42

SECTION 6. RANDOM GROUPS STRUCTURE

Table 6.1.

Mandatory keywords in primary header preceding random groups.

#

Keyword

1

SIMPLE = T

2

BITPIX

3

NAXIS

4

NAXIS1 = 0

5

NAXISn, n=2, . . . , value of NAXIS

.

.

.

(other keywords, which must include . . . )

GROUPS = T

PCOUNT

GCOUNT

.

.

.

last

END

NAXIS1 Keyword  The value field shall contain the integer 0, a signature of random

groups format indicating that there is no primary data array.

NAXISn Keywords (n=2, . . . , value of NAXIS) The NAXISn keywords must be

present for all values n = 2, ..., NAXIS, in increasing order of n, and for no larger

values of n. The value field shall contain an integer, representing the number of positions

along axis n-1 of the data array in each group.

GROUPS Keyword  The value field shall contain the logical constant T. The value T

associated with this keyword implies that random groups records are present.

PCOUNT Keyword  The value field shall contain an integer equal to the number of

parameters preceding each array in a group.

GCOUNT Keyword  The value field shall contain an integer equal to the number of

random groups present.

END Keyword This keyword has no associated value. Bytes 9 through 80 shall contain

ASCII spaces (decimal 32 or hexadecimal 20).

FITS Standard