SX BLUE GPS iSXblue II+ GNSSTM, User Manual

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SXblue Series User Manual 55
NTrip is a protocol for streaming differential GPS/GNSS (DGPS/DGNSS) data over
the Internet. NTrip is a generic, stateless protocol based on the Hypertext Transfer
Protocol HTTP/1.1 and is enhanced for GNSS data streams.
NTrip was developed by the German Federal Agency for Cartography and
Geodesy (BKG) and the Dortmund University Department of Computer Science.
NTrip was released in September 2004 as “RTCM Recommended Standards for
Networked Transport of RTCM via Internet Protocol (NTrip), Verion 1.0”. The
current version of the protocol is Version 2.0 with Amendment 1, June 28, 2011.
NTrip is an open standard protocol. The protocol can be freely downloaded from
BKG and there is an open source implementation available from their web site.
Refer to Appendix D for useful links.
The basic architecture of such a system is as follows. GNSS reference station
receivers are connected to NTrip Servers. These servers connect to a central
server called the NTrip Caster. The individual servers appear as Mountpoints on
the Caster. An NTrip Client in the field connects to the NTrip Caster and
automatically downloads a table containing all the mountpoints. Most NTrip
Casters offer both single baseline connection to a specific mountpoint and
connection to a virtual mountpoint where a specific solution is computed based on
user’s location.
The main advantage of using an RTK network is the convenience of not having to
operate a reference station (especially if the network is free and if adequate cellular
phone coverage is available). These networks can cover a region, a state or a full
country. One key feature as stated above is the ability of these networks to
compute virtual solutions based on users’ locations. The NTrip client such as the
SXblue RTN (running on the user’s computer), automatically handles the
transmission of the user’s location by sending the GGA message to the NTrip
caster at a regular interval.
2.5 Atlas GNSS Global Correction Services (for SXblue
Platinum)
Atlas® is a worldwide terrestrial DGPS service that provides correction data to
subscribers of the system with the use of a geostationary transponder.
2.5.1 System Overview
Atlas
®
is a wide area DGPS service. The information broadcast by this service is
based upon a network of reference stations placed at geographically strategic
locations. The network stations communicate GPS correction data to control
centers where it is decoded, checked, and repackaged into a proprietary format
for transmission to a geostationary L-band communications satellite. The satellite
rebroadcasts the correction information back to earth over a large signal footprint