ntrip-rtcm3-to-rtcm2p3

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

Built incrementally with a full test suite; every conversion stage is cross-checked against independent implementations (see the Validation docs).

📖 Documentation (Read the Docs)

Why

Modern correction networks (e.g. Geoscience Australia's AUSCORS) broadcast RTCM 3.x only. A u-blox 7 / NEO-7 accepts RTCM 2.3 DGPS corrections but has no RTCM3 decoder. No off-the-shelf tool converts RTCM3 → RTCM 2.3 (RTKLIB's str2str can only emit RTCM3; 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.

Pipeline

        obs + base position                 broadcast ephemeris
   (RTCM3 MSM7 1077, 1006)                 (RTCM3 1019, separate mount)
             │                                       │
             ▼                                       ▼
      decode pseudoranges  ───────────────►  satellite position + clock
             │                                       │
             └───────────────┬───────────────────────┘
                             ▼
                   per-SV PRC / RRC  (DGPS reference-station math)
                             ▼
                   encode RTCM 2.3 Type 1 / 3 (parity, IOD, scaling)
                             ▼
              serve as a local NTRIP mount alongside the raw RTCM3

Install

The packages are published as a signed apt repository per Debian suite: trixie, forky and sid. They are Architecture: all, so the one build serves every architecture. Put your suite's name in place of trixie below.

sudo install -d -m0755 /etc/apt/keyrings
curl -fsSL https://mith.ro/ntrip-rtcm3-to-rtcm2p3/ntrip-rtcm3-to-rtcm2p3.gpg | sudo tee /etc/apt/keyrings/ntrip-rtcm3-to-rtcm2p3.gpg > /dev/null
echo "deb [signed-by=/etc/apt/keyrings/ntrip-rtcm3-to-rtcm2p3.gpg] https://mith.ro/ntrip-rtcm3-to-rtcm2p3/trixie/ ./" \
  | sudo tee /etc/apt/sources.list.d/ntrip-rtcm3-to-rtcm2p3.list
sudo apt update
sudo apt install ntrip-rtcm3-to-rtcm2p3

The repository is signed with the key 36E5 D845 2935 9CFE 8874 F1F1 44EA 5E20 5EE9 F42E (gpg --show-keys /etc/apt/keyrings/ntrip-rtcm3-to-rtcm2p3.gpg shows it). It also carries python3-pyrtcm and python3-pynmeagps, which Debian doesn't have, so apt finds every dependency.

ntrip-rtcm3-to-rtcm2p3 is the systemd service; python3-ntrip-rtcm3-to-rtcm2p3 alone is the library and the command. Set the upstream caster, credentials and bind addresses in /etc/ntrip-rtcm3-to-rtcm2p3/env, then sudo systemctl restart ntrip-rtcm3-to-rtcm2p3. See the usage documentation.

Development

uv run --extra dev pytest        # test suite
uv run --extra dev ruff check .  # lint

The Debian packages workflow runs the tests in each suite's container, then builds the packages with mithro/apt-repo-action's shared build-deb action, install-tests them (packaging/install-test.sh) and, from main, publishes them. The version comes from git describe plus the suite's ~deb<R> (0.1.0.post25~deb13; nothing for sid). There is no committed debian/changelog: the build writes one with just its own entry, and git ignores it.

License

Apache-2.0. See LICENSE.