Table of contents The Registry of FITS (Flexible Image Transport System) Conventions provides a central and authoritative repository for documenting conventions that have been developed by the FITS user community for storing and transmitting various types of information in FITS format data files. A FITS convention is defined as a set of related FITS header keywords, and optionally, other data structures within FITS tables, FITS images, or other types of conforming FITS extensions that are to be used for a specific purpose. The IAU (International Astronomical Union) FITS Working Group is responsible for the this Registry and for the rules and procedures for entering new conventions into it.These conventions are not necessarily recommended by the IAU FITS Working Group (IAUFWG) for reuse in new applications. The registration process is mainly designed to ensure that the documentation about the existing FITS convention meets a minimum level of completeness and clarity. A separate and more rigorous review process is required before a FITS convention is endorsed by the IAUFWG and is approved as part of the FITS Standard.See also the local FITS conventions, the registered extension names, and keyword dictionaries. Conventions That Have Been Reviewed and Incorporated Into the FITS StandardThe following six conventions were reviewed by the IAU FITS Working Group in 2016 and have been officially incorporated into version 4.0 of the FITS Standard. The documentation about these conventions provided here may contains additional details than is given in the FITS Standard, but in case of any discrepancies, the specifications in the Standard shall supersede what is given here. Header Space Convention A simple convention for pre-allocating scratch space in a FITS header for later use when writing keywords.Submitted: 9-December-2014 by W. Pence, NASA/GSFC (Goddard Space Flight Center)Registered: April 2015Date and Place of First Usage: circa 1996, in the CFITSIO software library for reading and writing FITS filesExtent of Usage: Moderate usage, especially in data files produced by high energy astrophysics missions (e.g., from the HEASARC (High Energy Astrophysics Science Archive Research Center)).Full Header Space Convention PDF Format DocumentationFull Header Space Convention Postscript Format DocumentationSample FITS File: headerspace.fits - This file has scratch space in the header for about 100 more keywords.Sample Header Listing: headerspace.txt - This listing suppresss the non-significant blank keywords, so they are not visible. CONTINUE Long String Keyword Convention The CONTINUE long string keyword convention may be used to assign a character string value to a FITS keyword that is longer than the 68-character limit for the value of a single FITS keyword. Under this convention, the long string value is divided into multiple substrings, each of which is no longer than 67 characters in length. An ampersand character ("&") is appended to every substring, except for the last one. Each substring, enclosed in single quote characters, is written in order to the FITS header. The first substring is given as the value of the specified keyword; the remaining substrings are all written to keywords that have the name CONTINUE in bytes 1 through 8, and have space characters in bytes 9 and 10. Since the CONTINUE keywords do not have the "=" value indicator in byte 9, they have no formal value. FITS readers that do not support this convention should interpret the CONTINUE keywords as being equivalent to a COMMENT keyword.The following is an example of this convention:SVALUE = 'This is a long string value &' CONTINUE 'extending& ' CONTINUE ' over 3 lines.'that is equivalent to the following single keyword:SVALUE = 'This is a long string value extending over 3 lines.'See the full documentation (available below) for the complete set of rules and recommendations regarding the use of this convention.See also the extensive discussion of earlier versions of this convention on the FITSBITS email list in May 1993 and July/August 1994.Submitted: 11-July-2007 by W. Pence, NASA/GSFC (on behalf of the HEASARC)Registered: October 2007Date and Place of First Usage: circa 1994, HEASARCExtent of Usage: Extensively used in data files from the Rossi Timing Explorer (RXTE) mission, and occasionally in data files from other high energy astrophysics missions supported by the HEASARC. It has also been used in some the Chandra data files produced by Chandra X-ray data center. This convention is supported by the CFITSIO library for reading and writing FITS files.CONTINUE Long String PDF Documentation; CONTINUE Long String Postscript DocumentationFITSBITS discussion of CONTINUE Long String ConventionSample FITS File: rxte.fits (from the RXTE mission). In particular, note the descriptive keywords for column 12 of the first table extension in this file.Sample Header Listing: rxte.txt Column Limits Convention Keywords to describe the minimum and maximum values in table columns: TDMINn, TDMAXn, TLMINn, and TLMAXnSubmitted: 15-June-2006 by