f. Multiple/Repeat Baseline Connections. Table 5-3, pages 5-17 and 5-18 shows the recommended
criteria for baseline connections between stations, repeat baseline observations, and multiple station
occupations. Many of these standards were developed by the Federal Geodetic Control Subcommittee
(FGCS) for performing high-precision geodetic-control surveys.
g. Loop Requirements. A loop (traverse) provides the mechanism for performing field data
validation as well as final-adjustment accuracy analysis. Since loops of GPS baselines are comparable
to traditional EDME/taped traverse routes, misclosures and adjustments can be handled similarly. Most
GPS-S nets (static or kinematic) end up with one or more interconnecting loops that are either internal
from a single fixed point or external through two or more fixed network points. Loops should be closed
off at the spacing, as indicated in Table 5-3, pages 5-17 and 5-18. Loop closures should meet the criteria
specified in Table 5-3, based on the total loop length.
5-32. Network Design and Layout. A wide variety of survey configuration methods may be used to
densify project control using GPS-S techniques. Unlike conventional triangulation and EDME traverse
surveying, the shape or geometry of the GPS network design is not as significant. The following
guidelines for planning and designing proposed GPS-Ss are intended to support lower-order (second-
order, Class I or 1:50,000 or less accuracy) military control surveys where relative accuracies at the
centimeter level or better are required over a small project area.
a. Incorporate Newly Established Global Positioning System Control. Newly Established GPS
control may or may not be incorporated into the NGRS, depending on the adequacy of the connection to
the existing NGRS network or whether it was tied only internally to existing project control.
b. Develop a Network Design. When developing a network design, it is important to obtain the
most economical coverage within the prescribed project accuracy requirements. The optimum network
design provides a minimum amount of baseline/loop redundancy without an unnecessary amount of
observation. Obtaining this optimum design (cost versus accuracy) is difficult and changes constantly
due to evolving GPS technology and satellite coverage.
c. Plan a Global Positioning System Survey Network. Planning a GPS-S network is similar to
planning for conventional triangulation or traversing. The type of survey design used is dependent on
the GPS technique and the user requirements. A GPS network is proposed when established survey
control is used in precise-network densification (1:50,000 to 1:100,000). When the networking method
is selected, the surveyor should devise a survey network that is geometrically sound. Figure 5-2 shows
an example of a step-by-step method to build a GPS-S network.