Spectra Precision Survey Pro v4.6 Recon and Nomad User Manual - Manual (Page 235)

GPS Overview
225
GPS Network Servers, NTRIP, and
VRS
Traditionally, RTK GPS was done with a base and rover receiver
setup on the survey site and using a radio data modem to get the
observations from the base to the rover for the real time solution.
Another way to do RTK GPS is to use one or more permanently
operating base stations connected to an Internet network. You then
use only a rover at the survey site, and an Internet capable modem to
connect to the IP address of the network server and get corrections
from the base.
The following section explains some of the concepts and terminology
associated with getting GPS observations to the rover from one or
more base receivers connected to the Internet.
GPS Network Servers
There are several different GPS network server software packages
available. Each one offers different types of services using different
technologies. However, the different services can be classified into one
of three general categories:
• Single Base: This type of service is most like traditional RTK.
With this type of service, GPS observations from a single base
station connected to the server software are sent to the rover. The
base station observations used are determined by what base the
user selects to connect to.
• Nearest Base: Similar to single base, with this type of service
you get GPS observations from a single base station connected to
the server software. However, the server software automatically
selects the base station observations to use to supply the rover
with data from the nearest base.
• Networked RTK: This type of service uses the information from
more than one continuously operating receiver connected to the
network to model errors in the GPS solution. Then, the base
observations sent to the rover are modified to apply the calculated
corrections. The benefit to a networked RTK service is that you
can get measurement precisions similar to short baselines even
though the distance to the nearest real base station may be quite
far. There are different proven technologies used to calculate