W. Pence, NASA/GSFC (on behalf of the HEASARC)Registered: 10-October-2006Date and Place of First Usage: circa 1993, HEASARCExtent of Usage: Widely used, especially in data files produced by high energy astrophysics missions, e.g., from the HEASARC, Chandra X-ray Center (CXC), and XMM (X-ray Multi-Mirror Mission) Newton.Column Limits PDF Documentation; Column Limits Word Format DocumentationSample FITS File: swift_events.fits (from the Swift X-ray and Gamma-ray mission)Sample Header Listing: swift_events.txt Checksum Keyword Convention The CHECKSUM and DATASUM keywords that are embedded in the FITS header are used to verify the integrity of the HDU (Header Data Unit). Verifying that the accumulated 32-bit 1's complement checksum of the HDU is equal to -0 provides a fast and fairly reliable way to determine that the HDU has not been modified or corrupted.Submitted: June 2007 by Rob Seaman (NOAO (National Optical Astronomy Observatory)), William Pence (NASA/GSFC), and Arnold Rots (CXC/SAO (Smithsonian Astrophysical Observatory))Registered: July 2007Date and Place of First Usage: 1994, in the "Save the Bits" data archive at NOAO {See the 1994 ADASS conference paper).Extent of Usage: The checksum keyword convention is used in data files from many different observatories, including KPNO (Kitt Peak National Observatory) and the Chandra X-ray Center.CHECKSUM PDF Documentation; CHECKSUM Postscript DocumentationPublic Comments about this convention: The North American FITS committee reviewed this convention for possible adoption as a FITS Standard. The comments may be seen in these archives of the WGAS (Working Group on Astronomical Software) email list: April 2002 WGAS Discussion Archive, May 2002 WGAS Discussion Archive, and November 2002 WGAS Discussion Archive.Sample FITS File: checksum.fitsSample Header Listing: checksum.txt Tiled Image Compression Convention A convention for compressing FITS images and storing the compressed byte stream in a variable-length array column in a FITS binary table. Optionally, the image may be divided into rectangular tiles, and each tile is compressed separately. Any number of different compression algorithms can be supported. Current implementations support GZIP, RICE, H-Compress, and the IRAF (Image Reduction and Analysis Facility) pixel list compression technique (PLIO) algorithms. The fpack FITS file compression utility supports this table compression convention. The fpack Users Guide contains useful general information and tips regarding image compression.Submitted: Version 2.0 in November-2006 by W. Pence, NASA/GSFC (on behalf of the authors).Registered: March 2007Date and Place of First Usage: circa 2001: support for this image compression convention was implementd in the CFITSIO library that is maintained by the HEASARC. Soon after, support for pixel lists in this compressed format was added to IRAF.Extent of Usage: This convention has been used by various astronomical data archives, including, the Canadian Astronomy Data Center (CADC), the Optical Gravitational Lensing Experiment (OGLE), and the NOAO Science Archive.Full Documentation:Latest 2.3 version (July 2013): Version 2.3 PDF format, Version 2.3 Postscript format, Version 2.3 Latex source. Updates include:added support for a new variant of the GZIP algorithm, called GZIP_2, in which the bytes in the pixel array are shuffled into decreasing order of significant before being compressed with gzip. This is especially effective with floating point arrays.added new variant to the algorithm for dithering floating-point pixels in which the pixels that are equal to 0.0 are not dithered.added support for the '1Q' variable-length array FITS format, to support compressed files that are too large to be represented with the 32-bit pointer addresses in the '1P' variable-length array format.Latest 2.2 version (May 2011): Version 2.2 PDF format, Version 2.2 Postscript format, Version 2.2 Latex source - Modified Section 3 to document the optional "GZIP_COMPRESSED_DATA" column, which provides an alternative compression method for floating-point image tiles that cannot be compressed with the usually quantization method.Previous 2.1 version (August 2009): Version 2.1 PDF format, Version 2.1 Postscript, Version 2.1 Latex source - Modified Section 4 and Appendix A to describe a new "subtractive dithering" technique which preserves more information when quantizing floating-point FITS images.Previous 2.0 version (November 2006): Version 2.0 PDF format, Version 2.0 Postscript, Version 2.0 Latex source.Comments: Tiled Image Compression FITSBITS discussion.Sample FITS Files (all files contain the same image of Messier 13)16-bit integer pixels, original, and compressed using rice, gzip, H-compress, and PLIO algorithms. (Note: the PLIO algorithm is not intended for general use, but is included here for completeness).32-bit floating point pixels, original, and rice compressedSample Header Listing: rice compressed image header listing Tiled Table Compression Convention A convention for compressing FITS binary tables and storing the compressed