GDM2000

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GEOCENTRIC DATUM FOR MALAYSIA :THE REALIZATION OF GDM2000

Paper presented at the Department of Geodesy and Remote Sensing, GeoForschungszentrum Potsdam, Berlin, Germany. 4 May 2004.

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Historical Perspective

■ There are 2 local geodetic datum- Malayan Revised Triangulation (MRT)- Borneo Triangulation 1968 (BT68)

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Geodetic Reference System■ MRTEllipsoid: Everest (Modified)a : 6 377 304.063 m f : 1/300.8017

BT68Ellipsoid: Everest (Modified) a : 6 377 298.556 mf :1/300.8017

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Shortcomings

■ Existing datum of MRT and BT68 becomes obsolete for GPS and GIS applications over large areas

■ Accuracy needed for new application cannot be satisfied by existing datum

■ Existing GPS network was established in a quasi WGS84 datum where their derived coordinates have absolute accuracy of 1 to 2m

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Why Geocentric Datum?

■ Wide spread use of satellite positioning systems

■ Existing datums not compatible

■ Unification of existing datums

■ In line international practices

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Characteristics■ 3D spatial referencing

■ Geocentric origin

■ In line with IAG recommendation to align with ITRS

■ GRS80 as reference ellipsoid

■ Nominated reference epoch

■ Coordinate velocity model

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Implementation of a Geocentric Datum

■ GPS data collection■ Data processing and adjustment of the GPS network■ Computation of a new geocentric datum coordinates

at a specific epoch■ Determination of coordinates velocity model■ Strengthening and readjustment of PMPGN and

EMPGN

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Realization of GDM2000

■ GDM2000 is based on a network of permanent GPS tracking stations known as Malaysia Active GPS System (MASS) stations

■ Two years spans of MASS data (1999 to 2000 for 15 stations) were used for processing to determine the reference frame.

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Realization of GDM2000 (cont)

■ Eleven International GPS for Geodynamic Services (IGS) stations in nearby region have been included and held fixed in the processing

■ Processing was carried out using precise orbits acquired from IGS

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Network Adjustments

Two strategies were employed:

■ Free network, and

■ Heavily constrained adjustment carried out with the introduction of reference velocity for the fixed stations.

■ The difference between the free and heavily constrained adjustment is at mm level.

■ The GDM2000 is now defined on ITRF2000 reference frame within 2 cm accuracy

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GPS Network in GDM2000■ Existing PMPGN and EMPGN must conform to GDM2000■ This was done thro’ the following steps:

The new GPS networks have an accuracy in the order of 1 to 3 cm

3. A network adjustment was carried out with vectors from original PMPGN and EMPGN together with the coordinates of the link stations.

2. A sufficient number of link and check stations were established to assess the absolute and relative accuracy

1. Re-observation of well distributed existing 34 stations in PMPGN and 30 stations in EMPGN and processed by constraining the 17 MASS stations

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Closing Remarks

■ The GDM2000 was successfully implemented

■ The GDM2000 is defined on ITRF Reference frame to within 2 cm of accuracy

■ Future coordinate systems for cadastral, GIS and Mapping work will be on GDM2000

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Geocentric System

■ Origin coincides with the centre mass of earth

■ The direction the axes are defined by convention

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PMPGN & EMPGN

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MASS

■ MASS consists of 17 active permanent station established since 1998 with 200km spacing

■ MASS stations form the so call Zero Order Geodetic Network

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IGS Stations

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Accuracy of MASS stations

■ For free Network : 5 to 11 mm (horizontal)5 to 15 mm (height)

■ Constraint Network : 3 to 4 mm (horizontal)4 to 13 mm (height)

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Link And Check Stations

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New PMPGN & New EMPGN

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Pelarasan Jaringan

Dua kaedah:

■ Pelarasan Gandadua Terdikit

■ Semi-rigorous atau ‘Equal Shift’

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Pelarasan Jaringan

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Pelarasan Jaringan

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Model Matematik Untuk Sudut

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Model Matematik Untuk Jarak

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Model Matematik Untuk Jarak

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Kaedah Semi-rigorous @ ‘Equal Shift’

Dua syarat mesti dipenuhi :

■ Syarat Sudut

■ Syarat Sisi

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■ Syarat Sudut

10 + 11 + 12 + 13 = 180

10 + 11 = 14 + 17

12 + 13 = 9 + 18

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Kaedah Semi-rigorous @ ‘Equal Shift’■ Syarat Sisi

Jika semua sisi dihitung:

Dari DE dalam ΔEDG dapatkan DG

Dari ΔDGF dapatkan GF

Dari ΔGFE dapatkan FE

Dari ΔFED dapatkan DE

1ED

FE

FE

FG

FG

DG

DG

ED

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■ Hanya gunakan sudut bukan sisi.

■ Syarat sisi perlu di tranform ke sudut melalui formula Sine.

113sin

10sin

17sin

12sin

9sin

14sin

11sin

18sin

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Kaedah Semi-rigorous @ ‘Equal Shift’Dalam bentuk logs:

113sin

10sin

17sin

12sin

9sin

14sin

11sin

18sin

Log sin 18 + log sin 14 + log sin 12 + log sin 10 - (log sin 11 + log sin 9 + log sin17 + log sin 13) = 0

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The End

GDM2000

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Transcript of GDM2000