I have set up a Raspberry PI with a RasPiGNSS GPS-Module. After some binary convertion I get the following RINEX(ftp://igs.org/pub/data/format/rinex210.txt) files.

.nav .obs .sbs

I'm a little confused about the difference between the obs and sbs files.

What information contain these files and from where the gps-receiver gets the messages?

If my understanding is correct: I get the sbs from a base station (in my case i will be a EGNOS in Zürich) and it contains real time information about time and orbit corrections.


1 Answer 1


You might want to look at RTKLib as an easy way to perform PPP (Precise Point Positioning) corrections on your GNSS data, with simple Linux command line interface that you can perform with your Pi. The first step in this (and most) programs is converting your position data into the format you have now, the file parts that make up RINEX. The OBS file is the observations, NAV contains data about the satellite navigation messages, and the SBS is a Satellite Based Augmentation file. The SBS file contains data (if there is any) from ground stations (your base station) - this data serves to enhance the accuracy attained by positioning through satellites. The observation file contains data not from the satellites but for your receiver - these observations are used as distance measurements to the satellites, whose orbits are represented in the NAV file.

Here's a solid walkthrough of RTKLib, although it seems like you have a good system already: http://wiki.openstreetmap.org/wiki/RTKLIB

  • Thank you for you answer. The observation contains only calculation that are done by the receiver? or sent the satellites these observation information? (That is still unclear for me)
    – james
    Commented Nov 2, 2017 at 10:12
  • Good question - yes the Observation data pertains to the receiver, but the data received is tagged from available satellites. The data file contains precise ping times (accurate to two nanoseconds or so), satellite ID, and distance to the satellite. These data points are combined to triangulate approximate position - distance to satellites at precise times (and therefore known satellite position) allow for geometric correction to the receiver's position. In post-processing (PPP or other method), GNSS Correction involves correcting for atmospheric distortion (which dilutes positioning)
    – AlecZ
    Commented Nov 2, 2017 at 16:37
  • Also, base station data is input in post-processing. This allows for an even more accurate estimate of receiver's position, as the distance to the base station is less and the position of the base station is precisely known. As an optional step, more precise positions (called ephemerides) for satellites (and their routes) can be incorporated for even more precise positioning.
    – AlecZ
    Commented Nov 2, 2017 at 16:38
  • The .sbs files have some real-time orbital, clock and ionospheric correction information as determined by ground observations. These are then transmitted up to some geo-stationary satellites, which retransmit the corrections to listening receivers. You can get better correction information after the fact from other sources, but real-time, the EGNOS system delivers the correction data to the roving receivers, and they can use it internally or emit is as binary output which can be translated into the .sbs files.
    – Dave X
    Commented Jan 11, 2018 at 16:37

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