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geocentric coordinate system. The obtained system based on this set of parameters
is named the Geocentric Coordinate System 1978.
Based on the DX-1 transformation parameters, we can transform the geodetic
Cartesian coordinates in BJS54 into geocentric Cartesian coordinates in the Geo-
centric Coordinate System 1978:
2
4
3
5
2
4
3
5
2
4
3
5
X
Y
Z
X
Y
Z
Δ
X
o
ﾼ
þ
Δ
Y
o
DX
-
1
:
ð7:39Þ
Δ
Z
o
1978
1954
DX-1 excludes rotation and scale parameters. It was only a preliminary result to
meet the urgent needs of space technologies back then. Shortcomings were
unavoidable in the course of its establishment. For instance, the materials and
data used in calculations were limited and inaccurate, and the data processing
methods were not optimal. Hence, the direction of the coordinate axis of the
geocentric coordinates obtained by DX-1 transformation parameters is not clearly
defined. It is estimated that the mean square error of the coordinate component of
the Geocentric Coordinate System 1978 is approximately
10 m.
7.5.5 Geocentric Coordinate System 1988
Since 1979, some departments have done plenty of work in developing space
geodetic techniques. For instance, China established a Doppler network with
37 points across the country in 1980; another dynamic satellite geodetic network
was established in 1982, so geocentric coordinates with high precision were
obtained. In the meantime, an integrated adjustment of the nationwide astronomical
geodetic network was carried out, by which the geodetic coordinates of nearly
50,000 stations were determined. The height anomalies nationwide have been
obtained with quite high precision by means of the astro-gravimetric leveling. All
kinds of geocentric coordinate systems are continually updated internationally, and
some quite new data have appeared. All have created conditions for China to refine
its geocentric coordinate transformation parameters.
After years of preparation, some departments concerned established the DX-2
steering group for integrated data processing in May 1987. Eventually, by the end
of 1988, the geocentric coordinate transformation parameters of DX-2 were
completed.
The transformation parameters of DX-2 are obtained by integrating three
methods for establishing geocentric coordinate parameters:
1. Geocentric coordinates obtained by using an MX-1502 Doppler receiver to the
track transit satellite system (TRANSIT System) (Doppler network with
37 points nationwide)
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