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Raw data

This page is dedicated to recording raw data in SBF format (Septentrio Binary Format) with the MSX system, and to how to choose the recording rate (in Hz) according to the application.

What SBF is

SBF is the native binary format of the mosaic-X5 module. It is compact and efficient and contains everything needed for post-processing:

  • carrier-phase and code measurements on all frequencies (for RTK/PPK computation);
  • position solution (PVT) and ephemerides;
  • receiver status, DOP, signal quality.

Unlike NMEA (text, position only), SBF preserves the raw data: from an SBF log you can recompute positions afterwards (PPK) and convert to RINEX for third-party software.

Where it is recorded (mini carrier = over USB)

On the mini carrier there is no external SD slot: the SBF log is recorded on the PC, over USB, by capturing the module's data stream. In practice:

  • you use a logger on the PC (e.g. RxLogger / Data Link from Septentrio RxTools) connected to the receiver's USB COM port; or
  • you save to file the SBF stream from a COM port with a capture utility.

Note

The mosaic-X5 module also has a native SD card interface: the future carriers will be able to fit a microSD slot for stand-alone logging (without a PC). On the mini, however, logging is over USB.

SBF blocks to record

A useful log contains at least the raw-measurement blocks plus the solution:

SBF block What it is for
MeasEpoch raw measurements (pseudorange, phase, Doppler) → basis for RINEX and PPK
PVTGeodetic position solution (lat/lon/altitude) and its quality
PVTCartesian solution in ECEF coordinates
GPSNav / GALNav / … constellation ephemerides (for orbit computation)
DOP dilution of precision (satellite geometry)
ReceiverStatus receiver status (diagnostics)

Tip

For real-time RTK only, NMEA output is enough. SBF is needed when you want to reprocess the data (PPK), produce RINEX, or analyse the measurement quality.

Recording rate (Hz)

The rate is set as the interval between epochs. The mosaic-X5 supports up to 100 Hz. Interval-to-rate correspondences:

Interval Rate Typical use
sec1 1 Hz static survey, standard RINEX, geodetic post-processing
msec500 2 Hz light kinematic survey
msec200 5 Hz kinematic, GIS on the move
msec100 10 Hz fast kinematic, low-dynamics drone
msec50 20 Hz machines on the move, automatic guidance
msec20 50 Hz high dynamics
msec10 100 Hz special applications (see below)

The 100 Hz case (special applications)

Recording at 100 Hz (msec10) is reserved for very-high-dynamics applications, where many samples per second are needed:

  • monitoring athletes on the track (e.g. 400 m): speed, acceleration, splits and high-resolution trajectory → see 400m on the track;
  • drones / UAVs in fast flight and aggressive manoeuvres;
  • vibration monitoring and structural dynamics (bridges, antennas, towers);
  • vehicles and machines at high speed or with sudden movements;
  • testing and commissioning (fine trajectory analysis, IMU synchronisation);
  • wideband deformation/seismology.

Warning

100 Hz is not the default and should be used only when really needed:

  • it generates very large files (tens of MB per minute) → disk space;
  • it easily saturates the port bandwidth → manageable over USB, but on future UART logging the baud rate must be raised;
  • it increases the load on the PC logger;
  • it does not improve the absolute precision of a single point: it only provides temporal resolution.

For classic topographic surveying 1–10 Hz is more than enough.

Note

The position value (PVT) can be generated up to 100 Hz; for very-high-rate raw measurements, check the enabled constellations/signals, as they affect the data load. (detailed parameters to be confirmed on the MSX Main configuration)

How to set up logging

  1. Connect USB and open http://192.168.3.1.
  2. Go to the Logging section.
  3. Create a new SBF stream and select the blocks (e.g. MeasEpoch + PVTGeodetic + ephemerides).
  4. Set the interval/rate (e.g. sec1 for 1 Hz, msec10 for 100 Hz).
  5. Start the recording (on the PC via RxLogger/Data Link, or to SD on carriers that provide it).

Via ASCII command (on the port)

Conceptual example of a Septentrio command to direct SBF to a stream with a given interval:

setSBFOutput, Stream1, <destination>, MeasEpoch+PVTGeodetic, msec100

where msec100 = 10 Hz (use msec10 for 100 Hz, sec1 for 1 Hz).

Note

The exact command syntax (stream, destination, file naming) is described in the mosaic-X5 Reference Guide. (to be confirmed for the MSX configuration)

From SBF log to RINEX

To use the data with third-party software, convert the SBF to RINEX with the sbf2rin utility (Septentrio):

sbf2rin -f log.sbf -o output.obs

From there you proceed with post-processing (PPK) or geodetic analysis.

See also