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3 Definitions, Acronyms, and Symbols

 
Used to designate an ASCII blank.
ANSI
American National Standards  Institute.
Array
A sequence of data values.  This sequence corresponds to the elements in a rectilinear, n-dimension matrix ( $0 \leq n \leq 999$ ).
Array value
The  value of an element of an array in a FITS file, without the application of the associated linear transformation to derive the physical  value.
ASCII
American National Standard Code for Information
[1] Interchange.
ASCII blank
The ASCII character for blank  which is represented by hexadecimal 20 (decimal 32).
ASCII character
Any  member of the 7-bit ASCII character set.
ASCII NULL
Hexadecimal  00.
ASCII text
ASCII characters  hexadecimal 20-7E.
Basic FITS
The FITS structure  consisting of  the primary header  followed by a single primary  data array.
Bit
A single binary digit.
Byte
An ordered sequence of eight consecutive bits treated as a single entity.
Card image
A sequence of 80 bytes containing  ASCII text , treated as a logical entity.
Conforming extension
An extension whose keywords and organization  adhere to the requirements for conforming extensions defined in §4.4.1 of this standard. 
DAT
4mm Digital Audio Tape.
Deprecated
This term  is used to refer to obsolete structures that should not be used for new applications but remain valid.
Entry
A single value in a table.
Extension
A  FITS HDU appearing  after the primary HDU in a FITS file.
Extension name
The identifier used to distinguish a particular extension HDU from others of the same type, appearing as the value of the  EXTNAME keyword. 
Extension type
An extension  format.
Field
A set of zero or more table entries collectively described by a single format.
File
A sequence of one or more records terminated by an end-of-file indicator appropriate to the medium.
FITS
Flexible Image Transport System.
FITS file
A file with a format that conforms to the specifications in this document.
FITS structure
One  of the components of a FITS file: the primary  HDU, the random groups  records, an extension , or, collectively, the special records  following the last extension.
Floating point
A computer representation of a real number.
Fraction
The  field of the mantissa  (or significand) of a floating point number that lies to the right of its implied binary point.
Group parameter value
The  value of one of the parameters preceding a group in the random groups structure, without the application of the associated linear transformation.
GSFC
Goddard Space Flight Center.
HDU
Header and Data Unit. A data structure consisting of a header and the data the header describes. Note that an  HDU may consist entirely of a header with no data records.
Header
A series of card images organized within one or more FITS logical records that describes structures and/or data which follow it in the FITS file.
Heap
A supplemental data area, currently defined to follow the table in a  binary table extension.
IAU
International Astronomical  Union.
IAUFWG
  International Astronomical Union FITS Working Group.
IUE
International Ultraviolet Explorer. 
IEEE
Institute of Electrical and Electronic  Engineers.
IEEE NaN
IEEE Not-a-Number  value.
IEEE special values
Floating point number byte patterns that have a special, reserved meaning, such as -0, $\pm \infty$, ± underflow, ± overflow, ± denormalized, ± NaN.  (See Appendix H).
Indexed keyword
A  keyword that is of the form of a fixed root with an appended positive integer count.
Keyword
The first eight bytes of a header card image.
Logical record
A record comprising 2880 8-bit bytes.
Mandatory keyword
A  keyword that must be used in all FITS files or a keyword required in conjunction with particular  FITS structures.
Mantissa
Also  known as  significand. The component of an IEEE floating point number consisting of an explicit or implicit leading bit to the left of its implied binary point and a fraction field to the right.
Matrix
A data array of two or more dimensions.
NOST
NASA/Science Office of Standards and Technology .
Physical value
The  value in physical units  represented by an element of an array and possibly derived from the array value  using the associated, but optional, linear transformation.
Picture element
A single location within an array.
Pixel
Picture element.
Primary data array
The  data array contained in the  primary HDU.
Primary HDU
The first HDU in a FITS file.
Primary header
The  first header in a FITS file, containing information on the overall contents of the file as well as on the primary data array.
Record
A sequence of bits treated as a single logical entity.
Reference point
The point along a given  coordinate axis , given in units  of pixel number, at which a value and increment are defined.
Repeat count
The  number of values represented in a binary table  field.
Reserved keyword
An  optional keyword that may be used only in the manner defined in this standard.
Special records
A series of 23040-bit (2880 8-bit byte) records, following the primary  HDU,  whose internal structure does not otherwise conform to that for the primary HDU or to that specified for a conforming extension  in  this standard.
Standard extension
A  conforming  extension  whose  header and data content are specified explicitly in this standard.
Type name
The value of the XTENSION keyword , used to identify the type  of the extension  in the data following.
Valid value
A member of a data array or table corresponding to an actual physical quantity.

next up previous contents index
Next: 4 FITS File Organization Up: Definition of the Flexible Previous: 2 References

5/13/1999