libgnss-rtcm-swift

libgnss-rtcm-swift is a high-performance, type-safe Swift library for decoding and encoding RTCM (Radio Technical Commission for Maritime Services) messages.

It is a modern Swift port of the core logic of a Orientable AI internal C/C++ project, optimized for real-time differential GNSS (DGNSS) and RTK applications.

Philosophy

"Festina lente" (Hasten slowly). This library prioritizes architectural correctness and numerical precision without sacrificing the performance required for real-time GNSS processing.

Features

• RTCM3 Decoder: Stream-based decoding with automatic synchronization, length validation, and CRC24Q verification.
• Bit-level Precision: Specialized BitReader and BitWriter for efficient field extraction and packing.
• GNSS Time Engine: Robust handling of GPS and BeiDou epochs, including leap second conversions and Time of Week (TOW) calculations.
• Type-safe Models: Idiomatic Swift structures for Ephemeris, Observations, Station coordinates, and SSR corrections.
• Concurrency Ready: Designed for Swift 6 structured concurrency with Sendable compliance.
• Numerical Parity: Verified against the reference C implementation to ensure floating-point precision in orbital parameters and coordinate transforms.

Documentation

Comprehensive API documentation is available at shuwang1.github.io/libgnss-rtcm-swift.

You can also generate documentation locally:

swift package generate-documentation --target RTCM

Supported Messages (RTCM3)

• 1005/1006: Stationary RTK Reference Station ARP.
• 1019: GPS Broadcast Ephemeris.
• More coming soon (MSM support in progress).

Quick Start

Decoding a Stream

import Foundation
import RTCM

let decoder = RTCM3Decoder()

// Simulate receiving bytes from a socket or serial port
let byteStream: [UInt8] = [0xD3, 0x00, 0x13, ...] 

for byte in byteStream {
    let status = decoder.inputByte(byte)
    
    switch status {
    case .station:
        print("Received Station ID: \(decoder.context.staid)")
        print("Coordinates: \(decoder.context.sta.pos)")
    case .ephemeris:
        if let latestEph = decoder.context.nav.eph.last {
            print("Received Ephemeris for Sat: \(latestEph.sat)")
        }
    case .noMessage:
        break // Synchronization or partial message
    default:
        print("Message type \(decoder.context.outtype) received.")
    }
}

Project Structure

• Sources/RTCM: Core logic and decoder.
• Sources/RTCM/Models: Data structures for GNSS data.
• Sources/RTCM/BitUtilities.swift: Low-level bit manipulation.
• Sources/RTCM/GNSSTime.swift: GNSS-specific time conversions.
• Tests/RTCMTests: Unit tests and validation suites.

License

This project is licensed under a proprietary and confidential license - see the LICENSE.md file for details.