56

SECTION 7. STANDARD EXTENSIONS

Table 7.5.

Mandatory keywords in binary table extensions.

#

Keyword

1

XTENSION= 'BINTABLE'

2

BITPIX = 8

3

NAXIS = 2

4

NAXIS1

5

NAXIS2

6

PCOUNT

7

GCOUNT = 1

8

TFIELDS

.

.

.

(other keywords, including (if TFIELDS is not zero) . . . )

TTYPEn, n=1, 2, . . . , k where k is the value of TFIELDS (Recommended)

TFORMn, n=1, 2, . . . , k where k is the value of TFIELDS (Required)

.

.

.

last

END

7.3

Binary Table Extension

The binary table extension is similar to the ASCII table in that it provides a means

of storing catalogs and tables of astronomical data in FITS format, however, it offers

more features and provides more efficient data storage than ASCII tables. The numerical

values in binary tables are stored in more compact binary formats rather than coded

into ASCII, and each field of a binary table can contain an array of values rather than

a simple scalar as in ASCII tables. The first keyword in a binary table extension shall

be XTENSION= 'BINTABLE'.

7.3.1

Mandatory Keywords

The XTENSION keyword is the first keyword of all binary table extensions. The seven

keywords following (BITPIX . . . TFIELDS) must be in the order specified in Table 7.5,

with no intervening keywords.

XTENSION Keyword

The value field shall contain the character string 'BINTABLE'.

FITS Standard