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there would be a great volume of work to connect the old and new coordinate
systems. Therefore, implementing a new map coordinate system not only involves
its scientific worth and accuracy but also its practicability, feasibility, economic
returns, and social benefits. We should not only take into consideration the history
of surveying and mapping over the past three decades and its status quo, but also its
development in the days and years to come.
The new BJS54 emerged in such a context. The results offered by this coordinate
system are obtained based on the XAS80 by transforming the GRS75 Ellipsoid into
the Krassowski Ellipsoid and then translating and transforming along the three
spatial axes. Hence, its coordinates have not only embodied the superiority of the
integrated adjustments, i.e., its accuracy is the same as that of the XAS80, but have
also overcome the deficiencies of local adjustment of the original BJS54. In
addition, the new BJS54 employs the same ellipsoidal parameters as the old
BJS54, and the orientation of the new BJS54 also approximates that of the old
BJS54; thus its coordinate values do not differ much from those of the old BJS54
obtained from local adjustment. According to statistics, as for the projected plane
coordinates, the coordinate difference between the new and old BJS54 is within 5 m
in 80 % of the area of China. Those with a coordinate difference of greater than 5 m
are primarily in the northeast and those greater than 10 m are only in a few fringe
areas, with the maximum difference being 12.9 m. The difference along the vertical
x-axis ranges from
6.5 to +7.8 m, and the difference along the horizontal y-axis
ranges from
12.9 to +9.0 m. Such differences are still within the scope of the
differences between the provisional coordinates and the adjusted coordinates,
reflected on the 1:50,000 scale topographic maps, and most of them are less than
0.1 mm. In this sense, the splicing between the old and new maps will be almost
seamless. Hence, the new map not only employs the high-precision integrated
adjustment but also brings clear economic benefits because no particular treatment
needs to be carried out in order to connect together the old and new maps.
Especially in the military system, maps that can show a larger area are mostly at
a scale smaller than 1:50,000. Using this new BJS54 as the map coordinate system
has some distinct advantages in terms of updating maps, offering fast combat
support and making it convenient for officers and men to use the maps.
The relationships between the BJS54, XAS80 and the new BJS54 are depicted
vividly in Fig.
7.10
.
In Fig.
7.10
, O
1980
X
1980
Y
1980
Z
1980
, O
new1954
X
new1954
Y
new1954
Z
new1954
, and
O
1954
X
1954
Y
1954
Z
1954
are the spatial rectangular coordinate systems with respect
to the XAS80, the new BJS54, and the old BJS54, respectively. The direction of the
Z
1954
-axis is not specified. It is defined as non-parallel to the direction from the
Earth's center of mass to the polar origin JYD
1968.0
. The Krassowski Ellipsoid
parameters are adopted and the size of the ellipsoid is not drawn in order to keep the
map clear. The coordinate systems of the O
new1954
X
new1954
Y
new1954
Z
new1954
and
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