The purpose of BNC is to

• retrieve real-time GNSS data streams available through NTRIP transport protocol,
• retrieve real-time GNSS data streams via TCP directly from an IP address without using the NTRIP transport protocol,
• retrieve real-time GNSS data streams from a local UDP or serial port without using the NTRIP transport protocol,
• generate high-rate RINEX Observation and Navigation files to support near real-time GNSS post-processing applications,
• generate ephemeris and synchronized or unsynchronized observations epoch by epoch through an IP port to support real-time GNSS network engines,
• generate clock and orbit corrections to Broadcast Ephemeris through an IP port to support real-time Precise Point Positioning on GNSS rovers,
• generate synchronized or unsynchronized clock and orbit corrections to Broadcast Ephemeris epoch by epoch through an IP port to support the (outside) combination of such streams as coming simultaneously from various correction providers,
• monitor the performance of a network of real-time GNSS data streams to generate advisory notes in case of outages or corrupted streams,
• scan RTCM streams for incoming antenna information as well as message types and their repetition rates,
• feed a stream into a GNSS receiver via serial communication link,
• carry out a real-time Precise Point Positioning to determine a GNSS rover position,
• simultaneously process several incoming orbit and clock correction streams to produce, encode and upload a combination solution,
• upload a Broadcast Ephemeris stream in RTCM Version 3 format,
• read GNSS clocks and orbits in a plain ASCII format from an IP port - they can be produced by a real-time GNSS engine such as RTNet and should be referenced to the IGS Earth-Centered-Earth-Fixed (ECEF) reference system and
• convert the IGS Earth-Centered-Earth-Fixed clocks and and orbits into corrections to Broadcast Ephemeris with radial, along-track and cross-track components,
• upload the clock and orbit corrections as an RTCM Version 3 stream to an NTRIP Broadcaster,
• refer the clock and orbit corrections to a specific reference system,
• log the Broadcast Ephemeris clock corrections as Clock RINEX files for further processing using other tools than BNC,
• log the Broadcast Ephemeris orbit corrections as SP3 files for further processing using other tools than BNC,
• edit or concatenate RINEX files or check their quality.

BNC supports decoding the following GNSS stream formats and message types:

• RTCM Version 2 message types for GPS and GLONASS observations,
• RTCM Version 3 'conventional' message types for observations and Broadcast Ephemeris for GPS, GLONASS, SBAS, Galileo, COMPASS, and QZSS,
• RTCM Version 3 'State Space Representation' (SSR) messages for GPS, GLONASS and Galileo,
• RTCM Version 3 'Multiple Signal Messages' (MSM) and 'High Precision Multiple Signal Messages' (HP MSM),
• RTNET, a plain ASCII format defined within BNC to receive orbits and clock from a serving GNSS engine.

The first of the following figures shows a flow chart of BNC connected to a GNSS receiver providing observations via serial or TCP communication link for the purpose of Precise Point Positioning. The second figure shows the conversion of RTCM streams to RINEX files. The third figure shows a flow chart of BNC feeding a real-time GNSS engine which estimates Broadcast Corrections. BNC is used in this scenario to encode correctors to RTCM Version 3 and upload them to an NTRIP Broadcaster. The fourth figure shows BNC combining several Broadcast Correction streams to disseminate the combination product while saving results in SP3 and Clock RINEX files.

Figure: Flowchart, BNC connected to a GNSS receiver for Precise Point Positioning.

Figure: Flowchart, BNC converting RTCM streams to RINEX batches.

Figure: Flowchart, BNC feeding a real-time GNSS engine and uploading an encoded Broadcast Corrections stream.

Figure: Flowchart, BNC combining Broadcast Correction streams.

Although BNC is mainly a real-time tool to be operated online, it can be run offline

• to simulate real-time observation situations for debugging purposes,
• for post-processing purposes.

Unless it runs offline, BNC

• requires access to the Internet with a minimum of about 2 to 6 kbits/sec per stream depending on the stream format and the number of visible satellites. You need to make sure that the connection can sustain the required bandwidth.
• requires the clock of the host computer to be properly synchronized.
• has the capacity to retrieve hundreds of GNSS data streams simultaneously. Please be aware that such usage may incur a heavy load on the NTRIP Broadcaster side depending on the number of streams requested. We recommend limiting the number of streams where possible to avoid unnecessary workload.

The main window of BNC shows a 'Top menu bar' section, a 'Settings' sections with tabs to set processing options, a 'Streams' section, a section for 'Log' tabs, and a 'Bottom menu bar' section, see figure below.

Figure: Sections on BNC's main window.

This chapter describes how to handle BNC and how to set the program options. It explains the top menu bar, the processing options, the 'Streams' and 'Log' sections, and the bottom menu bar.

The usual handling of BNC is that you first select a number of streams ('Add Stream'). Any stream configured to BNC shows up on the 'Streams' canvas in the middle of BNC's main window. You then go through BNC's various configuration tabs to select a combination of input, processing and output options before you start the program ('Start'). Most configuration tabs are dedicated to a certain functionality of BNC. If the first option field on such a configuration tab is empty, the affected functionality is - apart from a few exceptions - deactivated.

As a default, configuration files for running BNC on Unix/Linux/Mac systems are saved in directory '${HOME}/.config/BKG'. On Windows systems, they are typically saved in directory 'C:/Documents and Settings/Username/.config/BKG'. The default configuration file name is 'BNC.ini'.

The default file name 'BNC.ini' can be changed and the file contents can easily be edited. On graphical user interfaces it is possible to Drag & Drop a configuration file icon to start BNC (not on Mac systems). Some configuration options can be changed on-the-fly. See annexed 'Configuration Example' for a complete set of configuration options. It is also possible to start and configure BNC via command line.

The top menu bar allows to select a font for the BNC windows, save configured options, or quit the program execution. It also provides access to a program documentation.

The 'File' button lets you

• select an appropriate font.
  Use smaller font size if the BNC main window exceeds the size of your screen.
• save selected options in configuration file.
  When using 'Save & Reread Configuration' while BNC is already processing data, some configuration options become immediately effective on-the-fly without interrupting uninvolved threads. See annexed section 'Configuration Example' for a list of on-the-fly changeable configuration options.
• quit the BNC program.

The 'Help' button provides access to

• help contents.
  You may keep the 'Help Contents' window open while configuring BNC.
• a 'Flow Chart' showing BNC linked to a real-time GNSS network engine such as RTNet.
• general information about BNC.
  Close the 'About BNC' window to continue working with BNC.

BNC comes with a help system providing online information about its functionality and usage. Short descriptions are available for any widget. Focus to the relevant widget and press Shift+F1 to request help information. A help text appears immediately; it disappears as soon as the user does something else. The dialogs on some operating systems may provide a "?" button that users can click; they then click the relevant widget to pop up the help text.

You may need to specify a proxy when running BNC in a protected network. You may also like to use the Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL) cryptographic protocols for secure NTRIP communication over the Internet.

If you are running BNC within a protected Local Area Network (LAN), you might need to use a proxy server to access the Internet. Enter your proxy server IP and port number in case one is operated in front of BNC. If you don't know the IP and port of your proxy server, check the proxy server settings in your Internet browser or ask your network administrator.

Note that IP streaming is often not allowed in a LAN. In this case you need to ask your network administrator for an appropriate modification of the local security policy or for the installation of a TCP relay to the NTRIP Broadcasters. If these are not possible, you might need to run BNC outside your LAN on a host that has unobstructed connection to the Internet.

Communication with an NTRIP Broadcaster over SSL requires the exchange of client and/or server certificates. Specify the path to a directory where you save certificates on your system. You may like to check out http://software.rtcm-ntrip.org/wiki/Certificates for a list of known NTRIP Server certificates. Don't try communication via SSL if you are not sure whether this is supported by the involved NTRIP Broadcaster.

SSL communication may involve queries coming from the NTRIP Broadcaster. Tick 'Ignore SSL authorization erros' if you don't want to be bothered with this. Note that SSL communication is usually done over port 443.

The following defines general settings for BNC's logfile, file handling, reconfiguration on-the-fly, and auto-start.

Records of BNC's activities are shown in the 'Log' tab on the bottom of the main window. These logs can be saved into a file when a valid path is specified in the 'Logfile (full path)' field. The logfile name will automatically be extended by a string '_YYMMDD' carrying the current date. This leads to series of daily logfiles when running BNC continuously for extended. Message logs cover the communication status between BNC and the NTRIP Broadcaster as well as problems that may occur in the communication link, stream availability, stream delay, stream conversion etc. All times are given in UTC. The default value for 'Logfile (full path)' is an empty option field, meaning that BNC logs will not saved into a file.

When BNC is started, new files are created by default and any existing files with the same name will be overwritten. However, users might want to append existing files following a restart of BNC, a system crash or when BNC crashed. Tick 'Append files' to continue with existing files and keep what has been recorded so far. Note that option 'Append files' affects all types of files created by BNC.

When operating BNC online in 'no window' mode (command line option -nw), some configuration options can nevertheless be changed on-the-fly without interrupting the running process. For that you force the program to reread parts of its configuration in pre-defined intervals from the disk. Select '1 min', '1 hour', or '1 day' to let BNC reread on-the-fly changeable configuration options every full minute, hour, or day. This lets in between edited options become effective without interrupting uninvolved threads. See annexed section 'Configuration Example' for a configuration file example and a list of on-the-fly changeable options.

You may like to auto-start BNC at startup time in window mode with pre-assigned configuration options. This may be required i.e. immediately after booting your system. Tick 'Auto start' to supersede the usage of the 'Start' button. Make sure that you maintain a link to BNC for that in your Autostart directory (Windows systems) or call BNC in a script below directory /etc/init.d (Unix/Linux/Mac systems).

See BNC's command line option -nw for an auto-start of BNC in 'no window' mode.

BNC can save all data coming in through various streams in one daily file. The information is recorded in the specified 'Raw output file' in the received order and format. This feature allows a BNC user to run the PPP option offline with observations, Broadcast Corrections, and Broadcast Ephemeris being read from a previously saved file. It supports the offline repetition of a real-time situation for debugging purposes. It is not meant for post-processing.

Data will be saved in blocks in the received format separated by ASCII time stamps like (example):

2010-08-03T18:05:28 RTCM3EPH RTCM_3 67

The default value for 'Raw output file' is an empty option field, meaning that BNC will not save all raw data into one single daily file.

Observations will be converted to RINEX if they come in either RTCM Version 2 or RTCM Version 3 format. Depending on the RINEX version and incoming RTCM message types, the files generated by BNC may contain data from GPS, GLONASS, Galileo, SBAS, QZSS, and COMPASS. In case an observation type is listed in the RINEX header but the corresponding observation is unavailable, its value is set to zero '0.000'. Note that the 'RINEX TYPE' field in the RINEX Version 3 Observation file header is always set to 'M(MIXED)' or 'Mixed' even if the file only contains data from one system.

The screenshot below shows an example setup of BNC when converting streams to RINEX. Streams are coming from various NTRIP Broadcasters as well as from a serial communication link. Specifying a decoder string 'ZERO' would have meant to not convert the affected stream contents but save its contents as received.

Figure: BNC translating incoming streams to 15 min RINEX Version 3 files.

RINEX file names are derived by BNC from the first 4 characters of the corresponding stream's mountpoint (4Char Station ID). For example, data from mountpoints FRANKFURT and WETTZELL will have hourly RINEX Observation files named

FRAN{ddd}{h}.{yy}O
WETT{ddd}{h}.{yy}O

where 'ddd' is the day of year, 'h' is a letter which corresponds to an hour long UTC time block and 'yy' is the year.

If there are more than one stream with identical 4Char Station ID (same first 4 characters for their mountpoints), the mountpoint strings are split into two sub-strings and both become part of the RINEX file name. For example, when simultaneously retrieving data from mountpoints FRANKFURT and FRANCE, their hourly RINEX Observation files are named as

FRAN{ddd}{h}_KFURT.{yy}O
FRAN{ddd}{h}_CE.{yy}O.

If several streams show exactly the same mountpoint name (example: BRUS0 from www.euref-ip.net and BRUS0 from www.igs-ip.net), BNC adds an integer number to the file name leading i.e. to hourly RINEX Observation files like

BRUS{ddd}{h}_0.{yy}O
BRUS{ddd}{h}_1.{yy}O.

Note that RINEX file names for all intervals less than 1 hour follow the file name convention for 15 minutes RINEX Observation files i.e.

FRAN{ddd}{h}{mm}.{yy}O

where 'mm' is the starting minute within the hour.

Here you can specify the path to where the RINEX Observation files will be stored. If the specified directory does not exist, BNC will not create RINEX Observation files. Default value for 'Directory' is an empty option field, meaning that no RINEX Observation files will be written.

Select the length of the RINEX Observation file generated. The default value is 15 minutes.

Select the RINEX Observation sampling interval in seconds. A value of zero '0' tells BNC to store all received epochs into RINEX. This is the default value.

Whenever BNC starts generating RINEX Observation files (and then once every day at midnight), it first tries to retrieve information needed for RINEX headers from so-called public RINEX header skeleton files which are derived from sitelogs. A HTTP link to a directory containing these skeleton files may be available through data field number 7 of the affected NET record in the source-table. See http://www.epncb.oma.be:80/stations/log/skl/brus.skl for an example of a public RINEX Version 2 header skeleton file for the Brussels EPN station.

However, sometimes public RINEX header skeleton files are not available, its contents is not up to date, or you need to put additional/optional records in the RINEX header. For that BNC allows using personal skeleton files that contain the header records you would like to include. You can derive a personal RINEX header skeleton file from the information given in an up to date sitelog. A file in the RINEX Observations 'Directory' with a 'Skeleton extension' suffix is interpreted by BNC as a personal RINEX header skeleton file for the corresponding stream.

Examples for personal skeleton file name convention: RINEX Observation files for mountpoints WETTZELL, FRANKFURT and FRANCE (same 4Char Station ID), BRUS0 from www.euref-ip.net and BRUS0 from www.igs-ip.net (same 4Char Station ID, identical mountpoint stings) would accept personal skeleton files named

WETT.skl
FRAN_KFURT.skl
FRAN_CE.skl
BRUS_0.skl
BRUS_1.skl

if 'Skeleton extension' is set to 'skl'.

Note the following regulations regarding personal RINEX header skeleton files:

• If such a file exists in the 'RINEX directory', the corresponding public RINEX header skeleton file is ignored. The RINEX header is generated solely from the contents of the personal skeleton.
• Personal skeletons should contain a complete first header record of type
  -   RINEX VERSION / TYPE
  Note the small differences mentioned below with regards to RINEX Version 2 and RINEX Version 2 skeletons.
• They should then contain an empty header record of type
  -   PGM / RUN BY / DATE
  BNC will complete this line and include it in the RINEX file header.
• They should further contain complete header records of type
  -   MARKER NAME
  -   OBSERVER / AGENCY
  -   REC # / TYPE / VERS
  -   ANT # / TYPE
  -   APPROX POSITION XYZ
  -   ANTENNA: DELTA H/E/N
  -   WAVELENGTH FACT L1/2 (RINEX Version 2)
• They may contain any other optional complete header record as defined in the RINEX documentation.
• They should then contain empty header records of type
  -   # / TYPES OF OBSERV (RINEX Version 2)
  -   SYS/ # / OBS TYPES (RINEX Version 3)
  -   TIME OF FIRST OBS
  BNC will include these lines in the final RINEX file header together with an additional
  -   COMMENT
  line describing the source of the stream.
• They should finally contain an empty header record of type
  -   END OF HEADER (last record)

If neither a public nor a personal RINEX header skeleton file is available for BNC, a default header will be used.

