The
OGS RTK service, which disseminates differential
correction (phase and code),
permits, adopting GPS&GLONASS technology, a positioning with a centimetrical precision in the Friuli
Venezia Giulia area.
The whole system is constituted by few permanent GPS receivers
FReDNet
and a process and distribuition server (caster).
The data are available through a generic, stateless application-level protocol:
NTRIP
(Networked Transport of RTCM via Internet Protocol) and the service, managed by the
Centro di Ricerche Sismologiche - CRS, is free.
The NTRIP Caster addresses are the following:
Address |
Username |
Password |
Notes |
158.110.30.81:2110 |
[user] |
[password] |
The following mountpoints are available:
Frednet single station;
A. Marussi single station
Frednet network solution:
- NEAREST;
- VRS;
|
The service access ways to the real time positioning are the following:
SERVICE |
DESCRIPTION |
SINGLE STATION |
The rover receives differential corrections from the single station (master) selected by
the user.
In this case, the server redirect data from the master station to the rover.
More then one rover can access at the same time at the same master. In this case, the
server increase data flow as many as the number of requests.
The comunication form server to rover is monodirectional.
|
NEAREST |
The working mode is the same of the 'single station' mode.
In this case, the user doesn't need to know the master station for connecting. The
caster will distribute automatically
the differential correction from the nearest permanent station. Adopting this mode, the
server need the rover approximate position.
The communication server-rover is bidirectional.
|
VRS |
The rover receive differential corrections from a Virtual Reference Station (VRS).
The caster, using data coming from all the station of the network and the approximate
rover position,
calculates a 'network solution' which create a VRS near the rover (few km). The rover
must send his approximate coordinates (NMEA format) to the server;
the communication server-rover is bidirectional. Differential correction provided
are compliant with the RTCM3.x protocol
|
SLO |
- |
AU |
- |
The OGS caster further to the
convention with Regione Friuli Venezia
Giulia, disseminates
also the single station differential correction of
'Rete
A. Marussi', some of the
Austrian EPOSA network
and some sites belonging to the
MPRI not-for-profit
organisation and to the
University of Ljubiana in
Slovenia.
All the real time services are distribuited respect to the new reference system
ETRF2000(2008.0)
scheme by Istituto Geografico Militare (IGM) to set of Rete Dinamica Nazionale (RDN).
This system (ETRF2000(2008.0)) will be early adopted also in the services distribuited by
'Rete A.Marussi' which now use the reference system ETRF89.
The user who connects his receiver to the caster has at his disposal several access points
called mountpoint.
The name 'mountpoint' identify:
- the owner of the service (OGS or RAFVG)
- the access service:
- from single station if the name contain the name of the GPS station;
- NEAR means from the GPS station nearest to the receiver;
- VRS or FKP for network solutions;
EXAMPLES |
OGS_JOAN |
The rover establish a connection in 'single station' modality with the OGS permanent
site of JOAN. |
OGS_NEA |
The rover establish a connection in 'single station' modality to the nearest OGS
permanent site |
OGS_FKP |
The rover establish a connection in FKP modality to the FReDNet Network |
OGS_VRS |
The rover establish a connection in VRS modality to the FReDNet Network |
RAFVG_BARC |
The rover establish a connection in 'single station' modality with the Regione Friuli
Venezia Giulia permanent site of BARC. |
NTRIP
To broadcast differential corrections is used the protocol RTCM (Radio Technical Commission for Maritime Services).
The RTCM contains informations classifieds as TYPES. The RTCM can?t support modern
service because doesn?t permits
the contemporary access to more then one receiver to the same master.
The RTCM data (differential correction) are broadcast through NTRIP protocol based on
HTTP (Hyper Text Transfer Protocol).
Ntrip is implemented in three system software components: NtripClients, NtripServers and
NtripCasters.
The NtripCaster is the actual HTTP server program whereas NtripClient and NtripServer
are acting as HTTP clients.