First vertical datum used for Peninsular Malaysia is LAND

SURVEY DATUM (LSD1912)

Establish in 1912 by British Admiralty Surveyors

At Port Swettenham (Port Kelang)

Based on 1 year tidal observations

No records and evidences

In 1983, DSMM began to redetermine the precise MSL value in

conjunction with the establishment of the new Precise

Levelling Network for Peninsular Malaysia.

This was carried out by the setting-up of a Tidal Observation

Network that consists of 12 tidal stations.

Port Kelang was selected for the adoption as a reference for

the NGVD origin, based upon a 10-year tidal observations

period (1984-93).

BACKGROUND

PRECISE LEVELLING

In 1994, a monument to signify the establishment of the NGVD

was built within the DSMM compound in Kuala Lumpur.

Port Kelang Datum was extended to the new monument via

precise levelling and gravity survey.

The Precise Levelling Network project was conducted in 1984.

The project consists of establishing a first-order levelling

survey along main roads and highways.

It consists of 2089 precise levelling bench marks over a

distance of 1946 km

Second class levelling were also carried out to densify the

network.

A total of 824 bench marks have been established using this

technique, covering a distance of 1158 km.

The whole network has precision ranging from 3 to 12 mm per

km which correspond to first and second class requirements.

It incorporate corrections for rod scale, temperature, level

collimation and refraction.

PRECISE LEVELLING

INTRODUCTION

Precise levelling is used where a high degree of

accuracy is required for determination of the

elevations of various points.

Also known as First Order Levelling

Being used as a method of height transfer from one

point to another

Also required to set up critical engineering structure

such as dam, tunnel etc.

PRECISE LEVELLING METHOD

CONVENTIONAL PRECISE LEVELLING

DIGITAL PRECISE LEVELLING

MOTORISED LEVELLING

Used optical precise levelling and parallel plate micrometer

Graduated invar staff

Manually recorded

Used digital automatic level

Barcodes staff

Observed and recorded automatically

Reduced human and gross errors

Conventional level and transport (modified)

Time saving

DIGITAL LEVEL

DIGITAL LEVEL

GENERAL GUIDELINES

The following are the general guidelines which should be

considered while planning precise levelling.

• Always set-up the tripod on a firm ground. Push the tripod

legs firmly into the ground.

• The BS and FS distance should be balanced. Take

minimum possible time between BS and FS readings at

each set up to reduce errors due to changes in

atmospheric conditions.

• Select suitable turning point/change point. The selected

point should not settle between BS and FS.

• Use precise levelling instruments and precise staffs.

• Avoid levelling during the period of severe heat waves.

Levelling in cloudy weather is preferable. Use an umbrella

to shade the instrument on sunny day. Levelling should be

done in the morning or evening to reduced the refraction

effects.

• Stop the work when there are strong winds.

• Keep the line of sight at least 0.3 meter above ground

surface to reduce shimmering effects.

• Keep the instruments in perfect adjustments. Test the

instruments frequently.

• Special base plates with rounded tops should be used for

turning point/change point so that the base of the staff can

be kept at same position for the BS and FS.

The levels used should be the precise type.

The level instrument must be fitted with a Parallel

Plate Micrometer attachment.

The glass diaphragms should be fitted with at least

one vertical line

a leveling line

two stadia lines

Instruments

INSTRUCTIONS FOR PRECISE LEVELLING REFER TO

SURVEY REGULATIONS SEMENANJUNG MALAYSIA 1965

Classical Precise Level

PRECISE LEVEL WITH PARALEL PLATE MICROMETER

PARALLEL-PLATE MICROMETER

A parallel-plate micrometer is the device which is either

attached to the levelling instrument or build into the levelling

instrument itself.

This is a modification of the conventional level in which a

parallel plate micrometer is placed in front of the objective

lens.

This allows the image of the staff graduation to be moved up

or down by very small measurable amounts.

Used to read the smallest fraction of the precise staff

The movement of cross hair from its original position to the

nearest staff segment can be obtained from the micrometer

reading

This eliminates gross estimation.

For sight lengths of under 50m, single reading accuracies of

0.02mm to 0.03mm can be achieved.

Two precise staffs are to be used.

Graduation are marked in 0.01 meter

Before use and thereafter at intervals of 3

months the staffs are to be calibrate.

Staffs

Staff are to be supported on turning points.