Whenever a RINEX Observation file is saved, you might want to compress copy or upload it immediately via FTP. BNC allows you to execute a script/batch file to carry out these operations. To do that specify the full path of the script/batch file here. BNC will pass the RINEX Observation file path to the script as a command line parameter (%1 on Windows systems, $1 on Unix/Linux/Mac systems).

The triggering event for calling the script or batch file is the end of a RINEX Observation file 'Interval'. If that is overridden by a stream outage, the triggering event is the stream reconnection.

As an alternative to initiating file uploads through BNC, you may like to call an upload script or batch file through your crontable or Task Scheduler (independent from BNC) once every one or two minutes after the end of each RINEX file 'Interval'.

The default format for RINEX Observation files is RINEX Version 2.11. Select 'Version 3' if you would like to save observations in RINEX Version 3 format.

Broadcast ephemeris can be saved as RINEX Navigation files when received via RTCM Version 3 e.g. as message types 1019 (GPS) or 1020 (GLONASS) or 1045 (Galileo). The file name convention follows the details given in section 'RINEX File Names' except that the first four characters are 'BRDC' and the last character is

• 'N' or 'G' for GPS or GLONASS ephemeris in two separate RINEX Version 2.11 Navigation files, or
• 'P' for GPS plus GLONASS plus Galileo ephemeris saved together in one RINEX Version 3 Navigation file.

Note that streams dedicated to carry Broadacst Ephemeris messages in RTCM Version 3 format in high repetition rates are listed on http://igs.bkg.bund.de/ntrip/ephemeris.

Specify a path for saving Broadcast Ephemeris data as RINEX Navigation files. If the specified directory does not exist, BNC will not create RINEX Navigation files. Default value for Ephemeris 'Directory' is an empty option field, meaning that no RINEX Navigation files will be created.

Select the length of the RINEX Navigation file generated. The default value is 1 day.

BNC can output Broadcast Ephemeris in RINEX Version 3 format on your local host (IP 127.0.0.1) through an IP 'Port'. Specify an IP port number to activate this function. The default is an empty option field, meaning that no ASCII ephemeris output via IP port is generated.

The source code for BNC comes with an example perl script 'test_tcpip_client.pl' that allows you to read BNC's ASCII ephemeris output from the IP port.

Default format for RINEX Navigation files containing Broadcast Ephemeris is RINEX Version 2.11. Select 'Version 3' if you want to save the ephemeris in RINEX Version 3 format.

Note that this does not concern the Broadcast Ephemeris output through IP port which is always in RINEX Version 3 format.

BNC allows to concatenate RINEX files and edit their contents. Observation and navigation files can be handled. BNC can also carry out a quality check of the contents of RINEX files. This functionality in BNC stands for

• t = translation (from RTCM to RINEX)
• e = editing and concatenation
• qc = quality check

Select an action. Options are 'Edit/Concatenate' and 'Analyze'.

• Select 'Edit/Concatenate' if you want to edit RINEX file contents according to options specified under 'Set Edit Options' or if you want to concatenate several RINEX files.
• Select 'Analyze' if you are interested in a quality check of your RINEX file contents.

Once the 'Edit/Concatenate' action is selected, you have to 'Set Edit Options'. BNC lets you specify the RINEX version, sampling rate, begin and end of file and marker, antenna, receiver details.

When converting RINEX Version 2 to RINEX Version 3, the tracking mode or channel information in the (last character out of the three characters) observation code is left blank if unknown. When converting RINEX Version 3 to RINEX Version 2

• C1P in RINEX Version 3 is mapped to P1 in RINEX Version 2
• C2P in RINEX Version 3 is mapped to P2 in RINEX Version 2
• If several observations in RINEX Version 3 come with the same observation type, same band/frequency but different tracking modes, BNC uses only the one provided first for creating RINEX Version 2 while ignoring others.

If you specify a 'New' but no 'Old' marker/antenna/receiver name, the corresponding data field in the emerging new RINEX file will be filled accordingly. If you in addition specify an 'Old' marker/antenna/receiver name, the corresponding data field in the emerging new RINEX file will only be filled accordingly where 'Old' specifications match existing file contents.

Specify full path to input RINEX observation file(s), and
specify full path to input RINEX navigation file(s).

When specifying several input files BNC will concatenate their contents.

Figure: Example for RINEX file editing with BNC in post-processing mode.

Mandatory if 'Edit/Concatenate' selected:
Specify full path to output RINEX observation file(s) and specify full path to output RINEX navigation file(s).

Mandatory if 'Analyze' selected:
Specify logfile(s) to output analysis results.

BNC applies options from the configuration file but allows updating any of them on the command line while the contents of the configuration file remains unchanged, see 'Command Line Options' section below. The syntax for that looks as follows

--key <keyName> <keyValue>

where <keyName> stands for the name of an option contained in the configuration file and <keyValue> stands for the value you want to assign to it. This functionality may be helpful in the 'RINEX Editing & QC' context when running BNC on a routine bases for maintaining a RINEX file archive.

./bnc -nw --conf rnx.conf --key --key reqcAction Edit/Concatenate --key reqcObsFile "tlse119b00.12o,tlse119b15.12o,tlse119b30.12o,tlse119b45.12o" --key reqcOutObsFile tlse119b.12o --key reqcRnxVersion 3 --key reqcSampling 30

The following is a list of available keynames for 'RINEX Editing & QC' options and their meaning (cf. section 'Configuration Example'):

Differential GNSS and RTK operation using RTCM streams is currently based on corrections and/or raw measurements from single or multiple reference stations. This approach to differential positioning is using 'observation space' information. The representation with the RTCM standard can be called 'ObservationSpace Representation' (OSR).

An alternative to the observation space approach is the so called 'sate space' approach. The principle here is to provide information on individual error sources. It can be called 'State Space Representation' (SSR). For a rover position, state space information concerning precise satellite clocks, orbits, ionosphere, troposphere et cetera can be converted into observation space and used to correct the rover observables for more accurate positioning. Alternatively the state information can directly be used in the rover's processing or adjustment model.

RTCM has developed Version 3 messages to transport satellite clock and orbit corrections in real-time. The current set of messages concerns:

• Orbit corrections to Broadcast Ephemeris
• Clock corrections to Broadcast Ephemeris
• Code biases
• Combined orbit and clock corrections to Broadcast Ephemeris
• User Range Accuracy (URA)
• High-rate GPS clock corrections to Broadcast Ephemeris

RTCM Version 3 streams carrying these messages may be used i.e. to support real-time Precise Point Positioning (PPP) applications.

When using clocks from Broadcast Ephemeris (with or without applied corrections) or clocks from SP3 files, it may be important to understand that they are not corrected for the conventional periodic relativistic effect. Chapter 10 of the IERS Conventions 2003 mentions that the conventional periodic relativistic correction to the satellite clock (to be added to the broadcast clock) is computed as dt = -2 (R * V) / c^2 where R * V is the scalar product of the satellite position and velocity and c is the speed of light. This can also be found in the GPS Interface Specification, IS-GPS-200, Revision D, 7 March 2006.

Orbit corrections are provided in along-track, cross-track and radial components. These components are defined in the Earth-centered, Earth-fixed reference frame of the broadcast ephemerides. For an observer in this frame, the along-track component is aligned in both direction and sign with the velocity vector, the cross-track component is perpendicular to the plane defined by the satellite position and velocity vectors, and the radial direction is perpendicular to the along track and cross-track ones. The three components form a right-handed orthogonal system.

After applying corrections, the satellite position and clock is referred to the 'ionospheric free' phase center of the antenna which is compatible with the broadcast orbit reference.

The orbit and clock corrections do not include local effects (like Ocean Loading or Solid Earth Tides) or atmospheric effects (Ionosphere and/or troposphere). Depending on the accuracy of your application you should correct for such effects by other means. There is currently no RTCM SSR message for ionospheric state parameters. Such messages are needed for accurate single frequency applications. The development of Iono messages will be the next step in the schedule of the RTCM State Space Representation Working Group.

Broadcast Corrections can be saved by BNC in files. The file name convention for Broadcast Correction files follows the convention for RINEX files except for the last character of the file name suffix which is set to "C".

Saved files contain blocks of records in plain ASCII format where - separate for each GNSS, message type, stream, and epoch - the begin of a block is indicated by a line like (examples):

! Orbits/Clocks: 30 GPS 0 Glonass CLK11
or
! Orbits/Clocks: 0 GPS 19 Glonass CLK11

Such line informs you about the number of records (here 30 and 19) carrying GPS or GLONASS related parameters you should receive next.

The first five parameters in each Broadcast Corrections record are:

• RTCM Version 3 message type number
• SSR message update interval indicator
• 0 = 1 sec
• 1 = 2 sec
• 2 = 5 sec
• 3 = 10 sec
• 4 = 15 sec
• 5 = 30 sec
• 6 = 60 sec
• 7 = 120 sec
• 8 = 240 sec
• 9 = 300 sec
• 10 = 600 sec
• 11 = 900 sec
• 12 = 1800 sec
• 13 = 3600 sec
• 14 = 7200 sec
• 15 = 10800 sec
• GPS Week
• Second in GPS Week
• GNSS Indicator and Satellite Vehicle Pseudo Random Number

In case of RTCM message types 1057 or 1063 (see Annex) these parameters are followed by

• IOD referring to Broadcast Ephemeris set
• Radial Component of Orbit Correction to Broadcast Ephemeris [m]
• Along-track Component of Orbit Correction to Broadcast Ephemeris [m]
• Cross-track Component of Orbit Correction to Broadcast Ephemeris [m]
• Velocity of Radial Component of Orbit Correction to Broadcast Ephemeris [m/s]
• Velocity of Along-track Component of Orbit Correction to Broadcast Ephemeris [m/s]
• Velocity of Cross-track Component of Orbit Correction to Broadcast Ephemeris [m/s]

Undefined parameters are set to zero "0.000".
Example:

...
1057 0 1538 211151.0 G18     1      0.034    0.011   -0.064      0.000    0.000    0.000
1057 0 1538 211151.0 G16    33     -0.005    0.194   -0.091      0.000    0.000    0.000
1057 0 1538 211151.0 G22    50      0.008   -0.082   -0.001      0.000    0.000    0.000
...
1063 0 1538 211151.0 R09   111     -0.011   -0.014    0.005      0.000    0.000    0.000
1063 0 1538 211151.0 R10    43      0.000   -0.009   -0.002      0.000    0.000    0.000
1063 0 1538 211151.0 R21    75     -0.029    0.108    0.107      0.000    0.000    0.000
...

In case of RTCM message types 1058 or 1064 (see Annex) the first five parameters are followed by

• IOD set to zero "0"
• C0 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m]
• C1 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m/s]
• C2 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m/s**2]

...
1058 0 1538 211151.0 G18     0      1.846       0.000    0.000
1058 0 1538 211151.0 G16     0      0.376       0.000    0.000
1058 0 1538 211151.0 G22     0      2.727       0.000    0.000
...
1064 0 1538 211151.0 R08     0      8.956       0.000    0.000
1064 0 1538 211151.0 R07     0     14.457       0.000    0.000
1064 0 1538 211151.0 R23     0      6.436       0.000    0.000
...

In case of RTCM message types 1060 or 1066 (see Annex) the first five parameters are followed by

• IOD referring to Broadcast Ephemeris set
• C0 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m]
• Radial Component of Orbit Correction to Broadcast Ephemeris [m]
• Along-track Component of Orbit Correction to Broadcast Ephemeris [m]
• Cross-track Component of Orbit Correction to Broadcast Ephemeris [m]
• C1 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m]
• Velocity of Radial Component of Orbit Correction to Broadcast Ephemeris [m/s]
• Velocity of Along-track Component of Orbit Correction to Broadcast Ephemeris [m/s]
• Velocity of Cross-track Component of Orbit Correction to Broadcast Ephemeris [m/s]
• C2 polynomial coefficient for Clock Correction to Broadcast Ephemeris [m]

...
1060 0 1538 211610.0 G30    82      2.533      0.635   -0.359   -0.598    0.000    0.000    0.000    0.000    0.000
1060 0 1538 211610.0 G31     5     -4.218     -0.208    0.022    0.002    0.000    0.000    0.000    0.000    0.000
1060 0 1538 211610.0 G32    28     -2.326      0.977   -0.576    0.142    0.000    0.000    0.000    0.000    0.000
...
1066 0 1538 211610.0 R22    27      1.585      2.024    2.615   -2.080    0.000    0.000    0.000    0.000    0.000
1066 0 1538 211610.0 R23    27      6.277      2.853    4.181    1.304    0.000    0.000    0.000    0.000    0.000
1066 0 1538 211610.0 R24    27      0.846      1.805   13.095    6.102    0.000    0.000    0.000    0.000    0.000
...

In case of RTCM message types 1059 or 1065 (see Annex) the first five parameters are followed by

• Number of Code Biases
• Indicator to specify the signal and tracking mode
• Code Bias
• Indicator to specify the signal and tracking mode
• Code Bias
• etc.

...
1059 0 1538 211151.0 G18 2 0   -0.010 11   -0.750 
1059 0 1538 211151.0 G16 2 0   -0.040 11   -0.430
1059 0 1538 211151.0 G22 2 0   -0.630 11   -2.400
...

Specify a directory for saving Broadcast Corrections in files. If the specified directory does not exist, BNC will not create Broadcast Correction files. Default value for Broadcast Corrections 'Directory' is an empty option field, meaning that no Broadcast Correction files will be created.

Select the length of the Broadcast Correction files. The default value is 1 day.

BNC can output epoch by epoch synchronized Broadcast Corrections in ASCII format on your local host (IP 127.0.0.1) through an IP 'Port'. Specify an IP port number to activate this function. The default is an empty option field, meaning that no Broadcast Correction output via IP port is generated.

The output format equals the format used for saving Broadcast Corrections in a file with the exception that the Mountpoint is added at each line's end.

