Beyond Standard GPX: Why RINEX 3.04 Matters for Geodesy

The Inherent Limitations of Standard GPX

The GPS Exchange Format (GPX 1.1) is the global standard for outdoor activities, cycling computers, and route planning. A typical GPX track point records latitude, longitude, altitude, and a timestamp:

<trkpt lat="48.01452" lon="7.88124">
  <ele>642.4</ele>
  <time>2026-08-16T10:30:00Z</time>
</trkpt>

While GPX is excellent for lightweight visualization on map canvases, it suffers from a fatal limitation for high-precision geodesy: it is an irrevocable output of an on-device Kalman filter. The raw pseudoranges, satellite geometries, carrier phases, and clock states that produced the coordinate have been permanently discarded.

If atmospheric conditions, ionospheric scintillations, or multipath reflections caused a 3-meter error at the time of recording, that error is permanently baked into the GPX polyline. It cannot be retroactively corrected.

Enter RINEX: The Receiver Independent Exchange Format

In scientific geodesy and surveying, the gold standard is RINEX (Receiver Independent Exchange Format), currently in version 3.04 / 3.05. Instead of recording estimated coordinates, a RINEX observation file records the raw signals received at every epoch from every visible satellite across all GNSS constellations (GPS, GLONASS, Galileo, BeiDou, QZSS, SBAS):

• Pseudoranges (C1C, C5Q): The raw transit time of the code signal from satellite to receiver antenna.
• Carrier Phase (L1C, L5Q): The exact cycle count of the carrier sine wave (wavelength \(\approx 19\text{ cm}\) for L1, \(\approx 25.5\text{ cm}\) for L5).
• Doppler Frequency Shift (D1C, D5Q): Relative radial velocity between receiver and satellite.
• Signal-to-Noise Ratio (S1C, S5Q): Carrier-to-noise ratio \(C/N_0\) in \(\text{dB-Hz}\).

Architectural Comparison: GPX vs. RINEX

Post-Processing Kinematic (PPK) Workflow

With RINEX 3.04 files exported from FluxMap’s .fluxraw container, users can perform Post-Processing Kinematic (PPK) workflows against national reference stations (such as SAPOS in Germany, IGN in France, or NGS CORS in the USA):

1. Extract observation.rnx and navigation.rnx from the FluxMap recording directory.
2. Download the corresponding base station RINEX files from a nearby permanent reference station within 20–50 km.
3. Run differential carrier phase double-differencing in open-source engines like RTKLIB.
4. Achieve decimeter-level track reconstruction across the entire journey.