7.3. BINARY TABLE EXTENSION

59

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

ASCII spaces.

7.3.2

Other Reserved Keywords

In addition to the reserved keywords defined in §4.4.2 (except for EXTEND and BLOCKED),

the following other reserved keywords may be used to describe the structure of a binary

table data array. They are optional, but if they appear within a binary table extension

header, they must be used as defined in this section of this standard.

TTYPEn Keywords  The value field for this indexed keyword shall contain a character

string giving the name of field n. It is strongly recommended that every field of the table

be assigned a unique, case-insensitive name with this keyword, and it is recommended

that the character string be composed only of upper and lower case letters, digits, and

the underscore (`_', decimal 95, hexadecimal 5F) character. Use of other characters is

not recommended because it may be difficult to map the column names into variables in

some languages (e.g., any hyphens, `*' or `+' characters in the name may be confused

with mathematical operators). String comparisons with the TTYPEn keyword values

should not be case sensitive (e.g., 'TIME' and 'Time' should be interpreted as the same

name).

TUNITn Keywords  The value field shall contain a character string describing the

physical units in which the quantity in field n, after any application of TSCALn and

TZEROn, is expressed. Units must follow the prescriptions in §4.3.

TSCALn Keywords  This indexed keyword shall be used, along with the TZEROn key-

word, to linearly scale the values in the table field n to transform them into the physical

values that they represent using Eq. 7.1. It must not be used if the format of field n is

A, L, or X. For fields with all other data types, the value field shall contain a floating-

point number representing the coefficient of the linear term in Eq. 7.1, which is used to

compute the true physical value of the field, or, in the case of the complex data types C

and M, of the real part of the field, with the imaginary part of the scaling factor set to

zero. The default value for this keyword is 1.0. For fields of type P or Q, the values of

TSCALn and TZEROn are to be applied to the values in the data array in the heap area,

not the values of the array descriptor (see §7.3.5).

TZEROn Keywords  This indexed keyword shall be used, along with the TSCALn key-

word, to linearly scale the values in the table field n to transform them into the physical

values that they represent using Eq. 7.1. It must not be used if the format of field n is A,

L, or X. For fields with all other data types, the value field shall contain a floating-point

number representing the true physical value corresponding to a value of zero in field n

FITS Standard