GribApi.NET

What it is

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

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. GribApi.NET and grib_api are licensed under the friendly Apache License 2.0.

Special thanks to John L'Heureux, Meteorological Data Analyst at aWhere, Inc., for his contributions as scientific advisor.

Features

• Read and write GRIB 1 and 2 messages
• Easy to understand API
• Thread safe
• JPEG and PNG compression support
• Multi-field support

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Docs

The documentation is very much a WIP, but you'll find grib_api's wiki, helpful.

• Key Concepts
• Example Key Dump

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Usage

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

PM> Install-Package Grib.Api 

Shadow Copying

ASP.NET, NUnit, and other frameworks employ a technique called "shadow copying". When Grib.Api.dll is shadow copied, GribApi.NET may have difficulty locating the Grib.Api directory, which is required for proper operation.

There are several ways to deal with this issue. The simplest is to set theGRIB_API_DIR_ROOT before calling GribApi.NET for the first time. The value should be the directory containing the Grib.Api directory. E.g., for C:\Some\Path\Grib.Api, set:

Environment.SetEnvironmentVariable("GRIB_API_DIR_ROOT", "C:\\Some\\Path", EnvironmentVariableTarget.Process);

Examples

Getting grid information from a GRIB message:

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

		Console.WriteLine("Grid Type: " + msg.GridType);
		
		double latInDegrees = msg["latitudeOfFirstGridPoint"].AsDouble();
		// GribApi.NET automatically converts coordinate values to degrees. This follows the best practice
		// advised by ECMWF and normalizes the values returned by the API. You can opt-out of degree
		// conversion by calling `AsDouble(false)`, e.g.:
		//     double rawValue = msg["latitudeOfFirstGridPoint"].AsDouble(false);
		// Only values capable of degree conversion are affected.
		
		// all values are also accessible as strings
		Console.WriteLine("latitudeOfFirstGridPointInDegrees = " + msg["latitudeOfFirstGridPoint"].AsString());
	}

Iterating multiple messages:

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

Iterating lat/lon/value:

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

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

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

Getting raw data:

	GribMessage msg = gribFile.First();
	double[] rawValues;
	
	// 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);
		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. :)

To build, you can use build/Grib.Api.Master.sln. The native projects are set to use the v110 (Visual Studio 2012) Cpp build tools. However, you can change these to match your version of VS in the native projects' Properties > General > Platform Toolset field.

To run a full release build, you'll need NUnit and Nuget on PATH. Then run:

build/build_gribapi.cmd [build|rebuild] [VS version, 11|12|14]

E.g., to build with Visual Studio 2012 (VS version 11):

build/build_gribapi.cmd build 11

Running SWIG

Most of the interop interfaces are generated using SWIG and included in the repository. If you want generate the interfaces yourself, you'll need SWIG installed and available on PATH. Then run build/swig_gen.cmd.

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