The main input data to GPSdancer consists of GPS observation data from permanent geodetic reference stations. The observations that are analyzed by GPSdancer are the so-called ionosphere-free linear combinations of code and phase data, usually indicated as P3 and L3 respectively. Clearly, modern GNSS receivers produce many more observables than these, and at some point these other observations may also be processed by GPSdancer (...already to offer accurate bias information between signals and/or between carrier frequencies). This observation data is currently read in RINEX format, where both RINEX 2 and RINEX 3 are supported. Hatenaka compressed RINEX files are OK, they are read directly by the GPSdancer software itself without requiring external decompression.

In case of a cold start (network restart without assuming availability of a previous batch solution) the satellite orbit information is initialized from the broadcast navigation messages, also in RINEX format. This data must also come from the CORS stations, although we could download it from the IGS data centres in near real-time (note that it is not critical that the last hours of the 48-hour solution arc are missing).

In addition to the observation data (which come from the CORS stations), several other inputs are needed. In particular all estimated parameters need to have some a priori value, which typically comes from an (overlapping) previous solution process. There are still some external inputs that GPSdancer cannot determine autonomously, notably:

  • Differential code bias information (downloaded from IGS or CODE Berne)
  • A priori polar motion information from the predicted part of the IERS Bulletin B files. This data is in particular used as long-term reference for absolute UT1 definition, as polar motion parameters are estimeted by GPSdancer itself.
  • At a network start, no a priori solution is assumed to be available in which case the orbits and satellite clocks are initialized from the broadcast navigation messages (....which come from the CORS stations, along with the observation data)
  • Tables with coefficients for various models, notably:
    • FES2004 ocean tide coefficients file
    • Ocean loading coeffcients (per CORS station) in standard *.blq format 
    • Absolute antenna phase centre variations in ANTEX format, as regularly updated from new IGS publications
    • Troposphere interpolation grid for the vienese model (gpt2_5.grd)

Any further inputs (e.g. gravity coefficients, or the various tables of the IERS conventions regarding precession, nutation etc.) are embedded in the software itself.  

Project details

Ultimate Browsers SupportThe GPS Dancer project started in 2007 as a voluntary project of a working group of the International Association of Geodesy.

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Square dance algorithm

Great Docs and SupportThe GPS Dancer system was named after its "square dance" exchange algorithm. Of course, it also wants to to make the GPS reference frame denser.

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Here, there be pirates

The Dancer on-line network became immune against internet connection problems by leaving the US marines, and becoming a pirate.

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