described as "image/fits", but the first axes SHOULD be non-
degenerate (i.e., the degenerate axes SHOULD be the highest
dimensions). An algorithm designed to render only two-dimensional
images will be capable of displaying such an NAXIS=3 or NAXIS=4 FITS
array that has one or two of the axes consisting of a single pixel,
and an application writer SHOULD consider coding this capability into
the application. Writers of new applications which generate FITS
files intended to be described as "image/fits" SHOULD consider using
the WCSAXES keyword [WCS1] to declare the dimensionality of such
degenerate axes, so that NAXIS can be used to convey the number of
non-degenerate axes.
Magic number(s): "SIMPLE = T"
Jeff Uphoff of the National Radio Astronomy Observatory (NRAO) has
contributed database entries for the magic number file which is used
by the Unix "file" command. Magic number files with these entries
are distributed with a variety of Unix-like operating systems. In
addition to recognizing a FITS file using the string given above, the
Uphoff entries also recognize the data type of the pixels in the
PHDU.
File extension(s): fits
This file extension SHOULD NOT be interpreted as a prescription.
The FITS standard originated in the era when files were stored and
exchanged via magnetic tape; it does not prescribe any nomenclature
for files on disk. Various sites within the FITS community have
long-established practices where files are presumed to be FITS by
context. File extensions used at such sites commonly indicate
content of the file instead of the data format.
In the absence of other information it is reasonably safe to presume
that a file name ending in ".fits" is intended to be a FITS file.
Nevertheless, there are other commonly used extensions; e.g., ".fit",
".fts", and many others not suitable for listing in a media type
registration.
Intended usage: Common
Persons to contact for further information:
"Steve Allen"
"Don Wells"
Author/Change controller:
"Steve Allen"
The IAU FITS Working Group may authorize changes to this document.
6. References
6.1. Normative References
[Require] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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