1. Unit 5. Levelling

2. Unit 4: Plane table surveying
Topics covered
Definition,
Terms associated with levelling
Spirit levelling
Instruments for spirit levelling
Simple numerical examples
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Unit 4: Plane table surveying

3. Unit 4: Plane table surveying
5.1 Definition
Levelling
Branch of surveying that deals about the measurement in vertical plane
Determines the difference in elevation between points on the ground
Establishes the points on the given elevation
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Unit 4: Plane table surveying

4. 5.1 Terms associated with levelling
Level surface
Level line
Horizontal plane
Horizontal line
Vertical line
Datum
Elevation
Vertical angle
Mean sea level
Bench mark
18/01/2019
Unit 4: Plane table surveying

5. Unit 4: Plane table surveying
Levelling
Methods of levelling
Barometric levelling
Trigonometric levelling ( Indirect levelling)
Spirit levelling
Instruments used
A level
A levelling staff
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Unit 4: Plane table surveying

6. Unit 4: Plane table surveying
Levelling
Level
The purpose of level is to provide horizontal line of sight
It consists of
A telescope to provide line of sight
Level tube to make line of sight horizontal
Levelling head to bring the bubble in its centre
A tripod to support the instrument
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Unit 4: Plane table surveying

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

8. 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

9. 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

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

11. So we can repeat the process RL C = HPC - FS RL B + BSHI
RL A
RL B A B C
RL C BS FS
HPC = HI
(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 C =
HPC - FS
RL B + BS
Generally : HI = Known RL Back Sight
Unknown RL = HI - Fore Sight

12. Thank you for your attention!
Any questions? Querries?
18/01/2019
Unit 4: Plane table surveying