7.3. BINARY TABLE EXTENSION

57

BITPIX Keyword  The value field shall contain the integer 8, denoting that the array

is an array of 8-bit bytes.

NAXIS Keyword  The value field shall contain the integer 2, denoting that the included

data array is two-dimensional: rows and columns.

NAXIS1 Keyword  The value field shall contain a non-negative integer, giving the

number of 8-bit bytes in each row of the table.

NAXIS2 Keyword  The value field shall contain a non-negative integer, giving the

number of rows in the table.

PCOUNT Keyword  The value field shall contain the number of bytes that follow the

table in the supplemental data area called the heap.

GCOUNT Keyword

The value field shall contain the integer 1; the data blocks contain

a single table.

TFIELDS Keyword  The value field shall contain a non-negative integer representing

the number of fields in each row. The maximum permissible value is 999.

TFORMn Keywords  The TFORMn keywords must be present for all values n = 1, ...,

TFIELDS and for no other values of n. The value field of this indexed keyword shall

contain a character string of the form rTa. The repeat count r is the ASCII representa-

tion of a non-negative integer specifying the number of elements in field n. The default

value of r is 1; the repeat count need not be present if it has the default value. A zero

element count, indicating an empty field, is permitted. The data type T specifies the

data type of the contents of field n. Only the data types in Table 7.6 are permitted.

The format codes must be specified in upper case. For fields of type P or Q, the only

permitted repeat counts are 0 and 1. The additional characters a are optional and are

not further defined in this standard. Table 7.6 lists the number of bytes each data type

occupies in a table row. The first field of a row is numbered 1. The total number of

bytes nrow in a table row is given by

nrow  =

summation over all TFIELD fields of ribi

(7.2)

where ri is the repeat count for field i, bi is the number of bytes for the data type in

field i, and TFIELDS is the value of that keyword, must equal the value of NAXIS1.

FITS Standard