nmea-kit

Bidirectional NMEA 0183 parser/encoder with AIS decoding and transponder-message encoding, written in Rust.

Crate	nmea-kit
Version	0.8.7
MSRV	1.85.0
Edition	2024
Dependencies	0
License	MIT OR Apache-2.0
NMEA sentences	80 (bidirectional: parse + encode)
AIS application sentences	2 (bidirectional: parse + encode)
AIS message types	All numeric Types 1-27 decoded; Types 1/2/3, 4, 5, 9, 11, 12, 14, 18, 19, 21, 24 and 27 also encoded

• Shared frame layer — handles $ parametric and ! encapsulated framing, IEC 61162-450 tag blocks
• 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::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").expect("valid depth sentence");
// "$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);
}

Encode an AIS transponder message

use nmea_kit::ais::messages::NavigationStatus;
use nmea_kit::ais::transmit::{
    AisChannel, AisEncodable, AisTransmitOptions, ClassAPosition, ClassAPositionType,
};

let report = ClassAPosition {
    message_type: ClassAPositionType::PositionReport,
    repeat_indicator: 0,
    mmsi: 244_670_316,
    navigation_status: NavigationStatus::UnderWayEngine,
    rate_of_turn: None,
    sog: Some(10.0),
    position_accuracy: true,
    longitude: Some(4.379_285),
    latitude: Some(51.894_750),
    cog: Some(70.6),
    heading: Some(71),
    timestamp: Some(5),
    maneuver_indicator: 0,
    raim: false,
    communication_state: 0,
};

let sentences = report
    .to_sentences(AisTransmitOptions::vdm(AisChannel::A))
    .expect("valid Type 1 report");
// `sentences` contains complete, checksummed !AIVDM lines ready for the simulator.

AisTransmitOptions::vdo() emits !AIVDO instead. Messages that require several fragments, including Type 5 and long Type 12/14 safety text, require .with_sequence_id(0..=9). Every emitted line is at most 82 characters, including the checksum and CRLF terminator. The crate constructs sentences only: the simulator owns cadence, TDMA access, and reactions to Type 15.

Encode an AIS application-layer sentence

use nmea_kit::ais::sentences::Abm;

let abm = Abm {
    num_frags: Some(1),
    frag_num: Some(1),
    msg_id: Some(0),
    mmsi: Some(123456789),
    channel: Some('1'),
    vdl_msg_num: Some(6),
    payload: Some("testpayload".to_string()),
    fill_bits: Some(0),
};

let sentence = abm.to_sentence("AI").expect("valid AIS sentence");
// "!AIABM,1,1,0,123456789,1,6,testpayload,0*08\r\n"

Architecture

flowchart TD
    raw["raw line"] --> pf["parse_frame()"]
    pf --> frame["NmeaFrame\nprefix · talker · sentence_type · fields"]
    frame --> known["$ + known type (incl. VSD)"]
    frame --> unknown["$ + unknown type"]
    frame --> ais_in["! AIVDM/AIVDO"]
    frame --> ais_sentence["! AIS app sentence"]
    known --> typed["Typed struct\nMwd, Rmc…"]
    unknown --> raw_fields["Raw fields\npass-through"]
    ais_in --> ais_msg["AisMessage enum\nAll numeric Types 1-27"]
    ais_sentence --> ais_typed["AIS sentence struct\nAbm, Bbm"]

Loading

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 AIVDM/AIVDO 6-bit ASCII armor into a bitstream, handles multi-fragment reassembly, and extracts typed fields. ais::transmit encodes complete !AIVDM or !AIVDO lines for Types 1/2/3, 4, 5, 9, 11, 12, 14, 18, 19, 21, 24 and 27. It owns sentence fragmentation, while the simulator remains responsible for choosing its emission cadence. The !-prefixed AIS application sentences ABM and BBM live under ais::sentences. VSD is a conventional NMEA sentence ($--VSD) exposed under nmea::sentences.

Supported types

NMEA 0183 sentences (bidirectional) — full coverage list

Category	Sentences
Position	DTM, RMC, GGA, GLL, GNS
Satellites	GBS, GSA, GSV, GST
Wind	MWD, MWV, VPW, VWR, VWT
Heading	HDT, HDG, HDM, THS
Course & Speed	RPM, VBW, VDR, VLW, VTG, VHW
Depth	DPT, DBT, DBS, DBK
Steering	HSC, ROT, RSA
Environment	MDA, MTA, MTW, XDR¹
Waypoints & Routes	AAM, APB, BEC, BOD, BWC, BWR, BWW, RMB, RTE, WCV, WPL, XTE
Radar / Targets	OSD, RSD, TLL, TTM
Safety & Alarms	ACK, ACN, ALA, ALC, ALF, ALR, ARC, DOR, DSC, DSE, EVE, FIR, HBT
AIS interface	VSD ($--VSD)
Communication	TXT
Time	ZDA
Proprietary	PASHR, PGRME, PSKPDPT

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

AIS application sentences (bidirectional)

