Proposed FITS Standard
World Coordinate Systems

Twenty-five projections are supported by the FITS WCS standard, which is documented by Eric Greisen and Mark Calabretta and implemented in Mark's WCSLIB software library. A twenty-sixth, NCP, which is supported by classic AIPS software is computed using the worldpos and worldpix subroutines written by Bill Cotton and Eric Greisen of NRAO. That original source code is available at the NRAO FITS WCS site.

The FITS data format is best described by the current FITS standard, NOST 100-2.0 available from the NASA FITS Support Office as a 597K uncompressed Postscript, 239K gz-compressed Postscript, or 386K PDF file.

Steve Allen and Doug Mink proposed a method of specifying dependent WCS projections in an unpublished appendix to Calabretta and Griesen's paper, available in PDF and Postscript.

Projections included in WCSLIB are

WCSTools versions 2.9 and later implement the use of multiple world coordinate systems, with the WCS to which a keyword applies designated by an appended character. Thus CTYPE1 applies to the default WCS, which may be named using WCSNAME. A second WCS would use keywords such as CTYPE1A and WCSNAMEA. An additional nonstandard feature has been added, the keyword WCSDEPx, which is set equal to the name of a WCS which would be found in a WCSNAMEx keyword value or a single character which is assumed to be the suffix for the WCS

Last updated 19 May 2014 by Jessica Mink

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