Turning points

Precise Staffs

Readings

Readings are to be made in the following order:

1. lower stadia line

2. upper stadia line

3. leveling line

4. leveling line

5. lower stadia line

6. upper stadia line

8. leveling line only

7. leveling line only

Odd staff

Even staff

Even staff

Odd staff

The time taken between readings 3 and 4 and between

readings 7 and 8 should be reduced to a minimum.

Between readings 6 and 7 the telescope is to be

dislevelled by turning the gradienter screw and carefully

relevelled by the use of the same screw only

The same staff , say the odd , shall always be used at

bench marks. Staff numbers should be entered in the

appropriate space in the field book.

The back staff will be read first at the odd stations and the

forward staff first at even stations.

Booking will be carried out in field books designed for this

method of observation.

Readings are to be made to the nearest 0.00001 meter by

estimation on the micrometer drum

Readings

Readings

Readings

The sum of the stadia readings and the sum of

the two level readings on the same staff are

within 0.0050 meter.

The difference between the two level readings

on the same staff is not more than 0.0006

meter.

Tolerences

To eliminate axis irregularities, the level should

always be placed in the same position relative to

the staffs one particular footscrew always

pointing to the same staff.

Footscrews must not be altered during a sight,

bubble adjustment being made by the use of the

gradienter screw.

Setting up

Bubble adjustments

Line of sight

Staff and instrument stations must be carefully

selected so that the line of sight does not pass

close to the ground. Readings must not be made

to the lowest 0.3 meter of the staff.

The optimum length of sight is normally 40 meters,

but under favorable condition it may be extended

to 50 meters.

The back and forward staff should be equidistant

from the level to within 1 meter.

Observations should be made in the very early morning

and late afternoon and must be discontinued when the

atmospheric conditions make observations difficult.

Staff must be tested weekly by plumbob for

verticality and also be compared with each

other face to face and back to back.

Verticality of Staffs

Observations periods

Turning points should be in position at least

half an hour before use and staffs must not

be held on them until the surveyor is ready

for observation.

The day’s work must always be closed on a

permanent bench mark or culvert.

Setting of turning point

Each section is to be levelled in one direction in

the morning and in the opposite direction in the

afternoon. The direction of the morning leveling is

to be reversed in alternate sections. In single line

leveling the direction is to be reversed in alternate

sections.

Directions

Sections must be relevelled in both directions when

the discrepancy between forward and backward

levelling exceed 0.003 / K meters where K is the

distance in Kilometers.

The difference in level will be obtained from the

mean difference of the two level line reading.

Stadia line readings are to serve as a check on gross

error only and are not to be included in the

computations.

Criterion for rejection

Difference in level

Observation No. :1 Date : 12-01-2006 Time : 09.00 am Temp. :25o C

Staff Reading

Back Sight Fore Sight Note :Back staff at BM A

Stadia Level Level Stadia Reduced Level Is : 10.000m

2 3 4 6 Diff. In Height :

1 8 7 5 Bring Forward :

Total :

Distance : Distance : Observer : CS Salleh

Booking Form

Observation No. : 1 Date :12-01-2006 Time :09.00 am Temp. :25o C

Staff Reading

Back Sight Fore Sight Note :Back staff at BM A

Stadia Level Level Stadia Book Staff At :

2 3 4 6 Reduced Level Is :17 = 10.000m

1 8 7 5 Diff. In Height : 18 = 10/2 – 11/2

9=2+1 10=3+8 11=4+7 12=6+5 Bring Forward : 17 = 10.00000

13=2-1 14=3-8 15=4-7 16=6-5 Total : 19=18 + 17

Distance :13 x 100 Distance :16 x 100 Observer : CS Salleh

Booking Form

Booking Form

Observation No. :1 Date :12-01-2006 Time : 09.00 am Temp. : 25o C

Staff Reading

Back Sight Fore Sight Note :Back staff at BM A

Stadia Level Level Stadia Book Staff At :

300.292 279.469 76.520 97.271 Reduced Level Is :10.000m

258.650 279.471 76.523 55.769 Diff. In Height : 2.02949

558.942 558.940 153.043 153.040 Bring Forward : 10.00000

41.642 - 0.002 - 0.003 41.502 Total : 12. 02949

Distance :41.642 m Distance :41.502 m Observer : CS Salleh

OBSERVATION PROCEDURES AND REQUIREMENTS

Planning

Field Instruction

Monumentation

Observations

Data Processing

• Network adjustment for final height

• Using Least Square Adjustment method

Documentation

• Final reduced level of BMs

• Identification number of BMs

• Locality information