12
January 2018
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
namely, China Geodetic Coordinate System 1980 (Xi’an
Coordinate System), which has a significantly-improved
precision than CGCS 1954; it has completed the National
Vertical Datum System 1985 comprised of the Class-A
national leveling network with 100 loops and a total distance
of 93,000 kilometers and the Class-B national leveling
networkwith a total distance of 136,000 kilometers. Compared
with the Huanghai Vertical Datum System 1956, National
Vertical Datum System 1985 features higher density, higher
precision and more rational structure; moreover, China has
completed its National Gravity Fundamental Network 1985,
which is comprised of 6 gravimetric datum points, 46 basic
gravimetric points and 163 first-class gravimetric points. As
the second-generation datum reference system for surveying
and mapping of China, Gravity Fundamental Network 1985
features higher density and precision compared with Gravity
Fundamental Network 1957.
Since 1990s, China has further accelerated the
modernization of the datum reference system for surveying
and mapping. In 1997, China completed its high-precision
national GPS Network A and Network B, realizing the
nationwide coverage with three-dimensional geocentric
coordinates, 2 orders of magnitude higher than the national
horizontal control network 1980. In 2003, China built the
national GPS geodetic control network 2000 that is comprised
of 2,500 points. In 2004, China built the national geodetic
control network 2000, which consists of approximately 50,000
points and enjoys much higher positioning precision than
ever. In 2003, China built the National Fundamental Gravity
Network 2000, which is a new-generation national gravity
datum comprised of 19 datum points and 119 fundamental
points. Compared with National Fundamental Gravity
Network 1985, National Fundamental Gravity Network
2000 features higher precision and more rational density
and distribution of points. In 2001, China set up its first
decimeter-level quasi-geoid model (CQG2000), on which the
sea level elevation can be determined rapidly by making use
of satellite space positioning technologies and geoid model,
thereby providing a supplementary approach to traditional
leveling height survey within a certain range of precision.
So far, China has basically set up a relatively complete
datum reference system for surveying and mapping, including
national GPS geodetic control network 2000 comprised
of over 2,500 points and national geodetic control network
2000 comprised of approximately 50,000 points, as well as
the national fundamental gravity network comprised of 19
datum points and 119 fundamental points, marking the start
of the construction of the modern Chinese datum reference
system for surveying and mapping.
Since 2006, China has further accelerated optimization
and upgrading of the existing datum reference system for
surveying and mapping, focused on replacing the traditional
reference ellipsoid-centric and two-dimensional coordinate
system with the geocentric and three-dimensional coordinate
system, intensified the construction of the reference station
for satellite positioning continuous operation and connected
it to the international coordinate reference framework and
maintained the coordinate framework through the reference
station and the satellite geodetic control network; meanwhile,
China has attached greater importance to acceleration of the
geoid refinement, improvement of the resolution and precision
of geoids as well as gradual replacement of traditional national
high-level leveling; in addition, China has strived to increase
the quantity of ground absolute gravimetric points, focused
on speeding up the development of measurement of airborne
gravity and satellite gravity and enriching gravimetric data
with different scales.
On July 1, 2008, the high-precision, geocentric, three-
dimensional and dynamic national geodetic coordinate
system 2000, which is China’s new-generation geodetic
coordinate system, was officially put into operation. Now,
the state-level fundamental surveying & mapping results
have been transferred to the National Geodetic Coordinate
System 2000, and the existing fundamental surveying &
mapping results have been or have been basically shifted to
the Geodetic Coordinate System 2000 in Zhejiang, Gansu,
Jiangxi, Fujian, Guangdong, Shandong, Henan, Beijing
and Shanghai. The construction of satellite positioning
