3. Concluding Remarks
Evidently there are many advantages of a wide-area
GNSS network that include, but not limited to no need
for a user base station, orbital and atmospheric errors are
estimated at the user’s location based on a network
model, and ease of GPS equipment set-ups that would
result in higher productivity. In the case of a RTN however,
the communication links between the network
server and the rover remain an issue when wireless or
radio broadcasts are lost. For example, this is not unusual
scenario with wireless connections, which would not be
available in some remote areas, or radio broadcast which
basically depends on the length of the baseline and the
clarity of the line of sight. This later scenario becomes
obvious when positioning is sought outside the RTN envelope
resulting in coordinate estimates with lower quality.
Another issue that applies not only to the RTN, but to
all GNSS products is related to interference and jamming
of the GPS signal, especially interference which can take
place due to increased solar activity or bad weather. Another
issue that worth mentioning is related to the quality
of positions estimated based on these wide-area GNSS
networks. This is the lack of standards, which applies not
only to wide-area GNSS networks positions, but to every
spatial data product. Technically, spatial data standards
do exist, however there are only used as guidelines because the enforcement of the standards in this case is not
practically feasible. In an effort to provide standards for
NGSS networks-based positioning, NGS has recently
released guidelines for RTN networks; specifying the
requirements from the GPS survey planning phase, to the
establishment and the operation phases. The development
of these guidelines was motivated in part by the need for
general standards for a rapidly growing nationwide infrastructure
of more than a hundred wide-area GNSS networks.
The release of the guidelines is also essential because
coordinates estimated within these networks are
commonly based on US national datums, which need to
be in harmony with the National Spatial Reference System
(NSRS).