The FITS Support Office has developed a simple C program called
headlist to read and list all the FITS headers in a file,
including extension headers as well as the primary header. It reads the
file from standard input and writes to standard output. This program
is useful when presented with a new and unfamiliar file. It does not
evaluate the file and is not guaranteed to work if there are serious
errors in the file, for example, if the size of the data in an extension
is not correctly described by the values of BITPIX, NAXIS,
the NAXIS
, PCOUNT, and GCOUNT.
The FITS Support Office has a software package written in C called
the FITS Product Conformance Tester (FPCT), which validates conformance
of primary HDUs to the FITS Standard. While limited to Basic FITS
structures, its diagnostics are more descriptive than those of other
packages; it is also more forgiving, as it attempts to continue past
errors by making its best guess at what was intended rather than
terminating on the first error. It is thus most useful for those new to
FITS. The FPCT checks the primary header of a FITS file for the
presence of all required keywords and their order. If it can retrieve
information (values of BITPIX, NAXIS, and the
NAXIS) needed to read the primary data array, and the data in
the array are integer, it will, at the user's option, produce an output
file containing array members selected by the user. If the header is in
conformance, it will print a message to that effect. If the header is
not in conformance, but the software has inferred a data description, it
will print a warning that retrieval of the data array may not be
correct, with an indication of the severity of the problem. If the FPCT
has been unable to retrieve the information needed to read the primary
data array, it will print a diagnostic with information about the header
errors and stop.
Both packages are available in the software subdirectory of the FITS anonymous ftp directories described in section 6.1.1 or can be obtained electronically by request from the FITS Support Office. The FPCT is accompanied by an instructions file. Read this file before using the software.
The errtest subdirectory contains a number of primary HDUs designed for checking the ability of FITS readers to cope with the unexpected. It includes one that is in compliance with the standard and a number of others that are identical except for deliberately inserted errors in syntax. One is simply a text extract, to test the behavior of the FITS reader when confronted with such a file, as might occur if such a file were mistakenly retrieved instead of a FITS file. An aaareadme.doc file describes the contents of this subdirectory. These files must be retrieved in binary format if they are to work properly. Many Web browsers interpret FITS files as text by default.