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Section 6

Random Groups Structure

The random groups structure allows a collection of `groups', where a group consists

of a subarray of data and a set of associated parameter values, to be stored within

the FITS primary data array. Random groups have been used almost exclusively for

applications in radio interferometry; outside this field, there is little support for reading

or writing data in this format. Other than the existing use for radio interferometry data,

the random groups structure is deprecated and should not be further used. For other

applications, the binary table extension (§7.3) provides a more extensible and better

documented way of associating groups of data within a single data structure.

6.1

Keywords

6.1.1

Mandatory Keywords

The SIMPLE keyword is required to be the first keyword in the primary header of all

FITS files, including those with random groups records. If the random groups format

records follow the primary header, the keyword records of the primary header must

use the keywords defined in Table 6.1 in the order specified. No other keywords may

intervene between the SIMPLE keyword and the last NAXISn keyword.

SIMPLE Keyword  The keyword record containing this keyword is structured in the

same way as if a primary data array were present (§4.4.1).

BITPIX Keyword

The keyword record containing this keyword is structured as pre-

scribed in §4.4.1.

NAXIS Keyword  The value field shall contain an integer ranging from 1 to 999, rep-

resenting one more than the number of axes in each data array.

FITS Standard