Geodetic Datum and Geodetic Control Networks - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 83

sight should go beyond or deviate from obstacles by a certain distance which, for
first- and second-order, respectively, should be no less than 4 m and 2 m in
mountainous areas while no less than 6 m and 4 m in plain areas.
Technical Design
Data Collection
Data relevant to the survey areas should be collected before planning, including
maps of various scales, aerial photo maps, traffic maps and meteorological infor-
mation, existing results of geodetic points, natural and social geographical envi-
ronments of the survey areas, transportation and material supplies, and so on. These
data should be analyzed and studied as the basis and reference for the technical
design.
Drawing Up Designs
Drawing up designs is a key aspect in technical design that deserves careful
consideration in order to facilitate site selection. Fieldwork will otherwise be
difficult.
Drawing up designs usually follows the steps and methods listed below:
1. Splicing the 1/50,000 or 1/100,000 scale topographic maps of the survey area
and marking the already established triangulation chains, GPS networks, tra-
verse networks, and leveling lines on the map.
2. Extending outward from the points of known control in a pointwise manner
according to the requirements for positions of control points while considering
creating the best figure possible. The points are laid out from higher to lower
orders, from points of known control to unknown control, and from the interior
to exterior in a pointwise fashion.
3. Drawing up the leveling connection lines according to the density requirements
for the zero elevation surface provided in the corresponding technical standards;
Trying to utilize the old network points already existing and to propose the plans
for a connection survey.
4. Ensuring intervisibility during the site selection. Several alternative plans should
be drawn up for the uncertain positions of points or directions.
Reconnaissance for Site Selection
The task of reconnaissance for site selection is to put the designs on the map into
practice. The most appropriate site available should be selected according to
requirements for the position of control points.