skytraq-parser-api — GNSS Stream Parser

A cross-platform console tool that parses mixed GNSS data streams containing SkyTraq Binary, NMEA 0183 (including SkyTraq proprietary $PSTI), and RTCM 3.3 messages — from a serial port or a captured log file.

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Features

• Auto-syncs on three protocol headers simultaneously (0xA0 0xA1, 0xD3, $/!)
• Cross-platform serial input (Linux termios, Windows Win32) at any baud rate
• Per-message checksum / CRC verification with red flagging on mismatch
• Pass-through of plain ASCII text not matching any protocol
• UTF-8 console output for non-ASCII glyphs (auto-enabled on Windows)
• Optional -a flag for pure-ASCII output on legacy terminals

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Supported Messages

SkyTraq Binary (AN0039 — Raw Measurement Data Extension)

ID	Name
0xB1	GPS Ephemeris Data
0xDC	Measurement Time
0xDD	Raw Measurements
0xDE	SV and Channel Status
0xDF	Navigation State
0xE0	GPS Subframe Data
0xE1	GLONASS String
0xE2	BeiDou2 D1 Subframe
0xE3	BeiDou2 D2 Subframe
0xE5	Extended Raw Measurement v1
0xE6	General Subframe Data
0xE7	GNSS SV and Channel Status
0xE8	GNSS SV Elevation / Azimuth
0xE9	Time Stamp Message

NMEA 0183

GGA, GLL, GSA, GSV, RMC, VTG, ZDA, THS, HDT

Proprietary $PSTI (SkyTraq)

Sub-ID	Description
005	Event-triggered Time Stamp (pin-4 trigger)
012	Authenticated Ephemeris Availability
013	OSNMA Status (Galileo authentication)
015	AJAS General Status (anti-jam / anti-spoof)
030	Recommended Minimum 3D GNSS Data (RTK + ENU velocity)
032	RTK Baseline Data
033	RTK RAW Measurement Monitoring (cycle slips)
035	RTK Baseline Data (Rover Moving Base)

RTCM 3.3

MT	Description
1005	Stationary ARP
1019	GPS Ephemeris
1020	GLONASS Ephemeris
1033	Receiver / Antenna Descriptors
1041	NavIC / IRNSS Ephemeris
1042	BeiDou Ephemeris
1046	Galileo I/NAV Ephemeris
1230	GLONASS L1/L2 Code-Phase Biases
1074 / 1077	GPS MSM4 / MSM7
1084 / 1087	GLONASS MSM4 / MSM7
1094 / 1097	Galileo MSM4 / MSM7
1104 / 1107	SBAS MSM4 / MSM7
1114 / 1117	QZSS MSM4 / MSM7
1124 / 1127	BeiDou MSM4 / MSM7
1134 / 1137	NavIC MSM4 / MSM7

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Installation

From source — Linux

git clone https://github.com/SkyTraqGit/skytraq-parser-api.git
cd skytraq-parser-api
make

From source — Windows MSYS2 (UCRT64)

# Inside the MSYS2 UCRT64 shell
pacman -S --needed make mingw-w64-ucrt-x86_64-gcc
git clone https://github.com/SkyTraqGit/skytraq-parser-api.git
cd skytraq-parser-api
make

Pre-built binaries

Each push triggers GitHub Actions to build for Linux and Windows. Download the latest artifact from the Actions tab.

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Usage

gnss_parser [OPTIONS]

  -h               Show help.
  -i <filename>    Read from a file instead of a serial port.
  -p <port>        Serial port (e.g. COM3 or /dev/ttyUSB0).
  -b <baudrate>    Baud rate (default: 115200).
  -a               ASCII-only output (replaces non-ASCII glyphs with text).

Examples

# Parse a captured log
gnss_parser -i mylog.bin

# Live capture from a SkyTraq receiver on Linux
gnss_parser -p /dev/ttyUSB0 -b 115200

# Live capture on Windows
gnss_parser -p COM3 -b 115200

Output colours

Colour	Meaning
Cyan	SkyTraq Binary message
Green	NMEA / $PSTI sentence
Magenta	RTCM 3 message
White	Plain text pass-through
Red	Checksum / CRC error indicator
Yellow	Security warning (PSTI 015 spoofing)

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Project Layout

skytraq-parser-api/
├── src/
│   ├── gnss_parser.h     # shared types, BitReader API
│   ├── util.c            # BitReader, CRC-24Q, NMEA checksum
│   ├── skytraq.c         # SkyTraq Binary decoders
│   ├── nmea.c            # NMEA + $PSTI decoders
│   ├── rtcm3.c           # RTCM 3.3 frame + message decoders
│   └── main.c            # stream sync, serial I/O, CLI
├── .github/workflows/    # CI builds (Linux + Windows MSYS2)
├── Makefile
├── LICENSE               # MIT
└── README.md

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Contributing

Pull requests are welcome. Please ensure:

1. Code compiles cleanly with -Wall -Wextra on both Linux GCC and MSYS2 UCRT64
2. New message decoders include a brief test sentence or frame in the PR description
3. Public API additions are documented in gnss_parser.h

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License

MIT — © 2026 SkyTraq Technology, Inc.

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References

• SkyTraq AN0039 — Binary Messages: Raw Measurement Data Extension
• SkyTraq PX1170AS / PX1120R / PX1125R datasheets — $PSTI proprietary sentences
• RTCM Standard 10403.3 — Differential GNSS (Global Navigation Satellite Systems) Services
• NMEA 0183 v4.x sentence specifications