GII: Current Status And Future Initiatives
MALAYSIAN ACTIVE GPS SYSTEM (MASS)
Since early 90s, Malaysia has
embarked on using GPS technology
with the objective of adopting a global
unified datum for Peninsula Malaysia,
Sabah, and Sarawak. Since then GPS has
unprecedented use for positioning within
JUPEM, leading to the establishment of
the Malaysia GPSScientific Network
(MGSN) comprising of 238 stations in
Peninsular Malaysia and 171 stations in
East Malaysia. However, these existing
GPS networks in Malaysia was established
in a quasi WGS84 datum in that it
referenced its coordinates to a derived
WGS84 coordinates which has only an
absolute accuracy of 1 - 2 m.
Subsequently, DSMM started establishing
permanent GPS tracking stations as
part of the Malaysia Active GPS System
(MASS) at the end of 1998. Currently,
DSMM has 18 permanent GPS tracking
stations operating 24 hours a day, which
provides positional solutions including
movement in their relative positions due
to tectonic plate activity. This network of
permanent GPS tracking stations, known
as the Zero Order Geodetic Network, complies
with international standards.
IMPLEMENTATION OF GDM2000
Historically, datums have been established
in many parts of the world
using conventional surveying techniques
and procedures. Most of them were confined
to small areas of the globe, fitted to
limited areas to satisfy national mapping
requirements. In the case of Malaysia two
conventional geodetic datums were
established, namely the Malayan Revised
Triangulation (MRT) for Peninsular
Malaysia and the Borneo Triangulation
1968 (BT68) for Sabah and Sarawak. However,
the advent of GPS and unified GIS
applications over large areas have caused
the existing MRT and BT68 datums to
become obsolete, increasingly inefficient
and difficult to relate to modern systems.
Current trend also shows that many
countries have implemented and adopted
a geocentric coordinate reference
frame for their geodetic datum. Therefore,
there is a need to upgrade the current
GPS network in Malaysia to a higher
order network with connection to a precise
geocentric reference system in the
International Terrestrial Reference Frame
(ITRF). The adoption of a geocentric
datum is moreover inevitable considering
that satellite positioning systems
would have widespread use in this millennium
and the positions referenced to
the existing datum would not be compatible
with such satellite derived positions.
This necessitates in the establishment
of the Geocentric Datum of Malaysia
(GDM2000) based on International Terrestrial
Reference Frame 2000 at epoch
ITRF2000@00.0 and which is computed
for 18 Malaysia Active GPS System (MASS)
stations. The upgrading of the existing
GPS Network has been carried out to provide
world class geodetic infrastructure
for the nation. This new Malaysia Primary
Geodetic Network (MPGN) is connected
to the International Terrestrial Reference
Frame 2000 (ITRF2000) at centimeter-
level accuracy. All new survey and
mapping products from JUPEM will be
referenced to GDM2000 which has a horizontal
difference of approximately 200-
metres from the MRT and BT68 ground
coordinates over Peninsular Malaysia,
Sabah and Sarawak. Its adoption will
enable the production of a homogeneous
series of Malaysian maps and nautical
charts which will meet international navigation
requirements.
All existing geospatial product shall carry
proper datum identification to avoid
any confusion; and to allow proper registration
of data layers. However, this
change will also have far-reaching implications
for the users and producers of
maps and spatial information systems in
Malaysia. These people will need to
become conversant with the respective
datums, acronyms, and their transformation,
in order to deal with the coordinate
sets that they will inevitably encounter.
There is now a need for a more general
awareness of the different datums that
will exist in Malaysia. It is envisaged that
this datum change will cause some confusion
in the interim, but this is outweighed
by the long-term benefits.
JUPEM'S LEVELLING NETWORK
Historically, the vertical control in
Peninsular Malaysia, Sabah and
Sarawak were established separately. The
new height datum for Peninsular
Malaysia was determined in 1994 based
on the mean sea level (MSL) value from
the tide gauge in Port Klang after more
than 10 years of observation (1984-1993).