byte stream in a variable-length array column in a FITS binary table. Optionally, the table may be divided into tiles each containing equal-sized blocks of rows that are compressed together. The current implementation supports the GZIP and RICE lossless compression algorithms. The fpack FITS file compression utility supports this table compression convention. The fpack Users Guide contains useful general information and tips regarding data compression.Submitted: Version 2.0 in November-2013 by W. Pence, NASA/GSFC (on behalf of the authors).Registered: 2015Date and Place of First Usage: 2010: The Fpack and Funpack FITS file compression utility programs have supported beta versions of this convention starting in 2010. The full implementation that supports all the documented features was introduced in 2013.Extent of Usage: limited mainly to experimental prototyping applicationsFull Documentation:Latest 2.0 version (November 2013): Version 2.0 PDF format, Version 2.0 Postscript, Version 2.0 Latex source.Previous 1.0 version (August 2009): Version 1.0 PDF format, Version 1.0 Postscript, Version 1.0 Latex source.Comments:Sample FITS Files original uncompressed table, and compressed tableSample Header Listing: uncompressed table header, and compressed table header. General Conventions Green Bank Keyword Convention This convention was originally developed at a meeting in Green Bank, West Virginia to address how to represent World Coordinate System (WCS) information for images that are stored within a vector column of a FITS binary table. This concept has since been generalized to have wider applications.Submitted: 23-Aug-2010 by W. Pence, NASA/GSFCRegistered: January 2015Date and Place of First Usage: circa 1989, Green Bank/NRAOExtent of Usage: Widely used, especially in radio astronomy data.Full Green Bank Keyword Convention Documentation (PDF)Sample FITS File: TREG_091209.cal.acs.fits - This file contains processed Green Bank Telescope (GBT) data.Sample Header Listing: TREG_091209.cal.acs.txt FITS Header Inheritance Convention If an extension header contains the keyword INHERIT = T, then that header should inherit the keywords from the primary header (except for the mandatory and commentary keywords).Submitted: March 2007 by N. Zarate (NOAO) and P. Greenfield (STScI (Space Telescope Science Institute))Registered: May 2007Date and Place of First Usage: 1995, at StScI and NOAO/KPNOExtent of Usage: Used in data sets destributed by the STScI from several instruments on the Hubble Space Telescope, including STIS (Space Telescope Imaging Spectrograph), NICMOS (Near Infrared Camera and Multi-Object Spectrometer), and ACS (Advanced Camera for Surveys). Also used in various data sets distributed from NOAO/KPNO and by various instruments and data pipelines operated by, or partly by, the United Kingdom, such as INT (Isaac Newton Telescope) WFC (Wide Field Camera), UKIRT (United Kingdom Infrared Telescope) WFCAM (Wide Field Camera), and ESO (European Southern Obsevatory) VISTA (Visible and Infrared Survey Telescope for Astronomy) VIRCAM (VISTA Infrared Camera).Full Header Inheritance Documentation; previous version of Header Inheritance documentation.Digest of Public Comments about this convention:FITSBITS Email List Header Inheritance DiscussionIAUFWG Email List Header Inheritance DiscussionSample FITS File: mef_inh.fits (uses the inheritance convention, size = 124 MB), mef_NOinh.fits (same file, without using the inheritance convention, size = 147 MB)Sample Header Listing: mef_inh.txt (with inheritance), mef_NOinh.txt (without inheritance) The HIERARCH Keyword Convention Description: Under this keyword convention, as originally defined by ESO, bytes 10 through 80 of the HIERARCH keyword record contain a series of ASCII (American Standard Code for Information Interchange) strings, or tokens, that serve to hierarchically classify the keyword, followed by an equals sign ("=") which is in turn followed by the keyword value field. An optional comment field may follow the value field. The value and comment fields conform to the rules for free-format keywords, as defined in the FITS Standard document.The following is an example of this convention:HIERARCH ESO INS OPTI-3 ID = 'ESO#427 ' / Optical element identifierThe hierarchical keywords can be mapped into descriptor names by concatenating the hierarchical tokens together, separating them with the full stop character. For example, the hierarchical keyword shown above corresponds to the descriptor name ESO.INS.OPTI-3.ID.See the full documentation (available below) for the complete set of rules and recommendations regarding the use of this convention.Submitted: Sept 2007Registered: 22-Sept-2009Date and Place of First Usage: circa 1990, ESO (the European Organization for Astronomical Research in the Southern Hemisphere)Extent of Usage: Extensively used in FITS data files generated by ESO. This keyword convention is supported by MIDAS (Munich Image Data Analysis System) and by the CFITSIO FITS I/O (input/output) library.Full Documentation: HIERARCH Keyword PDF