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 aperture 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 Flatter's first
draft and in Diamond's VLBA Correlator Memo No. 108.
It was last updated on August 29, 2000. A list of errata is available.
The FITS-IDI format was originally proposed as the export format
for the VLBA in VLBA Correlator Memo No. 108 by Phil Diamond. 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 16
1998.
Some typographical errors were corrected on December 3 1998 and a
number of other revisions and corrections have been made subsequently.