GNSS L1 Position Resolver

A lightweight C-based GNSS positioning engine that parses RTCM observation and ephemeris messages, computes GPS L1 receiver positions in ECEF and geodetic coordinates, and provides utilities for logging, plotting, and exporting results.

This project is designed as a reference framework for GNSS engineers, students, and developers who want to experiment with raw RTCM data and build a basic positioning solution.

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✨ Features

• RTCM Message Parsing
  • RTCM 1002: Legacy observations (L1 pseudorange + phase).
  • RTCM 1074 (MSM4): Modernized observation messages with multiple cells.
  • RTCM 1019: GPS ephemeris (orbital parameters).
• Positioning Engine
  • Receiver position estimates in ECEF (X, Y, Z).
  • Conversion to latitude, longitude, altitude (LLA) using WGS-84.
  • Epoch-by-epoch logging of receiver track.
• Input Sources
  • Parsed RTCM text logs (e.g., from PyRTCM).
  • TODO: Raw binary RTCM over serial input.
• Data Output
  • Receiver tracks (receiver_track_ecef.dat, receiver_track_geo.dat).
  • Satellite orbit samples (sat_track_ecef.dat, sat_xyz_km.dat).
  • Pseudorange vs. epoch time logs.
• Visualization
  • Plotting with Gnuplot: 2D and 3D orbit/track views.
  • Export to .kml for Google Earth mapping.

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📂 Project Structure

.
├── src/                 # Core C source files
│   ├── main.c           # Entry point
│   ├── app_menu.c       # User menu system
│   ├── app_cleanup.c    # Cleanup routine
│   ├── file_connect.c   # File input utilities
│   ├── serial_connect.c # Serial input (Win/Linux/macOS)
│   ├── df_parser.c      # RTCM message parsing
│   ├── all_plots.c      # Output logging utilities
│   ├── print_utils.c    # print helpers
│   └── ...
├── include/             # Header files
├── example/             # Sample RTCM log files
├── plots/               # Generated .dat files and gnuplot scripts
└── README.md

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🔧 Build Instructions

Requirements

• C compiler:
  • GCC / Clang (Linux, macOS)
  • MSVC or MinGW (Windows)
• Gnuplot (for plotting output data)
• Doxygen (optional, for documentation)

Build (macOS/Linux)

git clone https://github.com/adedolapoadegboye/L1_Position_Algorithm.git
cd L1-Position-Algorithm
make

Run

./bin/gps_resolver

You will see a terminal menu with RTCM input options. Select option 3 and paste the link to the pre-processed file.

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🖥️ Usage

1. Run the Application

• Select the RTCM input source:
  • 1 = Serial Port (raw binary) — not yet implemented
  • 2 = Live parsed text file — not yet implemented
  • 3 = Parsed RTCM text file (recommended)
  • 4 = Exit

2. Provide Input File

If you select option 3, the program will prompt for a parsed log file path. Press Enter to use the default example file in the /example directory.

3. Outputs

After processing, you will find files in the plots/ directory:

• receiver_track_ecef.dat — Receiver positions (ECEF, meters).
• receiver_track_geo.dat — Receiver positions (Lat/Lon, degrees).
• receiver_ecef_epoch_km.dat — Receiver track with epoch indices in kilometers.
• sat_track_ecef.dat — Satellite orbit tracks.
• sat_xyz_km.dat — Satellite XYZ samples in kilometers.

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📊 Visualization

Gnuplot

Run included scripts to generate 2D and 3D PNG plots:

gnuplot plots/plot_2d.gp

gnuplot plots/plot_3d.gp

Example plots:

Google Earth

Convert geodetic positions to KML:

awk 'BEGIN{
  print "<?xml version=\"1.0\" encoding=\"UTF-8\"?>";
  print "<kml xmlns=\"http://www.opengis.net/kml/2.2\"><Document>";
  print "<name>Receiver track</name><Placemark><name>Receiver track</name>";
  print "<Style><LineStyle><color>ff0066ff</color><width>3</width></LineStyle></Style>";
  print "<LineString><tessellate>1</tessellate><coordinates>";
}
{ printf "  %.8f,%.8f,0\n", $2, $1 }   # lon,lat,alt
END{
  print "</coordinates></LineString></Placemark></Document></kml>";
}' plots/receiver_track_geo.dat > plots/receiver_track.kml'

Open receiver_track.kml saved in /plots in Google Earth to view the path.

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📖 Documentations

This project uses Doxygen for code documentation.

The generated documentation is in the dir docs/html/index.html.

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🛠️ Roadmap

• Implement live raw RTCM parsing over serial port.
• Support additional RTCM messages (e.g., 1020, 1045, 1046).
• Add GLONASS, Galileo, BeiDou support.
• Extend positioning algorithms (e.g., Weighted Least Squares, EKF).
• Real-time visualization hooks.

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🤝 Contributing

Contributions are welcome!s

• Fork this repo
• Submit a pull request with clear commits
• Follow Doxygen doc style and consistent formatting

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📜 License

This project is licensed under the MIT License. See the LICENSE file for details.