Packet.Aprs 0.40.0

Packet.Aprs

Decode-focused APRS payload codec - position, Mic-E, message, object, item, status, telemetry.

Parses Automatic Packet Reporting System (APRS) information-field payloads per the APRS spec, with named strict-vs-pragmatic parse options for the quirks seen on the live APRS-IS firehose. Part of Packet.NET, a .NET amateur-radio / AX.25 packet stack - this package sits above Packet.Ax25 and decodes the bytes carried inside an AX.25 UI frame's info field.

Install

dotnet add package Packet.Aprs

Quick start

Each report type has a static TryDecode that takes the info-field bytes (with or without the leading data-type identifier) and yields a readonly record struct:

using Packet.Aprs;

// An uncompressed position report's info field (DTI '!' kept; it's stripped for you).
ReadOnlySpan<byte> info = "!4725.22N/00810.83E_WX-station"u8;

if (AprsPositionDecoder.TryDecode(info, out AprsPosition pos))
{
    Console.WriteLine($"{pos.Latitude:F5}, {pos.Longitude:F5}");  // 47.42033, 8.18050
    Console.WriteLine($"symbol {pos.SymbolTable}{pos.SymbolCode}, {pos.Format}");
    Console.WriteLine(pos.Comment);                                // WX-station
}

The decoder is strict on the fixed-position fields (digit ranges, hemisphere indicators, base-91 range) and returns false for any structural defect rather than throwing. For the payload types where real-world senders diverge from the spec (status text, telemetry, legacy Mic-E DTIs), pass an AprsParseOptions preset:

// Reject anything the spec forbids:
AprsTelemetryDecoder.TryDecode(info, AprsParseOptions.Strict, out var telemetry);

// Accept the firehose's quirks (this is also the parameterless default):
AprsStatusDecoder.TryDecode(info, AprsParseOptions.Lenient, out var status);

Mic-E is the exception: it splits data across the AX.25 destination address and the info field, so its decoder also needs the 6-character destination base:

AprsMicEDecoder.TryDecode("Q0PDN0", info, out AprsMicE micE);

Key types

• AprsPositionDecoder - uncompressed (DDMM.mmN) and base-91 compressed position reports; TryDecode strips DTI + timestamp, TryDecodePayload for embedded position payloads.
• AprsMicEDecoder / AprsMicE - Mic-E reports, decoded from the destination base + info field (MicEMessageType carries the standard/custom/emergency bits).
• AprsMessageDecoder / AprsMessage - text messages (DTI :) with addressee and optional message ID.
• AprsObjectDecoder / AprsItemDecoder - object (DTI ;) and item (DTI )) reports, with an embedded position.
• AprsStatusDecoder / AprsTelemetryDecoder - status text (DTI >) and telemetry (DTI T) reports.
• AprsParseOptions - strict-vs-pragmatic parse knobs with Strict / Lenient / Direwolf / AprsIs presets; each accommodation is a named, individually-toggleable flag.
• AprsCallsign - permissive monitor-layer callsign that round-trips APRS-IS spellings (letter SSIDs, lowercase, long bases) that strict Packet.Core.Callsign rejects, with coercion helpers.

See also

• Source & issues
• Packet.Ax25 - the AX.25 frames whose info field carries these payloads
• Packet.Core - shared primitives including the strict Callsign

AGPL-3.0-licensed. Part of the Packet.NET stack.