Astrophysics Group

Cavendish Laboratory

OIFITS: A Data Exchange Standard for Optical (Visible/IR) Interferometry


OIFITS is a standard for exchanging calibrated, time-averaged data from astronomical optical interferometers, based on the FITS Standard (OIFITS is a registered FITS convention). OIFITS may be used to combine data from multiple interferometer arrays for joint analysis and/or image reconstruction. OIFITS-format files can be prepared from the raw interferometer data without using information about the detailed structure of the target object (i.e. without doing any astrophysical interpretation), yet once the data is in the format, it can be analysed without knowing the details of the instrument. Calibrated data from different interferometers can be treated in the same way (provided there are no residual systematic errors).

See below for links to:


The idea of a common data format for optical and infrared interferometry arose through discussions at the June 2000 NSF-sponsored meeting in Socorro. From 2001 to 2008, Tom Pauls and John Young were responsible, under the auspices of the IAU (and encouraged by Peter Lawson), for coordinating discussion on this topic, and for producing and maintaining the specification document for a FITS-based format.

Preliminary drafts of the format specification were discussed by the community at the 198th Meeting of the American Astronomical Society in June 2001, and the IAU Working Group Meeting in August 2001. The discussion continued by email amongst various interested parties, and the document was revised.

A public pre-release of the format specification and accompanying C code was made in March 2002, followed by a second pre-release of the document in April 2002. This draft was discussed at the August 2002 IAU Working Group Meeting. Comments were presented by participants from the European Southern Observatory and the Interferometry Science Center at Caltech. Since the IAU WG meeting there were two further pre-releases of the format specification, prior to the first ‘production’ release.

The standard was frozen on 7 April 2003 (release 5 of the format specification). The revision numbers of all tables are currently equal to one. Future changes to the format specification will require increments of the revision numbers for the changed tables.

The standard was formalized in 2005 by publication in the Publications of the Astronomical Society of the Pacific. There were no changes to the format at this time.

The OIFITS standard is used in the biennial optical interferometry Imaging Beauty Contests:

Version 2 of the OIFITS standard is being developed. For further details please refer to the JMMC wiki page.




Example Datasets


JSY and TP would especially like to thank Bill Cotton, John Monnier, and David Buscher for their contributions to the first version of the format. Thanks also to the many people who have commented on the various drafts of the format specification.

Revision History

5 June 2015
Added/updated links.
8 July 2014
OIFITSlib links changed to github.
18 August 2010
New links added.
8 June 2009
OIFITSlib bugfix release.
2 July 2008
OIFITSlib released, replaces example C code.
11 January 2008
OIFITS page moved, now part of Cavendish OptInt pages.
19 February 2007
Added links to PASP paper. New-look page including ‘Purpose’ section at top.
22 March 2006
Bugfix in example C code (thanks to John Monnier for identifying the bug).
23 March 2005
COAST stations in test dataset distributed with example C code now use correct coordinate system.
5 July 2004
Added link to SPIE paper.
3 June 2004
Changed email list for discussion.
1 March 2004
Bugfix in Python module.
25 February 2004
Bugfix in example C code.
11 February 2004
Python module now works with pyfits 0.8.0, as well as earlier versions.
10 February 2004
oicopy script modified.
14 August 2003
Python module and example script modified.
1 August 2003
Python module incorporates better documentation and a bugfix. Added example script.
30 July 2003
Added Python module
18 July 2003
First public release of mfit (release 1.2.1)
7 April 2003
Freeze of format specification. Revision numbers of all tables set to unity – AnnouncementFormat Specification, release 5
20 February 2003
Bugfix release of example C code – fixed bugs reading MJD and writing FLAG columns
17 February 2003
Release of document, C and IDL code to fix problem in OI_TARGET table – AnnouncementFormat Specification, release 4
26 November 2002
Post-WG-meeting release of document and example code – AnnouncementFormat Specification, release 3
25 April 2002
Minor correction to document (thanks John Monnier) – Format Specification, release 2
25 March 2002
Pre-release of document and example code – Format Specification, release 1