SIP Convention for Representing FITS Image Distortions
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'
September 2008 by David L. Shupe (Infrared Processing and Analysis Center)
and Richard N. Hook (Space Telescope European Coordinating Facility)
Date 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, and the
astrometry.net astrometric calibration service use SIP.
Comments and/or critiques:
Sample FITS File:
Sample Header Listing:
sipsample.txt (edited to show only the relevant keywords)
Last revised: Wednesday, 12-May-2010 14:15:52 EDT
Contact us: fits @ fits.gsfc.nasa.gov
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