2.2 Random Groups

While FITS began as a means of transporting simple digitized images from machine to machine, it was soon realized that FITS could provide a framework for transporting other types of data. The first new FITS structure, designed by Greisen and Harten during late 1979 - early 1980 (Greisen and Harten 1981; hereafter FITS Paper II), was composed of a set of ``random groups'', each consisting of a sequence of parameters followed by a small array of data. The number and meaning of the parameters and the dimensions of the array would be the same for all groups. In some of the early literature, this structure is described as an ``extension'', but such terminology is now inappropriate, as the name ``extension'' refers to the structure described in sections 2.3 and 3.3. The principal application of this format was to radio astronomical aperture synthesis visibility data. These data consist of small groups of arrays that occur in a relatively random manner on one or more axes.

Random groups has failed to attain wide use in other areas and is now being replaced even for aperture synthesis data by binary tables. Future use is discouraged.

At the 1982 General Assembly, the IAU endorsed FITS, including the Random Groups format, as the recommended format for transport of binary data (IAU 1983).