format, HIERARCH Keyword Postscript formatComments and/or critiques: HIERARCH Keyword FITSBITS discussionSample FITS File: fors.fitsSample Header Listing: fors.txt The Substring Array Convention for Binary Tables The substring array convention may be used to specify that a character array field (TFORMn = 'rA') consists of an array of either fixed-length or variable-length substrings within the field. This convention utilizes the option described in the FITS Standard to have additional characters following the datatype code character in the TFORMn value field. The full form for the value of TFORMn within this convention is'rA:SSTRw/nnn'and a simpler form that may be used for fixed-length substrings only is'rAw'wherer is an integer giving the total length including any delimiters (in characters) of the field,A signifies that this is a character array field,: indicates that a convention indicator follows,SSTR indicates the use of this "Substring Array" convention,w is an integer $\leq$ {\tt r} giving the (maximum) number of characters in an individual substring (not including the delimiter), and/nnn if present, indicates that the substrings have variable-length and are delimited by an ASCII text character with decimal value nnn in the range 032 to 126 decimal, inclusive. This character is referred to as the delimiter character. The delimiter character for the last substring will be an ASCII NUL.To illustrate this usage:'40A:SSTR8' signifies that the field is 40 characters wide and consists of an array of 5 8-character fixed-length substrings. This could also be expressed using the simpler form as '40A8''100A:SSTR8/032' signifies that the field is 100 characters wide and consists of an array of variable-length substrings where each substring has a maximum length of 8 characters and, except for the last substring, is terminated by an ASCII SPACE (decimal 32) character.Submitted: 24-Mar-2009 by W. Pence, NASA/GSFCRegistered: 22-Sept-2009Date and Place of First Usage: circa 1996Extent of Usage: The simpler 'rAw' form of this convention has been supported by the CFITSIO library since 1996 and has been used in some publicly distributed FITS files produced by various projects. The longer 'rA:SSTRw/nnn' form has rarely been used, and, as far as currently known, never for arrays of variable-length strings.Full Documentation: Substring Array Convention PDF format, Substring Array Convention Postscript formatSample FITS File: chandra_caldb.fits: a calibration index file generated by the Chandra mission. The 7th column in the table has TFORM7 = '630A70 '.Sample Header Listing: chandra_caldb.txt Hierarchical Grouping Convention This grouping convention provides a general mechanism for defining hierarchical associations of HDUs. The group members may reside in a single FITS file or be distributed in many files which may reside on different computer systems. The convention uses a FITS table to record all the members of the group (one member per row of the table).Submitted: April 2007 by W. Pence (NASA/GSFC)Registered: June 2007Date and Place of First Usage: 1998, at the INTEGRAL Science Data Center (ISDC), Geneva, Switzerland.Extent of Usage: It is used in science data products from the INTEGRAL gamma-ray mission that was launched in October 2002. Each observation can consist of hundreds of individual FITS files representing each of the 'dithered' exposures. The grouping tables are used to form associations of related observation FITS files and the calibration data files.The fv FITS file viewer provides a convenient way to navigate through this hierarchial structure (via the "open" button display at the beginning of each row of the grouping table).Full Documentation: Hierarchical Grouping Convention PDF format, Hierarchical Grouping Convention Postscript formatDigest of Public Comments about the Hierarchical Grouping Convention.Support software: grouping.tar - Initial implimentation of the CFITSIO routines to support creation and reading of grouping tables.Sample FITS Files: group1.fits, group2.fits.Sample Header Listing: group1.txt, group2.txt Foreign File Encapsulation Convention The XTENSION = 'FOREIGN ' extension type puts a FITS wrapper about an arbitrary file, allowing a file or tree of files to be wrapped up in FITS and later restored to disk.Submitted: 11-August-2006 by R. Seaman (NOAO), N. Zarate (NOAO), and D. Tody (NRAO)Registered: October-2007Date and Place of First Usage: May 1999, at NOAO/KPNOExtent of Usage: Limited usage, mainly to encapsulate preview PNG-format graphics files into FITS files in the NOAO High Performance Pipeline System.Full Documentation: Foreign File Encapsulation PDF format, Foreign File Encapsulation Word formatComments and/or critiques: Foreign File Encapsulation IAUFWG discussionsSample FITS File: foreign.fits (from NOAO)Sample Header Listing: foreign.txt World Coordinate Systems Conventions Spatial Region File Convention A FITS Region binary table defines a spatial region of a 2-dimensional image. The region file is often used to define an area that is to be included or