The following is an example output for streams from mountpoints RTCMSSR, CLK10 and CLK11:

...
1057 0 1538 211151.0 G18     1      0.034    0.011   -0.064    0.000    0.000    0.000 RTCMSSR
1057 0 1538 211151.0 G16    33     -0.005    0.194   -0.091    0.000    0.000    0.000 RTCMSSR
1057 0 1538 211151.0 G22    50      0.008   -0.082   -0.001    0.000    0.000    0.000 RTCMSSR
...
1058 0 1538 211151.0 G18     0      1.846    0.000 RTCMSSR
1058 0 1538 211151.0 G16     0      0.376    0.000 RTCMSSR
1058 0 1538 211151.0 G22     0      2.727    0.000 RTCMSSR
...
1059 0 1538 211151.0 G18 2 0   -0.010 11   -0.750 RTCMSSR
1059 0 1538 211151.0 G16 2 0   -0.040 11   -0.430 RTCMSSR
1059 0 1538 211151.0 G22 2 0   -0.630 11   -2.400 RTCMSSR
...
1063 0 1538 211151.0 R09   111     -0.011   -0.014    0.005    0.0000    0.000    0.000 RTCMSSR
1063 0 1538 211151.0 R10    43      0.000   -0.009   -0.002    0.0000    0.000    0.000 RTCMSSR
1063 0 1538 211151.0 R21    75     -0.029    0.108    0.107    0.0000    0.000    0.000 RTCMSSR
...
1064 0 1538 211151.0 R08     0      8.956    0.000 RTCMSSR
1064 0 1538 211151.0 R07     0     14.457    0.000 RTCMSSR
1064 0 1538 211151.0 R23     0      6.436    0.000 RTCMSSR
...
1066 0 1538 211610.0 R24    27      0.846      1.805   13.095    6.102    0.000    0.000    0.000    0.000    0.000 CLK11
1066 0 1538 211610.0 R23    27      6.277      2.853    4.181    1.304    0.000    0.000    0.000    0.000    0.000 CLK11
1066 0 1538 211610.0 R22    27      1.585      2.024    2.615   -2.080    0.000    0.000    0.000    0.000    0.000 CLK11
...
1060 0 1538 211610.0 G32    28     -2.326      0.977   -0.576    0.142    0.000    0.000    0.000    0.000    0.000 CLK10
1060 0 1538 211610.0 G31     5     -4.218     -0.208    0.022    0.002    0.000    0.000    0.000    0.000    0.000 CLK10
1060 0 1538 211610.0 G30    82      2.533      0.635   -0.359   -0.598    0.000    0.000    0.000    0.000    0.000 CLK10
...

The source code for BNC comes with an example perl script 'test_tcpip_client.pl' that allows you to read BNC's Broadcast Corrections from the IP port.

When feeding a real-time GNSS network engine waiting epoch by epoch for synchronized Broadcast Corrections, BNC drops (only concerning IP port output) whatever is received later than 'Wait for full epoch' seconds. A value of 2 to 5 seconds could be an appropriate choice for that, depending on the latency of the incoming Broadcast Corrections stream and the delay acceptable by your application. A message such as "COCK1: Correction overaged by 5 sec" shows up in BNC's logfile if 'Wait for full epoch' is exceeded.

Specifying a value of '0' means that BNC immediately outputs all incoming Broadcast Ephemeris Corrections and does not drop any of them for latency reasons.

BNC can generate synchronized or unsynchronized observations epoch by epoch from all stations and satellites to feed a real-time GNSS network engine. Observations can be streamed out through an IP port and/or saved in a local file. The output is always in plain ASCII format and comprises the following parameters:

StationID | GPSWeek | GPSWeekSec | PRN, G=GPS, R=GLO | SlotNumber (if GLO) | Band/Frequency & trackingMode | Code | Phase | Doppler | SNR | SlipCount | ....

In case an observation is not available, its value is set to zero '0.000'.

Note on 'SlipCount':
It is the current understanding of BNC's authors that different slip counts could be referred to different phase measurements (i.e. L1C and L1P). The 'loss-of-lock' flags in RINEX are an example for making such kind of information available per phase measurement. However, it looks like we do have only one slip count in RTCM Version 3 for all phase measurements. As it could be that a receiver generates different slip counts for different phase measurements, we output one slip count per phase measurement to a listening real-time GNSS network engine.

The following is an output example for GPS and GLONASS:

...
CUT07 1683 493688.0000000 G05     1C   24584925.242  129195234.317       3639.020   38.812 40  2P   24584927.676  100671636.233 0.0   22.812 -1  2X   24584927.336  100671611.239 0.0   39.500 -1
CUT07 1683 493688.0000000 G04     1C   22598643.968  118756563.731      -1589.277   42.625 40  2P   22598649.391   92537559.230 0.0   29.125 -1
CUT07 1683 493688.0000000 G02     1C   23290004.062  122389588.008       -445.992   46.375 -1  2P   23290003.567   95368508.986 0.0   29.188 -1

CUT07 1683 493689.0000000 R16 -1  1C   19210052.313  102616872.230        364.063   53.375 42  1P   19210053.445  102616393.224 0.0   52.312 42  2P   19210057.785   79813218.557 0.0   50.188 -1
CUT07 1683 493689.0000000 R15  0  1C   20665491.149  110430900.266      -2839.875   49.188 -1  1P   20665491.695  110430900.278 0.0   47.625 -1  2P   20665497.559   85890714.522 0.0   48.000 -1
CUT07 1683 493689.0000000 R09 -2  1C   22028400.805  117630697.367       3584.840   47.625 -1  1P   22028401.586  117630607.367 0.0   45.688 -1  2P   22028406.746   91490549.182 0.0   41.625 -1
CUT07 1683 493689.0000000 R07  5  1C   24291127.360  130032400.255       4146.149   40.125 42  1P   24291128.492  130032400.259 0.0   39.312 42  2P   24291130.602  101136710.408 0.0   35.125 -1
CUT07 1683 493689.0000000 R05  1  1C   19740809.867  105526251.571       -921.679   54.125 42  1P   19740809.008  105526273.586 0.0   51.875 42  2P   19740814.051   82075815.588 0.0   50.812 -1
CUT07 1683 493689.0000000 R04  6  1C   23394651.125  125277095.951      -3385.191   40.875 42  1P   23394651.906  125277095.943 0.0   39.812 42  2P   23394658.125   97437771.004 0.0   39.000 -1
CUT07 1683 493689.0000000 G28     1C   25286905.648  132883677.970       4016.750   36.125 17  2P   25286911.715  103545663.916 0.0   14.812 11
CUT07 1683 493689.0000000 G23     1C   23018013.274  120961034.323      -1795.551   46.375 -1  2P   23018011.781   94255379.472 0.0   31.688 -1
CUT07 1683 493689.0000000 G20     1C   24055613.563  126413402.503      -3233.574   38.500 -1  2P   24055617.227   98504065.103 0.0   20.125 -1
CUT07 1683 493689.0000000 G16     1C   24846810.039  130571661.274      -2140.137   38.000 41  2P   24846811.477  101744166.486 0.0   18.625 -1
CUT07 1683 493689.0000000 G13     1C   21388182.664  112395102.592       -678.356   51.812 -1  2P   21388183.516   87580617.458 0.0   39.688 -1
CUT07 1683 493689.0000000 G10     1C   20656684.758  108551288.049       1726.191   52.875 -1  2P   20656687.016   84585420.340 0.0   42.625 -1
CUT07 1683 493689.0000000 G08     1C   20703057.860  108795261.566       1880.523   52.875 -1  2P   20703060.644   84775535.497 0.0   41.188 -1
CUT07 1683 493689.0000000 G07     1C   20200125.289  106152257.500       -603.082   53.312 41  2P   20200126.961   82716251.449 0.0   46.000 -1  2X   20200126.797   82716243.452 0.0   52.625 -1
CUT07 1683 493689.0000000 G05     1C   24584232.312  129191595.301       3639.047   38.875 41  2P   24584234.980  100668800.633 0.0   22.875 -1  2X   24584234.348  100668775.639 0.0   39.812 -1
CUT07 1683 493689.0000000 G04     1C   22598946.500  118758153.159      -1589.461   42.500 41  2P   22598951.570   92538797.744 0.0   29.125 -1
CUT07 1683 493689.0000000 G02     1C   23290088.758  122390034.211       -446.429   46.312 -1  2P   23290088.203   95368856.681 0.0   28.500 -1

CUT07 1683 493690.0000000 R16 -1  1C   19209984.633  102616508.497        363.305   53.500 43  1P   19209985.180  102616029.506 0.0   51.812 43  2P   19209989.871   79812935.655 0.0   50.188 -1
CUT07 1683 493690.0000000 R15  0  1C   20666023.047  110433740.264      -2840.242   49.188 -1  1P   20666023.945  110433740.275 0.0   47.500 -1  2P   20666029.574   85892923.403 0.0   47.625 -1
CUT07 1683 493690.0000000 R09 -2  1C   22027730.398  117627112.720       3584.305   47.688 -1  1P   22027730.828  117627022.726 0.0   46.188 -1  2P   22027735.988   91487761.121 0.0   41.688 -1
...

The source code for BNC comes with a perl script called 'test_tcpip_client.pl' that allows you to read BNC's (synchronized or unsynchronized) ASCII observation output from the IP port and print it on standard output.

Note that any socket connection of an application to BNC's synchronized or unsynchronized observations ports is recorded in the 'Log' tab on the bottom of the main window together with a connection counter, resulting in log records like 'New client connection on sync/usync port: # 1'.

The following figure shows the screenshot of a BNC configuration where a number of streams is pulled from different NTRIP Broadcasters to feed a GNSS engine via IP port output.

Figure: Synchronized BNC output via IP port to feed a GNSS real-time engine.

BNC can produce synchronized observations in ASCII format on your local host (IP 127.0.0.1) through an IP 'Port'. Synchronized means that BNC collects all data for any specific epoch which become available within a certain number of latency seconds (see 'Wait for Full Epoch' option). It then - epoch by epoch - outputs whatever has been received. Specify an IP port number here to activate this function. The default is an empty option field, meaning that no binary synchronized output is generated.

When feeding a real-time GNSS network engine waiting for synchronized input epoch by epoch, BNC drops whatever is received later than 'Wait for full epoch' seconds. A value of 3 to 5 seconds could be an appropriate choice for that, depending on the latency of the incoming streams and the delay acceptable for your real-time GNSS product. Default value for 'Wait for full epoch' is 5 seconds.

Note that 'Wait for full epoch' does not affect the RINEX Observation file content. Observations received later than 'Wait for full epoch' seconds will still be included in the RINEX Observation files.

Select the synchronized observation output sampling interval in seconds. A value of zero '0' tells BNC to send/store all received epochs. This is the default value.

Specifies the full path to a 'File' where synchronized observations are saved in plain ASCII format. The default value is an empty option field, meaning that no ASCII output file is created.

Beware that the size of this file can rapidly increase depending on the number of incoming streams. This option is primarily meant for testing and evaluation.

BNC can produce unsynchronized observations from all configured streams in ASCII format on your local host (IP 127.0.0.1) through an IP 'Port'. Unsynchronized means that BNC immediately forwards any received observation to the port. Specify an IP port number here to activate this function. The default is an empty option field, meaning that no binary unsynchronized output is generated.

You may use BNC to feed a serial connected device like an GNSS receiver. For that an incoming streams can be forwarded to a serial port. The following figure shows the screenshot of an example situation where BNC pulls a VRS stream from an NTRIP Broadcaster to feed a serial connected rover.

Figure: BNC pulling a VRS stream to feed a serial connected rover.

Enter a 'Mountpoint' to forward its corresponding stream to a serial connected GNSS receiver.

When selecting one of the serial communication options listed below, make sure that you pick those configured to the serial connected receiver.

Enter the serial 'Port name' selected on your host for communication with the serial connected receiver. Valid port names are

Windows:       COM1, COM2
Linux:         /dev/ttyS0, /dev/ttyS1
FreeBSD:       /dev/ttyd0, /dev/ttyd1
Digital Unix:  /dev/tty01, /dev/tty02
HP-UX:         /dev/tty1p0, /dev/tty2p0
SGI/IRIX:      /dev/ttyf1, /dev/ttyf2
SunOS/Solaris: /dev/ttya, /dev/ttyb

Note that you must plug a serial cable in the port defined here before you start BNC.

Select a 'Baud rate' for the serial output link. Note that using a high baud rate is recommended.

Select a 'Flow control' for the serial output link. Note that your selection must equal the flow control configured to the serial connected device. Select 'OFF' if you don't know better.

Select the 'Parity' for the serial output link. Note that parity is often set to 'NONE'.

Select the number of 'Data bits' for the serial output link. Note that often '8' data bits are used.

Select the number of 'Stop bits' for the serial output link. Note that often '1' stop bit is used.

Select 'Auto' to automatically forward all NMEA-GGA messages coming from your serial connected GNSS receiver to the NTRIP Broadcaster and/or save them in a file.

Forwarding valid NMEA-GGA messages to the NTRIP Broadcaster is required for receiving 'Virtual Reference Station' (VRS) streams. Thus, in case your serial connected receiver is not capable to provide them, the alternative for VRS streams is a 'Manual' simulation of an initial NMEA-GGA message. Its contents is based on the approximate (editable) latitude/longitude from the broadcaster's source-table and an approximate VRS height to be specified.

In summary: select 'Manual' only when handling a VRS stream and your serial connected GNSS receiver doesn't generate NMEA-GGA messages. Select 'Auto' otherwise.

Specify the full path to a file where NMEA messages coming from your serial connected receiver are saved.

Specify an approximate 'Height' above mean sea level in meter for your VRS to simulate an initial NMEA-GGA message. Latitude and longitude for that (editable) are taken from the broadcaster's source-table.

This option concerns only 'Virtual Reference Stations' (VRS). Its setting is ignored in case of streams coming from physical reference stations.

At any time an incoming stream might become unavailable or corrupted. In such cases, it is important that the BNC operator and/or the stream providers become aware of the situation so that necessary measures can be taken to restore the stream. Furthermore, continuous attempts to decode a corrupted stream can generate unnecessary workload for BNC. Outages and corruptions are handled by BNC as follows:

Stream outages: BNC considers a connection to be broken when there are no incoming data detected for more than 20 seconds. When this occurs, BNC will attempt to reconnect at a decreasing rate. It will first try to reconnect with 1 second delay, and again in 2 seconds if the previous attempt failed. If the attempt is still unsuccessful, it will try to reconnect within 4 seconds after the previous attempt and so on. The wait time doubles each time with a maximum wait time of 256 seconds.

Stream corruption: Not all bits chunk transfers to BNC's internal decoders return valid observations. Sometimes several chunks might be needed before the next observation can be properly decoded. BNC buffers all the outputs (both valid and invalid) from the decoder for a short time span (size derived from the expected 'Observation rate') and then determines whether a stream is valid or corrupted.

Outage and corruption events are reported in the 'Log' tab. They can also be passed on as parameters to a shell script or batch file to generate an advisory note to BNC operator or affected stream providers. This functionality lets users utilize BNC as a real-time performance monitor and alarm system for a network of GNSS reference stations.

BNC can collect all returns (success or failure) coming from a decoder within a certain short time span to then decide whether a stream has an outage or its content is corrupted. This procedure needs a rough a priory estimate of the expected observation rate of the incoming streams.

An empty option field (default) means that you don't want explicit information from BNC about stream outages and incoming streams that cannot be decoded.

Event 'Begin_Failure' will be reported if no data is received continuously for longer than the 'Failure threshold' time. Similarly, event 'Begin_Corrupted' will be reported when corrupted data is detected by the decoder continuously for longer than this 'Failure threshold' time. The default value is set to 15 minutes and is recommended so not to inundate user with too many event reports.

Note that specifying a value of zero '0' for the 'Failure threshold' will force BNC to report any stream failure immediately. Note also that for using this function you need to specify the 'Observation rate'.

Once a 'Begin_Failure' or 'Begin_Corrupted' event has been reported, BNC will check for when the stream again becomes available or uncorrupted. Event 'End_Failure' or 'End_Corrupted' will be reported as soon as valid observations are again detected continuously throughout the 'Recovery threshold' time span. The default value is set to 5 minutes and is recommended so not to innundate users with too many event reports.

