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SUG213 : ENGINEERING SURVEYING II

PRECISE
LEVELLING
INTRODUCTION AND INSTRUMENTATION

Lecture By:
Zuraihan Mohamad
Dept. of Surveying Sciences & Geomatics
FSPU
UiTM Arau

Aim Of The Topic

 At the end of this lecture, student should be
able to :

 Understand what is precise levelling and the needs.
 Understand the methods and instrumentation of
precise levelling

Lecture content
 Concept of levelling

 Historical background of Precise Levelling in Malaysia

 National Geodetic Vertical Datum (NGVD)

 Malaysia Tidal Network

 Types of Levelling

 Precise Levelling

 Equipment of precise levelling
 Optical precise levelling
 Motorized l precise levelling
 Digital precise levelling

�ϱ��ձ��… Before we begin

 What is P.L?
 Why do we need P.L?
 Are there any differences between P.L n
O.L??
 Say that that there are indeed differences,
they are in terms of what???

Concept of Levelling
 The concept of levelling is based on the horizontal line
of the instrument (level) with the level line of the point
on the earth.

 If the heights of A and B can be measured, the height
differences can be calculated using the formula :

h = a - b

 If the RLA is known, RLB can be calculated as:

RL B = RLA + h

Memory Test… Which is what???

Staff Staff

Level ???
a b
Level line through level instrument

Level Line through B
B
Level Line through A
A

???
???

???

Concept of Levelling
 The name given to the method of determining differences in
heights between points
 A method of height transfer from one point to another
 Being used in Geodetic and Engineering Surveys
 Using special instrument called : level

Historical Background
Several methods of height measurement are being used in
surveying and construction works;

 Trigonometric heighting - Theodolite
 Barometric heighting - Barometer (pressure)
 Hydrostatic Levelling - Water tube
 Tacheometry - Staff
 GPS - Receiver
 Direct measurement - Tape
 Levelling - Level

 1st vertical datum was established in 1912 based on Mean
Sea Level (MSL) produced by British Admiralty.

 At Port Swettenham (Port Kelang)

 1 year tidal observations

 Also known as Land Survey Datum (LSD)

 But no records and evidence available

 Mean Sea Level
 Average level taken up by the sea
 Coincide with the Geoid
 Change regularly due to tide
 Best observation period is 18.6 years
 Use of Tide Observation Data
 Determine precise vertical datum
 Information for research in geodesy, geodynamic and scientific studies
 Tide & flood prediction
 Port activities and navigation
 Marine boundaries, hydrography and aquaculture
 Delivery of fixed record of sea level
 To obtain tidal harmonic constant
 To study tidal characteristics
 For tidal prediction.

National Geodetic Vertical
Datum (NGVD)
 JUPEM initiated the establishment of NGVD
 12 tidal stations were established in 1981

Objectives:

 To observe tide levels continuously
 18.6 years complete cycle of moon regression
 To obtain tidal harmonic constants
 To study tidal characteristics
 For tidal prediction

Malaysia Tidal Network
 1995 (established n in operation) - 21 tidal stations
 12 are installed in Peninsular and 9 in east Malaysia
 Each station is connected by precise levelling networks

Types of Levelling
LEVELLING

Precise levelling Ordinary levelling

Optical level Motorized Optical Level Digital
level level

Digital level

Differentiated by the set of instruments, observation methods and accuracy

Precise Levelling
 Also known as the highest order of levelling works
 Readings observed and recorded to decimals of a millimeter
 Used for :
 Basic levelling framework of a country
 Transfer height to bench marks
 Precision engineering structure
 Irrigation Scheme, Dam, Tunnels
 Precision dimensional surveys

Equipments of Precise Levelling

 Level (Precise type)
 Invar or bar-coded staff
 Survey Tripods
 Change plate (staff support)
 Staff bubble
 Handles and steadying rods (bipod)
 Thermometer
 Umbrella

1. Optical Precise Level
 Precise type
 With parallel plate micrometer
 Manufacturer quote: “Std dev less than 1 mm per
double run of levels over a km” can be considered as
precise
 Glass diaphragms (eye piece) – vertical line, levelling
line and two stadia lines (upper and lower)

Components
1. Parallel Plate Micrometer

 To be used with precise
level
 To provide precise reading
(decimal of mm)

Micrometer readings

Components
2. Compensator

 Available for automatic level only
 To compensate error on collimation line

Components
3. Precise Staff

 Two precise/Invar staffs
 Invar Strip – stable material (low
sensitivity to heat)
 Small expansion coefficient
 Graduations 0.02ft / 0.01 m on
invar strip
 With handle / staff holder
 To be calibrated every 3 months

2. Motorized Precise Level
 Were used in the DSMM (Late 80s) - No longer used
 Modification of conventional method
 Three vehicles – 1 for the level and observer, 2 for the staffs
 Invar staffs are fitted to the vehicles

 Advantage:
 Faster and convenient

 Disadvantage:
 High cost
 Not suitable in busy roads

3. Digital Precise Level
 Use digital level (automatic level) and bar-coded
staffs
 Use infrared detector to scan the bar-coded staff
 Scanned staff image is compared to actual staff
pattern stored in the instrument
 Provide staff reading and horizontal distance
 Advantages:
 Levels are recorded automatically
 Reduce human error (reading and booking)
 Reduce observation time
 Include processing software

Example

Leica DNA 03 Digital Precise Level

 Elements:

1 On/ off button 16 PCMCIA or CF-card with
2 Base plate adapter (optional)
3 Foot screws 17 Battery GEB121 (optional)
4 Horizontal circle 18 Battery adapter GAD39; 6
5 Lever to unlatch battery single cells (optional)
6 Battery compartment 19 Light duct for circular level
7 Button to unlatch card compartment 20 Plug stopper for crosshair
cover adjustment knob
8 Card compartment cover 21 RS232 serial interface
9 Display with external power supply
10 Circular level 22 Measuring button
11 Hand grip with aiming sight 23 Focusing drive
12 Ocular 24 Endless horizontal drive
13 Keyboard (bi-directional)
14 Objective
15 Battery GEB111 (optional)

 Characteristics:
 Limited target distance <30m
 Minimum ground clearance of >0.5m required to
minimized refractionary influences of ground proximity.
 Double observance (BFFB, aBFFB) to increase the reliability
of measurement and to reduce possible errors caused by
staff sinking.
 Applying alternating observations procedures (aBFFB =
BFFB FBBF) to eliminate horizontal tilt ( residual error of
the automatic compensator)
 Use an umbrella in strong sunlight.

Change Plates
Bipods

ADDITIONAL EQUIPMENT IN PL

1. Base/Change Plate

 Staffs are to be supported on turning points
 Made from mild steel
 Round head and collars
 To reduce error during turning (for soft ground)

2. Handles/Bipods
 To support precise staff
 For long observation period
 Stable (verticality)

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Lecture 1 precise levelling

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