7.2. THE ASCII TABLE EXTENSION

53

of the previous row, independent of the FITS block structure. The positions in the last

data block after the last character of the last row of the table shall be filled with ASCII

spaces.

7.2.4

Fields

Each row in the array shall consist of a sequence of from 0 to 999 fields, as specified

by the TFIELDS keyword, with one entry in each field. For every field, the Fortran [17]

format of the information contained (given by the TFORMn keyword), the location in the

row of the beginning of the field (given by the TBCOLn keyword), and (optionally, but

strongly recommended) the field name (given by the TTYPEn keyword), shall be specified

in the associated header. The location and format of fields shall be the same for every

row. Fields may overlap, but this usage is not recommended. Only a limited set of

ASCII character values may appear within any field, depending on the field type as

specified below. There may be characters in a table row that are not included in any

field, (e.g., between fields, or before the first field or after the last field). Any 7-bit

ASCII character may occur in characters of a table row that are not included in a

defined field. A common convention is to include a space character between each field

for added legibility if the table row is displayed verbatim. It is also permissible to add

control characters, such as a carriage return or line feed character, following the last

field in each row as a way of formating the table if it is printed or displayed by a text

editing program.

7.2.5

Entries

All data in an ASCII table extension field shall be ASCII text in a format that conforms

to the rules for fixed field input in Fortran [17] format, as described below. The only

possible formats shall be those specified in Table 7.3. If values of -0 and +0 need to

be distinguished, then the sign character should appear in a separate field in character

format. TNULLn keywords may be used to specify a character string that represents

an undefined value in each field. The characters representing an undefined value may

differ from field to field but must be the same within a field. Writers of ASCII tables

should select a format for each field that is appropriate to the form, range of values, and

accuracy of the data in that field. This standard does not impose an upper limit on the

number of digits of precision, nor any limit on the range of numeric values. Software

packages that read or write data according to this standard could be limited, however,

in the range of values and exponents that are supported (e.g., to the range that can be

represented by 32-bit or 64-bit binary numbers).

The value of each entry shall be interpreted as described in the following paragraphs.

FITS Standard