Note that specifying a value of zero '0' for the 'Recovery threshold' will force BNC to report any stream recovery immediately. Note also that for using this function you need to specify the 'Observation rate'.

As mentioned previously, BNC can trigger a shell script or a batch file to be executed when one of the events described are reported. This script can be used to email an advisory note to network operator or stream providers. To enable this feature, specify the full path to the script or batch file in the 'Script' field. The affected stream's mountpoint and type of event reported ('Begin_Outage', 'End_Outage', 'Begin_Corrupted' or 'End_Corrupted') will then be passed on to the script as command line parameters (%1 and %2 on Windows systems or $1 and $2 on Unix/Linux/Mac systems) together with date and time information.

Leave the 'Script' field empty if you do not wish to use this option. An invalid path will also disable this option.

Examples for command line parameter strings passed on to the advisory 'Script' are:

FFMJ0 Begin_Outage 08-02-21 09:25:59
FFMJ0 End_Outage 08-02-21 11:36:02 Begin was 08-02-21 09:25:59

#!/bin/bash
sleep $((60*RANDOM/32767))
cat | mail -s "NABU: $1" email@address <<!
Advisory Note to BNC User,
Please note the following advisory received from BNC.
Stream: $*
Regards, BNC
!

Note the sleep command in this script which causes the system to wait for a random period of up to 60 seconds before sending the email. This should avoids overloading your mail server in case of a simultaneous failure of many streams.

This section describes several miscellaneous options which can be applied for a single stream (mountpoint) or for all configured streams.

The following figure shows RTCM message numbers contained in stream 'CONZ0' and the message latencies recorded every 10 seconds.

Figure: RTCM message numbers and latencies.

Specify a mountpoint to apply one or several of the 'Miscellaneous' options to the corresponding stream. Enter 'ALL' if you want to apply these options to all configured streams. An empty option field (default) means that you don't want BNC to apply any of these options.

BNC can average latencies per stream over a certain period of GPS time, the 'Log latency' interval. Mean latencies are calculated from the individual latencies of at most one (first incoming) observation or correction to Broadcast Ephemeris per second. The mean latencies are then saved in BNC's logfile. Note that computing correct latencies requires the clock of the host computer to be properly synchronized. Note further that the latencies available from the 'Latency' tab on the bottom of the main window represent individual latencies and not the mean latencies for the logfile.

Latency: Latency is defined in BNC by the following equation:

    UTC time provided by BNC's host
  - GPS time of currently processed epoch
  + Leap seconds between UTC and GPS time
  --------------
  = Latency

Statistics: BNC counts the number of GPS seconds covered by at least one observation. It also estimates an observation rate (independent from the a priory specified 'Observation rate') from all observations received throughout the first full 'Log latency' interval. Based on this rate, BNC estimates the number of data gaps when appearing in subsequent intervals.

Latencies of observations or corrections to Broadcast Ephemeris and statistical information can be recorded in the 'Log' tab at the end of each 'Log latency' interval. A typical output from a 1 hour 'Log latency' interval would be:

08-03-17 15:59:47 BRUS0: Mean latency 1.47 sec, min 0.66, max 3.02, rms 0.35, 3585 epochs, 15 gaps

Select a 'Log latency' interval to activate this function or select the empty option field if you do not want BNC to log latencies and statistical information.

When configuring a GNSS receiver for RTCM stream generation, the firmware's setup interface may not provide details about RTCM message types. As reliable information concerning stream contents should be available i.e. for NTRIP Broadcaster operators to maintain the broadcaster's source-table, BNC allows to scan RTCM streams for incoming message types and printout some of the contained meta-data. The idea for this option arose from 'InspectRTCM', a comprehensive stream analyzing tool written by D. Stoecker.

Tick 'Scan RTCM' to scan RTCM Version 2 or 3 streams and log all contained

• Numbers of incoming message types
• Antenna Reference Point (ARP) coordinates
• Antenna Phase Center (APC) coordinates
• Antenna height above marker
• Antenna descriptor.

Note that in RTCM Version 2 the message types 18 and 19 carry only the observables of one frequency. Hence it needs two type 18 and 19 messages per epoch to transport the observations from dual frequency receivers.

Logged time stamps refer to message reception time and allow understanding repetition rates. Enter 'ALL' if you want to log this information from all configured streams. Beware that the size of the logfile can rapidly increase depending on the number of incoming RTCM streams.

This option is primarily meant for testing and evaluation. Use it to figure out what exactly is produced by a specific GNSS receiver's configuration. An empty option field (default) means that you don't want BNC to print the message type numbers and antenna information carried in RTCM streams.

BNC can derive coordinates for a rover position following the Precise Point Positioning (PPP) approach. It uses either code or code plus phase data in ionosphere free linear combinations P3 or L3. Besides pulling a stream of observations from a dual frequency receiver, this also

• requires pulling in addition a stream carrying satellite orbit and clock corrections to Broadcast Ephemeris in the form of RTCM Version 3 'State Space Representation' (SSR) messages. Note that for BNC these Broadcast Corrections need to be referred to the satellite's Antenna Phase Center (APC). Streams providing such messages are listed on http://igs.bkg.bund.de/ntrip/orbits. Stream 'CLK11' on NTRIP Broadcaster 'products.igs-ip.net:2101' is an example.
• may require pulling a stream carrying Broadcast Ephemeris available as RTCM Version 3 message types 1019, 1020, and 1045. This is a must only when the stream coming from the receiver does not contain Broadcast Ephemeris or provides them only at very low repetition rate. Streams providing such messages are listed on http://igs.bkg.bund.de/ntrip/ephemeris. Stream 'RTCM3EPH' on caster 'products.igs-ip.net:2101' is an example.

The following figure provides the screenshot of an example PPP session with BNC.

Figure: Precise Point Positioning with BNC, PPP Panel 1.

Figure: Precise Point Positioning with BNC, PPP Panel 2.

PPP results are shown in the 'Log' tab on the bottom of BNC's main window. Depending on the processing options, the following values are shown about once per second (example):

10-09-08 09:14:06 FFMJ1  PPP 09:14:04.0 12    4053457.429 +-  2.323     617730.551 +-  1.630    4869395.266 +-  2.951

The 'PPP' string in that is followed by the selected mounpoint, a PPP time stamp in GPS Time, the number of processed satellites, and XYZ coordinates with their formal errors as derived from the implemented filter in [m]. The implemented algorithm includes outlier and cycle slip detection. The maximum for accepted residuals is hard coded to 10 meters for code observations and 10 centimeters for phase observations.

More detailed PPP results are saved in BNC's logfile. Depending on the selected processing options you find

• code and phase residuals for GPS and GLONASS and Galileo in [m],
• receiver clock errors in [m],
• a-priori and correction values of tropospheric zenith delay in [m],
• time offset between GPS time and Galileo time in [m],
• L3 biases, also known as 'floated ambiguities', given per satellite.

10-12-06 18:10:50 Single Point Positioning of Epoch 18:10:48.0
--------------------------------------------------------------
18:10:48.0 RES G04   L3    0.0165   P3   -0.1250
18:10:48.0 RES G11   L3    0.0150   P3    0.7904
18:10:48.0 RES G13   L3    0.0533   P3    0.4854
18:10:48.0 RES G17   L3   -0.0277   P3    1.2920
18:10:48.0 RES G20   L3   -0.0860   P3   -0.1186
18:10:48.0 RES G23   L3    0.0491   P3   -0.1052
18:10:48.0 RES G31   L3    0.0095   P3   -3.2929
18:10:48.0 RES G32   L3    0.0183   P3   -3.8800
18:10:48.0 RES R05   L3   -0.0077
18:10:48.0 RES R06   L3    0.0223
18:10:48.0 RES R15   L3   -0.0020
18:10:48.0 RES R16   L3    0.0156
18:10:48.0 RES R20   L3   -0.0247
18:10:48.0 RES R21   L3    0.0014
18:10:48.0 RES R22   L3   -0.0072
18:10:48.0 RES E52   L3   -0.0475   P3   -0.1628
18:10:48.0 RES G04   L3    0.0166   P3   -0.1250
18:10:48.0 RES G11   L3    0.0154   P3    0.7910
18:10:48.0 RES G13   L3    0.0535   P3    0.4855
18:10:48.0 RES G17   L3   -0.0272   P3    1.2925
18:10:48.0 RES G20   L3   -0.0861   P3   -0.1188
18:10:48.0 RES G23   L3    0.0489   P3   -0.1055
18:10:48.0 RES G31   L3    0.0094   P3   -3.2930
18:10:48.0 RES G32   L3    0.0183   P3   -3.8800
18:10:48.0 RES R05   L3   -0.0079
18:10:48.0 RES R06   L3    0.0223
18:10:48.0 RES R15   L3   -0.0020
18:10:48.0 RES R16   L3    0.0160
18:10:48.0 RES R20   L3   -0.0242
18:10:48.0 RES R21   L3    0.0016
18:10:48.0 RES R22   L3   -0.0072
18:10:48.0 RES E52   L3   -0.0474   P3    0.1385

    clk     =  64394.754 +-  0.045
    trp     =   2.185 +0.391 +-  0.001
    offset  =   -415.400 +-  0.137
    amb G17 =     11.942 +-  0.045
    amb G23 =    248.892 +-  0.044
    amb G31 =    254.200 +-  0.045
    amb G11 =    -12.098 +-  0.044
    amb G20 =   -367.765 +-  0.044
    amb G04 =    259.588 +-  0.044
    amb E52 =      6.124 +-  0.130
    amb G32 =    201.496 +-  0.045
    amb G13 =   -265.658 +-  0.044
    amb R22 =   -106.246 +-  0.044
    amb R21 =   -119.605 +-  0.045
    amb R06 =     41.328 +-  0.044
    amb R15 =    163.453 +-  0.044
    amb R20 =   -532.746 +-  0.045
    amb R05 =   -106.603 +-  0.044
    amb R16 =   -107.830 +-  0.044

Note that BNC's 'PPP Client' option can also be used offline for debugging purposes. Apply the 'File Mode' command line options for that to read a file containing synchronized observations, orbit and clock correctors, and Broadcast Ephemeris. Such a file must be generated using BNC's 'Raw output file' option. Example:

bnc.exe --conf c:\temp\BNC.ppp --file c:\temp\FFMJ1

When using the PPP option, it is important to understand which effects are corrected by BNC.

• BNC does correct for Solid Earth Tides and Phase Windup.
• Satellite Antenna Phase Center Offsets are not corrected because applied orbit/clock corrections are referred to the satellite's antenna phase center.
• Satellite Antenna Phase Center Variations are neglected because this is a small effect usually less than 2 centimeters.
• Observations can be corrected for a Receiver Antenna Offset. Depending on whether or not this correction is applied, the estimated position is either that of the receiver's antenna phase center or that of the receiver's Antenna Reference Point.
• Receiver Antenna Phase Center Variations are not included in the model. The bias caused by this neglect depends on the receiver antenna type. For most antennas it is smaller than a few centimeters.
• Ocean and atmospheric loading is neglected. Atmospheric loading is pretty small. Ocean loading is usually also a small effect but may reach up to about 10 centimeters for coastal stations.
• Rotational deformation due to polar motion (Polar Tides) is not corrected because this is a small effect usually less than 2 centimeters.

Specify the Point Positioning mode you want to apply and the mountpoints for observations and Broadcast Corrections.

Choose between plain Single Point Positioning (SPP) and Precise Point Positioning (PPP) in 'Realtime' or 'Post-Processing' mode.

Specify an 'Observations Mountpoint' from the list of selected 'Streams' you are pulling if you want BNC to derive coordinates for the affected rover position through a Point Positioning solution.

Specify a Broadcast Ephemeris 'Corrections Mountpoint' from the list of selected 'Streams' you are pulling if you want BNC to correct your positioning solution accordingly.

Enter the reference coordinate components X,Y,Z of the receiver's position in meters if known. This option makes only sense for static observations. Default are empty option fields, meaning that the antenna's XYZ position is unknown.

Once XYZ coordinate components are defined, the 'PPP' line in BNC's logfile is extended by Nort, East and Up displacements to (example):

10-08-09 06:01:56 FFMJ1  PPP 06:02:09.0 11    4053457.628 +-  2.639     617729.438 +-  1.180    4869396.447 +-  1.921  NEU   -0.908   -0.571    1.629

The parameters following the 'NEU' string provide Nort, East and Up components of the current coordinate displacement in meters.

You may like to specify North, East and Up components of an antenna eccentricity which is the difference between a nearby marker position and the antenna phase center. If you do so BNC will produce coordinates referring to the marker position and not referring to the antenna phase center..

BNC allows to output results from Precise Point Positioning in NMEA format. It can also plot a time series of North, East and UP displacements of coordinate components.

The NMEA sentences generated about once per second are pairs of

• GPGGA sentences which mainly carry the estimated latitude, longitude, and height values, plus
• GPRMC sentences which mainly carry date and time information.

Specify the full path to a file where Point Positioning results are saved as NMEA messages. The default value for 'NMEA file' is an empty option field, meaning that BNC will not saved NMEA messages into a file.

Note that Tomoji Takasu has written a program called RTKPlot for visualizing NMEA strings. It is available from http://gpspp.sakura.ne.jp/rtklib/rtklib.htm and compatible with the NMEA output of BNC's 'PPP Client' option.

Specify the IP port number of a local port where Point Positioning results become available as NMEA messages. The default value for 'NMEA Port' is an empty option field, meaning that BNC does not provide NMEA messages vi IP port. Note that the NMEA file output and the NMEA IP port output are the same.

NASA's 'World Wind' software (see http://worldwindcentral.com/wiki/NASA_World_Wind_Download) can be used for real-time visualization of positions provided through BNC's NMEA IP output port. You need the 'GPS Tracker' plug-in available from http://worldwindcentral.com/wiki/GPS_Tracker for that. The 'Word Wind' is not meant for showing centimeter level details.

PPP time series of North (red), East(green) and Up (blue) displacements will be plotted in the 'PPP Plot' tab when this option is ticked. Values will be either referred to an XYZ reference coordinate (if specified) or referred to the first estimated XYZ coordinate. The sliding PPP time series window will cover the period of the latest 5 minutes.

Note that a PPP time series makes only sense for a stationary operated receiver.

When in 'Post-Processing mode

• specifying a RINEX Observation, a RINEX Navigation and a Broadcast Corrections file leads to a PPP solution.
• specifying only a RINEX Observation and a RINEX Navigation file and no Broadcast Corrections file leads to a SPP solution.

BNC accepts RINEX Version 2 as well as RINEX Version 3 observation or navigation file formats. Files carrying Broadcast Corrections must have the format produced by BNC in the 'Broadcast Corrections' tab.

Post Processing PPP results can be saved in a specific output file.

BNC allows to correct observations for antenna phase center offsets and variations.

IGS provides a file containing absolute phase center corrections for GNSS satellite and receiver antennas in ANTEX format. Entering the full path to such an ANTEX file is required for correcting observations for antenna phase center offsets and variations. It allows you to specify the name of your receiver's antenna (as contained in the ANTEX file) to apply such corrections.

