What is RINEX? — The standard format for raw GNSS observations

RINEX is the world-standard format for recording a GNSS receiver's “raw observations” in a common, manufacturer-independent form. It is the gateway to the “post-processing” (computing precisely afterwards) used in surveying and drones — data from any receiver, u-blox, Septentrio or Trimble, can be handled in analysis software like RTKLIB once it is in RINEX.

The “answer” and the “ingredients” — the difference from NMEA

A receiver outputs two kinds of data. NMEA ($GPGGA, etc.) is the answer the receiver has finished computing — position and time. What RINEX records is the ingredients — the raw measurements (distance to the satellite = pseudorange, number of wave crests = carrier phase, signal strength). Precise post-processing needs the ingredients; you cannot make RINEX from answer-only NMEA (the ingredients have been thrown away).

What's inside RINEX

Mainly two files. The observation file (.obs) lists, at each moment (epoch), each satellite's pseudorange, carrier phase, SNR and Doppler. The navigation file (.nav) holds where the satellites were (the orbit ephemeris). Handing these two to analysis software yields a precise position. The contents are human-readable text, and you can check satellite availability in a browser viewer.

Why a “standard” is needed

Each receiver maker's raw format differs (u-blox is .ubx, Septentrio is .sbf…). Analysis software cannot read them as-is. Converting to the common RINEX format lets any software or service process them the same way. That is why RINEX is called an “exchange format”.

Versions and Hatanaka compression

RINEX has 2.11 (old), 3.xx (current, multi-GNSS) and 4.0; today 3.04 is common. Because observation files are text and grow large, the standard is to distribute them shrunk to under a third with Japan's Hatanaka compression (.crx) (used by IGS and others). At KUON you can do both compression / decompression and quality checking in the browser.

Use — post-processing (PPK / PPP)

Unlike real-time RTK, RINEX is computed afterwards using precise satellite orbits. Combining a base station's RINEX with a rover's RINEX is PPK; using precise orbits with a single receiver is PPP. Both target cm–dm accuracy, and you use them by feeding RINEX into RTKLIB, PRIDE-PPPAR or an online PPP service.