def is_proj_plane_distorted(wcs, maxerr=1e-05):
 cwcs = wcs.celestial
 return ((not _is_cd_orthogonal(cwcs.pixel_scale_matrix, maxerr)) or _has_distortion(cwcs))

def is_proj_plane_distorted ( wcs , maxerr = 1e-05 ) : cwcs = wcs . celestial return ( ( not _is_cd_orthogonal ( cwcs . pixel_scale_matrix , maxerr ) ) or _has_distortion ( cwcs ) )
for a wcs returns false if square image pixels stay square when projected onto the "plane of intermediate world coordinates" as defined in greisen & calabretta 2002 .