1. How to: Some Basic Principles for Leveling
TATVA INSTITUTE OF TECHNOLOGICAL STUDIES,MODASA(090)
How to: Some Basic Principles for Leveling
SUBJECT: SURVEYING ( )

2. Lecture Overview Equipment Introduction to Leveling
Observation, Field Notes, and Computation
Errors and their effects

3. Equipment

4. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

5. Equipment: Level Instrument
Automated Levels
Easy to use (not power!)
Needs experience
Robust even in hostile environment
Digital Levels
Push-button technique
No reading errors, special staff
Readings are stored and analyzed digitally

6. Automated Levels (Compensator)
Pendulum
Bull Eye
Tribrach
Courtesy: Deumlich, Vermessungskunde

7. Digital Levels Uses Barcode staffs Internal storage of data
Download to the computer
Automated height computation + adjustment
No feeling for quality anymore
You frequently need power plugs

8. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

9. Equipment: Tripod Wooden design or aluminum
From “easy to sit” to “ops, this is high”

10. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

11. Equipment: Staff/Pole
Wood, aluminum
INVAR type for high precision leveling
Barcode
for Digital Levels
Conventional (“E”-type)

12. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

13. Equipment: Change Plate
For long survey lines
Allows change of instruments
Best is a metal change plate
Screws e.g. at fences
Sharp stones or nails
Beware of dark colors
It’s not the Indonesian-
German Dictionary, It’s the nail!

14. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

15. Equipment: Bubble Keep the pole upright
Any tilt will disturb your readings

16. Equipment Level Instrument Tripod Staff/Pole
Change plate (German: Frog/Frosch)
Pole staff bubble (bull eye)
Marker

17. Survey Markers Gives you a fixed point Should be of good quality
Should be long-term
Preferable in bedrock, settled buildings, or bridges
Do not use fences or walls

18. Introduction to Leveling

19. Some Basic Definitions
Level surface (e.g. the geoid)
A water surface with no motion
Gravity gradient is the normal to the level surface
The Instrument’s Bubble is in the normal (!)
Horizontal surface
At the instruments axis, the horizontal surface is tangent to the level surface
Over short distances (<100 m) the horizontal surface and the level surface will coincide
For long leveling lines the effects of the gravity field must be considered

20. Basic Principle of Leveling
Measures height differences between points
Along a line
Several points from one occupation
Leveling rods
Line of sight
Back sight
Fore sight
Gravity Gradient fs bs
Dh = bs - fs

21. Definitions Back sight (BS) Fore sight (FS) Intermediate sight (IS)
The first reading from a new instrument stand point (i.e. take the height to the instrument)
Fore sight (FS)
The last reading from the current instrument station (i.e. give the height to a benchmark)
Intermediate sight (IS)
Any sighting that is not a back sight or fore sight

22. Reading a Staff Read the [m], [dm] & [cm] Estimate the [mm] 1422
Check yourself for frequent used numbers (2/3) or (7/8)
1422

23. Basic Rules for Leveling
Always start and finish a leveling run on a Benchmark (BM or TGBM) and close the loops
Keep fore sight and back sight distances as equal as possible
Keep lines of sight short (normally < 50m)
Never read below 0.5m on a staff (refraction)
Use stable, well defined change points
Beware of shadowing effects and crossing waters

24. Errors in leveling, e.g. Collimation, Parallax
Change point / staff instability
Instrument or Benchmark instability
Refraction
Uncalibrated staff or levels
Reading, booking, or computation errors
Fore- and backsight distances different

25. Systematic and Random Errors
Earth curvature
Refraction
Collimation errors

26. Effect of Earth Curvature
Horizontal Level
Curvature effect
(r +Dh)2 = r2 + s2
=>
Dh  s2/(2r)
Distance (s) in m 10 20 50
100
1000
Effect (Dh) in mm
0,008
0,03
0,2
0,8 80

27. Refraction Mean Gradient: 0,2 °C / m

28. Collimation error
Occurs when the line of sight (as defined by the lens axis and cross-hairs) is not horizontal
Leads to an incorrect staff reading
line of sight
error
horizontal line

29. Instrument test: Nähbauer
Stand point 1
Stand point 2
a′1 = a1+e
b′1 = b1+2e
Δh = a1−b1
Δh′1 = a′1−b′1 = a1−b1−e = Δh−e
With Δh′1+e = Δh′2−e
Δh′2−Δh′1 2
a′2 = a2+2e
b′2 = b2+e
Δh = a2−b2
Δh′2 = a′2−b′2 = a2+e−b2 = Δh+e
Δh =Δh′2−e
e =

30. Summary

31. Procedure of leveling
The instrument must be check before use! (see lecture)
The instrument and level must be stable settled-up
The bubble tube must be leveled before the reading
Beware of sun exposure (will wander)
Ensure the instruments pendulum is in-limit
The instrument must be set up in the middle between two staffs
Prevents curvature effects
If impossible, use the same distances, but opposite for the next readings
You must not use the parallax screw between the backsight and foresight readings

32. Procedure of Leveling Readings must be taken 30-50 cm above the ground
Surface refractions
Beware also of temperature gradients (inside/outside buildings) !!!!
Staff should be set up vertically
A change plate should be used
Leveling must be done in two opposite directions but the same line (beware of gravity gradients)
Staff should be calibrated, especially if INVAR
Be careful when crossing rivers (large water surfaces)
Use “same-time” (mutual) observations
Repeat it during different times of the day

33. An Unhappy Surveyor
… having a 2 centimeter difference