gdm2000
TRANSCRIPT
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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 Sudut
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Model Matematik Untuk Sudut
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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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Kaedah Semi-rigorous @ ‘Equal Shift’
■ Syarat Sudut
10 + 11 + 12 + 13 = 180
10 + 11 = 14 + 17
12 + 13 = 9 + 18
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Kaedah Semi-rigorous @ ‘Equal Shift’
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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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Kaedah Semi-rigorous @ ‘Equal Shift’
■ 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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Kaedah Semi-rigorous @ ‘Equal Shift’
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Kaedah Semi-rigorous @ ‘Equal Shift’
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Kaedah Semi-rigorous @ ‘Equal Shift’
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The End