GribApi.NET

What it is

GribApi.NET is a C# wrapper around the European Centre for Medium Range Weather Forecasting's powerful ecCodes, a C library for reading, writing, and converting GRIB1 and GRIB2 files. ecCodes is the successor to grib_api.

GRIB is a format commonly used in meteorology to store weather data. GribApi.NET makes it easy to encode and decode these data by providing access to both GRIB editions through a set of GRIB API keys. It can handle all common GRIB formats from centres such as NOAA's NCEP and the ECMWF. GribApi.NET and grib_api are licensed under the friendly Apache License 2.0.

Special thanks to John L'Heureux, for his contributions as scientific advisor.

Features

• Read and write GRIB 1 and 2 messages
• Easy to understand API
• Supports x86, x64, and "All CPU"
• Thread safe
• JPEG and PNG compression support
• Multi-field support
• Support for custom GRIB formats

GRIB Tools

You can also use grib_api via CLI. Checkout the GRIB tools package on Chocolatey. At the very least, you'll find it very helpful for debugging.

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Docs

The documentation is very much a WIP, but you'll find the ecCodes website helpful.

• GRIB Parameter Database
• Key Concepts
• Example Key Dump
• ecCodes API

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Usage

Make sure you have the MSVC 2015 redistributables installed. If you don't, you can use chocolatey,

C:\> choco install vcredist2015

Install GribApi.NET using Nuget. From Package Manager Console run

PM> Install-Package Grib.Api 

Troubleshooting

In general, GribApi.NET should "just work". In rare cases, GribApi.NET may have difficulty locating the definitions directory, which contains a number of dependencies.

To solve this problem, you can manually set the path to the definitions:

GribEnvironment.Init();
GribEnvironment.DefinitionsPath = "C:\\Some\\Path\\Grib.Api\\definitions";

Examples

Getting grid information from a GRIB message:

	using (GribFile file = new GribFile("mygrib2.grib"))
	{
		GribMessage msg = file.First();

		Console.WriteLine("Grid Type: " + msg.GridType);
		
      // GribApi.NET normalizes the coordinate values to degrees.
		double latInDegrees = msg["latitudeOfFirstGridPoint"].AsDouble();
		
		// values are also accessible as strings
		Console.WriteLine("latitudeOfFirstGridPoint = " + msg["latitudeOfFirstGridPoint"].AsString());
	}

Iterating messages in a file:

	using (GribFile file = new GribFile("mygrib1.grib"))
	{
		foreach (GribMessage msg in file)
		{
			// do something
		}
	}

Iterating messages in a stream Note: iterating streams is currently much slower than iterating a file:

   var gribStream = new GribStream(myStream);
   foreach (GribMessage msg in gribStream)
   {
      // do something
   }

Iterating lat/lon/value:

	GribMessage msg = gribFile.First();
	
	// the values in GridCoordinateValues are calculated by grid type
	foreach (GridCoordinateValue val in msg.GridCoordinateValues)
	{
		if (val.IsMissing) { continue; }

		Console.WriteLine("Lat: {0} Lon: {1} Val: {2}", val.Latitude, val.Longitude, val.Value);
	}

Finding the four nearest grid values to a coordinate

	GribMessage msg = gribFile.First();
   var referencePt = msg.GridCoordinateValues.First();
   
   Console.WriteLine("Getting the four nearest grid points to Lat: {0} Lon: {1}", referencePt.Latitude, referencePt.Longitude);

   var nearest = msg.FindNearestCoordinates(referencePt);
   
	foreach (var near in nearest)
	{
      GridCoordinateValue val = near.Value;
		Console.WriteLine("Lat: {0} Lon: {1} Val: {2} Distance: {3}", var.Latitude, val.Longitude, val.Value, near.Distance);
	}

Cherry-picking messages by parameter name

	using(GribFile file = new GribFile(@".\TestData\Pacific.wind.7days.grb"))
	{
		var vComp = file.Where(m => m.Name.Contains("V-component of wind m s**-1")).First();

		foreach (var val in vComp.GridCoordinateValues)
		{
			Console.WriteLine("Lat: {0} Lon: {1} Val: {2}", val.Latitude, val.Longitude, val.Value);
		}
	}

Dumping message keys to a pretty-printed string:

	using (GribFile file = new GribFile("mygrib.grb"))
	{
		GribMessage msg = file.First();
		
		Console.WriteLine(msg.Dump());
	}

Dumping grid values to a CSV:

	using (GribFile file = new GribFile("mygrib.grb"))
	{
		GribMessage msg = file.First();
		
		msg.WriteValuesToCsv("my\\file.csv");
	}

Getting raw data:

	GribMessage msg = gribFile.First();
	double[] rawValues;
	
	// get a copy of the raw values stored in the message
	msg.Values(out rawValues);

Editing a single message and saving to a new file:

	string outPath = "out.grb";
	string readPath = "some.grb";
	
	using (GribFile readFile = new GribFile(readPath))
	{
		Console.WriteLine("Writing 1 message from {0} to {1}", readPath, outPath);

		var msg = readFile.First();
		msg["latitudeOfFirstGridPoint"].AsDouble(42);
      
      double[] rawValues;
      msg.Values(out rawValues);
      // update the values
      // ...
      msg.SetValues(rawValues);
      
		GribFile.Write(outPath, msg);
	}

Appending multiple messages to an existing file:

	using (GribFile readFile = new GribFile(readPath))
	{                
		Console.WriteLine("Appending {0} messages from {1} to {2}", readFile.MessageCount, readPath, outPath);

		GribFile.Write(outPath, readFile as IEnumerable<GribMessage>, FileMode.Append);
		// or, more simply:
		//   GribFile.Write(outPath, readFile, FileMode.Append);
	}

For more examples, checkout the tests.

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Building

The current build is only designed for Windows and Visual Studio. I am eager to get it converted to CMake and make it cross-platform. Even a consistent build using make under msys2 would be great. I'd love some help doing this. :)

First, install the Nuget packages (this assumes you have nuget on PATH):

nuget install NUnit -Version 2.6.4 -O src\GribApi.NET\packages\

Install NUnit 2.6.4. Then run:

build\build_gribapi.cmd [build|rebuild] [VS version, 11|12|14] [Debug|Release] [nuget package version]

E.g., to build with Visual Studio 2015 (VS version 14):

build\build_gribapi.cmd build 14 Debug

Running Tests

1. Install NUnit and expose it on PATH.
2. Run build/run_tests <architecture> <configuration> [optional "1" to break the tests on start], e.g.

build/run_tests x64 Debug

or

build/run_tests x86 Debug 1