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| FITS World Coordinate System | |
|---|---|
| Name | FITS World Coordinate System |
| Developer | International Astronomical Union; NASA; European Space Agency |
| Released | 1990s |
| Latest release | WCS Papers and FITS Standards |
FITS World Coordinate System
The FITS World Coordinate System provides a standardized method to map pixel indices in Flexible Image Transport System files to physical coordinate systems used in astronomy and space science. It enables interoperability between observatories like Hubble Space Telescope, Chandra X-ray Observatory, and missions such as Gaia and Kepler, and supports data archives maintained by institutions like European Southern Observatory and Space Telescope Science Institute.
FITS WCS defines header conventions to express mappings from array coordinates to world coordinates relevant to instruments developed by Jet Propulsion Laboratory, National Radio Astronomy Observatory, and Max Planck Institute for Astronomy. The specification was advanced through working groups at the International Astronomical Union and influenced data centers including NASA/IPAC, CERN scientific computing projects, and archives at Smithsonian Astrophysical Observatory. WCS integrates with related standards such as the FITS image convention, metadata models used by HEASARC, and interoperability frameworks promoted by the Virtual Observatory initiative.
WCS supports multiple coordinate types including celestial coordinates (e.g., right ascension and declination used by Hipparcos and Sloan Digital Sky Survey), spectral coordinates adopted by Atacama Large Millimeter Array and Spitzer Space Telescope, and time coordinates used by Fermi Gamma-ray Space Telescope and XMM-Newton. Transformations include linear modeling employed by observatories like Keck Observatory, rotation matrices used in Very Large Telescope pipelines, and skew and scale corrections utilized by instruments on James Webb Space Telescope. The formalism references projection algorithms relevant to Besselian epoch and Julian Date conventions, and ties to reference frames such as International Celestial Reference Frame and FK5.
Core header keywords like CRPIX, CRVAL, CDELT, and CTYPE are central to implementations at institutions such as European Space Agency, NOAO, and Space Telescope Science Institute. Alternate keywords and conventions (e.g., PCi_j matrices versus CDi_j matrices) arose in software maintained by Astropy Project, IRAF communities, and analysis packages from STScI. Spectral and velocity conventions reference standards used by International Astronomical Union (IAU) working groups and align with Doppler definitions employed in datasets from Herschel Space Observatory and ALMA.
Software libraries that implement WCS include projects like Astropy Project's wcs module, WCSTools maintained by NASA collaborators, and utilities in CASA used by radio astronomers at NRAO. Visualization tools such as DS9 and Aladin Sky Atlas read and apply WCS headers for imagery from Hubble Space Telescope and survey data from Pan-STARRS and Two Micron All Sky Survey. Pipelines at institutions like European Southern Observatory and Space Telescope Science Institute embed WCS handling in reduction systems tied to instrument teams for Very Large Array and Subaru Telescope.
WCS accommodates optical distortion corrections developed for cameras on Hubble Space Telescope and James Webb Space Telescope, and radio interferometric projection treatments used by Very Large Array and Atacama Large Millimeter Array. Supported map projections (e.g., TAN, SIN, AIT) are applied in surveys like Sloan Digital Sky Survey and WMAP, and coordinate reference choices draw on frames such as Galactic coordinate system and Ecliptic coordinate system used in studies at Planck and Gaia missions. Polynomial and SIP distortion conventions are commonly adopted in data products from CFHT and Subaru Telescope instrument teams.
Typical use cases include astrometric calibration for catalogs produced by Gaia cross-matched with imaging from Pan-STARRS and DECam, spectral cube registration for datasets from ALMA and VLA, and time-tagged photon event localization for projects at Fermi Gamma-ray Space Telescope and Chandra X-ray Observatory. Survey pipelines at Sloan Digital Sky Survey and archives at NASA/IPAC rely on WCS for mosaicking, reprojection, and cross-instrument comparisons involving facilities such as Keck Observatory and NOAO.
Development of WCS conventions was driven by collaborations among organizations including International Astronomical Union, NASA, European Space Agency, and research centers like Space Telescope Science Institute and Harvard-Smithsonian Center for Astrophysics. Key publications and discussions appeared in meetings of the American Astronomical Society and in working groups that involved contributors from STScI instrument teams, NRAO staff, and software projects such as Astropy Project and WCSTools. The standard evolved alongside FITS updates endorsed by bodies like the International Organization for Standardization and through community feedback from archives such as HEASARC and observatory data centers.
Category:Astronomical imaging