The height was transferred from Port
Klang using precise levelling to a Height
Monument in Kuala Lumpur by 3 different
precise levelling routes. In Sarawak,
there are originally six vertical datums
namely Pulau Lakei Datum, Original
Datum, Bintulu Datum, Merapok Datum,
Limbang Datum and Sabah Datum. Pulau
Lakei Datum and Original Datum are
based on MSL 1955 and MSL 1935 respectively.
Meanwhile, Bintulu Datum and
Merapok Datum are based on triangulation
station network heights which are
connected to Pulau Lakei Datum and
Original Datum. Limbang Datum is
referred to a year of tidal observation at
Limbang Jetty and Sabah Datum refers to
one month tidal observation at Sipitang
in 1949. As for Sabah, beginning 1997, all
levelling network set up by JUPEM refers
to the MSL in Kota Kinabalu which is
based on 10 years of tidal observation
(1987-1997). For the purpose of homogeneity,
the levelling network in Sabah
and Sarawak has recently been unified by
adopting the MSL value from Kota Kinabalu
Tide Station. Establishment of
Malaysia Precise Geoid (MyGEOID)
JUPEM has embarked on an airborne
gravity survey project with the main
objective of establishing the local precise
geoid for Malaysia within centimetre level
of accuracy. The basic underlying survey
and computation work of the
Malaysian geoid project was done with
the cooperation of the Geodynamics
Department of the Danish National Survey
and Cadastre (KMS) which is currently
part of the Danish National Space Centre.
The airborne gravity survey was done
on a 5 km line spacing, covering Sabah
and Sarawak in 2002 and Peninsular
Malaysia in 2003. The airborne gravity
data system used was developed by the
Danish National Space Centre (DNSC) and
the University of Bergen. The system uses
differential GPS for positioning, velocity
and vertical accelerations determination;
and a modified marine Lacoste and
Romberg gravimeter for gravity sensing.
The system has a general accuracy of better
than 2 mgal at 5 km resolution. In
order to overcome the problem of datum
bias (differences between geoid and local
mean sea level), fitting of the gravimetric
geoid to the local mean sea level (NGVD)
was undertaken. In the case of Peninsular
Malaysia, a total of 39 benchmarks were
observed with GPS and later used in the
computation of Peninsular Malaysia fitted
geoid model (WMGeoid04). While for
Sabah and Sarawak, 60 benchmarks with
MSL values were used in the fitted geoid
model (EMGeoid05) computation. The
accuracy of WMGeoid04 and EMGeoid05
are 0.033 and 0.042 meter respectively,
and can be used for height determination.
MALAYSIA REAL TIME
KINEMATIC GPS NETWORK
SYSTEM (MYRTK-NET)
Classical kinematic survey (postprocessed)
can determine the precise
position of a roving receiver relative to a
stationary station. However, this technique
requires office procedure/work
before the coordinates of a station can be
derived which is thus time consuming.
The technique however allows only a
limited range from a single reference station.
Errors grow with baseline length
(ppm) while reliability and performance
decrease with distance to the next reference
station. Besides that, the technique
is also dependent on a single reference
station with no integrity monitoring.
In order to overcome these limitations,
JUPEM has embarked on real time kinematic
(RTK) surveying which is the latest
dynamic GPS survey technique. RTK-GPS
utilize short observation times and
enable users to move between stations.
RTK-GPS can instantly determine the
position of a roving unit to centimeterlevel
accuracy using carrier phase positioning.
This technique is ideal for various
applications such as engineering, cadastral,
topographic and detail surveys.
The use of a network of reference stations
instead of a single reference station
allows modeling of the systematic errors
in the region and thus provides the possibility
of an error reduction. This setup not
only increases the allowable distance at
which the rover receiver is located from
the reference, but also increases the reliability
of the system and reduces the RTK
initialization time. As part of the DGPS
and RTK setup JUPEM provides users with
network DGPS corrections for the whole
of Peninsular Malaysia and parts of East
Malaysia. It also provides network RTK
corrections around high population centres
in West Malaysia, specifically
Penang, Klang Valley and Johor. The accuracy
of RTK is in the order of +/- 2-3 cm
and for DGPSNet is within +/- 20-50 cm.