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on the basis of the control network, and thus the construction control network has
to be established beforehand with the required accuracy.
3. To build a special control network for observing deformation with the purpose of
monitoring deformation of buildings during the operation stage after completion
of the project. A change in the original state of the Earth's surface during project
construction, together with the weight of buildings, would cause inhomogeneous
changes in the ground base and its surrounding strata. Besides, the building itself
and its foundation will also deform due to changes in the ground base. Such
deformation, once exceeding a certain limit, would affect the normal use of the
building or even jeopardize its safety. In some cities (such as Shanghai and
Tianjin in China) overexploitation of underground water could cause land
subsidence in downtown areas on a large scale and bring about damage. There-
fore, during the operational phase after completion of the construction, defor-
mation needs to be monitored for these buildings or downtown. In this case, a
control network for deformation observation with high accuracy has to be
established.
With regard to transportation, geodetic surveying and positioning technology
has provided important guarantees for improving traffic efficiency and decreasing
traffic accidents.
The requirements of transportation for quantity, category, quality, and real-time
positioning information are dependent on the level of development of social
production, economy, science, and technology. The navigation and positioning
level of ancient transportation means is from several kilometers to tens of kilome-
ters whereas that of today's air and ocean transportation is from several meters to
tens of meters. Modern GPS equipment can provide real-time positioning with
decimeter-level or even centimeter-level accuracy, which is highly significant for
large airports with frequent take-offs and landings. Currently, the number of
automobiles in the world is increasing rapidly. According to statistics, traffic
accidents in recent years are mostly due to drivers' failure to quickly determine
the positions of and distances between automobiles and to their lack of quick-
response capability while passing obstacles. At present, automotive GPS auto-
positioning display and response systems are applied extensively, which will
effectively reduce traffic accidents caused by automobiles. Such installations are
also needed for inland navigation in narrow channels and ports to avoid ship
collision accidents. Satellite navigation and positioning ability with high efficiency
and accuracy enables traffic accidents to be greatly reduced and transportation
efficiency to be highly improved.
1.2.2 Applications of Geodesy in Space Technology
The launching, guidance, tracking, remote controlling, and return of spacecraft
need two basic types of support from geodesy: one is a precise geodetic coordinate
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