Geodetic Datum and Geodetic Control Networks - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 116

5. Points should be selected taking into account the convenience of using other
measurement techniques for connection and extension.
6. The point should be located in solid soil or, better, an outcrop of rock in order to
be better preserved.
7. The integrity and stability of the survey mark should be checked before using old
points.
Additionally, other conditions such as the nearby communication facilities and
power supplies should also be considered for the connections between points and
the electricity for equipment.
Marking the Position of the GPS Control Point
For long-term preservation, the GPS control point should usually be located on the
survey mark (monument) with an identifier in the center to mark the point precisely.
Both the survey mark and the identifier should be stable and firm. The mark can be
sunk into the ground or built into an observation stake or a stake with forced
centering devices. For the structure, type, and methods of construction of survey
marks, please refer to Sect. 3.1 and related technical standards.
Measurement Operations of GPS Control Networks
GPS measurement includes field observations and indoor data processing work.
The former consists of installation of antennae, observation operations, and record-
ing of field observation results whereas the latter consists of data extraction from
instruments, baseline solution, and adjustment calculations of three-dimensional
GPS control networks, etc. Below is an overview of field observations. For the
extraction of observation data and the indoor work of data processing, please refer
to annexed instructions and other relevant data.
Installation of Antennae
The precise installation of antennae is one of the prerequisites for precise position-
ing and should satisfy the following conditions:
1. Normally, the antenna should be installed in the vertical direction of the mark
center on a tripod, directly centered. Only in exceptional cases can eccentric
observations be allowed, where the centering elements should be precisely
determined by analytical methods.
2. When installing an antenna on the platform of the tower, in order to avoid
interference to signals, the top of the tower should be removed and the mark
center be projected onto the platform. Then the antenna can be placed according
to the projection point.