APRS

A pure Elixir library for parsing APRS (Automatic Packet Reporting System) packets.

It handles the full range of common APRS formats — position reports (uncompressed and compressed), Mic-E, weather, telemetry, objects, items, messages, status reports, PHG/DF data, NMEA and more — and returns a flat, predictable map for each packet. There are no runtime dependencies.

Installation

Add :aprs to your dependencies in mix.exs:

def deps do
  [
    {:aprs, "~> 2.0"}
  ]
end

Requires Elixir 1.17 or later.

Usage

Aprs.parse/1 takes a TNC2-format packet string and returns {:ok, packet} or {:error, reason}:

{:ok, packet} = Aprs.parse("N0CALL>APRS,TCPIP*,qAC,T2TEST:=4903.50N/07201.75W-Test message")

packet.data_type   #=> :position_with_message
packet.latitude    #=> 49.05833333333333
packet.longitude   #=> -72.02916666666667
packet.comment     #=> "Test message"

Every packet map carries the same envelope fields, the type-specific fields under :data_extended, and those same type-specific fields flattened into the top level for convenience:

%{
  id: "d00797958416d5581386",   # per-VM random prefix plus a counter
  sender: "N0CALL",
  path: "TCPIP*,qAC,T2TEST",
  destination: "APRS",
  information_field: "=4903.50N/07201.75W-Test message",
  data_type: :position_with_message,
  base_callsign: "N0CALL",
  ssid: "0",
  received_at: ~U[2026-09-01 17:03:51.259500Z],
  resultcode: "success",
  resultmsg: "OK",
  data_extended: %{
    data_type: :position_with_message,
    latitude: 49.05833333333333,
    longitude: -72.02916666666667,
    comment: "Test message",
    symbol_table_id: "/",
    symbol_code: "-",
    aprs_messaging?: true,
    compressed?: false,
    format: :uncompressed,
    has_position: true,
    position_ambiguity: 0,
    posambiguity: 0,
    posresolution: 18.52,
    messaging: 0,
    timestamp: nil,
    altitude: nil,
    course: nil,
    speed: nil,
    phg: nil,
    radiorange: nil,
    dao: nil,
    wx: nil
  },
  # ... flattened data_extended fields plus reference-parser aliases ...
}

Errors are returned rather than raised:

Aprs.parse("not a packet")
#=> {:error, :invalid_packet}

Coordinates are plain floats. Every packet format reports the same units, whichever way the packet encoded them: speed in knots, altitude in feet, course in degrees (1-360, where 360 is due north and 0 or a missing value means unknown) and posresolution in metres.

Reference-parser compatibility fields

Alongside the snake_case fields above, each packet includes field names matching the common reference APRS parsers, so output can be consumed by existing tooling:

srccallsign, dstcallsign, body, origpacket, header, alive, type, digipeaters, posambiguity, format, messaging, symboltable, symbolcode, daodatumbyte, gpsfixstatus, mbits, message, phg, wx, radiorange, itemname. Packets that carry a position also get posresolution.

type is the standard type string for the packet ("location", "wx", "object", "item", "message", "messageack", "messagerej", "telemetry", "telemetry-message", "status", "capabilities", …), and digipeaters is a list of %{call: String.t(), wasdigied: 0 | 1}.

format is how the position was encoded — :uncompressed, :compressed, :mice, :nmea, :maidenhead, or :unknown.

More examples

Compressed position:

{:ok, packet} = Aprs.parse("N0CALL>APRS,TCPIP*:!/5L!!<*e7> sTComment")

packet.data_type          #=> :position
packet.format             #=> :compressed
packet.latitude           #=> 49.5
packet.longitude          #=> -72.75000393777269
packet.data_extended.compression_type  #=> "T"

Mic-E:

{:ok, packet} = Aprs.parse(~s(KD8XYZ-9>T2SXTS,WIDE1-1:`(_fn"Oj/]"4H}Testing Mic-E))

packet.data_type                    #=> :mic_e
packet.latitude                     #=> 42.6405
packet.longitude                    #=> -112.129
packet.data_extended.speed          #=> 20.0
packet.data_extended.course         #=> 251
packet.data_extended.altitude       #=> 160.761154855
packet.data_extended.message_type   #=> :standard