Default is an empty option field meaning that you don't want to correct observations for antenna phase center offsets and variations.

Specify the receiver's antenna name as defined in your ANTEX file. Observations will be corrected for the antenna phase center's offset which may result in a reduction of a few centimeters at max. Corrections for phase center variations are not yet applied by BNC. The specified name must consist of 20 characters. Add trailing blanks if the antenna name has less than 20 characters. Examples:

'JPSREGANT_SD_E      ' (no radome)
'LEIAT504        NONE' (no radome)
'LEIAR25.R3      LEIT' (radome)

Default is an empty option field meaning that you don't want to correct observations for antenna phase center offsets.

BNC allows correcting observations for satellite antenna phase center offsets. (This option is not yet implemented.)

Satellite orbit and clock corrections refer to the satellite's antenna phase centers and hence observations are not to be corrected for satellite antenna phase center offsets. Tick 'Apply Sat. Ant. Offsets' to force BNC to correct observations for satellite antenna phase center offsets.

Default is to not correct observations for satellite antenna phase center offsets.

BNC allows using different Point Positioning processing options depending on the capability of the involved receiver and the application in mind. It also allows introducing specific sigmas for code and phase observations as well as for reference coordinates and troposphere estimates. You may also like to carry out your PPP solution in Quick-Start mode or enforce BNC to restart a solution if the length of an outage exceeds a certain threshold.

By default BNC applies a Point Positioning solution using an ionosphere free P3 linear combination of code observations. Tick 'Use phase obs' for an ionosphere free L3 linear combination of phase observations.

BNC estimates the tropospheric delay according to equation

T(z) = T_apr(z) + dT / cos(z)

By default BNC does not estimate troposphere parameters. Tick 'Estimate tropo' to estimate troposphere parameters together with the coordinates and save T_apr and dT in BNC's log file.

By default BNC does not process GLONASS but only GPS observations when in Point Positioning mode. Tick 'Use GLONASS' to use GLONASS observations in addition to GPS (and Galileo if specified) for estimating coordinates in Point Positioning mode.

By default BNC does not process Galileo but only GPS observations when in Point Positioning mode. Tick 'Use Galileo' to use Galileo observations in addition to GPS (and GLONASS if specified) for estimating coordinates in Point Positioning mode.

Zero value (or empty field) means that BNC processes each epoch of data immediately after its arrival using satellite clock corrections available at that time. Non-zero value 'Sync Corr' means that the epochs of data are buffered and the processing of each epoch is postponed till the satellite clock corrections not older than 'Sync Corr' are available. Specifying a value of half the update rate of the clock corrections as 'Sync Corr' (i.e. 5 sec) may be appropriate. Note that this causes an additional delay of the PPP solutions in the amount of the update rate.

Using observations in sync with the corrections can avoid a possible high frequency noise of PPP solutions. Such noise could result from processing observations regardless of how late after a clock correction they were received. Note that applying the 'Sync Corr' option significantly reduces the PPP computation effort for BNC.

Default is an empty option field, meaning that you want BNC to process observations immediately after their arrival through applying the latest received clock correction.

Enter the length of a sliding time window in minutes. BNC will continuously output moving average values ns and their RMS as computed from those individual values obtained most recently throughout this period. RMS values presented for XYZ coordinates and tropospheric zenit path delays are bias reduced while RMS values for Nort/East/Up (NEU) displacements are not. Averaged values for XYZ coordinates and their RMS are marked with string "AVE-XYZ" in BNC's log file and 'Log' section while averaged values for NEU displacements and their RMS are marked with string "AVE-NEU" and averaged values for the tropospheric delays and their RMS are marked with string "AVE-TRP". Example:

10-09-08 09:13:05 FFMJ1  AVE-XYZ 09:13:04.0   4053455.948 +-  0.284     617730.422 +-  0.504    4869397.692 +-  0.089
10-09-08 09:13:05 FFMJ1  AVE-NEU 09:13:04.0    1.043 +-  0.179    0.640 +-  0.456    1.624 +-  0.331
10-09-08 09:13:05 FFMJ1  AVE-TRP 09:13:04.0         2.336 +-  0.002

Entering any positive value up to 1440 (24h mean value) is allowed. An empty option field (default) means that you don't want BNC to output moving average positions into the log file and the 'Log' section. Note that averaging positions makes only sense for a stationary receiver.

Enter the lenght of a startup period in seconds for which you want to fix the PPP solution to a known XYZ coordinate. Constraining coordinate components is done in BNC through setting the 'XYZ White Noise' temporarily to zero.

This so-called Quick-Start option allows the PPP solutions to rapidly converge after startup. It requires that the antenna remains unmoved on the know position throughout the defined period. A value of 120 (default) is likely to be an appropriate choice for 'Quick-Start'

You may need to create your own reference coordinate through running BNC for an hour in normal mode before applying the Quick-Start option. Don't forget to introduce a realistic sigma 'XYZ Ini' according to the coordinate's precision.

Figure: BNC in 'Quick-Start' mode (PPP, Panel 1)

Figure: BNC in 'Quick-Start' mode (PPP, Panel 2)

Specify a 'Maximum Solution Gap' in seconds. Should the time span between two consecutive solutions exceed this limit, the algorithm returns into the Quick-Start mode and fixes the introduced reference coordinate for the specified Quick-Start period. A value of '120' seconds could be an appropriate choice.

This option makes only sense for a stationary operated receiver where solution convergence can be enforced because a good approximation for the rover position is known. Default is an empty option field, meaning that you don't want BNC to return into the Quick-Start mode after failures caused i.e. by longer lasting outages.

You may like to introduce specific sigmas for code and phase observations and for the estimation of troposphere parameters.

When 'Use phase obs' is set in BNC, the PPP solution will be carried out using both, code and phase observations. A sigma of 5.0 m for code observations and a sigma of 0.02 m for phase observations (defaults) are used to combine both types of observations. As the convergence characteristic of a PPP solution can be influenced by the ratio of the sigmas for code and phase, you may like to introduce you own sigmas for code and phase observations which differ from the default values.

• Introducing a smaller sigma (higher accuracy) for code observations or a larger sigma for phase observations leads to better results shortly after program start. However, it may take more time till you finally get the best possible solutions.
• Introducing a larger sigma (lower accuracy) for code observations or a smaller sigma for phase observations may lead to less accurate results shortly after program start and thus a prolonged period of convergence but could provide better positions in the long run.

Specify a sigma for code observations. Default is 5.0 m.

Specify a sigma for phase observations. Default is 0.02 m.

Enter a sigma in meters for the initial XYZ coordinate components. A value of 100.0 (default) may be an appropriate choice. However, this value may be significantly smaller (i.e. 0.01) when starting for example from a station with known XZY position in Quick-Start mode.

Enter a sigma in meters for the 'White Noise' of estimated XYZ coordinate components. A value of 100.0 (default) may be appropriate considering the potential movement of a rover.

Enter a sigma in meters for the a-priory model based tropospheric delay estimation. A value of 0.1 (default) may be an appropriate choice.

Enter a sigma in meters per second to describe the expected variation of the tropospheric effect. Supposing 1Hz observation data, a value of 3e-6 (default) would mean that the tropospheric effect may vary for 3600 * 3e-6 = 0.01 meters per hour.

BNC allows to process several orbit and clock corrections streams in real-time to produce, encode, upload and save a combination of Broadcast Corrections from various providers. It is so far only the satellite clock corrections which are combined while orbit corrections in the combination product as well as the product update rates are just taken over from one of the incoming Broadcast Correction streams. Combining only clock corrections using a fixed orbit reference has the possibility to introduce some analysis inconsistencies. We may therefore eventually consider improvements on this approach. The clock combination can be based either on a plain 'Single-Epoch' or on a 'Kalman' Filter approach.

In the Kalman Filter approach satellite clocks estimated by individual Analyses Centers (ACs) are used as pseudo observations within the adjustment process. Each observation is modeled as a linear function (actually a simple sum) of three estimated parameters: AC specific offset, satellite specific offset common to all ACs, and the actual satellite clock correction which represents the result of the combination. These three parameter types differ in their statistical properties. The satellite clock offsets are assumed to be static parameters while AC specific and satellite specific offsets are stochastic parameters with appropriate white noise. The solution is regularized by a set of minimal constraints.

Removing the AC-dependent biases as well as possible is a major issue with clock combinations. Since they vary in time, it can be tricky to do this. Otherwise, there will be artificial jumps in the combined clock stream if one or more AC contributions drop out for certain epochs. Here the Kalman Filter approach is expected to do better than the Single-Epoch approach.

In view of IGS real-time products, the 'Combination' functionality has been integrated in BNC because

• the software with its Graphic User Interface and wide range of supported Operation Systems represents a perfect platform to process many Broadcast Correction streams in parallel;
• outages of single AC product streams can be mitigated through merging several incoming streams into a combined product;
• generating a combination product from several AC products allows detecting and rejecting outliers;
• a Combination Center (CC) can operate BNC to globally disseminate a combination product via NTRIP broadcast;
• an individual AC could prefer to disseminate a stream combined from primary and backup IT resources to reduce outages;
• it enables a BNC PPP user to follow his own preference in combining streams from individual ACs for Precise Point Positioning;
• it allows an instantaneous quality control of the combination process not only in the time domain but also in the space domain; this can be done through direct application of the combination stream in a PPP solution even without prior stream upload to an NTRIP Broadcaster;
• it provides the means to output SP3 files containing precise orbit and clock information for further processing using other tools than BNC.

Note that the combination process requires real-time access to Broadcast Ephemeris. So, in addition to the orbit and clock corrections streams BNC must pull a stream carrying Broadcast Ephemeris in the form of RTCM Version 3 messages. Stream 'RTCM3EPH' on caster products.igs-ip.net is an example for that.

A combination is carried out every 5 seconds. If incoming streams have different rates, only epochs that correspond to the 5 seconds update rate are used.

Note further that you need to tick the 'Use GLONASS' option which is part ot the 'PPP (2)' panel in case you want to produce an GPS plus GLONASS combination.

With respect to IGS, it is important to understand that a major effect in the combination of GNSS orbit and clock corrections streams is the selection of ACs to include. It is likely that a combination product could be improved in accuracy by using only the best two or three ACs. However, with only a few ACs to depend on, the reliability of the combination product could suffer and the risk of total failures increases. So there is an important tradeoff here that must be considered when selecting streams for a combination. The major strength of a combination product is its reliability and stable median performance which can be much better than that of any single AC product.

This comment applies in situations where we have a limited number of solutions to combine and their quality varies significantly. The situation may be different when the total number of ACs is larger and the range of AC variation is smaller. In that case, a standard full combination is probably the best.

The following recursive algorithm is used to detect orbit outliers in the Kalman Filter combination when corrections are provided by several ACs:
Step 1: We don't produce a combination for a certain satellite if only one AC provides corrections for it.
Step 2: A mean satellite position is calculated as the average of positions from all ACs.
Step 3: For each AC and satellite the 3D distance between individual and mean satellite position is calculated.
Step 4: We find the greatest difference between AC specific and mean satellite positions.
Step 5: If that is less than 0.2 m the conclusion is that we don't have an outlier and can proceed to the next epoch.
Step 6: If that is greater 0.2 m then corrections of the affiliated AC are ignored for the affected epoch and the outlier detection restarts with step 1.

Note that BNC can produce an internal PPP solution from combined Broadcast Corrections. For that you have to specify the keyword 'INTERNAL' as 'Corrections Mounpoint' in the PPP (1) panel.

Note further that the combination procedure in BNC also - formally - works with only one Broadcast Corrections stream specified for combination.

The part of BNC which enables the combination of orbit and clock corrections streams is not intended for publication under GNU General Public License (GPL). However, pre-compiled BNC binaries which support the 'Combination' option will be available for personal usage.

Hit the 'Add Row' button, double click on the 'Mountpoint' field, enter a Broadcast Corrections mountpoint from the 'Streams' section and hit Enter. Then double click on the 'AC Name' field to enter your choice of an abbreviation for the Analysis Center (AC) providing the stream. Finally, double click on the 'Weight' field to enter a weight to be applied to this stream in the combination. The stream processing can already be started with only one corrections stream configured for combination.

Note that an appropriate 'Wait for full epoch' value needs to be specified for the combination under the 'Broadcast Corrections' tab. To give an example: a value of '15' sec would make sense if the update rate of incoming clock corrections is 10 sec.

The sequence of entries in the 'Combination Table' is not of importance. Note that the orbit information in the final combination stream is just copied from one of the incoming streams. The stream used for providing the orbits may vary over time: if the orbit providing stream has an outage then BNC switches to the next remaining stream for getting hold of the orbit information.

Default is an empty 'Combination Table' meaning that you don't want BNC to combine orbit and clock corrections streams.

Hit 'Add Row' button to add another row to the 'Combination Table' or hit the 'Delete' button to delete the highlighted row(s).

The following screenshots describe an example setup of BNC when combining Broadcast Correction streams and upload them to an NTRIP Broadcaster. Note that it requires specifying options under tabs 'Combination' and 'Upload (clk)'. The example uses the combination product to simultaneously carry out an 'INTERNAL' PPP solution in Quickstart mode which allows monitoring the quality of the combination product in the space domain.

Figure: BNC combining Broadcast Correction streams.

Figure: BNC uploading the combined Broadcast Corrections stream.

Figure: 'INTERNAL' PPP with BNC using combined Broadcast Corrections stream.

Select a clock combination method. Available options are Kalman 'Filter' and 'Single-Epoch. It is suggested to use the Kalman Filter approach in case the combined stream of Broadcast Corrections is intended for Precise Point Positioning support.

BNC combines all incoming clocks according to specified weights. Individual clock estimates that differ by more than 'Maximal Residuum' meters from the average of all clocks will be ignored.

Default is a 'Maximal Residuum' of 999.0 meters

BNC can upload streams carrying orbit and clock corrections to Broadcast Ephemeris in radial, along-track and cross-track components if they are

1. either generated by BNC as a combination of several individual Broadcast Correction streams coming from an number of real-time Analysis Centers (ACs), see section 'Combination',
2. or generated by BNC because the program receives an ASCII stream of precise satellite orbits and clocks via IP port from a connected real-time GNSS engine. Such a stream would be expected in a plain ASCII format and the associated 'decoder' string would have to be 'RTNET'.

• Continuously receive up-to-date Broadcast Ephemeris carrying approximate orbits and clocks for all satellites. Read new Broadcast Ephemeris immediately whenever they become available. This information may come via a stream of RTCM messages generated from a BNC instance.

• Continuously receive the best available clock and orbit estimates for all satellites in X,Y,Z Earth-Centered-Earth-Fixed IGS08 reference system. Receive them every epoch in plain ASCII format as provided by a real-time GNSS engine such as RTNet or generate them following a 'Combination' approach.
• Calculate X,Y,Z coordinates from Broadcast Ephemeris orbits.
• Calculate differences dX,dY,dZ between Broadcast Ephemeris and IGS08 orbits.
• Transform these differences into radial, along-track and cross-track corrections to Broadcast Ephemeris orbits.
• Calculate corrections to Broadcast Ephemeris clocks as differences between Broadcast Ephemeris and IGS08 clocks.
• Encode Broadcast Ephemeris clock and orbit corrections in RTCM Version 3 format.
• Upload corrections stream to NTRIP Broadcaster.

