Geodetic Datum and Geodetic Control Networks - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 113

At present, these high-precision GPS networks can be used as the basic geodetic
control network for China. Datum stations of continuous operation in the Crustal
Movement Observation Network can provide synchronous observation data for
GPS measurements. With these stations as the initial points, GPS measurements
will be more conveniently and efficiently carried out.
3.3.2 Establishment of Satellite Geodetic Control Networks
A scientific technological design of three-dimensional control networks is required
in order to obtain reliable observation results. Typically, three-dimensional control
networks such as VLBI and SLR are established worldwide by international
organizations based on need. Thus, the process of establishment is rather compli-
cated and time consuming. The so-called satellite geodetic control network usually
refers to the three-dimensional control network in engineering applications; to be
specific, the GPS control network. This section continues with an overview of the
principles and technical design for establishing GPS control networks.
Principles for Establishment of GPS Control Networks
Establishment Based on Hierarchical Orders
Setting GPS network into different orders is conductive to stage-wise establishment
according to the immediate needs and long-term development of survey areas.
Moreover, this principle enables the network structure to combine the long and
short sides. Compared to the Short-Side GPS Control Network, the network
established in such a way can reduce the accumulation of errors at its edge and
allows data processing and results checking of GPS networks to be carried out
easily in a piecemeal fashion.
For instance, we can first use GPS to establish a nationwide high-precision
backbone control network with low density (A- and B-order networks or first-
and second-order networks) and then further densify the network using GPS or
conventional methods based on the survey areas needed. In further densification,
with the help of GPS technology it is unnecessary to establish an overall geodetic
network in advance. Instead, one can establish and use the network at any time
according to the accuracy required by users. We can obtain directly the known
points from hundreds of kilometers away by GPS measurement, which not only
saves a lot of manpower and material resources but also fulfills the practical needs.