Geodetic Datum and Geodetic Control Networks - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 114

Density

Different task requirements and service targets have different requirements for
establishing the GPS network. For example, the national super-network (AA-order)
datum points are mainly used to provide national datums for orbit determination,
precise ephemeris calculations, and large-scale ground deformation monitoring,
with an average distance of hundreds of kilometers. The network required by a
general engineering survey with an average side length of several kilometers or
even shorter (within hundreds of meters) should cater for the needs of mapping
densification and engineering survey. Taking the above factors into account, a rule
for the distance between two adjacent points in GPS networks is made dependent on
various needs: the average distance between adjacent points in GPS at all orders
should meet the requirements of the data in Table 3.4 ; the shortest distance between
adjacent points can be 1/3 to 1/2 of the average distance while the longest is 2-3
times. Under special circumstances, depending on the network's task and target, the
distance between some points can require specific rules for the distribution of GPS
stations.

Accuracy

In the design of GPS networks, the order and accuracy standard should be designed
based on the size of survey areas and the use of the networks. The accuracy standard
of general GPS measurement is commonly expressed by the mean square error of
the distance between adjacent points in the networks as follows:

q

a 2

2

σ ¼ þ ð b d Þ , ð 3 : 2 Þ

where is the mean square error of distance (mm), a is the constant error (mm), b is

the coefficient of the ratio error, and d is the distance between adjacent points (km).
The national “GPS survey specifications” classify GPS measurement into six
orders, namely AA, A, B, C, D, E (as shown in Table 3.4 ). The Table lists the
distances between points and their accuracy indicators in GPS networks of different
orders (SBSM 2009).

σ

Technical Design of GPS Control Networks

Design of GPS Control Network Datum

The design of the GPS control network datum is fundamental to the implementation
of GPS measurement. It aims to find the best possible solution in terms of accuracy,
reliability, and economic efficiency of the network. With GPS measurement we can
obtain the GPS baseline vector between surface points, which belongs to the three-