Simple NMEA-0183 parser in C#.
This is a basic NMEA-0183 parser that processes bytes fed into its API. When a complete NMEA sentence is successfully read, application-level handlers are invoked.
This is the simplest scenario: using the DefaultNmeaHandler class. DefaultNmeaHandler implements the contract INmeaHandler, which defines support for the following NMEA-0183 data types:
- GGA : Global Positioning System Fix Data
- GSA : Satellite status
- GSV : Satellites in view
- GST : GPS Pseudorange Noise Statistics
- HDT : NMEA heading log
- RMC : Recommended Minimum data for gps
- VTG : Track made good and ground speed
DefaultNmeaHandler implements the contract by invoking the event handler LogNmeaMessage each time a supported NMEA sentence is successfully parsed.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using InvernessPark.Utilities.NMEA;
namespace NMEA.Demo {
class Program {
static void Main(string[] args) {
try {
// ... Sanity check on the arguments
if (args.Length == 0) {
throw new ArgumentException($"Usage: {System.AppDomain.CurrentDomain.FriendlyName} PATH");
}
string sampleFile = args[0];
if (!File.Exists(sampleFile)) {
throw new ArgumentException($"Error! file not found: {sampleFile}");
}
// ... Create an object to handle parsed NMEA messages
DefaultNmeaHandler nmeaHandler = new DefaultNmeaHandler();
nmeaHandler.LogNmeaMessage += str => {
Console.WriteLine("New NMEA Message: {0}", str);
};
// ... Create the NMEA receiver
NmeaReceiver nmeaReceiver = new NmeaReceiver(nmeaHandler);
// ... Attach handler for NMEA messages that fail NMEA checksum verification
nmeaReceiver.NmeaMessageFailedChecksum += (bytes, index, count, expected, actual) => {
Console.Error.WriteLine("Failed Checksum: {0}; expected {1} but got {2}",
Encoding.ASCII.GetString(bytes.Skip(index).Take(count).ToArray()).Trim(),
expected, actual);
};
// ... Attach handler for NMEA messages that contain invalid syntax
nmeaReceiver.NmeaMessageDropped += (bytes, index, count, reason) => {
Console.WriteLine("Bad Syntax: {0}; reason: {1}",
Encoding.ASCII.GetString(bytes.Skip(index).Take(count).ToArray()),
reason);
};
// ... Attach handler for NMEA messages that are ignored (unsupported)
nmeaReceiver.NmeaMessageIgnored += (bytes, index, count) => {
Console.WriteLine("Ignored: {0}",
Encoding.ASCII.GetString(bytes.Skip(index).Take(count).ToArray()));
};
// ... To simulate receiving data in partial chunks, we'll read the sample file
// up to 32 bytes at a time
byte[] buf = new byte[32];
int nReceived;
using (FileStream fs = File.OpenRead(sampleFile)) {
while ((nReceived = fs.Read(buf, 0, buf.Length)) > 0) {
// ... Feed the bytes into the NMEA receiver
nmeaReceiver.Receive(buf.Take(nReceived).ToArray());
}
}
}
catch ( Exception e ) {
Console.Error.WriteLine($"Error! {e.Message}");
}
finally {
Console.WriteLine("Hit ENTER to end program");
Console.ReadLine();
}
}
}
}
The above code can be used in a Windows console project. It take a single command line argument, which is a path to a sample file containging NMEA sentences. Running it with NMEA data will invoke the appropriate callbacks each time a NMEA sentence is received.
You can generate some sample NMEA data at: https://www.nmeagen.org