excluded from certain data processing operations on the image. The region is specified as the union or intersection of geometric shapes, such as "circle" or "rectangle." The REGION table is the FITS equivalent of the ASCII region file that has long been used by the ds9 image processing program and its predecessor, SAOimage.Submitted: August 2008 by Arnold Rots and Jonathan McDowell (Harvard/Smithsonian Center for Astrophysics)Registered: August 2012Date and Place of First Usage: circa 1998, within the Chandra data analysis system, CIAO (Chandra Interactive Analysis of Observations).Extent of Usage: The FITS region files have been extensively used in the analysis of Chandra images. This region format is supported by the ds9 image analysis program, and recently by the CFITSIO FITS I/O software library.Full Documentation: Spatial Region File Convention PDF format, Spatial Region File Convention Postscript formatComments and/or critques: Spatial Region File Convention FITSBITS discussionSample FITS File: region.fitsThe primary array of this file contains a 128 x 128 pixel image that has been spatially binned by a factor of 64 from the original high resolution Chandra image (represented in pixel list format). The 2nd HDU in the file is a region extension that applies to the primary array image. It is composed of 3 components: a circle, a box (rectangle), and an ellipse. The coordinates of the X and Y components are give in pixel units of the original unbinned image; the TCTYPn, TCRPXn, TCRVLn, and TCDLTn WCS keywords associated with these columns provide the parameters needed to transform to RA and Dec sky coordinates.Sample Header Listing: region.txt SIP Convention for Representing FITS Image Distortions Description: The SIP (Simple Imaging Polynomial) convention provides a convenient means of representing non-linear geometric distortion of the coordinate system as polynomials in FITS header keywords. The SIP convention derives its name from the four characters "-SIP" that are appended to the values of the CTYPEn WCS header keywords, for example:CTYPE1 = 'RA---TAN-SIP' CTYPE2 = 'DEC--TAN-SIP'Submitted: September 2008 by David L. Shupe (Infrared Processing and Analysis Center) and Richard N. Hook (Space Telescope European Coordinating Facility)Registered: 22-Sept-2009Date and Place of First Usage: circa 2004, at the Spitzer Science Center.Extent of Usage: The SIP convention was originally used by the Spitzer Science Center (SSC) in its imaging products. The SIP convention is supported by WCSTOOLS (written by D. Mink), the Starlink AST library, and the IDL ASTROLIB library. Tools that use these libraries (e.g., ds9 and the GAIA Graphical Astronomy and Image Analysis Tool) inherit support for SIP. Also, the drizzle program and related tools developed by STScI and ST-ECF (Space Telescope European Coordinating Facility), and the astrometry.net astrometric calibration service use SIP.Full Documentation: SIP Convention PDF formatComments and/or critiques: SIP Convention FITSBITS discussionSample FITS File: sipsample.fitsSample Header Listing: sipsample.txt (edited to show only the relevant keywords) TNX Convention for Representing FITS Image Distortions The TNX World Coordinate System is a non-standard coordinate system for evaluating celestial coordinates from the image pixel coordinates. It follows the FITS conventions for undistorted tangent plane projections but adds a non-linear distortion term to the evaluation.Submitted: September 2008 by Doug Tody (NRAO), Lindsey Davis (NOAO), and Frank Valdes (NOAO)Registered: 22-Sept-2009Date and Place of First Usage: circa 1998 for NOAO data and support within the IRAF system.Extent of Usage: The TNX convention is currently used in the FITS files produced by NOAO that are taken with a variety of different imaging instruments including MOSAIC and NEWFIRM.Full Documentation: TNX Convention PDF formatComments and/or critiques: TNX Convention FITSBITS discussionSample FITS File: tnx.fitsSample Header Listing: tnx.txt (edited to show only the relevant keywords) TPV Convention for Representing FITS Image Distortions The TPV World Coordinate System is a tangent plane projection with a polynomial distortion function described by coefficients provided in a set of PVi_m keywords. It derives from an early proposal by Calabretta and Greisen (2000) where the WCS axis type (as given by the CTYPEi keyword) is labeled as TAN but software is supposed to recognize the presence of the PV keywords.The purpose of registering this convention is to move away from a misleading TAN axis type which is now a published FITS standard that does not include distortions. It is also intended to provide advanced publication before the NOAO Dark Energy Camera begins producing and archive data in this convention.Submitted: September 2011 by Francisco Valdes (NOAO)Registered: August 2012Date and Place of First Usage: Proposed in 2000 by Calabretta and Greisen and used by some data providers, for instance CFHT (Canada France Hawaii Telescope).Related Conventions: Some data uses a WCS axis type of