1. Levelling Applications:
Art of measuring and calculating the height of a point relative to another point
High accuracy is required.
Measurement in a VP.
Applications:
We are used to measuring heights eg your height might be 1.83m or 1.55m
The height of the seat you are sitting on might be 0.45m. Above the floor.
On the other hand the height of the seat for you (4 ROWS BACK) would be 0.45m above your feet but 4*0.45m (1.80m) above my feet.
So it’s important that we start thinking about height relative to some point.
We could talk about each row of you being on a different level.
We could use a spirit level and straight edge to find the different heights or levels.
Ancient civilisations used Water levels.
We could use the ceiling to measure up to and down from to get difference in height or level from the back row to the front row.
That is OUR HORIZONTAL PLANE
Show an OPTICAL LEVEL and TRIPOD
Civil Engg Projects: Railways, Roadways, Bridges, Dams, Water Supply Schemes

2. Levelling Instruments
Level: A combination of telescope, level tube, levelling head and tripod
Types:
Dumpy Level
Wye Level
Reversible Level
Tilting Level
Automatic Level

5. Dumpy Level

6. 2. Levelling Staff A graduated rod, wood or Al Types:
Self Reading Type- Shorter distances
Target Type – Longer distances
Self Reading Type:
Smallest div. is 5mm
Each metre is 200div.
Black & White div. alternately
Numerals inverted, so that errect view through telescope
Types- a) Solid Staff
b) Telescopic Staff
c) Folding Staff

7. Telescopic staff

8. CROSS HAIRS

9. Levelling up bubble centering Eliminations of parallax
Adjustments of a level
Temporary
Permanent
Temporary
Setting up the level
Levelling up bubble centering
Eliminations of parallax
3.a) Focusing the eye piece
3.b) Focusing the objective

10. SETTING UP

12. Levelling Up

13. A surveying optical telescope
line of
collimation
diaphragm
focusing screw
eyepiece
focusing lens
object lens
Focusing
object lens
focusing lens
1. Rotate eyepiece to give a sharp,
clear image of the cross hairs
cross hairs
Typical diaphragms - in different makes of instrument
2. Rotate focusing screw to give a
sharp, clear image of the object
being observed.
The aim of focusing is to remove (eliminate) PARALLAX

14. Pond Bubble When pond bubble is centred the instrument’s standing axis
is approximately vertical.
The compensators in the instrument take over and adjust
the optical Line of Collimation so that it is horizontal (hopefully)
When the instrument is rotated the compensators ensure that
a horizontal plane of collimation is swept out (hopefully)

15. 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.

16. Elimination of Parallax
Focus the crosshairs
(using the Eyepiece)
Focus the object
(using the Focussing screw)

17. Survey of India-MSL at Mumbai
Terminolgy
Mean Sea Level(MSL)
By making hourly observations of tides at any place over a period of 19 years.
Survey of India-MSL at Mumbai
RL or Elevation
The height or depth of a point above or below the assumed datum
Benchmark (BM): Any datum of known elevation

18. Level Field Book
For entering and reducing the readings(sights at various points).
Printed in a tabular form to facilitate booking of readings and reduction of levels.
Height of Instrument(H.I) or Height of Collimation (H.C) Method
Rise and Fall method

19. Levelling RL B HPC = RL A + S1 S1 Levelling Staff Height of
the Plane of Collimation
(HPC) S2
Reduced
Level of B
RL A A B
RL B
RL B = HPC S2
DATUM

20. Some Terminology S1 BS RL A RL B RL C A B C Level staff on A
Back Sight (BS) reading is first reading

21. S2
Level staff on B FS
RL A
RL B A B C
RL C
Level staff on A
Back Sight (BS) reading is first reading
Fore Sight (FS) reading is last reading
Move instrument to new position

22. BS
Move instrument to new position
RL A
RL B
RL C A B C S3
(CP) CP
Level staff stays on B
The instrument has changed its position about point B
Point B is known as a Change Point
2nd instrument position starts with BS to B

23. S4 S3 BS
RL A
RL B
RL C A B C FS
FS to C
and finishes with

24. Unknown RL = HPC - Fore Sight
RL A
RL B A B C
RL C BS FS
HPC =
HPC
HPC =
HPC
(CP)
RL A is known
RL A + BS
RL B =
HPC - FS
Now the RL B is known
So we can repeat the process
RL B + BS
RL C =
HPC - FS
Generally : HPC = Known RL Back Sight
Unknown RL = HPC - Fore Sight

25. never move both Summary of Levelling Procedure
When the level has been set up we always start with a BS to
a point whose RL is known
The last reading at any instrument position is always a FS
Either the instrument moves or the staff moves -
never move both
We must always finish levelling at a point of known RL value
always close your levelling

26. Height of Instrument Method
The following readings are taken on a level instrument with the station A as a bench mark with R.L m. The instruments is shifted after 4th and 7th reading.
Readings are given in a tabular form below. Find out the R.L

27. Station
B.S
I.S
F.S
H.I
R.L
Remarks A
1.200 BM B
0.980 C
1.035 D
1.100
0.650
Change Point E
0.950 F
1.400
0.700 G
1.000 H
0.880
Sum

28. Check
∑BS-∑FS = Last RL – First RL

29. Problem
The following readings are taken on a level instrument with the station A as a bench mark with R.L m.
2.190, 3.150, 1.060, 0.230, 3.430, 3.170, 3.420, 3.720, 2.390
The instruments is shifted after the reading Enter these readings in level book and calculate the R.L of all points.