Geoscience Reference
In-Depth Information
The Demand for Holistic Geographical Information in the Spatial Domain
The Earth is the all and the one. Social and technological advancement will break
the traditional pattern of applying geographical information only within national
boundaries, and instead will spread it all over the geospace. Referring to the
geocentric datum is fundamental for the realization of such a transformation.
The geocentric datum is the precondition for ensuring a “seamless” splice
between nautical charts and topographic maps. The International Hydrographic
Bureau (IHB) has adopted the WGS84 (this system has been consistent with the
ITRF since 1994) as the datum for nautical charts. The practical significance of
unifying the datum of nautical charts in all countries using a geocentric datum is
evident in navigation. If the datum of topographic maps agrees with that of the
nautical charts, it will be favorable for inshore ships and aerial navigation. Other-
wise, additional external transformations will be needed between the navigation
system and map platform as well as between the nautical charts and
topographic maps.
The implementation of the transnational and intercontinental Geographic Infor-
mation System (GIS) and global mapping programs launched by international
organizations should refer to the geocentric system. High dynamic geodetic tech-
nologies can determine the instantaneous geocentric coordinates of the remote
sensing platform, which indicates that the remote sensing information directly
refer to the geocentric datum.
The Demand for Holistic Geographical Information in the Time Domain
The temporal database requires the reference datum to be maintained for a long
time. The non-geocentric coordinate system is static whereas the geocentric datum
can work long-term. In GIS, historical, current, and future information should refer
to the same datum, which requires the datum system to be continuous in the time
domain. The kinematic geocentric reference frame can simulate the position drift
generated by the tectonic plates. Although involved in the application of cartogra-
phy, this effect can be discounted within two to three decades, yet once it is taken
into consideration the geocentric datum can ensure system continuity.
Furthermore, high-precision data of the control points in the digital age have all
been stored in the spatial database. However, the precision of the control points on
the manual analog maps are subject to the accuracy of plotting. This is to say that
the digital maps will not negatively affect the use of high-precision datum.
The differential GPS technique has brought into reality the calculate-and-use
facility of the control point. The geocentric system is referred to as the datum and is
required to be continuous in time sequence, i.e., the points measured at different
time periods should belong to the same system.
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