TAN, and software may recognized the presence of PV keywords to be interpreted as per the early Calbretta and Greisen proposal. The functionality of a polynomial with both x/y and radial terms is effectively the same as the ZPX convention though coefficients are represented differently in the header.Extent of Usage: The submitter believes it is used by CFHT under the TAN extension convention. The TPV convention will be used by NOAO for data from the Dark Energy Camera. The TPV convention is supported by IRAF, Dark Energy Survey, DS9, Astromatics (e.g. SCAMP) as of this date. Further support will likely follow with registration of this convention.TPV WCS Full PDF DocumentationComments and/or critiques: tpv_zpx_comments.txtSample FITS File: tpv.fitsSample Header Listing: tpv-hdr.txt ZPX Convention for Representing FITS Image Distortions The ZPX World Coordinate System is a non-standard coordinate system for evaluating celestial coordinates from the image pixel coordinates. It follows the FITS conventions for undistorted zenithal plane projections but adds a non-linear distortion term to the evaluation.Submitted: September 2011 by Frank Valdes (NOAO)Registered: August 2012Date and Place of First Usage: circa 2000 for NOAO data and support within the IRAF system.Extent of Usage: The ZPX convention is currently used in the FITS files produced by NOAO that are taken with a variety of different imaging instruments including MOSAIC and NEWFIRM.ZPX WCS Full PDF DocumentationComments and/or critiques: tpv_zpx_comments.txtSample FITS File: zpx.fitsSample Header Listing: zpx-hdr.txt Conventions Applicable to Specific Types of Data FITS Interferometry Data Interchange Convention The FITS Interferometry Data Interchange (FITS-IDI) Convention is a set of conventions layered upon the standard FITS format to assist in the interchange of data recorded by interferometric telescopes, particularly at radio frequencies and very long baselines. This convention is intended to separate a standard set of conventions from those used within particular software packages such as AIPS.Submitted: May 2009 by Eric Greisen (NRAO)Registered: May 2010Date and Place of First Usage: 1997, by the VLBA (Very Long Baseline Array) system of radio telescope antennasExtent of Usage: This convention is in use for the VLBA telescope for data from the current hardware correlator and the future software correlator and has also been used with other correlators such as the Joint Institute for VLBI in Europe (JIVE) correlator for the European VLBI Network.Full Documentation: FITS-IDI definition document in PDF format (AIPS Memo 114); FITS-IDI definition document in Postscript formatComments and/or critiques: FITS-IDI FITSBITS discussionSample FITS File: BL146_1.fits - The original FITS-IDI file was very large (112 MB) and contained 96843 samples with 4 Stokes, 4 IFs and 8 Spectral channels per sample. The current file available here has been reduced in size by only preserving the first 1000 rows in the TAPE_STATISTICS and UV_DATA binary table extensions.Sample Header Listing: BL146_1.txt - listing of the header keywords in the sample FITS file. Single Dish FITS Convention for Radio Astronomy Data The SDFITS binary table convention is used for interchange of single dish data in radio astronomy.Submitted: August 2010 by Robert Garwood (NRAO) and Mark Calabretta (ATNF/CSIRO)Registered: August 2012Date and Place of First Usage: SDFITS was developed at a meeting of representatives from many major radio astronomy observatories at Green Bank, West Virginia in October 1989.Extent of Usage: Variants of the SDFITS convention are used by a number of radio observatories, including NRAO, Arecibo, Parkes, and Mopra (Australia). The definition document (below) specifically applies to the NRAO version of SDFITS; the data from other observatories may differ slightly.Full Documentation:SDFITS definition document in PDF format, SDFITS definition in Postscript formatsee also Garwood (2000)Comments and/or critiques:Discussion of differences between the NOAO and Parkes SDFITS formats.Sample FITS Files:Parkes_GASS.fits This file is from the Parkes Galactic All Sky Survey (GASS) of the atomic hydrogen (HI) emission in the southern Milky Way. It contains 7-beam, 2 polarization x 2049 channel, 8MHz bandwidth, dual-IF, scanned, frequency-switched Parkes multibeam GASS data. The data table has been truncated to 28 rows to reduce the size of the file. This file differs from the SDFITS documentation in having a vector TSYS column, with one value for each polarization.TREG_091209.cal.acs.fits, This file contains processed (by GBTIDL) Green Bank Telescope (GBT) data. Additional comments from Bob Garwood:This shows how we add a new extension when the data length changes. I don't believe it differs from the convention. For the GBT we always write one spectrum per row. I went that route rather than how I approached things for the aips++ sdfits writer (which is what Mark's example is closer to - i.e. both polarizations on the same row) after a conversation with Harvey about 6-7 