Fits-Cs

Fits-Cs is an attempt to bring FITS support to .NET environment. Currently, NASA lists only two .NET libraries written in C#, one of which is apparently unavailable, another - was updated in 2003.

In the era of .NET Core, there should be a better parsing option.

What this project is about?

This library is an updated version of the custom FITS IO lib that is used with the DIPOL-UF optical polarimeter. While polarimeter requires only basic support of (uncompressed) single-unit (i.e. no extensions) image support, it is good to have universal tool (or at least as flexible as possible) to deal with FITS. While FITS standard is quite complicated, the majority of the features are intended to be supported.

The concept

Fits-Cs is built around FitsReader/FitsWriter classes, which mimic the role of System.IO.StreamReader/StreamWriter. The stream is read as a sequence of 2880-bytes blobs, and a valid sequence of blobs can be converted into a data block, which stores header key collection, information about the data types and size of the data array and a buffer containing all the data corresponding to this unit. Another library will be used to parse this segmented data blocks into images/tables/other formats.

To send data to a stream, it should be first converted to correct data blocks, which represent one valid FITS unit, which are then written as as sequence of 2880-bytes blobs.

An example

// Assuming suport of C# 8.0
static async Task Example()
{
    var path = "path-to-some-fits.fits";
    using var fStr = new FileStream(path, FileMode.Open, FileAccess.Read);
    await using var fitsReader = new FitsReader(fStr);

    await foreach (var block in fitsReader.EnumerateBlocksAsync())
    {
        // block is a valid FITS unit, and reader enumerates through 
        // all valid units in the file
        foreach (var key in block.Keys)
            // Prints formatted key data with a data-type prefix
            // key in collection can be null only if parsing fails, 
            // which happens only if it does not conform to the standard
            Console.WriteLine(key?.ToString(true));
    }
}

To test the library, a set of default FITS files provided by NASA is used. The goal is to be able to reasonable parse everything presented there, including 64-bit integers in main data array and keywords (implemented) and CONTINUE special keyword-extension to regular strings (halfway there). No support for non-standard characters in key names is planned.