The usual handling of BNC when uploading a stream with Broadcast Corrections is that you first specify Broadcast Ephemeris and Broadcast Correction streams. You then specify an NTRIP Broadcaster for stream upload before you start the program.

BNC requires GNSS clocks and orbits in the IGS Earth-Centered-Earth-Fixed (ECEF) reference system and in a specific ASCII format. The clocks and orbits must be referred to satellite Center of Mass (CoM) and must not contain the conventional periodic relativistic effect. They may be provided by a real-time GNSS engine such as RTNet. The sampling rate for data transmission should not exceed 15 sec. Note that otherwise tools involved in IP streaming such as NTRIP Broadcasters or NTRIP Clients may respond with a timeout.

Below you find an example of precise clocks and orbits coming in ASCII format (named 'RTNET' in this document) from a real-time GNSS engine. Each epoch starts with an asterisk character followed by the time as year, month, day of month, hour, minute and second. Subsequent records provide the following set of parameters for each satellite:

• GNSS Indicator and Satellite Vehicle Pseudo Random Number
• X,Y,Z coordinates in Earth-Centered-Earth-Fixed system [km] at epoch T
• Satellite clock error [microsecond]
• Conventional periodic relativistic effect [microsecond]
• DX,DY,DZ [m] in Earth-Centered-Earth-Fixed system for translation CoM->APC
• Differential Code Bias P1C1 [m]
• Differential Code Bias P1P2 [m]
• Time increment dT [second]
• X,Y,Z coordinates in Earth-Centered-Earth-Fixed system [km] at epoch T+dT

...
PR22  24695.278546   4939.628474  -3498.468864     41.074663      0.000301  -2.458   0.059   0.259   0.000   0.369  60.0  24724.926665   4937.395818  -3285.525249
PR23  16644.528151  -4673.966731 -18755.727311   -381.408485     -0.000069  -1.484   0.958   1.597   0.000  -1.041  60.0  16794.540110  -4640.370673 -18629.931406
PR24   -835.564016 -11361.061950 -22837.329550    -67.978344     -0.000027   0.088   1.593   1.979   0.000   0.628  60.0   -654.746874 -11311.272410 -22867.926411
EOE
*  2012  4 13 18  5  20.00000000 
PG01 -17662.477581  -4690.968816  19273.403670    247.562657     -0.001403   1.173  -0.094  -1.222  -0.081  -3.222  60.0 -17723.637492  -4824.411250  19184.308406
PG02  13499.913230  23158.540481  -1230.022763    386.539840     -0.009664  -0.392  -0.672   0.036  -0.007   1.778  60.0  13488.200264  23175.574718  -1044.681214
PG03 -16691.614702 -11720.144912 -17619.363518     35.472262     -0.007906   1.785   0.965   1.939  -0.171  -0.769  60.0 -16563.914187 -11742.834794 -17725.636699
...
PG32 -16198.232316  -3364.836652  20899.169198   -432.258718     -0.025811   1.728   0.075  -2.191  -0.370  -1.040  60.0 -16107.271625  -3493.294042  20951.654447
PR01  18574.288277 -17410.663026  -1754.600023   -178.990271     -0.000082  -1.469   2.095   0.024   0.000   0.188  60.0  18556.963974 -17406.362476  -1967.750384
PR02   8030.345235 -18665.480490  15430.035833   -298.816088     -0.000568  -0.516   2.171  -1.184   0.000   0.221  60.0   8114.572636 -18759.449343  15271.294411
PR03  -6108.423573  -9263.873363  23002.679850   -129.074986      0.000627   0.523   1.396  -2.019   0.000   1.568  60.0  -5976.535477  -9398.317054  22982.703956
...
PR24   -820.514575 -11356.881507 -22839.954618    -67.978328     -0.000026   0.087   1.593   1.979   0.000   0.628  60.0   -639.657024 -11307.160404 -22870.387083
EOE
*  2012  4 13 18  5  25.00000000 
PG01 -17667.568396  -4702.119849  19266.035352    247.562677     -0.001403   1.173  -0.094  -1.222  -0.081  -3.222  60.0 -17728.740899  -4835.494883  19176.817383
PG02  13498.959815  23160.004885  -1214.580934    386.539856     -0.009647  -0.392  -0.672   0.035  -0.007   1.778  60.0  13487.197253  23176.941260  -1029.232392
PG03 -16680.999851 -11722.017340 -17628.269050     35.472285     -0.007882   1.783   0.966   1.940  -0.171  -0.769  60.0 -16553.240904 -11744.747432 -17734.434260
...

Note that each end of an epoch in the incoming stream is indicated by an ASCII string 'EOE' (for End Of Epoch).

When using clocks from Broadcast Ephemeris (with or without applied corrections) or clocks from SP3 files, it may be important to understand that they are not corrected for the conventional periodic relativistic effect. Chapter 10 of the IERS Conventions 2003 mentions that the conventional periodic relativistic correction to the satellite clock (to be added to the broadcast clock) is computed as dt = -2 (R * V) / c^2 where R *V is the scalar product of the satellite position and velocity and c is the speed of light. This can also be found in the GPS Interface Specification, IS-GPS-200, Revision D, 7 March 2006.

Hit 'Add Row' button to add another row to the stream 'Upload Table' or hit the 'Delete' button to delete the highlighted row(s).

Having an empty 'Upload Table' is default and means that you don't want BNC to upload orbit and clock correction streams to any NTRIP Broadcaster.

Specify the domain name or IP number of an NTRIP Broadcaster for uploading the stream. Furthermore, specify the caster's listening IP port, an upload mountpoint and an upload password. Note that NTRIP Broadcasters are often configured to provide access on more than one port, usually port 80 and 2101. If you experience communication problems on port 80, you should try to use the alternative port(s).

BNC uploads a stream to the Caster by referring to a dedicated mountpoint that has been set by the Caster operator. Specify here the mountpoint based on the details you received for your stream from the operator. It is often a four character ID (capital letters) plus an integer number.

The stream upload may be protected through an upload 'Password'. Enter the password you received from the Caster operator along with the mountpoint(s).

If 'Host', 'Port', 'Mountpoint' and 'Password' are set, the stream will be encoded in RTCM's 'State Space Representation' (SSR) messages and uploaded to the specified broadcaster following the NTRIP Version 1 transport protocol.

BNC allows to configure several Broadcast Correction streams for upload so that they refer to different reference systems and different NTRIP Broadcasters. You may use this functionality for parallel support of a backup NTRIP Broadcaster or for simultaneous support of several reference systems. Available options for referring clock and orbit corrections to specific target reference systems are

• IGS08 which stands for the GNSS-based IGS realization of the International Terrestrial Reference Frame 2008 (ITRF2008), and
• ETRF2000 which stands for the European Terrestrial Reference Frame 2000 adopted by EUREF, and
• NAD83 which stands for the North American Datum 1983 as adopted for the U.S.A., and
• GDA94 which stands for the Geodetic Datum Australia 1994 as adopted for Australia, and
• SIRGAS2000 which stands for the Geodetic Datum adopted for Brazil, and
• SIRGAS95 which stands for the Geodetic Datum adopted i.e. for Venezuela, and
• 'Custom' which allows a transformation of Broadcast Corrections from the IGS08 system to any other system through specifying up to 14 Helmert Transformation Parameters.

BNC only transforms the original IGS08 orbits in the Broadcast Corrections stream to a target reference system while leaving the clocks unchanged. From a theoretical point of view this leads to inconsistencies between orbits and clocks and is therefore not allowed. However, it has been shown by Huisman et al. 2012 that as long as involved scale parameters are small enough, this way of transforming corrections stream contents only leads to height biases less than about one centimeter. With regards to the systems listed above, the approach has therefore been implemented in BNC for practical reasons.

The transformation to GDA94 is an exception in this because it involves a ten times higher scale parameter compared to the other transformation implementations. Note that hence the resulting height biases for a BNC-transformed GDA94 corrections stream can increase up to about 10 centimeters.

IGS08: As the clocks and orbits coming from real-time GNSS engine are expected to be in the IGS08 system, no transformation is carried out if this option is selected.

ETRF2000: The formulas for the transformation 'ITRF2005->ETRF2000' are taken from 'Claude Boucher and Zuheir Altamimi 2008: Specifications for reference frame fixing in the analysis of EUREF GPS campaign', see http://etrs89.ensg.ign.fr/memo-V8.pdf. The following 14 Helmert Transformation Parameters were introduced:

Translation in X at epoch To:  0.0521 m
Translation in Y at epoch To:  0.0493 m
Translation in Z at epoch To: -0.0585 m
Translation rate in X:  0.0001 m/y
Translation rate in Y:  0.0001 m/y
Translation rate in Z: -0.0018 m/y
Rotation in X at epoch To:  0.891 mas
Rotation in Y at epoch To:  5.390 mas
Rotation in Z at epoch To: -8.712 mas
Rotation rate in X:  0.081 mas/y 
Rotation rate in Y:  0.490 mas/y
Rotation rate in Z: -0.792 mas/y
Scale at epoch To : 0.00000000134
Scale rate: 0.00000000008 /y
To: 2000.0

NAD83: Formulas for the transformation 'ITRF2005->NAD83' are taken from 'Chris Pearson, Robert McCaffrey, Julie L. Elliott, Richard Snay 2010: HTDP 3.0: Software for Coping with the Coordinate Changes Associated with Crustal Motion, Journal of Surveying Engineering'.

Translation in X at epoch To:  0.9963 m
Translation in Y at epoch To: -1.9024 m
Translation in Z at epoch To: -0.5219 m
Translation rate in X:  0.0005 m/y
Translation rate in Y: -0.0006 m/y
Translation rate in Z: -0.0013 m/y
Rotation in X at epoch To: 25.915 mas
Rotation in Y at epoch To:  9.426 mas
Rotation in Z at epoch To: 11.599 mas
Rotation rate in X:  0.067 mas/y 
Rotation rate in Y: -0.757 mas/y
Rotation rate in Z: -0.051 mas/y
Scale at epoch To : 0.00000000078
Scale rate: -0.00000000010 /y
To: 1997.0

GDA94: The formulas for the transformation 'ITRF2000->GDA94' are taken from 'John Dawson, Alex Woods 2010: ITRF to GDA94 coordinate transformations', Journal of Applied Geodesy, 4 (2010), 189¿199, de Gruyter 2010. DOI 10.1515/JAG.2010.019'.

Translation in X at epoch To: -0.07973 m
Translation in Y at epoch To: -0.00686 m
Translation in Z at epoch To:  0.03803 m
Translation rate in X:  0.00225 m/y
Translation rate in Y: -0.00062 m/y
Translation rate in Z: -0.00056 m/y
Rotation in X at epoch To:  0.0351 mas
Rotation in Y at epoch To: -2.1211 mas
Rotation in Z at epoch To: -2.1411 mas
Rotation rate in X: -1.4707 mas/y 
Rotation rate in Y: -1.1443 mas/y
Rotation rate in Z: -1.1701 mas/y
Scale at epoch To : 0.000000006636
Scale rate: 0.000000000294 /y
To: 1994.0

SIRGAS2000: The formulas for the transformation 'ITRF2005->SIRGAS2000' were provided via personal communication from CGED-Coordenacao de Geodesia, IBGE/DGC - Diretoria de Geociencias, Brazil..

Translation in X at epoch To: -0.0051 m
Translation in Y at epoch To: -0.0065 m
Translation in Z at epoch To: -0.0099 m
Translation rate in X:  0.0000 m/y
Translation rate in Y:  0.0000 m/y
Translation rate in Z:  0.0000 m/y
Rotation in X at epoch To:  0.150 mas
Rotation in Y at epoch To:  0.020 mas
Rotation in Z at epoch To:  0.021 mas
Rotation rate in X:  0.000 mas/y 
Rotation rate in Y:  0.000 mas/y
Rotation rate in Z:  0.000 mas/y
Scale at epoch To : 0.000000000000
Scale rate: -0.000000000000 /y
To: 2000.0

SIRGAS95: The formulas for the transformation 'ITRF2005->SIRGAS95' were provided via personal communication from Gustavo Acuha, Laboratorio de Geodesia Fisica y Satelital at Zulia University (LGFS-LUZ), parameters based on values from Table 4.1 of "Terrestrial Reference Frames (April 10, 2009), Chapter 4" in http://tai.bipm.org/iers/convupdt/convupdt_c4.html..

Translation in X at epoch To:  0.0077 m
Translation in Y at epoch To:  0.0058 m
Translation in Z at epoch To: -0.0138 m
Translation rate in X:  0.0000 m/y
Translation rate in Y:  0.0000 m/y
Translation rate in Z:  0.0000 m/y
Rotation in X at epoch To:  0.000 mas
Rotation in Y at epoch To:  0.000 mas
Rotation in Z at epoch To: -0.003 mas
Rotation rate in X:  0.000 mas/y 
Rotation rate in Y:  0.000 mas/y
Rotation rate in Z:  0.000 mas/y
Scale at epoch To : 0.00000000157
Scale rate: -0.000000000000 /y
To: 1995.4

Custom: The default numbers shown as examples are those for a transformation from ITRF2005 to ETRF2000'.

BNC allows to either refer Broadcast Corrections to the satellite's Center of Mass (CoM) or to the satellite's Antenna Phase Center (APC). By default corrections refer to APC. Tick 'Center of Mass' to refer uploaded corrections to CoM.

Specify a path for saving the generated orbit corrections as SP3 orbit files. If the specified directory does not exist, BNC will not create SP3 orbit files. The following is a path example for a Linux system:
/home/user/BNC${GPSWD}.sp3
Note that '${GPSWD}' produces the GPS Week and Day number in the file name.

Default is an empty option field meaning that you don't want BNC to save the uploaded stream contents in daily SP3 files.

As an SP3 file contents should be referred to the satellites Center of Mass (CoM) while Broadcast Corrections are referred to the satellites Antenna Phase Center (APC), an offset has to be applied which is available from an IGS ANTEX file (see section 'ANTEX File'). You should therefore specify the 'ANTEX File' path under tab 'PPP (2)' if you want to save the stream contents in SP3 format. If you don't specify an 'ANTEX File' path there, the SP3 file contents will be referred to the satellites APCs.

The file names for the daily SP3 files follow the convention for SP3 file names. The first three characters of each file name are set to 'BNC'. Note that clocks in the SP3 orbit files are not corrected for the conventional periodic relativistic effect.

The clock corrections generated by BNC for upload can be logged in Clock RINEX format. The file naming follows the RINEX convention.

Specify a path for saving the generated clock corrections as Clock RINEX files. If the specified directory does not exist, BNC will not create Clock RINEX files. The following is a path example for a Linux system:
/home/user/BNC${GPSWD}.clk
Note that '${GPSWD}' produces the GPS Week and Day number in the file name.

Note further that clocks in the Clock RINEX files are not corrected for the conventional periodic relativistic effect.

Select the length of Clock RINEX files and SP3 Orbit files. The default value is 1 day.

Select the Clock RINEX file sampling interval in seconds. A value of zero '0' tells BNC to store all available samples into Clock RINEX files.

Select the SP3 Orbit file sampling interval in seconds. A value of zero '0' tells BNC to store all available samples into SP3 Orbit files.

