culvert
46.25 Post
49.23 CP 2
50.14 MDn
51.18 CP 3
50.03 BM A

53. Adjusting the Misclose (Cont.)
Measured
RL
Point Adjustment Adjusted
RL
50.00 BM A 0.000 50.000
47.34 CP 1 0.008 47.332
48.65 Culvert
46.25 Post
49.23 CP 2
50.14 MDn
51.18 CP 3
50.03 BM A
=1*(0.03/4)

54. Adjusting the Misclose (Cont.)
Measured
RL
Point Adjustment Adjusted
RL
50.00 BM A 0.000 50.000
47.34 CP 1 0.008 47.332
48.65 Culvert 0.015 48.635
46.25 Post 0.015 46.235
49.23 CP 2 0.015 49.215
50.14 MDn
51.18 CP 3
50.03 BM A
=2*(0.03/4)

55. Adjusting the Misclose (Cont.)
Measured
RL
Point Adjustment Adjusted
RL
50.00 BM A 0.000 50.000
47.34 CP 1 0.008 47.332
48.65 Culvert 0.015 48.635
46.25 Post 0.015 46.235
49.23 CP 2 0.015 49.215
50.14 MDn 0.023 50.117
51.18 CP 3 0.023 51.157
50.03 BM A =3*(0.03/4)

56. Adjusting the Misclose (Cont.)
Measured
RL
Point Adjustmen
t
Adjusted
RL
50.00 BM A 0.000 50.000
47.34 CP 1 0.008 47.332
48.65 Culvert 0.015 48.635
46.25 Post 0.015 46.235
49.23 CP 2 0.015 49.215
50.14 MDn 0.023 50.117
51.18 CP 3 0.023 51.157
50.03 BM A 0.030 50.000
=4*(0.03/4)

57. Adjusting the Misclose (Cont.)
Measured
RL
Point Adjustment Adjusted
RL
50.00 BM A 0.000 50.000
47.34 CP 1 0.008 47.332
48.65 Culvert 0.015 48.635
46.25 Post 0.015 46.235
49.23 CP 2 0.015 49.215
50.14 MDn 0.023 50.117
51.18 CP 3 0.023 51.157
50.03 BM A 0.030 50.000

58. 58
 Parallax
◦ Focus eyepiece on cross-hairs, then focus
telescope on staff
 Collimation Error - Line of sight not horizontal
◦ Keep sight lengths from each instrument
position the same
◦ Check collimation error
• Magnetic field effects on Auto Level
Levelling – Errors in the Equipment

59. Parallax
 When focussing any optical instrument it
is vitally important that we eliminate
Parallax
 Move the eye up and down (or from left
to right) over the eyepiece of the
telescope
 If the cross hairs move relative to the
object being observed then Parallax exists
and the focussing is not satisfactory

60. Parallax (Cont.)
Focus the crosshairs
(using the Eyepiece)
Focus the object
(using the Focussing screw)
Images appear
to move
Parallax has been removed
Therefore focussing is good
Images appear
not to move
NOTE
make a parallax check at each
time when you observe a new
object

61. 61
 Change point instability
◦ Use stable, well defined, recoverable change points
◦ e.g. sharp rock, nail, change plate
 Staff Errors
◦ Zero error - base may be worn - doesn’t matter as
long as same staff is always used
 Tripod Errors
◦ Must be stable
Levelling – Errors in the Equipment

62. 62
 Staff not vertical
◦ Use pond bubble on staff
 Unstable equipment
◦ Watch out for soft ground under tripod or staff
◦ Don’t touch (or kick!) tripod
Levelling – Errors in the Field

63. 63
 Keep sightings short to estimate mm on staff
accurately
 Double check all readings
 Write clearly
 Carry out calculation checks
Levelling – Errors in Reading and/or
Booking

64. 64
 Wind causes level to vibrate, heat causes
‘shimmer’
 Refraction
◦ Readings below 0.5 m on a staff may be
affected by refraction
Levelling – Errors due to Weather

65. 65
 Point heights (relative to a datum)
 Height differences (independent of datum)
 Longitudinal Sections and Cross Sections
 Data for volume calculations
 Contouring
 Setting Out
Levelling – Applications

66. Establishing a New Point
Benchmark
New Point
RL BM
Datum
RL NEW

67. Measuring height differences
Benchmark
RLBM
Datum
H1
H2
H3

68. Profiles and Cross-Sections
RLBM
Benchmark
Datum

69. 69
 Contour – line drawn on a plan joining all
points of the same height above or below a
datum
 Contours cannot cross, split or join other
contours, except in the case of an overhang.
e.g. a cliff.
 The height between successive contours –
vertical interval/contour interval
 Its value depends on the variation in height
of the area being contoured
Levelling – Contouring

70. 70
 Contour interval is kept constant for a plan
or map
 Plan spacing between contour line indicates
steepness of slopes
 Closely spaced lines indicates a steep gradient
 Widely spaced lines indicate a flatter gradient
Levelling – Contouring

71. Contouring
5
10
15
20
25
5
10
15
20 25

72. Thank you ..