Sentences
ABM, BBM

AIS messages — full type list

Type(s)	Decoded struct	Encoded model	Description
1, 2, 3	PositionReport	ClassAPosition	Class A position report
4	BaseStationReport	BaseStation	Base station UTC + position
5	StaticVoyageData	ClassAStaticVoyage	Static and voyage data (Class A)
6	BinaryAddressed		Addressed binary message (DAC/FID + data)
7, 13	BinaryAck		Binary / safety acknowledge
8	BinaryBroadcast		Binary broadcast message (DAC/FID + data)
9	SarAircraftReport	SarAircraft	Standard SAR aircraft position
10	UtcDateInquiry		UTC/date inquiry
11	UtcDateResponse	UtcDateResponse	UTC/date response (mobile station)
12	SafetyAddressed	SafetyAddressed	Addressed safety-related message
14	SafetyBroadcast	SafetyBroadcast	Safety-related broadcast message
15	Interrogation		Interrogation (request data from vessel)
16	AssignmentModeCommand		Assigned mode command
17	DgnssBroadcast		DGNSS correction broadcast
18	PositionReport	ClassBPosition	Class B standard position
19	PositionReport	ClassBExtendedPosition	Class B+ extended position
20	DataLinkManagement		FATDMA slot reservations
21	AidToNavigation	AidToNavigation	Aid-to-navigation report (buoys, beacons)
22	ChannelManagement		Channel management
23	GroupAssignment		Group assignment command
24	StaticDataReport	ClassBStaticPartA, ClassBStaticPartB	Static data report (Class B)
25	BinarySingleSlot		Single-slot binary message
26	BinaryMultiSlot		Multiple-slot binary message
27	LongRangePosition	LongRangePosition	Long range position (satellite AIS, 1/10 minute precision)

Key improvements over existing crates

Issue	nmea 0.7 / ais 0.12	nmea-kit
NMEA sentence coverage	~10 types, rest manual	80 NMEA types + 2 AIS application sentences
AIS message coverage	~5 types	All numeric Types 1-27
Encoding	Read-only	All NMEA + Types 1/2/3, 4, 5, 9, 11, 12, 14, 18, 19, 21, 24, 27
Error distinction	Can't tell unsupported vs malformed	Frame errors vs content errors
AIS lat/lon precision	f32 (11m error)	f64
AIS sentinels	91/181/511 leak to caller	Filtered to None at decode
Tag blocks	Manual stripping	Built into frame layer
Dependencies	nom (AIS)	Zero

Features

[dependencies]
nmea-kit = "0.8"

Feature	Default	Enables
nmea	yes	All 80 NMEA sentence types
ais	yes	24 AIS message decoders, transponder encoding, and ABM/BBM application sentences
positioning	via nmea	GGA, GLL, RMC, GNS
speed	via nmea	VTG, VHW, VBW, RMC, RPM, VDR
heading	via nmea	HDG, HDM, HDT, THS
wind	via nmea	MWD, MWV
depth	via nmea	DBT, DBS, DBK, DPT
aam, ack, acn, ala, alc, alf, alr, arc, apb, bec, bod, bwc, bwr, bww, dbk, dbs, dbt, dor, dpt, dsc, dse, dtm, eve, fir, gbs, gga, gll, gns, gsa, gsv, gst, hbt, hdg, hdm, hdt, hsc, mda, mta, mtw, mwd, mwv, osd, pashr, pcdin, pgrme, pgrmt, phtro, pklid, pklds, pklsh, pknds, prdid, pskpdpt, rmb, rmc, rot, rpm, rsa, rsd, rte, tlb, tll, ttd, ttm, txt, vbw, vdr, vhw, vlw, vpw, vsd, vtg, vwr, vwt, wcv, wpl, xdr, xte, zda	via nmea	Individual NMEA sentence types
abm, bbm	via ais	Individual AIS application-layer sentence types

Use a group feature for common use cases:

# Only positioning sentences (GGA, GLL, RMC, GNS), no AIS
nmea-kit = { version = "0.8", default-features = false, features = ["positioning"] }

Cherry-pick individual sentences you need:

nmea-kit = { version = "0.8", default-features = false, features = ["rmc", "mwd"] }

NMEA-only (no AIS, all sentences):

nmea-kit = { version = "0.8", default-features = false, features = ["nmea"] }

Coordinate conversion

NMEA sentences encode lat/lon as DDMM.MMMM; AIS uses decimal degrees. Two helpers bridge the gap:

use nmea_kit::nmea::{ddmm_to_decimal, decimal_to_ddmm};

// Parse a GGA latitude field: "4807.038" N → 48.1173°
let lat = ddmm_to_decimal(4807.038); // → 48.1173

// Encode back for a sentence
let ddmm = decimal_to_ddmm(48.1173); // → 4807.038

Apply the N/S / E/W sign separately (negate for S or W).

Documentation

File	Purpose
CONTRIBUTING.md	Getting started, TDD workflow, test rules, adding a sentence type
SENTENCES.md	Full NMEA / AIS coverage matrix
CHANGELOG.md	Release history
AGENTS.md	API surface, struct fields, and patterns (optimized for LLMs)

License

MIT OR Apache-2.0