Hit 'Custom Trafo' to specify your own 14 parameter Helmert Transformation instead of selecting a predefined transformation through 'System' button.

The following screenshot shows the encoding and uploading of a stream of precise orbits and clocks coming from a real-time engine in 'RTNET' ASCII format. The stream is uploaded to NTRIP Broadcaster 'products.igs-ip.net'. It is referred to APC and IGS08. Uploaded data are locally saved in SP3 and Clock RINEX format. Required Broadcast Ephemeris are received via stream 'RTCM3EPH'.

Figure: Producing Broadcast Corrections from incoming precise orbits and clocks and uploading them to an NTRIP Broadcaster.

BNC can upload a stream carrying Broadcast Ephemeris in RTCM Version 3 format to an NTRIP Broadcaster.

Specify the 'Host' IP name or number of an NTRIP Broadcaster to upload the stream. An empty option field means that you don't want to upload Broadcast Ephemeris.

Enter the NTRIP Broadcaster's IP 'Port' number for stream upload. Note that NTRIP Broadcasters are often configured to provide access on more than one port, usually port 80 and 2101. If you experience communication problems on port 80, you should try to use the alternative port(s).

BNC uploads a stream to the Caster by referring to a dedicated mountpoint that has been set by the Caster operator. Specify the mountpoint based on the details you received for your stream from the operator. It is often a four character ID (capital letters) plus an integer number.

The stream upload may be protected through an upload 'Password'. Enter the password you received from the Caster operator along with the mountpoint(s).

Each stream on an NTRIP Broadcaster (and consequently on BNC) is defined using a unique source ID called mountpoint. An NTRIP Client like BNC access the desired data stream by referring to its mountpoint. Information about streams and their mountpoints is available through the source-table maintained by the NTRIP Broadcaster. Note that mountpoints could show up in BNC more than once when retrieving streams from several NTRIP Broadcasters.

Streams selected for retrieval are listed under the 'Streams' canvas section on BNC's main window. The list provides the following information either extracted from source-table(s) produced by the NTRIP Broadcasters or introduced by BNC's user:

'resource loader'	NTRIP Broadcaster URL and port, or TCP/IP host and port, or UDP port, or Serial input port specification.
'mountpoint'	Mountpoint introduced by NTRIP Broadcaster, or Mountpoint introduced by BNC's user.
'decoder'	Name of decoder used to handle the incoming stream content according to its format; editable.
'lat'	Approximate latitude of reference station, in degrees, north; editable if 'nmea' = 'yes'.
'long'	Approximate longitude of reference station, in degrees, east; editable if 'nmea' = 'yes'.
'nmea'	Indicates whether or not streaming needs to be initiated by BNC through sending NMEA-GGA message carrying position coordinates in 'lat' and 'long'.
'ntrip'	Selected NTRIP transport protocol version (1, 2, 2s, R, or U), or 'N' for TCP/IP streams without NTRIP, or 'UN' for UDP streams without NTRIP, or 'S' for serial input streams without NTRIP.
'bytes'	Number of bytes received.

• BNC automatically allocates one of its internal decoders to a stream based on the stream's 'format' and 'format-details' as given in the source-table. However, there might be cases where you need to override the automatic selection due to incorrect source-table for example. BNC allows users to manually select the required decoder by editing the decoder string. Double click on the 'decoder' field, enter your preferred decoder and then hit Enter. The accepted decoder strings are 'RTCM_2.x', 'RTCM_3.x' and 'RTNET'.
• In case you need to log the raw data as is, BNC allows users to by-pass its decoders and directly save the input in daily log files. To do this specify the decoder string as 'ZERO'. The generated file names are created from the characters of the streams mountpoints plus two-digit numbers each for year, month, and day. Example: Setting the 'decoder' string for mountpoint WTZZ0 to 'ZERO' and running BNC on March 29, 2007 would save the raw data in a file named WTZZ0_070329.
• BNC can also retrieve streams from virtual reference stations (VRS). To initiate these streams, an approximate rover position needs to be sent in NMEA format to the NTRIP Broadcaster. In return, a user-specific data stream is generated, typically by Network-RTK software. VRS streams are indicated by a 'yes' in the source-table as well as in the 'nmea' column on the 'Streams' canvas in BNC's main window. They are customized exactly to the latitude and longitude transmitted to the NTRIP Broadcaster via NMEA-GGA messages.
  If NMEA-GGA messages are not coming from a serial connected GNSS rover, BNC simulates them from the default latitude and longitude of the source-table as shown in the 'lat' and 'long' columns on the 'Streams' canvas. However, in most cases you would probably want to change these defaults according to your requirement. Double-click on 'lat' and 'long' fields, enter the values you wish to send and then hit Enter. The format is in positive north latitude degrees (e.g. for northern hemisphere: 52.436, for southern hemisphere: -24.567) and eastern longitude degrees (example: 358.872 or -1.128). Only streams with a 'yes' in their 'nmea' column can be edited. The position must preferably be a point within the VRS service area of the network. RINEX files generated from these streams will contain an additional COMMENT line in the header beginning with 'NMEA' showing the 'lat' and 'long' used.
  Note that when running BNC in a Local Area Network (LAN), NMEA strings may be blocked by a proxy server, firewall or virus scanner when not using the NTRIP Version 2 transport protocol..

To remove a stream from the 'Streams' canvas in the main window, highlight it by clicking on it and hit the 'Delete Stream' button. You can also remove multiple streams simultaneously by highlighting them using +Shift and +Ctrl.

The streams selection can be changed on-the-fly without interrupting uninvolved threads in the running BNC process.

Window mode: Hit 'Save & Reread Configuration' while BNC is in window mode and already processing data to let changes of your streams selection immediately become effective.

No window mode: When operating BNC online in 'no window' mode (command line option -nw), you force BNC to reread its 'mountPoints' configuration option from disk at pre-defined intervals. Select '1 min', '1 hour', or '1 day' as 'Reread configuration' option to reread the 'mountPoints' option every full minute, hour, or day. This lets a 'mountPoints' option edited in between in the configuration file become effective without terminating uninvolved threads. See annexed section 'Configuration Example' for a configuration file example and a list of other on-the-fly changeable options.

A tabs section on the bottom of the main window provides online control of BNC's activities. Tabs are available to show the records saved in a logfile, for a plot to control the bandwidth consumption, for a plot showing stream latencies, and for time series plots of PPP results.

Records of BNC's activities are shown in the 'Log' tab. They can be saved into a file when a valid path is specified in the 'Logfile (full path)' field.

The bandwidth consumption per stream is shown in the 'Throughput' tab in bits per second (bps) or kilo bits per second (kbps). The following figure shows the bandwidth comsumption of incoming streams.

Figure: Bandwidth consumption of incoming streams.

The latency of observations in each incoming stream is shown in the 'Latency' tab in milliseconds or seconds. Streams not carrying observations (i.e. those providing only Broadcast Ephemeris messages) or having an outage are not considered here and shown in red color. Note that the calculation of correct latencies requires the clock of the host computer to be properly synchronized. The next figure shows the latency of incoming streams.

Figure: Latency of incoming streams.

Precise Point Positioning time series of North (red), East (green) and Up (blue) coordinate components are shown in the 'PPP Plot' tab when a 'Origin' option is defined. Values are either referred to reference coordinates (if specified) or referred to the first estimated set of coordinate components. The time as given in format [hh:mm] refers to GPS Time. The sliding PPP time series window covers a period of 5 minutes. Note that it may take up to 30 seconds or more till the first PPP solutions becomes available. The following figure shows the screenshot of a PPP time series plot of North, East and Up coordinate components.

Figure: Time series plot of PPP session.

The bottom menu bar allows to add or delete streams to BNC's configuration and to start or stop it. It also provides access to BNC's online help function. The 'Add Stream' button opens a window that allows user to select one of several input communication links, see figure below.

Figure: Steam input communication links.

Button 'Add Stream' > 'Coming from Caster' then opens a window that allows user to select data streams from an NTRIP Broadcaster according to their mountpoints and show a distribution map of offered streams.

Enter the NTRIP Broadcaster host IP and port number. Note that EUREF and IGS operate NTRIP Broadcasters at http://www.euref-ip.net/home and http://www.igs-ip.net/home and http://www.products.igs-ip.net/home.

It may be that your are not sure about your NTRIP Broadcasters host and port number or you are interested in other broadcaster installations operated elsewhere. Hit 'Show' for a table of known broadcasters maintained at www.rtcm-ntrip.org/home. A window opens which allows to select a broadcaster for stream retrieval, see figure below.

Figure: Casters table.

Some streams on NTRIP Broadcasters may be restricted. Enter a valid 'User' ID and 'Password' for access to protected streams. Accounts are usually provided per NTRIP Broadcaster through a registration procedure. Register through http://igs.bkg.bund.de/ntrip/registeruser for access to protected streams on www.euref-ip.net or www.igs-ip.net or products.igs-ip.net.

Use the 'Get Table' button to download the source-table from the NTRIP Broadcaster. Pay attention to data fields 'format' and 'format-details'. Keep in mind that BNC can only decode and convert streams that come in RTCM Version 2, RTCM Version 3, or RTNET format. For access to observations, ephemeris or ephemeris corrections, an RTCM Version 2 streams must contain message types 18 and 19 or 20 and 21 while an RTCM Version 3 streams must contain

• GPS or SBAS message types 1002 or 1004, or
• GLONASS message types 1010 or 1012, or
• proposed State Space Representation messages for GPS and GLONASS, types 1057-1068, or
• proposed 'Multiple Signal Messages' (MSM) for GPS, GLONASS, or Galileo, types 1071-1077, 1081-1087, or 1091-1097.

The contents of data field 'nmea' tells you whether a stream retrieval needs to be initiated by BNC through sending an NMEA-GGA message carrying approximate position coordinates (virtual reference station).

Hit 'OK' to return to the main window. If you wish you can click on 'Add Stream' and repeat the process again to retrieve streams from different casters.

Figure: Broadcaster source-table.

Button 'Map' leads to the presentation of a map showing the distribution of streams offered through the downloaded source-table.

Figure: Stream distribution map derived from NTRIP Broadcaster source-table.

Some limitations and deficiencies of the NTRIP Version 1 stream transport protocol are solved in NTRIP Version 2. Improvements mainly concern a full HTTP compatibility in view of requirements coming from proxy servers. Version 2 is backwards compatible to Version 1. Options implemented in BNC are:

  1:  NTRIP Version 1, TCP/IP.
  2:  NTRIP Version 2 in TCP/IP mode.
  2s:  NTRIP Version 2 in TCP/IP mode via SSL.
  R:  NTRIP Version 2 in RTSP/RTP mode.
  U:  NTRIP Version 2 in UDP mode.

If NTRIP Version 2 is supported by the broadcaster:

• Try using option '2' if your streams are otherwise blocked by a proxy server operated in front of BNC.
• Option 'R' or 'U' may be selected if latency is more important than completeness for your application. Note that the latency reduction is likely to be in the order of 0.5 sec or less. Note further that options 'R' (RTSP/RTP mode) and 'U' (UDP mode) are not accepted by proxy servers and a mobile Internet Service Provider may not support it.

Select option '1' if you are not sure whether the broadcaster supports NTRIP Version 2.

Button 'Map' opens a window to show a distribution map of the casters' streams. You may like to zoom in or out using option 'Zoom +' or 'Zoom -'. You may also like to 'Clean' or 'Reset' a map or let it 'Fit' exactly to the current size of the window. Option 'Close' shuts the window.

Button 'Add Stream' > 'Coming from TCP/IP Port' allows to retrieve streams via TCP directly from an IP address without using the NTRIP transport protocol. For that you:

• Enter the IP address of the stream providing host.
• Enter the IP port number of the stream providing host.
• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTNET', and 'ZERO'.
• Enter the approximate latitude of the stream providing rover in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing rover in degrees. Example: -15.20.

Streams directly received from a TCP/IP port show up with an 'N' for 'No NTRIP' in the 'Streams' canvas section on BNC's main window. Latitude and longitude are to be entered just for informal reasons.

Button 'Add Stream' > 'Coming from UDP Port' allows to pick up streams arriving directly at one of the local host's UDP ports without using the NTRIP transport protocol. For that you:

• Enter the local port number where the UDP stream arrives.
• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTNET', and 'ZERO'.
• Enter the approximate latitude of the stream providing rover in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing rover in degrees. Example: -15.20.

Streams directly received at a UDP port show up with a 'UN' for 'UDP, No NTRIP' in the 'Streams' canvas section on BNC's main window. Latitude and longitude are to be entered just for informal reasons.

Button 'Add Stream' > 'Coming from Serial Port' allows to retrieve streams from a GNSS receiver via serial port without using the NTRIP transport protocol. For that you:

• Specify a mountpoint. Recommended is a 4-character station ID. Example: FFMJ
• Specify the stream format. Available options are 'RTCM_2', 'RTCM_3', 'RTNET', and 'ZERO'.
• Enter the approximate latitude of the stream providing receiver in degrees. Example: 45.32.
• Enter the approximate longitude of the stream providing receiver in degrees. Example: -15.20.
• Enter the serial 'Port name' selected on your host for communication with the receiver. Valid port names are

  Windows:       COM1, COM2
  Linux:         /dev/ttyS0, /dev/ttyS1
  FreeBSD:       /dev/ttyd0, /dev/ttyd1
  Digital Unix:  /dev/tty01, /dev/tty02
  HP-UX:         /dev/tty1p0, /dev/tty2p0
  SGI/IRIX:      /dev/ttyf1, /dev/ttyf2
  SunOS/Solaris: /dev/ttya, /dev/ttyb
  

• Select a 'Baud rate' for the serial input. Note that using a high baud rate is recommended.
• Select the number of 'Data bits' for the serial input. Note that often '8' data bits are used.
• Select the 'Parity' for the serial input. Note that parity is often set to 'NONE'.
• Select the number of 'Stop bits' for the serial input. Note that often '1' stop bit is used.
• Select a 'Flow control' for the serial link. Select 'OFF' if you don't know better.

When selecting one of the serial communication options listed above, make sure that you pick those configured to the serial connected GNSS receiver.

Streams received from a serial connected GNSS receiver show up with an 'S' (for Serial Port, no NTRIP) in the 'Streams' canvas section on BNC's main window . Latitude and longitude are to be entered just for informal reasons.

The following figure shows a BNC example setup for pulling a stream via serial port on a Linux operating system.

Figure: BNC setup for pulling a stream via serial port.

Hit 'Start' to start retrieving, decoding, and converting GNSS data streams in real-time. Note that 'Start' generally forces BNC to begin with fresh RINEX which might overwrite existing files when necessary unless the option 'Append files' is ticked.

Hit the 'Stop' button in order to stop BNC.

Command line options are available to run BNC in 'no window' mode or let it read data offline from one file or several files for debugging or post processing purposes. BNC will then use processing options from the configuration file. Note that the self-explaining contents of the configuration file can easily be edited. It is possible to introduce a specific configuration file name instead of using the default name 'BNC.ini'.

Apart from its regular windows mode, BNC can be started on all systems as a background/batch job with command line option '-nw'. BNC will then run in 'no window' mode, using processing options from its configuration file on disk. Terminate BNC using Windows Task Manager when running it in 'no window' mode on Windows systems.

