nmea-kit

Bidirectional NMEA 0183 parser/encoder with AIS message decoding, written in Rust.

• 25 NMEA sentence types — parse and encode with checksum
• 9 AIS message types — decode Class A/B position, base station, safety broadcasts, AtoN, long range
• Shared frame layer — handles $ (NMEA) and ! (AIS) framing, IEC 61162-450 tag blocks
• Zero dependencies
• No nom, no proc-macro — FieldReader/FieldWriter helpers for clean sequential parsing

Quick start

Parse an NMEA sentence

use nmea_kit::{parse_frame, NmeaSentence};

let frame = parse_frame("$IIMWD,046.,T,046.,M,10.1,N,05.2,M*43").unwrap();
let sentence = NmeaSentence::parse(&frame);

match sentence {
    NmeaSentence::Mwd(mwd) => {
        println!("True wind dir: {:?}°", mwd.wind_dir_true);
        println!("Wind speed: {:?} kts", mwd.wind_speed_kts);
    }
    _ => {}
}

Encode and send an NMEA sentence

use nmea_kit::nmea::NmeaEncodable;
use nmea_kit::nmea::sentences::Dbt;

let dbt = Dbt {
    depth_feet: Some(7.7),
    depth_meters: Some(2.3),
    depth_fathoms: Some(1.3),
};

let sentence = dbt.to_sentence("SD");
// "$SDDBT,7.7,f,2.3,M,1.3,F*05\r\n"

Decode AIS messages

use nmea_kit::parse_frame;
use nmea_kit::ais::{AisParser, AisMessage};

let mut parser = AisParser::new();
let frame = parse_frame("!AIVDM,1,1,,A,13aEOK?P00PD2wVMdLDRhgvL289?,0*26").unwrap();

if let Some(AisMessage::Position(pos)) = parser.decode(&frame) {
    println!("MMSI: {}, lat: {:?}, lon: {:?}", pos.mmsi, pos.latitude, pos.longitude);
}

Architecture

raw line ──→ parse_frame() ──→ NmeaFrame { prefix, talker, sentence_type, fields }
                                    |
                     +--------------+--------------+
                     v              v               v
               $ + known      $ + unknown     ! (AIVDM/AIVDO)
                     |              |               |
                     v              v               v
              Typed struct    Raw fields      AisMessage enum
              (Mwd, Apb..)   (pass-through)  (Types 1-5,14,18,19,21,24,27)

Frame layer validates checksum, strips tag blocks, extracts talker ID and sentence type. Shared by both NMEA and AIS.

NMEA content uses FieldReader/FieldWriter for sequential field parsing and encoding. Each sentence type is a standalone struct with parse(), encode(), and to_sentence(). Parsing is lenient: parse() always returns Some for known types, mapping missing or malformed fields to None. This is intentional for marine instruments that often produce partial data.

AIS content decodes 6-bit ASCII armor into a bitstream, handles multi-fragment reassembly, and extracts typed fields. Read-only (transmitting AIS requires certified hardware).

Supported types

NMEA 0183 sentences (bidirectional) — full coverage list

¹ Xdr has an additional to_sentences() -> Vec<String> method that automatically splits many measurements into multiple sentences to stay within the 82-character NMEA line limit.

AIS messages (read-only) — full type list

Key improvements over existing crates

Features

[dependencies]
nmea-kit = "0.2"

Use a group feature for common use cases:

# Only positioning sentences (GGA, GLL, RMC, GNS), no AIS
nmea-kit = { version = "0.2", default-features = false, features = ["positioning"] }

Cherry-pick individual sentences you need:

nmea-kit = { version = "0.2", default-features = false, features = ["rmc", "mwd"] }

NMEA-only (no AIS, all sentences):

nmea-kit = { version = "0.2", default-features = false, features = ["nmea"] }

Adding a new sentence type

Create src/nmea/sentences/xyz.rs:

use crate::nmea::field::{FieldReader, FieldWriter, NmeaEncodable};

#[derive(Debug, Clone, PartialEq)]
pub struct Xyz {
    pub some_value: Option<f32>,
    pub some_flag: Option<char>,
}

impl Xyz {
    pub fn parse(fields: &[&str]) -> Option<Self> {
        let mut r = FieldReader::new(fields);
        Some(Self {
            some_value: r.f32(),
            some_flag: r.char(),
        })
    }
}

impl NmeaEncodable for Xyz {
    const SENTENCE_TYPE: &str = "XYZ";

    fn encode(&self) -> Vec<String> {
        let mut w = FieldWriter::new();
        w.f32(self.some_value);
        w.char(self.some_flag);
        w.finish()
    }
}

Then add mod xyz; pub use xyz::*; (feature-gated) to sentences/mod.rs, one line to the nmea_sentences! invocation in nmea/mod.rs, and xyz = [] to [features] in Cargo.toml.

License

MIT OR Apache-2.0