NAisParser 0.2.0

NAisParser is an AIVDM/AIVDO Parser for .NET

NAisParser is a marine Automatic Identification System (AIS) AIVDM/AIVDO NMEA message decoder for .NET Standard.

The library is Written in F# using FParsec. The main advantage of using a parser combinator library such as FParsec, and using an applicative (functor) style is that the implementation looks very similar to the specification, thus the code is clean, easy to extend and validate against the specification.

Currently parses:

• Types 1, 2 and 3: Position Report Class A
• Type 4: Base Station Report
• Type 5: Static and Voyage Related Data

The parser works in two stages. In the first stage you parse the outer layer of the AIS data packet:

var line = "!BSVDM,1,1,,A,13mAwp001m0MMrjSoomG6mWT0<1h,0*16";
var result = parser.TryParse(line, out AisResult aisResult); // Returns true

If result is true then you have a valid AisResult such as:

{Vdm = BS;
 Count = 1uy;
 Number = 1uy;
 Seq = None;
 Channel = A;
 Payload =
  [3; 53; 17; 63; 56; 0; 0; 1; 53; 0; 29; 29; 58; 50; 35; 55; 55; 53; 23; 6; 53;
   39; 36; 0; 12; 1; 48];
 Type = 1uy;}

If false then the packet if fragmented and you will need to supply more data by calling TryParse again with another line of data, e.g.

var line1 = "!BSVDM,2,1,2,A,53mDDD02>EjthmLJ220HtppE>2222222222222164@G:34rdR?QSkSQDp888,0*15";
var line2 = "!BSVDM,2,2,2,A,88888888880,2*3F";

var result1 = parser.TryParse(line1, out AisResult aisResult); // Returns false
var result2 = parser.TryParse(line2, out AisResult aisResult); // Returns true

If an error occurs while parsing TryParse will raise an ArgumentException.

In the second stage you parse the AIS payload data depending on the type of message. The type of message is available in the Type property of a valid AisResult from stage 1. To parse a message of type 1 you call TryParse with an out parameter of type MessageType123. To parse a message of type 5 you call TryParse with an out parameter of type MessageType5.

var result = parser.TryParse(aisResult, out MessageType123 type123Result);

If result is true then you have a valid MessageType123 such as:

{Repeat = 0uy;
 Mmsi = 257196000;
 Status = UnderWayUsingEngine;
 RateOfTurn = 0.0;
 SpeedOverGround = 117;
 PositionAccuracy = 0;
 Longitude = 62.69262167;
 Latitude = 6.437268333;
 CourseOverGround = 181.9;
 TrueHeading = 179;
 TimeStamp = 50;
 ManeuverIndicator = NoSpecialManeuver;}

Se below for a full example. Enjoy!

Dependencies

• .NETStandard 1.6
• FParsec (>= 1.0.3)
• FSharp.Core (>= 4.3.4)

Install

NAisParser is available as a NuGet package.

dotnet add package NAisParser

C# Example

using NAisParser;

...

var parser = new Parser();

using (StreamReader reader = new StreamReader(stream))
{
    string line;
    while ((line = reader.ReadLine()) != null)
    {
        var result = parser.TryParse(line, out AisResult aisResult);
        if (!result) continue;

        switch (aisResult.Type)
        {
            case 1:
            case 2:
            case 3:
                result = parser.TryParse(aisResult, out MessageType123 type123Result);
                Console.WriteLine(type123Result.ToString());
                break;
            case 5:
                result = parser.TryParse(aisResult, out MessageType5 type5Result);
                Console.WriteLine(type5Result.ToString());
                break;
            default:
                break;
        }
    }
}