Weather:

{:ok, packet} =
  Aprs.parse("N0CALL>APRS,TCPIP*,qAC,T2TEST:_12345678c000s000g000t000r000p000P000h00b00000")

packet.data_type  #=> :weather
packet.wx
#=> %{
#     wind_direction: 0, wind_speed: 0, wind_gust: 0, temperature: 0,
#     rain_1h: 0.0, rain_24h: 0.0, rain_since_midnight: 0.0,
#     humidity: 100, pressure: 0.0, luminosity: nil, snow: nil,
#     timestamp: "12345678", raw_weather_data: "c000s000g000t000r000p000P000h00b00000"
#   }

A field the report leaves out is nil, so a station that sends no snow gauge reading is distinguishable from one reporting no snow.

Weather data embedded in a position comment is detected and extracted automatically into the same :wx field, and the comment is cleaned of it.

Telemetry:

{:ok, packet} = Aprs.parse("N0CALL>APRS,TCPIP*:T#005,199,000,255,073,123,01101001")

packet.data_type            #=> :telemetry
packet.data_extended.telemetry
#=> %{seq: "005", vals: [199.0, 0.0, 255.0, 73.0, 123.0], bits: "01101001"}

Message:

{:ok, packet} = Aprs.parse("N0CALL>APRS,TCPIP*,qAC,T2TEST::WU2Z     :Hello there{001")

packet.data_type                  #=> :message
packet.data_extended.addressee    #=> "WU2Z"
packet.data_extended.message_text #=> "Hello there"
packet.data_extended.message_number #=> "001"

Object:

{:ok, packet} = Aprs.parse("N0CALL>APRS,TCPIP*:;LEADER   *092345z4903.50N/07201.75W>088/036")

packet.data_type                 #=> :object
packet.data_extended.object_name #=> "LEADER"
packet.data_extended.live_killed #=> "*"
packet.data_extended.course      #=> 88
packet.data_extended.speed       #=> 36.0

Supported packet types

The legacy rule that ! may appear anywhere in the first 40 bytes of the information field is honoured when the leading byte is not itself a data type indicator.

Additional handling for position-bearing packets, following the same order as the reference Ham::APRS::FAP parser:

• A leading data extension — course/speed (088/036), PHG (PHG5132), RNG (RNG0050) or DFS (DFS2360) — parsed as mutually exclusive alternatives and removed from the comment; a course/speed pair followed by /BRG/NRQ is decoded as a DF report (bearing, nrq, df_hits, df_range, df_quality)
• Altitude anywhere in the comment (/A=001234), validated to −10 000..500 000 ft
• Base91 telemetry embedded in the comment (|SS...|), removed from the comment and decoded into telemetry: %{seq: integer, vals: [integer], bits: String.t() | nil} (the key is absent when the comment carries no telemetry)
• DAO precision extensions (!W12!), exposed as dao and daodatumbyte, with the extra digit applied to the returned coordinates
• Position ambiguity, with the matching posresolution in metres
• Weather data on the _ symbol, exposed as :wx and :weather
• Device identification from the TOCALL, or from the Mic-E comment prefix/suffix (Aprs.DeviceParser)

Other public helpers

• Aprs.version/0 — library version string
• Aprs.parse_datatype/1 — the data type of an information field, without parsing it
• Aprs.AX25 — callsign and path parsing/validation
• Aprs.KISSHelpers — KISS ↔ TNC2 frame conversion
• Aprs.DeviceParser — device identification from a packet or raw string
• Aprs.PHGHelpers — decode the digits of a PHG or DFS value
• Aprs.Convert — Ultimeter unit conversions

Development

mix deps.get
mix test                    # full suite (unit + StreamData property tests)
mix test --stale            # only what your changes affect
mix format                  # formats and applies Styler
mix credo                   # static analysis
mix dialyzer                # type analysis
mix docs                    # generate HexDocs output

Elixir/OTP versions are pinned in .tool-versions. A Nix flake dev shell is provided — nix develop, or automatically via direnv (.envrc). CI runs the format check, Credo, and the test suite on GitHub Actions.

Contributions should go on a feature branch and be opened as a pull request against main.

License

GNU General Public License v3.0 or later — see LICENSE.