Project: datamanagement
Issue DM-5206: Please do not write garbage to the FITS EQUINOX
The equinox is not relevant when dealing with ICRS coordinates. When {{afw}} manipulates {{Wcs}} objects, it simply doesn't bother initializing the {{equinox}} field of its {{_wcsInfo}} struct when dealing with an ICRS system. When {{afw}} persists the {{Wcs}} to FITS, it blindly writes whatever happens to be in that uninitialized field to the FITS header. Thus, we end up with something like: {code} EQUINOX = 9.87654321E+107 / Equinox of coordinates {code} This should be no problem, since, per the [FITS standard|http://fits.gsfc.nasa.gov/standard30/fits_standard30aa.pdf] (page 30), the {{EQUINOX}} is "not applicable" if they {{RADESYS}} is {{ICRS}}. The reader should thus ignore this value. However, [SAOimage DS9|http://ds9.si.edu] version 7.4.1 (the latest release at time of writing) does _not_ ignore the {{EQUINOX}}. Rather, it refuses to handle the WCS for the image. Note that version 7.3 of DS9 does not seem to have the same issue. While this does seem to be a bug in DS9, it's easy enough to work around by simply not writing {{EQUINOX}}.
Story points: 1