next up previous contents index
Next: 7.1.2 Reserved Keywords Up: 7.1 Keywords Previous: 7.1 Keywords

Subsections

7.1.1 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  card images of the primary header must use the keywords defined in Table 7.1 in the order   specified. No other keywords may intervene between the SIMPLE keyword and the last NAXISn keyword.


 
Table 7.1: Mandatory keywords in primary header preceding random groups.
1 SIMPLE
2 BITPIX
3 NAXIS
4 NAXIS1
5 NAXISn, n=2, ..., value of NAXIS
   
  (other keywords, which must include ...)
  GROUPS
  PCOUNT
  GCOUNT
   
last END

The total number of bits in the random groups records exclusive of the fill described in §7.2 is given by the following  expression:


Nbits = |BITPIX| × GCOUNT × (PCOUNT + NAXIS2 × NAXIS3 × ... × NAXISm),(7.1)

where Nbits is  non-negative and the number of bits excluding fill, m is the value  of NAXIS, and  BITPIX, GCOUNT, PCOUNT, and  the NAXISn represent  the  values associated with those keywords.

7.1.1.1SIMPLE Keyword

The card image containing this keyword is structured in the  same way as if a primary data array  were present (§5.4.1).

7.1.1.2BITPIX Keyword

The card image containing this keyword is structured as prescribed in  §5.4.1.

7.1.1.3NAXIS Keyword

The value field shall contain an integer ranging from 1 to  999, representing one more than the number of axes in each data array.

7.1.1.4 NAXIS1 Keyword

The value field shall contain the integer 0, a signature of  random groups format indicating that there is no  primary data array.

7.1.1.5 NAXISn Keywords (n=2, ..., value of NAXIS)

The value field shall contain an integer, representing the  number of positions along axis n-1 of the data array in each group.

7.1.1.6 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.

7.1.1.7 PCOUNT Keyword

The value field shall contain an integer equal to the number  of parameters  preceding each array in a group.

7.1.1.8GCOUNT Keyword

The value field shall contain an integer equal to the  number of random groups present.

7.1.1.8 END Keyword

The card image containing this keyword is structured as described in  §5.4.1.


next up previous contents index
Next: 7.1.2 Reserved Keywords Up: 7.1 Keywords Previous: 7.1 Keywords

5/13/1999