years ago where he said that it was his impression that the sdfits convention was never meant to hold more than one spectrum per row because of the scalar nature of the TSYS column.I've used fv on this example file to pare it down from it's original size of 30 rows in the first extension and 300 rows in the second extension to something more manageable. The first extension is calibrated individual integrations from an observation of a galaxy. There's 2 polarizations and one spectral window. The raw data is position switched data. The second extension is 2 polarizations and 2 spectral windows of a different galaxy. It's also calibrated individual integrations and the raw data were 2-beam nodding data (one scan with one beam on source followed by a second scan with the other beam being on source) - it's shorter integrations so the emission is harder to see in the individual integrations than it is for the data in the other extension.Sample Header Listings:Parkes_GASS.txtTREG_091209.cal.acs.txt Multi-Beam FITS Raw Data Format Convention MBFITS is the raw data format for multibeam receivers based on FITS to be used at the IRAM 30m and APEX 12m mm/submm and other telescopes. This format is suitable for single-dish bolometer and heterodyne observations. MBFITS borrowed some of its design concepts from the ALMA-TI FITS format, but has added new structures and keywords to accommodate multiple beam observing and multiple frontend or backend combinations.Submitted: April 2007 by Dirk Muders (Max-Planck Institute, Bonn, Germany)Registered: July 2007Date and Place of First Usage: 2002, at the IRAM 30m and APEX telescopes.Extent of Usage: Used in routine production of data taken with the IRAM, APEX, Effelsberg 100m, Yebes 40m, and SRT 64m telescopes.Full Documentation:MBFITS Summary PDF document, 20 October 2007 (previous 2 April 2007 version)Full MBFITS specification PDF document, version 1.67. (Previous versions: MBFITS Specification 1.66, MBFITS Specification 1.65, MBFITS Specification 1.64, MBFITS Specification 1.63, MBFITS Specification 1.62, MBFITS Specification 1.61)Sample FITS File:APEX-64691-2018-10-12-T-0101.F-9993A-2018.tgz - Version 1.67 format (164 MB gzipped tar file).APEX-48698-2011-08-04-T-087.F-0001-2011.tgz - Version 1.63 format (19 MB gzipped tar file). Euro3D: A Data Standard for 3D Spectroscopy Euro3D is an interchange data format for integral field spectroscopy in which 1-dimensional spectra are obtained at multiple positions over a 2-dimensional spatial field of view. Each spectrum is stored as a vector in one row of a binary table, along with other columns containing parameters describing the spectrum (such as it's location in the 2D field). More information about the development of this format is available on the Euro3D website.Submitted: Novenber 2007 by Markus Kissler-Patig (ESO)Registered: June 2008Date and Place of First Usage: circa 2002, for data from numerous telescopes, including the VLT and GEMINIExtent of Usage: has been used for spectral data obtained with a variety of ESO instrumentsFull Documentation: Euro3D Data Format Definition (PDF).Comments and/or critiques: Euro3D FITSBITS discussion.Sample FITS File: e3d_agn.fitsSample Header Listing: e3d_agn.txt OIFITS: A Data Standard for Optical Interferometry Data OIFITS is a standard for exchanging calibrated, time-averaged data from astronomical optical interferometers, based on the FITS Standard. 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).Submitted: June 2007 by Thomas Pauls (Naval Research Lab)Registered: July 2007Date and Place of First Usage:2004, in the Interformetry Imaging Beauty ContestFirst Publication: Monnier et al., 2004, ApJ, 605, 436Extent of Usage: This standard is supported by the majority of optical interferometer projects, including COAST, NPOI, IOTA, CHARA, VLTI, PTI, and the Keck Interferometer.Full Documentation: 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.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.Version 2 of the OIFITS2 standard: OIFITS2An online validator tool: OIVALSample FITS File (from the 2006 Beauty Contest): double.fitsSample Header Listing: double.txt PSRFITS: A Standard for Pulsar Data Storage PSRFITS is a standard FITS-based format for pulsar data files. Both mean pulse profile ("fold-mode") and streamed ("search-mode") multi-channel full-polarisation data are supported.Submitted: 29 November, 2013 by R N Manchester (dick.manchester@csiro.au).Registered: 2014Date and Place of First Usage: December 2002 at CSIRO Australia Telescope National FacilityExtent of Usage: PSRFITS is used as a data storage template by on-line pulsar observation systems at CSIRO Parkes (Australia), Arecibo Observatory (Puerto Rico) and the National Radio Astronomy Observatory (Green Bank, West Virginia). It is supported by off-line signal-processing systems including PSRCHIVE (fold-mode data), and DSPSR and PRESTO (search-mode or streamed data).Full Documentation: Available at PSRFITS. It includes the rationale for the creation of PSRFITS, the current template definition, documentation