NEWS from the Radio Technical Commission for Maritime Services (RTCM)

NEWS from the Radio Technical Commission for Maritime Services (RTCM=
)
July 8, 2009

The Radio Technical Commission for Maritime Services (RTCM) Publishe=
s
Revised Standard for Networked Transfer of RTCM via Internet Protoco=
l
(Ntrip)

Summary: RTCM Special Committee 104 (SC104) has completed a new revis=
ion
of its standard on =E2=80=9CNetworked Transport of RTCM via Interne=
t Protocol
(Ntrip)=E2=80=9D. Designated as RTCM Standard 10410.1, it defines a pr=
otocol for
streaming differential correction data or other kinds of Global Navigat=
ion
Satellite System (GNSS) data to stationary or mobile users over =
the
Internet. Although named for the widely used RTCM data format, it can a=
lso
be used for other data formats. The standard is available from RTCM at =
its
secure online publication store. Visit www.rtcm.org and click =
on
=E2=80=9CPublications.=E2=80=9D

Global Navigation Satellite Systems (GNSS) provide geographical positioni=
ng
information from a constellation of satellites in orbit to receivers at
sea, on the ground, and in the air. The best known of these systems is t=
he
U.S. Global Positioning System (GPS), but the Russian GLONASS system
provides a similar service, as will the European Galileo system. Togethe=
r
they are known as Global Navigation Satellite Systems, and they can provi=
de
position accuracies in the 10 meter to 15 meter range. Although the
satellites have the potential to provide more accurate positions,
atmospheric and other effects degrade the quality of the satellite signal=
s.
As impressive as GNSS systems are, they do not directly provide accuracie=
s
that are good enough to rely on for ships entering harbors, or docking, f=
or
example. The satellite signals can be corrected by using a reference
stations at precisely known locations, which broadcast corrections to GNS=
S
receivers nearby. This technique is known as Differential GNSS (DGNSS)
service, and it has enabled precise navigation not only by ships, but als=
o
aircraft, and ground vehicles. Now centimeter level accuracy can be
obtained, providing surveyors and geodesists with the precision they need=
=2E
New applications continue to be developed.

Typically, differential corrections have been broadcast over radio d=
ata
links from single reference stations located in precisely known locatio=
ns,
to mobile receivers (rovers) located on the equipment whose position ne=
eds
to be known. As the uses of DGNSS services have grown, governments =
and
commercial service providers have established networks of refere=
nce
stations. One way to further increase accuracy is to use correction d=
ata
from multiple reference stations, such as these networks provide. For =
all
these applications, replacing the radio data link with data streaming o=
ver
the Internet to stationary or mobile users using the Ntrip protocol, can =
be
advantageous, and its use has grown since RTCM published the origi=
nal
version of its standard in 2004.

The Ntrip project was initiated by the German Federal Agency =
for
Cartography and Geodesy (Bundesamt f=C3=BCr Kartographie und Geod=C3=A4=
sie, BKG).
Although there are uses for stationary DGNSS receivers that could acc=
ess
the Internet via landline, the growing availability of Internet serv=
ice
through the mobile telephone network was a persuasive reason to develop =
and
formalize a publicly available Internet protocol for streaming DGNSS da=
ta.
Ntrip is designed to distribute differential correction data or other ki=
nds
of GNSS streaming data to stationary or mobile users over the Intern=
et,
allowing simultaneous PC, Laptop, PDA, or receiver connections to=
a
broadcasting host. Ntrip supports wireless Internet access through Mob=
ile
IP Networks like GSM, GPRS, EDGE, or UMTS.

Ntrip is meant to be an open non-proprietary protocol. Ma=
jor
characteristics of Ntrip=E2=80=99s dissemination technique are the follow=
ing:

=E2=80=A2 It is based on the popular HTTP standard, and is comparativel=
y easy to
implement when limited client and server platform resources are
available.
=E2=80=A2 Its application is not limited to one particular plain or cod=
ed stream
content; it has the ability to distribute any kind of GNSS data.
=E2=80=A2 It has the potential to support mass usage; it can disseminat=
e hundreds
of streams simultaneously for up to a thousand users when applying
modified Internet Radio broadcasting software.
=E2=80=A2 Regarding security needs, stream providers and users are not =
necessarily
in direct contact, and streams are usually not blocked by firewalls o=
r
proxy servers protecting Local Area Networks.
=E2=80=A2 It enables streaming over any mobile IP network using TCP/IP.=


Correction data supporting precision navigation applications through Ntri=
p
is available now through several hundred services worldwide, many of them=

in Europe.

The new standard describes Ntrip Version 2.0. Major changes compared to
Version 1.0 are:
=E2=80=A2 Cleared and fixed design problems and HTTP protocol violation=
s;
=E2=80=A2 Replaced non standard directives;
=E2=80=A2 Adds chunked transfer encoding;
=E2=80=A2 Improves header records;
=E2=80=A2 Provides for sourcetable filtering; and
=E2=80=A2 Provides for Real Time Streaming Protocol (RTSP) communicatio=
n.

I look forward to them posting the URL for this open protocol to the
net.

From the announcement and the fact that they want you to go to their
"secure store" to download the document, I suspect their usage of the
term "open protocol" is vastly different from most people's
understanding of that same term.

-wolfgang
--
Wolfgang S. Rupprecht Android 1.5 (Cupcake) and Fedora-11

Wolfgang S. Rupprecht wrote:

Yes--It would seem that is the case. Rather disappointing!
-Sam

There seems to be some confusion here between RTCM and NTRIP.

The RTCM is not an open thing. To cover costs the documents are only freely
accessible for members.

NTRIP on the other hand is fully public domain. Documentation and even all
the software is freely downloadable. Please check the following link:
http://igs.bkg.bund.de/index_ntrip.htm

Tim
http://gnss.servolux.nl/gnss_blog.html

Thanks Tim!

-wolfgang
--
Wolfgang S. Rupprecht Android 1.5 (Cupcake) and Fedora-11