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respectively. Both of the versions were revised using a similar procedure where the
set of new coordinate data were brought to the ITRF2000 at epoch 2000.0, which
is the original of GDM2000. In the case of GDM2000 (2009), the reference
stations, i.e. the IGS stations, in ITRF2005 at epoch 2007.67 were brought to
ITRF2000 at epoch 2000.0 using published velocity models. Based on the Helmert
Transformation, root mean square (RMS) fitting for the coordinates of four ref-
erence stations (KUCH, BINT, KINA and MIRI) were less than 1 cm in the north,
east and height components, respectively (Department Survey and Mapping
(DSMM)
2009
). Therefore, the coordinates of these four reference stations were
fixed, in the final local combined adjustment, with respect to the original
GDM2000 (Department Survey and Mapping (DSMM)
2009
). However, the set of
coordinates of MyRTKnet in GDM2000 (2006) are still being adopted at present.
It is due to the discrepancy involved between the new set of coordinates GDM2000
(2009) and the existing database in GDM2000.
3 The Shift of GDM2000
As aforementioned, the GDM2000 has been revised to take into account the
co-seismic motions. However, there are no further actions to revise and update the
GDM2000, especially with the consideration of post-seismic motion as well at
every MyRTKnet station. In order to test the compatibility of GDM2000 with the
current position, GPS observation data on Day of Year (DoY) 001 until 023 in year
2011 have been processed by using Bernese GPS processing software. The pro-
cessing stage involved 63 MyRTKnet stations and 22 IGS stations using the
double-difference with Quasi Ionosphere Free (QIF) strategy. The data was pro-
cessed in ITRF2008 as well as in ITRF2000. The idea was to compare the two set
of coordinates in ITRF2000 and ITRF2008 for DoY 001 until 023 with the
available set of GDM2000 (2006) coordinates in ITRF2000 epoch 2000.
3.1 Test I: Comparison Between Epoch 2000 and 2011
in the Same Reference Frame ITRF2000
In this test, the set of coordinates at epoch 1st January 2011 was compared to the
published set of coordinates of GDM2000 (2006), where both were in ITRF2000.
Figure
3
shows the differences of these two set of coordinates in terms of vector
displacements. It can be deduced that the position of the sites moved with an
average magnitude of 25.5 cm and orientation of 118.8 from epoch 2000 to epoch
2011.