for the complete version history for the template.Comments:Sample FITS FilesFold-mode file: PDFB3_Fold_J1744-1134.rcf32t4. This file contains fold-mode data from a 1-hr Parkes observation of PSR J1744-1134 with the instrument PDFB3 recording full polarisation data. The centre frequency is 732 MHz and the recorded bandwidth 64 MHz. The observation has been processed using PSRCHIVE routines to remove narrow-band RFI and give zero weight to the band edges, calibrate the instrumental gain and phase, and compress to 16 sub-bands (originally 512) and 16 sub-integrations (originally 64).Search-mode file: PDFB4_Search_J0437-4715.sf. This 21 MB file was recorded at Parkes using the instrument PDFB4 and contains 15 seconds of streamed or search-mode data from PSR J0437-4715. The centre frequency is 1369 MHz and there are 512 channels across the 256-MHz bandwidth. The data are total intensity (approximately Stokes I) with 2-bit sampling of each frequency channel at 96-microsecond intervals.Sample Header Listing:PDFB3_Fold_J1744-1134.txt andPDFB4_Search_J0437-4715.txt FITS Headers for Scans of Photographic Plates We describe a FITS header structure suitable for the annotation of scans of photographic plates and similar historic observational material containing sky images intended for scientific use. This metadata structure is general enough to cover several observational techniques common in the plate era, such as multiply exposed plates or objective prism spectroscopy.Submitted: 10 December 2022 by Markus Demleitner (gavo@ari.uni-heidelberg.de).Registered: 2022Date and Place of First Usage: Early 2010s in APPLAUSE.Extent of Usage: This annotation has been taken up by the IVOA interest group on Data Curation and Preservation, which has adopted it as an IVOA note. Implementations that facilitate annotation are available in PyPlate and DaCHS; examples for annotation by the latter are found in the Potsdam Kapteyn service.Full Documentation: Available as an IVOA Note. Source code and edit history are available from github.Comments: None so farSample FITS FilesAPPLAUSE plate LA02333 with multiple exposures and a decent amount of metadata, created by pyplateKapteyn plate POT015_004630 (scaled down 4x for size), created by DaCHS Local FITS ConventionsThe following FITS conventions have been locally developed by various groups or projects. While it is believed that these conventions represent valid FITS usage and conform to the rules specified in the FITS Standard, they currently have no official endorsement by the IAU FITS Working Group. They are presented here for reference only. See the FITS Registry for a compilation of registered FITS conventions.Table Indexing — a convention for creating indices on FITS tables (Postscript)Conventions adopted by the HEASARC FITS Working Group:RA and Dec keywords for giving the position of the observed object, the telescope pointing, and the spacecraft axes (text version)The CATIDn FITS keywords to contain source catalog identifications (text version)The CREATOR keyword to denote the name and version of the software program that generated that FITS file/extension (text version)The HDUCLASn/HDUVERS keywords to provide a hierarchical classification scheme for the various types of FITS extensions (text version). Also available is a list of all HDUCLASn/HDUVERS values currently defined by the HFWG.Quality flags with a value of zero should be reserved to indicate GOOD (not rejected) quality data. Non-zero quality flag values may be used to indicate varying degrees of 'badness'. (text version)Keywords to define channel & energy boundaries (text version)Keywords and definitions relating to exposure times (text version)Standard strings to denote the mission, instrument and filters within X- and gamma-ray astronomy. This recommendation is contained in OGIP memo ogip_93_013 (postscript, latex).TSORTKEY - a keyword for specifying the sort order of a FITS Table (text version)Recommendations for naming columns in a FITS table (text, latex, postscript)Image Compression: A 1991 proposal by Archibald Warnock, Robert Hill, Barbara Pfarr (all at GSFC), and D. Wells (NRAO) for storing compressed images in FITS format. See the FITSBITS email list archive of postings for September and October 1991 for a discussion of image compression in general and this proposal in particular. This compression proposal was never implemented, but some of the same ideas were used in the tiled image compression convention that is described in the FITS Registry of conventions.MAST Data Format Guidelines - general FITS format guidelines for data files in the STScI multimission archive (MAST).SDAC FITS Keyword Conventions - FITS conventions adopted at the Solar Data Analysis Center (SDAC) at Goddard Space Flight Center for several solar missions.Chandra FITS File Designers Guide - details the FITS conventions adopted by the Chandra X-Ray Satellite project for its archival data sets. (40 pages, postscript file)If you know of other items that should be listed on this page, please contact the FITS Support Office.