Example:

bnc.exe -nw

Although BNC is primarily a real-time online tool, for debugging purposes it can be run offline to read data from a file previously saved through option 'Raw output file'. Enter the following command line option for that

--file <inputFileName>

Note that when running BNC offline, it will use options for file saving, interval, sampling, PPP etc. from its configuration file.

Note further that option '--file' forces BNC to appy the '-nw' option for running in 'no Window' mode.

Example:

./bnc --conf MyConfig.ini

This leads to a BNC job using configuration file 'MyConfig.ini'. The configuration file will be saved in the current working directory.

On a Mac-OS X v10.6 (or higher) system the command line would be

open -a /Applications/bnc.app --args -conf /Users/tsyan/MyConfig.ini

if the program is in /Applications and the configuration file 'MyConfig.ini' in /Users/tsyan.

BNC applies options from the configuration file but allows updating any of them on the command line while the contents of the configuration file remains unchanged. The command line syntax for that looks as follows

--key <keyName> <keyValue>

where <keyName> stands for the name of an option contained in the configuration file and <keyValue> stands for the value you want to assign to it. The following is a syntax example for a complete command line:

bnc --nw --conf <confFileName> --key <keyName1> <keyValue1> --key <keyName2> <keyValue2> ...

Example:

./bnc --conf CONFIG.bnc --key proxyPort=8001 --key rnxIntr="1 day"

• In Qt-based desktop environments (like KDE) on Unix/Linux platforms it may happen that you experience a crash of BNC at startup even when running the program in the background using the '-nw' option. This is a known bug most likely resulting from an incompatibility of Qt libraries in the environment and in BNC. Entering the command 'unset SESSION_MANAGER' before running BNC may help as a work-around.
• BNC has some limits with regards to handling data from new GNSS like COMPAS and QZSS. Which observables become available on a particular stream also depends on the setup of source receiver and the data format used.
• Using RTCM Version 3 to produce RINEX files, BNC will properly handle most message types. However, when handling message types 1001, 1003, 1009 and 1011 where the ambiguity field is not set, the output will be no valid RINEX. All values will be stored modulo 299792.458 (speed of light).
• Using RTCM Version 2, BNC will only handle message types 18 and 19 or 20 and 21 together with position and the antenna offset information carried in types 3 and 22. Note that processing carrier phase corrections and pseudo-range corrections contained in message types 20 and 21 needs access to Broadcast Ephemeris. Hence, whenever dealing with message types 20 and 21, make sure that Broadcast Ephemeris become available for BNC through also retrieving at least one RTCM Version 3 stream carrying message types 1019 (GPS ephemeris) and 1020 (GLONASS ephemeris).
• BNC's 'Get Table' function only shows the STR records of a source-table. You can use an Internet browser to download the full source-table contents of any NTRIP Broadcaster by simply entering its URL in the form of http://host:port. Data field number 8 in the NET records may provide information about where to register for an NTRIP Broadcaster account.
• EUREF as well as IGS adhere to an open data policy. Streams are made available through NTRIP Broadcasters at www.euref-ip.net, www.igs-ip.net and products.igs-ip.net free of charge to anyone for any purpose. There is no indication up until now how many users will need to be supported simultaneously. The given situation may develop in such a way that it might become difficult to serve all registered users at the same times. In cases where limited resources on the NTRIP Broadcaster side (software restrictions, bandwidth limitation etc.) dictates, first priority in stream provision will be given to stream providers followed by re-broadcasting activities and real-time analysis centers while access to others might be temporarily denied.
• Once BNC has been started, many of its configuration options cannot be changed as long as it is stopped. See chapter 'Reread Configuration' for on-the-fly configuration exceptions.

The BKG Ntrip Client (BNC) Qt Graphic User Interface (GUI) has been developed for the Federal Agency for Cartography and Geodesy (BKG) by Leos Mervart, Czech Technical University Prague, Department of Geodesy. BNC includes the following GNU GPL software components:

• RTCM 2 decoder, written by Oliver Montenbruck, German Space Operations Center, DLR, Oberpfaffenhofen
• RTCM 3 decoder, written for BKG by Dirk Stoecker, Alberding GmbH, Schoenefeld

Georg Weber
Federal Agency for Cartography and Geodesy (BKG)
Frankfurt, Germany
[euref-ip@bkg.bund.de] or [igs-ip@bkg.bund.de]

Acknowledgements
BNC's Help Contents has been proofread by Thomas Yan, University of New South Wales, Australia.
Scott Glazier, OmniSTAR Australia has been helpful in finding BNC's bugs.
James Perlt, BKG, helped fixing bugs and redesigned BNC's main window.
Andre Hauschild, German Space Operations Center, DLR, revised the RTCM Version 2 decoder.
Zdenek Lukes, Czech Technical University Prague, Department of Geodesy, extended the RTCM Version 2 decoder to handle message types 3, 20, 21, and 22 and added loss of lock indicator.
Jan Dousa, Geodetic Observatory Pecny, Czech Republic, provided a tool for drawing stream distribution maps and also helped with fixing bugs.
Denis Laurichesse, Centre National d'Etudes Spatiales (CNES), suggested synchronizing observations and clock corrections to reduce high frequency noise in PPP solutions.

The Radio Technical Commission for Maritime Services (RTCM) is an international non-profit scientific, professional and educational organization. Special Committees provide a forum in which governmental and non-governmental members work together to develop technical standards and consensus recommendations in regard to issues of particular concern. RTCM is engaged in the development of international standards for maritime radionavigation and radiocommunication systems. The output documents and reports prepared by RTCM Committees are published as RTCM Recommended Standards. Topics concerning Differential Global Navigation Satellite Systems (DGNSS) are handled by the Special Committee SC 104.

Personal copies of RTCM Recommended Standards can be ordered through http://www.rtcm.org/orderinfo.php.

'Networked Transport of RTCM via Internet Protocol' Version 1.0 (NTRIP) stands for an application-level protocol streaming Global Navigation Satellite System (GNSS) data over the Internet. NTRIP is a generic, stateless protocol based on the Hypertext Transfer Protocol HTTP/1.1. The HTTP objects are enhanced to GNSS data streams.

NTRIP Version 1 is an RTCM standard designed for disseminating differential correction data (e.g. in the RTCM-104 format) or other kinds of GNSS streaming data to stationary or mobile users over the Internet, allowing simultaneous PC, Laptop, PDA, or receiver connections to a broadcasting host. NTRIP supports wireless Internet access through Mobile IP Networks like GSM, GPRS, EDGE, or UMTS.

NTRIP is implemented in three system software components: NTRIP Clients, NTRIP Servers and NTRIP Broadcasters. The NTRIP Broadcaster is the actual HTTP server program whereas NTRIP Client and NTRIP Server are acting as HTTP clients.

NTRIP is an open none-proprietary protocol. Major characteristics of NTRIP's dissemination technique are:

• Based on the popular HTTP streaming standard; comparatively easy to implement when having limited client and server platform resources available.
• Application not limited to one particular plain or coded stream content; ability to distribute any kind of GNSS data.
• Potential to support mass usage; disseminating hundreds of streams simultaneously for thousands of users possible when applying modified Internet Radio broadcasting software.
• Considering security needs; stream providers and users don't necessarily get into contact, streams often not blocked by firewalls or proxy servers protecting Local Area Networks.
• Enables streaming over mobile IP networks because of using TCP/IP.

The NTRIP Broadcaster maintains a source-table containing information on available NTRIP streams, networks of NTRIP streams and NTRIP Broadcasters. The source-table is sent to an NTRIP Client on request. Source-table records are dedicated to one of the following: Data Streams (record type STR), Casters (record type CAS), or Networks of streams (record type NET).

Source-table records of type STR contain the following data fields: 'mountpoint', 'identifier', 'format', 'format-details', 'carrier', 'nav-system', 'network', 'country', 'latitude', 'longitude', 'nmea', 'solution', 'generator', 'compr-encryp', 'authentication', 'fee', 'bitrate', 'misc'.

Source-table records of type NET contain the following data fields: 'identifiey', 'operator', 'authentication', 'fee', 'web-net', 'web-str', 'web-reg', 'misc'.

Source-table records of type CAS contain the following data fields: 'host', 'port', 'identifier', 'operator', 'nmea', 'country', 'latitude', 'longitude', 'misc'.

The major changes of NTRIP Version 2 compared to Version 1.0 are:

• cleared and fixed design problems and HTTP protocol violations;
• replaced non standard directives;
• chunked transfer encoding;
• improvements in header records;
• source-table filtering; and
• RTSP communication.

NTRIP Version 2 allows to either communicate in TCP/IP mode or in RTSP/RTP mode or in UDP mode whereas Version 1 is limited to TCP/IP only. It furthermore allows using the Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL) cryptographic protocols for secure NTRIP communication over the Internet.

Transmitting GNSS carrier phase data can be done through RTCM Version 2 messages. Please note that only RTCM Version 2.2 and 2.3 streams may include GLONASS data. Messages that may be of some interest here are:

• Type 1 message is the range correction message and is the primary message in code-phase differential positioning (DGPS). It is computed in the base receiver by computing the error in the range measurement for each tracked SV.
• Type 2 message is automatically generated when a new set of satellite ephemeris is downloaded to the base receiver. It is the computed difference between the old ephemeris and the new ephemeris. Type 2 messages are used when the base station is transmitting Type 1 messages.
• Type 3 and 22 messages are the base station position and the antenna offset. Type 3 and 22 are used in RTK processing to perform antenna reduction.
• Type 6 message is a null frame filler message that is provided for data links that require continuous transmission of data, even if there are no corrections to send. As many Type 6 messages are sent as required to fill in the gap between two correction messages (type 1). Message 6 is not sent in burst mode.
• Type 9 message serves the same purpose as Type 1, but does not require a complete satellite set. As a result, Type 9 messages require a more stable clock than a station transmitting Type 1 's, because the satellite corrections have different time references.
• Type 16 message is simply a text message entered by the user that is transmitted from the base station to the rover. It is used with code-phase differential.
• Type 18 and 20 messages are RTK uncorrected carrier phase data and carrier phase corrections.
• Type 19 and 21 messages are the uncorrected pseudo-range measurements and pseudo-range corrections used in RTK.
• Type 23 message provides the information on the antenna type used on the reference station.
• Type 24 message carries the coordinates of the installed antenna's ARP in the GNSS coordinate system coordinates.

RTCM Version 3 has been developed as a more efficient alternative to RTCM Version 2. Service providers and vendors have asked for a standard that would be more efficient, easy to use, and more easily adaptable to new situations. The main complaint was that the Version 2 parity scheme was wasteful of bandwidth. Another complaint was that the parity is not independent from word to word. Still another was that even with so many bits devoted to parity, the actual integrity of the message was not as high as it should be. Plus, 30-bit words are awkward to handle. The Version 3 standard is intended to correct these weaknesses.

RTCM Version 3 defines a number of message types. Messages that may be of interest here are:

• Type 1001, GPS L1 code and phase.
• Type 1002, GPS L1 code and phase and ambiguities and carrier to noise ratio.
• Type 1003, GPS L1 and L2 code and phase.
• Type 1004, GPS L1 and L2 code and phase and ambiguities and carrier to noise ratio.
• Type 1005, Station coordinates XYZ for antenna reference point.
• Type 1006, Station coordinates XYZ for antenna reference point and antenna height.
• Type 1007, Antenna descriptor and ID.
• Type 1008, Antenna serial number.
• Type 1009, GLONASS L1 code and phase.
• Type 1010, GLONASS L1 code and phase and ambiguities and carrier to noise ratio.
• Type 1011, GLONASS L1 and L2 code and phase.
• Type 1012, GLONASS L1 and L2 code and phase and ambiguities and carrier to noise ratio.
• Type 1013, Modified julian date, leap second, configured message types and interval.
• Type 1014 and 1017, Network RTK (MAK) messages (under development).
• Type 1019, GPS ephemeris.
• Type 1020, GLONASS ephemeris.
• Type 4088 and 4095, Proprietary messages (under development).

The following are proposed 'Multiple Signal Messages' (MSM) under discussion for standardization:

• Type 1045, Galileo ephemeris.
• Type 1071, Compact GPS pseudo-ranges
• Type 1072, Compact GPS carrier phases
• Type 1073, Compact GPS pseudo-ranges and carrier phases
• Type 1074, Full GPS pseudo-ranges and carrier phases plus signal strength
• Type 1075, Full GPS pseudo-ranges, carrier phases, Doppler and signal strength
• Type 1076, Full GPS pseudo-ranges and carrier phases plus signal strength (high resolution)
• Type 1077, Full GPS pseudo-ranges, carrier phases, Doppler and signal strength (high resolution)
  
• Type 1081, Compact GLONASS pseudo-ranges
• Type 1082, Compact GLONASS carrier phases
• Type 1083, Compact GLONASS pseudo-ranges and carrier phases
• Type 1084, Full GLONASS pseudo-ranges and carrier phases plus signal strength
• Type 1085, Full GLONASS pseudo-ranges, carrier phases, Doppler and signal strength
• Type 1086, Full GLONASS pseudo-ranges and carrier phases plus signal strength (high resolution)
• Type 1087, Full GLONASS pseudo-ranges, carrier phases, Doppler and signal strength (high resolution)
  
• Type 1091, Compact Galileo pseudo-ranges
• Type 1092, Compact Galileo carrier phases
• Type 1093, Compact Galileo pseudo-ranges and carrier phases
• Type 1094, Full Galileo pseudo-ranges and carrier phases plus signal strength
• Type 1095, Full Galileo pseudo-ranges, carrier phases, Doppler and signal strength
• Type 1096, Full Galileo pseudo-ranges and carrier phases plus signal strength (high resolution)
• Type 1097, Full Galileo pseudo-ranges, carrier phases, Doppler and signal strength (high resolution)
  

The following are so-called 'State Space Representation' (SSR) messages:

• Type 1057, GPS orbit corrections to Broadcast Ephemeris
• Type 1058, GPS clock corrections to Broadcast Ephemeris
• Type 1059, GPS code biases
• Type 1060, Combined orbit and clock corrections to GPS Broadcast Ephemeris
• Type 1061, GPS User Range Accuracy (URA)
• Type 1062, High-rate GPS clock corrections to Broadcast Ephemeris
• Type 1063, GLONASS orbit corrections to Broadcast Ephemeris
• Type 1064, GLONASS clock corrections to Broadcast Ephemeris
• Type 1065, GLONASS code biases
• Type 1066, Combined orbit and clock corrections to GLONASS Broadcast Ephemeris
• Type 1067, GLONASS User Range Accuracy (URA)
• Type 1068, High-rate GLONASS clock corrections to Broadcast Ephemeris

The following table's left column is an example for the contents of a configuration file 'BNC.ini'. It enables the retrieval of an observations stream via NTRIP for the generation of 15 min RINEX files:

Note that the following configuration options saved on disk can be changed/edited on-the-fly while BNC is already processing data:

• 'mountPoints' to change the selection of streams to be processed, see section 'Streams',
• 'waitTime' to change the 'Wait for full epoch' option, see section 'Feed Engine', and
• 'binSampl' to change the 'Sampling' option, see section 'Feed Engine'.