Precise Levelling


			Introduction	Leveling Bench

	Introduction		Peninsular L. Network
	South Pen. L. Network		North Pen. L. Network
	East Malaysia L. Network		GPS Levelling

Introduction
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. Subsequently, Port Kelang was selected for the adoption as a reference for the NGVD origin, based upon a 10-year tidal observations period (1984-93). In 1994, a monument to signify the establishment of the NGVD was built within the DSMM compound in Kuala Lumpur. Here, the Port Kelang Datum was extended to the new monument via precise levelling and gravity survey.
Present Levelling Network in Peninsular Malaysia
The Precise Levelling Network project was conducted in 1984. The project consists of establishing a first-order levelling survey along main roads and newly completed highways. It consists of 2089 precise levelling bench marks over a distance of 1946 km as shown in map 5. Apart from this, 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. The network was divided into two parts: the Southern and the Northern parts of Peninsular Malaysia

The Southern Pen. Malaysia
Precise Levelling Network

The network covers the southern and central part of Peninsular Malaysia. The network, started in 1984, consists of 45 junction points, 59 lines of double run first order levelling and 12 circuits with a total perimeter of 3,945 km. It was completed in 1995. Motorised Levelling technique was used in 70% of the levelling network, whilst the remaining part was measured conventionally. The network is connected to 6 tidal benchmarks and was measured using Zeiss NI002A and Wild NA3000. All observed data are stored in a computer readable form for processing and adjustment. RAPC-1 and DELTA softwares were used for data processing and GEOLAB software for the network adjustment.
The Northern Pen. Malaysia Precise Levelling Network
The network was started in 1995 following the completion of the southern loop. It runs through 9 main routes, covering a distance of 1745 km with 1950 bench marks planted. The northern network was completed in December 1998.
Levelling Networks in Sabah and Sarawak
Presently, six different height datums are used for various purposes. This is mainly due to the lack of good roads connecting the tide gauges in the region. Action has been taken by DSMM to set-up a levelling route from Kuching to Miri in Sarawak as in map 6. For Sabah, precise levelling routes are being set-up to connect the north, east and west of the region as in map 7.
GPS Levelling
Apart from geocentric coordinates, GPS also provides heights or height differences with respect to WGS-84 ellipsoid. These heights can be related to those obtained from conventional levelling techniques which are referenced to the geoid. This geoid-ellipsoid separation (N) need to be determined in order to relate both systems. DSMM intend to use the approach of integrating GPS derived ellipsoidal heights and EGM96 into the levelling networks with the final aim of producing a homogeneous heighting system.