Information About the FITS Interferometry Data Interchange Format
This web page provides basic information about the FITS Interferometry
Data Interchange (or FITS-IDI) format. The FITS-IDI format is a variant
of FITS that may be used to transport radio interferometry data.
FITS-IDI files store radio interferometry data and associated calibration
data as a sequence of FITS binary tables. Different types of tables are
used to carry visibility measurements, information about the aperature
synthesis arrays, calibration data and so on.
This format was designed to be used to export raw data from aperture
synthesis arrays and to be written in near real-time as the data are correlated.
The following VLBI correlators export data in FITS-IDI format.
The FITS-IDI format can be read using the AIPS
task FITLD. FITS-IDI files containing calibration information in the form
of FLAG, SYSTEM_TEMPERATURE, GAIN_CURVE, or
PHASE-CAL tables can only be read by the version of FITLD in the
15OCT98 release of AIPS (or later releases).
A document describing the FITS-IDI format is available as both a PDF
document and a PostScript
document. This document describes the FITS-IDI format as it is
interpreted by the version of FITLD in the 15OCT98 release of AIPS and
supercedes the description of the FITS-IDI format in VLBA
Correlator Memo No. 108.
This document is maintained by Chris Flatters at NRAO. It is currently
in draft form and you should feel free to mail any comments or corrections
The document was last updated on September 16 1998. A list of errata
The FITS-IDI format was originally proposed as the export format for the
VLBA in VLBA
Correlator Memo No. 108. This was intended to be a general format that
could be used by other instruments and was also adopted by the Canadian
S2 correlator and by Mitaka.
Over time, a number of practical difficulties were encountered which
led to the FITS-IDI format that was actually implemented at the VLBA being
slightly different from that described in the original memo. Many of the
changes were negotiated privately between the VLBA correlator group and
the AIPS group and were not published. This meant that there was no single
document that described the FITS-IDI format.
This was clearly an undesirable situation and a decision was made to
produce a document that defined the FITS-IDI document as it was currently
implemented. This document would then become the new specification for
the FITS-IDI format and would be the basis for future enhancements.
The first draft of the new specification was made public on September
Maintained by Chris Flatters
Last updated on September 16 1998