ntrip-rtcm3-to-rtcm2p3

An NTRIP receiver + LAN rebroadcaster that also converts an RTCM 3.x reference-station stream into RTCM 2.3 DGPS corrections, so legacy single-band receivers that only understand RTCM 2.3 (e.g. the u-blox 7 / NEO-7) can benefit from a modern RTCM3-only correction network such as Geoscience Australia’s AUSCORS.

Why this exists

Modern correction networks broadcast RTCM 3.x only. A u-blox 7 accepts RTCM 2.3 DGPS corrections but has no RTCM3 decoder, and no off-the-shelf tool converts between them — RTKLIB’s str2str can only emit RTCM3, and the BKG NTRIP Client (BNC) only decodes RTCM2. RTCM 2.3 Type 1 messages are derived pseudorange corrections, not a reformat: they must be computed from the base station’s observations, its known position, and satellite positions from broadcast ephemeris.

This project does that computation and re-serves both streams on the LAN.

Verified end-to-end

Every conversion stage is cross-checked in the automated test suite against independent implementations — gpsd’s gpsdecode and an RTKLIB-derived decoder (RTCM 2.3 output), gnss_lib_py (satellite position and clock), and RTKLIB’s str2str (NTRIP transport). As a hardware check, feeding the generated corrections to a real u-blox 7 produced a differential (DGPS) fix; that step is manual (it needs the receiver on a serial port) and is reproduced by scripts/validate_ublox_hardware.py, not run in CI. See Validation & cross-checks.

Contents

• Usage
  • Install
  • Running
  • Options
  • Deploying as a service
  • Which receivers benefit
• Architecture
  • Pipeline
  • The DGPS computation
  • The RTCM 2.3 wire encoding
  • Scope and limitations
• The RTCM 3.x → RTCM 2.3 conversion, in detail
  • Why a conversion is even needed
  • Part 1 — the theory
  • Part 2 — the practice (numerical accuracy)
  • Validation
  • Primary references
• Validation & cross-checks
  • Summary
  • Word parity
  • RTCM 2.3 output — three independent decoders
  • Satellite position and clock
  • Whole conversion — live
  • NTRIP transport interoperability
• API reference
  • modified_zcount()
  • extract_rtcm3_frames()
  • Converter
  • Config
  • Service
  • raw_correction()
  • udre_index()
  • DgpsGenerator
  • Ephemeris
  • satellite_position()
  • satellite_clock_bias()
  • parse_station()
  • parse_ephemeris()
  • parse_gps_msm7()
  • Correction
  • Rtcm2Encoder
  • parity_bits()
  • encode_word()
  • word_to_bits()
  • Feed
  • MountInfo
  • NtripClient
  • NtripCaster
  • BitWriter
  • BitReader