Astrophysics Group

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

Purpose

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:

Resources related to OIFITS
Revision history of OIFITS and related software

Background

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.

Resources

Documentation

The specification for the OIFITS standard was published most recently in T. A. Pauls, J. S. Young, W. D. Cotton, and J. D. Monnier (2005). A data exchange standard for optical (visible/IR) interferometry. Pub. Astron. Soc. Pac., 117, 1255. [PDF of paper]
The paper T. A. Pauls, J. S. Young, W. D. Cotton, and J. D. Monnier (2004), Proc. SPIE 5491, 1231 is intended as a companion to the Format Specification, and gives an overview of OIFITS, explains some of the design decisions, and outlines some software resources for reading and writing the format.
Page on representation of complex visibilities, from NPOI (accompanied an early discussion on the oi-data mailing list)
2003 IAU Working Group Meeting, including presentation by Tom Pauls (PDF)
2002 IAU Working Group Meeting, including presentation by JSY (PDF)
2001 IAU Working Group Meeting and report by Bill Cotton

Software

OIFITSlib. OIFITSlib is a C library for input/output, merging, filtering and checking of optical/IR interferometry datasets in the OIFITS exchange format. OIFITSlib supersedes the example software in C
John Monnier’s OI-DATA: OIFITS support for IDL
Paul Boley’s OIFITS Python module
JSY’s Python module for reading/writing the exchange format. Requires Python 2.2.2 or above and numarray (the newer numpy has also been reported to work) and PyFITS from STScI. Please refer to the module’s docstring for instructions. The oicopy script is provided as an example of how to use the module. Note thatб Paul Boley’s OIFITS Python module and the python interface to OIFITSlib are possible alternatives to this module
mfit model-fitting software (reads the common data format)
Visibility Modelling Tool (VMT) from NExScI
Christian Hummel’s OYSTER IDL-based data reduction and model-fitting software
LITpro model-fitting software from JMMC
OIVAL OIFITS validator from JMMC

Example Datasets

Interferometry Imaging Beauty Contest datasets: 2004, 2006, 2008, 2010
Example datasets at JMMC

Acknowledgments

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 – Announcement – Format 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 – Announcement – Format Specification, release 4
26 November 2002: Post-WG-meeting release of document and example code – Announcement – Format 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

Cavendish Laboratory